This is the complete revision for GCSE biology

By Priyank Shah

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  • Created on: 18-05-11 09:24

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B3 Revision
Exchange of Materials
Active transport is the movement of substances from an area of low concentration to an area
of high concentration (against the concentration gradient)
It requires energy from cellular respiration, because the active transport system has to carry
a molecule across the membrane, and then return to its original position
The more active transport that takes place, the more mitochondria are needed (for energy)
Breathing is the constant intake of oxygen, and the removal of carbon dioxide
Lungs are found in the upper part of the body (chest/thorax), protected by the rib cage
Lower part of the body is the abdomen
The diaphragm is a sheet of muscle separating the thorax form the abdomen
When you breathe in, the rib move up and out and the diaphragm flattens from its dome
shape, allowing air to move in
The lungs are made up of clusters of alveoli, which are tiny air sacs
Have a large surface area
Have a rich blood supply, maintaining a concentration gradient in both directions
(oxygen is constantly removed into the blood and carbon dioxide in constantly
delivered to the lungs
Thin alveolus walls decreases diffusion distance
Moist surfaces allow gases to dissolve, making diffusion easier
Food in your gut is broken down into simple sugars (glucose, amino acids, fatty acids and
Food moves from the inside of the small intestine into the bloodstream by diffusion and
active transport
There is a high concentration of food molecules in the gut, and a low concentration in the
bloodstream, so food molecules diffuse into the blood across a concentration gradient
Villi are tiny finger-like projections that line the small intestine, and have some features to
increase the uptake of digested food by diffusion (only a certain number of food molecules
can diffuse over a given area of gut lining at any one time)
They have:
A large surface area for more diffusion to take place
Lining of small intestine has excellent blood supply, maintaining steep concentration
Thin wall for short diffusion distance
Glucose and other dissolved molecules move from small intestine into the blood by active
transport so no digested food is wasted
Gills in fish are made up of many thin layers of tissue with a rich blood supply, and moist
Tadpoles have external gills, which are then reabsorbed into the body when the tadpole
becomes a frog, via metamorphosis
Adult frog has moist skin, rich blood supply, gas exchange take place through skin, and a pair
of simple lungs

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Insects have an internal respiratory system, supplying oxygen directly to the cells
Insects have spiracles that open when the insect needs oxygen, and these lead to the
The tracheoles are minute breathing tubes which penetrate right through the tissues- they
have a large surface area, moist lining, air is pumped in and out of them and they are freely
permeable to gases (no blood supply in an insect)
Plants have some features to allow maximum efficiency in gas exchange:
Flattened shape of leaves increases…read more

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Red blood cell adaptations for efficiency in picking up oxygen:
They are biconcave discs, giving them an increased surface area: volume ratio
Packed full of haemoglobin, which carries oxygen
No nucleus, so more space to pack haemoglobin
Haemoglobin reacts to form oxyhaemoglobin with oxygen, and where oxygen concentration
is lower, the oxyhaemoglobin reverses to form oxygen and haemoglobin again
Haemoglobin is based on iron, so if you lack iron, your body cannot make enough red blood
cells and you suffer from anaemia (your pale and…read more

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Dialysis machine carries out the functions of the kidney
Person's blood leaves body and flow between partially permeable membranes
Other side of membranes is dialysis fluid, and the concentration of this fluid means that
unwanted substances in the blood pass into the fluid (urea, excess ions and water)
Dialysis fluid contains same concentration of glucose and mineral ions (so no net movement
of glucose, but excess mineral ions are lost)
Dialysis fluid contains no urea, so strong concentration gradient form blood to fluid
A kidney…read more

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Bacteria break down lactose in the milk to produce lactic acid- this is called lactic
Lactic acid causes milk to clot and solidify into yoghurt
Yoghurt-forming bacteria help to prevent the growth of bacteria which make milk go
To make cheese:
Add a starter culture of bacteria to warm milk (the type of bacteria added is
different from the type used to make yoghurt)
The bacteria break down lactose into lactic acid, but this time much more lactic acid is
produced, so the…read more

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Cost- continuous generators are more expensive
Convenience- batch generators are less convenient
Efficiency- need to be well insulated and no leaks
Position- away form homes
Many different organisms are involved in the breakdown of material in biogas production
Sugar cane contains sucrose (high in carbohydrates) and maize contains starch which can be
broken down using carbohydrase
Yeast + sugary products from cane and maize = ethanol and water (anaerobic respiration)
Ethanol can then be extracted by distillation
Advantages of ethanol as a fuel:
Does not…read more


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