biology paper 2


what is homeostasis

the regulations of the conditions inside the body to maintain a stable internal environment.

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what conditions do homeostasis control?

. blood glucose level,body temperature and water content of the blood

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the body has control systems that regulate interna

receptors, a coordination centre and effectors

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why is negative feedback important?

negative feedback helps to maintain a stable internal environment. it acts againest a change in a condition to return it back to normal levels.

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what is a stimulus?

a detectable change in the internal or external environment

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the nervous system

this means humans can react to their surroundings and coordinate their behaviour

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what diffferent parts are the nervous system made

central nervous system - in vertebrates ( animals with backbones) this consists of the brain and spinal cord.

sensory neurones- the neurones carry information as electrical impulses from the receptors to the central nervous system.

motor neurones- the neurones that carry electrical impulses from the central nervous system to effectors.

effectors- all your muscles and glands which respond to nervous impulses.

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receptors and effectprs can form part of complex o

receptors are the cells that detect stimuli

there are many different types of receptors such as taste receptors on the tongue and sound receptors in ears.

effectors respond to nervous impulses and bring about a change.

muscles and glands are known as effectors. they respond in different ways.

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the central nervous system coordinates the respons

the central nervous system is a cooridation centre- it recives information from the receptors and then cooridnates a response. the response is carried out by effectors.


a small bird is eating some seed

when it suddenly sports a cat coming toward it this is the stimulus

the receptors in the birds eye are stimulated

sensory neurones carry the information from the receptors to the central nervous system.

the central nervous system decides what to do about it

the central nervous system sends info to the muscles in the birds wings ( the effectors) along motor neurones

the muscles contract and the burd flies away to safety.

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synapses connect neurones

the connection between two neurones is called a synapse

the nerve signal is transferred by chemicals which diffuse across the gap

these chemicals then set of a new electrical signal in the next neurone.

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rapid, automatic responses to certain stimuli that dont involve the conscious part of the brain.. thye can reduce the chances of being injured.


if someone shines a bright light in your eyes your pupils automatically get smaller so that less light gets into your eyes.

the passage of info in a reflex is called a reflex arc.

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