NCERT Class 11 Biology Chapter 15 Notes Plant Growth And Development- Download PDF Notes

Plant growth and development is a very important NCERT plant growth and development, Botany chapter, from an exam point of view. The NCERT Class 11 Biology Chapter 15 notes give you a basic idea of the botany chapter, plant growth and development phenomenon in higher plants. The notes for Class 11 biology chapter 15 are a part of Biology class 11 unit 4 Plant physiology. The main topics covered in NCERT Class 11 Biology notes are definitions, growth, Phases of Growth, Growth Rates, differentiation, dedifferentiation, redifferentiation, development, plant growth regulators and Physiological Effects, photoperiodism, and vernalisation. Download the CBSE Notes for Class 11 Biology, Chapter 15, PDF to use offline anywhere. Students must go through each topic of plant growth and development Class 11 Notes Biology in the easiest and most effective way possible with the help of NCERT Notes for Class 11.

Class 11 Biology chapter 15 notes also cover all the important concepts related to growth and development, which are useful in various competitive exams. Plant growth and development NCERT Notes for Class 11 Biology help you revise these major concepts given in the NCERT Book in a short period of time for CBSE Board exam preparation. CBSE Class 11 Biology Chapter 15 notes will help you with quick revision. The Plant Growth and Development chapter covers all headings of NCERT. CBSE Class 11 Biology chapter 15 notes also contain important diagrams, graphs, and examples that have been frequently asked in the various exams. Having revision notes and NCERT Solutions for Class 11 Biology Chapter 15 handy saves you time. The NCERT Class 11 notes pdf can be downloaded through the link given below.

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• NCERT Solutions for Class 11 Biology Chapter 15 Plant Growth and Development
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NCERT Class 11 Chapter 15 Class Notes

Plant Growth And Development

Definition of growth: Growth is regarded as one of the most fundamental and conspicuous characteristics of a living being. What is growth? An irreversible, permanent increase in an organ's size, one of its parts, or even a single cell's size is referred to as growth. Generally, growth is accompanied by metabolic processes (both anabolic and catabolic), that occur at the expense of energy. Therefore, for example, the expansion of a leaf is growth.

• To begin with, it is essential and sufficient to know that the development of a mature plant from a zygote (fertilised egg) follow a precise and highly ordered succession of events.
• During this process a complex body organisation is formed that produces roots, leaves, branches, flowers, fruits, and seeds, and eventually they die.
• Lets study some of the factors which govern and control these developmental processes. These factors are both intrinsic (internal) and extrinsic (external) to the plant.

Growth

• Both growth and differentiation are required for development to happen in plants.
• Mature plants are a result of the development of a single-cell zygote.
• A highly ordered succession of events happens in the zygote to give rise to complex structures like leaves, stems, flowers, seeds, and fruit.
• Seed germination takes place only under favorable environmental conditions, otherwise, it will remain in the suspended stage until viable. Development is influenced by extrinsic (external) and intrinsic (internal) factors.
• Growth is an irreversible permanent increase in size, this can take place at cellular, tissue, or organ level. Growth is partnered with metabolism and it’s an active process.

Plant Growth Generally Is Indeterminate

• Plant growth is open (unlimited).
• Plants have meristematic tissues at certain locations; therefore, they retain their capacity for unlimited growth throughout their life.
• Shoot apical meristem (SAM) and root apical meristem (RAM) are responsible for elongation of the plant along the shoot axis and root axis respectively, hence they perform primary growth.
• Lateral meristems that appear in the later stages of dicotyledons and gymnosperms cause secondary growth, it increases the girth (circumference) of the plant.
• Secondary growth is also caused by vascular cambium and cork cambium.

Growth Is Measurable

• An increase in protoplasm is considered as growth at a cellular level, but this change is difficult to measure.
• Changes in plant height, dry weight, area, volume, and the number of cells can be tracked with much ease and they are proportional to growth at the cellular level. For example:
• More than 17,500 cells can be added within an hour in maize plants by a single root apical meristem.
• Watermelon cells can increase in size by up to 3,50,000 times.
• Pollen tube development is measured by measuring the length of the pollen tube.
• Growth in leaves is measured by an increase in surface area.

Phases Of Growth

• There are 3 broad phases of growth namely, the meristematic phase, an elongation phase, and maturation phase.
• The meristematic phase has constantly dividing cells at RAM and SAM, cells at this phase have rich protoplasm and thin primary cell walls.
• Thickening of cell walls and increase in volume and vacuole size occurs in the elongation phase.
• In the maturation phase, cells attain their maximum size.

Growth Rates

• Growth is measured by a growth rate that is the increased growth per unit time.
• Arithmetic growth (constant growth rate) is seen when after mitosis only one cell continues to proliferate while the rest daughter cells differentiate and cease to perform mitosis.
• A linear curve is obtained when the growth of an organ is plotted against time.
• Geometric growth happens when both daughter cells produced via mitosis continue to divide further into two by mitosis.
• The curve obtained by plotting the growth of the organ against time shows a characteristic sigmoid-shaped curve.
• An initial lag phase is where the growth rate is very slow, this is followed by an exponential phase, but since resources are not unlimited, therefore the exponential phase is followed up by a stationary phase.
• Mathematically, arithmetic growth is expressed as

L_t = L₀ + rt

L_t = length at time ‘t’

L₀ = length at time ‘zero’

r = growth rate / elongation per unit time.

The exponential growth can be expressed as:

W₁ = W₀ e^rt

W₁ = final size (weight, height, number etc.)

W₀ = initial size at the beginning of the period

r = growth rate

t = time of growth

e = base of natural logarithms

Growth Between Organs Can Be Compared Either In:

1. Absolute terms i.e., total growth in unit time, or,

2. Relative terms i.e., growth of system per unit time expressed on a common basis.

Conditions for Growth

• The availability of a sufficient amount of water, oxygen, and nutrients are the most important conditions for growth.
• Water maintains cell turgidity required for extension; it is the medium for enzymatic activity.
• Oxygen is required for aerobic respiration that will generate metabolic energy.
• Nutrients are required for the synthesis of protoplasm and are a source of energy for plants.
• Environmental conditions such as temperature, light intensity, and gravity must be within the optimum range for growth to successfully take place.

Differentiation, Dedifferentiation, and Redifferentiation

Differentiation

• Differentiation or maturing of meristems takes place for them to get specialized in their functions.
• During differentiation, cells undergo structural changes in their cell wall and protoplasm.
• For example, tracheary elements lose protoplasm to develop a strong, plastic secondary cell wall composed of lignin and cellulose to make water transport efficient even at high tensile strength.

Dedifferentiation

• Cells that have lost their dividing capacity restart dividing under certain conditions, this phenomenon is called dedifferentiation.
• For example- Fully differentiated parenchyma cells dedifferentiate to form meristems- interfascicular cambium and cork cambium.

Redifferentiation

• Dedifferentiated cells lose their capacity to divide and become mature to attain a specialized function. This process is known as redifferentiation.

Development

• All changes that an organism goes through throughout its life cycle from germination to senescence is known as development.
• Development is the sum of growth and differentiation.
• Plants follow different pathways in response to the environment to form different structures.
• Cotton, coriander, and larkspur are a few plants that show heterophylly, in these plants leaves of juvenile and mature stages are morphologically distinct.
• In buttercup, the leaves are differently shaped (heterophyllous development) when in air versus as in water.

Plant Growth Regulators: Auxins, Gibberellins, Cytokinins, Abscisic acid, Ethylene

Characteristics:

• Plant growth regulators (PGRs) are broadly characterized into two as plant growth promoters and inhibitors.
• Plant growth-promoting hormones promote cell division, cell enlargement, pattern formation, tropic growth, flowering fruiting, and seed formation.
• Auxins, Gibberellins, and Cytokinins are growth-promoting phytohormones.
• Inhibitory plant growth regulators are released in response to wounds, biotic and abiotic stresses.
• Inhibitors induce dormancy and abscission.
• Abscisic acid is an example of inhibitory phytohormone.
• Though ethylene gas shows characteristics of both promoter and inhibitor of plant growth, it is largely an inhibitor.

The Discovery of Plant Growth Regulators

• The Discovery of all of the 5 major PGRs was accidental.
• Charles Darwin and his son Francis Darwin observed coleoptile canary grass responds towards unilateral illumination by growing towards the light source. The tip of the coleoptile is the site of transmittable influence that is responsible for the bending of the entire coleoptile. Auxins were isolated by F.W. Went from the tips of coleoptiles of oat seedlings.
• ‘Bakane’ (foolish seedling) disease of rice seedlings is caused by fungal pathogen Gibberella Fujikuroi. In 1926 E. Kurosawa observed symptoms that appeared when treated with sterile filtrate of fungi, the active substance was found to be gibberellic acid.
• F. Skoog and co-workers observed that in internodal segments of tobacco stems, the callus (mass of undifferentiated cells) proliferated only if auxins were supplemented with either vascular tissue extracts, yeast extract, coconut milk, and DNA. Skoog and Miller crystallized the cytokinesis promoting active substances i.e., kinetin.
• Abscisic acid was discovered independently by three researchers in the mid-1960s.

Physiological Effects of Plant Growth Regulators

Auxins

• Auxin was first isolated from human urine. Indole-3-acetic acid (IAA) is a natural auxin. Auxins are produced by growing apices, then translocated to the site of action. IAA and Indole Butyric acid (IBA) are natural auxins found in plants. Naphthalene acetic acid (NAA) and 2,4-dichlorophenoxyacetic (2,4-D) are synthetic auxins. Auxins have agricultural and horticultural applications.
• Auxins help to initiate root formation in stem cutting.
• They help in plant propagation, promote flowering in plants like pineapple, inhibit fruits and leaf fall in the early stage.
• Auxins promote abscission at maturity.
• Growing apical bud inhibits the growth of lateral buds, this effect is called apical dominance. Removal of shoot tips (reduce auxin synthesis) increases the growth of lateral buds; this step is followed in tea plantations and hedge making.
• Auxins induce parthenocarpy in plants like tomatoes.
• They are also used as herbicides; 2,4-D is used to kill dicot weeds in monocot crop fields.
• It also controls xylem differentiation and helps in cell division.

Gibberellins

• Gibberellins are denoted as GA1, GA2, GA3 …. And so on. GA3 was the first gibberellic acid and continues to be the most studied gibberellin out of more than 100 gibberellins reported not only in higher plants but fungi also. These are growth-promoting hormones.
• Gibberellins are acidic and have a wide range of physiological responses.
• It increases length along the plant axis; therefore, it’s used to increase the length of grape stalks.
• GAs induce fruit elongation and improve shape in fruits like apples. GA3 fastens up malting, so they are used in the brewing industry.
• They are used to increase the length of sugarcane stem, thereby increasing yield by 20 tonnes per acre.
• GAs fasten the maturity of juvenile conifers by early seed production.
• Gibberellins promote bolting (internode elongation) in beet, cabbages, and many plants with rosette habits.

Cytokinins

• Cytokinins affect cytokinesis.
• Kinetin was discovered from autoclaved herring of sperm DNA but does not occur naturally in plants.
• Biochemically, kinetin is a modified form of adenine.
• Zeatin was found in corn kernels and coconut milk and it has cytokinin-like activity.
• Cytokinins are naturally produced in parts where cells proliferate quickly, such as root apices, developing shoot buds, and early fruits.
• Apical dominance can be suppressed by Cytokinins. It delays leaf senescence.

Ethylene

• Ethylene (C₂H₄ ) is a gaseous hormone that’s produced by tissues undergoing senescence and ripening fruits.
• It causes horizontal growth of seedlings and swelling of the axis.
• It also causes the formation of apical hook in dicot seedlings and initiates germination in some plants like peanut seeds, sprouting of potato tubers.
• Ethylene helps in the ripening of fruits as it increases the rate of respiration.
• It promotes senescence and abscission of plant organs (leaves and flowers specifically).
• Ethylene promotes root growth and root hair formation; this increases surface area for water and mineral absorption.

• Ethylene initiates flowering in mango and synchronizes fruit set in pineapple.
• Ethylene gas is widely used in agriculture.
• The aqueous solution of ethephon is widely used as an artificial ethylene source as it releases ethylene slowly.
• Ethephon is used to hasten fruit ripening in plants like tomato, apples, etc., and accelerates abscission in flowers and fruits.
• It is used to increase the yield of cucumbers as it promotes female flowers.

Abscisic Acid

• Abscisic acid is a growth inhibitor phytohormone.
• It inhibits seed germination and stimulates the closing of stomata.
• It increases the plant’s tolerance towards stresses; therefore, it’s called the stress hormone.
• Abscisic acid plays an important role in seed maturation and dormancy.
• It also helps seeds to withstand desiccation and conditions unfavorable for growth.

Photoperiodism

• Plants can measure the duration of sunlight exposure. Some plants induce flowering only when periodic exposure to light is there. This critical duration of light exposure differs among plants. Some plants flower only when the duration of light exposure is more than the critical duration; such plants are called long-day plants.
• Whereas some plants flower only when the duration of light exposure is less than the critical duration; such plants are called short-day plants.
• This response is called photoperiodism. Many plants are day-neutral plants, i.e., flowering in them is not related to the duration of light exposure. Shoot apex can’t perceive photoperiodism, but they get modified to the flowering apex before flowering. Leaves are the site of light perception; they release flowering hormones that induce flowering when exposed to the necessary photoperiod.

Vernalisation

• Flowering in both qualitative and quantitative aspects depends on exposure to low temperature, this effect is called vernalization.
• Vernalisation prevents untimely reproductive development and therefore plants get sufficient time to reach maturity.
• It promotes flowering in some important food plants- wheat, barley, and rye.
• Winter varieties are planted in autumn, small seedlings are produced in the winter season, and growth is resumed on the advent of spring and finally harvested in mid-summer.
• Spring varieties are planted in spring and produce fruit before the season ends.

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Plant growth and development class 11 notes will help students revise the chapter and have a better understanding of the major concepts addressed. This NCERT class 11 biology chapter 15 notes can also be used to cover the important concepts of the CBSE Biology Syllabus in Class 11 as well as for competitive examinations such as the AIPMT, AIIMS, NEET and other exams. Class 11 Biology chapter 15 notes pdf download can be utilized for offline preparation.

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