Biology B4, B5 and B6 (Found this online!) OCR BOARD

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  • Created on: 01-11-12 18:49
Preview of Biology B4, B5 and B6 (Found this online!) OCR BOARD

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Biology B4- Homeostasis
Keeping a steady state:
Automatic control systems in the body keep factors steady, including body temperature and
water level.
Artificial control systems are similar to body control systems; they both have receptors, a
processing centre and also effectors.
Strenuous (tiring) exercises and extreme climates can affect homeostasis. Homeostasis
includes; body temperature, water balance, blood level and salt level)
Negative Feedback is used in many control systems, so that any change from the normal level
causes a response that returns the system back to normal.
Some Effectors work antagonistically (violently), which gives a more sensitive response.
The body's normal temperature is between 36oc and 37.5oc.
Moving in and out of cells
Chemicals move in and out of cells by diffusion, e.g. O2, CO2, dissolved food.
Diffusion is the passive movement of molecules from where they are in high concentration to
in an area of low concentration.
Osmosis is the movement of water molecules from a dilute to a more concentrated area
through the semi permeable membrane.
Keeping the body's water level balanced is important so that cell contents are at the correct
concentration for the cell to work properly.
Some chemicals, e.g. Glucose, are moved in or out of cells by active transport, which requires
Active transport is the movement of molecules in or out of cells which requires energy.
Enzymes are proteins that speed up chemical reactions in cells.
A small part of an enzyme which is called the active site, is shaped so that only molecules with
the correct shape can fit with the enzyme; this is also known as the "lock-and-key "model.
The "lock-and-key" model explains why each type of enzyme only speeds up one particular
chemical reaction.
Enzymes work best at a certain temperature which is why the body's temperature must be
kept at a constant level.
At low temperature, increasing the temperature will increase the rate of a reaction because
the molecules would collide more often and with more energy. (collision theory)
At high temperature an enzyme stops working because it has become denatured and
therefore, does not fit because the active site shape has changed.
Body Temperature
Energy gain and loss must be balanced to keep a steady body temperature
Receptors in the skin and brain detect changes in temperature of the air and the blood.

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The brain processes information about temperature control in the hypothalamus, and
effectors (sweat glands and muscles) produce responses to keep the body temperature
Vasodilatation and vasoconstriction control the amount of blood flowing near the skin
Vasodilatation widens the blood vessels and Vasoconstriction narrows the blood vessels.
Hypothermia: causes: getting too cold, symptoms: shivering, memory loss, depending on
how bad. Look at link:
Heatstroke: causes: body temperature is too hot, symptoms: weakness, tiredness,
nauseous. Check link:…read more

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B5- Growth and Development
The cell cycle
Cells go through cycles of growth and divisions:
I. During cell growth the number of organelles increases, and chromosomes are
II. During cell division copies of the chromosomes separate, and then the cells divide.
Cell division by mitosis produces two new cells identical to the parent cell
Cell division by meiosis leads to four gamete cells with half the chromosome number of the
parent cell.…read more

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Meristem cells can re-grow whole parts of the plant, which means that gardeners can make
new plants from cuttings.
Plant hormones (auxins) affect how plant cells develop.
Plants grow towards the light; this response is called phototropism.
Auxin builds up in cells on a shoot's shady side, which make the cells grow longer, so the
shoot bends towards the light.…read more

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B6- Brain and Mind
A mammal's nervous system
The nervous system is made up of the central nervous system (CNS) and peripheral nervous
The CNS coordinates an animal's response via sensory and motor neurons.
Receptors and effectors can be single cells or parts of complex organs.
Nerve Impulses
The structure of a neuron means that it can carry electrical impulses.
Neurons are separated by tiny gaps called synapses.
Some drugs and toxins affect the transmission of impulses across synapses.…read more

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This is the end of B4, B5 and B6 summary. I hope it's helped. Thank you & Good luck in the exam.…read more


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