Summary
Summary GCSE Biology revsion notes
This is a summary of some of the main aspects of AQA gcse biology for example the heart, respiration, excercise, diffusion etc. It contains diagrams, tables and graphs to aid your learning
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BiologyAQA
, diffusion
This means if we have a group of
molecules all bunched up together
in one place
Over time they'll slowly spread
out due to their random motion If molecules are left alone they'll
until their pretty evenly distributed move around randomly
This process of
spreading out is
known as diffusion
diffusion
The net movement of
particles from an area of
higher concentration to
an area of lower
concentration.
Diffusion can happen in both gases and liquids
Diffusion can also take place through some materials such as cell membranes
cell membranes - partially permeable
only some molecules can diffuse through
generally only very small molecules that are Diffusion is a passive process
dissolved in the fluid inside or outside the cell ( It doesn't need any energy from the cell )
can diffuse through
for E.g : water, glucose , amino acids
whereas larger molecules cant fit through the
membrane because there too big
E.g : proteins , starch
3 factors that affect the rate of diffusion
Concentration Gradient
Difference in concentration between two places
The larger the concentration gradient = higher rate of diffusion
Temperature
Surface Area
Higher temperatures give particles more energy
larger surface are= higher rate of diffusion
so particles move around faster
so overall they'll diffuse more quickly
higher temperature= higher rate of diffusion
, osmosis
The movement of water molecules across a
partially permeable surface across a region of higher water
concentration to an area of lower water concentration
water concentration - the amount of water as compared to the
other molecules such as sugars or salts that are dissolved in that
water. these dissolved molecules are known as solutes
osmosis occurs across cell membranes:
cytoplasm within cells generally has a relatively high concentration of
solutes because of all the sugar and salts a cell needs to survive
so it has a relatively low concentration of water
so water from outside of the cell will diffuse into the cell through osmosis
but if too much water diffuses into the cell it may burst
however if its a plant cell and there too much water the cell wall prevents it
from bursting - this is called 'turgid'
on the other hand if you place the cell in a very sugary solution the water
concentration outside the cell is likely to be lower than the inside.
If this causes to much water to leave the cell it may become dehydrated -
this known as flaccid
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