Diffusion and Osmosis and Active Transport

Hello everyone, I have my GCSE Biology papers in May and June 2016 so this is my daily revision from my DG Mackean book. If you find anything incorrect just message me and I'll change it. Thank you very much everyone! 

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Science Revision
D.G. Mackean Pages 26-30
Christopher Caden…read more

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Cells need to get food substances so they can digest the food and
respire, and cells need water to stay alive and they also need to
expel carbon dioxide, because in large quantities it is harmful to the
cell. This is done by the process of diffusion. Diffusion is the idea
that molecules (whether they gas or liquid) will spread to an area of
high concertation to an area of low concertation. The final goal of
diffusion is to have all the molecules equally spaced out and for
them to be evenly distributed. This can happen with cells,
molecules can enter a cell if there is a low concertation inside the
cell and a high concertation on the outside of the cell.…read more

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Cell Membrane
Whether this diffusion into or out of a cell happens is down to the
cell membrane. Remember that the cell membrane acts as a
bouncer and allows things into or out of the cell. As a rule of thumb
however small molecules like water, carbon dioxide and oxygen are
easily allowed to pass through the cell membrane. This is very
beneficial for the cell. For example if a cell oxidises food the
concertation of oxygen in the cell will decrease and oxygen will
diffuse into the cell or if carbon dioxide builds up in the cell due to
respiration the carbon dioxide due to diffusion will leave the cell.
Both of these benefit the cell and are helpful for the cell.…read more

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Diffusion Rate Factors
There are factors that can affect the rate of diffusion into or out of
a cell. These factors are temperature, pressure, distance it has to
diffuse, concertation and the size of the molecules. The cell can
also impact the rate of diffusion. One example is the thickness of
the cell membranes or cell walls. Generally the thicker the cell
membranes and cell walls the slower the rate of diffusion. Another
factor is the concertation gradient or the difference between the
high and low concertation numbers. The higher the gradient the
higher the rate of diffusion. It can also be down to the molecule
itself, water diffuses slower than amino acids do. Enzymes can also
speed up the rate of diffusion.…read more

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Surface Area
Surface is one of the biggest factors in determining how fast
diffusion takes place. The greater the surface area, the greater the
rate of diffusion. Some places in the human body require rapid
diffusion, for example the intestines. The cells in the intestines are
special and maximise the surface area because the cells are in long
finger like shapes that boost surface area. It gets better though as
these cells, called villi, has smaller versions of themselves
projecting out from the cell membrane and these are called
microvilli.…read more

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Endo- and Exocytosis.
Cells can take in or expel solids or liquids through the cell
membrane. Endocytosis (taking in a solid or liquid) happens with a
particular white blood cell called phagocytes. Phagocytes engulf and
digest bacteria and this engulfing has a special name specific to
phagocytes and it is called phagocytosis. Exocytosis happens in
glands and this is where cells form vacuoles that hold a digestive
enzymes. The enzyme filled vacuole makes its way to the cell
membrane where it is secreted and leaves the cell.…read more

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Hi at many points through the presentation it mentions conceration which i think should be concentration thanks



thanks man

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