Case Study Questions Class 11 Biology Chapter 15 Plant Growth and Development
CBSE Class 11 Case Study Questions Biology Plant Growth and Development. Important Case Study Questions for Class 11 Board Exam Students. Here we have arranged some Important Case Base Questions for students who are searching for Paragraph Based Questions Plant Growth and Development.
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CBSE Case Study Questions Class 11 Biology Plant Growth and Development
CASE 1
The cells derived from root apical and shoot-apical meristems and cambium differentiate and mature to perform specific functions. This act leading to maturation is termed as differentiation. During differentiation, cells undergo few to major structural changes both in their cell walls and protoplasm. For example, to form a tracheary element, the cells would lose their protoplasm. They also develop a very strong, elastic, lignocellulosic secondary cell walls, to carry water to long distances even under extreme tension.
Plants show another interesting phenomenon. The living differentiated cells that by now have lost the capacity to divide can regain the capacity of division under certain conditions. This phenomenon is termed as dedifferentiation. For example, formation of meristems – interfascicular cambium and cork cambium from fully differentiated parenchyma cells. While doing so, such meristems/tissues are able to divide and produce cells that once again lose the capacity to divide but mature to perform specific functions, i.e., get redifferentiated. List some of the tissues in a woody dicotyledenous plant that are the products of redifferentiation.
Development is a term that includes all changes that an organism goes through during its life cycle from germination of the seed to senescence. Plants follow different pathways in response to environment or phases of life to form different kinds of structures. This ability is called plasticity, e.g., heterophylly in cotton, coriander and larkspur. In such plants, the leaves of the juvenile plant are different in shape from those in mature plants. On the other hand, difference in shapes of leaves produced in air and those produced in water in buttercup also represent the heterophyllous development due to environment. This phenomenon of heterophylly is an example of plasticity.
Development is considered as the sum of growth and differentiation. Development in plants is under the control of intrinsic and extrinsic factors. The former includes both intracellular (genetic) or intercellular factors (chemicals such as plant growth regulators) while the latter includes light, temperature, water, oxygen, nutrition, etc.
1.) The time differentiated cells have lost the capacity to divide, such cell regain the capacity of division under certain conditions,such phenomenon is termed as
a) Differentiation
b) Dedifferentiation
c) Redifferentiation
d) None of the above
2.) Cell produced after dedifferentiation that cell once again lose the capacity to divide but mature enough to perform certain functions are termed as
a) Dedifferentiation
b) Dedifferentiation
c) Redifferentiation
d) None of the above
3.) Give the examples of plant which shows heterophylly phenomenon.
4.) Name the factors that can affect the development of plants and animals.
5.) What is mean by plasticity? Give its example.
Answer key
1.) b
2.) c
3.) Plants likecotton, coriander and larkspur are the examples of plasticity, which shows heterophylly phenomenon.
4.) Development in plants is controlled by intrinsic and extrinsic factors. The intrinsic factor includes both intracellular (genetic) or intercellular factors (chemicals such as plant growth regulators). The extrinsic factors includes light, temperature, water, oxygen, nutrition, etc.
5.) Plants follow different pathways in response to the external environment and phases of life to form different kinds of structures. This ability of plant is known as plasticity, e.g., heterophylly in cotton, coriander and larkspur.
In such plants, the leaves of the juvenile plant are different in shape from those in mature plants. On the other hand, difference in shapes of leaves produced in air and those produced in water in buttercup also represent the heterophyllous development due to environment.
CASE 2
It has been observed that some plants require a periodic exposure to light to induce flowering. It is also seen that such plants are able to measure the duration of exposure to light. For example, some plants require the exposure to light for a period exceeding a well-defined critical duration, while others must be exposed to light for a period less than this critical duration before the flowering is initiated in them. The former group of plants are called long day plants while the latter ones are termed short day plants. The critical duration is different for different plants. There are many plants, however, where there is no such correlation between exposure to light duration and induction of flowering response; such plants are called day-neutral plants. It is now also known that not only the duration of light period but that the duration of dark period is also of equal importance. Hence, it can be said that flowering in certain plants depends not only on a combination of light and dark exposures but also their relative durations. This response of plants to periods of day/night is termed photoperiodism. It is also interesting to note that while shoot apices modify themselves into flowering apices prior to flowering, they (i.e., shoot apices of plants) by themselves cannot percieve photoperiods. The site of perception of light/dark duration are the leaves. It has been hypothesised that there is a hormonal substance(s) that is responsible for flowering. This hormonal substance migrates from leaves to shoot apices for inducing flowering only when the plants are exposed to the necessary inductive photoperiod.
1.) Plants which requires the exposure to light for a well-defined critical duration, such plants are termed as ____________
a) Short-day plants
b) Long-day plants
c) Day-neutral plants
d) None of the above
2.) __________________ Plant requires exposure to light for a period of less than critical duration.
a) Short-day plants
b) Long-day plants
c) Day-neutral plants
d) None of the above
3.) Define photoperiodism.
4.) Define Day-neutral plants with suitable example.
5.) How photoperiod correlate with hormonal substances.
Answer key
1.) b
2.) a
3.) Photoperiodism – The effect of light availableor day duration of light hours and dark periods on the growth and development of plants, specifically on flowering, this phenomenon is known as photoperiodism.
4.) Day-neutral plants – Plants in which no such correlation between exposure to the light duration and induction of flowering response, such type of plants are termed as day-neutral plants e.g. tomato, cucumber, etc
5.) It has been discovered that there is a hormonal substances that is responsible for flowering in plants. This hormonal substance migrates from leaves to shoot apices for inducing flowering only when the plants are exposed to the necessary inductive period of light.
CASE 3
Plant growth regulators are the chemical substances which govern all the factors of development and growth within plants. Some other names used to refer to it are phytohormones and plant growth hormones. Phytohormones are organic compounds which are either synthesized in laboratories or produced naturally within the plants. They profoundly control and modify the physiological processes like the growth, development, and movement of plants. Based on their actions, plant growth regulators are broadly classified into two major groups: Plant growth promoters
Plant growth inhibitors.
Auxins, Gibberellins, and Cytokinins are grouped into Plant growth promoters while Abscisic acid and Ethylene are grouped into Plant growth inhibitors. Ethylene can be grouped either into the promoters or into the plant inhibitors.
Auxins was first isolated from human urine. The term ‘auxin’ is applied to the indole-3-acetic acid (IAA), and to other natural and synthetic compounds having certain growth regulating properties. They are generally produced by the growing apices of the stems and roots, from where they migrate to the regions of their action. Auxins like IAA and indole butyric acid (IBA) have been isolated from plants. NAA (naphthalene acetic acid) and 2, 4-D (2, 4-dichlorophenoxyacetic) are synthetic auxins. All these auxins have been used extensively in agricultural and horticultural practices. They help to initiate rooting in stem cuttings, an application widely used for plant propagation. Auxins promote flowering e.g. in pineapples. They help to prevent fruit and leaf drop at early stages but promote the abscission of older mature leaves and fruits. In higher plants, the growing apical bud inhibits the growth of the lateral (axillary) buds, a phenomenon called apical dominance. Removal of shoot tips (decapitation) usually results in the growth of lateral buds. It is widely applied in tea plantations, hedge-making. Auxins also induce parthenocarpy, e.g., in tomatoes. They are widely used as herbicides. 2, 4-D, widely used to kill dicotyledonous weeds, does not affect mature monocotyledonous plants. It is used to prepare weed-free lawns by gardeners. Auxin also controls xylem differentiation and helps in cell division.
1.) Identify the incorrect statement about PGR.
Statement 1 – 2, 4-dichlorophenoxyacetic is natural auxins.
Statement 2 – Auxin controls xylem differentiation and helps in cell division.
Statement 3 – Auxins was first isolated from human urine.
Statement 4 – Indole acetic acid are isolated from plants.
2.) ___________________ is synthetic auxins
a) Indole butyric acid
b) 2, 4-dichloroethynoxyacetic
c) Naphthalene acetic acid
d) 4, 2-dichlorophenoxyacetic
3.) Name the plant growth regulator was first isolated from human urine?
4.) Define phytohormones.
5.) Explain apical dominance. Name the hormone that controls it.
Answer key
1) a
2.) c
3.) Auxin was the first plant growth regulator isolated from human urine.
4.) Phytohormones are organic compounds which are either synthesized in laboratories or produced naturally within the plants. They profoundly control and modify the physiological processes like the growth, development, and movement of plants.
5.) Apical dominance is defined as phenomenon in which the apical bud become dominant and suppresses the growth of lateral buds into branches. Auxin is the plant growth regulator that controls apical dominance.
CASE 4
Gibberellins are another kind of promontory PGR. There are more than 100 gibberellins reported from widely different organisms such as fungi and higher plants. They are denoted as GA1 , GA2 , GA3 and so on. However, Gibberellic acid (GA3 ) was one of the first gibberellins to be discovered and remains the most intensively studied form. All GAs are acidic. Their ability to cause an increase in length of axis is used to increase the length of grapes stalks. Gibberellins, cause fruits like apple to elongate and improve its shape. They also delay senescence. Thus, the fruits can be left on the tree longer so as to extend the market period. GA3 is used to speed up the malting process in brewing industry. Sugarcane stores carbohydrate as sugar in their stems. Spraying sugarcane crop with gibberellins increases the length of the stem, thus increasing the yield by as much as 20 tonnes per acre. Spraying juvenile conifers with GAs hastens the maturity period, thus leading to early seed production. Gibberellins also promotes bolting (internode elongation just prior to flowering) in beet, cabbages and many plants with rosette habit.
Cytokinins have specific effects on cytokinesis, and were discovered as kinetin (a modified form of adenine, a purine) from the autoclaved herring sperm DNA. Kinetin does not occur naturally in plants. Search for natural substances with cytokinin-like activities led to the isolation of zeatin from corn-kernels and coconut milk. Since the discovery of zeatin, several naturally occurring cytokinins, and some synthetic compounds with cell division promoting activity, have been identified. Natural cytokinins are synthesised in regions where rapid cell division occurs, for example, root apices, developing shoot buds, young fruits etc. It helps to produce new leaves, chloroplasts in leaves, lateral shoot growth and adventitious shoot formation. Cytokinins help overcome the apical dominance. They promote nutrient mobilisation which helps in the delay of leaf senescence.
1.) Identify the incorrect function of PGR
a) Cytokinins help to counter apical dominance.
b) Cytokinins were discovered as kinetin.
c) Cytokinins are adenine or purine derivatives
d) Zeatin is the artificial Cytokinin.
2.) ______________________ is the natural Cytokinin that was extracted and isolated from corn Kernels and Coconut milk.
a) Kinetin
b) Zeatin
c) Adenine
d) Purine
3.) Name the first gibberellins discovered ever?
4.) Name the plant growth regulator that delay fruit senescence& give its functions.
5.) Define bolting.
6.) Where are cytokinins synthesised in plants? Mention their functions.
Answer key
1.) d
2.) b
3.) Gibberellic acid (GA3) was one of the first gibberellins to be discovered and remains the most intensively studied form
4.) Gibberellins also delay senescence. Thus, the fruits can be left on the tree longer so as to extend the market period.
Functions of Gibberellins;
- Gibberellins produce a wide range of physiological responses in plants
- They can cause an increase in the length of grapes stalks as they are capable to bring about an increase in the length of axis.
- They cause fruits such as apples to elongate and improve its shape.
- They are responsible in delaying the process of senescence.
5.) Bolting is internode elongation just prior to flowering. Gibberellins promotes bolting in beet, cabbages and many plants with rosette habit.
6.) Cytokinins are synthesised in plant parts where rapid cell division occurs, like root apices, shoot buds, young fruits, etc. The functions of cytokines are as follows: Cytokinins influence cell division (cytokinesis), cell enlargement and differentiation.
CASE 5
Ethylene is a simple gaseous PGR. It is synthesised in large amounts by tissues undergoing senescence and ripening fruits. Influences of ethylene on plants include horizontal growth of seedlings, swelling of the axis and apical hook formation in dicot seedlings. Ethylene promotes senescence and abscission of plant organs especially of leaves and flowers. Ethylene is highly effective in fruit ripening. It enhances the respiration rate during ripening of the fruits. This rise in rate of respiration is called respiratory climactic. Ethylene breaks seed and bud dormancy, initiates germination in peanut seeds, sprouting of potato tubers. Ethylene promotes rapid internode/petiole elongation in deep water rice plants. It helps leaves/ upper parts of the shoot to remain above water. Ethylene also promotes root growth and root hair formation, thus helping the plants to increase their absorption surface. Ethylene is used to initiate flowering and for synchronising fruit-set in pineapples. It also induces flowering in mango. Since ethylene regulates so many physiological processes, it is one of the most widely used PGR in agriculture. The most widely used compound as source of ethylene is ethephon. Ethephon in an aqueous solution is readily absorbed and transported within the plant and releases ethylene slowly. Ethephon hastens fruit ripening in tomatoes and apples and accelerates abscission in flowers and fruits (thinning of cotton, cherry, walnut). It promotes female flowers in cucumbers thereby increasing the yield.
1.) ___________ is responsible for enhancing the rate respiration during ripening of the fruits.
a) Indole buteric acid
b) Ethanol
c) Abscisic acid
d) ethylene
2.) Identify the correct function of ethylene
a) Ethylene promotes senescence of leaves.
b) Ethylene is used to inhibit the flowering.
c) Ethylene cause stunted growth of roots.
d) Ethylene inhibit root hair formation.
3.) What is ethephon? How it is useful as PGR.
4.) What is mean by Respiratory climactic?
5.) Give the functions of ethylene related to flowering in plants.
Answer key
1.) d
2.) a
3.) Ethephon – It is a compound used as a source of ethylene for plant growth.
Use of ethephon as PGR;
- Ethephon hastens fruit ripening.
- It accelerates abscission in flowers and thinning in cotton, walnut, and cherry, etc.
- It promotes the development of female flowers.
4.) Respiratory climactic – Ethylene has very important application as PGR. It’s effective in fruit ripening. It is condition in which ethylene enhances the respiration rate during ripening of the fruits. This rise in rate of respiration is named as respiratory climactic.
5.) Functions of ethylene in case of flowering;
Ethylene is used to initiate flowering and for synchronising fruit-set in pineapples.
Ethylene promotes female flowers in cucumbers thereby increasing the yield.