INTRODUCTION — HOW DO LIVING ORGANISMS RESPOND?
Every living organism continuously interacts with its
surroundings. A cat runs after a mouse, plants bend towards sunlight, and we
quickly pull our hand away after touching a hot object. These responses do not
happen randomly. They are carefully controlled and coordinated.
Living organisms must:
- Detect
changes in the environment
- Process
the information
- Produce
an appropriate response
This entire process is called:
Control and Coordination
WHY IS CONTROL AND COORDINATION NECESSARY?
Different activities inside the body must work together in a
proper manner.
For example:
- Muscles
should move only when needed.
- Eyes
should blink when bright light falls.
- We
should move away from danger quickly.
- Plants
should grow towards sunlight.
Without coordination:
- Body
organs would not function properly.
- Responses
would become slow and unorganised.
- Survival
would become difficult.
CONTROL AND COORDINATION IN ANIMALS
Animals perform control and coordination mainly through:
- Nervous
System
- Endocrine
System (Hormonal System)
6.1 ANIMALS – NERVOUS SYSTEM
The nervous system controls:
- Movement
- Sensations
- Thinking
- Memory
- Coordination
of body organs
It helps the body react quickly to changes in surroundings.
WHAT HAPPENS WHEN WE TOUCH A HOT OBJECT?
Suppose you accidentally touch a hot pan.
Immediately:
- Skin
detects heat.
- Message
travels through nerves.
- Hand
pulls back quickly.
This rapid response protects the body from injury.
NEURON — STRUCTURAL UNIT OF NERVOUS SYSTEM
The nervous system is made up of specialised cells called:
Neurons (Nerve Cells)
STRUCTURE OF A NEURON
A neuron consists of:
|
Part |
Function |
|
Dendrites |
Receive information |
|
Cell body |
Processes information |
|
Axon |
Carries impulses away |
|
Nerve ending |
Transfers message |
HOW DOES A NERVE IMPULSE TRAVEL?
- Stimulus
is received by dendrites.
- Electrical
impulse is generated.
- Impulse
travels through axon.
- Chemicals
are released at nerve ending.
- Message
passes to next neuron.
SYNAPSE
The tiny gap between two neurons is called:
Synapse
At the synapse:
- Electrical
signal converts into chemical signal.
- Chemicals
carry message across gap.
TYPES OF RECEPTORS
Receptors detect different stimuli.
|
Receptor Type |
Function |
|
Gustatory receptors |
Detect taste |
|
Olfactory receptors |
Detect smell |
|
Photoreceptors |
Detect light |
|
Auditory receptors |
Detect sound |
ACTIVITY 6.1 — ROLE OF SMELL IN TASTE
Experiment
- Put
sugar in mouth and taste it.
- Now
block your nose and taste again.
Observation
Taste becomes weaker when nose is blocked.
Conclusion
Smell helps us experience taste properly.
This is why food tastes less when we have a cold.
REFLEX ACTION
A sudden, automatic, and immediate response to a stimulus is
called:
Reflex Action
Examples:
- Pulling
hand away from flame
- Blinking
eyes
- Sneezing
- Knee-jerk
reaction
WHY ARE REFLEX ACTIONS IMPORTANT?
Reflex actions protect the body from harm.
They are:
- Fast
- Automatic
- Do
not require thinking
If we waited for the brain to think before reacting, injury
could occur.
REFLEX ARC
The pathway followed during reflex action is called:
Reflex Arc
PATH OF REFLEX ARC
Stimulus → Receptor → Sensory neuron → Spinal cord → Motor
neuron → Effector organ
ROLE OF SPINAL CORD IN REFLEX ACTION
Reflex actions are mainly controlled by:
Spinal Cord
The brain receives information later, but the spinal cord
gives immediate response for quick protection.
EXAMPLE — TOUCHING A HOT OBJECT
- Skin
receptors detect heat.
- Message
goes to spinal cord.
- Spinal
cord sends response.
- Muscles
pull hand away.
This happens instantly without conscious thinking.
HUMAN BRAIN — CONTROL CENTRE OF BODY
The brain is the main coordinating centre of the body.
The:
- Brain
- Spinal
cord
together form the:
Central Nervous System (CNS)
PERIPHERAL NERVOUS SYSTEM
The nerves arising from:
- Brain
→ Cranial nerves
- Spinal
cord → Spinal nerves
form the:
Peripheral Nervous System
It connects CNS to body organs.
MAJOR PARTS OF THE HUMAN BRAIN
The brain has three major regions:
|
Brain Part |
Main Function |
|
Forebrain |
Thinking and intelligence |
|
Midbrain |
Relay centre |
|
Hindbrain |
Balance and involuntary actions |
FOREBRAIN
The forebrain is the:
Thinking part of brain
Functions:
- Intelligence
- Memory
- Decision
making
- Interpretation
of sensory information
Different regions are specialised for:
- Sight
- Hearing
- Smell
- Taste
VOLUNTARY ACTIONS
Actions performed under conscious control are called:
Voluntary Actions
Examples:
- Writing
- Speaking
- Walking
- Clapping
These are controlled by the forebrain.
HUNGER CENTRE
A special area in forebrain controls:
Hunger sensation
This tells us when we feel hungry or full.
MIDBRAIN
The midbrain helps in:
- Relay
of impulses
- Control
of some involuntary actions
HINDBRAIN
The hindbrain includes:
- Cerebellum
- Pons
- Medulla
CEREBELLUM
Functions:
- Maintains
balance
- Maintains
posture
- Coordinates
muscular movement
Examples:
- Riding
bicycle
- Walking
straight
- Picking
up objects
MEDULLA
The medulla controls involuntary activities such as:
- Breathing
- Heartbeat
- Blood
pressure
- Salivation
- Vomiting
These actions continue automatically without conscious
control.
INVOLUNTARY ACTIONS
Actions not controlled by conscious thinking are called:
Involuntary Actions
Examples:
- Heartbeat
- Digestion
- Breathing
HOW ARE BRAIN AND SPINAL CORD PROTECTED?
Since the nervous system is delicate, the body provides
protection.
PROTECTION OF BRAIN
The brain is protected by:
- Skull
(cranium)
- Fluid
called cerebrospinal fluid
The fluid acts as:
Shock Absorber
PROTECTION OF SPINAL CORD
The spinal cord is protected by:
Vertebral Column (Backbone)
HOW DO MUSCLES PRODUCE MOVEMENT?
Muscles contain special proteins.
When nerve impulses reach muscles:
- Proteins
change arrangement.
- Muscle
fibres shorten.
- Movement
occurs.
VOLUNTARY VS INVOLUNTARY MUSCLES
|
Voluntary Muscles |
Involuntary Muscles |
|
Under conscious control |
Not under conscious control |
|
Example: Hand muscles |
Example: Stomach muscles |
6.2 COORDINATION IN PLANTS
Plants do not have:
- Brain
- Nerves
- Muscles
Yet they respond to stimuli.
Examples:
- Touch-me-not
plant folds leaves
- Shoots
bend towards sunlight
- Roots
grow downward
TYPES OF MOVEMENTS IN PLANTS
|
Type |
Example |
|
Growth-dependent movement |
Phototropism |
|
Growth-independent movement |
Folding of Mimosa leaves |
IMMEDIATE RESPONSE TO STIMULUS
The touch-me-not plant (Mimosa) folds its leaves when
touched.
Features
- Rapid
movement
- No
growth involved
HOW DOES MIMOSA SHOW MOVEMENT?
Plants use:
Electrochemical Signals
Plant cells change shape by:
- Gaining
water
- Losing
water
This causes:
- Swelling
- Shrinking
leading to movement.
MOVEMENT DUE TO GROWTH
Some plant movements occur due to unequal growth.
Example:
Tendrils of pea plant
When tendrils touch support:
- Side
touching support grows slowly.
- Opposite
side grows faster.
- Tendril
coils around support.
TROPISM
Directional growth movement in response to stimulus is
called:
Tropism
TYPES OF TROPISM
|
Tropism |
Stimulus |
|
Phototropism |
Light |
|
Geotropism |
Gravity |
|
Hydrotropism |
Water |
|
Chemotropism |
Chemicals |
PHOTOTROPISM
Movement in response to light.
Example
- Shoot
bends towards light.
- Roots
bend away from light.
GEOTROPISM
Movement in response to gravity.
Example
- Roots
grow downward
- Shoots
grow upward
CHEMOTROPISM
Movement in response to chemicals.
Example
Pollen tube grows towards ovule.
ACTIVITY 6.2 — PHOTOTROPISM
Observation
- Shoots
bend towards light.
- Roots
bend away from light.
Conclusion
Plants show directional growth in response to light.
PLANT HORMONES
Plants coordinate activities using chemicals called:
Plant Hormones
These regulate:
- Growth
- Development
- Responses
to environment
AUXINS
Auxins are growth-promoting hormones.
Function
- Promote
cell elongation
- Help
shoots bend towards light
HOW AUXINS CAUSE PHOTOTROPISM
When light falls from one side:
- Auxin
moves to shaded side.
- Cells
on shaded side grow faster.
- Shoot
bends towards light.
GIBBERELLINS
Functions:
- Promote
stem growth
- Increase
plant height
CYTOKININS
Functions:
- Promote
cell division
- Found
in fruits and seeds
ABSCISIC ACID
A growth-inhibiting hormone.
Functions:
- Stops
growth
- Causes
wilting of leaves
DIFFERENCE BETWEEN NERVOUS AND HORMONAL COMMUNICATION
|
Nervous Communication |
Hormonal Communication |
|
Fast |
Slow |
|
Uses electrical impulses |
Uses chemicals |
|
Short-lasting effect |
Long-lasting effect |
6.3 HORMONES IN ANIMALS
Animals also use chemical coordination through:
Hormones
Hormones are secreted by:
Endocrine glands
ADRENALINE — EMERGENCY HORMONE
When we face danger:
- Heart
beats faster
- Breathing
increases
- More
blood reaches muscles
This is due to:
Adrenaline
secreted by adrenal glands.
FUNCTIONS OF ADRENALINE
- Prepares
body for emergency
- Increases
heartbeat
- Increases
breathing rate
- Supplies
more oxygen to muscles
This is called:
Fight or Flight Response
ENDOCRINE GLANDS
Major endocrine glands:
- Pituitary
gland
- Thyroid
gland
- Pancreas
- Adrenal
glands
- Testes
- Ovaries
THYROXIN
Secreted by:
Thyroid Gland
Functions:
- Regulates
metabolism
- Helps
body growth
ROLE OF IODINE
Iodine is necessary for synthesis of thyroxin.
Deficiency causes:
Goitre
Symptoms:
- Swollen
neck
This is why:
Iodised salt is important.
GROWTH HORMONE
Secreted by:
Pituitary Gland
Functions:
- Controls
growth and development
DWARFISM
Deficiency of growth hormone during childhood causes:
Dwarfism
PUBERTY HORMONES
|
Hormone |
Secreted By |
Function |
|
Testosterone |
Testes |
Male characteristics |
|
Oestrogen |
Ovaries |
Female characteristics |
These hormones bring changes during puberty.
INSULIN
Secreted by:
Pancreas
Function:
- Controls
blood sugar level
DIABETES
If insulin secretion is insufficient:
- Blood
sugar rises
- Diabetes
occurs
Patients may require:
Insulin injections
FEEDBACK MECHANISM
Hormone secretion is controlled by:
Feedback Mechanism
Example:
- High
blood sugar → More insulin secreted
- Low
blood sugar → Less insulin secreted
IMPORTANT HORMONES AND FUNCTIONS
|
Hormone |
Gland |
Function |
|
Growth hormone |
Pituitary |
Growth |
|
Thyroxin |
Thyroid |
Metabolism |
|
Insulin |
Pancreas |
Blood sugar control |
|
Testosterone |
Testes |
Male characters |
|
Oestrogen |
Ovaries |
Female characters |
|
Adrenaline |
Adrenal gland |
Emergency response |
