biology paper 2



regulating conditions inside the body to maintain a stable internal environment in response to changes in both internal and external conditions.

negative feedback

automatic control system to keep internal environment stable. for example, receptors detecting a stimulus (level of something is too high), sends information to co ordination centre which processes the information and arranges a response. the effector produces the response to counteract the change (restore optimum level so levels decrease). 

nervous system

 reflex arc

stimulus - what is detected

receptor is stimulated 

sensory neurone carries information

CNS decides what to do with the information

motor neurone 



synapse connects neurones, the nerve signal is transferred across the junction by chemicals that diffuse across the gap


rapid, automatic responses to certain stimuli that don't involve conscious part of the brain , reduces the chance of an injury, light entering eye- pupil shrinks

reaction time practical

reaction time is the time it takes to respond to stimulus. it can be affected by age, gender and drugs

1. person being tested should sit with their arm on the edge of the table

2. hold the ruler between thumb and fore finger vertically, make sure the 0 end of the ruler is at level with the thumb

3. let the ruler go with no warning, person being tested should catch ruler

4. reaction time measured by number on ruler where caught

5. repeat, calculate a mean

6. test the person again once they have consumed a caffinated drink, wait 10 minutes before doing so to make sure the caffiene has gone into the blood stream

7. control any variables- same person, drop ruler at same height

reaction time can also be measured with a computer that gets the person being tested to react to a colour change and click the mouse. the computer is more precise as it measures reaction time in milliseconds and reduces chances of human error


controlling body temperture

the body needs to balance energy gained and energy lost, regulated by thermoregulatory centre that contains receptors sensitive to the temperature of blood flow through the brain, also recieves impulses from temperature receptors through the brain.

too hot- glands produce sweat that evaporates from the skin, blood vessels dilate (vasodilation) so more blood flows closer to the skin to transfer energy to the environment 

too cold- hairs stand and trap an insulating layer of air, blood vessels constrict (vasoconstriction) and you shiver which requires respiration  and releases energy to warm the body. 


endocrine system, all the hormones in the body.

Hormones are chemical molecules released directly into the blood and are carried to target organs. they are produced by endocrine glands and have long lasting effects.

pituaitary gland/master gland- regulates body conditions, acts on other glands so they release hormones that cause change

ovaries- produce oestrogen in the menstrual cycle

testes- produce testosterone, control puberty and sperm production 

thyroid- produces thyroxine regulates




n worrd



perfecto, gracias






this is so useful and helpful, thank  you so much 









my paper two exam is next week and omg you saved my life