Growth and Development in Plants
In plants, growth and development include cell division, elongation, and differentiation of cells into tissues and after that organs. Growth is an irreversible increase in size and development is a configured series of stages from a simpler to more complicated form. As development progresses, cellular differentiation of structure and function takes place.
A plant has a development pattern called open growth. Throughout life, the plant includes new organs such as branches, leaves, and roots, enlarging from the tips of roots and shoots but the rate of growth is not uniform throughout the plant body.
In the beginning, the growth is slow, but slowly it becomes fast, attains a maximum, then slowly decreases. In vascular plants, growth occurs through the activity of meristems. Meristems are young tissues or groups of cells that keep the potential to divide.
In lower plants, the whole plant body can grow, but in higher plants, the whole plant body is not capable of growing but development is limited to certain areas referred to as growing points.
These growing points consist of groups of cells that are capable of division, these growing points are called meristems.
These meristematic cells are located at the stem and root and they are of the following types.
(i) Apical Meristems
The apical meristems are discovered at the tips of roots and shoot and are primarily concerned with the extension of the plant body. These are perpetual growth zones discovered at the apices of roots and stems. They are accountable for the increase in the number of cells at the tips of roots and stem, so they play an essential role in primary growth.
(ii) Intercalary Meristems
These are the parts of apical meristem that get separated from the pinnacle by permanent tissues. They are situated at the bases of internodes in many plants. They play an important function in the production of leaves and flowers. These are of temporary nature.
(iii) Lateral Meristems
Lateral meristems are cylinders of dividing cells. They are present in dicots and gymnosperms. Vascular and cork cambium are examples of the lateral meristem. They play an essential role in the increase in the size of stem and root and in secondary growth are determinate i.e. they grow to a particular size and after that stop e.g. leaves, flowers and fruits; while others are indeterminate i.e. they- grow by meristems that continually renew themselves, staying youthful e.g. vegetative root and stem.
Kinds of Growth
(i) Primary Growth: Primary tissue is added by the apical meristem.
(ii) Secondary Growth: Secondary tissue is added by the intercalary or vascular cambium causing an increase in density.
Stages of Growth
The growth of the multicellular plants is divided into 4 stages, cellular division, elongation, maturation, and differentiation.
During cell division, the number of cells increases by mitosis. It occurs at the tip of the root and shoots where cells are small, have spherical nuclei lying in the center of the cytoplasm, which is non-vacuolated. As a result of cellular division, each daughter cell proceeds to increase the size. Synthesis of cytoplasm and cell wall material likewise takes place in this zone.
A little distance from the apex of root and shoot lies in the zone of elongation and is only of few millimeters in length. During elongation, the cell volume increases up to 150 fold due to the uptake of water. Plasticity of the cell wall increases and wall pressure is lowered. Synthesis of new cytoplasm and cell wall material continues.
During maturation, the final size of a given type of cell is attained. The cells which develop into pith, cortex, and particular other tissues do not elongate further along the axis, while other cells like fibers and tracheids extend lengthwise more than in other directions.
When cell enhancement ceases, the procedure of differentiation starts. Throughout this development stage the walls of cells become thicker, the walls of lots of kinds of cells and tissues end up being pitted; thickening appears on the walls of xylem vessels, cells of different tissues differ in spatial dimensions and numerous new structural features develop.
Conditions of Growth
The growth rate is influenced by a number of aspects both external and internal. External aspects are temperature level, light, oxygen, carbon dioxide, water, nutrition, and so on, while internal elements are hormonal agents, vitamins, etc.
(A) External elements
(i) Temperature: Temperature influences the rate of growth within a certain range (0-35 ° C). Generally, the rate of growth increases with the rising of temperature level and reduces with a reduction in temperature. For optimal development, the optimal temperature is 25-30 ° C and it is least at 5-10 ° C. However, at a very high temperature (35-40 ° C), the rate of growth stops, and the plant might pass away.
(ii) Light: Light plays an extremely essential function in the growth of plants. By light, we imply the fractions of light, which is taken in by plants throughout photosynthesis. Normally, light influences development in three ways; intensity, quality, and duration. The increase in the intensity of light increases the number of cell divisions. The red light favors the elongation of cells and blue light improves cell division but slows down cell enlargement.
Likewise, ultraviolet rays also retard cell elongation. Duration of light impacts the growth of vegetative and reproductive structures. It also contributes to causing or suppressing flowering. The phenomenon is called photoperiodism.
(iii) Oxygen: For effective growth, a regular supply of oxygen is needed. Without oxygen, no metabolic activity is possible and no growth occurs. A really high supply of oxygen, however, prevents growth.
(iv) CO2:We knowCO2 is necessary for performing the typical process of photosynthesis however a really high concentration of it can retard growth.
(v) Water: By absorbing water, the cells elongate. The plant growth stops in the absence of water.
(vi) Nutrition: Nutrients supply energy to growing plants. With the increase in nutrition, development increases, whereas a decrease in nutrition causes retardation of growth.
(B) Internal Factors
(i) Hormones: Plant hormones also influence growth e.g. Indole-3-acetic acid/ (IAA) causes elongation of cells.
(ii) Vitamins: Vitamins are organic compounds synthesized within the plant bodies in the existence of light. If the plants are grown in dark, the vitamin deficiencies are induced and the development of the plant body ceases.
MCQs with Answers:
- What is growth in plants?
- A. Reversible increase in size
- B. Irreversible increase in size (Answer)
- C. Reduction in size
- D. Constant size
- Which type of growth involves the addition of secondary tissue by the vascular cambium?
- A. Primary Growth
- B. Tertiary Growth
- C. Secondary Growth (Answer)
- D. Intermediary Growth
- Where are apical meristems primarily located?
- A. Bases of internodes
- B. Tips of roots and shoots (Answer)
- C. Cylinders of dividing cells
- D. Vascular cambium
- What is the nature of intercalary meristems?
- A. Perpetual
- B. Temporary (Answer)
- C. Determinate
- D. Indeterminate
- Which meristem is responsible for the increase in the size of stem and root during secondary growth?
- A. Apical Meristem
- B. Intercalary Meristem
- C. Lateral Meristem (Answer)
- D. Tertiary Meristem
- What characterizes the zone of elongation during stages of growth?
- A. Spherical nuclei
- B. Mitosis
- C. Increased cell volume (Answer)
- D. Maturation
- During which growth stage does the synthesis of new cytoplasm and cell wall material occur?
- A. Cellular division
- B. Elongation
- C. Maturation
- D. All of the above (Answer)
- What is the growth pattern called in plants?
- A. Closed growth
- B. Restricted growth
- C. Open growth (Answer)
- D. Limited growth
- Which kind of growth involves the addition of primary tissue by the apical meristem?
- A. Primary Growth (Answer)
- B. Secondary Growth
- C. Tertiary Growth
- D. Intermediary Growth
- What is the primary role of apical meristems?
- A. Increase stem diameter
- B. Promote secondary growth
- C. Extension of the plant body (Answer)
- D. Synthesize secondary tissue
- Which type of meristem is of temporary nature?
- A. Apical Meristems
- B. Intercalary Meristems (Answer)
- C. Lateral Meristems
- D. Vascular Cambium
- What marks the beginning of the zone of elongation?
- A. Synthesis of new cytoplasm
- B. Increased cell volume (Answer)
- C. Differentiation of cells
- D. Maturation of cells
- Which factor influences the growth rate of plants externally?
- A. Hormones
- B. Vitamins
- C. Light (Answer)
- D. Oxygen
- What phenomenon is associated with the duration of light and its effect on growth?
- A. Photoperiodism (Answer)
- B. Photosynthesis
- C. Phototropism
- D. Photolysis
- What is the effect of a very high concentration of CO2 on plant growth?
- A. Accelerates growth
- B. Retards growth (Answer)
- C. Halts growth
- D. Promotes flowering
FAQs – Growth and Development in Plants
1. What is the fundamental difference between growth and development in plants?
- Answer: Growth is an irreversible increase in size, while development is a series of stages involving the differentiation of cells into tissues and organs.
2. What is open growth in plants?
- Answer: Open growth refers to the pattern in which plants continuously add new organs (branches, leaves, roots) throughout their life, enlarging from the tips of roots and shoots.
3. What are meristems, and where are they located in plants?
- Answer: Meristems are young tissues or groups of cells capable of division. They are located at the stem and root and are of three types: apical meristems, intercalary meristems, and lateral meristems.
4. What is the role of apical meristems in plant growth?
- Answer: Apical meristems, found at the tips of roots and shoots, are perpetual growth zones responsible for the extension of the plant body, playing a crucial role in primary growth.
5. Are intercalary meristems permanent or temporary?
- Answer: Intercalary meristems are temporary and are parts of the apical meristem separated from the pinnacle by permanent tissues.
6. Which cells are involved in secondary growth, and how is it achieved?
- Answer: Secondary growth involves the addition of secondary tissue by the intercalary or vascular cambium, causing an increase in density.
7. What are the stages of growth in multicellular plants?
- Answer: The stages are cellular division, elongation, maturation, and differentiation.
8. What is the zone of elongation, and what happens during this stage?
- Answer: The zone of elongation is a few millimeters from the apex of the root and shoot. During elongation, cell volume increases up to 150-fold due to water uptake, and synthesis of new cytoplasm and cell wall material continues.
9. How are external factors like temperature and light influencing plant growth?
- Answer: Temperature affects growth within a certain range (0-35°C), and light intensity, quality, and duration influence the number of cell divisions, elongation, and flowering through photoperiodism.
10. What internal factors influence plant growth? – Answer: Internal factors include hormones (e.g., Indole-3-acetic acid/IAA) and vitamins synthesized within the plant bodies, which affect elongation and overall growth.
Summary: Growth and Development in Plants
Key points:
- Fundamental Concepts:
- Growth involves an irreversible increase in size, while development is a series of stages from simpler to more complex forms.
- Cellular differentiation of structure and function occurs as development progresses.
- Development Pattern:
- Plants exhibit open growth, continually adding new organs like branches, leaves, and roots throughout their life.
- Meristems:
- Meristems are young tissues capable of division and are crucial for plant growth.
- Three types of meristems include apical, intercalary, and lateral meristems.
- Types of Meristems:
- Apical Meristems: Located at tips of roots and shoots, responsible for primary growth.
- Intercalary Meristems: Found at the bases of internodes, crucial for leaf and flower production.
- Lateral Meristems: Cylinders of dividing cells, contributing to the increase in stem and root size.
- Kinds of Growth:
- Primary Growth: Driven by apical meristems, adding primary tissue.
- Secondary Growth: Involves the addition of secondary tissue by intercalary or vascular cambium.
- Stages of Growth:
- Four stages include cellular division, elongation, maturation, and differentiation.
- Cellular Division and Elongation:
- Mitosis increases cell number, and elongation occurs in the zone near the apex, driven by water uptake.
- Maturation and Differentiation:
- Maturation leads to the final size of cells, and differentiation involves the development of new structural features.
- Conditions of Growth:
- External factors (temperature, light, oxygen, CO2, water, nutrition) and internal factors (hormones, vitamins) influence growth.
- Impact of External Factors:
- Temperature, light intensity, quality, and duration, oxygen, CO2, water, and nutrition play crucial roles.
- Internal Factors:
- Hormones like Indole-3-acetic acid (IAA) and vitamins influence elongation and growth.
- Conclusion:
- Understanding the intricate processes of growth and development is crucial for cultivating healthy plants, involving a delicate balance of internal and external factors.
This comprehensive tutorial provides insights into the dynamic processes governing plant growth and development, offering a foundation for plant biology enthusiasts and researchers.