1. Need for Control and Coordination

Living organisms continuously respond to changes in their surroundings.

A stimulus is a change in the environment that produces a response.
The response must be controlled and appropriate to the stimulus.
In animals, control and coordination mainly involve the nervous system, muscles and hormones.
Plants lack a nervous system and muscles, so they coordinate mainly through chemical signals and growth-based movements.

2. Nervous System in Animals

Neuron

A neuron is the basic structural and functional unit of nervous tissue.

Path of a nerve impulse:

Dendrite → Cell body → Axon → Synapse → Next neuron / muscle / gland

Dendrites receive information.
The information is converted into an electrical impulse.
The impulse travels through the cell body and axon.
At the axon ending, chemicals are released.
These chemicals cross the synapse and initiate an impulse in the next neuron.

Synapse: The small gap between two neurons through which information is passed using chemical signals.

3. Reflex Action

A reflex action is a rapid response to a stimulus that does not require conscious thinking before the response occurs.

Example: Quickly withdrawing your hand after touching something hot.

Reflex Arc

The pathway followed during a reflex response is called a reflex arc.

Stimulus → Receptor → Sensory nerve → Spinal cord → Motor nerve → Muscle → Response

Reflex arcs are generally formed in the spinal cord.
They provide a quick response because the signal does not have to wait for detailed processing by the brain.
Information can still reach the brain afterward.

Reflex Action vs Walking

Reflex action	Walking
Very rapid response	Requires coordinated control
Usually automatic	Normally a voluntary action
Reflex arc is important	Brain coordinates the activity

4. Human Brain

The brain and spinal cord together form the central nervous system (CNS).

The peripheral nervous system (PNS) connects the CNS with the rest of the body through cranial and spinal nerves.

Major regions of the brain

Fore-brain

Main thinking region.
Receives sensory information.
Different areas process sensations such as sight, hearing and smell.
Association areas interpret information using present sensory input and stored information.
Helps make decisions and control voluntary movements.
Also contains a centre associated with hunger and feeling full.

Mid-brain and Hind-brain

They are involved in many involuntary activities.

Medulla (hind-brain):
Controls involuntary activities such as:

Blood pressure
Salivation
Vomiting

Cerebellum (hind-brain):

Maintains posture and balance.
Ensures precision and coordination of voluntary movements.
Important in activities such as cycling and picking up objects.

Protection of brain and spinal cord

Brain: Protected by the skull and a fluid-filled covering that helps absorb shocks.
Spinal cord: Protected by the vertebral column/backbone.

5. How Nervous Tissue Produces Movement

A nerve impulse reaching a muscle causes changes in special proteins inside muscle cells.

These proteins change their shape and arrangement, causing the muscle fibre to shorten and produce movement.

6. Coordination in Plants

Plants do not possess:

A nervous system
Muscles

Yet they respond to stimuli.

Plants show two broad types of movement:

A. Movement independent of growth

Example: Touch-me-not (Mimosa/chhui-mui) leaves fold when touched.

This response is rapid.
It does not depend on growth.
Information is transmitted through electrical-chemical signals from cell to cell.
Plant cells change shape by altering their water content, causing swelling or shrinking.

B. Movement dependent on growth

This occurs because different parts grow at different rates.

Example:

Tendrils coil around a support after contact.
Growth towards or away from environmental stimuli produces tropic movements.

7. Tropic Movements

Tropism = directional growth of a plant part in response to a stimulus.

Tropism	Stimulus	Example
Phototropism	Light	Shoot bends towards light
Geotropism	Gravity	Roots grow downward; shoots generally upward
Hydrotropism	Water	Directional growth in response to water
Chemotropism	Chemicals	Pollen tube grows towards ovule

A tropic movement may be towards or away from the stimulus.

Phototropism — key mechanism

When light comes from one side:

Auxin produced at shoot tip → moves towards shaded side → cells there elongate more → shoot bends towards light.

8. Plant Hormones

Plant hormones are chemical substances that coordinate growth, development and responses to the environment.

Hormone	Major function
Auxin	Promotes cell elongation; involved in phototropism
Gibberellins	Promote stem growth
Cytokinins	Promote cell division
Abscisic acid (ABA)	Inhibits growth; associated with leaf wilting

Plant hormones are produced at one location and can move to their site of action.

9. Nervous vs Chemical Coordination

Electrical coordination

Advantages: Very fast transmission.

Limitations:

Mainly reaches cells connected through nervous tissue.
A neuron needs time to reset before generating another impulse.

Chemical coordination

Hormones provide chemical communication.

Advantages:

Can reach cells throughout the body.
Can produce effects that are slower but more steady and persistent.
Does not require every target cell to have a nervous connection.

10. Hormones in Animals

Animal hormones are secreted by endocrine glands and form another major system of control and coordination.

Adrenaline — emergency response

Adrenaline is released by the adrenal glands during situations requiring rapid preparation for action.

It:

Increases heart rate.
Helps supply more oxygen to muscles.
Diverts blood away from digestive organs and skin towards skeletal muscles.
Increases breathing rate.

Thus, the body becomes prepared to respond to a threatening situation.

11. Important Animal Hormones

Hormone	Source	Main role
Growth hormone	Pituitary	Promotes growth and development
Thyroxin	Thyroid	Regulates metabolism
Insulin	Pancreas	Regulates blood glucose
Testosterone	Testes	Associated with male reproductive development and puberty changes
Oestrogen	Ovaries	Associated with female reproductive development and related functions
Adrenaline	Adrenal glands	Prepares body for emergency activity

The chapter specifically links growth hormone deficiency during childhood with dwarfism and explains that iodine is necessary for production of thyroxin.

12. Iodine, Thyroxin and Goitre

Iodine → required for thyroxin synthesis → thyroxin regulates metabolism → supports proper growth and development.

If the diet lacks sufficient iodine, goitre may occur, one feature being swelling of the neck. Therefore, iodised salt is recommended as a source of dietary iodine.

13. Insulin and Blood Sugar

Insulin is produced by the pancreas.
It helps regulate blood glucose levels.
When blood sugar rises, pancreatic cells respond by producing more insulin.
As blood sugar decreases, insulin secretion decreases.

This is an example of a feedback mechanism controlling hormone secretion.

14. Feedback Mechanism

Hormones must be released in the correct amount and at the appropriate time.

A feedback mechanism helps regulate hormone secretion.

Example:

Blood glucose rises → more insulin released → blood glucose falls → insulin secretion decreases

This prevents excessive hormonal activity and helps maintain proper internal conditions.

⭐ High-Yield Differences

Reflex vs Involuntary Action

Reflex action

Rapid response to a stimulus.
Reflex pathway is involved.
Example: withdrawing hand from a hot object.

Involuntary action

Happens without conscious control.
Includes processes such as heartbeat, digestion-related activities and blood pressure regulation.
Many are controlled by parts of the brain such as the medulla.

Sensitive Plant vs Human Leg Movement

Sensitive plant:

No muscles or nervous system.
Uses electrical-chemical signalling.
Cells change shape through changes in water content.

Human leg:

Nervous system sends signals.
Muscles respond to nerve impulses.
Muscle proteins change arrangement, causing contraction.

🧠 Chapter in One Flow

Stimulus
↓
Receptor detects change
↓
Information transmitted
↓
Coordination centre / chemical signal processes information
↓
Response produced

Animals

Stimulus → Receptor → Nervous system / hormones → Muscles or glands → Response

Plants

Stimulus → Electrical/chemical signalling → Growth or water-content changes → Response

🎯 Must-Remember for Exams

Feedback mechanism = regulates hormone secretion.
Neuron = basic unit of nervous tissue.
Synapse = gap between neurons.
Reflex arc = pathway involved in rapid reflex response.
CNS = brain + spinal cord.
Cerebellum = posture, balance and precision of voluntary movement.
Medulla = important involuntary functions.
Phototropism = response to light through directional growth.
Geotropism = response to gravity.
Auxin = important in shoot growth and phototropism.
Cytokinins = cell division.
ABA = growth inhibitor.
Adrenaline = prepares body for emergency action.
Thyroxin = metabolism; iodine is needed for its synthesis.
Growth hormone = body growth and development.
Insulin = blood-glucose regulation.