Growth | Mitosis, Aspect of Growth, Hormones, Animal

What is Growth?

Growth refers to a progressive and irreversible expansion in the volume, size, and quantity of parts, as well as the length and weight of an organism. It is an organic progression that requires a certain amount of time to complete.

The growth process encompasses three distinct mechanisms:

1. Cell division: This is the process through which cells multiply, accomplished via cell division known as mitosis. Prior to dividing into two daughter cells, the chromosomes within the parent cell undergo replication, leading to a doubling of their number. As a result, each daughter cell possesses an identical set of chromosomes as the parent cell.

2. Cell enlargement: Following cell division, this process occurs as the daughter cells absorb nutrients from their surroundings, utilizing them to increase their mass and size. Some of the nutrients are converted into energy, while the rest are assimilated, causing the cells to enlarge.

3. Cell differentiation: Occurring subsequent to cell enlargement, this process involves the transformation of each cell into a specialized cell type, achieved by altering its shape and structure. This specialization allows the cells to perform specific functions necessary for growth.


Mitosis is the process of cellular division that generates two identical cells with the same number of chromosomes and characteristics as the parent cell. It is a crucial form of cell division for growth and occurs in somatic cells (body cells) such as those found in the skin, bone marrow, lymph nodes, injured areas, and plant meristematic tissues. Mitosis consists of five stages: interphase, prophase, metaphase, anaphase, and telophase.

Interphase: This is a resting stage of the cell, during which it appears as a non-dividing cell. The chromosomes are not clearly visible.

Prophase: Chromosomes become visible as chromatin threads. They become shorter, thicker, and distinct. Each chromosome consists of two distinct chromatids joined by a centromere. The nucleolus gradually disappears, and spindle fibers begin to form.

Metaphase: Chromosomes (now in pairs called chromatids) align themselves along the middle or equator of the spindle. The chromatids are attached to the spindle through centromeres.

Anaphase: The chromatids of each chromosome separate and start moving towards opposite poles of the cell, facilitated by the elongation of the spindle axis. Eventually, the chromatids reach the poles.

Telophase (cytokinesis): The cell initiates division by forming a dividing line at the equator. The chromosomes lose their condensed appearance, and the nuclear material, nucleus, and nuclear membrane reform. The spindle structure disappears, and the cell completely splits into two daughter cells, resembling the interphase condition. The division of the cell during telophase into daughter cells is referred to as cytokinesis.

Aspect of Growth

Growth in plants is not a random occurrence that happens throughout all parts of the plant body. Instead, it specifically occurs in certain tissues and regions. The tissues responsible for growth in plants are referred to as meristem or meristematic tissue. Meristem is a specialized tissue that possesses the remarkable ability to undergo cell division through mitosis, giving rise to new cells. Various meristematic tissues can be found in different parts of the plant, including the root apex, stem or shoot apex, base or internodes, and vascular cambium.

The growth that takes place in the apical meristem of both the stem and root is known as apical growth. It contributes to the elongation and development of the plant body. This type of growth enables the plant to extend its roots further into the soil and elevate its shoot towards the sunlight, facilitating overall upward growth.

In addition to apical growth, there is another form of growth called auxiliary growth, which occurs at the meristem base of internodes. This type of growth is responsible for the lateral or sideways expansion of the plant body. It leads to the formation of branches, leaves, and other secondary structures, contributing to the overall shape and size of the plant.

By having specialized meristematic tissues in specific regions, plants can strategically regulate their growth and adapt to their environment. These meristems ensure that growth occurs in the appropriate locations and allows plants to attain the desired form and structure as they develop and mature.

Regulation of growth by Hormones

Hormones play a crucial role in regulating growth processes in both plants and animals. These chemical or biochemical substances are produced in small quantities by cells within the bodies of plants and animals, exerting profound effects on other parts of their respective organisms where they are needed for various forms of growth.

In the case of plants, hormones are primarily produced in the actively growing regions, such as the apical meristem of shoots or roots. These regions, such as the shoot tip or root tip, serve as the source of hormone production, which is then transported to other parts of the plant through diffusion.

There are several types of plant hormones, including auxin, gibberellin, cytokinin, abscisic acid, and florigens. Each hormone plays specific roles in promoting and regulating various aspects of plant growth.

One of the primary functions of plant hormones is to promote stem elongation. They stimulate cell division and expansion, leading to the elongation of the plant’s stems, allowing it to reach towards light sources and optimize its exposure to sunlight.

Plant hormones also enable plants to respond to tropism, which is the growth or movement of a plant in response to external stimuli, such as light (phototropism) or gravity (gravitropism). Hormones facilitate the bending and curving of plant parts in response to these stimuli, enabling them to adapt to their environment.

Additionally, hormones are involved in initiating and regulating the division of cells in the root and stem apical meristems. This cell division is essential for the growth and development of new tissues, facilitating root and stem elongation and branching.

Furthermore, plant hormones contribute to fruit growth and ripening. They regulate the enlargement of fruits and the processes associated with maturation, such as changes in color, flavor, and texture.

Finally, hormones play a vital role in initiating and regulating the growth and development of flower buds and lateral roots. They stimulate the formation and differentiation of these structures, contributing to the reproductive capabilities and overall health of the plant.

In summary, hormones in plants serve as chemical messengers, coordinating and regulating various aspects of growth and development. Their production and transport from the growing regions to other parts of the plant ensure that growth processes are orchestrated and synchronized, allowing plants to adapt and thrive in their environments.

Animal Hormones

In animals, hormones are synthesized and secreted by specialized ductless glands, collectively known as the endocrine system. These glands release hormones directly into the bloodstream, allowing them to be transported throughout the body and reach their target organs and tissues. The endocrine system plays a vital role in regulating various physiological processes and maintaining homeostasis.

There are numerous hormones in the animal kingdom, each with distinct functions and effects on the body. Some of the key animal hormones include:

1. Insulin: Produced by the pancreas, insulin is responsible for regulating glucose metabolism and maintaining blood sugar levels. It promotes the uptake of glucose by cells and helps to store excess glucose as glycogen.

2. Thyroid hormones: Produced by the thyroid gland, thyroid hormones (such as thyroxine) regulate metabolism, growth, and development. They influence processes like body temperature, heart rate, and energy production.

3. Adrenaline (epinephrine) and noradrenaline (norepinephrine): These hormones are released by the adrenal glands in response to stress or emergencies. They increase heart rate, blood pressure, and respiration, preparing the body for a “fight or flight” response.

4. Growth hormone: Produced by the pituitary gland, growth hormone stimulates overall growth and development in animals. It promotes the growth of bones, muscles, and other tissues during childhood and adolescence.

5. Estrogen and progesterone: These female sex hormones are primarily produced by the ovaries. They regulate the menstrual cycle, promote the development of secondary sexual characteristics, and play a crucial role in reproductive processes.

6. Testosterone: This male sex hormone is predominantly produced by the testes. It regulates the development of male secondary sexual characteristics, such as facial hair growth and deepening of the voice, and is essential for reproductive functions.

7. Melatonin: Produced by the pineal gland, melatonin helps regulate the sleep-wake cycle and plays a role in seasonal rhythms and biological clock synchronization.

8. Oxytocin: Known as the “love hormone” or “cuddle hormone,” oxytocin is produced by the hypothalamus and released by the pituitary gland. It is involved in social bonding, childbirth, and milk ejection during breastfeeding.

These are just a few examples of the many hormones that contribute to the intricate regulation of physiological processes in animals. Through their actions on target organs and tissues, hormones ensure the proper functioning and coordination of various bodily functions, enabling animals to adapt, reproduce, grow, and maintain internal balance.

GLANDS                                SITE                                        HORMONE

  1. Pituitary gland                      base of head                               Pituitrin
  2. Thyroid                                   gland Neck                               Thyroxine
  3. Parathyroid                            Neck                                        Parathormone
  4. Pancreas                                  Loop of Duodenum               Insulin
  5. Adrenal gland                         Top of each kidney                 Adrenaline
  6. Testes                                        Testes                                  Testosterone
  7. Ovaries                                      Ovaries                                 Progesterone


Animal hormones serve a variety of important functions in the body. These hormones are chemical messengers that regulate and coordinate various physiological processes, maintaining homeostasis and facilitating proper functioning of the body. Some key functions of animal hormones include:

1. Regulation of Metabolism: Hormones, such as thyroid hormones, play a crucial role in regulating metabolism, influencing the rate at which cells convert nutrients into energy. They help control processes like energy expenditure, thermoregulation, and nutrient utilization.

2. Growth and Development: Hormones like growth hormone (GH) and insulin-like growth factors (IGFs) promote growth and development in animals. They stimulate cell division, protein synthesis, and tissue growth, contributing to the growth of bones, muscles, and other body tissues.

3. Reproduction and Sexual Development: Animal hormones play a vital role in reproductive processes, including the regulation of the menstrual cycle in females and the production of sperm and testosterone in males. Hormones such as estrogen and progesterone in females and testosterone in males are essential for sexual development, fertility, and the maintenance of reproductive organs.

4. Maintenance of Water and Electrolyte Balance: Hormones like antidiuretic hormone (ADH) and aldosterone regulate the balance of water and electrolytes in the body. They influence the reabsorption of water and electrolytes by the kidneys, helping to maintain proper fluid balance, blood pressure, and electrolyte concentrations.

5. Stress Response: Hormones like adrenaline (epinephrine) and cortisol are involved in the body’s response to stress. They increase heart rate, blood pressure, and energy availability, preparing the body for a fight-or-flight response during times of perceived danger or stress.

6. Blood Sugar Regulation: Hormones like insulin and glucagon regulate blood glucose levels. Insulin facilitates the uptake and storage of glucose, while glucagon promotes the release of stored glucose from the liver, helping to maintain stable blood sugar levels.

7. Calcium Regulation: Parathyroid hormone (PTH) and calcitonin are involved in maintaining calcium homeostasis in the body. PTH increases blood calcium levels by stimulating calcium release from bones and enhancing its reabsorption in the kidneys, while calcitonin lowers blood calcium levels by promoting its deposition in bones.

8. Circadian Rhythms: Hormones, such as melatonin, regulate circadian rhythms and the sleep-wake cycle. They help synchronize biological processes and regulate sleep patterns in response to light-dark cycles.

Certainly! Here are some additional functions of animal hormones:

9. Blood Pressure Regulation: Hormones like angiotensin and aldosterone help regulate blood pressure. Angiotensin constricts blood vessels, increasing blood pressure, while aldosterone promotes the reabsorption of sodium and water by the kidneys, contributing to increased blood volume and, consequently, blood pressure.

10. Immune System Regulation: Certain hormones, such as glucocorticoids, have immunomodulatory effects. They regulate immune responses, inflammation, and the balance between immune activation and suppression.

11. Bone Density and Calcium Balance: Hormones like estrogen and testosterone play a crucial role in maintaining bone density. They promote bone formation, regulate bone resorption, and help maintain proper calcium levels in the body.

12. Body Fluid Balance: Hormones like atrial natriuretic peptide (ANP) and vasopressin regulate body fluid balance. ANP helps regulate sodium and water excretion by the kidneys, while vasopressin (also known as antidiuretic hormone) controls water reabsorption by the kidneys.

13. Mood and Emotions: Neurotransmitters and hormones, such as serotonin, dopamine, and oxytocin, influence mood and emotions. They play a role in regulating feelings of happiness, pleasure, love, and bonding.

14. Thermoregulation: Hormones, such as thyroid hormones and adrenaline, help regulate body temperature. Thyroid hormones influence the metabolic rate, which affects heat production, while adrenaline can stimulate heat-generating processes like shivering.

15. Blood Cell Production: Hormones like erythropoietin (EPO) stimulate the production of red blood cells in the bone marrow. They help regulate the balance of different blood cell types in the body.

16. Appetite and Satiation: Hormones like ghrelin and leptin regulate appetite and satiety. Ghrelin stimulates hunger, while leptin signals fullness and helps control food intake.

17. Muscle Contraction: Hormones like insulin and growth hormone influence muscle growth and protein synthesis. They contribute to muscle development, strength, and repair.

18. Wound Healing: Several hormones, such as growth factors like platelet-derived growth factor (PDGF) and transforming growth factor-beta (TGF-β), play a role in wound healing processes. They promote cell proliferation, tissue repair, and the formation of new blood vessels.

19. Behavior and Social Interactions: Hormones, including oxytocin and testosterone, influence behavior and social interactions in animals. They play a role in bonding, aggression, mating behavior, and parental care.

20. Circulation and Oxygen Delivery: Hormones like erythropoietin (EPO) and adrenaline help regulate the production and release of red blood cells, enhancing oxygen-carrying capacity and improving circulation.

These 20 functions highlight the wide-ranging and intricate roles that hormones play in the overall functioning of the animal body. Hormones work together in a complex network, ensuring proper communication and coordination among different body systems to maintain homeostasis and support optimal physiological functioning.

These are examples of the diverse functions performed by animal hormones. Overall, hormones play a critical role in maintaining physiological balance, coordinating bodily processes, and allowing animals to adapt and respond to their environment effectively.


Irritability refers to the capacity of an organism to detect and react to changes occurring in its internal or external environment, commonly known as stimuli. A stimulus is any alteration in conditions that elicits a response in the organism or a specific part of its body. Stimuli can be classified as either external or internal. External stimuli are environmental factors that evoke a response. Organisms exhibit three types of responses to stimuli: tactic response, nastic response, and tropic response.

Tactic Response, also known as taxis, is a directed form of movement or response in which the entire organism relocates from one location to another in reaction to an external stimulus such as light, temperature, water, or specific chemicals. The response can be considered directional and positive if the organism moves toward the stimulus or negative if it moves away from the stimulus.

– Phototaxis refers to the response to variations in light intensity.
– Chemotaxis is the response to changes in the concentration of chemical substances.

Nastic Response, or nastism, is a type of response in which a specific part of a plant undergoes movement in reaction to a non-directional stimulus such as changes in light intensity, temperature, or humidity. Nastic responses are often categorized based on the stimulus that triggers them.

– Nyctinasty is the response to changes in day and night conditions (temperature) or light. For example, the opening of sunflower petals in the presence of light and their closing in darkness.
– The closing of morning glory flowers when light intensity is low.
– Haptonasty is the response to contact or touch.
– The folding of leaflets in the mimosa plant when touched.
– The closing of leaflets in a flamboyant tree.

Tropic Response, or tropism, is a type of response in which a specific part of a plant undergoes movement in reaction to a directional stimulus.

Tropisms are named according to the stimulus that triggers them, such as phototropism, hydrotropism, chemotropism, haptotropism (thigmotropism), or geotropism.

– Phototropism is the growth movement in response to light, with the direction of growth determined by the direction of light. The shoot of a plant exhibits positive phototropism.
– Geotropism refers to the response to gravitational force, with the shoot of a plant displaying negative geotropism while the root exhibits positive geotropism.
– Chemotropism is the response of a plant to the concentration of chemical substances. For instance, roots respond positively to the presence of calcium salts but negatively to alkaline or acidic conditions.
– Haptotropism (also known as thigmotropism) is the response of a plant to physical contact. It is commonly observed in tendrils and other structures that plants use for support. Tendrils show a positive response to touch by coiling around a support, while roots exhibit a negative response to touch by growing away from obstacles such as stones.

These various types of responses highlight the diverse ways in which organisms and plants interact with their surroundings and adjust their growth and movements accordingly.


Movement is a fundamental ability exhibited by living organisms, enabling them to transition from one location to another. This capability serves several essential purposes for survival and reproductive success.

1. Searching for Food: Organisms move to explore and locate sources of nutrition. Whether it is a predator searching for prey or a herbivore seeking suitable plants to feed on, movement plays a critical role in acquiring sustenance. This search for food resources is often driven by the organism’s need for energy and essential nutrients.

2. Escaping from Danger: Movement is crucial for avoiding threats and escaping potentially harmful situations. When faced with predators or unfavorable environmental conditions, organisms can respond by employing various forms of movement to relocate to safer environments. This ability to escape danger is vital for survival and minimizing the risk of harm or predation.

3. Responding to Stimuli: Organisms possess the capability to respond to external stimuli, either positively or negatively, through movement. Positive responses involve moving towards stimuli that provide benefits or opportunities, such as light, warmth, or potential mates. Negative responses, on the other hand, involve moving away from stimuli that are potentially harmful, such as extreme temperatures, toxins, or physical disturbances.

4. Reproduction: Movement is often integral to the process of reproduction in many organisms. It allows individuals to find mates, engage in courtship behaviors, and disperse offspring to new habitats or environments. Whether through active locomotion or passive means like wind or water currents, movement facilitates the distribution and successful propagation of offspring, contributing to the survival and genetic diversity of the species.

5. Exploration and Habitat Expansion: Movement allows organisms to explore and expand into new habitats. This enables them to access untapped resources, colonize new areas, and adapt to changing environmental conditions. By moving to different locations, organisms can increase their chances of survival and find suitable conditions for growth, reproduction, and sustenance.

6. Social Interactions and Communication: Movement plays a crucial role in social interactions among organisms. Many species exhibit complex movements and behaviors as part of communication within their social groups. For example, in some bird species, coordinated movements like flocking and formation flying serve to enhance communication, predator avoidance, and navigation. Social movements also contribute to the development and maintenance of social hierarchies, mating systems, and cooperative behaviors.

7. Migration: Migration is a remarkable form of movement observed in many animal species. It involves the regular, long-distance movement of individuals or populations between different habitats or regions. Migration often occurs in response to seasonal changes, such as temperature, food availability, or breeding opportunities. Animals migrate to find suitable breeding grounds, escape harsh weather conditions, or access abundant food sources. This behavior is prevalent in birds, mammals, fish, insects, and even some reptiles and amphibians.

8. Locomotion and Physical Performance: Different organisms have evolved diverse locomotion strategies that enable them to move efficiently in their environments. These include walking, running, swimming, flying, climbing, burrowing, and gliding. Locomotion abilities are often optimized for specific habitats, such as the streamlined bodies and fins of fish for swimming or the wings and aerodynamic structures of birds for flight. Adaptations for movement, such as limbs, muscles, and specialized appendages, allow organisms to navigate and interact with their surroundings effectively.

9. Fitness and Natural Selection: Movement is a significant factor in an organism’s fitness and its ability to survive and reproduce. Natural selection favors individuals with effective movement strategies, such as those capable of obtaining resources, avoiding predators, or accessing potential mates. Over time, advantageous movement traits are passed on to future generations, contributing to the evolutionary success of a species.

10. Ecosystem Functioning and Biodiversity: Movement plays a vital role in maintaining ecosystem functioning and biodiversity. Organisms that move contribute to various ecological processes, including nutrient cycling, seed dispersal, pollination, and predator-prey interactions. Movement helps to connect different habitats, facilitating gene flow and promoting species diversity by allowing for the exchange of individuals and genetic material between populations.

The movement serves numerous functions in the lives of organisms, ranging from individual survival and reproduction to ecosystem dynamics and evolutionary processes. It is an essential attribute that enables organisms to adapt to their environments, find resources, avoid threats, communicate, and fulfill their ecological roles.

Across the animal kingdom, movement strategies vary greatly, ranging from the intricate flight patterns of birds to the coordinated swimming of fish, the agile running of mammals, and the crawling or slithering of reptiles and invertebrates. Similarly, plants exhibit movement in response to stimuli, such as the bending of leaves towards light (phototropism) or the closing of flowers in the absence of sunlight (nyctinasty).

Overall, movement is an essential attribute of living organisms, enabling them to adapt, thrive, and fulfill vital functions such as finding food, escaping danger, responding to stimuli, and ensuring successful reproduction.


Cyclosis, also known as cytoplasmic streaming, refers to the fascinating phenomenon of mass rotational movement or streaming of the cytoplasm and its contents within cells that possess a vacuole. This dynamic process involves the continuous flow and circulation of cytoplasmic components, such as organelles, vesicles, and other cellular materials, throughout the cell’s interior.

In some instances, cyclosis may be localized and restricted to a specific region within the cell, while in other cases, the entire cytoplasm undergoes cyclical movement. This movement is facilitated by the coordinated actions of actin filaments and myosin motor proteins. The actin filaments, often organized into a network, provide the tracks or pathways along which the cytoplasmic materials move, while myosin motors generate the contractile forces required for the streaming motion.

Cyclosis can be observed in a variety of cell types, including plant cells, animal cells, and certain unicellular organisms. It serves multiple purposes and contributes to various cellular functions:

1. Distribution of Cellular Components: Cyclosis plays a critical role in the distribution and movement of cellular components within the cell. Organelles, such as mitochondria, endoplasmic reticulum, and Golgi apparatus, as well as vesicles carrying molecules, can be transported throughout the cytoplasm via cytoplasmic streaming. This movement ensures the efficient distribution and exchange of essential materials, facilitating cellular processes such as protein synthesis, energy production, and secretion.

2. Nutrient and Waste Transport: Cyclosis aids in the transport of nutrients and metabolic waste products within the cell. The streaming movement of the cytoplasm helps to deliver nutrients to various regions of the cell where they are needed, promoting cellular metabolism and function. Additionally, it assists in the removal of waste materials and byproducts from cellular processes, preventing their accumulation and potential toxicity.

3. Response to Environmental Stimuli: Cyclosis can be influenced by external stimuli and environmental factors. For example, changes in light intensity, temperature, or the presence of certain chemicals can affect the rate and direction of cytoplasmic streaming. This responsiveness allows the cell to adapt and respond to its surroundings, optimizing its metabolic activities and ensuring proper cellular function.

4. Distribution of Hormones and Signaling Molecules: In certain specialized cells, cyclosis facilitates the distribution of hormones, signaling molecules, and other regulatory substances. The streaming movement of the cytoplasm helps to transport these molecules to their target sites within the cell, allowing for the coordination of cellular responses and signaling cascades.

Overall, cyclosis or cytoplasmic streaming is a dynamic process that contributes to the efficient organization and functioning of cellular activities. The continuous movement and distribution of cytoplasmic contents, it enables cells to carry out essential functions, maintain homeostasis, and respond to their environment effectively.

Organisms                    Organelles for movement                      Mechanism of movement

Amoeba                                 Pseudopodia                                            Cytoplasmic streaming (cyclosis)

Paramecium                         Cilia                                                             Beating the cilia against water

Euglena                                Flagellum                                                   Lashing movement of flagellum

Hydra                                   Tentacles                                                Swimming, swaying, hoping & Somersaulting

Earthworm                           Chaetae                                                                   Crawling

Fishes                                     Fins                                                                           Swimming

Toads and frog Limbs                                                                                               Hopping


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