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

Download NCERT notes for class 11 Biology chapter 13 PDF

Students can download the notes for Plant Growth and Development in PDF format from the link given below. By referring to the NCERT notes for class 11 Biology chapter 13 PDF, they can understand topics like plant hormones and factors affecting growth. It is useful for both quick revision and daily study. The NCERT Notes for Class 11 Biology also help in remembering important diagrams and definitions for NEET.

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Plant Growth and Development Class 11 Notes

These notes explain the important topics related to how plants grow and develop over time. Different concepts like growth phases, plant hormones, and seed germination. The Plant Growth and Development Class 11 Notes are simple, clear, and useful for quick revision.

Plant Growth And Development

Growth is 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, it is accompanied by metabolic processes (both anabolic and catabolic) that occur at the cost of energy. Therefore, for example, the expansion of a leaf is growth.

Growth

Growth in plants refers to an irreversible increase in size, volume, or mass due to cell division and enlargement throughout life and is observed in various structures such as roots, leaves, and flowers. It is influenced by both internal and external factors. Unlike animals, plant growth is continuous and occurs at a specific region, such as the Meristems. This dynamic process helps plants adapt to environmental changes and ensure survival and reproduction.

Plant Growth Generally Is Indeterminate

Unlike animals, plants exhibit indeterminate growth, meaning they continue growing throughout their lifespan. This is due to the presence of meristematic tissues at the shoot and root tips, which divide continuously to produce new cells. Some parts, such as leaves and flowers, exhibit determinate growth, meaning the growth with a specific size, but the structures like roots and stems, maintain the growth potential infinitely, allowing plants to regenerate and adapt efficiently.

Growth Is Measurable

Since growth involves an increase in size and mass, it can be measured quantitatively by various parameters such as length (stem elongation), volume (fruit expansion), surface area (leaf expansion), and dry weight (biomass accumulation) to help assess plant growth. Instruments like auxanometers measure shoot elongation, while dry weight estimation provides insights into overall biomass production. Growth measurement helps in studying plant responses to different environmental and genetic factors

Phases Of Growth

• There are 3 broad phases of growth, namely, the meristematic phase, the elongation phase, and the maturation phase.

• The meristematic phase has actively dividing cells that are present at the root and shoot tips.

• The elongation phase has newly formed cells that increase in size due to water absorption, protoplasm expansion, and cell wall modification

• In the maturation phase, the cells differentiate into specialised tissues like the xylem and phloem, achieving their final functional form.

Growth Rates

Growth in plants can be classified into arithmetic and geometric growth, both of which describe how plant cells divide and expand over time. In arithmetic growth, one daughter cell continues to divide while the other is divided into specialised tissue and stops dividing. This type of growth is linear and constant over time, leading to a steady increase in size. In geometric growth, both daughter cells retain the ability to divide, leading to exponential growth. Initially, growth is slow (lag phase), followed by a rapid increase (log phase), and finally, growth slows down (stationary phase) as nutrients or space become limiting.

The mathematical form of Arithmetic and Geometric Growth is explained below-

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

Plant growth depends on both internal and external factors. There are various factors affecting plant growth. The internal factors, such as genetic makeup, hormones, and metabolic activity, regulate growth and development. They can either help in the development or inhibit the growth. External factors such as light, temperature, water, oxygen, and nutrients are essential for various plant processes, such as photosynthesis, respiration, and cell division. The optimal conditions make sure healthy plant development, flowering, fruiting, and seed production are achieved.

Differentiation, Dedifferentiation, and Redifferentiation

The processes are explained below-

Differentiation

Differentiation is the process by which unspecialised cells develop into specialised tissues like xylem, phloem, and epidermis. It is important for plant structure and function, enabling efficient transport of nutrients and water. Cells undergo morphological and physiological changes to perform specific roles, ensuring overall plant efficiency.

Dedifferentiation

Dedifferentiation occurs when mature specialised cells revert to an undifferentiated state to regain the ability to divide. For example, parenchyma cells transform into meristematic cells to form vascular cambium. This ability allows plants to repair injuries, regenerate lost parts, and sustain secondary growth.

Redifferentiation

Redifferentiation is when previously differentiated cells regain their specialised function. For example, the vascular cambium for secondary xylem and phloem during secondary growth. This process is important for regeneration, healing wounds, and producing new tissues and mature plants.

Development

Development in plants includes all changes from germination to senescence involving growth, differentiation, and reproduction. It is controlled by various factors such as genetic, environmental, and plant hormones. The developmental process includes seed, germination, flowering, fruiting, and ageing, ensuring the plant completes its full life cycle.

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

The characteristics of different plant hormones are given below-

Characteristics:

Plant growth regulators (PGRs) are chemical messengers that regulate growth and development. They can be growth promoters, such as auxins, gibberellins, and cytokinins, or growth inhibitors such as abscisic acid and ethylene. These hormones influence processes such as cell division, elongation, flowering, dormancy, and stress responses.

The Discovery of Plant Growth Regulators

• The Discovery of all 5 major PGRs was by chance.

• Charles Darwin and Francis Darwin conducted experiments on coleoptiles of canary grass and observed that the tip of the coleoptile was responsible for bending towards light. Therefore, the hypothesis is that a chemical signal was transmitted from the tip of the flower to the lower part of the plant. Went then isolated this growth-promoting substance from the coleoptile and named it auxin.

• Elichi Kurosawa was a scientist studying the foolish seedling disease in Rice plants. This disease is caused by the fungus Gibberella fujikuroi, which leads to the excessive elongation of rice seedlings. Yabuta and Sumuki isolated the active compound responsible for this abnormal growth and named it Gibberellins.

• Skoog and Miller discovered a growth-promoting substance while studying the effect of coconut milk and yeast extract on tobacco pit cells. They identified the first cytokinin, called kinetin, from the herring sperm DNA.

• Addicott and colleagues identified growth-inhibiting hormones in leaf abscission and seed dormancy. They named abscisic acid because it was first associated with leaf abscission.

• Dimitry Nelijubov discovered that ethylene gas released from burning gas lamps caused the triple response in plants,i.e., elongation of seeds, swelling of stems, and horizontal growth instead of vertical growth. Then, R. Gane, in 1934, confirmed that ethylene is a naturally occurring plant hormone responsible for fruit ripening, leaf abscission, and senescence.

Physiological Effects of Plant Growth Regulators

Auxins

Auxins are growth-promoting hormones that regulate elongation, root initiation, and apical dominance. They are mainly synthesised at shoot tips and young leaves and promote phototropism and gravitropism. They promote cell elongation, apical dominance, and vascular differentiation. They are also used in tissue culture, fruit development, and weed control.

Gibberellins

Gibberellins stimulate cell elongation, germination, fruit development, and seed dormancy and promote flowering in the Long-Day plants. Long plants are the kind of plants that require a longer duration of sunlight than normal plants. They also stimulate cell elongation, seed germination, and bolting in rosette plants. They also break seed dormancy and enhance fruit size and yield.

Cytokinins

Cytokinins are plant hormones that promote cell division, delay leaf senescence, and enhance shoot growth. They work in coordination with auxins to regulate root and shoot development. Naturally occurring cytokinin is zeatin, found in young fruit seeds and roots. Synthetic cytokinins like kinetin are used in plant tissue culture.

Ethylene

Ethylene is a gaseous hormone that regulates fruit ripening, leaf abscission, and stress response. It also promotes seed germination and flowering. It is widely used in commercial agriculture to promote fruit ripening and ensure flower longevity.

Abscisic Acid

Abscisic Acid is a stress hormone that helps plants survive unfavourable conditions by inducing seed dormancy, closing stomatal pores to prevent water loss and regulating leaf abscission. It plays an important role in drought resistance by signalling the closure of stomata during water deficiency.

Also, Read

• NCERT Notes for Class 11 Physics
• NCERT Notes for Class 11 Chemistry
• NCERT Notes for Class 11 Mathematics

Chapter 13 Biology: Previous Year Questions and Answers

Solving past year questions from this chapter, which are given below, helps students understand the topic better. Students can use the NCERT Class 11 Biology Chapter 13 Notes Plant Growth and Development to prepare well for exams.

Question 1. Monocarpic plants are those that

Option 1. Bear flowers with one ovary

Option 2. Flower once and die

Option 3. Bear only one flower

Option 4. All of the above

Answer:

Flowering plants that only produce flowers and seeds once in their lifespan before dying are known as monocarpic plants. The Greek terms monos, which means "single," and karpos, which means "fruit," are the origin of the word "monocarpic." Examples of monocarpic plants are Bamboo, Banana, etc.

Hence, the correct answer is option (2), Flower once and die.

Question 2. Growth can be measured in various ways. Which of these can be used as parameters to measure growth?

Option 1. Increase in cell number

Option 2. Increase in cell size

Option 3. Increase in length and weight

Option 4. All the above

Answer:

Generally speaking, plant growth is indeterminate; plants can continue to develop for the duration of their lives. This is because specific parts of their bodies contain meristems, which can divide and reproduce themselves. Growth is Measurable: Growth at the cellular level results from an increase in protoplasm, which is hard to quantify. Plant growth is quantified using a variety of techniques, such as a rise in fresh weight, volume, dry weight, or cell number.

Hence, the correct answer is option 4. All the above

Question 3. Ethylene is used for

Option 1. Retarding ripening of tomatoes

Option 2. Hastening of the ripening of fruits

Option 3. Slowing down the ripening of apples

Option 4. Both b and c

Answer:

Ethylene is a naturally occurring hormone within fruits that monitors the ripening of the fruit by inducing and regulating many chemical and biochemical activities. Fruit Ripening: In climacteric fruits such as apples, bananas, tomatoes, etc., exposure of mature fruits to ethylene results in respiration climacteric followed by additional production of ethylene, leading to the hastening of the ripening process.

Hence, the answer is option (2), hastening the ripening of fruits is correct.

Also Read:

• NCERT Solution

• NCERT Solutions for Class 11

• NCERT Solutions for Class 11 Biology

Features of the Class 11 Biology Chapter 13 Notes

These notes have several useful features, some of which are listed below.

• Topics are explained in simple and easy-to-understand language for quick learning and revision.

• Important definitions and processes are highlighted in the Class 11 Biology chapter 10 notes.

• Step-by-step illustrations and diagrams are included. This clarifies complex topics like meristematic activity and plant hormones.

• Real-life examples of plant growth regulators are provided in the Class 11 Biology chapter 10 notes.

• These notes are organised systematically according to the latest syllabus.

Chapter-Wise NCERT Class 11 Notes Biology

Here are the links to the notes for each chapter to help with the Biology revision.