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Living organisms respond to change in

the internal environment and the

external environment.

Stimulus (plural:stimuli) change in

the external environment or in the

internal environment

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Response and Coordination

Animals need to

respond because :

Adapt to environment

Protection fromdanger

Safety (move to safer

place)

Regulate internal

environment(homeostasis)

Plants need to

respond because :

Receive more

sunlight for

photosynthesis

Obtain bettersupport

Obtain enough water

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Stimuli and Response

Stimuli

External stimuli changes that occur in

external environment e.g light, sound,

smell, taste, temperature, pressure, touch Internal stimuli changes in the internal

environment of the body e.g sugar level,

body temperature, osmotic pressure of

blood

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Detecting and Responding to

External Stimuli

Organisms have specialised group of

cell (receptors) that detect stimulus in

the afferent neuron.

One receptorforone stimulus.

Receptor will generate nerve impulse

transmitted to the central nervous

system via the afferent neurone. Effectorwill produce response.

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Detecting and Responding to

External Stimuli

The nervous system (integrating centre)

interpret nerve impulses and then

transmit nerve impulses to effectorto

produce response. Impulse from receptoris transmitted

by afferent neurone.

Impulse to effectoris transmitted byefferent neurone.

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Detecting and Responding to

External Stimuli

Effectors such as skeletal muscles will

contract/relax to produce movement.

Effectors can be secretory glands:

Endocrine glands secretes hormones when

stimulated

Exocrine glands e.g salivary glands secretes

enzymes when stimulated

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Detecting and Responding to

External Stimuli

Nervoussystem

Effector

ResponseStimulus

Receptor

detected by produce

Nerve impulses

via afferent neurone via efferent neurone

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Detecting and Responding to

External Stimuli

Nervoussystem

Effector

ResponseStimulus

Receptor

detected by produce

Nerve impulses

via afferent neurone via efferent neurone

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Detecting and Responding to

Internal Stimuli

To regulate the internal environment so

that it is at an optimum condition.

Homeostasis regulation of the

internal environment so thatequilibrium is maintained.

Involves negative feedback

When a factor in the internal environmentincrease above normal range, negative

feedback will occur to lowerit.

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Detecting and Responding to

Internal Stimuli

Stimulus Change in blood

temperature

Receptors

Hypothalamus

Integration

Thermoregulationcentre

Effector Sweat gland etc