Biology Module 3 notes

Condensed version of the AQA CPG revision guide (higher tier) with bullet-pointed and numbered sections and fewer pages.....was intended basically for me to get the revision guide into my head more by typing it up and rewording it a bit, but felt like uploading it as it may be useful for some people, especially those without revision guides :) Good luck!

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  • Created on: 12-05-11 12:21
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Biology
Unit 3 (i) Life Processes 2
Gas and Solute Exchange
Substances move by diffusion, active transport and osmosis
1) Life processes need gases / dissolved substances. E.g. photosynthesis needs CO2
and water, respiration needs glucose + oxygen. Waste needs to leave the cell so
organisms can get rid of them.
2) Diffusion = particles moving from an area of high concentration to an area of low
concentration
3) Osmosis = the movement of water across a partially permeable membrane from an
area of high water concentration to an area of low water concentration
4) Active Transport = the movement of particles against a concentration gradient, from
a lower concentration to a higher concentration
5) Substances move through an exchange surface, which have to allow enough
necessary substance to pass through it. Exchange surfaces are adapted to maximise
effectiveness.
The structure of leaves allows gases to diffuse in and out
CO2 diffuses into air spaces within the leaf, to diffuse into cells where
photosynthesis occurs. The leave has an adapted structure to facilitate this:
1) The Exchange Surface (underneath the leaf) is covered in stomata (small holes)
which CO2 diffuses through
2) Water vapour and oxygen diffuse out through the stomata
3) Guard cells control the size of the stomata ­ they close if the plant is losing water
faster than it is being replaced by the roots, preventing wilting.
4) Flattened leaves mean the area of exchange surface is increased, so is more effective
5) Walls of cells inside the leaf form another exchange surface. Air spaces inside
increase area of this surface, allowing CO2 more chance to get into the cells.
Water vapour escapes by diffusion as there is more water inside the leaf than outside. This
diffusion is called TRANSPIRATON and occurs more quickly in hot, dry, sunny and windy
conditions (when you put your washing out)
Breathing System
Lungs are in the Thorax:
1) Thorax is the top part of the body
2) Separated from the lower part by the
diaphragm
3) Lungs are protected by the ribcage
4) Air you breathe in goes through the
trachea, splitting into two tubes called
bronchi, one to each lung.
5) The bronchi split into smaller tubes,
bronchioles
6) Bronchioles end at small bags, alveoli,
where gas exchange occurs.

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Breathing IN:
1) Intercostal muscles + diaphragm
contract
2) Thorax volume increases
3) Decrease of pressure, drawing air
in.
Breathing OUT:
1) Intercostal muscles + diaphragm
relax
2) Thorax volume decreases
3) Air is forced out
Diffusion through Cell Membranes
Gas exchange happens in the lungs
Lungs use alveoli to transfer oxygen to the blood and remove CO2. This is gas
exchange.…read more

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Active Transport
Root hairs are specialised for absorbing water & minerals
1) Cells on surface of plant roots grow into long "hairs", sticking out into the soil
2) Gives plant a big surface area for absorbing water & mineral ions from the soil
Root hairs take in minerals using active transport
1) Concentration of minerals is higher in the root hair than the soil around.
2) Active transport is responsible ­ cannot occur by diffusion.…read more

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Red blood cells:
1) Carry oxygen from the lungs
2) Doughnut shape with a large surface area to absorb oxygen
3) No nucleus ­ more room for oxygen
4) Contain haemoglobin
5) In lungs, haemoglobin becomes oxyhaemoglobin after combining with oxygen. In
body tissues, the reverse occurs.…read more

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Kidneys
Nephrons are filtration units in a kidney.
Ultrafiltration:
1) High pressure is built up, pushing water, urea, ions and sugar out of the blood into
the Bowman's capsule.
2) Membranes between blood vessels and Bowman 's capsule act like filters ­
proteins and blood cells are too big to be squeezed out, so remain in the blood.…read more

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This has to be done regularly, keeping concentrations of dissolved substances at
normal levels and removing waste substances from the blood.
2) In the machine, blood flows along a selectively permeable barrier surrounded by
dialysis fluid. This is permeable to ions and waste substances, but not large
molecules like proteins
3) The dialysis fluid has the same concentration of dissolved ions and glucose as
healthy blood
4) Useful dissolved ions and glucose therefore won't be lost from the blood during
dialysis.…read more

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Moulds are added to blue cheese to give colour and taste.
Yoghurt is made from bacteria:
1) Bacteria are used to clot milk during yoghurt making
2) Milk is heat treated to kill off bacteria, then cooled
3) A starter culture of bacteria is added. This ferments the lactose sugar present in the
milk to lactic acid
4) The acid causes milk to clot and solidify to yoghurt
5) Sterilised flavours can be added (eg fruit)
Using Yeast
Yeast is a microorganism.…read more

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Mycoprotein
1) Mycoprotein ­ protein from fungi. A type of singlecelled protein
2) It is used to make meat substitutes like QuornTM
3) Fusarium, a fungus, is the main source of mycoprotein
4) It is grown in fermenters, using glucose syrup as food which is obtained by
digesting maize starch with enzymes.
5) The fungus respires aerobically so oxygen, nitrogen (as ammonia) and other
minerals are supplied.
6) The fermenter is initially sterilised using steam to prevent other microorganisms
growing.…read more

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Different microorganisms are used to produce this, fermenting plant and animal
waste containing carbohydrates.…read more

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The raw material is readily available and cheap
5) The digested material is a better fertiliser than undigested dung
6) Women have to spend hours collecting wood for fuel in rural communities ­ biogas
saves them from doing this.
7) Generators act as a waste disposal system, getting rid of human and animal waste
that would cause disease and pollute water systems.…read more

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