Important Questions Class 11 Biology Chapter 15

Class 11 Biology Chapter 15 Important Questions – Plant growth and development

Biology is the science of life. It helps us understand various science fields like taxonomy, heredity and evolution. Biologists contribute to conserving the environment by determining ways to protect and conserve our planet for future generations. Educating more people on the importance of preserving various plants and animal species can instil responsibility in every citizen. Chapter 15, Class 11 Biology important questions discuss plant growth and development. 

Growth is a permanent, irreversible process that increases an organism’s physical and mental capabilities. The three phases of plant growth are meristematic, elongation and maturation. Plant growth and development are crucial for competitive examinations like NEET, MH- CET, and board examinations. Students must practice regularly and solve NCERT exercises and exemplar questions to have  a thorough understanding of  the chapter for an excellent preparation.

Biology is a lengthy subject, with a lot of information to remember. Students often find it challenging to memorise it all together. At Extramarks, we value regular revision through question-solving, which greatly benefits our students studying across different schools in India. 

Our experienced  Biology faculty compiles these Important Questions. These questions have been taken from the NCERT textbook, NCERT Exemplar, past examination questions, and other sources. Our Biology experts  have designed a list of step-by-step answers to help students comprehend each topic along with its  exercises and summary. .

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Access Plant Growth and Development Class 11 Important Questions & Answers for the Academic Year 2022-23.

Class 11 Biology Chapter-wise important questions are available for free to students, and these questions are perfect for self-study.

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Important Questions Class 11 Biology Chapter 15 With Solutions

Our Biology experts have carefully curated Class 11 Biology Chapter 15 important questions which strictly follows NCERT books and provides solved exercises and practice questions to step up their learning experience . The entire list of questionnaires were  prepared by following the latest CBSE guidelines. The chapter elaborates on various topics like intrinsic and extrinsic factors affecting plant growth and differentiation, descriptions of root apical, shoot apical and intercalary meristems, phases of enlargement and maturation, growth rate, arithmetic and geometric growth, plant growth regulators like auxin, gibberellins, cytokinins, ethylene, abscisic acid and others, photoperiodism and vernalisation. Solutions to the Important Questions Class 11 Biology Chapter 15 cover all these essential concepts with explanations.

The list of questions prepared in Important Questions Class 11 Biology Chapter 15 will provide an overview of the chapter and help students summarise the chapter easily. The solutions provided to Important Questions Class 11 Biology Chapter 13 contain explanations for all these essential concepts.

Here is a set of Questions from Important Questions from Class 11 Biology Chapter 15 with their solutions:

Question 1. Winter varieties, when planted in spring, do not produce flowers or mature grains within the span of a flowering season. Explain?

Answer 1: In a few plants, flowering is either qualitatively or quantitatively. Flowering is reliant on its subjection to various internal and environmental factors. Subjection to lower temperatures is referred to as vernalisation. Vernalisation limits the plant’s advanced reproductive development rate. Hence these plants have enough time to gain maturity as it hampers plant growth and development in the maturing season. Vernalisation promotes flowering in plants by a span of low temperatures. Some plants like wheat and barley show two types of varieties, spring and winter. The plants of the spring variety are planted in the spring. The flowers produce grains towards the termination of the growing season. At the same time, the winter varieties planted in spring fail. The winter varieties flower or generate mature grains within their flowering season. Hence they are planted in autumn. Over winter, they germinate and produce tiny seedlings. They restart development in the spring and are gathered in mid-summer.

Question 2. Is there a difference in the growth pattern of plants and animals? Do all parts of the plant grow endlessly? List the regions of the plant that can grow endlessly.

Answer 2: Yes, the growth pattern of plants and animals differs.

Growth in plants happens in indeterminate format. That is plants can grow during their entire life because of the availability of meristematic tissues present in specific parts of the plants i.e. apical intercalary and lateral. These cells of the meristems possess the ability to divide through their lifetime and grow constantly and locally. The rest of the plant body consists of cells eventually losing their capacity to divide. The growth form, in which cells are constantly added to the plant body through the action of meristems, is termed the open form of growth. 

On the other hand the growth in animals happens over a limited period of time after which their body stops growing.

Even in plants all the parts do not grow indefinitely. The shoot apex and root apex having apical meristematic tissues will keep growing and give the vertical elongation of the plants. 

Question 3. What do you understand about photoperiodism and vernalisation? Describe their significance.

Answer 3: A plant’s response to the duration of day and night is known as photoperiodism. Plants primarily respond to the amount of daylight they receive. Based on their response to the duration of light, different plants may be classified as short-day plants, long-day plants, or day-neutral plants. Photoperiodism provides stimuli in addition to flowering induction. The light stimulus in photoperiodism is received only by green leaves. Photoperiodism is mainly mediated by a hypothetical hormone called florigen. Photoperiodism may be nullified by exposing the plant to unfavourable photoperiods. 

Vernalisation is the phenomenon of inducing flowering in plants by exposing them to cold temperatures. In plants of the winter varieties like wheat and some biennials like carrot and cabbage, exposure to cold temperature is necessary to induce flowering. The winter varieties of crops like rye and wheat are usually planted in autumn. They remain in the seedling stage through winter and then flower during the summer. However, if we sow these varieties of crops in spring, flowering will not be seen.

The hormone hypothetically named florigen is believed to be responsible for flowering and is formed in the leaves. Florigen subsequently migrates to the shoot apices and modifies them into flowering apices. 

Vernalisation only prepares the plant to perceive flowering stimuli. It is not observed to induce flowering. Leaves, embryos, and meristems receive the cold treatment stimulus. Vernalisation can be nullified through exposure to high temperatures.

Students should visit the Extramarks website and access Important Questions Class 11 Biology Chapter 15 for further explanation on photoperiodism and vernalisation.

Question 4. Why is abscisic acid called a stress hormone?

Answer 4: Abscisic acid is termed as a stress hormone. It causes different plant responses to act against stress conditions. Abscisic acid helps the plant to survive in unfavourable conditions of the environment. It facilitates the seed dormancy and ensures it gets germinated under favourable circumstances. It also causes the stomata to close when there is a drought. They are also observed to be critical in withstanding desiccation.

Furthermore, they also help the plant by assisting in inducing dormancy in plants towards the termination of the growing season. As a result, they help facilitate the abscission of fruits, leaves and flowers. It is observed that when there is a water deficiency in leaves, i.e. the leaves become dry, ABA concentration increases. Abscisic acid promotes the closure of stomata; hence it is called the stress hormone. 

Question 5. Explain in 2-3 lines each of the following terms with the help of examples taken from different plant tissues? 

(a) Differentiation.

(b) Dedifferentiation 

(c) Re-differentiation

Answer 5:

1. Differentiation:

When meristematic cells become specialised for performing a particular function, they lose their ability to divide. This phenomenon, called differentiation, is permanent in the size, structure, composition and function of cells, tissue or organs. 

For example, the meristematic tissues in plants give rise to new cells. These cells mature and differentiate into a particular tissue or a different plant organ. For example, cells from root cap distal to root apical meristem, cells of the periphery form epiblema, followed by cortex endodermis, pericycle and vascular dermis. During differentiation, cells undergo significant structural changes in their protoplasm and cell wall.

2. De-differentiation:

De-differentiation is the phenomenon in which differentiated living cells regain the capacity of division. The ability of de-differentiation occurs only under particular conditions. In this process, the specialisation of differentiated cells takes place. Hence the cells gain the ability to divide again. For example, in the dicot stem, the cortical cells of the plant get de-differentiated and change into meristematic cells to form cambiums such as interfascicular cambium and fascicular cambium. These meristems are formed from fully developed parenchyma due to the de-differentiation property.

3. Re- differentiation:

It is called Re-differentiation when de-differentiated cells mature and gain the specialised function again. The cambium cells that are formed again undergo Re-differentiation to form secondary cortex cells. In the case of secondary growth in woody dicot plants, the secondary cortex cells give rise to secondary xylem, phloem elements, and phelloderm. Cambium forming into the cortex is an example of Re-differentiation.

Question 6. While experimentation, why do you think it is difficult to assign any effect seen to any single hormone?

Answer 6: Plant hormones usually work in a combination. Some plant hormones are observed to have antagonistic effects. At the same time, some others may have augmentative effects. It is nearly impossible to pinpoint any single hormone responsible for a particular effect in a plant part. Phytohormones are synthesised by plant cells individually. These phytohormones are auxin, GA, ABA, ethylene and cytokinin. There is not a separate system for their translocation within plants. So, their effects on plants also remain intermixed.

Many effects of auxin GA show the same function as some other plant hormones. Similarly, ethylene and ABA support each other for various roles in plants. Secondly, the effects of phytohormone in vitro and in vivo will also differ.

Moreover, these plant hormones bring out their effect in coordination with different extrinsic factors. Therefore, it is difficult to assign any effect seen to any single hormone.

Key Topics Covered in Important Questions Class 11 Biology Chapter 15

 Following key points that are covered in Important Questions Class 11 Biology Chapter 15 are as follows:

• Plants complete their vegetative phase to move into a reproductive phase in which flowers and fruits are formed for the continuation of the life cycle of the plant. Development happens due to two processes: growth and differentiation. Intrinsic and extrinsic factors control the growth and development of plants.
• Growth is a permanent or irreversible change. In plants, growth is accomplished by cell division, increasing cell number and enlargement. Root apical meristem and shoot apical meristem are responsible for primary growth. In contrast, plants’ secondary growth is due to lateral meristems like vascular cambium and cork cambium. The three growth phases include the formative phase, phase of enlargement and phase of maturation, in which the plant undergoes structural and physiological differentiation.
• The increase in growth per unit time is called the growth rate. The growth rate can be arithmetic or geometric.
• Comparison and measurement of the total growth per unit time are called the absolute rate. Some parts of plant cells become specialised and undergo differentiation, de-differentiation and  re-differentiation.
• Plant development is the sequence of events in the life history of a cell, organ or organism, including seed germination, growth, differentiation, maturation, flowering, seed formation and senescence. Development is induced through certain plant growth regulators. Some growth-promoting plant regulators include auxin, gibberellin and cytokinins. Ethylene and abscisic acid are termed growth inhibiting regulators.
• The effect of light hours’ duration on plant growth and development is called photoperiodism. Based on this, plants are classified as long days, short days and day-neutral plants. Vernalisation is the process of shortening the vegetative phase by cold temperatures. This stimulus is perceived by meristematic cells.

Benefits of Solving Chapter 15 Biology Class 11 Important Questions

Biology lays  greater emphasis on  conceptual learning and understanding. After reading and solving exercises, students get well prepared for their examinations. We suggest students register themselves at Extramarks and access the study materials designed by our expert faculty for a wide range of subjects. Students can revise different chapters multiple times using our wide range of study materials. This will benefit them in building more robust conceptual knowledge and help them secure good grades.

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