TN Board 11th Bio Botany Important Questions Chapter 15 Plant Growth and Development

Students get through the TN Board 11th Bio Botany Important Questions Chapter 15 Plant Growth and Development which is useful for their exam preparation.

TN State Board 11th Bio Botany Important Questions Chapter 15 Plant Growth and Development

Very short answer questions

Question 1.
Give the definition for Growth.
Answer:
Growth is defined as an irreversible permanent increase in size, shape, number, volume, and dry weight.

Question 2.
Explain the term ‘Monocarpic perennial’.
Answer:
Monocarpic perennials produce flowers only once during their lifetime but the plants survive for many years. Example: Bamboo.

Question 3.
Define the grand period of growth and mention its phases.
Answer:
The total period from the initial to the final stage of growth is called the grand period of growth. They are:

1. Lag phase,
2. Log phase,
3. Decelerating phase and
4. Maturation phase.

Question 4.
Plot a graph depicting the constant linear growth.
Answer:

Question 5.
Compare absolute growth rate with relative growth rate.
Answer:
Comparison between Absolute and Relative Growth Rates

Absolute Growth Rate	Relative Growth Rate
Increase in total growth of two organs measured and compared per unit time is called absolute growth rate.	The growth of the given system per unit time expressed per unit initial parameter is called relative growth rate.

Question 6.
Define Differentiation.
Answer:
The process of maturation of meristematic cells to specific types of cells performing specific functions is called differentiation.

Question 7.
What is Re-differentiation?
Answer:
Differentiated cells, after multiplication again lose the ability to divide and mature to perform specific functions. This is called redifferentiation.

Question 8.
What are Plant Growth Regulators (PGR’s)?
Answer:
Plant Growth Regulators are defined as organic substances which are synthesized in minute quantities in one part of the plant body and transported to another part where they influence specific physiological processes.

Question 9.
Mention any four Phytohormones.
Answer:
Auxins, gibberellins, cytokinin, ethylene, abscisic acid.

Question 10.
Define the term Bioassay.
Answer:
Bioassay means-testing of substances for their activity in causing a growth response in a living plant or its part.

Question 11.
Explain Anti-auxins.
Answer:
Anti-auxin compounds when applied to the plant inhibit the effect of auxin. Example: 2, 4, 5-Tri Iodine Benzoic Acid (TIBA) and Napthylpthalamine.

Question 12.
Apical dominance – Explain.
Answer:
Suppression of growth in the lateral bud by apical bud due to auxin produced by apical bud is termed as apical dominance.

Question 13.
Mention the precursors of (a) Auxin, (b) Gibberellin, (c) Cytokinin and (d) Abscisic acid.
Answer:

S. No.	Plant Hormones	Precursors
(a)	Auxin	Tryptophan
(b)	Gibberellin	Acetate
(c)	Cytokinin	Adenine
(d)	Abscisic acid	Xanthophylls

Question 14.
How Gibberellins are transported from their site of production?
Answer:
The transport of gibberellins in plants is non-polar. Gibberellins are translocated through the phloem and also occur in the xylem due to lateral movement between vascular bundles.

Question 15.
What do you mean by the term – Basipetal transport and Acropetal transport?
Answer:
Basipetal means transport through the phloem from shoot to root and acropetal means transport through the xylem from root to shoot.

Question 16.
Define Bolting.
Answer:
Rosette plants (genetic dwarfism) plants exhibit excessive intermodal growth when they are treated with gibberellins. This sudden elongation of a stem followed by flowering is called bolting.

Question 17.
Which plants are affected by Bakanae’s disease? Name the causative organism.
Answer:
Bakanae’s disease affects the rice plants. It is caused by a fungus called Gibberella fujikuroi.

Question 18.
Biennials usually flower at the second year of growth. Is it possible to make them flower in the first year itself? How?
Answer:
Many biennials usually flower during the second year of their growth. For flowering to take place, these plants should be exposed to the cold season. Such plants could be made to flower without exposure to the cold season in the first year itself when they are treated with gibberellins.

Question 19.
Where cytokinin is synthesized in plants?
Answer:
Cytokinin is formed in root apex, shoot apex, buds, and young fruits.

Question 20.
Give an account on neem Coty Ledon assay.
Answer:
Bioassay (Neem Cotyledon Assay): Neem cotyledons are measured and placed in cytokinin solution as well as in ordinary water. Enlargement of cotyledons is an indication of cytokinin activity.

Question 21.
State Richmond Lang effect.
Answer:
Application of cytokinin delays the process of aging by nutrient mobilization. It is known as the Richmond Lang effect.

Question 22.
Write a note on Bioassay of Ethylene.
Answer:
Ethylene can be measured by gas chromatography. This technique helps in the detection of the exact amount of ethylene from different plant tissues like lemon and orange.

Question 23.
What are climacteric fruits? Give example.
Answer:
In most of the plants, there is a sharp rise in respiration rate near the end of the development of fruit, called climacteric rise. Such fruits are called climacteric fruits. Example: Tomato, Apples, Banana, Mango.

Question 24.
ABA is called the stress hormone – Justify.
Answer:
It inhibits the shoot growth and promotes the growth of the root system. This character protects the plants from water stress. Hence, ABA is called the stress hormone.

Question 25.
Define photoperiodism. Name the person who coined this term.
Answer:
The physiological change on flowering due to relative length of light and darkness (photoperiod) is called Photoperiodism. The term photoperiodism was coined by Gamer and Allard.

Question 26.
Define the term photo neutrals.
Answer:
There are a number of plants that can flower in all possible photoperiods. They are also called photo neutrals or indeterminate plants. Example: Potato, Rhododendron, Tomato, and Cotton.

Question 27.
Point out the importance of photoperiodism.
Answer:
Importance of photoperiodism

1. The knowledge of photoperiodism plays an important role in hybridization experiments.
2. Photoperiodism is an excellent example of physiological pre-conditioning that is using an external factor to induce physiological changes in the plant.

Question 28.
Vernalisation – Define.
Answer:
Many species of biennials and perennials are induced to flower by low-temperature exposure ‘ (0°C to 5°C). This process is called Vernalization.

Question 29.
How vernalisation is carried out?
Answer:
The seeds are first soaked in water and allowed to germinate at 10°C to 12°C. Then seeds are transferred to low temperature (3°C to 5°C) from few days to 30 days. Germinated seeds after this treatment are allowed to dry and then sown. The plants will show quick flowering when compared to untreated control plants.

Question 30.
Define Seed germination and state its types.
Answer:
The activation and growth of an embryo from seed into seedling during favorable conditions is called seed germination. There are two methods of seed germination. Epigeal and hypogeal.

Question 31.
What are photoelastic seeds?
Answer:
There are many seeds that respond to light for germination and these seeds said to be photoelastic.

Question 32.
How can we overcome dormancy in photoelastic seeds?
Answer:
The dormancy of photoelastic seeds can be broken by exposing them to red light.

Question 33.
Senescence-Define.
Answer:
Old age is called senescence in plants. Senescence refers to all collective, progressive and deteriorative processes which ultimately lead to complete loss of organization and function.

Question 34.
What field do phytogerontology deal with?
Answer:
The branch of botany that deals with aging, abscission, and senescence is called Phytogerontology.

Question 35.
Mention the types of senescence.
Answer:
Leopold (1961) has recognized four types of senescence:

1. Overall senescence
2. Top senescence
3. Deciduous senescence
4. Progressive senescence

Question 36.
Where the abscission zone is formed?
Answer:
Leaf abscission takes place at the base of the petiole which is marked internally by a distinct zone of few layers of thin-walled cells arranged transversely. This zone is called the abscission zone or abscission layer. An abscission layer is greenish-grey in color and is formed by rows of cells of 2 to 15 cells thick.

Question 37.
Expand PCD and define it.
Answer:
Death of the plant or its parts consequent to senescence is called Programmed Cell Death (PCD).

Short answer questions

Question 1.
Draw a graph of the sigmoid curve.
Answer:

Question 2.
Correlate the terms light & etiolation in the plant.
Answer:
Light has its own contribution to the growth of the plant. Light is important for growth and photosynthesis. Light stimulates healthy growth. The absence of light may lead to yellowish in color. This is called etiolation.

Question 3.
List out the internal factors that affect growth.
Answer:
a. Genes are intracellular factors for growth.
b. Phytohormones are intracellular factors for growth. Example: auxin, gibberellin, cytokinin.
c. C/N ratio.

Question 4.
Give an account on Dedifferentiation.
Answer:
The living differentiated cells which had lost capacity to divide, regain the capacity to divide under certain conditions. Hence, dedifferentiation is the regaining of the ability of cell division by the differentiated cells. Example: Interfascicular cambium and Vascular cambium.

Question 5.
Explain synergistic & Antagonistic effects of plant hormones.
Answer:
Synergistic and Antagonistic effects

1. Synergistic effects: The effect of one or more substances in such a way that both promote each other’s activity. Example: Activity of auxin and gibberellins or cytokinins.
2. Antagonistic effects: The effect of two substances in such a way that they have opposite effects on the same process. One accelerates and the other inhibits. Example: ABA and gibberellins during seed or bud dormancy. ABA induces dormancy and gibberellins break it.

Question 6.
Name any three synthetic auxins.
Answer:
1. 2,4-Dichloro Phenoxy Acetic Acid (2,4-D)
2. 2,4,5-Trichloro Phenoxy Acetic Acid (2,4,5-T)
3. Naphthalene Acetic Acid (NAA).

Question 7.
Describe the procedure of the Avena curvature test.
Answer:
When the Avena seedlings have attained a height of 15 to 30 mm, about 1mm of the coleoptile tip is removed. This apical part is the source of natural auxin. The tip is now placed on agar blocks for few hours. During this period, the auxin diffuses out of these tips into the agar. The auxin containing agar block is now placed on one side of the decapitated stump of Avena coleoptile. The auxin from the agar blocks diffuses down through coleoptile along the side to which the auxin agar block is placed. An agar block without auxin is placed on another decapitated coleoptile. Within an hour, the coleoptiles with auxin agar block bend on the opposite side where the agar block is placed. This curvature can be measured.

Question 8.
How auxin is useful in tissue culture technique?
Answer:
Auxin is responsible for the initiation and promotion of cell division in the cambium, which is responsible for secondary growth and tumor. This property of induction of cell division has been exploited for tissue culture techniques and for the formation of callus.

Question 9.
Mention the role of ethylene in the agriculture field.
Answer:

1. Ethylene normally reduces flowering in plants except in Pineapple and Mango.
2. It increases the number of female flowers and decreases the number of male flowers.
3. Ethylene spray in the cucumber crops produces female flowers and increases the yield.

Question 10.
Give an answer for the following with regard to abscisic acid.
(a) Chemical structure (b) Precursor (c) Bioassay
Answer:
(a) Chemical structure – carotenoid structure
(b) Precursor – Mevalonic acid pathway or Xanthophyll
(c) Bioassay – Rice coleoptile.

Question 11.
How ABA involves stomatal closure.
Answer:
ABA helps in reducing the transpiration rate by closing stomata. It inhibits K+ uptake by guard cells and promotes the leakage of malic acid. It results in the closure of stomata.

Question 12.
Enumerate the practical application of vernalization.
Answer:

1. Vernalization shortens the vegetative period and induces the plant to flower earlier.
2. It increases the cold resistance of the plants.
3. It increases the resistance of plants to fungal disease.
4. Plant breeding can be accelerated.

Question 13.
Write a note on Epigeal & hypogeal germination.
Answer:

1. Epigeal Germination: During epigeal germination, cotyledons are pushed out of the soil. This happens due to the elongation of the hypocotyl. Example: Castor and Bean.
2. Hypogeal Germination: During hypogeal germination cotyledons remain below the soil due to rapid elongation of epicotyls. Example: Maize.

Question 14.
Discuss seed viability.
Answer:
Viability: Usually seeds remain viable or living only for a particular period. Viability of seeds ranges from a few days (Example: Oxalis) to more than a hundred years. Maximum viability (1000 years) has been recorded in lotus seeds. Seeds germinate only within the period of viability.

Question 15.
Comment on seed dormancy and its reason.
Answer:
The condition of a seed when it fails to germinate even in suitable environmental conditions is called seed dormancy. There are two main reasons for the development of dormancy: Imposed dormancy and innate dormancy. Imposed dormancy is due to low moisture and low temperature. Innate dormancy is related to the properties of the seed itself.

Question 16.
Which is the final stage of senescence? Define it.
Answer:
The final stage of senescence is abscission. Abscission is a physiological process of shedding of organs like leaves, flowers, fruits, and seeds from the parent plant body.

Question 17.
Mention the role of hormones in Abscission.
Answer:
All naturally occurring hormones influence the process of abscission. Auxins and cytokinins retard abscission, while abscisic acid (ABA) and ethylene induce it.

Question 18.
Why Abscission has to take place?
Answer:
Significance of abscission

1. Abscission separates dead parts of the plant, like old leaves and ripe fruits.
2. It helps in the dispersal of fruits and continuing the life cycle of the plant.
3. Abscission of leaves in deciduous plants helps in water conservation during summer.
4. In lower plants, shedding of vegetative parts like gemmae or plantlets helps in vegetative reproduction.

Long answer questions

Question 1.
Enumerate the characteristics of growth.
Answer:

1. Growth increases in protoplasm at the cellular level.
2. Stem and roots are indeterminate in growth due to continuous cell division and are called an open form of growth.
3. The primary growth of the plant is due to the activity of apical meristem where new cells are added to the root and shoot apex causing linear growth of the plant body.
4. The secondary vascular cambium and cork cambium add new cells to cause an increase in girth.
5. Leaves, flowers, and fruits are limited in growth or of determinate or closed-form growth.

Question 2.
Explain the three phases of growth.
Answer:
Phases of growth
There are three phases of growth, 1. Formative phase, 2. Elongation phase and 3. Maturation phase

1. Formative phase: Growth in this phase occurs in meristematic cells of the shoot and root tips. These cells are small in size, have dense protoplasm, large nucleus, and small vacuoles. Cells divide continuously by mitotic cell division. Some cells retain the capability of cell division while other cells enter the next phase of growth.
2. Elongation Phase: Newly formed daughter cells are pushed out of the meristematic zone
   and increase the volume. It requires auxin and food supply, deposition of new cell wall materials (intussusception), the addition of protoplasm, and development of central vacuole take place.
3. Maturation Phase: During this stage cells attain mature form and size. Thickening and differentiation take place. After differentiation, the cells do not grow further.

Question 3.
Give a detailed account of the geometric growth rate.
Answer:
This growth occurs in many higher plants and plant organs and is measured in size or weight. In-plant growth, geometric cell division results if all cells of an organism or tissue are active mitotically. Example: Round three in the given figure 15.5, produces 8 cells as 23 5 8 and after round 20 there are 220 5 1,048,576 cells. The large, plant, or animal parts are produced this way. In fact, it is common in animals but rare in plants except when they are young and small.

An exponential growth curve can be expressed as,
W₁ = W₀e^rt
W₁ = Final size (weight, height and number)
W₀ = Initial size at the beginning of the period
r = Growth rate
t = Time of growth
e = Base of the natural logarithms
Here r is the relative growth rate and also a measure of the ability of the plant to produce new plant material, referred to as efficiency index. Hence, the final size of W₁ depends on the initial size W₀.

Question 4.
List out the characteristics of phytohormones.
Answer:
Characteristics of phytohormones

1. Usually produced in tips of roots, stems, and leaves.
2. The transfer of hormones from one place to another takes part through conductive systems.
3. They are required in trace quantities.
4. All hormones are organic in nature.
5. There are no specialized cells or organs for their secretion.
6. They are capable of influencing physiological activities leading to promotion, inhibition, and modification of growth.

Question 5.
List out the physiological effects of Auxin.
Answer:
Physiological Effects

1. They promote cell elongation in stem and coleoptile.
2. At higher concentrations, auxins inhibit the elongation of roots but induce more lateral roots. Promotes growth of root-only at extremely low concentrations.
3. Suppression of growth in the lateral bud by apical bud due to auxin produced by apical bud is termed as apical dominance.
4. Auxin prevents abscission.
5. It is responsible for the initiation and promotion of cell division in the cambium, which is responsible for secondary growth and tumor. This property of induction of cell division has been exploited for tissue culture techniques and for the formation of callus.
6. Auxin stimulates respiration.
7. Auxin induces vascular differentiation.

Question 6.
Mention the role of Auxin in Agri-field.
Answer:

1. It is used to eradicate weeds. Example: 2,4-D and 2,4,5-T.
2. Synthetic auxins are used in the formation of seedless fruits (Parthenocarpic fruit).
3. It is used to break the dormancy in seeds.
4. Induce flowering in Pineapple by NAA & 2,4-D.
5. Increase the number of female flowers and fruits in cucurbits.

Question 7.
Mention the role of Gibberellin in agriculture.
Answer:

1. The formation of seedless fruits without fertilization is induced by gibberellins. Example: Seedless tomato, apple, and cucumber.
2. It promotes the formation of male flowers in Cucurbitaceae. It helps in crop improvement.
3. Uniform bolting and increased uniform seed production.
4. Improves the number and size of fruits in grapes. It increases yield.
5. Promotes elongation of inter-node in sugarcane without decreasing sugar content.
6. Promotion of flowering in long-day plants even under short-day conditions.
7. It stimulates seed germination.

Question 8.
Explain the physiological effect of Ethylene.
Answer:

• Ethylene stimulates respiration and ripening in fruits.
• It stimulates radial growth in stem and root and inhibits linear growth.
• It breaks the dormancy of buds, seeds, and storage organiser.
• It stimulates the formation of the abscission zone in leaves, flowers, and fruits. This makes the leaves shed prematurely.
• Inhibition of stem elongation (shortening the internode).
• In low concentrations, ethylene helps in root initiation.
• Growth of lateral roots and root hairs. This increases the absorption surface of the plant roots.
• The growth of fruits is stimulated by ethylene in some plants. It is more marked in climacteric fruits.
• Ethylene causes epinasty.

Question 9.
List out the physiological effects of Abscisic acid.
Answer:

• It helps in reducing the transpiration rate by closing stomata. It inhibits K+ uptake by guard cells and promotes the leakage of malic acid. It results in the closure of stomata.
• It spoils chlorophylls, proteins, and nucleic acids of leaves making them yellow.
• Inhibition of cell division and cell elongation.
• ABA is a powerful growth inhibitor. It causes 50% inhibition of growth in Oat coleoptile.
• It induces bud and seed dormancy.
• It promotes the abscission of leaves, flowers, and fruits by forming abscission layers.
• ABA plays an important role in plants during water stress and during drought conditions. It results in loss of turgor and closure of stomata.
• It has anti-auxin and anti-gibberellin properties.
• Abscisic acid promotes senescence in leaves by causing loss of chlorophyll pigment decreasing the rate of photosynthesis and changing the rate of proteins and nucleic acid synthesis.

Question 10.
Classify and explain the plants based on photoperiodism.
Answer:

1. Long day plants: The plants that require long critical day length for flowering are called long-day plants or short night plants. Example: Pea, Barley, and Oats.
2. Short long-day plants: These are long-day plants but should be exposed to short-day lengths during the early period of growth for flowering. Example: Wheat and Rye.
3. Short-day plants: The plants that require a short critical day length for flowering are called short-day plants or long night plants. Example: Tobacco, Cocklebur, Soybean, Rice, and Chrysanthemum.
4. Long short day plants: These are actually short-day plants but they have to be exposed to long days during their early periods of growth for flowering. Example: Some species of Bryophyllum and Night jasmine.
5. Intermediate day plants: These require a photoperiod between long days and short days for flowering. Example: Sugarcane and Coleus.
6. Day-neutral plants: There are a number of plants that can flower in all possible photoperiods. They are also called photo neutrals or indeterminate plants. Example: Potato, Rhododendron, Tomato, and cotton.

Question 11.
Describe the concept of Phytochrome.
Answer:
Phytochrome is a bluish biliprotein pigment responsible for the perception of light in a photo physiological process. Butler et al, (1959) named this pigment and it exists in two interconvertible forms: (i) red light-absorbing pigment which is designated as P_r and (ii) far-red light-absorbing pigment which is designated as P_fr. The P_r form absorbs red light in 660 nm and changes to P_fr. The P_fr form absorbs far-red light in 730 nm and changes to P_r. The P form is biologically inactive and it is stable whereas P_fr form is biologically active and it is very unstable. In short-day plants, P_r promotes flowering and P_fr inhibits the flowering whereas in long-day plants flowering is promoted by P_fr and inhibited by P_r form. P_fr is always associated with a hydrophobic area of membrane systems while P_r is found in the diffused state in the cytoplasm. The interconversion of the two forms of phytochrome is mainly involved in flower induction and also additionally plays a role in seed germination and changes in membrane conformation.

Question 12.
Explain the theories involved in the mechanism of vernalization.
Answer:
Mechanism of Vernalization:
Two main theories to explain the mechanism of vernalization is:
i. Hypothesis of phasic development,
ii. The hypothesis of hormonal involvement.

1. The hypothesis of phasic development: According to Lysenko, the development of an annual seed plant consists of two phases. The first phase is a thermostat, which is a vegetative phase requiring low temperature and suitable moisture. The next phase is the photo stage which requires high temperature for the synthesis of florigen (flowering hormone).
2. The hypothesis of hormonal involvement: According to Purvis (1961), the formation of a substance A from its precursor, is converted into B after chilling. The substance B is unstable. At a suitable temperature, B is converted into stable compound D called Vemalin. Vemalin is converted to F (Florigen). Florigen induces flower formation. At high-temperature B is converted to C and devemalization occurs.

Question 13.
Discuss the external factors that affect seed germination.
Answer:
External Factors:
a. Water: It activates the enzymes which digest the complex reserve foods of the seed. If the water content of the seed goes below a critical level, seeds fail to germinate.
b. Temperature: Seeds fails to germinate at very low and high temperature. The optimum temperature is 25°C to 35°C for most tropic species.
c. Oxygen: It is necessary for germination. Since aerobic respiration is a physiological requirement for germination most will germinate well in air containing 20% oxygen.
d. Light: There are many seeds that respond to light for germination and these seeds said to be photoelastic.
e. Soil Conditions: Germination of seed in its natural habit is influenced by soil conditions such as holding capacity, mineral composition, and aeration of the soil.

Question 14.
Illustrate the various methods of breaking seed dormancy.
Answer:
Methods of breaking dormancy:
The dormancy of seeds can be broken by different methods. These are:

1. Scarification: Mechanical and chemical, treatments like cutting or chipping of hard tough
   seed coat and use of organic solvents to remove waxy or fatty compounds are called as Scarification. •
2. Impaction: In some seeds, water and oxygen are unable to penetrate micropyle due to blockage by cork cells. These seeds are shaken vigorously to remove the plug which is called Impaction.
3. Stratification: Seeds of rosaceous plants (Apple, Plum, Peach, and Cherry) will not germinate until they have been exposed to well-aerated, moist conditions under low temperatures (0°C to 10°C) for weeks to months. Such treatment is called Stratification.
4. Alternating temperatures: Germination of some seeds is strongly promoted by alternating
   daily temperatures. An alternation of low and high temperature improves the germination of seeds. .
5. Light: The dormancy of photoblastic seeds can be broken by exposing them to red light.

Question 15.
Give a detailed account of different types of senescence.
Answer:

1. Overall senescence: This kind of senescence occurs in annual plants when the entire plant gets affected and dies. Example: Wheat and Soybean. It also occurs in few perennials also. Example: Agave and Bamboo.
2. Top senescence: It occurs in aerial parts of plants. It is common in perennials, underground and root system remains viable. Example: Banana and Gladiolus.
3. Deciduous senescence: It is common in deciduous plants and occurs only in the leaves of plants, the bulk of the stem and root system remains alive. Example: Elm and Maple.
4. Progressive senescence: This kind of senescence is gradual. First, it occurs in old leaves followed by new leaves then stems, and finally root system. It is common in annuals.

Question 16.
Explain the physiology of senescence.
Answer:
Physiology of Senescence

• Cells undergo changes in structure.
• Vacuole of the cell acts as a lysosome and secretes hydrolytic enzymes.
• The starch content is decreased in the cells.
• Photosynthesis is reduced due to loss of chlorophyll accompanied by synthesis and accumulation of anthocyanin pigments, therefore the leaf becomes red.
• There is a marked decrease in protein content in the senescing organ.
• RNA content of the leaf particularly rRNA level is decreased in the cells due to increased activity of the enzyme RNAase.
• DNA molecules in senescencing leaves degenerate by the increased activity of enzyme DNAase.

Question 17.
What are the physiological changes occurring in plants during Abscission?
Answer:
Morphological and Anatomical changes during abscission:
Leaf abscission takes place at the base of the petiole which is marked internally by a distinct zone of few layers of thin-walled cells arranged transversely. This zone is called the abscission zone or abscission layer. An abscission layer is greenish-grey in color and is formed by rows of cells of 2 to 15 cells thick. The cells of the abscission layer separate due to the dissolution of the middle lamella and primary wall of cells by the activity of enzymes pectinase and cellulase resulting in the loosening of cells. Tyloses are also formed blocking the conducting vessels. Degrading of chlorophyll occurs leading to the change in the color of leaves, leaf detachment from the plant, and leaf fall. After abscission, the outer layer of cells becomes suberized by the development of periderm.

Higher Order Thinking Skills (HOTs)

Question 1.
A farmer grows cucumber plants in his field. He wants to increase the number of female flowers in them. Which plant growth hormone can be applied to achieve this.
Answer:
Auxin can be used to increase the number of female flowers.

Question 2.
In the figure of the sigmoid and curve given below, label the segments A, B, and C.

Answer:
A = lag phase, B = log phase and C = Steady state phase.

Question 3.
In most plants, the terminal bud suppresses the development of lateral buds. What is this phenomenon called? Name the phytohormone that promotes this phenomenon.
Answer:
Suppression in the development of lateral buds due to terminal bud is called apical dominance. Auxins are the phytohormones that can promote this phenomenon.

Question 4.
The physiological effects of ethylene are both positive and negative. Comment.
Answer:

Positive Aspect of Ethylene	The negative aspect of Ethylene
Ethylene plays a crucial role in the ripening of fruits. Hence called as fruit ripening hormone.	It inhibits the longitudinal growth of stem and root.
It breaks the dormancy in seeds and buds.	It stimulates abscission causing leaves, flowers and fruits to shed prematurely.

Question 5.
Light plays an important role in the life of all organisms. Name any two physiological processes in plants that are affected by light.
Answer:
In plants, light plays a vital role in photosynthesis and growth.

Question 6.
Classify the following plants into long-day plants, short-day plants, and day-neutral plants, Wheat, sunflower, maize, tobacco, oats, chrysanthemum.
Answer:
Long Day plants – Wheat, Oats.
Short Day plants – Tobacco, chrysanthemum.
Day Neutral plants – Sunflower, maize.

Choose the correct answer.

1. Identify the monocarpic perennial plant from the following list.
(a) Paddy
(b) Bean
(c) Bamboo
(d) Coconut
Ans.
(c) Bamboo

2. Growth rate is maximum in ……….. phase.
(a) Lag
(b) Log
(c) Decelerating
(d) Maturation
Ans.
(b) Log

3. Proper plant growth occurs at a temperature between …………
(a) 25°C to 28°C
(b) 28°C to 45°C
(c) 25°C to 35°C
(d) 28°C to 30°C
Ans. (d) 28°C to 30°C

4. The process by which differentiated cell regain the ability of cell division ………….
(a) Differentiation
(b) Dedifferentiation
(c) Redifferentiation
(d) Totipotency
Ans.
(b) Dedifferentiation

5. The term Auxin was first used by ………….
(a) Kogl Smith
(b) Darwin
(c) F.W. Went
(d) Kurosawa
Ans.
(c) F.W. Went

6. Auxin was first isolated from ……….
(a) Com grain oil
(b) Human blood
(c) Human urine
(d) Rice bran oil
Ans.
(c) Human urine

7. Which is NOT a natural auxin?
(a) IAA
(b) PAA
(c) IPA
(d) NAA
Ans.
(d) NAA

8. The amino which is a precursor of IAA is ……….
(a) Methionine
(b) Valine
(c) Isoleuine
(d) Tryptophan
Ans.
(d) Tryptophan

9. Identify the wrong statement regarding the physiological effects of Auxin.
(i) Auxin prevents abscission
(ii) Auxin inhibits respiration
(iii) Auxin promotes cell elongation
(iv) Auxin breaks seed dormancy
(a) (i) only
(b) (ii) only
(c) (iii) only
(d) (i), (ii) and (iv)
Ans.
(b) (ii) only

10. How many number of giberellins were discovered so far?
(a) 50
(6) 70
(c) 100
(d) 80
Ans.
(c) 100

11. Foolish seedling disease affects ………….
(a) Maize
(b) Rice
(c) Sorghum
(d) Wheat
Ans.
(b) Rice

12. Bakanae’s disease was first noticed by …………
(a) F.W. Went
(b) Kurosawa
(c) Cocken
(d) Denny
Ans.
(b) Kurosawa

13. Apical dominance is due to the effect of ………….
(a) Auxin
(b) Gibberellin
(c) Ethylene
(d) Cytokinin
Ans.
(a) Auxin

14. Match the following:
(a) a- iii, b – iv, c – ii, d – i
(b) a – i, b- iii, c – iv, d – ii
(c) a – iii, b – ii, c – iv, d – i
(d) a – ii, b – iii, c – iv, d – i
Ans.
(a) a- iii, b – iv, c – ii, d – i

15. The most widely occuring cytokinin in plants is ………..
(a) Iso propyl adenine
(b) Iso pentenyl adenine
(c) Indole propionic acid
(d) Iso propionic adenine
Ans.
(b) Iso pentenyl adenine

16. Which of the following does not act as a precursor of ethylene?
(a) Fumaric acid
(b) Malic acid
(c) Linolenic acid
(d) Methionine
Ans.
(b) Malic acid

17. Identify the non-climacteric fruit.
(a) Tomato
(b) Grapes
(c) Apples
(d) Mango
Ans.
(b) Grapes

18. ……….. is a stress hormone.
(a) Ethylene
(b) Cytokinin
(c) Auxin
(d) Abscissic acid
Ans.
(d) Abscissic acid

19. Which of the following plant hormone functions against auxin?
(a) Gibberellin
(b) Cytokinin
(c) Ethylene
(d) Abscissic acid
Ans.
(d) Abscissic acid

20. Closure of stomato can be induced by ………..
(a) Abscissic acid
(b) Ethylene
(c) NAA
(d) Cytokinin
Ans.
(a) Abscissic acid

21. Maryland mammoth requires …………. hours of light.
(a) 8
(b) 10
(c) 12
(d) 15.05
Ans.
(c) 12

22. Identify the day neutral plants.
(a) Pea
(b) Wheat
(c) Tomato
(d) Soyabean
Ans.
(c) Tomato

23. The Pr form absorbs red light in ………… nm.
(a) 730
(b) 620
(c) 660
(d) 635
Ans.
(c) 660

24. The term vernalisation was first used by …………
(a) Chailakyan
(b) Gamer & Allard
(c) Lysenko
(d) F.W. Went
Ans.
(c) Lysenko

25. …………. seeds show a maximum viability of 1000 years.
(a) Orange
(b) Oxalis
(c) Lotus
(d) Coconut
Ans.
(c) Lotus

26. Shaking the seeds vigorously to remove the plug in the microphyle is the method of …………..
(a) Stratification
(b) Impaction
(c) Scarification
(d) Emaciation
Ans.
(b) Impaction

27. After abicission, outer layer of cells becomes ………….. by periderm.
(a) Lignified
(b) Pectinised
(c) Suberized
(d) Stratified
Ans.
(c) Suberized