Growth | Mitosis, Hormones, Irritability, Movement & Cyclosis

Growth is the irreversible increase in volume, size, and number of an organism’s parts, length, and weight. It is an organic process that takes time to accomplish.   There are three processes involved in growth: Cell division: This process involves an increase in the number of cells and is achieved through mitosis. Before cell division, […]

Growth is the irreversible increase in volume, size, and number of an organism’s parts, length, and weight. It is an organic process that takes time to accomplish.

 

There are three processes involved in growth:

  1. Cell division: This process involves an increase in the number of cells and is achieved through mitosis. Before cell division, replication occurs, leading to the doubling of the chromosome number. Each daughter cell inherits the same chromosomes as the parent cell.
  2. Cell enlargement: After cell division, daughter cells absorb nutrients from their surroundings, using them to increase in mass and size. Some nutrients are utilized for energy generation, while the rest contribute to cell enlargement.
  3. Cell differentiation: Following cell enlargement, cells develop into specialized types by altering their shape and structure to perform specific functions in the growth process.

 

Mitosis:

Mitosis is a cell division process that produces two identical cells with the same chromosome number as the parent cell. It is crucial for growth and occurs in somatic cells (body cells) such as skin, bone marrow, lymph nodes, injured places, and plant meristematic tissues. Mitosis involves stages like interphase, prophase, metaphase, anaphase, and telophase (cytokinesis).

 

Aspect of Growth:

Growth occurs in specific tissues and places in plant bodies, mainly in meristematic tissues. Meristems are tissues capable of mitotic division, and they include root apex, stem or shoot apex, base or internodes, and vascular cambium. Growth in the apical stem and root meristem is termed apical growth, while growth at the meristem base of internodes is called auxiliary growth.

 

Regulation of Growth by Hormones:

Hormones are biochemical substances produced in small quantities by cells in plant and animal bodies. Plant hormones, such as auxin, gibberellin, cytokinin, abscisic acid, and florigens, play roles in stem elongation, tropism response, root and stem apical division, fruit growth and ripening, flower bud and lateral root initiation. Animal hormones, produced in endocrine glands, control body metabolism, promote animal growth, and stimulate reproduction.

 

Irritability:

Irritability is an organism’s ability to perceive and respond to changes in the internal and external environment or stimuli. Stimuli can be external or internal, and organisms respond through tactic, nastic, and tropic responses.

  1. Tactic Response: Directional movement in response to external stimuli such as light, temperature, water, or chemicals.
  2. Nastic Response: Movement in response to non-directional stimuli like changes in light intensity, temperature, and humidity.
  3. Tropic Response: Movement in response to directional stimuli, named according to the stimulus (e.g., phototropism, hydrotropism, chemotropism, haptotropism or thigmotropism, geotropism).

 

Movement:

Movement is the ability of living organisms to change location, motivated by reasons such as searching for food, escaping danger, responding to stimuli, or reproducing.

 

Cyclosis:

Cyclosis, or cytoplasmic streaming, involves the rotational movement of the cytoplasm and its contents within cells. Different organisms use various organelles and mechanisms for movement, such as pseudopodia in amoeba, cilia in paramecium, flagellum in Euglena, tentacles in Hydra, and limbs in animals like earthworms, fishes, toads, and frogs.

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