CIE IGCSE Biology Unit 14: Coordination and response

nerve impulse

an electrical signal that passes along nerve cells called neurones

human nervous system

Central nervous system: made up of two organs, spinal cord and brain

Peripheral nervous system: connected to the limbs, linked with central nervous system

central nervous system

the complex of nerve tissues that controls the activities of the body

peripheral nervous system

The nervous system outside the brain and spinal cord

coordination and regulation of body functions

voluntary actions

Requires decision making from the brain, is slower compared to involuntary action as it requires impulse to travel to brain

involuntary actions (reflex)

Does not require decision making, is fast as impulse does not require to travel to brain

Sensor, relay, and motor neurons

Sensory neurone detects stimuli and transfer impulse through sensory neurone and relay neurone in brain transfers signal to motor neurone that sends the impulse to the effector in which a response is made

simple reflex arc

receptor, sensory neurone, relay neurone,

motor neurones and effector

reflex action

a means of automatically and rapidly integrating and coordinating stimuli with the responses of effectors (muscles and glands). The synapses ensure that impulses travel in one direction only.

synapse

a junction between two neurones

How impulses travels

an impulse triggers the release of a neurotransmitter from vesicles into the synaptic gap, the neurotransmitter diffuses across to bind with receptor molecules, in the membrane of the neurone after the synaptic gap, causing the impulse to

continue

Sense organs

groups of receptor cells responding to specific stimuli: light, sound, touch, temperature and chemicals

Eye structures

- cornea - refracts light

- iris - controls how much light enters pupil

- lens - focuses light onto retina

- retina - contains light receptors, some sensitive to light of different colours

- optic nerve - carries impulses to the brain

pupil reflex

light intensity and antagonistic action of circular and radial muscles in the iris

accommodation to view near and distant objects

*in the contraction and relaxation of the ciliary muscles, tension in the suspensory ligaments, shape of the lens and refraction of light

distribution of rods and cones in the retina

rod and cone cells are equally distributed in the retina, but the yellow spot contains only cone cells

function of rods

greater sensitivity of rods for night vision

function of cones

three different kinds of cones absorbing light of different colours for colour vision

fovea

yellow spot, contains only cone cells

Hormones

a chemical substance, produced by a gland and carried by the blood, which alters the activity of one or more specific target organs

endocrine glands and secretion

adrenal glands- adrenaline

pancreas-insulin

testes-testosterone

ovaries-oestrogen

adrenaline

the hormone secreted in 'fight or flight' situations and its effects, limited to increased breathing and pulse rate and widened pupils, produced by the adrenal gland above the kidney

role of the hormone adrenaline in the chemical control of metabolic activity

increasing the blood glucose concentration and pulse rate

nervous and hormonal control systems in terms of speed and longevity of action

Is slow and long lasting

homeostasis

the maintenance of a constant internal environment by the control of internal conditions within set limits

Explain the concept of control by negative

feedback

Negative feedback ensures that, in any control system, changes are reversed and returned back to the set level. For body temperature, if surrounding temperature is low, body will sense that as negative feedback, and body will raise body heat

Structure of skin

hairs, hair erector muscles, sweat glands,

receptors, sensory neurones, blood vessels

and fatty tissue

maintenance of a constant internal body temperature

*in terms of vasodilation and vasoconstriction of

arterioles supplying skin surface capillaries

gravitropism

a response in which parts of a plant grow towards or away from gravity

phototropism

A response in plants to light

phototropism and gravitropism in shoots

gravitropism is negative in shoots as it grows against gravity and phototropism is positive as shoot grows toward light

role of auxin in controlling shoot growth

- auxin made in shoot tip (only)

- auxin spreads through the plant from the

shoot tip

- auxin is unequally distributed in response to

light and gravity

- auxin stimulates cell elongation

synthetic plant hormone 2,4-D

herbicide,causes uncontrolled growth in broad leaved weeds