B4, B5, B6 Complete OCR Revision Notes

Everything for the exam on the 22nd June

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  • Created on: 08-06-11 13:13
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Biology Modules: B4, B5 and B6
B4 ­ Homeostasis:
The basics of homeostasis:
Homeostasis ­ Maintaining a constant internal environment.
o Keeping everything functioning properly.
o Water content ­ Balance between water you gain (food, drink and respiration) and
the water you lose (wee, sweat and breathing out). Managed by kidneys.
o Body Temperature ­ Whether it's cold or warm outside your body keeps a pretty
average temperature.
Exercise and climate can affect homeostasis.
o Strenuous exercise.
Temperature ­ When you exercise you generate heat, so your body
temperature increases.
Water content ­ You sweat and breathe out more water as respiration rate
Salt Levels ­ Sweat contains salt, so when you sweat it decreases.
o Extreme Climates.
Hot climates ­ Same as exercise (usually).
Cold climates ­ Can cause your body temperature to decrease rapidly.
Mountain climbing
o Strenuous exercise and cold climate. High altitudes also affect blood oxygen levels
so less to breathe contributing to altitude sickness.
Scuba diving
o Temperature drops in cold water, pressure means more oxygen is pushed into your
blood and if too much is pushed you can develop oxygen toxicity.
Negative Feedback:
Negative feedback
counteracts changes.
o Effectors will keep
producing response
until everything is
back to the norm.
Some artificial systems
work like body control
o Like the thermostat, too hot switch off, too cold switch on.
Diffusion is the passive overall movement of particle from a region of higher concentration to
a region of lower concentrations.
o The bigger the difference in concentration, the faster the diffusion rate.
Some chemicals can move in and out of cells by diffusion.
o Cells produce CO which means there's always more of it in cells than the blood. It
diffuses into the blood to be carried away.

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Cells need oxygen and dissolved foods, lower concentration in cells than blood so it
diffuses out of cells and into blood.
Osmosis and Active Transport:
Osmosis is a special case of diffusion.
o Osmosis is the overall movement
of water from a dilute to a more
concentrated solution through a
partially permeable membrane.
Animals must regulate water content.
o Too much water can cause a cell
to burst.
o Too little causes it to shrivel up
and not function properly.…read more

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Controlling Body Temperature:
Body temperature must be kept constant.
o Most reactions in the body work best at around 2-3 degrees.
o Hypothalamus regulates temperature using negative feedback.
When you're too hot.
o Blood vessels go to skins surface and get a bigger diameter to lose heat.
o Sweat, which cools body as it cools.
Too cold.
o Blood vessels get smaller diameter so less heat lost to surroundings.
o You shiver, rapid muscle contraction. Increases respiration and warms surrounding
tissue.…read more

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Ecstasy increases ADH secretion so more water is reabsorbed so concentrated urine.
B6 - Growth and Development
DNA - Making Proteins
DNA is a double helix of paired bases.
o Each strand made of small groups called nucleotides.
o Each nucleotide is a small molecule "base."
o Bases A-T and G-C or the other way round.
DNA controls the production of proteins in a cell
o A gene is a section of DNA.
o Cells make proteins by joining amino acids in a particular order.…read more

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You now have 2 mini cells.
o In each mini cell, the chromosomes line up and the arms are pulled apart.
o You get four gametes with only a single set of chromosomes in it.
Development from a single cell
Cells in an early embryo can turn into any type of cell.
o A zygote divides by mitosis to make a bundle of cells.
o They are all the same at the start. They are undifferentiated, they can become any
cell.…read more

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When a shoot is exposed to light the auxin accumulates on the shady side, making
cells elongate and push the tip towards the light.
Auxins help cutting grow into a complete plant.
o Rooting powder contains auxin which means the plant will produce shoots rapidly and
start growing as new plants.
o This helps growers produces copies of a really good plant fast.
Module B6 ­ Brain and Mind
More on the Nervous System:
The nervous system detects and reacts to stimuli.…read more

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Reflexes are involuntary responses.
o Rapid, automatic responses to certain stimuli.
o They can protect you or help you.
The reflex arc goes through the central nervous system.
o The neurones in the reflex arc go through spinal cord or unconscious part of the brain.
o Let's say you get stung by a bee...
o Impulse down sensory neurone.
o The CNS passes it onto a relay neurone (a new type of neurone!!)...
o Relay neurones relay the impulse to a motor neurone.…read more

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Learning Skills and Behaviour:
Being able to learn means you can adapt to new situations.
o Simpler animals have fewer pathways, so they are more predictable and less
Some skills only develop at certain ages.
o Learning to talk has to happen roughly before about 10, after that, the critical period
learning to talk will probably never happen.
o Like feral children struggle to learn grammar and lots of words.
Different parts of the brain process different information.…read more







these are fantastic!!! I don't suppose you have P4, P5 and P6? But thank you so much! :D


This is fantastic! 

Thank You sooooo much :-)


i fingered myself



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