Control and Coordination

1. The Nature and Necessity of Movement

Movement is an important characteristic of living organisms. It may occur because of growth or due to a response to changes in the surroundings.

Movement: A change in position or activity of an organism or one of its parts.

Types of Movement

Growth-Dependent Movement

Movements caused by growth in a particular direction.

Example: A germinating seed pushing through the soil.

Growth-Independent Movement

Movements that do not result from growth.

Examples: A cat running or buffaloes chewing cud.

Movement as a Response

Movements are controlled responses to environmental changes. These responses generally help the organism survive or perform necessary functions.

Sunlight: Plants grow towards light to increase photosynthesis.
Protection: We withdraw our hand from a hot object and blink in bright light.
Functional needs: Buffaloes chew cud to help break down tough food.

Different environmental changes require different responses. Therefore, organisms need specialised tissues for recognising stimuli and coordinating suitable actions.

2. Animal Nervous System

In animals, coordination is mainly carried out by two specialised tissues:

Nervous tissue for receiving and transmitting information.
Muscular tissue for producing movement.

Sensory Receptors

Receptors are specialised nerve-cell endings that detect changes in the environment. They are present in sense organs such as the eyes, ears, nose, tongue and skin.

Gustatory receptors: Detect taste.
Olfactory receptors: Detect smell.

Taste and smell work together. This is why food may taste different when the nose is blocked.

The Neuron

The neuron is the structural and functional unit of the nervous system.

Main Parts of a Neuron

Dendrites: Receive information or stimuli.

Cell body: Contains the nucleus and coordinates cellular activities.

Axon: Carries the electrical impulse away from the cell body.

Nerve ending: Releases chemicals to transmit the signal to the next cell.

Transmission of a Nerve Impulse

1. Information is received at the dendritic tip.

2. A chemical reaction generates an electrical impulse.

3. The impulse travels through the dendrite and cell body.

4. The impulse moves along the axon.

5. Chemicals are released at the nerve ending.

6. These chemicals cross the gap and start a new electrical impulse in the next neuron.

Synapse

A synapse is the small gap between two neurons across which chemical signals transmit the nerve impulse.

Neuromuscular Junction

A neuromuscular junction is a similar connection between a neuron and a muscle cell. It allows a nerve impulse to produce muscular movement.

3. Reflex Actions and Reflex Arc

Reflex action: A sudden and automatic response to a stimulus that occurs without conscious thinking.

Why Are Reflex Actions Necessary?

Thinking involves complex networks of neurons in the fore-brain. This process takes time. In dangerous situations, waiting for conscious thinking may result in injury.

Therefore, quick responses are coordinated through the spinal cord.

Reflex Arc

The pathway followed by a nerve impulse during a reflex action is called the reflex arc.

Receptor → Sensory Neuron → Relay Neuron → Motor Neuron → Effector

Example: Withdrawing the Hand from a Hot Object

1. Heat or pain receptors in the skin detect the stimulus.

2. The sensory neuron carries the impulse to the spinal cord.

3. A relay neuron in the spinal cord passes the impulse onward.

4. The motor neuron carries the impulse to the arm muscle.

5. The muscle contracts and the hand is withdrawn.

Reflex arcs evolved because the brain's thinking process is not fast enough to handle certain immediate dangers.

4. Human Brain and Nervous System

The brain is the main coordinating centre of the human body.

Central Nervous System

Consists of the:

Brain
Spinal cord

Peripheral Nervous System

Connects the central nervous system to the rest of the body through:

Cranial nerves
Spinal nerves

Protection of the Nervous System

The brain is protected by the bony cranium or skull.
The brain is surrounded by a fluid-filled protective covering that absorbs shocks.
The spinal cord is protected by the vertebral column.

5. Functional Regions of the Brain

Fore-brain

The fore-brain is the main thinking and voluntary control centre.

Controls voluntary actions.
Contains areas responsible for hearing, smell and sight.
Contains association areas that interpret sensory information.
Uses memory and information from different receptors.
Contains motor areas controlling voluntary movements.
Includes a centre related to hunger and feeling full.

Mid-brain

The mid-brain helps control several involuntary responses and connects different parts of the brain.

Hind-brain

The hind-brain controls many involuntary activities and helps maintain balance and coordination.

Part	Main Functions
Medulla	Controls involuntary actions such as blood pressure, salivation and vomiting.
Cerebellum	Maintains posture, balance and precision of voluntary movements.
Mid-brain	Controls certain involuntary responses and helps coordinate signals.

Activities such as riding a bicycle, writing neatly and picking up a pencil require the cerebellum for precision and balance.

6. How Do Muscles Produce Movement?

Muscles produce movement by shortening their cells.

Special proteins present inside muscle cells change their shape and arrangement when stimulated by electrical impulses from nerves.

Nervous electrical impulse reaches the muscle.

Special muscle proteins respond to the impulse.

The muscle cells shorten.

The attached body part moves.

7. Coordination in Plants

Plants do not possess a nervous system or muscles. However, they respond to stimuli using electrical and chemical methods.

Immediate Plant Responses

Some plant movements are rapid and do not depend on growth.

Example: The leaves of Mimosa pudica fold when touched.

This movement occurs because plant cells change their water content. Cells swell or shrink, causing movement in a different part of the plant from the point of touch.

Growth-Related Plant Responses

Directional growth movements in response to stimuli are called tropic movements.

Type of Tropism	Stimulus	Example
Phototropism	Light	Shoots grow towards light; roots generally grow away from light.
Geotropism	Gravity	Roots grow towards gravity; shoots grow away from gravity.
Hydrotropism	Water	Roots grow towards water.
Chemotropism	Chemicals	Pollen tubes grow towards ovules.
Thigmotropism	Touch	Tendrils coil around a support.

Thigmotropism in Tendrils

When a tendril touches a support, the side in contact grows more slowly than the outer side. This unequal growth causes the tendril to bend, circle and cling to the support.

8. Plant Hormones

Plant hormones, also called phytohormones, are chemical substances produced in one part of a plant and transported to their site of action mainly by diffusion.

Hormone	Source or Location	Function
Auxin	Shoot tip	Promotes cell elongation and helps shoots bend towards light.
Gibberellins	Growing regions	Promote stem growth.
Cytokinins	Fruits and seeds	Promote cell division.
Abscisic Acid	Various plant parts	Acts as a growth inhibitor and causes wilting of leaves.

Role of Auxin in Phototropism

1. Auxin is produced at the shoot tip.

2. Light causes auxin to accumulate more on the shady side.

3. Cells on the shady side elongate more.

4. The shoot bends towards the light.

9. Animal Hormones and Endocrine System

Nervous impulses are fast but reach only cells connected by nervous tissue. Hormones provide chemical communication through the blood and can affect target organs for a longer duration.

Hormones: Chemical messengers secreted by endocrine glands and transported through the blood to specific target organs.

Important Animal Hormones

Hormone	Gland	Function
Adrenaline	Adrenal glands	Prepares the body for emergency situations.
Thyroxine	Thyroid gland	Regulates metabolism of carbohydrates, proteins and fats.
Growth Hormone	Pituitary gland	Controls growth and development.
Testosterone	Testes	Produces male pubertal changes.
Oestrogen	Ovaries	Produces female pubertal changes.
Insulin	Pancreas	Regulates blood glucose level.

Adrenaline: Fight-or-Flight Hormone

Adrenaline is secreted during stress, fear, anger or emergencies.

Increases heart rate.
Increases breathing rate.
Increases blood supply to skeletal muscles.
Diverts blood away from the skin and digestive system.
Helps the body prepare for immediate action.

Thyroxine

Thyroxine is secreted by the thyroid gland and controls the metabolism of carbohydrates, proteins and fats.

Iodine is essential for the production of thyroxine. Iodine deficiency may cause enlargement of the thyroid gland, known as goitre.

Growth Hormone

Secreted by the pituitary gland.
Deficiency during childhood may cause dwarfism.
Excess secretion may cause gigantism.

Puberty Hormones

Testosterone: Secreted by testes and produces male secondary sexual characteristics.
Oestrogen: Secreted by ovaries and produces female secondary sexual characteristics.

Insulin

Insulin is secreted by the pancreas and controls the amount of glucose in the blood.

Lack of insulin can result in increased blood glucose levels and may cause diabetes.

Hypothalamus and Pituitary Gland

The hypothalamus releases releasing hormones that stimulate the pituitary gland to secrete its hormones.

For example, Growth Hormone Releasing Factor stimulates the pituitary gland to release growth hormone.

10. Feedback Mechanism

Hormone secretion must be controlled carefully so that the correct quantity is released at the correct time.

Example: Regulation of Blood Sugar

1. Blood glucose level rises.

2. Pancreatic cells detect the increase.

3. More insulin is secreted.

4. Cells take up more glucose and blood sugar decreases.

5. As glucose reaches a normal level, insulin secretion is reduced.

Feedback mechanism: A regulatory process in which the level of a substance controls the further release of a hormone responsible for regulating it.

11. Nervous Control vs Hormonal Control

Feature	Nervous Control	Hormonal Control
Type of signal	Electrical impulses and chemicals	Chemical hormones
Transport	Through neurons	Through blood
Speed	Very fast	Usually slower
Duration	Usually short-lived	Often longer-lasting
Area of effect	Specific connected cells	Target organs throughout the body

12. Quick Revision

Neuron

Structural and functional unit of the nervous system.

Synapse

Gap between two neurons through which chemical signals pass.

Reflex Arc

Receptor → Sensory neuron → Relay neuron → Motor neuron → Effector.

Fore-brain

Thinking, interpretation and voluntary actions.

Cerebellum

Balance, posture and precision of movement.

Medulla

Controls involuntary actions such as blood pressure and vomiting.

Auxin

Promotes cell elongation and phototropic bending.

Adrenaline

Emergency hormone responsible for the fight-or-flight response.

Thyroxine

Controls metabolism and requires iodine.

Insulin

Regulates blood glucose level.

Phototropism

Growth movement in response to light.

Feedback Mechanism

Controls the quantity and timing of hormone secretion.