RBSE Class 12 Biology Chapter 13- Plant Growth, provides complete information related to growth, different phases of growth, growth sites, factors affecting the growth in plants, plant growth hormones, its types, physiological effects of hormones on plants, structure and features of plant growth hormones and growth inhibitors.
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The Rajasthan Board Class 12 Biology Chapter 13 important questions are the best study material for both class assignments and other board examinations. By practising these important questions, students can gain deep knowledge about the topics explained in this chapter and also help them to be well prepared for their upcoming examinations.
RBSE Class 12 Biology Chapter 13 Important Questions
RBSE Biology Chapter 13: MCQ Type Questions
Q.1. Which of the following hormones is sprayed on the rosette plant of cauliflower to convert it into a long shoot?
Sol: (c) GA.
Q.2. Which of the following hormones is found in a gaseous state?
Sol: (d) Ethylene.
Q.3. Which of the following plant hormones is active at the time of leaf shedding?
(d) All of the above.
Sol: (b) ABA.
Q.4. Which of the following plant hormones is still not isolated?
Sol: (b) Florigen.
Q.5. ___________hormones promote the growth of the apical part of the plant.
(d) All of the above.
Sol: (a) Auxin.
Q.6. _________ plant hormone controls the dicotyledonous weeds in the field.
Sol: (b) 2-4D.
Q.7. ______ is also known as the stress hormones in plants.
Sol: (b) ABA.
Q.8. Who discovered phytochrome?
(b) Borthwick and Hendricks.
(d) Garner – Allard.
Sol: (b) Borthwick and Hendricks.
Q.9. Which of the following is the first plant hormone to be discovered?
Sol: (a) Auxin.
Q.10. _______ is caused due to the change in the hormone balance.
Sol: (a) Abscission.
RBSE Biology Chapter 13:Short Answer Type Questions.
Q.1. Define Growth.
Sol. Growth is defined as a characteristic feature of every living organism. It is a permanent and irreversible change in the shape and size of a living being, which results in an increase in the dry weight of the body.
Q.2.What is Arithmetic and Geometric growth?
Sol. In plants, there are two types of growth – Arithmetic growth and Geometric growth, which are differentiated according to the increase shown by the growth rate.
Arithmetic growth –In this type of growth, one of the daughter cells continues to divide whereas the other daughter cells differentiate or mature. Example – root elongating at a constant rate.
Geometric Growth – In this type of growth, the initial growth is slow, followed by a rapid increase in growth, and followed by a phase where growth slows down. Example − all cells, tissues and organs show this type of growth.
Q.3.What is a sigmoid growth curve?
Sol. When a graph is plotted between the rate of growth and time, as the S-shaped curve is formed. This is called the sigmoid growth curve. this growth curve can be divided into four different parts:
Lag phase or lag period.
Log phase or log period.
Decline growth period.
Stationary phase or stationary period.
Q.4.What is Bakanae disease?
Sol. In the crop field of paddy in Japan, some plants showed excessive growth in length and failed to produce flowers. These plants were found to be infected with a fungus named Gibberella fuji-Karo. Hori in the year 1898 studied about this disease and named it a Baknae disease. These plants were commonly named as foolish seeding because of their unusual appearance in the crop field. In Japanese language Baknae refers to foolish. Therefore, this disease is named as Bakanae.
Q.5.Define Zeatin and Vernalin?
Sol. Zeatin is defined as the first and naturally occurring cytokinin. Miller and Letham are two scientists who isolated the zeatin hormone from the endosperm of the maize plant during the 1960s.
Vernalin is a hormone-like substance, which is produced from the leaves during the process of cold therapy or treatment. This hormone-like substance acts as a precursor of florigen hormone which includes the flower induction.
Q.6.What do you understand by the term phases of growth?
Sol. Growth is an irreversible and permanent metabolic process. The entire process of growth and development in plants is carried out by the specialized – meristems. The three phases of growth in plants are:
- The phase of cell formation.
- The phase of cell elongation.
- The phase of cell differentiation.
Q.7.What is the plant hormone? Which plant hormone was first discovered?
Sol: Plant hormones are also called plant growth regulators. They are chemical substances that influence the growth and differentiation of plant cells. They are chemical messengers that facilitate intracellular communication. Auxins were the first plant hormones discovered.
Q.8.What are the characteristics of plant growth regulators?
Sol: Plants growth hormones or plant growth regulators exhibit the following characteristics:
- Seed dormancy.
- Ripening of fruit.
- Wilting of leaves.
- Differentiation and elongation of cells.
- Formation of leaves, flowers, and stems.
Q.9.Which plant hormone promotes plant growth, delays senescence and acts as a growth inhibitor?
Sol: Auxin is an example of a plant hormone, which promotes the growth of the plant. Gibberellin’s hormone is involved in the process of delaying senescence. Abscisic acid is one plant growth inhibitor. It controls organ size and stomatal closure. It also facilitates bud and seed dormancy.
Q.10. What are the different types of plant growth regulators?
Sol: There are five different types of plant growth regulators and they are involved in inhibiting the growth of the plants. Listed below are the different types of plant hormones and their site of production or synthesis in the plants:
- Auxin – It is synthesized at the points of the stem, buds, and root tips.
- Cytokinin – It is synthesized in roots.
- Gibberellins- It is produced within the cell’s plastids.
- Abscisic acid- It is produced in the roots and in the terminal buds at the top of the plant.
- Ethylene- It is produced essentially by different parts of the plants, including the roots, stems, leaves, flowers, fruits, tubers, and seeds.
Q.11. What is apical dominance?
Sol: The growth of the lateral and axillary buds, which remain suppressed partially or completely under the influence of the apical bud. This effect of the apical bud is called apical dominance. Auxin and Gibberellins are the plant hormones, which are the main causes of apical dominance.
Q.12. What is phytochrome? What is its significance?
Sol. Phytochrome is a bright bluish-green protein, which is found in the plant cells and acts as photoreceptor pigments. There are two types of phytochrome:
PFR – Phytochrome far-red p 700.
PR – Phytochrome red p 660.
These two forms of Phytochrome are interconvertible and are mainly involved in controlling the production of the hormones required for the flowering of plants.
Q.13. What is dormancy? Which seeds are called photoelastic?
Sol: Dormancy is defined as the state of the temporary arrest of germination of seeds even during the presence of favourable conditions. In some rare conditions, the germination in seeds is influenced by photoperiod, such seeds are called photoelastic.
Q.14.What is the function of auxin in plants? How is free auxin different from bound auxin?
Sol: Auxin is produced by the tip of the stem and helps in the elongation of cells. It promotes cell elongation, root growth and shoot growth.
The free auxin is the plant’s hormones, which can be easily isolated from the cells, whereas the bound auxin plant hormones are isolated with difficulty with the help of organic solvents.
Q.15. Why is abscisic acid called stress hormone?
Sol: Abscisic acid is called the stress hormone, as it helps the plant to survive even under the unfavourable conditions of the environment. It is observed that plants growing in an area with deficiency of water or during the deficiency of water in leaves, the concentration of the abscisic acid increases and promotes the stomata to close.
Q.16. What is meant by bolting effect?
Sol: The stimulation of internode elongation just before flowering is called bolting.
In some higher plants, leaves are borne on the axis in the crowded form on short internodes. Such a form of growth is called a rosette. It has been observed in a few plants which show excessive internode elongation just before the process of flowering.
Q.17. What is Growth measurement?
Sol: Growth rate in plants can be measured by the growth in shape, size and its organs – leaves, flowers and fruits. The growth rate in plants is usually measured in the following ways:
- By linear measurement.
- By the increase in the number of cells.
- By the increase in the dry weight of the plant.
- By the increase in the shape of cells, tissues and other organs.
There are different methods of growth measurements which have been used to measure the plant growth rate.
Q.18. Define after-ripening period.
Sol: Seeds of some plants do not germinate immediately after their formation and they enter into the resting phase. During the resting phase, some internal changes occur in the seed, later they acquire the capacity to germinate. The resting phase or period is called the ripening period.
Q.19. What are Gibberellins? How many gibberellins are there?
Sol: Gibberellins are the plant growth regulators involved in regulating the growth and influencing different developmental processes which include stem elongation, germination, flowering, enzyme induction, etc. There are more than 70 gibberellins isolated. They are GA1, GA2, GA3 and so on. GA3 Gibberellic acid is the most widely studied plant growth regulator.
Q.20. What is the growth regulatory substance?
Sol: All higher plants contain some chemical substances, which are directly synthesised by plants but are in very little quantity. These chemical substances control the growth and other cellular functions of the plants and are called the growth regulatory substance. The first scientist to present the concept of growth-promoting hormones in the plant was a German scientist J.Von Sachs in the year 1882. Later in 1900, many other scientists were involved in the discovery of different plant hormones.
RBSE Biology Class 12: Long Answer Type Questions
Q.1. What are Plant Hormones? Explain its types.
Sol. As all green plants require external factors such as sunlight, water, oxygen, minerals for their growth and development. These are a few intrinsic factors that regulate the growth and development of plants. These are called plant hormones or plant growth regulators.
Plant hormones are defined as the chemical compounds, which are directly synthesised by plants but are in very little concentration by different parts of the plant and are transmitted to various parts of the plant. There are five different types of plant hormones, which vary in their structure and functions.
Listed below are the five different types of plant hormones:
Auxin – They are widely used in agricultural and horticultural practices. They are found in growing apices of roots and stems and then migrate to other parts to act. It is synthesized at the points of the stem, buds and root tips.
Cytokinin – They are the naturally synthesised plant hormones, which are involved in the cell-division. It is synthesized in roots.
Gibberellins- There are more than 70 gibberellins isolated. GA3 Gibberellic acid is the most widely studied plant growth regulator. It is produced within the cell’s plastids.
Abscisic acid- It is a growth-inhibiting hormone, which inhibits plant metabolism and regulates abscission and dormancy. It is produced in the roots and in the terminal buds at the top of the plant. It is also called “stress hormone” as it increases tolerance of plants.
Ethylene- The growth promoter as well as an inhibitor of plants. It is the only plant hormone, which occurs in the gaseous state. It is produced essentially by different parts of the plants, including the roots, stems, leaves, flowers, fruits, tubers, and seeds.
Q.2.Write a short note on the growth phase.
It is also called the phases of growth. The plant’s growth is completed in three phases.
The three phases of growth in plants are:
The phase of cell division.
This is the initial phase. In this phase, the meristematic cells divide mitotically and pass new cells continuously. This is also called the phase of formation.
The phase of cell elongation.
In this phase of cell elongation, the newly formed cells elongate in a particular direction. The thin and the elastic cell wall stretches and a large vacuole begins to develop within the centre of the cell. This phase is also called the phase of enlargement.
The phase of cell differentiation.
In this phase of cell differentiation, the cell matures, secondary wall material is deposited and cells stop dividing. Depending upon the functions, the cells undergo physiological and biochemical changes. This phase is also called the phase of maturation.
Q.3.Brief out the structure and functions of Gibberellins?
Sol. Gibberellins are the plant growth regulators involved in regulating the growth and developmental processes, including stem elongation, germination, flowering, enzyme induction, etc. There are more than 70 gibberellins isolated. They are GA1, GA2, GA3 and so on. GA3 Gibberellic acid is the most widely studied plant growth regulator.
Structure and function of Gibberellins
Gibberellin is a diterpenoid in structure, which forms the basis of molecules such as vitamins A and E. The main functions of Gibberellin is to facilitate cell elongation, inhibition of growth, and help the plants to grow taller. They also play major roles in germination, elongation of the stem, fruit ripening and flowering.
Q.4.Write a brief note about the classification of plant hormones?
Sol. Plant hormones are defined as the chemical compounds, which are directly synthesised by plants but are in very little concentration by different parts of the plant and are transmitted to various parts of the plant. Plant hormones are classified into two major groups.
Growth promoting hormones
The group of growth-promoting hormones, which functions by promoting the growth of a plant or increasing the growth rate are called Growth promoting hormones. These include Auxin, Gibberellin, Cytokinin, Ethylene, etc.
Growth inhibiting hormones
The group of growth-inhibiting hormones, which functions by inhibiting or reducing the growth rate of plants are called Growth inhibiting hormones. Abscisic acid is an example of growth-inhibiting hormones,
Q.5.What is called dormancy? Describe the causes of dormancy and the preventive measure to control it.
A fully developed seed must germinate if the conditions are favourable for germination. But in some plants, the fully formed seeds don’t germinate immediately even under favourable conditions.This state of temporary suspension of germination seeds is called dormancy.
This period of temporary suspension varies in plants.
The dormancy may be on an account of the following factors:
- Hard seed coat.
- Immature embryo.
- Presence of germination inhibitor.
- Presence of high concentrate solutes.
- A requirement of specific temperature and light.
When the seeds are fully developed, seeds germinate immediately after their formation under favourable conditions. The dormancy period of seeds varies from one plant to another plant. Some plants like desert habitat take 5 to 10 years for dormancy. Most of the crop plants take 2 to 5 years for dormancy and in some plants like pulses and pea plants there is no dormancy or dormancy is absent.
The factors affecting dormancy.
There are many factors affecting seed dormancy. These include both the internal and external factors . Listed below are a few of them.
Hard seed coat
Some of the higher plants have a very hard seed coat, which is impermeable to both water and oxygen, which is most essential during the process of germination in seeds. This seed coat also acts as a mechanical barrier and resists the development of an embryo.
Immaturity of an embryo.
Seeds are dispersed even before the maturity of the embryo. Therefore, germination of seeds will not occur until and unless the embryo fully matures.
The requirement of the after ripening period.
Seeds of some plants do not germinate immediately after their formation. But they germinate after the completion of a certain resting phase. During the resting stage,they acquire the capacity of germination.This resting period is called embryo, which varies from weeks to months.
A requirement of specific temperature and light.
Seeds of some plants require a cold temperature before germination. During the winter season the seeds germinate naturally and in some cases cold treatment is given for the plants to germinate it seeds.The optimum temperature required for cold treatment ranges between 0℃ to 5℃ .
Presence of germination inhibitors.
There are certain substances present in fleshy fruits, which inhibit germination. It includes abscisic acid – ABA, para abscisic acid, phenolic acid, etc. In some cases, the inhibitory effects of these substances can be neutralised by the application of gibberellin.
Preventive measure to control dormancy
There are various preventive measures to control dormancy or method of breaking seed dormancy. Depending upon the reason, the following methods are used for breaking the seed dormancy. These include:
- Chilling treatment.
- Exposure of specific light.
- Exposure of alternate temperature.
- Exposure to pressure.
The hard seed coat is worn or weakened either by breaking or scratching, so that the seeds can absorb water easily. The seeds are also made soft either by soaking them in a dilute sulphuric acid, or in hot water or in fat solvents.
Those seeds which require chilling treatment for breaking dormancy are exposed to an artificial chilling treatment and the optimum temperature required for cold treatment ranges between 0℃ to 5℃ .
Exposure to alternate temperature.
Seed dormancy in some plants can be broken easily by exploring the seeds to alternate high and low temperature .
Exposure to specific light.
Exposure of positive photoelastic seed with red light can increase the efficiency of seed germination.
Exposure to pressure.
Seeds are applied to a pressure of 2000 atmospheric pressure at 18℃ to 20℃ t. This increases the seed germinating capacity because of the softening of seed coat and increase in the permeability.
Q.6.How is growth measured? List out the different factors affecting the rate of growth in plants.
Sol. Growth in plants are measured by the following methods. Any of these methods can be used to measure the growth rate in plants.
- By linear measurements.
- By increasing the dry weight of a plant.
- By increasing the number of cells produced.
- By measuring the length and girth of the stem and root.
- By measuring the increase in the size of cells, tissues, and plant parts such as leaves, flowers and fruits.
There are two different methods used for measuring the growth rate in plants.
Simple or Direct method.
The most important and the simple method for measuring the growth in plants is measuring the length of a plant or any organ of a plant . The initial length can be measured by a scale.
After a particular interval of time, the length is again measured by the scale.
The increase in the length denoted the growth in that time period.
Normally, the growth of a plant is measured by linear growth. For this purpose, an Auxanometer instrument is used.
Factors Affecting the Plants growth
Factors affecting the growth rate in plants include both the internal and external factors.The internal or physiological factors include the absorption of nutrition, water, rate of respiration, photosynthesis and plant growth hormone. The external factors include all the environmental issues like:
The availability of light.
The high intensity of light slows down the growth of the plants.
The availability of water.
The availability of light water is directly correlated with the growth rate. All biological processes of plants including the osmosis, transportation, photosynthesis, respiration, germination depends on water.
The variations in temperature directly affect the growth rate of the plants. The normal growth of the plants requires a temperature ranging between 5 to 35. Increase in temperature above the 35 causes damage to plants and below 0 temperature leads to freezing of water in plant cells, results in inactive of protoplasm which causes the cell to die.
The quantity of the oxygen increases the growth in plants because oxygen is also involved in all biological processes and during the cellular respiration, potential energy is converted into kinetic energy.
Deficiency of mineral salts or nutrients leads to deficiency disorders, which leads to the stunted growth in plants.
Q.7.What are the main functions of plant hormones?
Sol: Plant hormones are involved in a variety of function, which includes:
Shoot growth in culture.
Inhibits seed germination.
Cell elongation of stems and roots.
Induces abscission of leaves and fruits.
Promotes flowering in all angiosperms.
Helps in cell division and xylem differentiation.
Stimulate the formation of chloroplast in leaves.
Prevents premature fall of leaves, flowers, fruits.
Promotes nutrient mobilisation and delay leaf senescence.
Used to stimulate the ripening of fruits. For example, tomatoes and citrus fruits.
Some are used as a herbicide to kill undesirable weeds without affecting monocot plants.
Breaks seed dormancy and promotes lateral and adventitious shoot growth and used to initiate.
Q.8.How is auxin discovered? Draw the structure of auxin and list out its functions.
Sol: Auxins were the first plant hormones discovered. Auxin is produced by the tip of the stem and helps in the elongation of cells. It promotes cell elongation, root growth and shoot growth.
Structure of Auxin.
Function of Auxin.
- Initiate root formation in the stem cuttings.
- Helps in Apical Dominance and Parthenocarpy.
- Induces phototropism, gravitropism and thigmotropism.
- Used for the production of fruit without preceding fertilization.
- Induces callus formation in the ex-plants and stimulates morphogenesis.
- Promotes secondary growth and induces cell division in the vascular cambium.
- Synthetic auxins are widely used to kill weeds. It does not affect grasses (monocotyledons)
- Stimulates the fruit development, promotes flowering in plants and delays senescence of both fruits and flowers
- Auxin promotes healing and helps in cell differentiation and regeneration of vascular tissues -phloem and xylem.
- Involved in promoting the elongation in shoots and coleoptiles. Plasticity of the cell wall is increased by acidification.
Q.9.Describe the factors affecting the rate of growth in plants.
Sol: There are four major factors that affect the growth of the plants. They are:
As plants are autotrophs, they require light for the synthesis of their food. Therefore, the absence of light greatly affects the growth of the plant. The intensity, quality, and light duration influence the various physiological factors and also encourages flowering and fruiting.
Plants cannot survive without water. Around 90% of the plant body comprises water. Plants become stressed in the absence of water and die.
Plant growth is greatly influenced by temperatures. Higher the temperature, the rate of growth in plants is also high. High temperature increases the rate of transpiration, photosynthesis, and germination processes. Low temperatures, slows down the growth of the plants.
All plants require proper nutrients for their growth and development. The nutrients include both macronutrients and micronutrients. Deficiency of these nutrients in plants makes them prone to several diseases and also results in stunted growth of the plant.
Q.10.Define the following terms: Abscisic acid, Gibberellin, Cytokinin, Auxin, Ethylene
It is a growth-inhibiting hormone. ABAs act as an antagonist to GAs. It inhibits plant metabolism and regulates abscission and dormancy. It is also called “stress hormone” as it increases tolerance of plants.
Gibberellins are an extensive chemical family based on the gibberellin structure. The first gibberellin to be discovered was gibberellic acid. Now, there are more than 100 types of gibberellins (GA1, GA2, GA3…..) found. These hormones are mainly obtained from a variety of organisms from fungi to higher plants. They are acidic in nature. These are found in higher plants and fungi.
These are produced in the regions where cell division occurs; mostly in the roots and shoots. They help in the production of new leaves, lateral shoot growth, chloroplasts in leaves etc. They help in overcoming apical dominance and delay ageing of leaves. Cytokinins play an important role in the cytokinesis process.
They are one of the most important plant hormones. The chief naturally occurring auxin is indole-3 acetic acid – IAA and other related compounds. They are found in growing apices of roots and stems and then migrate to other parts of the plant.
It acts as a growth promoter as well as an inhibitor. Occurs in gaseous form. It is synthesised in the ripening fruits and tissues undergoing senescence. It regulates many physiological processes and is one of the most widely used hormones in agriculture.
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