GCSE AQA Biology Unit 3

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  • Created on: 29-05-12 22:54
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Gas and Solute exchange:
Diffusion: Particles move from high to low conc. OR dissolved particles can diffuse in and out
through a cell membrane.
Osmosis: Water moving through a partially permeable membrane from high to low conc.
Exchange surfaces are adapted to maximise effectiveness.
Leaves allow gases to diffuse into air spaces, and then into the cells. The exchange surface is
covered in stomata (small holes). Size of stomata is controlled by guard cells. Flatness increases
surface area.
TRANSPIRATION IS QUICKEST IN hot, dry and windy conditions.
The Breathing System:
Lungs are in the thorax (top half of body) and are separated from the lower part with the diaphragm.
Breathe air through the trachea, then splits into bronchi, then bronchioles and then alveoli, small
bags where the gas exchange takes place.
When you breathe in, intercostal muscles and diaphragm contract, thorax increases, pressure
The purpose of the lungs is to transfer oxygen to the blood and remove waste CO2.
Alveoli are specialised as they have large surface area, moist lining to dissolve, thin walls and a
copious blood supply.
Active Transport: (moving against the concentration gradient, so low to high conc.)
Root hair cells are specialised for this as they have a large surface area due to hairs in soil.
Conc. Of minerals is usually higher in cell than in soil surrounding, so active transport is essential for
growth. It requires energy from respiration.
Active transport is also used in the gut. It allows nutrients to be taken into the blood.
Carrier molecule is specific, like an enzyme. Uses energy to carry across membrane and release in
Circulation system:
The right side pumps
deoxygenated into the lungs
to add o2 and remove co2. Left
side pumps around body.
Arteries carry blood
from heart at a high pressure.
The pulmonary are
exceptions! The pulmonary
Vein carries oxygenated from
lungs to hear and pulmonary
ARTERY carries Deoxygenated
from heart to lungs.
Ventricles = lower
chambers. Atria's= upper
Aorta ­ oxygenated blood to body tissues.
Arteries : small lumen, thick wall, many elastic fibres, more muscle, high pressure.

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Veins: large lumen, thin wall, few elastic fibres, less muscle, lower pressure.
Capillaries: use diffusion to deliver food and oxygen and take CO2. One cell thick endothelium.
Blood is made up of : red and white blood cells, plasma and platelets (help blood to clot)
Red blood cells have a large surface area to absorb oxygen and no nucleus to allow more room.
The haemoglobin in these cells combines with oxygen in lungs. When it reaches cells, it reverses.…read more

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Food and Drink from Microorganisms:
Theory of Biogenesis = Theory that living things are created from other living organisms.
People used to think that things spontaneously generate.
1765 : Spallanzani ­ one sealed one open. Boiled to kill microbes. Only open one went off, showing
microbes got in through air. Opponents thought air outside flask was necessary to start change.…read more

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Biofuels are carbon neutral (CO2 produces when burning is equal to amount that went in), no
sulphur production, cheap, readily available, better fertilizer, saves fuel collection in some countries,
can act as waste disposal system. No methane released in atmosphere.…read more


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