Plant Growth and Development: Topics, Overview, Phases, Factors, Books, Tips, Questions

What Is Plant Growth?

Growth can be defined as a permanent increase in the size and mass of a plant and involves cellular enlargement and cell division. Development would then be the series of events that happen in the life history of a plant from germination through flowering, fruiting, and senescence. In this context, development will be key to the mere existence of a plant and reproductive success since it allows plants to produce seeds for the next generation.

Various factors influence the growth and development of plants. Among which, some are controllable or uncontrollable to man, like the genetic make-up, the environmental conditions such as light, temperature, water, and nutrients, and hormonal regulation. Knowing and understanding all these would be of much help in maximising these agricultural practices for the sake of healthy plant development.

Characteristics of Plant Growth

Plant growth has several unique characteristics that distinguish it from growth in animals. As we had already studied, it is a permanent and irreversible process that occurs throughout the life of a plant due to the presence of meristematic tissue. Understanding the characteristics of plant growth helps students learn important concepts and prepares them for facing NEET Biology questions asked from this chapter.

Some important characteristics are:

• Growth is a permanent and irreversible process.

• Growth is measurable in terms of size, length, area, volume, or weight.

• Growth is indeterminate in most plants due to the presence of meristematic tissues.

• Growth occurs through cell division and cell enlargement.

• Growth is influenced by both internal and external factors.

Phases of Growth in Plants

Plant growth occurs in three phases: the meristematic phase, the elongation phase, and the maturation phase. All these phases together contribute to the overall growth and development of a plant.

Meristematic Phase

The meristematic phase occurs at the root and shoot apices, where cells divide continuously by mitosis.

Elongation Phase

In the elongation phase, there is an increase in size and length of newly formed cells due to cell enlargement. This leads to an increase in the length of roots and shoots.

Maturation Phase

During this phase, the cells become mature and attain their maximum size. These cells undergo differentiation and develop into specialised tissues that perform a specific function in the plant.

Growth Rate in Plants

Growth rate is the increase in growth of a plant per unit time. This rate may vary depending on the plant species, age of the plant, and environmental conditions.

Arithmetic Growth

In arithmetic growth, only one daughter cell continues to divide while the other differentiates and becomes mature. This results in a straight-line graph when growth is plotted against time.

Geometric Growth

In geometric growth, both of the daughter cells continue to divide, which causes an increase in the number of cells. This leads to the production of a J-shaped growth curve.

Important Formulae of Growth

Here are some formulas that can help measure plant growth over time.

1. Arithmetic Growth Formula

Lt = L₀ + rt

• Lt = Length at time t

• L₀ = Initial length

• r = Growth rate

• t = Time

2. Geometric Growth Formula

W₁ = W₀eʳᵗ

• W₁ = Final size or biomass

• W₀ = Initial size or biomass

• r = Relative growth rate

• t = Time

• e = Base of natural logarithm

Growth Curve in Plants

A growth curve is a graphical representation of plant growth over a period of time. Under natural conditions, the plant generally follows a sigmoid or S-shaped growth curve.

It consists of four phases:

• Growth is slow during the initial stage.

• This is followed by a phase of rapid growth called the exponential phase.

• After some time, the growth rate gradually decreases.

• Finally, growth reaches a stationary phase when the plant organ becomes mature.

Key Processes In Plant Growth

Cell division is the basis of growth in plants.

Cell Division

Role of Mitosis and Meiosis

Mitosis results in a process in which one cell divides and gives rise to two identical daughter cells that are mirror images of each other, and the mother cell process is used to help in growth, repairing, and amoebic or asexual reproduction in plants. Conversely, meiosis takes place in the reproductive organs of the organism and varieties of gametes, that is, the sperm and egg, to quickly enhance the ability of the species to carry on with the sexual means of reproduction.

• Prophase: The chromosomes begin to condense and may now be visible.

• Metaphase: The chromosomes orient themselves at the cell's equatorial plate.

• Anaphase: Sister chromatids separate, moving toward opposite poles.

• Telophase: Nuclear membranes re-establish around each set of chromosomes.

• Cytokinesis: The cleavage of the cell into two separate daughter cells.

Cell Enlargement

Mechanism of Cell Enlargement

The cells take up water, increase in volume, and tend to force the cell walls from outside during cell turgor pressure. This is due to the water intake in the central vacuole, which causes the swelling of the cell.

Role of Turgor Pressure

Turgor pressure is the pressure exerted on the cell wall by the cell membrane. When this is absent, the cells are flaccid. It is therefore responsible for the stiffness of cells, hence cell enlargement. It is the result of the osmotic flow of water into a cell and it provides the force for cell growth, leading to the extension of plant tissues.

Cell Differentiation

Definition and Importance

Cell differentiation is a process in which the cells are cast into different classes of cells, each having distinct functions. This makes the process of cell differentiation indispensable for the development of tissues and organs which helps a plant carry on several of these kinds of complex activities like nutrient absorption, photosynthesis, and reproduction later on.

Example: Differentiation in Root and Shoot Systems

In the root system, cells differentiate into root hair cells, thus expanding the surface area for the absorption of water and nutrients. In the shoot system, cells differentiate into a variety of cell types, including xylem and phloem cells that function in water and nutrient transport and photosynthetic cells in leaves.

Important Concepts in Plant Growth and Development

Plant growth and development involve a few important processes that help plants to grow, adapt, and complete their life cycle. Some of which include dedifferentiation and redifferentiation.

Plasticity in Plants

Plasticity is the ability of a plant to change its growth pattern or produce different structures in response to the developmental stage or the surrounding environment. This helps the plant to adapt to different conditions and increases its chances of survival. Example - environmental heterophylly seen in buttercup, and developmental heterophylly in cotton.

Stages in the Plant Life Cycle

There are various stages of Plant Growth.

Germination

Stages of Seed Germination

• Imbibition: The seed imbibes water, swells, and the seed coat cracks.

• Activation: Metabolic processes go active, enzymes are activated, and stored food reserves are mobilized.

• Emergence of Radicle: First, the root appears and anchors the seedling. The radicle then begins to take in water and nutrients.

• Emergence of Plumule: The shoot is next to appear, growing directionally toward the light

Factors Affecting Germination

• Water: Important for the process of imbibition and the activation of enzymes.

• Oxygen: this is required to provide energy for growth by respiration.

• Temperature: It requires an optimum temperature for enzyme activity.

• Light: Many seeds germinate in response to light, others in darkness.

Vegetative Growth

Definition and Characteristics

Vegetative growth can be described as the stage at which the plant's development becomes more considerable and more covering of root, stem, and leaf growth. This undertaking is at a sensitive period when the tough frame that eventually will support reproductive growth is put in place.

Role of Meristems

• Apical Meristems: Found in the root and shoot apices, they account for primary growth, for elongation.

• Lateral Meristems: The vascular and cork cambium; account for secondary growth; for thickening.

• Intercalary Meristems: Found in the base of leaf blades or internodes, which cause grass to sprout

Reproductive Growth

Vegetative to the Reproductive Phase

The process is accompanied by alteration of gene expression and hormonal regulation and concludes with flowers, fruits, and seeds. The transition is often environmental, induced by stimuli such as light, temperature, and photoperiod, among others.

Flowering and Fruiting

Flowering is the formation of flowers. These are essentially the sexual organs of the plant. In fruiting, the fruits in post-fertilization, are structures that primarily protect the seeds but aid in their dispersal as well.

Environmental Factors Affecting Plant Growth

The environmental factors affecting the plant growth are:

Light

Light is one of the factors in photosynthesis, which is the process by which plants transform light energy into chemical energy to synthesize glucose and oxygen. Photoperiodism is responsible for the control of flowering, seed germination, and other developmental processes and is considered as the plant response to the length of day and night

Water

Water maintains cell turgor and hence keeps the cells turgid, providing the plant with the erect form it holds. Water further acts as a solvent that acts in nutrient translocation between different parts of the plant through the xylem and phloem.

Effects of Water Deficiency and Excess

• Water Deficiency: It results in wilting, stunted growth, and hampers physiological activities.

• Water Excess: Root rotting, oxygen lack in the soil, and inhibition of nutrient uptake.

Temperature

Temperature essentially changes the rate at which the enzymatic activities within the plants occur, affecting the growth and development of organisms. The optimal temperature ranges allow the maximum efficiency of the enzymatic activities and growth rate. Temperatures above or below could completely inhibit these functions from occurring altogether.

Nutrients

Plants need some macronutrients, such as nitrogen, phosphorus, and potassium, and other nutrients such as iron, manganese, and zinc, which are micronutrients, for development and to grow. These nutrients have their functionality in the physiological process.

Soil fertility can be defined as a state where soil possesses all the required nutrients for plant growth. Such a soil with required nutrients will support the profuse growth of plants by developing a healthy competent root system that can pick up the required nutrients from the environment at a fast rate.

Differentiation in Plant Growth & Development

Differentiation is a process by which nonspecialized cells get to be specialized to perform distinct functions. It is the process of development which is important to develop most tissues and organs of plants. This gives way to complex structures and functions.

Examples

• Collenchyma Cells: They provide support and elasticity to young stems and leaves, respectively.

• Sclerenchyma Cells: They provide mechanical support and strength with thick and lignified cell walls.

• Vascular Tissue: xylem cells differentiate to conduct water and minerals while conducting sugars and other organic compounds is done by the phloem.

• Specialize – leaves mesophyll cells to – palisade parenchyma photosynthesis, spongy parenchyma perform exchange of gases

Role of Differentiation in Adaptation

The role of differentiation in adaptation includes:

• Leads to the formation of specialised structures like leaves, stems, and roots; in further vascular plants, it also leads to reproductive organs.

• A means of adjustability to the environment, where cell differentiation enables the plant to develop its cells of a particular kind

Plant Growth Regulators

Plant growth regulators (PGRs) are organic substances that control and influence the growth, development, and various physiological activities of plants.

Auxins

Auxins help in root formation and maintain apical dominance. Not only this, but it also plays an important role in the development of fruit.

Ethylene

Ethylene is a gaseous plant growth regulator. It promotes ripening of fruit, leaf abscission, and flower senescence.

Gibberellins

Gibberellins promote stem elongation, seed germination, flowering, and fruit growth.

Cytokinins

Cytokinins promote cell division and delay leaf ageing.

Abscisic Acid (ABA)

It is called the stress hormone because it induces seed dormancy and promotes stomatal closing during stress conditions.

Plant Growth & Development NEET MCQs (With Answers & Explanations)

Important topics for NEET are:

• Key Processes in Plant Growth

• Phases of Plant Growth

• Environmental factors

Previous Year Questions from Plant Growth and Development

Question 1

Which of the following phytohormones promotes nutrient mobilization, helping to delay leaf senescence in plants?

A) Gibberellin

B) Cytokinin

C) Ethylene

D) Abscisic acid

Correct Option: B) Cytokinin

Explanation: Cytokinins delay senescence (the Richmond-Lang effect) by promoting nutrient mobilisation and helping the leaf remain green longer.

Question 2

The gaseous plant growth regulator (Ethylene) is used in plants to:

A) Speed up the malting process

B) Promote root growth and root hair formation to increase the absorption surface

C) Help overcome apical dominance

D) Kill dicotyledonous weeds in the fields

Correct Option: B) Promote root growth and root hair formation to increase the absorption surface

Explanation: Ethylene promotes root hair formation and enhances root growth, thereby increasing the surface area available for the absorption of water and minerals.

Question 3

The process of growth is maximum during:

A) Senescence

B) Dormancy

C) Log phase

D) Lag phase

Correct Option: C) Log phase

Explanation: In the "Log" or exponential phase, the rate of growth is very rapid and reaches its maximum until nutrients become limiting.

Practice Questions for NEET

Q1. The occurrence of more than one type of leaves in rooted emergent water plant is known as

1. Phyllotaxy

2. Heterophylly

3. Aestivation

4. Anisophylly

Correct answer: 2) Heterophylly

Explanation:

The occurrence of multiple leaf types in rooted aquatic plants is termed heterophylly. This phenomenon is categorized into three distinct types:

1. Developmental Heterophylly: This involves the formation of varied leaf types during different growth phases of the plant, such as juvenile and adult stages.
2. Environmental Heterophylly: Here, leaf morphology is influenced by external conditions, with specific leaf types developing in response to environmental factors like water depth. For instance, submerged leaves might differ from those that emerge above water.
3. Habitual Heterophylly: In this case, the plant exhibits dissimilar leaf types across various regions of its structure, such as underwater, floating, and above-water parts.

Examples of heterophylly can be seen in species like Potamogeton and water lilies. These emergent water plants have large, broad leaves that extend above the water surface for photosynthesis. In contrast, their submerged leaves are often more intricately divided or structurally adapted to enhance their functionality within the water column. This dual-leaf strategy allows them to efficiently inhabit and thrive in their aquatic surroundings.

Hence, the correct answer is option 2) Heterophylly.

Q2. Plants display

1. Definite growth

2. Indefinite growth

3. Fixed growth

4. Steady growth

Correct answer: 2) Indefinite growth

Explanation:

Having meristems—areas of actively dividing cells—allows plants to expand indefinitely. Located at the tips of roots and shoots, these meristems enable plants to continue developing for the duration of their lives. By becoming taller, extending their roots, or spreading their branches as necessary, this kind of growth aids plants in adjusting to their surroundings.

Hence, the correct answer is option 2)Indefinite growth.

Q3. What happens to seeds when favourable conditions for growth are absent?

1. They grow rapidly

2. They enter a period of suspended growth or rest

3. They continue metabolic activities

4. They form roots

Correct answer: 2) They enter a period of suspended growth or rest

Explanation:

Seeds enter a period of dormancy or rest when conditions for growth are not favourable, such as in the absence of adequate moisture, temperature, light, or oxygen. During dormancy, metabolic activities in the seed are greatly reduced, and the seed remains in a state of suspended growth. This dormancy period is a survival mechanism, allowing the seed to wait for optimal environmental conditions before beginning germination. The seed coat, hormones like abscisic acid (ABA), and other factors regulate this dormant state. Once the conditions are favourable, such as when water, temperature, and light signals are appropriate, the seed can overcome dormancy and begin the germination process.

Hence, the correct answer is option 2) They enter a period of suspended growth or rest

Plant Growth and Development Quick Revision Notes

• Plant growth is a permanent and irreversible increase in the size of a plant.

• Plants show indeterminate growth due to the continuous activity of meristematic tissues.

• Growth mainly occurs through cell division and cell enlargement.

• The three phases of plant growth are the meristematic phase, the elongation phase, and the maturation phase.

• Arithmetic growth follows a linear pattern, where only one daughter cell continues to divide.

• Geometric growth follows an exponential pattern, where both daughter cells continue to divide.

• Under natural conditions, plant growth generally follows a sigmoid (S-shaped) growth curve.

• Germination, vegetative growth, and reproductive growth are the major stages in the plant life cycle.

• Light, water, oxygen, temperature, and nutrients are important factors that influence plant growth.

• Differentiation leads to the formation of specialised cells, tissues, and organs in plants.

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