Control and Coordination
The changes in the environment (or environmental factors) to which the organisms respond and react are called stimuli (singular stimulus).
The working together of various organs (parts) of the body of an organism in a proper manner to produce proper reaction to a stimulus is called coordination.
Coordination in animals
1. Nervous system
The nervous system is composed of specialized cells called neurons (nerve cells) which exercise control by sending electrical signals called nerve impulses. The nervous control is speedy and flexible but its effect is localized.
2. Endocrine system
The endocrine system consists of specialized glands (endocrine glands) which bring about control by sending chemical messengers termed hormones. The hormonal control is usually slow acting and its effect is diffuse.
Reflex actions
A reflex action may be defined as a spontaneous, automatic and mechanical response to a stimulus, acting on a specific receptor, without the will of an animal.
What happens in reflex actions?
In reflex action, fine tips (dendrites) of receptors (sensory neurons) quickly relay a message (electric impulse) via sensory nerves to the spinal cord. The spinal cord then sends information (impulse) via motor nerves to effectors (muscles or glands) which show response. The path taken by nerve impulses in a reflex action is called reflex arc.
Involuntary actions
Involuntary muscular actions are performed by the animal without its will. These occur automatically and the animal has no choice in it. Such actions are meant for controlling and coordinating the functioning of internal organs. Many of these involuntary actions are controlled by the midbrain and hind brain.
Voluntary actions
Voluntary muscular actions are performed by the animal with its will. In each voluntary action, the animal exercises its choice so that the same stimulus may receive different responses at different times depending upon the situation.
Human nervous system is the most complex. It is divided into two main parts:
1. Central nervous system
2. Peripheral nervous system
| Cerebrum | Cerebellum |
| 1. It is the part of forebrain | 1. It is the part of hind brain. |
| 2. It is the largest part constituting 80% of the brain. | 2. It is much smaller, constituting 12.5% of the brain. |
| 3. It forms the front, superior and lateral sides of the brain. | 3. It lies in the posterior region of the brain. |
| 4. It has two parts called cerebral hemispheres. | 4. It has three parts: two lateral cerebellar hemispheres and one central vermis. |
| 5. It has two cavities called lateral ventricles. | 5. Cavity is nearly absent. |
| 6. Cerebrum is the seat of intelligence and memory. | 6. Cerebellum coordinates muscular activity. |
| 7. It controls movements, speech, sight, smell, taste, hearing, intelligence etc. | 7. It maintain equilibrium of the body. |
Coordination in plants
Control and coordination in plants is not as elaborate as in animals. Plants do not have nervous system, muscles and sense organs (eg., eyes, ears, nose etc.) like the animals. Still, they can respond and react to various environmental stimuli such as light, gravity, water, touch, chemicals etc. Plants, in fact, show two different types of movements in response to various stimuli. One type of movements are dependent of growth (eg., movement of leaves of ‘touch-me-not’ plant, also called chhui-mui or ‘sensitive plant’, in response to touch). Other type of movements are dependent on growth (eg., directional movement of seedling with root going down and stem coming up). Bothe these types of movements are effected by the action of plant hormones (phytohormones).
Differences between tropic movements and nastic movements
| Tropic movements | Nastic movements |
| 1. These are directional movements or orientations of the part of the plant in response to specific stimulus. The movement can be towards the stimulus or away from the stimulus. | 1. These are not directional movements, ie., these movements are neither towards the stimulus now away from the stimulus. |
| 2. These are plant movements of curvature caused by unilateral growth, ie., one side of an organ grows faster than the other causing curvature. | 2. These movements are caused due to variations in environmental conditions, ie., they are variation movements. These are also movements of curvature but these occur due to turgor changes. |
| 3. Bending of stem towards light (phototropism), and downward growth of roots in response to gravity (geotropism) are some examples. | 3. Folding and drooping of leaves of Mimosa plant (‘touch-me-not’ plant) in response to touch is the example. |
Difference between nervous and hormonal information.
| Nervous information | Hormonal information |
| 1. It is sent as an electrical impulse along axons, and as a chemical across synapse. | 1. It is sent as a chemical messenger via blood stream. |
| 2. Information travels rapidly, in milliseconds. | 2. Information travels slowly. |
| 3.Information is directed to specific receptors-one or a few nerve fibres, gland cells or other neurons, ie., it is addresses by name. | 3. Information is spread throughout the body by blood from which the target cells or organs pick it up, ie., it is addressed to ‘whom it may concern’ |
| 4. It gets response immediately | 4. It gets response usually slowly. |
| 5. Its effect are short-lived. | 5. Its effect are generally more prolonged. |
Coordination in plants
Plants coordinate their responses against environmental stimuli by using hormones.
Classification of Induced Plant Movements
Induced plant movements are broadly classified into two types:
1. Nastic movements
2. Tropic movements
Nastic movements
Nastic movements are induced by external stimuli such as light, temperature, touch. However, these are not directional movements. Here, the part of the plant does not respond towards or away from the stimulus.
Tropic movements or tropisms
Directional movements or orientations of specific part of a plant revealing growth in response to external stimuli are called tropisms o tropic movement.
| Tropic movements | Nastic movements |
| 1. These are directional movements or orientations of the part of the plant in response to specific stimulus. The movement can be towards the stimulus or away from the stimulus. | 1. These are not directional movements, ie., these movements are neither towards the stimulus nor away from the stimulus. |
| 2. These are plant movements of curvature caused by unilateral growth, ie., one side of an organ grows faster than the other causing curvature. | 2. These movements are caused due to variations in environmental conditions, ie., they are variation movements. These are also movements of curvature but these occur due to turgor changes. |
| 3. Bending of stem towards light (phototropism), and downward growth of roots in response to gravity (geotropism) are some examples. | 3. Folding and drooping of leaves of Mimosa plant (‘touch-me-not’ plant) in response to touch is the example. |
Plant hormones and their functions
| Sr. No. | Plant Hormones | Functions |
| 1. | Auxins (naturally occurring auxin is indole 3-acetic acid) | These promote cell enlargement and cell differentiation in plants.These also promote stem and fruit growthThese regulate important plant growth movements, ie., tropisms.These induce parthenocarpy (ie., the formation of seedless fruits without fertilization) in number of plants. |
| 2. | Gibberellins (gibberellic acid) | These promote cell enlargement and cell differentiation in plants in the presence of auxins.These also promote growth in stems and fruits.Rosette plants (ie. Plants that show profuse leaf development but reduced internode growth) show bolting* and flowering when treated with gibberellins.These also induce parthenocarpy in many palnts. |
| 3. | Cytokinins | These promote cell division in plants.These play vital role in the morphogenesis in plants.These help in breaking the dormancy of seeds and buds.These delay the ageing in leaves.These promote the opening of stomata.These also promote fruit growth. |
| 4. | Ethene (Ethylene) | It promotes growth and ripening of fruits.It helps in breaking the dormancy in buds and seeds.It stimulates the formation of separation layer (abscission zone) in leaves, flowers and fruits.It promotes yellowing and senescence of leaves. |
| 5. | Abscisic acid (ABA) | It promotes the dormancy in seeds and buds and thus inhibits growth.It also promotes the closing of stomata and thus effects wilting of leaves.It also promotes the falling of leaves (abscission) and senescence in leaves. |
Chemical coordination in animals
In animals, the message, communicated in the form of nerve impulses, from receptors (sensory neurons) to central nervous system and from latter to the effectors (muscle and glands) is very quick. The nervous coordination in animals, however, has certain limitations. For instance,
(i) Nerve impulses can reach only those animal cells which are connected by nervous tissue, and
(ii) Such cells, after generation and transmission of nerve impulses, take some time to reset their mechanisms before a new impulse is generated and transmitted.
Differences between nervous and hormonal information
| Nervous information | Hormonal Information |
| 1. It is sent as an electrical impulse along axons, and as a chemical across synapse. | 1. It is sent as a chemical messenger via blood stream. |
| 2. Information travels rapidly, in milliseconds. | 2. Information travels slowly. |
| 3. Information is directed to specific receptors- one or a few nerve fibres, gland cells or other neurons, ie., it is addressed by name. | 3. Information is spread throughout the body by blood from which the target cells or organs pick it up, ie., it is addressed to ‘whom it may concern’. |
| 4. It gets response immediately. | 4. It gets response usually slowly. |
| 5. Its effects are short-lived. | 5. Its effects are generally more prolonged. |
Hormones
Hormones are chemical messengers secreted by ductless endocrine glands that regulate the biological processes in the living organisms.
Difference between Exocrine glands and Endocrine glands
| Exocrine Glands | Endocrine Glands |
| 1. These glands possess ducts. | 1. These glands lack ducts. |
| 2. These glands pour their secretions to the target directly or through ducts. | 2. These glands pour their secretions into blood. |
| 3. Secretions are various enzymes, mucus, excretory substances, lubricants etc. | 3. Secretions consist of hormones (chemical messengers). |
| 4. These glands do not occur in isolation. | 4. These glands usually occur in isolation. |
| 5. The target sites are adjacent to the glands. | 5. The target sites far away from the glands. |
Summary of hypothalamic hormones and pituitary response
| S. No. | Hypothalamic hormone | Response of pituitary | Target organ |
| 1. | Thyrotrophin-releasing hormone (T-RH) | Thyroid stimulating hormone (TSH) secretion | Thyroid |
| 2. | Adrenocorticotrophin-releasing hormone(A-RH) | Adrenocortincotrophic hormone (ACTH) secretion | Adrenal cortex |
| 3. | Follicle stimulating hormone-releasing hormone (FSH-RH) | Follicle stimulating hormone (FSH) secretion | Ovary/Testis |
| 4. | Luteinising hormone-releasing hormone (LH-RH) | Luteinising hormone (LH) secretion | Ovary/Testis |
| 5. | Growth hormone-releasing hormone (GH-RH) | Growth hormone (GH) or somatotrophic hormone (STH) secretion | Most tissues |
| 6. | Growth hormone release-inhibiting hormone (GH-RIH) or somatostatin | Growth hormone secretion inhibited | —– |
| 7. | Prolactin-releasing hormone (P-RH) | Protactin hormone (PH) or luteotrophic hormone (LTH) secretion | Mammary glands |
| 8. | Prolactin release-inhibiting hormone (P-RIH) | Prolactin secretion inhibited | —– |
| 9. | Melanocyte stimulating hormone-releasing-inhibiting hormone (MSH-RIH) | Melanocyte stimulating hormone (MSH) secretion | Skin Pigment cells |
| 10. | Melanocyte stimulating hormone release-inhibiting hormone (MSH-RIH) | Melanocyte stimulating hormone secretion inhibited | —– |
1. Hypothalamus
It is situated at the base of the brain and is composed of nervous tissue. The neurosecretary cells of the hypothalamus secrete several neurohormones called Releasing Hormones (RH) and Inhibiting Factors or Hormones (IF or IH).
2. Pituitary gland (hypophysis)
Pituitary gland is present just below the brain. It is a small, red grey, pea-shaped gland attached to the hypothalamus of the brain by stalk or infundibulum.
The pituitary gland consists of three lobes-
1. Anterior lobe,
2. Intermediate lobe, and
3. Posterior lobe
All the three lobes of the pituitary secrete separate hormones.
3. Thyroid gland
It is the largest endocrine gland. It is a bilobed or H-shaped structure, situated in the neck region.
The endocrine gland secrets three hormones:
1. Thyroxine (T4)1,
2. Triiodothyronine (T3)2, and
3. Calcitonin
4. Parathyroid glands
These are four small, flat, oval glands situated on the posterior surface of the thyroid gland, two in each lobe of thyroid. They secrete parahormone (PTH). It is also called Collip’s hormone.
5. Adrenal glands
These are a pair of glands situated on upper side of each kidney. Therefore, they are also called suprarenals. Each endocrine gland has two distinct portions:
1. Outer adrenal cortex
2. Inner adrenal medulla
6. Pancreas
Pancreas lies below the stomach in the loop of duodenum part of small intestine. It is an elongated, yellowish heterocrine gland. Its exocrine part consists largely of lobules that secrete pancreatic juice which contains digestive enzymes (e.g., trypsin, amylase, lipase) for the digestion of proteins, carbohydrates and fats respectively.
Endocrine part of pancreas (Islets of Langerhans) secretes two hormones:
1. Insulin
2. Glucagon
7. Testes
In males, a pair of testes are extra abdominal in position and located in scrotum. Testes secrete male sex hormones (e.g., testosterone).
8. Ovaries
Unlike testes in males, a pair of ovaries lie in the abdomen in females. They secrete three female sex hormones:
1. Estrogen,
2. Progesterone,
3. Relaxin.
9. Pineal
It is a very small, reddish-grey, vascular, solid body lying between the two cerebral hemispheres of the brain. It secretes melatonin hormone. It regulates the working of gonads.
10. Thymus gland
It is situated in the upper chest near the front side of the heart. Thymus is soft, pinkish, bilobed structure and is a prominent gland in the young child. However, it gradually atrophies in the adult. It secretes thymosin hormone which stimulates the development and differentiation of lymphocytes and thereby increasing resistance to infection.
Q1. What is Stimuli and Coordinations?
Q2. Parts of Human nervous system?
Q3. Names Different Plant hormones?
3.Auxin , Gibberellins , Cytokinin ,Abscisic acid and Ethhene
Right answer
Homework
Ans1. A enviroment and enviromental factor is change and the all organisms are react are called stimuli.and the our body organs work various activities in organisms a proper manner help of stimuli is called coordination.
Ans2. The nervous system is produced good cell this cell are called nervous cell. And is sending electric signals are called electric impulses.
Ans3. Name the 5 plant hormones
(1) Ethene.
(2) Auxins.
(3)Gibberellins.
(4)Cytokins.
(5)Abscisic.
1.The changes in the environment to which the organisms respond and react is called stimuli.
The working together of various organs of a living organisms in a systematic, controlled and efficient way to produce proper response to various stimuli is known as coordination.
Ans2 Human nervous system consists of two main parts : 1)Central nervous system and 2)Peripheral nervous system