CBSE Class 10 Science Control And Coordination Notes Set 07

QUICK RECAP

All movements in living organisms occur in response to changes in the environmental factors. All living organisms respond and react to environmental factors (stimuli) such as light, heat, cold, sound, smell, taste, pressure, etc., and this response involves coordination of many organs in our body.

Coordination in animals: Unicellular organisms respond to environmental stimuli by moving towards or away from it. Such response is termed as taxis. Movement towards the source of stimulus is positive taxis and movement away from stimulus is negative taxis. In lower multicellular organisms, coordination takes place through nervous system.

Control and coordination in humans: There are two systems of coordination of activities in humans: nervous system and endocrine system. Both the systems of coordination consist of a number of organs working together in a systematic way.

Human Nervous System: Human nervous system is the most complex system. The main parts of the nervous system are: brain, spinal cord and nerves. The sense organs can be considered to be other organs of the nervous system because they help in the functioning of the nervous system. We receive a variety of information from the environment around us through the sense organs. There are five sense organs in our body: eyes, ears, nose, tongue and skin.

The sense organs contain receptors. A receptor is a cell (or a group of cells) in a sense organ which is sensitive to a particular type of stimulus. Different sense organs contain receptors for detecting different stimuli.

• The common types of receptor are photoreceptors (detect light, present in eyes), phonoreceptors (detect sound, present in ears), olfactory receptors (detect smell, present in nose), gustatory receptors (detect taste, present in tongue) and thermoreceptors (detect heat or cold, present in skin).
• Neurons are the structural and functional unit of nervous system. Neuron is the longest cell in human body.

Components of Neuron

• Cell body: The cell body of a neuron is also called cyton which is broad, rounded, pyriform or stellate part of the neuron. It has abundant cytoplasm, called neuroplasm which contains Nissl’s granules and a relatively large, spherical nucleus and is mainly concerned with metabolic maintenance and growth. It also receives nerve impulses from dendrites and transmits them to axon.
• Dendrites: These are several short, tapering, much branched protoplasmic processes stretching out from the cell body of a neuron. Here sensation (information) is acquired which then travels as an electric impulse towards the cell body.
• Axon: It is a single, very long, cylindrical nerve fibre of uniform diameter arising from the cell body. At its terminal end, axon is highly branched. Axon terminals are often knob-like and these may end in nerve fibres that form synapses with dendrites of other neurons. The axon conducts nerve impulses away from the cell body.

Types of neuron

• Sensory (receptor): Transmits impulse from sensory cells to CNS.
• Motor (effector): Transmits impulse from CNS to muscle cells.
• Relay or Connector: Serves as link between sensory and motor neurons.

Nervous System Classification

• Central Nervous System (CNS): Consists of the Brain and Spinal Cord.
• Peripheral Nervous System (PNS): Consists of nerves arising from the CNS.

Central Nervous System (CNS)

Brain:

• Brain is the highest coordinating centre in the body. The brain is located inside the skull of our body (at the top of the spinal cord). It is protected by a bony box in the skull called cranium. It is surrounded by three membranes called meninges, which help to protect it. The space between the membranes (or meninges) is filled with a cerebro-spinal fluid which protects the brain from mechanical shocks. Pairs of cranial nerves arise from the brain.
• The brain is broadly divided into three regions: forebrain, midbrain and the hindbrain. The forebrain consists mainly of cerebrum. The midbrain does not have any further divisions. It consists of two fibre tracts called crura cerebri which connect hindbrain with forebrain. The hindbrain consists of three parts called pons, cerebellum and medulla.
• The cerebrum (or forebrain) is the main thinking part of the brain. It is the site of our faculties such as learning, reasoning, intelligence, personality and memory. All our thoughts, sensations, actions and movements are controlled by the cerebrum.
• The midbrain controls reflex movements of the head, neck and trunk in response to visual and auditory stimuli. It also controls the reflex movements of the eye muscles, changes in pupil size and shape of the eye lens.
• Pons varolii takes part in regulating respiration.
• Cerebellum helps in maintaining posture and balance of the body.
• Medulla oblongata controls various involuntary actions such as heart beat (blood circulation), breathing, blood pressure and peristaltic movements of alimentary canal. Medulla is also the controlling centre for reflexes such as swallowing, coughing, sneezing, secretion of saliva and vomiting.

Spinal cord:

Spinal cord is a cylindrical structure that begins in continuation with the medulla oblongata of brain and extends downwards upto early part of lumbar region. It then extends to the end of vertebral column as fibrous connective. It is enclosed in a bony cage called vertebral column. Spinal cord is also surrounded by membranes called meninges. As many as 31 pairs of nerves arise from the spinal cord. The spinal cord is concerned with spinal reflex actions and the conduction of nerve impulses to and from the brain. Spinal cord performs two important functions: it conducts sensory and motor impulses to and from the brain and it acts as a centre for the reflex actions. Thus, it reduces brain’s work.

Reflex action and reflex arcs: The simplest form of response in the nervous system is reflex action. This is a rapid, automatic response to a stimulus which is not under the voluntary control of the brain. It is described as an involuntary action which aims to protect ourselves. A knee jerk, movement of diaphragm (during respiration), coughing, yawning, blinking of eyes and sneezing are all reflex actions. Coughing is a reflex action which clears our windpipe. The pupils of our eyes get smaller in bright light. This protects the retina of our eyes from damage due to too much light.

Reflex Arc: The pathway taken by nerve impulses in a reflex action is called the reflex arc. Reflex arcs allow rapid response.

Depicting a reflex action:
Stimulus received by the receptor (sensory neurons)
\( \implies \) Spinal cord (Relay neuron)
\( \implies \) Motor neuron
\( \implies \) Effector (Muscle or gland)

Human Endocrine System

Endocrine system is comprised of endocrine glands and the hormones released by them.

Hormones: These are the chemical substances which coordinate the activities of living organisms and also their growth. The various characteristics of hormones are:

• They are secreted in small amounts by the endocrine glands.
• They are poured directly into the blood and carried throughout the body by circulatory system.
• They have their effects at the sites different from the sites where they are made. So, they are also called chemical messengers.
• They act on specific tissues or organs (called target organs).
• They coordinate the activities of the body and also its growth.

Endocrine glands: A gland is a structure (cell, tissue or organ) which secretes certain useful chemicals or substances in the body. There are two types of gland in the body: exocrine gland and endocrine gland. Exocrine glands are the glands having ducts whereas endocrine glands are ductless glands.

Table: Endocrine glands – Their hormones and functions

• Hypothalamus:
  (a) Releasing hormones (RH): Stimulate anterior/ intermediate pituitary to secrete hormones.
  (b) Inhibiting hormones (IH): Inhibit the secretion of hormones from anterior / intermediate pituitary gland.
• Pituitary gland: (Attached to the lower surface of the brain).
  (a) Growth hormone (GH): Controls the overall development or growth of the body, muscles, bones and tissues. Lack of this hormone (hypoactivity) causes dwarfness. Its excessive secretion (hyperactivity) causes excessive growth of bones making the person very tall (gigantism).
  (b) Thyroid stimulating hormone (TSH): Controls the growth and functioning of the thyroid gland. Stimulates the thyroid gland to produce thyroxine.
• Thyroid gland: (Situated in the neck region).
  (a) Thyroxine or \( T_4 \) and Triiodothyronine or \( T_3 \): \( T_3 \) and \( T_4 \) stimulate the rate of cellular oxidation and metabolism.
  (b) Calcitonin: Calcitonin lowers calcium level by suppressing release of calcium ions from the bones, when calcium level is high in blood.
• Adrenal gland: (A pair on top of each kidney). Hormones adrenaline (stress hormone) and nor-adrenaline are secreted by adrenal medulla.
• Pancreas: (Compound gland posterior to stomach).
  (a) Insulin: Regulates the conversion of glucose to glycogen, i.e., it lowers blood glucose level.
  (b) Glucagon: Regulates the conversion of glycogen back to glucose, i.e., it increases blood glucose level.
• Ovaries: (Pair in the lower abdominal region in females).
  (a) Estrogen: Plays an important role in ovulation. It is responsible for development of secondary sexual characteristics in females like mammary glands, voice, hair pattern, etc.
  (b) Progesterone: Helps in the preparation of uterus for the reception of fertilised ovum. Also helps in the maintenance of pregnancy.
• Testes: (Extra-abdominal). Testosterone: Stimulates spermatogenesis, regulates the growth, development and functioning of accessory sex organs and controls the secondary sexual characteristics in males, such as enlargement of penis and scrotum, growth of facial and pubic hair and enlargement of larynx that causes deepening of voice.

Feedback mechanism: The timing and amount of hormones released by various glands are controlled by the ‘feedback mechanism’ which is in-built in our body. For example, if the sugar level in the blood rises too much, they are detected by the cells of pancreas which respond by producing and secreting more insulin into blood. And as the blood sugar falls to a certain level, the secretion of insulin is reduced automatically.

Control and coordination in plants

Plants coordinate their behaviour against environmental changes by using hormones. The hormones in plants coordinate their behaviour by affecting their growth. And the effect on growth of the plant can result in the movement of its part like shoot (stem) or root, etc. The plants respond to various stimuli very slowly by growing. Hence, in most of the cases, the response of a plant to a stimulus cannot be observed immediately. It usually takes a considerable time to observe the effect of a stimulus on a plant.

Plant hormones (or Phytohormones): The plant hormones coordinate the activities of the plant by controlling one or the other aspect of the growth of the plant. So, they are also known as plant growth substances. The growth of a plant can be divided into three stages: cell division, cell enlargement and cell differentiation (or cell specialisation).

Plant hormones and their functions

• Auxins: These promote cell enlargement and cell differentiation in plants. They promote stem and fruit growth. They regulate important plant growth movements, i.e., tropisms. They induce parthenocarpy (i.e., the formation of seedless fruits without fertilisation) in number of plants.
• Gibberellins: These promote cell enlargement and cell differentiation in plants in the presence of auxins. They also promote growth in stems and fruits. Rossette plants show bolting and flowering when treated with gibberellins. They also induce parthenocarpy in many plants.
• Cytokinins: These promote cell division in plants. They play vital role in the morphogenesis in plants. They help in breaking the dormancy of seeds and buds. They delay the ageing in leaves. They promote the opening of stomata. They also promote fruit growth.
• Ethylene: It is largely an inhibitor of growth activities. It helps in ripening of fruits and 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.
• Abscisic acid (ABA): It promotes the dormancy in seeds and buds and thus inhibits growth. It also promotes the closing of stomata and thus affects wilting of leaves. It also promotes the falling of leaves (abscission) and senescence in leaves.

Plant movements

Plants do not show locomotion (movement of the entire body). However, movements of the individual parts or organs of a plant (like shoot, root, leaves, etc.) are possible when they are subjected to some external stimuli like light, force of gravity, chemical substances, water and touch, etc. These movements of the plant parts are usually caused by an unequal growth in their two regions by the action of plant hormones, under the influence of the stimulus. When a plant part shows movement, it remains attached to the main body of the plant.

Types of plant movements:

• Nastic movements: Movements independent of growth.
  • Seismonastic movements: Such movements occur in response to touch (shock). These movements are very quick and are best seen in ‘touch-me-not’ plant (Mimosa pudica).
• Tropic movements: Movements due to growth.
  • Phototropism: Directional movement or orientation of the plant part in response to light stimulus. Stem shows positive phototropism; roots show negative phototropism.
  • Geotropism: Directional movement or orientation of the plant part in response to gravity. Roots show positive geotropism; stems show negative geotropism.
  • Chemotropism: Directional movement or orientation of the plant part in response to chemical stimulus. Example: Growth of pollen tube towards the ovule.
  • Hydrotropism: Directional movement or orientation of the plant part in response to water stimulus. Bending of roots towards water signifies positive hydrotropism.