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Biology
Cell Transport
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Created by
Freddie Golding
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Diffusion
The movement of particles from an area of
high
concentration to an area of low concentration. Particles move
down
a concentration gradient.
Why can we
smell
things which are
far away
?
Diffusion
Occurs in liquids and
gases
where
molecules
are constantly moving and bumping into each other, allowing them to spread out
Does not occur in
solids
where particles are tightly
packed
As temperature
increases
Kinetic energy
of particles increases, so they move around faster and
diffusion
is more rapid
Concentration gradient
The difference in
concentration
between two areas
The
larger
the concentration gradient, the
higher
the rate of diffusion
Where diffusion occurs in living organisms
Animal
cells
Plant
cells
Unicellular
organisms
Substances that diffuse in and out of an animal cell
Glucose
(from food)
Oxygen
(from lungs)
Carbon dioxide
(excreted via lungs)
Urea
from liver cells (excreted via
kidneys
)
Words that describe diffusion
Occurs in
Solids
Movement
of molecules from an area of
lower
to higher concentration
Passive
process (doesn't require extra input of energy)
Movement is
Random
Occurs in
Fluids
Active
process (requires extra input of energy)
Movement of molecules from an area of
higher
to
lower
concentration
Diffusion
The movement of particles from an area of
high
concentration to an area of
low
concentration
As temperature increases
Particles have higher
kinetic
energy
The higher the concentration gradient
The
higher
the rate of
diffusion
Every organism, whatever its
size
, needs to exchange materials with the
environment
Surface area
to
volume ratio
(SA:V ratio)
How
easy the exchange of substances is
, depends on the
organism's surface area to volume ratio
An ant has a much
larger
surface area to
volume
ratio than an elephant
As the size of an organism gets
bigger
The
surface area to volume ratio
(SA:V) gets
smaller
Large organisms, like humans, cannot absorb enough
oxygen
through our skin surface, so we need efficient
gas exchange surfaces
such as lungs
Features of a good gas exchange system
Folded shape
- large surface area
Thin
- to provide a short diffusion pathway
Efficient blood supply
- to maintain a high concentration gradient
Ventilation
- ensuring there is always lots of oxygen to maintain a high concentration gradient
A good blood supply in the lungs and small intestine
Maintains a
high concentration gradient
, which increases the rate of
diffusion
Features of a good gas exchange system
Non-flat
shape - increases surface area
Thin
- reduces diffusion distance
Good blood supply
- maintains high concentration gradient
Ventilation
- maintains high concentration gradient
Soil has a lower concentration of
mineral ions
than
root hair cells
Root hair cells need to use
active transport
to move
mineral ions
from an area of lower to higher concentration
Active transport
Using energy to move molecules against a
concentration gradient
with the help of a
transport protein
Organisms use
active transport
when molecules need to move from
low
to high concentration