# NCERT Solutions Class 7 Science

Class 7 forms the foundation of a student’s academic path. Since Class 8th, 9th and 10th are some of the important years, it is essential for students to master the concepts in Class 7th. Extramarks is a one-stop platform to access diversified study materials. Students can get past years’ question papers, revision notes, study notes, important questions, etc on the website. They can solve them and strengthen their conceptual understanding. In addition to this, they can check the NCERT solutions for class 7 Science and understand the topics that need more practice.

## NCERT Class 7 Science Solution

NCERT solutions for class 7 Science from Extramarks enable students to refer to the answers post solving the question paper. The  7th Science NCERT solutions involve subjects like Physics, Chemistry and Biology. The solutions have been developed in a way that will help students in mastering the foundation. Students can get their concepts cleared after checking the question. This will help them prioritise as well as save their time from wasting.  Students can click the link below and access the NCERT Class 7 Science Solution.

### How areClass 7 Science Solutions by Extramarks helpful?

NCERT solutions for class 7 Science by Extramarks helps the students to get their concepts clear while they go through the solutions to the questions. Extramarks have come up with questions which are mostly expected in the examination of class 7. All these questions along with their solutions cover all the important topics and concepts. While preparing for any competitive exam,it is important to have a strong command of the basics. Extramarks helps the students to understand all the chapters thoroughly. All the questions and solutions are made by strictly following the latest guidelines of CBSE and NCERT. Therefore, students can easily rely on all these solutions. Students can visit Extramarks to get all the study materials required for their examination.

### NCERT Class 7 Science Chapter wise Solutions

Class 7 Science syllabus is very vast and it is important for the students to cover all the topics to score well in their examination. Thus, Extramarks has come up with NCERT Class 7 Science Chapter wise Solutions which will help students in preparing all the chapters thoroughly. The link for the NCERT solution for class 7th Science is given below. Students can easily access the chapter-wise solution by visiting Extramarks.

### NCERT Class 7 Science Chapterwise Solutions in Hindi Medium

Gradually as years progress, the level of Hindi also becomes challenging as higher classes emerge. Students can readily access the Hindi Medium Syllabus and check out NCERT solutions for class 7 Science. Considering the complexities in Hindi medium, the subject matter experts at Extramarks have provided simplified versions of all the documents. Students can click on the link below and access NCERT Class 7 Science Chapterwise Solutions in Hindi Medium.

### NCERT Solutions for Class 7 Science

All the chapter-wise solutions for class 7 are given below. The students preparing for their examination can access the solutions to get their concepts clear and score more in the examination.

Chapter 1: Nutrition in Plants

Chapter 2: Nutrition in Animals
Chapter 3: Fibre to Fabric
Chapter 4: Heat
Chapter 5: Acids, Bases, and Salts
Chapter 6: Physical and Chemical Changes

Chapter 7: Weather, Climate and Adaptations of Animals to Climate
Chapter 8: Winds, Storms and Cyclones
Chapter 9: Soil

Chapter 10: Respiration in Organisms
Chapter 11: Transportation in Animals and Plants

Chapter 12: Reproduction in Plants
Chapter 13: Motion and Time
Chapter 14: Electric Current and its Effects
Chapter 15: Light
Chapter 16: Water: A Precious Resource
Chapter 17: Forests: Our Lifeline
Chapter 18: Wastewater Story

### Here Are Some Tips to Ace your Class 7 Science Exam

NCERT books are one of the reliable books to prepare. Students should however follow some tips to ace their Class 7 Science examination:

1. They should start reading from NCERT books.
2. Students should practise past years’ question papers to get an expertise and confidence in solving paper
3. They should refer to the solutions after attempting the paper. This will aid students in knowing topics or areas to improve.
4. Students should visit Extramarks and access all the related study material such as Class 7 Science question papers, solutions, answers, etc.

Q.1 Explain why there is no waste in a forest.

Ans

There is no waste in a forest because animal droppings, dead remains of plants and animals, are acted upon by the decomposers which convert them back into useful nutrients. These recycled nutrients are utilised by the plants and microorganisms for growth and reproduction. Thus, all the waste material generated in the forest is converted into useful materials and no waste is left in the forest.

Q.2 List five products we get from forests?

Ans

The five products which we get from the forests are as follows:

1. Timber
2. Firewood
3. Wax
4. Gum
5. Spices

Q.3 Fill in the blanks:
(a) The insects, butterflies, honeybees and birds help flowering plants in_______.
(b) A forest is a purifier of________ and_________.
(c) Herbs form the ________layer in the forest.
(d) The decaying leaves and animal droppings in a forest enrich the_______.

Ans

(a) pollination
(b) air, water
(c) lowest
(d) soil

Q.4 Why should we worry about the conditions and issues related to forests far from us?

Ans

We should be concerned with the conditions and issues related to forests because of the following reasons:

1. Forests maintain the balance between oxygen and carbon dioxide in the atmosphere. This helps in preventing the increase in temperature of earth’s atmosphere.
2. Forests prevent floods and erosion of soil.
3. Forests provide us with many important products like, timber, firewood, honey, beeswax, herbal medicines etc.
4. Forests help a region in receiving sufficient amount of rainfall.
5. Forests also curb noise pollution.

Q.5 Explain why there is a need of variety of animals and plants in a forest.

Ans

Large variety of plants and animals provide greater choice of food resources to all the life forms. This helps in growth in populations and varieties of both herbivores and carnivores. These animals play important roles in circulation of nutrients and energy through food chain and dispersal of seeds to larger distances. Such processes define and contribute in the growth, expansion, development and regeneration of a forest.

Q.6 In Fig. 17.15, the artist has forgotten to put the labels and directions on the arrows. Mark the directions on the arrows and label the diagram using the following labels: clouds, rain, atmosphere, carbon dioxide, oxygen, plants, animals, soil, roots, water table.

Ans

The correctly labelled diagram with arrow marks is as shown below:

Q.7 Which of the following is not a forest product?
(i) Gum
(ii) Plywood
(iii) Sealing wax
(iv) Kerosene

Ans

(iv) Kerosene

Q.8 Which of the following statements is not correct?
(i) Forests protect the soil from erosion.
(ii) Plants and animals in a forest are not dependent on one another.
(iii) Forests influence the climate and water cycle.
(iv) Soil helps forests to grow and regenerate.

Ans

The incorrect statement is: (ii) Plants and animals in a forest are not dependent on one another.

Q.9 Micro-organisms act upon the dead plants to produce
(i) sand
(ii) mushrooms
(iii) humus
(iv) wood

Ans

Micro-organisms act upon the dead plants to produce (iii) humus

Q.10 Why do organisms take food?

Ans

Organisms take food to meet their requirements of nutrients and energy. Nutrients and energy enable the organisms to grow, reproduce and repair their damaged body parts.

Q.11 Distinguish between a parasite and a saprotroph.

Ans

A parasite derives nutrition from the body of a living host by invading its tissues whereas, a saprotroph derives its nutrition from dead and decaying organic matter.
Examples of parasite: Cuscuta and leech
Examples of saprotrophs: Fungi and bacteria

Q.12 How would you test the presence of starch in leaves?

Ans

The presence of starch in the leaves can be tested with the help of iodine solution that gives blue-black colour with starch. Boil few green leaves in alcohol in a test tube, till they turn colourless or pale green. Then wash the leaves in tap water and transfer them into a petridish. Add some drops of iodine. A change in colour of leaves to blue-black indicates the presence of starch in them.

Q.13 Give a brief description of the process of synthesis of food in green plants.

Ans

The leaves of green plants contain chlorophyll pigment which traps solar energy. This energy is utilized by the leaves for the synthesis of organic food from water and carbon dioxide. Water is absorbed by the roots and carbon dioxide is taken up from the atmosphere through the tiny pores present on the leaf surface called stomata. Thus, sunlight, chlorophyll, water and carbon dioxide are the important raw materials required for photosynthesis.

Q.14 Show with the help of a sketch that plants are the ultimate source of food.

Ans

The following diagram depicts the synthesis of carbohydrates or glucose by the green plants in the presence of sunlight and the transfer of energy to herbivores and then, to carnivores on consumption:

Explanation: In this food chain, we observe that carnivores (like tigers, lions) depend on herbivores (like deer) for food and energy. A herbivore gets it food and energy by consuming plants. Plants manufacture their food with the help of sunlight. Thus, herbivores and carnivores are all directly or indirectly dependent on plants for food.

Q.15 Fill in the blanks:
(a) Green plants are called _________________ since they synthesise their own food.
(b) The food synthesised by plants is stored as _________________.
(c) In photosynthesis solar energy is absorbed by the pigment called ___________.
(d) During photosynthesis plants take in ______________________ and release __________________.

Ans

(a) Autotrophs
(b) Starch
(c) Chlorophyll
(d) Carbon dioxide, Oxygen

Q.16 Name the following:

(i) A parasitic plant with yellow, slender and branched stem.
(ii) A plant that is partially autotrophic.
(iii) The pores through which leaves exchange gases.

Ans

(i) Cuscuta
(ii) Pitcher plant
(iii) Stomata

(a) Cuscuta is an example of:
(i) autotroph
(ii) parasite
(iii) saprotroph
(iv) host

(b) The plant which traps and feeds on insects is:
(i) Cuscuta
(ii) china rose
(iii) pitcher plant
(iv) rose

Ans

(a) Cuscuta is an example of: (ii) parasite
(b) The plant which traps and feeds on insects is: (iii) pitcher plant

Q.18 Match the items given in Column I with those in Column II:

 Column I Column II Chlorophyll Rhizobium Nitrogen Heterotrophs Cuscuta Pitcher Plant Animals Leaf Insect Parasite

Ans

The correctly matched contents of Column I and Column II are as follows:

 Column I Column II Chlorophyll Leaf Nitrogen Rhizobium Cuscuta Parasite Animals Heterotrophs Insect Pitcher Plant

Q.19 Mark ‘T’ if the statement is true and ‘F’ if it is false:
(i) Carbon dioxide is released during photosynthesis. (T/F)
(ii) Plants that synthesise their food are called saprotrophs. (T/F)
(iii) The product of photosynthesis is not a protein. (T/F)
(iv) Solar energy is converted into chemical energy during photosynthesis. (T/F)

Ans

(i) False
(ii) False
(iii) True
(iv) True

Q.20 Choose the correct option from the following:
Which part of the plant takes in carbon dioxide from the air for photosynthesis?
(i) Root hair
(ii) Stomata
(iii) Leaf veins
(iv) Petals

Ans

(ii) Stomata

Q.21 Choose the correct option from the following:
Plants take carbon dioxide from the atmosphere mainly through their:
(i) roots
(ii) stem
(iii) flowers
(iv) leaves

Ans

(iv) leaves

Q.22 Why do farmers grow many fruits and vegetable crops inside large green houses? What are the advantages to the farmers?

Ans

Green house provides a suitable climatic condition for the plants’ growth by maintaining an average temperature.
This method protects the fruits and vegetables from winds, birds and insects.

Q.23 Fill in the blanks:

(a) The main steps of nutrition in humans are __________, __________, __________, _________ and __________.
(b) The largest gland in the human body is __________.
(c) The stomach releases hydrochloric acid and ___________ juices which act on food.
(d) The inner wall of the small intestine has many finger-like outgrowths called _________.
(e) Amoeba digests its food in the ____________.

Ans

(a) ingestion, digestion, absorption, assimilation, egestion
(b) liver
(c) digestive
(d) villi
(e) food vacuole

Q.24 Mark ‘T’ if the statement is true and ‘F’ if it is false:
(a) Digestion of starch starts in the stomach. (T/F)
(b) The tongue helps in mixing food with saliva. (T/F)
(c) The gall bladder temporarily stores bile. (T/F)
(d) The ruminants bring back swallowed grass into their mouth and chew it for some time. (T/F)

Ans

(a) False
(b) True
(c) True
(d) True

Q.25 Tick (√) mark the correct answer in each of the following:

(a) Fat is completely digested in the
(i) stomach
(ii) mouth
(iii) small intestine
(iv) large intestine

(b) Water from the undigested food is absorbed mainly in the
(i) stomach
(ii) food pipe
(iii) small intestine
(iv) large intestine

Ans

(a) Fat is completely digested in the: (iii) small intestine
(b) Water from the undigested food is absorbed mainly in the: (iv) large intestine

Q.26 Match the items of Column I with those given in Column II:

 Column I Food components Column II Product(s) of digestion Carbohydrates Fatty acids and glycerol Proteins Sugar Fats Amino acids

Ans

 Column I Food components Column II Product(s) of digestion Carbohydrates Sugar Proteins Amino acids Fats Fatty acids and glycerol

Q.27 What are villi? What is their location and function?

Ans

Thousands of minute finger-like projections or outgrowths found in the inner wall of small intestine are called villi. These increase the surface area for maximum and quick absorption of digested food from small intestine into the blood stream.

Q.28 Where is the bile produced? Which component of the food does it help to digest?

Ans

Bile is produced in the liver. It acts upon the fat component of food and breaks down large-sized fat droplets into smaller ones.

Q.29 Name the type of carbohydrate that can be digested by ruminants but not by humans. Give the reason also.

Ans

Cellulose is the type of carbohydrate that can be digested by ruminants and not by humans. It is so because a large sac-like structure called rumen is found in the ruminants between food pipe and small intestine; that contains numerous bacteria which can digest cellulose. Human alimentary canal does not contain such cellulose digesting bacteria and thus, cannot digest cellulose.

Q.30 Why do we get instant energy from glucose?

Ans

We get instant energy from glucose because it is the simplest sugar that readily breaks down into water and carbon dioxide with the release of energy in a living cell. All the food components ultimately get converted into glucose.

Q.31 Which part of the digestive canal is involved in:
(i) absorption of food ________________.
(ii) chewing of food ________________.
(iii) killing of bacteria ________________.
(iv) complete digestion of food ________________.
(v) formation of faeces ________________.

Ans

(i) Small intestine
(ii) Buccal cavity
(iii) Stomach
(iv) Small intestine
(v) Large intestine

Q.32 Write one similarity and one difference between the nutrition in amoeba and human beings.

Ans

1. Nutrition in Amoeba is similar to that of human beings because both comprise of five basic steps, which are ingestion, digestion, absorption, assimilation and egestion.

2. One of the important differences in the nutrition in Amoeba with that of human beings is the lack of alimentary canal and digestive organs. Amoeba being a single-celled organism contains organelles for performing different set of functions instead of organs and organ systems.

Q.33 Match the items of Column I with suitable items in Column II

 Column I Column II (a) Salivary gland (i) Bile juice secretion (b) Stomach (ii) Storage of undigested food (c) Liver (iii) Saliva secretion (d) Rectum (iv) Acid release (e) Small intestine (v) Digestion is completed (f) Large intestine (vi) Absorption of water (vii) Release of faeces

Ans

 Column I Column II (a) Salivary gland (iii) Saliva secretion (b) Stomach (iv) Acid release (c) Liver (i) Bile juice secretion (d) Rectum (vii) Release of faeces (e) Small intestine (v) Digestion is completed (f) Large intestine (vi) Absorption of water

Q.34 Label Fig. 2.11 of the digestive system.

Ans

The well labeled diagram of the given figure is as follows:

Q.35 Can we survive only on raw, leafy vegetables / grass? Discuss.

Ans

No, we cannot survive only on raw, leafy vegetables and grass. It is so because main component present in such a diet is cellulose which cannot be digested by human beings. Cellulose can only be digested by certain bacteria which are present in the rumen of ruminant animals. These bacteria breakdown the cellulose and produce nutrients and energy for themselves and the ruminants. Therefore, only ruminants can survive on diet consisting of raw vegetables and grass.

Q.36 Name the elements that determine the weather of a place.

Ans

Some important elements that determine the weather of a place are as follows:

1. Temperature
2. Rainfall
3. Humidity
4. Wind-speed

Q.37 When are the maximum and minimum temperatures likely to occur during the day?

Ans

The maximum temperature of a day is likely to occur in the afternoon while minimum temperature of a day is likely to occur in the early morning.

Q.38 Fill in the blanks:
(i) The average weather taken over a long time is called ___________.
(ii) A place receives very little rainfall and the temperature is high throughout the year, the climate of that place will be___________ and ___________ .
(iii) The two regions of the earth with extreme climatic conditions are ___________ and __________.

Ans

(i) Climate
(ii) dry, hot
(iii) tropical region, polar region

Q.39 Indicate the type of climate of the following areas:
(a) Jammu and Kashmir: ____________
(b) Kerala: ______________________
(c) Rajasthan: _______________
(d) North-east India: _______________

Ans

(a) Jammu and Kashmir: moderately hot and wet for a part of the year
(b) Kerala: very hot and wet
(c) Rajasthan: hot and dry
(d) North-east India: wet

Q.40 Which of the two changes frequently, weather or climate?

Ans

Weather of a place changes on a day to day basis while climate remains unchanged for years. Thus, we can say that weather changes frequently and not the climate.

Q.41 Following are some of the characteristics of animals:
(i) Diets heavy on fruits
(ii) White fur
(iii) Need to migrate
(iv) Loud voice
(vi) Layer of fat under skin
(vii) Wide and large paws
(viii) Bright colours
(ix) Strong tails
(x) Long and large beak
For each characteristic indicate whether it is adaptation for tropical rainforests or polar regions. Do you think that some of these characteristics can be adapted for both regions?

Ans

The given characteristics can be classified as follows:

 S.no Characterisic Adaptations for Tropical Rainforest Polar Regions 1 Diets heavy on fruits White fur 2 Loud voice Layer of fat under skin 3 Sticky pads on feet Wide and large paws 4 Bright colors Need to migrate 5 Strong tails 6 Long and large break

Each of the given characteristics is an adaption for a particular type of region. Therefore, none of the characteristics can be considered as an adaptation for both tropical rainforests and polar regions.

Q.42 The tropical rainforest has a large population of animals. Explain why it is so.

Ans

Tropical rainforests have large population of animals because these areas have high temperature and plenty of rainfall throughout the year. Such continuous hot and humid conditions provide these areas with rich nutrient resources to support large variety and population of plants and animals.

Q.43 Explain, with examples, why we find animals of certain kind living in particular climatic conditions.

Ans

Animals of certain kind are found living in a particular set of climatic conditions because they are well-adapted to survive and flourish in them. For instance, polar bear is found only in polar regions, as it is best adapted to cold climatic conditions. Its characteristics like, thick white fur, fat layer beneath the skin, large wide paws for walking on snow and swimming are all adaptations for the cold climate. On the other hand, monkeys have characteristics like, limbs to climb on trees, long tails, feeding on fruits, sharp hearing sense and eyesight. These characteristics make them suitable to live in hot and humid climatic conditions like those of tropical rainforests.

Q.44 How do elephant living in the tropical rain forest adapt itself?

Ans

The elephant possesses following characteristics which adapt it to survive in the tropical rain forest:

1. Sharp sense of smell
2. Strong teeth and tusk to obtain food and feed on variety of foods
3. Large pinna to hear even faintest of sounds and for fanning to keep cool under hot conditions
4. Loud voice for making warning calls
5. Large and strong trunk to protect as well as in picking up food

Q.45 Choose the correct option which answers the following question:
A carnivore with stripes on its body moves very fast while catching its prey. It is likely to be found in
(i) polar regions
(ii) deserts
(iii) oceans
(iv) tropical rainforests

Ans

(iv) tropical rainforests

Q.46 Choose the correct option which answers the following question:
Which features adapt polar bears to live in extremely cold climate?
(i) A white fur, fat below skin, keen sense of smell.
(ii) Thin skin, large eyes, a white fur.
(iii) A long tail, strong claws, white large paws.
(iv) White body, paws for swimming, gills for respiration.

Ans

(i) A white fur, fat below skin, keen sense of smell.

Q.47 Choose the correct option which answers the following question:
Which option best describes a tropical region?
(i) hot and humid
(ii) moderate temperature and heavy rainfall
(iii) cold and humid
(iv) hot and dry

Ans

(i) hot and humid

Q.48 Tick the most suitable answer.
In addition to the rock particles, the soil contains
(i) air and water
(ii) water and plants
(iii) minerals, organic matter, air and water
(iv) water, air and plants

Ans

In addition to the rock particles, the soil contains (iii) minerals, organic matter, air and water.

Q.49 Tick the most suitable answer.
The water holding capacity is the highest in
(i) sandy soil
(ii) clayey soil
(iii) loamy soil
(iv) mixture of sand and loam

Ans

The water holding capacity is the highest in (ii) clayey soil.

Q.50 Match the items in Column I with those in Column II:

 Column I Column II (i) A home for living organisms (a) Large particles (ii) Upper layer of the soil (b) All kinds of soil (iii) Sandy soil (c) Dark in colour (iv) Middle layer of the soil (d) Small particles and packed tight (v) Clayey soil (e) Lesser amount of humus

Ans

The correctly matched contents of Column I and Column II are as follows:

 Column I Column II (i) A home for living organisms (b) All kinds of soil (ii) Upper layer of the soil (c) Dark in colour (iii) Sandy soil (a) Large particles (iv) Middle layer of the soil (e) Lesser amount of humus (v) Clayey soil (d) Small particles and packed tight

Q.51 Explain how soil is formed.

Ans

Soil is formed by the process of weathering. In this process, rocks are broken into smaller particles by the action of wind, water and various other climatic factors. The slow and continuous action of these factors converts massive rocks into fine particles of soil over a period of millions of years.

Q.52 How is clayey soil useful for crops?

Ans

Clayey soil has maximum water holding capacity due to which it retains water for absorption by the plants for longer period of time. Also, clayey soil is rich in humus that provides nutrients to the plants for their growth. Thus, clayey soil is very useful for the crops.

Q.53 List the differences between clayey soil and sandy soil.

Ans

The differences between clayey soil and sandy soil are as follows:

 S. no. Clayey soil Sandy soil 1. Soil particles are very fine. Soil particles are very large. 2. Soil particles are compactly bound to each other. Soil particles are not bound to each other. 3. Soil has high water holding capacity. Soil has poor water holding capacity. 4. Soil supports the growth of most of the crops. Soil supports the growth of only few types of crops.

Q.54 Sketch the cross section of soil and label the various layers.

Ans

Following is the well-labelled sketch of the cross-section of soil and its various layers:

Q.55 Razia conducted an experiment in the field related to the rate of percolation. She observed that it took 40 min for 200 mL of water to percolate through the soil sample. Calculate the rate of percolation.

Ans

The percolation rate is given by the following expression:
Percolation rate = amount of water (mL)/time taken(min)
Therefore, Percolation rate = 200 mL/40min
= 5 mL/min

Q.56 Explain how soil pollution and soil erosion could be prevented.

Ans

Ways of preventing soil pollution are as follows:

1. Minimising the use of pesticides and fertilisers
2. Banning the use of polythene
3. Treating chemicals and other waste products of industries before releasing them into soil or water
4. Abandoning the practice of defecation in open

Ways of preventing soil erosion are as follows:
1. Planting of trees at large scale
2. Putting check on deforestation
3. Protecting and expanding forest covers

Q.57 Solve the following crossword puzzle with the clues given:

Across
2. Plantation prevents it.
5. Use should be banned to avoid soil pollution.
6. Type of soil used for making pottery.
7. Living organism in the soil.

Down
1. In desert soil erosion occurs through.
3. Clay and loam are suitable for cereals like.
4. This type of soil can hold very little water.
5. Collective name for layers of soil.

Ans

The correctly solved crossword puzzle is as follows:

Q.58 Why do we often sneeze when we inhale a lot of dust-laden air?

Ans

We often sneeze on inhaling dust-laden air because dust particles get entangled in the hair present in the nostrils which irritate the nasal membrane and cause sneezing. Hair found in the nostrils prevents entry of dust particles into lungs and sneezing expels them from the nose, allowing only clean air to enter the lungs.

Q.59 Take three test-tubes. Fill ¾th of each with water. Label them A, B and C. Keep a snail in test-tube A, a water plant in test-tube B and in C, keep snail and plant both. Which test-tube would have the highest concentration of CO2?

Ans

All the organisms produce carbon dioxide and water as the final products of respiration.
Test tube A will have the highest concentration of CO2 because the snail kept in it produces carbon dioxide by the process of respiration. On the other hand, test tube B will have the least concentration of carbon dioxide among the three because the water plant performs photosynthesis during which carbon dioxide is utilised and oxygen is produced. In the test tube C, carbon dioxide produced by the snail and by the plant is used up in the process of photosynthesis performed by the plant.

(a) In cockroaches, air enters the body through
(i) lungs
(ii) gills
(iii) spiracles
(iv) skin

(b) During heavy exercise, we get cramps in the legs due to the accumulation of
(i) carbon dioxide
(ii) lactic acid
(iii) alcohol
(iv) water

(c) Normal range of breathing rate per minute in an average adult person at rest is:
(i) 9-12
(ii) 15-18
(iii) 21-24
(iv) 30-33

(d) During exhalation, the ribs
(i) move outwards
(ii) move downwards
(iii) move upwards
(iv) do not move at all

Ans

(a) In cockroaches, air enters the body through (iii) spiracles.
(b) During heavy exercise, we get cramps in the legs due to the accumulation of (ii) lactic acid.
(c) Normal range of breathing rate per minute in an average adult person at rest is: (ii) 15-18.
(d) During exhalation, the ribs (ii) move downwards.

Q.61 Match the items in Column I with those in Column II:

 Column I Column II (a) Yeast (i) Earthworm (b) Diaphragm (ii) Gills (c) Skin (iii) Alcohol (d) Leaves (iv) Chest cavity (e) Fish (v) Stomata (f) Frog (vi) Lungs and skin (vii) Tracheae

Ans

The correctly matched contents of Column I with Column II are as follows:

 Column I Column II (a) Yeast (iii) Alcohol (b) Diaphragm (iv) Chest cavity (c) Skin (i) Earthworm (d) Leaves (v) Stomata (e) Fish (ii) Gills (f) Frog (vi) Lungs and skin

Q.62 Mark ‘T’ if the statement is true and ‘F’ if it is false:
(i) During heavy exercise the breathing rate of a person slows down. (T/F)
(ii) Plants carry out photosynthesis only during the day and respiration only at night. (T/F)
(iii) Frogs breathe through their skins as well as their lungs. (T/F)
(iv) The fishes have lungs for respiration. (T/F)
(v) The size of the chest cavity increases during inhalation. (T/F)

Ans

(i) False
(ii) False
(iii) True
(iv) False
(v) True

Q.63 The mountaineers carry oxygen with them because:
(a) At an altitude of more than 5 km there is no air.
(b) The amount of air available to a person is less than that available on the ground.
(c) The temperature of air is higher than that on the ground.
(d) The pressure of air is higher than that on the ground.

Ans

The mountaineers carry oxygen with them because:
(b) The amount of air available to a person is less than that available on the ground.

Q.64 Match the structures given in Column I with functions given in Column II.

 Column I Column II (i) Stomata (a) Absorption of water (ii) Xylem (b) Transpiration (iii) Root hairs (c) Transport of food (iv) Phloem (d) Transport of water (e) Synthesis of carbohydrates

Ans

The correctly matched contents of Column I with Column II are as follows:

 Column I Column II (i) Stomata (b) Transpiration (ii) Xylem (d) Transport of water (iii) Root hairs (a) Absorption of water (iv) Phloem (c) Transport of food

Q.65 Fill in the blanks.

(i) The blood from the heart is transported to all parts of the body by the ___________.
(ii) Haemoglobin is present in __________ cells.
(iii) Arteries and veins are joined by a network of ________.
(iv) The rhythmic expansion and contraction of the heart is called ___________.
(v) The main excretory product in human beings is _________.
(vi) Sweat contains water and _________.
(vii) Kidneys eliminate the waste materials in the liquid form called __________.
(viii) Water reaches great heights in the trees because of suction pull caused by ____________.

Ans

(i) arteries
(ii) red blood
(iii) capillaries
(iv) Heartbeat
(v) urea
(vi) salts
(vii) urine
(viii) transpiration

Q.66 Choose the correct option:
(a) In plants, water is transported through
(i) xylem
(ii) phloem
(iii) stomata
(iv) root hair

(b) Water absorption through roots can be increased by keeping the plants
(ii) in dim light
(iii) under the fan
(iv) covered with a polythene bag

Ans

(a) In plants, water is transported through (i) xylem
(b) Water absorption through roots can be increased by keeping the plants (iii) under the fan

Q.67 Why is transport of materials necessary in a plant or in an animal? Explain.

Ans

The transport of materials is necessary in all organisms because it allows exchange of gases, supply of nutrients and removal of waste materials. All plants and animals have well developed transport systems to ensure continuous supply of oxygen, water and food to all parts of the body. Also, the toxic waste materials generated due to various activities is removed from the body by means of transport system only.

Q.6 8 What will happen if there are no platelets in the blood?

Ans

In the absence of platelets, clot formation will not take place that will result in severe blood loss in case of injury. When a blood vessel is injured, platelets form blood clot that covers the wound protecting it from disease causing microorganisms and preventing blood loss.

Q.69 What are stomata? Give two functions of stomata.

Ans

Stomata are small pores present on the surface of the leaves forming an opening for exchange of materials. Two important functions of stomata are as follows:

1. Stomata allow exchange of gases, that is, intake of carbon dioxide and release of oxygen through it.
2. Stomata regulate rate of evaporation of water from the leaf surface, which is called transpiration.

Q.70 Does transpiration serve any useful function in the plants? Explain.

Ans

Transpiration is the loss of water molecules from stomata that causes a suction pull on the water column in xylem. Due to this suction pressure, water is transported to a great height in large trees through the xylem.

Q.71 What are the components of blood?

Ans

There are four major components of blood:

1. Plasma
2. Red blood cells
3. White blood cells
4. Platelets

Q.72 Why is blood needed by all the parts of a body?

Ans

Blood is the only means of supplying oxygen and nutrients derived from digested food to all parts of the body and removing waste products from them. As blood is the sole means of transport of materials, it is needed by all parts of the body.

Q.73 What makes the blood look red?

Ans

Blood appears red because of the presence of a red-coloured pigment in red blood cells called haemoglobin. This pigment binds with oxygen and carries it to all parts of body.

Q.74 Describe the function of the heart.

Ans

Heart is a muscular organ that pumps blood to each and every organ of the body. It helps in pumping the blood to lungs for oxygenation. Pumping action of heart keeps blood circulating in the vessels through which various important substances, like respiratory gases and nutrients, are transported. Heart consists of two atria and two ventricles, which contract and relax rhythmically to give rise to the pumping action.

Q.75 Why is it necessary to excrete waste products?

Ans

Waste products need to be excreted because these are toxic in nature and their circulation or presence in body cause damage to various organs of the body.

Q.76 Draw a diagram of the human excretory system and label the various parts.

Ans

A well-labelled diagram of human excretory system is as follows:

Q.77 Fill in the blanks:
(a) Production of new individuals from the vegetative part of parent is called _____________.
(b) A flower may have either male or female reproductive parts. Such a flower is called _____________.
(c) The transfer of pollen grains from the anther to the stigma of the same or of another flower of the same kind is known as _____________.
(d) The fusion of male and female gametes is termed as _____________.
(e) Seed dispersal takes place by means of _____________, _____________ and _____________.

Ans

(a) Vegetative propagation
(b) Unisexual flower
(c) Self-pollination
(d) Fertilisation
(e) wind, water and animals

Q.78 Describe the different methods of asexual reproduction. Give examples.

Ans

There are four different methods of asexual reproduction which are as follows:

Fragmentation- In this process, an organism, like algae, breaks down into two or more fragments and each fragment gives rise to a new individual. For example, Spirogyra undergoes fragmentation as shown below:

Budding- In this process,a small bulb-like projection emerges from the mother cell that grows and develops into a new individual. Yeast undergoes budding to reproduce asexually that takes place in the following manner:

Spore formation- Most of the fungi reproduce asexually by forming tiny spores, which germinate to give rise to new individuals in the following manner

Vegetative propagation- It is seen in many plants in which vegetative plant parts give rise to new plants. For example, leaf of Bryophyllum and eyes of potato form new plants as shown below

Q.79 Explain what you understand by sexual reproduction.

Ans

Sexual reproduction is the process of producing offspring by an organism with involvement of male and female sexes. It involves fusion of male and female gametes that leads to the formation of zygote. The male and female gametes are produced by male and female flower parts, respectively. Male part of the plant is stamen that bears male gametes inside the pollens and female part of the plant is pistil that bears ovary containing female gamete or ovum. Pollens fall on stigma of the flower and germinate to form pollen tubes containing male gametes. Pollen tube enters the ovary releasing male gametes. One of the gametes fuses with ovum and undergo fertilisation to form zygote, completing the process of sexual reproduction.

Q.80 State the main difference between asexual and sexual reproduction.

Ans

In asexual reproduction, single parent gives rise to the offspring without producing seeds whereas, in sexual reproduction two parents of opposite sex participate to produce a seed from which a new individual emerges.

Q.81 Sketch the reproductive parts of a flower.

Ans

Various male and female reproductive parts of the flower can be sketched as follows:

Q.82 Explain the difference between self-pollination and cross-pollination.

Ans

In self-pollination, the pollens are deposited on the stigma of either the same flower or another flower on the same plant. In cross-pollination, pollens are deposited from one flower to another flower of the same kind, borne on another plant.

Q.83 How does the process of fertilisation take place in flowers?

Ans

The process of fertilisation takes place after pollination. Pollens on reaching the stigma of the flower germinate to form pollen tubes that carry male gametes. One of the male gametes fuses with female gamete on reaching ovary forming zygote.

Q.84 Describe the various ways by which seeds are dispersed.

Ans

Seed are carried by wind, water and animals for dispersal.

1. Some seeds, which are light and have wings or hair, are easily carried away by wind. For example, seeds of maple have wings and seeds of madar have hair.
2. Some other seeds develop thick fibrous coating to acquire floating ability and are dispersed by water. For example, coconut seed has fibrous seed coat.
3. Some other plants produce seeds with hook-like structures or spines with the help of which they get attached to the bodies of animals and disperse to larger distances. For example, seeds of Xanthium and Urena have hooks and spines.

Q.85 Match ite ms in Column I with those in Column II:

 Column I Column II (a) Bud (i) Maple (b) Eyes (ii) Spirogyra (c) Fragmentation (iii) Yeast (d) Wings (iv) Bread mould (e) Spores (v) Potato (vi) Rose

Ans

The correctly matched contents of Column I with Column II are as follows:

 Column I Column II (a) Bud (iii) Yeast (b) Eyes (v) Potato (c) Fragmentation (ii) Spirogyra (d) Wings (i) Maple (e) Spores (iv) Bread mould

Q.86 Tick (√) the correct answer:

(a) The reproductive part of a plant is the
(i) leaf
(ii) stem
(iii) root
(iv) flower

(b) The process of fusion of the male and the female gametes is called
(i) fertilisation
(ii) pollination
(iii) reproduction
(iv) seed formation

(c) Mature ovary forms the
(i) seed
(ii) stamen
(iii) pistil
(iv) fruit

(d) A spore producing organism is
(i) rose
(iii) potato
(iv) ginger

(e) Bryophyllum can reproduce by its
(i) stem
(ii) leaves
(iii) roots
(iv) flower

Ans

(a) The reproductive part of a plant is the (iv) flower.
(b) The process of fusion of the male and the female gametes is called (i) fertilisation.
(c) Mature ovary forms the (iv) fruit.
(d) A spore producing plant is (ii) bread mould.
(e) Bryophyllum can reproduce by its (ii) leaves.

Q.87 Mark ‘T’ if the statement is true and ‘F’ if it is false:
(a) The freshwater stored in the ground is much more than that present in the rivers and lakes of the world. (T/F)
(b) Water shortage is a problem faced only by people living in rural areas. (T/F)
(c) Water from rivers is the only source for irrigation in the fields. (T/F)
(d) Rain is the ultimate source of water. (T/F)

Ans

(a) True
(b) False
(c) False
(d) True

Q.88 Explain how groundwater is recharged?

Ans

Groundwater is recharged by the seepage of water through cracks and gaps present in the layers of soil from rivers, ponds, streams and rainwater. There are small crevices and empty spaces present between the rocks through which rainwater infiltrates, reaches to the water table and replenishes it.

Q.89 There are ten tubewells in a lane of fifty houses. What could be the long term impact on the water table?

Ans

Tubewells are used to draw underground freshwater to the surface to meet growing demands of water for domestic, industrial and agricultural consumption. If ten tubewells are installed in a lane of fifty houses, the ground water is drawn out at a faster rate that results in rapid depletion of water table in that area.

Q.90 You have been asked to maintain a garden. How will you minimise the use of water?

Ans

The usage of water required for maintaining a garden can be minimised by using drip irrigation. In this technique, a network of narrow pipes is used for delivering water directly at the base of the plant. This technique prevents wastage of water in watering the garden plants as well as in irrigating the agricultural fields.

Q.91 Explain the factors responsible for the depletion of water table.

Ans

The factors responsible for the depletion of water table are as follows:

1. Increasing requirements of water due to ever rising population, rapid industrial growth and agricultural activities
2. Decreasing effective area for seepage of water due to expansion of road networks, townships and cities
3. Large scale deforestation
4. Wastage of water
5. Increased dependence on ground water as a source of freshwater due to pollution of rivers and ponds

Q.92 Fill in the blanks with the appropriate answers:
(a) People obtain groundwater through________ and ________.
(b) Three forms of water are ________, ________ and ________.
(c) The water bearing layer of the earth is ________.
(d) The process of water seepage into the ground is called ________.

Ans

(a) tube wells, hand pumps
(b) ice, water, vapour
(c) Aquifer
(d) Infiltration

Q.93 Which one of the following is not responsible for water shortage?
(i) Rapid growth of industries
(ii) Increasing population
(iii) Heavy rainfall
(iv) Mismanagement of water resources

Ans

(iii) Heavy rainfall

Q.94 Choose the correct option. The total water
(i) in the lakes and rivers of the world remains constant.
(ii) under the ground remains constant.
(iii) in the seas and oceans of the world remains constant.
(iv) of the world remains constant.

Ans

The total water (iv) of the world remains constant.

Q.95 Make a sketch showing groundwater and water table.Label it.

Ans

Following sketch shows groundwater and water table:

Q.96 Fill in the blanks:
(a) Cleaning of water is a process of removing _________.
(b) Wastewater released by houses is called _________.
(c) Dried _________ is used as manure.
(d) Drains get blocked by _________ and _________.

Ans

(a) Cleaning of water is a process of removing pollutants.
(b) Wastewater released by houses is called sewage.
(c) Dried sludge is used as manure.
(d) Drains get blocked by cooking oil and fats.

Q.97 What is sewage? Explain why it is harmful to discharge untreated sewage into rivers or seas.

Ans

Sewage is wastewater having dissolved and suspended impurities released from homes, industries, hospitals, offices and other users.

It is harmful to discharge untreated sewage into rivers or seas because:

1. Untreated sewage contaminates seas and rivers.
2. Sewage contains various contaminants including disease causing bacteria and other microorganism. Disease causing bacteria and other microorganism may cause dysentery, cholera, typhoid, etc.
3. Pesticide, herbicides present in the sewage may cause various disorders in living beings.

Therefore, it is harmful to discharge untreated sewage into rivers or seas.

Q.98 Why should oils and fats be not released in the drain? Explain.

Ans

Oils and fats should not be released in the drain because they can harden and block the pipes. In an open drain the fats clog the soil pores which affect its water filtering efficiency. Therefore, oils and fats should be thrown in dustbins.

Q.99 Describe the steps involved in getting clarified water from wastewater.

Ans

Steps involved in getting clarified water from wastewater are as follows:

1. Wastewater is passed through bar screens. Large objects like rags, plastic packets and napkins are separated by passing water through bar screens.
2. Water is then passed through grit and sand removal tank. Here, water is passed at a slow speed to allow pebbles and grit to settle down.
3. Water is then allowed to settle in a large tank which is sloped towards the middle. Here, solid wastes like faeces settle down at the bottom. These solid wastes are called sludge. Sludge is removed with a scraper. A skimmer removes the floating wastes like oil and grease. Water is then passed through water clarifier. Water cleared by this process is called clarified water.

Q.100 What is sludge? Explain how it is treated.

Ans

Semi-solid wastes such as faeces that settle down at the bottom during wastewater treatment are called sludge. Sludge is removed with a scraper. The sludge is then transferred to a separate tank where it is decomposed by the anaerobic bacteria. In this process biogas is produced.

The biogas produced can be used as a fuel or can be used to produce electricity.

Q.101 Untreated human excreta is a health hazard. Explain.

Ans

Untreated human excreta is a health hazard because it pollutes soil and water. Both the surface water and ground water gets polluted. Due to contamination of ground water, various water bodies such as wells, tube wells, ponds, etc. also get contaminated as ground water is the source of water for them. When water from these contaminated sources is used for domestic purposes, it may cause several water borne diseases such as cholera, dysentery, meningitis, etc.

Q.102 Name two chemicals used to disinfect water.

Ans

Two chemicals used to disinfect water are chlorine and ozone.

Q.103 Explain the function of bar screens in a wastewater treatment plant.

Ans

In wastewater treatment plant bar screens are used to separate large objects like rags, plastic packets, napkins, etc. by passing water through them.

Q.104 You must be familiar with the following nursery rhymes:

1. ‘Baa baa black sheep, have you any wool.’
2. ‘Mary had a little lamb, whose fleece was white as snow.’

1. Which parts of the black sheep have wool?
2. What is meant by the white fleece of the lamb?

Ans

1. Wool is obtained from fleece (hair) of sheep.
2. White fleece refers to white thick hairy coat of lamb.

Q.105 Explain the relationship between sanitation and disease.

Ans

Lack of sanitation may cause diseases. Large fraction of people defaecate in open, on dry river boards, railway tracks and many times directly in water. It results in pollution of water and many diseases. Diseases like typhoid, meningitis, hepatitis, dysentery, etc. are caused due to poor sanitation.

Q.106 Outline your role as an active citizen in relation to sanitation.

Ans

Our role as an active citizen should be in maintaining sanitation in neighbourhood and at public places. We can limit the type of waste and quantity of waste produced. For this every citizen should follow these steps.

1. Do not drop litter. Carry the litter to home if any dustbin is not found nearby.
2. Contribute and coordinate with government plans.
3. If drains are not covered, report it to municipality.
4. If the sewage of any particular house makes the neighbourhood dirty, request them to be more considerable about others health.

Q.107 The silkworm is (a) a caterpillar, (b) a larva. Choose the correct option.

1. a
2. b
3. both a and b
4. neither a nor b

Ans

The correct option is iii. both a and b.

Q.108 Which of the following does not yield wool?

1. Yak
2. Camel
3. Goat
4. Woolly dog

Ans

4. Woolly dog

Q.109 Study the following statements about ozone:
(a) It is essential for breathing of living organisms.
(b) It is used to disinfect water.
(c) It absorbs ultraviolet rays.(d) Its proportion in air is about 3%.

Which of these statements are correct?
(i) (a), (b) and (c)
(ii) (b) and (c)
(iii) (a) and (b)
(iv) All four

Ans

The correct option is option (ii).

Q.110 What is meant by the following terms?

1. Rearing
2. Shearing
3. Sericulture

Ans

1. Rearing: Bringing up and looking after farm animals is known as rearing.
2. Shearing: The process of removing the fleece of sheep along with a thin layer of skin is called shearing.
3. Sericulture: Rearing (raising) of silkworms for producing silk is known as sericulture.

Q.111 Given below is a sequence of steps in the processing of wool. Which are the missing steps? Add them.
Shearing, __________, sorting, __________, ___________.

Ans

Shearing, scouring, sorting, drying, carding.

Q.112 Make sketches of the two stages in the life history of the silk moth which are directly related to the production of silk.

Ans

Q.113 Out of the following, which are the two terms related to silk production?
Sericulture, floriculture, moriculture, apiculture and silviculture.
Hint:
(i) Silk production involves cultivation of mulberry leaves and rearing silkworms.
(ii) Scientific name of mulberry is Morus alba.

Ans

Out of the given terms, those related to silk production are sericulture and moriculture.
Note:
Sericulture: Rearing of silkworms for the production of silk is known as sericulture.
Moriculture: Science of mulberry plant cultivation is known as moriculture.

Q.114 Match the words of column I with those given in Column II:

 Column I Column II 1. Scouring (a) Yields silk fibres 2. Mulberry leaves (b) Wool yielding animal 3. Yak (c) Food of silk worm 4. Cocoon (d) Cleaning sheared skin

Ans

 Column I Column II 1. Scouring (d) Cleaning sheared skin 2. Mulberry leaves (c) Food of silk worm 3. Yak (b) Wool yielding animal 4. Cocoon (a) Yields silk fibres

Q.115 Draw the circuit diagram to represent the circuit shown in Fig.14.21.

Ans

The electrical components and their relation with each other shown above can be represented by following circuit diagram:

Q.116 State similarities and differences between the laboratory thermometer and the clinical thermometer.

Ans

Similarities between clinical and laboratory thermometers are as follows:

1. Both of them are used for measuring temperature.
2. Both of them use mercury as an indicator for rise and fall in temperature.

Differences between clinical and laboratory thermometers are as follows:

1. Clinical thermometer is used to measure body temperature whereas; laboratory thermometer is used to measure temperature of substances.
2. The range of clinical thermometer is from 35°C to 42°C while that of laboratory thermometer is from minus 10°C to 110°C.

Q.117 Give two examples each of conductors and insulators of heat.

Ans

The examples of conductors of heat are as follows:

1. Aluminium
2. Copper

The examples of insulators of heat are as follows:

1. Wood
2. Rubber

Q.118 Classify the changes involved in the following processes as physical or chemical changes:
(a) Photosynthesis
(b) Dissolving sugar in water
(c) Burning of coal
(d) Melting of wax
(e) Beating aluminium to make aluminiun foil
(f) Digestion of food

Ans

(a) Photosynthesis: Chemical change
(b) Dissolving sugar in water: Physical change
(c) Burning of coal: Chemical change
(d) Melting of wax: Physical change
(e) Beating aluminium to make aluminium foil: Physical change
(f) Digestion of food: Chemical change

Q.119 Fill in the blanks :
(a) The hotness of an object is determined by its __________.
(b) Temperature of boiling water cannot be measured by a _____________ thermometer.
(c) Temperature is measured in degree ______________.
(d) No medium is required for transfer of heat by the process of __________.
(e) A cold steel spoon is dipped in a cup of hot milk. Heat is transferred to its other end by the process of ______________.
(f ) Clothes of ______________ colours absorb more heat better than clothes of light colours.

Ans

(a) The hotness of an object is determined by its temperature.
(b) Temperature of boiling water cannot be measured by a clinical thermometer.
(c) Temperature is measured in degree Celsius.
(d) No medium is required for transfer of heat by the process of radiation.
(e) A cold steel spoon is dipped in a cup of hot milk. Heat is transferred to its other end by the process of conduction.
(f ) Clothes of dark colours absorb more heat better than clothes of light colours.

Q.120 Fig.14.22 shows four cells fixed on a board. Draw lines to indicate how you will connect their terminals with wires to make a battery of four cells.

Ans

The correct connection of the terminals of four cells with wires to make a battery is as follows, in which positive side of one battery to the negative side of the other:

Q.121 State whether the following statements are true or false. In case a statement is false, write the corrected statement in your notebook.
(a) Cutting a log of wood into pieces is a chemical change. (True/False)
(b) Formation of manure from leaves is a physical change. (True/False)
(c) Iron pipes coated with zinc do not get rusted easily. (True/False)
(d) Iron and rust are the same substances. (True/False)
(e) Condensation of steam is not a chemical change. (True/False)

Ans

(a) Cutting a log of wood into pieces is a chemical change. (False)
Corrected statement: Cutting a log of wood into pieces is a physical change.

(b) Formation of manure from leaves is a physical change. (False)
Corrected statement: Formation of manure from leaves is a chemical change.

(c) Iron pipes coated with zinc do not get rusted easily. (True)

(d) Iron and rust are the same substances. (False)
Corrected statement: Iron and rust are different substances.

(e) Condensation of steam is not a chemical change. (True)

Q.122 Match the following:

 (i) Land breeze blows during (a) summer (ii) Sea breeze blows during (b) winter (iii) Dark coloured clothes are preferred during (c) day (iv) Light coloured clothes are preferred during (d) night

Ans

The correctly matched contents of the two given columns are as follows:

 (i) Land breeze blows during (d) Night (ii) Sea breeze blows during (c) Day (iii) Dark coloured clothes are preferred during (b) Winter (iv) Light coloured clothes are preferred during (a) Summer

Q.123 Fill in the blanks in the following statements:
(a) When carbon dioxide is passed through lime water, it turns milky due to the formation of ________.
(b) The chemical name of baking soda is ________.
(c) Two methods by which rusting of iron can be prevented are _________ and _________.
(d) Changes in which only ________ properties of a substance change are called physical changes.
(e) Changes in which new substances are formed are called _________ changes.

Ans

(a) When carbon dioxide is passed through lime water, it turns milky due to the formation of calcium carbonate.
(b) The chemical name of baking soda is sodium hydrogencarbonate.
(c) Two methods by which rusting of iron can be prevented are painting and galvanisation.
(d) Changes in which only physical properties of a substance change are called physical changes.
(e) Changes in which new substances are formed are called chemical changes.

Q.124 Discuss why wearing more layers of clothing during winter keeps us warmer than wearing just one thick piece of clothing.

Ans

Wearing more layers of clothing during winter keeps us warmer than wearing just one thick piece of clothing because in between the multiple layers of clothing, air is trapped that prevents the loss of heat from the body to the surroundings. Air is a poor conductor of heat and prevents the transfer of heat from one region to the other. This trapped air in between the layers of clothing keeps us warmer than the single thick clothing.

Q.125 The bulb in the circuit shown in Fig.14.23 does not glow. Can you identify the problem? Make necessary changes in the circuit to make the bulb glow.

Ans

The bulb in the given diagram does not glow because positive sides of the cells are shown connected to each other. Rearrange the cells in a manner that negative side of one cell comes in contact with positive side of the other. By reversing the sides of cell, the circuit will complete and bulb will glow.

Q.126 Classify the following as motion along a straight line, circular or oscillatory motion:
(i) Motion of your hands while running.
(ii) Motion of a horse pulling a cart on a straight road.
(iii) Motion of a child in a merry-go-round.
(iv) Motion of a child on a see-saw.
(v) Motion of the hammer of an electric bell.
(vi) Motion of a train on a straight bridge.

Ans

 S.No. Straight Line Motion Circular Motion Oscillatory Motion 1. Motion of a horse pulling a cart on a straight road. Motion of a child in a merry-go-round. Motion of your hands while running. 2. Motion of a train on a straight bridge. Motion of a child on a see-saw. 3. Motion of the hammer of an electric bell.

Q.127 Name any two effects of electric current.

Ans

The two effects of electric current are as follows:

1. Heating effect
2. Magnetic effect

Q.128 When baking soda is mixed with lemon juice, bubbles are formed with the evolution of a gas. What type of change is it? Explain

Ans

When baking soda (sodium hydrogencarbonate) is mixed with lemon juice (citric acid), bubbles are produced due to the formation of carbon dioxide and other substances. It is a chemical change. Therefore, we cannot get back the original substances, i.e., lemon juice and baking soda.

Q.129 When the current is switched on through a wire, a compass needle kept nearby gets deflected from its north-south position. Explain.

Ans

The deflection of compass needle in north-south position indicates that as soon as current is switched on through a wire, a magnetic field develops around it. Due to this magnetic field, the wire acts like a magnet which has north and south poles. Formation of magnetic north and south poles deflects the compass needle in north-south position.

Q.130 When a candle burns, both physical and chemical changes take place. Identify these changes. Give another example of a familiar process in which both the chemical and physical changes take place.

Ans

When a candle burns, both physical and chemical changes take place.When we burn a candle, the wax melts which can be converted back into solid wax on cooling. This shows that melting of wax is a physical change. Burning of a candle also produces light along with some gases like carbon dioxide. Hence, burning of the wick of a candle is a chemical change.
Cooking food is another example in which both physical and chemical changes take place.
Physical change: appearance of ingredients
Chemical change: new substances are formed

Q.131 Which of the following are not correct?
(i) The basic unit of time is second.
(ii) Every object moves with a constant speed.
(iii) Distances between two cities are measured in kilometres.
(iv) The time period of a given pendulum is constant.
(v) The speed of a train is expressed in m/h.

Ans

Following statements are not correct:

(ii) Every object moves with a constant speed.

(v) The speed of a train is expressed in m/h.

Q.132 Will the compass needle show deflection when the switch in the circuit shown by Fig.14.24 is closed?

Ans

Yes, compass needle will show deflection when switch is closed in the given circuit.

Q.133 How would you show that setting of curd is a chemical change?

Ans

Setting of curd is type of chemical change as new substance is formed which has different properties from milk. Once curd is formed, milk cannot be re-obtained from it.

Q.134 A simple pendulum takes 32 s to complete 20 oscillations. What is the time period of the pendulum?

Ans

$\begin{array}{l}\text{Time period of a simple pendulum is the time taken to complete one oscillation.}\\ \text{The time period is given by,}\\ \text{Time period =}\frac{\text{Time taken}}{\text{Number of oscillations}}=\frac{32\mathrm{s}}{20}=1.6\mathrm{s}\end{array}$

Q.135 Fill the missing word in the blank spaces in the following statements:
(a) Wind is —————— air.
(b) Winds are generated due to —————— heating on the earth.
(c) Near the earth’s surface __________ air rises up whereas ___________ air comes down.
(d) Air moves from a region of ——— pressure to a region of ——— pressure.

Ans

(a) Wind is moving air.
(b) Winds are generated due to uneven heating on the earth.
(c) Near the earth’s surface hot air rises up whereas cool air comes down.
(d) Air moves from a region of high pressure to a region of low pressure.

Q.136 Explain why burning of wood and cutting it into small pieces are considered as two different types of changes.

Ans

Cutting of wood into small pieces is a physical change because no new substance is formed and only the shape and size of wood changes.When we burn wood, carbon dioxide along with some other new substances is formed. Therefore, burning of wood is a type of chemical change.

Q.137 Fill in the blanks:
(1) Longer line in the symbol for a cell represents its_________ terminal.
(2) The combination of two or more cells is called a___________.
(3) When current is switched ‘on’ in a room heater, it__________.
(4) The safety device based on the heating effect of electric current is called a_______.

Ans

(1) Longer line in the symbol for a cell represents its positive terminal.
(2) The combination of two or more cells is called a battery.
(3) When current is switched ‘on’ in a room heater, it produces heat.
(4) The safety device based on the heating effect of electric current is called a electric fuse.

Q.138 The distance between two stations is 240 km. A train takes 4 hours to cover this distance. Calculate the speed of the train.

Ans

$\begin{array}{l}\text{Distance travelled = 240 km}\\ \text{Time taken = 4 hours}\\ \text{Let the speed of the train be x km/h}\\ \text{Speed =}\frac{\mathrm{distance}}{\text{time taken}}\\ \therefore \text{speed of train =}\frac{240\text{km}}{4\text{h}}=\text{60 km/h}\end{array}$

Q.139 Describe how crystals of copper sulphate are prepared.

Ans

Crystal of copper sulphate is obtained by the process of crystallisation. For the preparation of crystals of copper sulphate take some water in a beaker and add a few drops of dilute sulphuric acid. Heat the water. When it starts boiling add copper sulphate powder slowly while stirring continuously. Continue adding copper sulphate powder till it stops dissolving. Filter the solution into a china dish and allow it to cool. Do not disturb the solution while it cools. Slowly, the crystals of copper sulphate separate out.

Q.140 Explain how painting of an iron gate prevents it from rusting.

Ans

The presence of both oxygen (air) and water (moisture) is essential for rusting to take place.When an iron gate is painted, oxygen and water do not come in contact with iron. Hence, rusting is prevented.

Q.141 Mark ‘T’ if the statement is true and ‘F’ if it is false:
(a) To make a battery of two cells, the negative terminal of one cell is connected to the negative terminal of the other cell. (T/F)
(b) When the electric current through the fuse exceeds a certain limit, the fuse wire melts and breaks. (T/F)
(c) An electromagnet does not attract a piece of iron. (T/F)
(d) An electric bell has an electromagnet. (T/F)

Ans

(a) False
(b) True
(c) False
(d) True

Q.142 Suggest two methods to find out wind direction at a given place.

Ans

The direction of wind can be found by following two methods:

1. Hold a small piece of cloth and raise your hand high in the air. The cloth will flow in the direction of the wind.
2. Pick some sand in your fist and allow it to fall slowly. The direction of fall of sand is same as that of the wind. This method of determining the direction of wind is widely used in desert areas by the travellers.

Q.143 Explain why rusting of iron object is faster in coastal areas than in deserts.

Ans

The presence of both oxygen and water is essential for rusting. Greater humidity indicates presence of more amount of water vapours in air, therefore, faster rate of rusting. In coastal areas humidity is high as compared to deserts. Moreover, the presence of salty water also speeds up the process of rusting in coastal areas. Thus, the iron objects rust faster in coastal areas.

Q.144 Do you think an electromagnet can be used for separating plastic bags from a garbage heap? Explain.

Ans

Plastic bags are not magnetic substances and thus, electromagnets cannot be used for separating them from garbage heap.

Q.145 The odometer of a car reads 57321.0 km when the clock shows the time 08:30 AM. What is the distance moved by the car, if at 08:50 AM, the odometer reading has changed to 57336.0 km? Calculate the speed of the car in km/min during this time. Express the speed in km/h also.

Ans

$\begin{array}{l}\text{Difference in the readings of odometer =}\left(\text{final – initial}\right)\text{readings = distance travelled}\\ \text{= 57336}\text{.0 km = 15 km}\\ \text{Difference in readings of clock = time taken = 08}\text{.50 AM – 08}\text{.30 AM = 20 min}\\ \therefore \text{the speed of car in km/min =}\frac{\text{distance}}{\text{time taken}}\text{=}\frac{\text{15 km}}{\text{20 min}}\text{= 0}\text{.75 km / min}\\ \text{The speed of the car in km/h =}\frac{\text{15 km}}{\text{1/3h}}\text{= 45 km/h}\end{array}$

Q.146 An electrician is carrying out some repairs in your house. He wants to replace a fuse by a piece of wire. Would you agree? Give reasons for your response.

Ans

No, electric fuse should not be replaced by a piece of wire. It is so because electric fuse protects the circuit against the flow of large amount of electric current which may cause short circuit and eventually fire in the house. Wire in the electric fuse is made up of some special material such that immediately melts down, if large amount of electric current passes through it and breaks down the circuit. Thus, electric fuse prevents short circuit and fires caused by electric current.

Q.147 The gas we use in the kitchen is called liquefied petroleum gas (LPG). In the cylinder it exists as a liquid. When it comes out from the cylinder it becomes a gas (Change – A) then it burns (change – B). The following statements pertain to these changes. Choose the correct one.
(i) Process – A is a chemical change.
(ii) Process – B is a chemical change.
(iii) Both processes A and B are chemical changes.
(iv) None of these processes is a chemical change.

Ans

The correct option is (ii). Process – B is a chemical change.

Q.148 State two experiences that made you think that air exerts pressure (other than those given in the text).

Ans

The experiences which show that air exerts pressure are as follows:

1. Blowing air in a balloon exerts pressure on its walls and causes it to inflate.
2. Paper bits spread on a cardboard moves and show displacement when air is blown over them.

Q.149 Salma takes 15 minutes from her house to reach her school on a bicycle. If the bicycle has a speed of 2 m/s, calculate the distance between her house and the school.

Ans

Time taken by Salma = 15 min = 15 × 60 s = 900 s

Speed of bicycle = 2 m/s

Let the distance between school and house be x m

Distance travelled = time taken × speed

∴ Distance, x = 900 s × 2 m/s = 1800 m = 1.8 km

Q.150 Anaerobic bacteria digest animal waste and produce biogas (Change – A). The biogas is then burnt as fuel (Change – B). The following statements pertain to these changes. Choose the correct one.
(i) Process – A is a chemical change.
(ii) Process – B is a chemical change.
(iii) Both processes A and B are chemical changes.
(iv) None of these processes is a chemical change.

Ans

The correct option is (iii). Both processes A and B are chemical changes.

Ans

One should not buy a house having windows but no ventilators because this interrupts cross-ventilation in the house. Cool fresh air enters the house through windows while dispensed heated air generated due to various human activities like, cooking, breathing etc; is removed through ventilators. Heated air being light rises up towards the roof and takes route through ventilators towards outside.

Q.152 Zubeda made an electric circuit using a cell holder shown in Fig. 14.4, a switch and a bulb. When she put the switch in the ‘ON’ position, the bulb did not glow. Help Zubeda in identifying the possible defects in the circuit.

Ans

The possible defects which may be found in Zubeda’s circuit are as follows:

1. The terminals of cells are not connected to each other in the correct manner.
2. The connections of wires are loose.
3. The bulb used may have fuse.

Q.153 Look at Fig. 4.13. Mark where the heat is being transferred by conduction, by convection and by radiation.

Ans

Various modes of transfer of the heat in the given diagram can be shown as follows:

Q.154 Explain why holes are made in hanging banners and hoardings.

Ans

Holes are made in hanging banners and hoardings in order to equalise the air pressure on both sides of them. Higher pressure on one side of the hanging banners and hoardings may blow or torn them away when wind blows from one side at a high speed. Presence of holes allows air to pass through and prevents building up high pressure on one side.

Q.155 In places of hot climate it is advised that the outer walls of houses be painted white. Explain.

Ans

The outer walls are advised to be painted white in hot climate conditions because white colour reflects maximum amount of heat back into the surroundings, that falls on it. Therefore, white coloured walls absorb least amount of heat and keep the house cool.

Q.156 In the circuit shown in Fig. 14.25

(i) Would any of the bulbs glow when the switch is in the ‘OFF’ position?
(ii) What will be the order in which the bulbs A, B and C will glow when the switch is moved to the ‘ON’ position?

Ans

(i) None of the bulbs will glow when switch is in the ‘OFF’ position because circuit remains incomplete and thus, no current will flow in it.
(ii) All the bulbs will glow at once when switch is moved to the ‘ON’ position.

Q.157 One litre of water at 30°C is mixed with one litre of water at 50°C. The temperature of the mixture will be
(a) 80°C
(b) more than 50°C but less than 80°C
(c) 20°C
(d) between 30°C and 50°C

Ans

Correct option is (d).

Explanation:
As heat will flow from one litre of water at 50°C to one litre of water at 30°C, so the temperature of the mixture will be between 30°C and 50°C.

Ans

In case of cyclone approaching our village or town, we can help our neighbours in following ways:

1. Making them aware of the warnings issued by the meteorological department through TV, radio, or newspapers.
2. Advising them to choose safer places to shift whenever necessary and make arrangements to move essential household goods, domestic animals and vehicles, etc.
3. Circulating the phone numbers of all emergency services like police, fire brigade and hospitals to all.
4. Asking them to avoid travelling on roads with standing water, as floods might have damaged the roads.
5. Storing sufficient amount of drinking water and eatables for emergencies.
6. Extending cooperation to all for meeting the state of emergency.

Q.159 An iron ball at 40°C is dropped in a mug containing water at 40°C. The heat will
(a) flow from iron ball to water
(b) not flow from iron ball to water or from water to iron ball
(c) flow from water to iron ball
(d) increase the temperature of both

Ans

Correct option is (b).

Explanation:
As both the water and the iron ball have the same temperature, so the heat will not flow from iron ball to water or from water to iron ball.

Q.160 State differences between acids and bases.

Ans

 Acids Bases Acids are sour in taste. Bases are bitter in taste Acids are non-soapy to touch. Bases are soapy to touch. Acids turn blue litmus red. Bases do not change colour of blue litmus. They do not change colour of red litmus. They turn red litmus blue. Acids do not change the colour of turmeric indicator. Bases turn the colour of turmeric indicator to red. Acids give magenta colour with china rose indicator. Bases give green colour with china rose indicator. Examples of acids are citric acid, lactic acid, tartaric acid, etc. Examples of bases are sodium hydroxide, magnesium hydroxide, calcium hydroxide, etc.

Q.161 A wooden spoon is dipped in a cup of ice cream. Its other end
(a) becomes cold by the process of conduction
(b) becomes cold by the process of convection
(c) becomes cold by the process of radiation
(d) does not become cold

Ans

Correct option is (d).

Explanation: Wood is a bad conductor of heat.

Q.162 What planning is required in advance to deal with the situation created by a cyclone?

Ans

Given steps should be followed in advance to deal with the situation created by a cyclone:

1. An efficient weather forecast and warning system should be in place for timely action.
2. Rapid communication systems like, TV, radio etc, should be geared up for giving warnings to government agencies, ports, ships and fishermen in advance.
3. Cyclone management centres should be constructed in cyclone prone areas.
4. Rescue teams should be formed in advance for rapid shifting of people to safer places.
5. Safe drinking water and eatables should always be kept stored for providing relief in emergencies.

Q.163 Ammonia is found in many household products, such as window cleaners. It turns red litmus blue. What is its nature?

Ans

Ammonia is basic in nature as it turns red litmus blue. Bases turn red litmus blue.

Q.164 Stainless steel pans are usually provided with copper bottoms. The reason for this could be that
(a) copper bottom makes the pan more durable
(b) such pans appear colourful
(c) copper is a better conductor of heat than the stainless steel
(d) copper is easier to clean than the stainless steel

Ans

Correct option is (c).

Explanation:
Copper is a good conductor of heat, so it allows the heat to distribute evenly throughout the utensil, and heats the stainless steel pans faster.

Q.165 Name the source from which litmus solution is obtained. What is the use of this solution?

Ans

Litmus is obtained from Lichens.
Uses of Litmus solution

1. Litmus solution is used as an indicator. It is used to find the nature (acidic/basic/neutral) of the solution.
2. Acid solution turns blue litmus solution red.
3. Basic solution turns red litmus solution blue.

Q.166 Show the shape of the distance-time graph for the motion in the following cases:
(i) A car moving with a constant speed.
(ii) A car parked on a side road.

Ans

(i) The shape of the distance-time graph for the motion of car with constant speed will be as follows:

(ii) The shape of the distance-time graph for the motion of car parked on a side road will be as follows:

Q.167 Is the distilled water acidic/basic/neutral? How would you verify it?

Ans

Distilled water is neutral in nature. The same can be tested by using red and blue litmus paper. Acidic solution turns blue litmus paper red while basic solution turns red litmus paper blue. Distilled water neither turns blue litmus paper red nor red litmus paper blue. Therefore, distilled water is neutral.

Q.168 Which one of the following place is unlikely to be affected by a cyclone.
(i) Chennai
(ii) Mangaluru (Mangalore)
(iii) Amritsar
(iv) Puri

Ans

Correct option is (iii).
Explanation:
Indian coastline regions are most vulnerable to cyclones.

Q.169 Fill in the blanks:
(a) An image that cannot be obtained on a screen is called____________.
(b) Image formed by a convex __________ is always virtual and smaller in size.
(c) An image formed by a __________ mirror is always of the same size as that of the object.
(d) An image which can be obtained on a screen is called a _________ image.
(e) An image formed by a concave ___________ cannot be obtained on a screen.

Ans

(a) An image that cannot be obtained on a screen is called virtual image.
(b) Image formed by a convex mirror is always virtual and smaller in size.
(c) An image formed by a plane mirror is always of the same size as that of the object.
(d) An image which can be obtained on a screen is called a real image.
(e) An image formed by a concave lens cannot be obtained on a screen.

Q.170 Mark ‘T’ if the statement is true and ‘F’ if it is false:

(i) Nitric acid turns red litmus blue.
(ii) Sodium hydroxide turns blue litmus red.
(iii) Sodium hydroxide and hydrochloric acid neutralise each other and form salt and water.
(iv) Indicator is a substance which shows different colours in acidic and basic solutions.
(v) Tooth decay is caused by the presence of a base.

Ans

(i) Nitric acid turns red litmus blue. (F)
(ii) Sodium hydroxide turns blue litmus red. (F)
(iii) Sodium hydroxide and hydrochloric acid neutralise each other and form salt and water. (T)
(iv) Indicator is a substance which shows different colours in acidic and basic solutions. (T)
(v) Tooth decay is caused by the presence of a base. (F)

Q.171

$\begin{array}{l}\mathrm{Which}\mathrm{of}\mathrm{the}\mathrm{following}\mathrm{relation}\mathrm{is}\mathrm{correct}?\\ \left(\text{i}\right)\text{ }\mathrm{speed}=\mathrm{Distance}\text{ }×\text{ }\mathrm{time}\\ \left(\mathrm{ii}\right)\text{ }\mathrm{speed}=\frac{\mathrm{Distance}}{\mathrm{time}}\\ \left(\mathrm{iii}\right)\text{ }\mathrm{speed}=\frac{\mathrm{time}}{\mathrm{Distance}}\\ \left(\mathrm{iv}\right)\text{ }\mathrm{speed}=\frac{1}{\mathrm{Distance}\text{ }×\text{ }\mathrm{time}}\end{array}$

Ans

Correct option is (ii).
Explanation: Speed is the distance traveled per unit of time.

Q.172 Dorji has a few bottles of soft drink in his restaurant. But unfortunately, these are not labelled. He has to serve the drink on the demand of customers. One customer wants acidic drink, another wants basic and third one wants neutral drink. How will Dorji decide which drink is to be served to whom?

Ans

Since, soft drinks are edible; Dorji can decide acidic, basic and neutral soft drinks by tasting them. Acidic soft drink will be sour in taste whereas basic soft drink will be bitter in taste. Neutral soft drink will has neither sour taste nor bitter.

Acidic, basic and neutral soft drinks can also be decided by using blue and red litmus paper.

Dorji can pour a few drops of one soft drink on red and blue litmus paper. If red litmus turns blue, then it will be a basic soft drink and if blue litmus changes to red, then it will be an acidic soft drink. If colour of both the litmus papers remains same, then it will be a neutral drink.

The same process can be repeated with the other soft drinks also.

Q.173 Mark ‘T’ if the statement is true and ‘F’ if it is false:
(a) We can obtain an enlarged and erect image by a convex mirror. (T/F)
(b) A concave lens always form a virtual image. (T/F)
(c) We can obtain a real, enlarged and inverted image by a concave mirror. (T/F)
(d) A real image cannot be obtained on a screen. (T/F)
(e) A concave mirror always form a real image. (T/F)

Ans

(a) False

(b) True

(c) True

(d) False

(e) False

Q.174 Explain why.

(a) An antacid tablet is taken when you suffer from acidity.
(b) Calamine solution is applied on the skin when an ant bites.
(c) Factory waste is neutralised before disposing it into the water bodies.

Ans

(a) Hydrochloric acid present in our stomach helps in the digestion of food. But excess of it causes acidity. To relieve from acidity, antacid tablets are taken as it contains base such as magnesium hydroxide that neutralises the acid present in the stomach.

(b) Formic acid is present in ant’s sting. When an ant bites, it injects the solution of formic acid into skin. The effect of sting can be neutralised by rubbing calamine solution on the stung area. Calamine solution being basic in nature neutralises the formic acid.

(c) The factory wastes contain acids. If such water is released into a water body, it can harm aquatic animals like fishes. Factory wastes should be treated with calcium hydroxide to neutralise acid before it is disposed off in water.

Q.175 Three liquids are given to you. One is hydrochloric acid, another is sodium hydroxide and third is a sugar solution. How will you identify them? You have only turmeric indicator.

Ans

Put a drop each of hydrochloric acid, sodium hydroxide and sugar solution on the turmeric indicator. The solution which changes the colour of turmeric indicator to red will be basic that is sodium hydroxide.

Now add a few drops of sodium hydroxide solution in remaining two solutions i.e. both in hydrochloric acid and sugar solution. After that, put some drops of these mixtures on turmeric indicator separately.

Drop that changes the colour of turmeric indicator will be neutral in nature i.e. sugar solution. Mixture of basic solution and neutral solution will be basic in nature and change the colour of turmeric indicator to red.

Drop that does not change the colour of turmeric indicator will be acidic in nature i.e. hydrochloric acid. This is because hydrochloric acid being acidic in nature neutralises the sodium hydroxide solution.

Q.176 Blue litmus paper is dipped in a solution. It remains blue. What is the nature of the solution? Explain.

Ans

The nature of the solution will be either basic or neutral. This is because both basic solution and neutral solution do not change the colour of blue litmus paper.

Q.177 Consider the following statements:
(a) Both acids and bases change colour of all indicators.
(b) If an indicator gives a colour change with an acid, it does not change colour with a base.
(c) If an indicator changes colour with a base, it does not change colour with an acid.
(d) Change of colour in an acid and a base depends on the type of the indicator.

Which of these statements are correct?
(i) All four
(ii) a and d
(iii) b and c
(iv) only d

Ans

The correct option is (iv) only d.

Q.178 Match the items given in Column I with one or more items of Column II.

 Column I Column II A plane mirror Used as a magnifying glass A convex mirror Can form image of objects spread over a large area A convex lens Used by dentists to see enlarged image of teeth A concave mirror The images is always inverted and magnified A concave lens The images is erect and of the same size as the object The image is erect and smaller in size than the object

Ans

The correctly matched contents of Column I and Column II are as follows:

 Column I Column II A plane mirror The images is erect and of the same size as the object A convex mirror Can form image of objects spread over a large area A convex lens Used as a magnifying glass A concave mirror The images is always inverted and magnified Used by dentists to see enlarged image of teeth A concave lens The image is erect and smaller in size than the object

Q.179 State the characteristics of the image formed by a plane mirror.

Ans

The characteristics of the image formed by a plane mirror are as follows:

1. Image is erect and virtual.
2. Image is formed at the same distance behind the mirror as the object is placed in front of the mirror.
3. Image is of the same size as that of the object.
4. Image is laterally inverted.

Q.180 The basic unit of speed is:
(i) km/min
(ii) m/min
(iii) km/h
(iv) m/s

Ans

Correct option is (iv).
Explanation: Speed is the distance traveled per unit of time. The standard unit of distance is metre (m) and standard unit of time is second (s).

Q.181 Which of the statements given below is correct?
(i) In winter the winds flow from the land to the ocean.
(ii) In summer the winds flow from the land towards the ocean.
(iii) A cyclone is formed by a very high-pressure system with very high-speed winds revolving around it.
(iv) The coastline of India is not vulnerable to cyclones.

Ans

The correct statement is:
(i) In winter the winds flow from the land to the ocean.

Q.182 A car moves with a speed of 40 km/h for 15 minutes and then with a speed of 60 km/h for the next 15 minutes. The total distance covered by the car is:
(i) 100 km
(ii) 25 km
(iii) 15 km
(iv) 10 km

Ans

Average speed of car = (40 km/h + 60 km/h)/2 = 50 km/h
Total distance travelled = speed × total time taken = 50 km/h × (½) h = 25 km/h

Q.183 Find out the letters of English alphabet or any other language known to you in which the image formed in a plane mirror appears exactly like the letter itself. Discuss your findings.

Ans

The letters of English alphabets, whose image formed by the plane mirror is exactly like the letter itself, are as follows:

A, H, I, M, O, T, U, V, W, X and Y

All of these letters can be divided into two equal halves through a vertical plane. Therefore, even their images after undergoing lateral inversion would appear same as that of letter itself. Thus, we can say that all vertically symmetrical objects will produce image same as themselves when placed in front of a plane mirror.

Q.184 What is a virtual image? Give one situation where a virtual image is formed.

Ans

The image which cannot be obtained on a screen is called a virtual image. When we see ourselves in a plane mirror, the image formed cannot be obtained on a screen. It is one of the situations where a virtual image is formed.

Q.185 State two differences between a convex and a concave lens.

Ans

The two differences between a convex and a concave lens are as follows:

1. A convex lens forms a real and inverted image while a concave lens forms a virtual and erect image.
2. A convex lens can also form a virtual and erect image when object is placed very close to it whereas, a concave lens cannot form a real and inverted image at all.

Q.186 Give one use each of a concave and a convex mirror.

Ans

Use of concave mirror:
As concave mirror produces large magnified image, it is used by the doctors to examine eye, ears, nose and throat etc.

Use of convex mirror:
Convex mirror forms small and virtual image due to which it is used as the side rear view mirror in vehicles to see the large area for a better view of traffic on road.

Q.187 Which type of mirror can form a real image?

Ans

Concave mirror can form a real image.

Q.188 Which type of lens forms always a virtual image?

Ans

Concave lens always forms a virtual image.

Q.189 Suppose the two photographs, shown in Fig. 13.1 and Fig. 13.2, had been taken at an interval of 10 seconds. If a distance of 100 metres is shown by 1 cm in these photographs, calculate the speed of the blue car.

Ans

The steps to be followed are as follows:
1.
Find the distance travelled by blue car in photographs by measuring distance taking mid-points of car in following manner:

(Here, distance may vary in centimeters due to difference in the size of photographs taken. So, follow only the method for finding right answer, which may vary.)

2. According to the question, 1 cm is equivalent to 100 m.
Therefore, distance travelled = 0.5 cm x 100m = 50m

3. Speed = distance travelled / time taken
Therefore, speed = 50m / 10s = 5 m/s

Q.190 A virtual image larger than the object can be produced by a
(i) concave lens
(ii) concave mirror
(iii) convex mirror
(iv) plane mirror

Ans

Correct option is (ii).
Explanation:
When the object is placed very close to the concave mirror, the image formed is virtual, erect and magnified.

Q.191 David is observing his image in a plane mirror. The distance between the mirror and his image is 4 m. If he moves 1 m towards the mirror, then the distance between David and his image will be
(i) 3 m
(ii) 5 m
(iii) 6 m
(iv) 8 m

Ans

Correct option is (iii).
Explanation:
Distance between the mirror and David’s image = 4 m
If David moves 1 m towards the mirror, then his distance from the mirror = 4 m − 1 m = 3 m
Therefore, the distance between David and his image = 3 m + 3 m = 6 m

Q.192 Fig.13.15 shows the distance-time graph for the motion of two vehicles A and B. Which one of them is moving faster?

Ans

Among the vehicles, vehicle A is moving faster than B. It is so because A has travelled greater distance in shorter period of time in comparison to that of vehicle B. Vehicle B has moved lesser distance in greater period of time as depicted in graph.

Q.193 The rear view mirror of a car is a plane mirror. A driver is reversing his car at a speed of 2 m/s. The driver sees in his rear view mirror the image of a truck parked behind his car. The speed at which the image of the truck appears to approach the driver will be
(i) 1 m/s
(ii) 2 m/s
(iii) 4 m/s
(iv) 8 m/s

Ans

Correct option is (iii).
Explanation:
Speed of truck in the mirror = 2v
where v is original speed.
Speed of truck in the mirror = 2 × 2 m/s = 4 m/s

Q.194 Which of the following distance-time graphs shows a truck moving with speed which is not constant?

Ans

Among the given distance-time graphs, following graph shows the movement of a truck with speed which is not constant:

It is so because in this graph vehicle is not covering equal distances in equal intervals of time.

Q.195 Given below is a crossword puzzle based on this lesson. Use hints to fill in the blank spaces with letters that complete the words.

 Down Across (D) 1: Through Washing (A) 1: Keeps Warm 2: Animal Fibre 2: Its leaves are eaten by silkworm 3: Long thread like Structure 3: Hatches from egg or moth

Ans

Q.196 Here is a crossword puzzle. Good luck!

Across
3. Liquid waste products
4. Solid waste extracted in sewage treatment
6. A word related to hygiene
8. Waste matter discharged from human body

Down
1. Used water
2. A pipe carrying sewage
5. Micro-organism which causes cholera
7. A chemical to disinfect water

Ans

Q.197 Describe the process of neutralisation with the help of an example.

Ans

The reaction between the acid and the base is known as neutralisation reaction. In the neutralisation reaction, salt and water are produced with the evolution of heat.
Acid + Base → Salt + Water + Heat

Example:
Hydrochloric acid (acid) reacts with sodium hydroxide (base) to form sodium chloride (salt) and water. Heat is evolved in this process.

$\underset{\left(\mathrm{Acid}\right)}{\mathrm{Hydrochloric}\mathrm{Acid}}+\underset{\left(\mathrm{Base}\right)}{\mathrm{Sodium}\mathrm{Hydroxide}}\to \underset{\left(\mathrm{Salt}\right)}{\mathrm{Sodium}\mathrm{Chloride}}+\mathrm{Water}+\mathrm{Heat}$

Q.198 Why does an athlete breathe faster and deeper than usual after finishing the race?

Ans

The body of an athlete, who runs in a race, requires more oxygen. Therefore, his breathing rate increases so as to supply more oxygen to the body cells. This is why an athlete, after finishing the race, breathes deeper and faster than usual.

Q.199 List the similarities and differences between aerobic and anaerobic respiration.

Ans

Similarities between aerobic and anaerobic respiration are:
1. Energy is produced.
2. Carbon dioxide is released.

Differences between aerobic and anaerobic respiration are:

 Aerobic Respiration Anaerobic Respiration 1. It takes place using oxygen. 1. It takes place without using oxygen. 2. It releases large amount of energy. 2. It releases small amount of energy. 3. Water and carbon dioxide are produced. 3. Alcohol and carbon dioxide are produced.

Q.200 Draw in your notebook the symbols to represent the following components of electrical circuits: connecting wires, switch in the ‘OFF’ position, bulb, cell, switch in the ‘ON’ position, and battery.

Ans