CBSE Class 11 Biology Revision Notes Chapter 15

CBSE Class 11 Biology Revision Notes Chapter 15 – Plant Growth and Development

Class 11 Biology Chapter 15 is entirely based on the growth and development of plants. Growth is the irreversible increase in the number of cells, size, and the whole organism, whereas development is defined as the complete change that occurs in the organism from birth to death. In plants, growth is categorised into two parts, i.e. primary and secondary growth. 

Revision Notes for this chapter prepared by Extramarks summarise all the important concepts covered in this chapter in a clear and concise manner. Students can access these notes at any time from the Extramarks website and use them for their preparation.

Revision Notes for CBSE Class 11 Biology Chapter 15 – Free Download

Class 11 Biology Notes

CBSE Class 11 Biology Chapter 15 notes are accessible online, which can be read on any device at your convenience and downloaded and can be used offline. These notes will assist the students in going through the concepts and getting the information whenever they need it. The study material will aid the students in getting good grades in their exams.

Revision Notes For Class 11 Biology Chapter 15 Plant Growth and Development

15.1 Growth

Plants grow gradually from their stems, roots, leaves, flowers, fruits, and seeds. The following is the progression of the growth:

• After the vegetative phase, the plants enter their reproductive phase, in which flowers and fruits are grown to continue the plant’s life cycle.
• Development is the sum of two processes which includes growth and differentiation. A few internal and external variables influence development and growth.
• Growth is an irreversible increase in dry weight, size, mass, or volume of a cell, organ, or organism which is permanent. In the living organism, it is usually internal. 
• In plants, growth is accomplished through cell division, which increases cell number and cell size. As a result, growth is a quantitative factor that can be evaluated via time.
• Plant growth is often unpredictable due to their lifetime capability for infinite expansion. Meristem tissues can be found in plants in several locations and are responsible for the unlimited growth of the plant.

15.2 Growth is Measurable

• At the cellular level, growth is defined as a rise in protoplasm. This rise is difficult to measure. Hence, we can track the growth of the cell, its number, and its size.
• The increase in fresh weight, length, dry weight, area, volume, and cell number determines growth. Some can be used to measure specific types of development.
• The formative phase refers to the stage of cell division or development. It occurs in the shoot apex, root apex, and other meristematic tissue-rich locations. In the formative phase, the respiration rate in cells undergoing mitosis division is high.
• Enlargement Phase: The newly generated cells produced during the formative phase will undergo enlargement. This causes the formation of vacuoles, which increases cell volume.
• Cell enlargement occurs in all directions, with optimum elongation in conducting tissues and fibres.
• The Phase of Maturation: The cell undergoes enlargement by structural and physiological differentiation to become a specific kind of cell.
• Growth rate: It is an increase in growth per unit of time. It may differ in nature and can be arithmetic or geometric. 

Arithmetic Growth: In this type of nature, the growth rate is constant, and an increase in growth follows an arithmetic progression- 2,4,6,…

It occurs in shoot and root elongation and can be expressed algebraically as follows:

Lt = L0 + rt

Where Lt is the length after time t, L0 is the length at the beginning, and r is the growth rate.

Geometric Growth: The initial growth in this method is modest at first, then accelerates. Every cell divides. The daughter cells divide and grow, and the granddaughter cells result in exponential growth. It is pretty frequent in unicellular organisms.

The sigmoid growth curve includes the stationary phase and fast dividing exponential phase. It is very typical of most living beings in their natural habitat.

Exponential growth can be represented and can be expressed as follows:

Wt =W0ert 

Here,

Wt = final size

W0 = initial size

r = growth rate

t = time of growth, and

e is the base of natural logarithms (2.71828) 

Quantitative comparison between the growth of the living system can be made by:

1. The absolute rate means the measurement and comparison of total growth per unit of time.
2. The relative growth rate is the growth of a given system per unit of time, expressed on a shared basis.

15.3 Condition of Growth

• Water, oxygen, and vital elements are necessary for development. Water is essential for all cell enlargement and regulates turgidity. It also serves as a medium for enzymatic processes.
• Water is essential for protoplasm formation, while micro and macronutrients generate energy.
• Plants require ideal temperature and other environmental variables.
• Differentiation is how cells produced by the apical meristem turn into specialised cells that fulfil a specific purpose.
• Differentiated living cells that can no longer divide can recover the ability to divide. This is known as dedifferentiation, which occurs in cork cambium, interfascicular cambium, and cork cambium.
• Redifferentiation is the phenomenon by which dedifferentiated cells mature and lose their cell division ability to perform specific roles.

15.4 Development 

It is the order of the events in the life span of a cell, organ, or organism, including growth differentiation, seed germination, growth, flowering, senescence, and seed formation.

The sequence of the development process  in the plant cell is as follows: 

Plants develop different structures at different stages of growth and in reaction to their surroundings. Plasticity can alter in response to internal or external stimuli, such as Heterophylly in cotton plants.

Plant Growth Regulators are simple molecules of diverse chemical composition, including the adenine derivatives, indole compounds, or derivatives of carotenoids.

Auxin: Also referred to as indole-3-acetic acid (IAA). It is produced at the stem and root apex and often migrates to the site of action.

The functions of  auxin are as follows: 

1. Cell enlargement
2. Cell division
3. Apical dominance
4. Induce Parthenocarpy
5. Inhibition of abscission

Cytokinins have specific effects on cytokinesis and were discovered as kinetin (a modified form of adenine, a purine) from the autoclaved herring sperm DNA. The most common forms are zeatin, kinetin, etc. They are mainly produced in the roots.

The functions of  cytokinins are as follows:

1. Cell differentiation and cell division
2. Get rid of apical dominance.
3. Enhance nutrient mobilisation
4. Vital for tissue culture

Abscisic Acid: Also known as dormin or stress hormone. It works like a general plant growth inhibitor. It is formed at the terminal buds of the plant top or in the roots of the plants.

The functions of  abscisic  acid are as follows:

1. Bud dormancy.
2. Induce Parthenocarpy.
3. Seed development and maturation.
4. Leaf senescence.

Ethylene: The gaseous hormone stimulates isodiametric or transverse growth and retards the longitudinal one.

The functions of ethylene are as follows:

1. Inhibition of longitudinal Growth.
2. Senescence.
3. Enhance apical dominance.
4. Fruit ripening.

Gibberellins: They are promoters of PGR seen in more than 100 forms named as They are denoted as GA1, GA2, GA3, and so on. The most common is gibberellic acid. 

The functions of  gibberellins are as follows:

1. Cell elongation.
2. Early maturity.
3. Seed germination.
4. Breaking of dormancy.

Photoperiodism: It is defined as the effect of photoperiods or the day duration of light hours on the growth and development of plants, especially flowering. The flowering plants have been divided into three categories based on the photoperiodic response, which are described below: 

1. Short Day Plants – The flowers need exposure to light for a period less than this critical duration before the flowering is initiated. For instance- Xanthium, Sugarcane, and Potato Rice.
2. Long Day Plants – When they need a long photoperiod of light, the plant flowers are more significant than the critical period. For instance – Barley, Radish, and Lettuce.
3. Day Neutral Plants – These plants can blossom throughout the year. For instance – Wild Kidney, Bean.

Vernalisation: It is the process in which cold treatment is used to shorten the juvenile or vegetative period and accelerate the blooming process. Meristematic cells aid in the perception of the vernalisation stimulation.

• It lowers the plant’s vegetative period and promotes early blooming
• It applies to temperate plants like Rice, Wheat, etc.

Conclusion

Students can get notes for Class 11 Biology Chapter 15 notes on the Extramarks website. All the concepts related to the chapter are covered in the curriculum briefly and the notes with detailed explanations have been provided. Students can make effective use of these notes prepared by the subject matter experts  s of Extramarks to practice and prepare all the essential concepts and to have a thorough understanding of numerous topics and sub-topics connected to various themes. Plant development and growth Class 11 Biology Chapter 15 notes help to speed up their learning and improve their academic performance, through revisions and make them aware of their mistakes through guided practice and help to get the best results.