Science GCSE Revision

Homoeostasis, Forces and Chemical Patterns.

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  • Created on: 17-01-11 17:46
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BIOLOGY: Homoeostasis
Control Systems:
­ Cells only work if the conditions are correct.
­ Automatic control systems keep the body conditions constant.
­ Keeping a constant environment is called homoeostasis.
­ Receptors are to detect stimuli.
­ Processing centres receive information and coordinate responses.
­ Effectors produce responses.
­ A baby incubator is an artificial control system because it has a temperature sensor, a thermostat
with a switch and a heater.
The sensor detects the temperature. If it is cooler than 32'c, the thermostat switches on the heater.
The thermostat switches off the heater when the temperature rises back to 32'c.
­ In a control system, any change leads to something that reverses the change.
­ Negative feedback makes this happen.
­ Some effectors have opposite effects to each other, they work 'antagonistically'.
­ This makes the response very sensitive.
­ Strenuous exercise: affects temperature, hydration (water levels), salt levels and blood oxygen
­ Surviving in hot and cold climates: affects temperature, hydration and salt levels.
­ Scuba diving: affects blood oxygen levels.
­ Mountain climbing: affects blood oxygen levels.
­ Speed up chemical reactions.
­ Enzymes work best in certain conditions.
­ Enzymes are protein molecules.
­ Every type of enzyme speeds up a particular reaction.
­ The molecules must fit exactly into the enzymes active site.
­ Lock and key
­ In humans work best at 37'c.
­ Below 37'c, reactions are too slow. Fewer collisions.
­ At 37'c, The reactions is faster. More collisions. Collisions have energy.
­ Above 37'c, enzymes denature (don't work).
­ Denaturing: shape of active site changes. Molecules no longer fit into the active site. Reaction
cannot happen.
­ Changes in pH cause same problem as denaturing.
The Body:
­ Must be kept at 37'c.
­ Respiration releases energy from your food your body uses.
­ Gain energy from your environment (if hotter than you)
­ Body must balance energy gain and energy loss to keep a constant temperature.
­ Body core warmer than 'extremities' e.g. hands and feet.
The body's temperature control system:
­ Temperature receptors in the skin detect the temperature outside the body.

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Temperature receptors in the brain detect the bloods temperature (in the hypothalamus)
­ A processing centre in the brain (in the hypothalamus) which receives information about from
receptors and triggers responses in effectors.
­ Effectors such as sweat glands and muscles.
­ High body temperatures: body makes sweat. Sweat evaporates and cools skin down.
Vasodilation: Blood vessels get wider so more blood flows and body loses more energy.
­ Low temperatures: shivering (muscles contracting fast) makes respiration increase therefore energy
as heat is produced.…read more

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Send all the urea and some water and salt to the bladder. This is urine stored in the bladder then
later excreted.
­ They reabsorb molecules that the body needs, including all the glucose and some water and salt,
back into the blood.
­ Control water levels by making different amounts of urine.
­ On hot days we sweat more so kidneys make less urine.
­ Make less urine if you exercise & not drunk much or eaten salty foods.…read more

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Changing Momentum: When a resultant acts on the object, the momentum of the object changes in the
direction of the force. If the resultant force on an object is zero, its momentum does not change. If its
stationary, it stays still. If it is already moving, it continues at a steady speed in a straight line.
If two cars collide, there is a change in momentum. When the cars stop, the momentum decreases to zero.
­ Car crumple zones squash slowly in a collision.…read more

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Sodium melts and whizzes round on surface of water. Sometimes, hydrogen catches fire
Potassium melts and may jump from surface of water. Hydrogen immediately catches fire
­ Alkali metals also react vigorously with chlorine gas to make chlorides.
­ The chlorides are colourless crystalline solids
e.g. lithium + chlorine lithium chloride
Group 7: the halogens.
­ Halogen molecules are diatomic ­ they are made from two atoms joined together. e.g.…read more

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Balancing Equations:
­ Make the number of atoms on each side of the arrow the same.
­ Balancing an equation means making both side of the equation the same.…read more


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