Samacheer Class 11 Bio Botany - Plant Growth and Development

options are wrong, (correct Ans = 1.5 inches)
Step I:
Diameter of the Pulley=6 inches
Radius of the pulley \(=\frac{6}{2}\)= 3 inches
Actual growth in length= Distance travailed by pointer x Radius of the pulley Length of the pointer
=\(\frac{5 \times 3}{10}\) =1.5=1.5.
1.5 inches

Growth in plants can be measured in terms, of
* Increase in length or girth (roots and stems)
* Increase in fresh or dry weight
* Increase in area or volume (fruits and leaves)
* Increase in a number of cells produced.

Plasticity refers to the environmental heterophylly seen in Butter cup plant (Ranunculus). In this aquatic plant, the leaves in the air is normal, where as the leaves submerged underwater are highly thin and hairy highly adapted to do carbon assimilation Developmental heterophlly seen in the juvenile plant leaves of cotton and corianter. Where the young leaves have a different shape from the mature leaves is not considered as plasticity.

• Cytokinin promotes cell division in the presence of auxin (IAA).
• Induces cell enlargement associated with IAA and gibberellins
• Cytokinin can break the dormancy of certain light-sensitive seeds like tobacco and induces seed germination.
• Cytokinin promotes the growth of lateral bud in the presence of apical bud.
• Application of cytokinin delays the process of aging by nutrient mobilization. It is known as the Richmond Lang effect.
• Cytokinin:
• increases rate protein synthesis
• induces the formation of inter-fascicular cambium
• overcomes apical dominance
• induces the formation of new leaves, chloroplast and lateral shoots.
• Plants accumulate solutes very actively with the help of cytokinins.

Mechanism of photoperiodic induction of flowering.
* The physiological change on flowering due to the relative length of light and darkness (photoperiod) is called Photoperiodism.
* The photoperiod required to induce flowering is called critical day length. Eg. 12 hours in Maryland Mammoth’s Tobacco Xanthium 15.05 hours.
Photoperiodic induction:
* An appropriate photoperiod in 24 hours cycle constitutes one inductive cycle. Plants may require one or more inductive cycles for flowering.
* The phenomenon of conversion of leaf primordia into flower primordia under the influence of suitable inductive cycles is called photoperiodic induction. Example: Xanthium (SDP) -1 inductive cycle and Plantago (LDP) -25 inductive cycles.
Site of photoconductive perception:
* Leaves are the parts that receive photoperiodic stimulus (PPS), again it is only leaves that synthesize floral hormones and translocate them to the apical tip to promote flowering.
* This can be demonstrated by experiments conducted in the Cocklebur plant. Which is an SD plant. The nature of flower-producing stimulus has been elusive so far. It is believed by physiologists that a hormone is responsible for it, Chailakyan (1936) named it as Florigen It is not possible to isolate it.
Procedure
Observation
Inference
1. Take potted plant A and defoliate the plant subject it to SD – a condition
There is no induction of flowering
No leaf to receive stimulus or induction of flowering
2. Take potted plant B – and defoliate all, except one leaf subject it to SD – condition.
There is the induction of flowering
One leaf is enough to receive stimulus or induction of flowering.
3. Take potted plant C – and defoliate it and subject it to LD condition
There is no induction of flowering
no leaf to receive stimulus or induction of flowering
4. Take potted plant D and subject all leaves to LD but one leaf to SD
There is the induction of flowering
One leaf is enough to receive an induction in the SD condition

Senescence is controlled by plants’ own genetic program and the death of the plant or plants part consequent to senescence is called Programmed Cell Death. In short senescence of an individual cell is called PCD. The proteolytic enzymes involving PCD in plants are phytases and in animals are caspases. The nutrients and other substrates from senescing cells and tissues are remobilized and reallocated to other parts of the plant that survives.
The protoplasts of developing xylem vessels and tracheids die and disappear at maturity to make them functionally efficient to conduct water for transport. In aquatic plants, aerenchyma is normally formed in different parts of the plant such as roots and stems which enclose large air spaces that are created through PCD. In the development of unisexual flowers, male and female flowers are present in earlier stages, but only one of these two completes its development while the other aborts through PCD.
Part-II.
11th Bio Botany Guide Plant Growth and Development Additional Important Questions and Answers
I. Choose The Correct Answer

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

* Viable means the living condition of the seed
* The shelf life of the seed after which it cannot germinate is known as the viable period
* It varies from plant to plant
Name of the plant
Viability
1. Oxalis seeds
Few days
2. Lotus seeds
More than 1000 years
3. Judean Dale palm (Methuselah)
More than 2000 years

Climacteric fruits
Non-Climacteric fruits
1.There is a sharp rise in respiration rate near the end of the development of fruit.
2. The ripening on demand can be induced in these fruits by exposing them to normal air conditioning.
3. Epthan secrete Ethylene continuously about 1 ppm of ethylene Eg. Lemon, Apples, Banana, Mango
These fruits cannot be ripened by exposure to ethylene so-known as non-climacteric fruits.
Eg. Grapes, Watermelon orange.

Scarification
Stratification
Mechanical and chemical treatment either by cutting, chipping or use of organic solvents to remove waxy or fatty compounds is called scarification.
Rosaceous plants (Apple, Plum Peach, and Cherry) will not germinate until they have been exposed to well derated, moist conditions under low temperature (1°c to 10°c) for weeks to months and this treatment is known as stratification.

• Hard, tough seed coat causes barrier effect as impermeability of water, gas and restriction of the expansion of embryo prevents seed germination.
• Many species of seeds produce imperfectly developed embryos called rudimentary embryos which promotes dormancy.
• Lack of specific light requirement leads to seed dormancy.
• A range of temperatures either higher or lower cause dormancy.
• The presence of inhibitors like phenolic compounds which inhibits seed germination cause dormancy.

Name of the factor
Effect of senescence
ABA & Ethylene
Accelerates
Auxin & Cytokinin Nitrogen deficiency
reduces increases
Nitrogen supply
retards
High temperature in vernalized seeds
Accelerates
Low temperature
Retards
Water stress
Accumulation of ABA leading to senescence

• Abscission Zone: formed at the base of petiole
• Greenish grey in colour by rows of 2 to 15 cells thick primary wall and middle lamella
• The dissolution of by pectinase & Cellulase
• Formation tyloses – that block conduction of vessels
• Degradation of chlorophyll – Colour of leaves changes and leaves fall off.
• After Abscission – Suberization of outer layer of cells by the development of periderm.

1. Abscission separates dead parts of the plant like old leaves and ripe fruits.
2. Helps in dispersal of fruits and continuing the life cycle.
3. Abscission of leaves (in deciduous plants) helps in water conservation during summer.
4. Helps in vegetative propagation (Shedding of gemmae or plantlets) Eg. Bryophyta.
V. 5 Mark Questions

Absolute growth
Relative growth
An increase in the 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

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

The total period from initial to the final stage of growth is called Grand period of growth.
When plotted against time the growth curve is ‘S’ shaped, (sigma curve) it is also known as Grand Period curie consists of 4 phases
* Lag,
* Log,
* Decelerating,
* Maturation.

The chemical substances synthesized by plants and thus naturally occuring are known as Phytohormones. Eg. Auxin, Gibberellins.
Recently 2 groups – Brassinosteroids, Polyamines were also known to behave like hormones.

• They are produced in root tips and stem tips and leaves (do not have specialized cells or organs for secretion)
• The transfer of hormones takes place through the conducting system (xylem and phloem)
• They are required in trace quantities
• They either promote, inhibit or modify growth.

• Mixture of two phenoxy herbicides – 2.4. D and 2.4.5 T together known as Agent orange.
• This Agent orange, was used by USA in Vietnam war as chemical warfare weapon to defoliate forests in Vietnam.

• Yes, trimming of plants removes apical buds and hence apical dominance is prevented the lateral buds sprout and give a beautiful bushy appearance and aesthetic value.
• Also in tea estates, this trimming develops more lateral branches and more tea leaves thus it has commercial significance.

The distribution of cytokinin in plants is not as wide as those of auxin and gibberellins but found mostly in roots. Cytokinins appear to be translocated through xylem.

* The physiological change on flowering due to relative length of light and darkness (Photoperiod) is called
Photoperiodism.
* The photoperiod required to induce flowering is called critical day length Eg.
* Mary land mammoth (tobacco variety) requires 12 hours of light.
* Cocklebur required 15.05 hours of light.

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

• The knowledge of photoperiodism an important role in hybridization experiments.
• It is an excellent example of physiological preconditioning that is using an external factor to induce physiological changes in the plant.

Epigeal
Hypogeal
Cotyledons pussed out of the soil
Cotyledons remain below the soil due to rapid elongation of epicotyls.
Happens due to the elongation of the hypocotyl Eg. Castor & Bean
Eg. Maize

The condition of a seed when it fails to germinate even in suitable environmental condition is called seed dormancy.
There are two types
(I) Innate dormancy (II) Imposed dormancy.

• By mechanical and chemical treatments like cutting or chipping of hard tough sed coat and use of organic solvents to remove waxy or fatty compounds are called scarification.
• It is a method of breaking dormancy of the seeds.

Redifferentiation
Devernalization
Differentiated cells after multiplication again lose the ability to divide and mature to perform specific functions, is called Re differentiation.
Eg. Sec.Xylem & Sec.
Phloem The reversal of the effect of vernalization is called Devemalization.

• Ageing or getting old is called senescence.
• It refers to all collective, progressive and deteriorative processes which ultimately lead to complete loss of organization and function (Eg. leaves turn yellow and fall off from plant).

• 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
• The process of removing the plug or block is called impactation.

• The break dormancy, some plant seeds have to be exposed to well aerated, moist conditions under low temperature (0°c to 10°c) for weeks to months.
• This kind of seed dormancy breaking treatment is known as stratification.
• The stratified soil layers should be given a low-temperature treatment for a certain period so as to induce germination.
• Eg. the Seeds of Rosaceae plants Apple, Plum, Peach, etc.

Abscission is marked internally at the place of petiole by a distance zone of few layers of thin-walled cells arranged transversely. This zone is called Abscission Zone, which leads to Abscission of the leaf.

• It is a bioassay technique by which Ethylene can be measured.
• It helps in the detection of the exact amount of ethylene from different plant tissues like lemon and orange.

Character
Gibberellins
Cytokinin
Occurrence
Produced by plant parts like an embryo, roots, and young leaves near the tip. Immature seeds are rich in Gibberellins.
Formed in root apex shoot apex like Auxin. Also formed in buds & young fruits.
Precursor
Formed by 5C precursor, Iso prenoidunit called Iso Pentenyl Pyrophosphate (IPP) through a number of intermediates primary precursor – Acetate.
Derived from purine-Adenine.
IV. 3 Mark Questions

* The total period from the initial to the final stage of growth is called the Grand period of growth.
* The graph that is drawn by taking time and rate of growth is ‘S’ shaped. It is known as a sigmoid curve.
It has 4 stages:
* Lag phase
* Log phase
* Decelerating phase
* Maturation phase

• Eradicate weeds: Eg. 2.4 D and 2.4.5.7
• Formation of seedless fruits: (Parthenocarpic fruits) Eg. Synthetic Auxin.
• Break dormancy.
• Induction of flowering: In pineapple NAA induce flowering
• Increase the number of female flowers: Eg. Cucurbita.

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

• Gibberellins are chemically related to terpenoids (natural rubber, Carotenoids, and steroids) formed by 5-C precursors and an Isoprenoid unit called Iso Pentenyl Pyrophosphate (IPP) through a number of intermediates.
• The primary precursors are Acetate.

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

Experiment:
1. Arc auxanometer:
The increase in the length of the stem tip can easily by measured by an arc auxanometer. If consists of a small pulley to the axis of which is attached a long pointer sliding over a graduated arc. A thread one end of which is tied to the stem tip and another and to a weight passes over the pulley tightly. As soon as the stem tip increases in length, the pulley moves and the pointer slide over the graduated arc (Refer Figure) The reading is taken. The acutal increase in the lengthwm stem is then calculated by knowing the length of the pointer and the radius of the pulley. If the radius of the pulley is 4 inches and the length of pointer 20 inches the actual growth is measured as follows:
Actual growth in length\(=\frac{\text { Distance travelled by the pointer radius of the }}{\text { Length of the pointer }}\)
For example, actual growth in length \(=\frac{10 \times 4 \text { inches }}{20 \text { inches }}\) = 2 inches

Cell elongation:
Promotes cell elongation in stem & Coleoptile
Root growth:
At extremely low concentration – promote root growth, at high concentrations it inhibits elongation of roots, but induce more lateral roots
Apical dominance:
Suppression of growth of lateral buds – by apical bud is known as Apical dominance
Prevents Abscission
Secondary growth:
Promotion of cell division in the cambium, responsible for secondary growth this property is exploited in tissue culture. (Callus foundation)
Respiration Stimulates respiration Induces Vascular differentiation.

Weedicide
2.4.D & 2.4.5. T – Weedicides to remove weeds
Induce parthenocarpy
Synthetic auxins used to induce parthenocarpy (formation of seedless fruits).
Break dormancy
Used to break seed dormancy.
Induce flowering in Pineapple Eg. NAA & 2.4.D
Induce female flowers (numbers)
Eg. Cucumber.

• Induction of cell division & cell elongation – Extraordinary stem elongation.
• Reversal of dwarfism & Bolting – Rosette (genetic dwarfism) plants when treated with Gibberellins exhibit excessive enter nodal growth – This sudden elongation of a stem followed by flowering is called Bolting.
• Breaks dormancy – in Potato tubers.
• Biennials flower in the 1 st year – Instead of cold exposure, if biennials treated with Gibberellins flower in the 1st year itself.

Almost all plant tissues produce ethylene gas in minute quantities.
1. Discovery:
In 1924, Denny found that ethylene stimulates the ripening of lemons. In 1934, R. Gane found that ripe bananas contain abundant ethylene. In 1935, Cocken et al., identified ethylene as a natural plant hormone.
2. Occurrence:
Maximum synthesis occurs during climacteric ripening of fruits and tissues undergoing senescence. It is formed in almost all plant parts like roots, leaves, flowers, fruits and seeds.
3. Transport in plants:
Ethylene can easily diffuse inside the plant through intercellular spaces.
4. Precursor:
It is a derivative of amino acid methionine, linolenic acid and fumaric acid.
5. Bioassay (Gas Chromatography):
Ethylene can be measured by gas chromatography. This technique helps in the detection of exact amount of ethylene from different plant tissues like lemon and orange.
6. Physiological Effects:
* Ethylene stimulates respiration and ripening in fruits.
* It stimulates radial growth in sterft and roof and inhibits linear growth.
* It breaks the dormancy of buds, seeds and storage organs.
* It stimulates the formation of an abscission zone in leaves, flowers and fruits. This makes the leaves to shed prematurely.
* Inhibition of stem elongation (shortening the internode).
* In low concentration, 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.
7. Agricultural role:
* Ethylene normally reduces flowering in plants except in Pineapple and Mango.
* It increases the number of female flowers and decreases the number of male flowers.
* Ethylene spray in cucumber crops produces female flowers and increases the yield.

• With IAA – Promotes cell division With IAA & GA – Induces cell enlargement
• Breaks dormancy of light-sensitive seeds (tobacco) induces seed germination.
• Promotes growth of lateral
• buds even in the presence of apical bud.
• Delays the process of aging by nutrient mobilization known as Richmond Lang effect.
• Induces rate of protein synthesis.
• Induces the formation of interfascicular cambium Overcomes apical dominance
• Induces the formation of new leaves chloroplast and lateral shoots.
• Induces Accumulation of solutes.

• Stimulates respiration and thereby ripening of fruits
• Stimulates radial growth in stem and root and inhibits linear growth.
• breaks dormancy of
• buds
• Seeds
• Storage Organs
• Stimulates abscission 2 one formation in
• leaves
• flowers
• fruits (so leaves shed prematurely)
• Prevents stem elongation by preventing internodal growth
• Root growth in low concentration
• Stimulates growth of lateral roots and root hairs and increase the absorptive surface
• Ripening of fruits – Increases ripening in climacteric fruits (Mango, banana) etc.
• It causes epinasty

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 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 temperature (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 photoelastic seeds can be broken by exposing them to red light.

a. The physiological change on flowering due to the relative length of light and darkness is called photoperiodism.
* Gamer and Allard (1920) coined the term
* They studied photoperiodism in Biloxi variety of soybean (Glycine max) and Many land mammoth varieties of tobacco.
b. Depending on photoperiodic responses plants are classified into several types.
1. L.D. Plants (Long Day) The photoperiod required to induce flowering is called critical day length depending on critical day length if it is long (more than 12 hours) and with short nights. Eg. Pea Barley and Oats
Short LD Plants: These are Long day plants but need short day length during the early period of growth for flowering Eg. Wheat, Rye
2. SD Plants: Plants requiring short critical day length for flowering or a long night.
Eg. Tobacco, Cocklebur, Soya, Rice, and Chrysanthemum.
Long SD Plants: Actually SD plants but need long days during the early period of growth for flowering Eg. Some SPS of Bryophyllum & Night Jasmine.
3. Intermediate day plants:
These require a photoperiod between a long day and a short day for flowering Eg. Sugarcane and coleus.
4. Day Neutral plants:
There are a number of plants which can flower in all possible photoperiods, known as photo neutral or hiterterminate plants. Eg. Potato, Rhododendron, Tomato & Cotton.

Definition:
It is a bluish biliprotein responsible for the perception of light in the photophysiological process, existing in two different forms is mainly involved in flower induction, (i.e) Pr and PFr.
* Butler et al(1959) named the pigment.
* It exists in two interconvertible forms
Pr
PFr
1. red light absorbing form
2. Absorbs red lgiht of wavelength 660 nm
3. Biologically inactive form & stable found in the diffused state in cytoplasm
4. Promotes flowering in SD plants and inhibits flowering LD plants.
1. Far-red light absorbing form
2. Absorbs far-red light of wavelength 730 nm
3. Biologically active and it is unstable Associated with a hydrophobic area of the membrane system
4. Promotes flowering in LD plants and inhibit flowering in SD plants.
Mechanism:
Other functions:
Play a role in seed germination and changes in membrane conformation.

Definition:
* Many biennials and perennials are induced to flower by low-temperature exposure (O°c to 5°c) This process is called Vernalization.
* T.D. Lysenko – Coined the term.
Mechanism of Vernalization:
2 theories explain the mechanism of vernalization.
1. Hypothesis of Phasic development (T.D. Lysenko),
The development of the annual plant has 2 phases.
* Thermostate-Vegetatine stage requiring low temperature and suitable moisture.
* Photo stage -high temperature needs to synthesize florigen.
2. Hypothesis of hormonal involvement (Purvis 1961)
Vernalization has several steps
The technique of Vernalization:
* Seeds soaked in water
* Allowed to germinate at 10°C to 12°C
* Transferred to low temperature for few days to 30 days (3°C to 5°C).
* Germinated seeds after the low temp, treatment are allowed to dry & then sown.
* Quickened flowering than untreated (control seedling)
Devernalization:
The reversal of the effect of vernalization is called Devemalization.
* Practical Applications:
* Vernalization shortens the vegetative period and induces the plant to flower earlier
* It increases cold resistance
* It increases fungal resistance
* It accelerates Plant Breeding.

Definition:
Getting old or Ageing is call d senescence in plants.
It refers to all collective, progressive, and deteriorative processes which ultimately lead to complete loss of organization and function.
Types – 4 types (Leopold -1961)
* Overall senescence: When the entire plant gets affected and dies – Eg. Annuals – Wheat & Soybeans, Perennials – Agave & Bamboo
* Top senescence: Occur in aerial parts only Eg. Parrennials – Banana and Gladiolus
* Deciduous senescence: Occur only in leaves Eg. Decidual plants – Elm and Maple
* Progressive Senescence: Occur in Annuals occur in old leaves first followed by new leaves than stem and finally root system.

* Change in the structure of cells
* Vacuoles act like lysosome-secrete hydrolytic enzymes.
* Reducation in photosynthetic rate (due to loss of chlorophyll & accumulation of anthocyanin)
* The decrease in Starch content, Protein content
* Decrease in …………. r RNA level due to increased activity of enzyme RNA ase
* Degeneration of DNA – by increased activity of enzyme DNA ase
Factors affecting senescence:
Name of the factor
Effect of senescence
ABA & Ethylene
Accelerates
Auxin & Cytokinin Nitrogen deficiency
reduces increases
Nitrogen supply
retards
High temperature in vernalized seeds
Accelerates
Low temperature
Retards
Water stress
Accumulation of ABA leading to senescence