Table of Contents
Growth: Plant Growth is Generally Indeterminate
Plants are either determinate or indeterminate. Determinate plants grow to a certain size and stop. Indeterminate plants continue to grow. They are often vine-like plants.
Indeterminate plants have a growth habit that is generally characterized as indeterminate. This means the plants will continue to grow and produce new shoots and flowers until they are either killed by frost or disease, or they run out of food energy reserves.
Growth: Phases Of Growth
1. Infancy
2. Childhood
3. Adolescence
4. Young adulthood
5. Middle adulthood
6. Late adulthood
Growth Rate
The growth rate of a population is the change in the size of the population over a given period of time, usually expressed as a percentage. The growth rate can be positive (the population size increases) or negative (the population size decreases).
The growth rate of a population is determined by two factors: the birth rate and the death rate. The birth rate is the number of births per unit of time, and the death rate is the number of deaths per unit of time.
The growth rate of a population can be affected by a number of factors, including:
-The birth rate: The birth rate can be affected by a number of factors, including the level of education and access to contraception.
-The death rate: The death rate can be affected by a number of factors, including the level of health care and sanitation.
-The level of immigration: The level of immigration can affect the growth rate of a population by adding new members to the population or by subtracting members from the population.
-The level of emigration: The level of emigration can affect the growth rate of a population by subtracting members from the population.
Differentiation, Dedifferentiation And Redifferentiation
Differentiation is the process of cells becoming more specialized as they mature. For example, a stem cell may become a muscle cell, a blood cell, or a nerve cell.
Dedifferentiation is the process of a specialized cell returning to a more primitive state. For example, a muscle cell may dedifferentiate into a stem cell.
Redifferentiation is the process of a cell becoming specialized again after dedifferentiation. For example, a stem cell may redifferentiate into a muscle cell, a blood cell, or a nerve cell.
Plant Growth Regulators
Plant growth regulators (PGRs) are natural or synthetic chemicals that control the growth or other physiological processes of plants. They are used in horticulture to regulate the growth of plants, to improve crop yields, to hasten the ripening of fruits, and to control the size and shape of plants.
There are three main types of plant growth regulators:
1. Auxins – Auxins are a class of plant hormones that stimulate plant growth and development. They are produced in the shoots of plants and are responsible for the elongation of stems and the development of leaves and flowers.
2. Gibberellins – Gibberellins are a class of plant hormones that promote plant growth and germination. They are produced in the seeds of plants and are responsible for the growth of seedlings and the production of flowers.
3. Cytokinins – Cytokinins are a class of plant hormones that stimulate cell division and the growth of new shoots. They are produced in the roots of plants and are responsible for the growth of lateral shoots and the production of flowers.
Growth Inhibitors
Growth inhibitors are a type of antimicrobial agent that inhibits the growth of bacteria, viruses, or other microorganisms. They can be used to prevent the spread of infection, or to treat an infection that has already been diagnosed. Growth inhibitors work by disrupting the growth of the microorganisms, which can either kill them outright or slow their growth enough to allow the body’s natural defenses to fight them off.
Growth Promoters
Growth promoters are a type of feed additive that are used to increase the rate at which animals grow. They are usually a combination of hormones and nutrients that are designed to stimulate the animal’s metabolism and promote growth. Growth promoters are used in livestock farming to increase the yield of meat, milk, and eggs from the animals.
Photoperiodism
The plant’s biological clock is regulated by the length of the day (photoperiod).
The response of an organism to the length of the day or night is called photoperiodism. The circadian rhythm is an endogenous biological clock that regulates many aspects of an organism’s physiology and behavior. The circadian rhythm is entrained to the 24-hour light-dark cycle. The photoperiod affects the circadian rhythm.
The circadian rhythm is responsible for the sleep-wake cycle, body temperature, hormone secretion, and other physiological processes. The circadian rhythm is also responsible for the animals’ behavior. For example, some animals become active during the day, while others become active at night.
The photoperiod affects the circadian rhythm by affecting the intensity of light. The intensity of light affects the production of melatonin. Melatonin is a hormone that is produced by the pineal gland. Melatonin is responsible for the regulation of the circadian rhythm. When the light is bright, the production of melatonin is inhibited. When the light is dim, the production of melatonin is increased.
Vernalization
The process of vernalization is the exposure of a plant to cold temperatures for a period of time. This process causes the plant to produce flowers earlier in the season.
In horticulture, vernalization is the process of treating dormant seeds so that they will germinate in the spring. This is done by exposing the seeds to a period of cold followed by a period of warm temperatures. The cold treatment simulates winter, and the warm treatment simulates spring. Vernalization is used to treat seeds of plants that are not winter-hardy.
MCQ on Plant Hormones
1. What is the main function of plant hormones?
A. To promote the growth of plants
B. To help the plant fight off diseases
C. To help the plant adapt to its environment
D. To help the plant produce food
The main function of plant hormones is to promote the growth of plants.
2. What is the main role of plant hormones?
The main role of plant hormones is to regulate plant growth and development.
3. What are the three main categories of plant hormones?
The three main categories of plant hormones are auxins, gibberellins, and cytokinins.
4. What is the primary role of auxins?
The primary role of auxins is to stimulate cell elongation and root growth.
5. What is the primary role of gibberellins?
The primary role of gibberellins is to stimulate stem growth and seed germination.
6. What is the primary role of cytokinins?
The primary role of cytokinins is to stimulate cell division
MCQ on Plant Hormones
1. What is the difference between auxin and gibberellin?
Auxin is a plant hormone that is responsible for cell elongation, while gibberellin is a plant hormone that is responsible for cell division.
2. What is the difference between an endogenous and an exogenous plant hormone?
Endogenous plant hormones are those that are produced by the plant itself, while exogenous plant hormones are those that are introduced to the plant from an external source.
