CBSE Important Questions Class 9 Science Chapter 5 – The Fundamental Unit of Life
Class 9 Science Chapter 5 The Fundamental Unit of Life is part of the CBSE Class 9 Science syllabus. It explains how the cell was discovered, the cell theory, and the difference between prokaryotic and eukaryotic cells. Students learn about the plasma membrane and how substances move across it by diffusion and osmosis, the cell wall, the nucleus, and the cell organelles such as mitochondria, plastids, the endoplasmic reticulum, the Golgi apparatus, lysosomes and vacuoles.
These CBSE important questions for Class 9 Science Chapter 5 cover ATP as the energy currency, guard cells and stomata, why cell parts are stained, the plasma membrane and selective permeability, osmosis in hypotonic and hypertonic solutions, the nucleus and mitochondria, the cell theory, and the differences between plant and animal cells and between prokaryotic and eukaryotic cells. Every question has a clear step-by-step answer in simple English, so students can practise on their own, parents can check the answers, and teachers can use them for class tests.
Important Questions Class 9 Science Chapter 5 Exploring Mixtures and their Separation
Exploring Mixtures and Their Separation
Medium
Exploring Mixtures and Their Separation
Medium
Exploring Mixtures and Their Separation
Medium
Exploring Mixtures and Their Separation
Medium
Exploring Mixtures and Their Separation
Medium
Exploring Mixtures and Their Separation
Medium
Q1. The energy currency of the cell is
(a) ADP
(b) ATP
(c) NADP
(d) FADP
Answer: (b) ATP
ATP is called the energy currency of the cell because the energy released during respiration is stored in it, and the cell uses this energy for all its activities. It is being used up and made again all the time. ADP and NADP take part in energy transfer but are not the direct energy currency.
Q2. The full form of ATP is
(a) Adenosine tetraphosphate
(b) Adenosine triphosphate
(c) Adenine triphosphate
(d) Adenine tripentose
Answer: (b) Adenosine triphosphate
ATP is made of adenosine (adenine joined to a ribose sugar) and three phosphate groups. When one phosphate group is removed, energy is released and ADP is formed.
Q3. The small components of a section are seen under a microscope after
(a) staining with water
(b) putting glycerine on it
(c) staining with coloured dyes
(d) covering it with a coverslip
Answer: (c) staining with coloured dyes
Most cell parts are colourless and transparent, so they cannot be seen clearly. Dyes such as safranin or methylene blue colour the different parts differently. This increases the contrast and makes the small components clearly visible.
Q4. Name the plant cells that control the opening and closing of stomata.
Answer: Guard cells control the opening and closing of stomata.
They are bean-shaped cells on either side of the stomatal pore. When water enters them they swell up (become turgid) and the pore opens. When they lose water they become flaccid and the pore closes.
Q5. The plasma membrane is made up of
(a) lipids
(b) proteins
(c) lipids and proteins
(d) carbohydrates and proteins
Answer: (c) lipids and proteins
The plasma membrane is made of a double layer of lipids with protein molecules fitted into it. Because of this structure it is flexible and selectively permeable, which means it lets only certain substances pass in and out of the cell.
Q6. Why is the plasma membrane called a selectively permeable membrane?
Answer: The plasma membrane is called selectively permeable because it allows only some substances to pass through it and stops others.
Small molecules such as oxygen, carbon dioxide and water move across it freely by diffusion and osmosis, while large molecules and most ions cannot pass on their own. In this way the cell controls what enters and leaves it.
Q7. Define osmosis. What will happen if a plant cell is placed in (a) a hypotonic solution and (b) a hypertonic solution?
Answer: Osmosis is the movement of water molecules through a selectively permeable membrane, from a place where there is more water to a place where there is less water.
(a) In a hypotonic solution (dilute, more water outside), water enters the cell. The cell swells up and becomes turgid. The cell wall stops it from bursting.
(b) In a hypertonic solution (concentrated, less water outside), water leaves the cell. The cell shrinks and the plasma membrane pulls away from the cell wall. This is called plasmolysis.
Q8. Why is the nucleus called the control centre of the cell? Mention its main functions.
Answer: The nucleus is called the control centre because it contains the chromosomes, which carry the genes (DNA). The genes decide which proteins are made, and the proteins control all the activities of the cell.
Main functions:
1. It controls all the chemical activities of the cell.
2. It carries the hereditary information from one generation to the next.
3. It controls cell division, that is, how the cell reproduces.
4. The nucleolus inside it makes ribosomes.
Q9. Why are mitochondria called the powerhouse of the cell?
Answer: Mitochondria are called the powerhouse of the cell because this is where respiration takes place. Here food (glucose) is broken down with the help of oxygen and the energy released is stored in the form of ATP molecules. The cell then uses this ATP for all its work, such as making new substances and moving materials.
Mitochondria also have their own DNA and ribosomes, so they can make some of their own proteins.
Q10. Write any three differences between a plant cell and an animal cell.
Answer:
| Plant cell | Animal cell |
|---|---|
| Has a rigid cell wall outside the plasma membrane. | Has no cell wall, only a plasma membrane. |
| Contains plastids such as chloroplasts. | Does not contain plastids. |
| Has one large central vacuole. | Has many small vacuoles or none. |
| Centrioles are usually absent. | Centrioles are present. |
Q11. Who discovered the cell and how? What is the cell theory?
Answer: The cell was discovered in 1665 by Robert Hooke. He cut a thin slice of cork and looked at it through his own simple microscope. He saw many tiny box-like compartments and called them 'cells', which means small rooms.
Cell theory was given by Schleiden and Schwann and later added to by Virchow. It states:
1. All living organisms are made of cells.
2. The cell is the basic structural and functional unit of life.
3. All cells arise from pre-existing cells (given by Virchow).
Q12. What is the difference between prokaryotic and eukaryotic cells? Give one example of each.
Answer:
| Prokaryotic cell | Eukaryotic cell |
|---|---|
| Size is generally small (1–10 µm). | Size is generally large (5–100 µm). |
| The nuclear region is not covered by a membrane; it is called a nucleoid. | A true nucleus with a nuclear membrane is present. |
| Membrane-bound organelles such as mitochondria and plastids are absent. | Membrane-bound organelles are present. |
| Only one chromosome is present. | More than one chromosome is present. |
| Example: bacteria, blue-green algae. | Example: plant cells, animal cells, fungi. |
Related Study Material on Extramarks
- CBSE Important Questions Class 9 Science Chapter 1
- CBSE Important Questions Class 9 Science Chapter 2
- CBSE Important Questions Class 9 Science Chapter 3
- CBSE Important Questions Class 9 Science Chapter 4
- CBSE Important Questions Class 9 Science Chapter 6
- CBSE Important Questions Class 9 Science Chapter 7
- CBSE Important Questions Class 9 Science Chapter 8
- CBSE Important Questions Class 9 Science Chapter 9
- CBSE Important Questions Class 9 Science Chapter 10
- CBSE Important Questions Class 9 Science Chapter 11
- CBSE Important Questions Class 9 Science Chapter 12
Q.1 Complete the boxes with appropriate natural resources and define the zone that comprises of all the three forms of life.
Marks:3
Ans
The biosphere is the life supporting zone of earth where all 3 forms of life – air, land and water co-exists.
Q.2 What is humus? Explain the role of earthworms in the formation of humus.
Marks:2
Ans
Humus is the decomposed plant and animal material which makes the soil fertile. Earthworms play a major role in converting large pieces of organic matter into rich humus, improving soil fertility.
Q.3 Smog is a serious problem in many countries and continues to harm human health. Justify.
Marks:3
Ans
Smog is a visible indication of air pollution. It is a combination of various suspended particles with water vapour and dust. These suspended particles are unburnt carbon particles called hydrocarbons, produced due to combustion of fossil fuels. Ground-level ozone, sulphur dioxide, nitrogen dioxide and carbon monoxide are harmful for senior citizens, children and people with heart and lung problems such as asthma. Smog hampers the visibility and harms the environment.