Download B-4 Notes

Unit B: Cells and Systems
Topic 4: Fluid Movement in
Cells
Movement Through a Cell
Membrane
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To be permeable means you let
everything go through, to be
impermeable means you never let
things through.
Cell membranes are selectively
permeable. This means that they let
some things through them (water
particles), but control the movement of
others (wastes and food particles).
Diffusion
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Diffusion is how particles move.
Particles move from an area of high
concentration (there are lots of
particles) to an area of low
concentration (few of those particles
are in that area).
An example of diffusion is how
perfume particle spread throughout a
room.
Why does diffusion happen?
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It happens because particles bump
into each. The more they bounce
around, the more they spread out. This
happens until they fill the area they are
in.
Diffusion in Cells
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If there are more particles of sugar
outside of a cell than inside, than
diffusion would cause the particles to
spread into the cells (as long as the
cell membrane allowed the particles
in).
Osmosis
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Osmosis is basically diffusion, but
focussing strictly on water.
Water will move from an area of low
concentration (pure water) to an area
of high concentration (salt water) to
balance the two sides out.
Osmosis in Cells
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Water can freely move across cell
membranes.
So if you eat salty foods, your cells will
become highly concentrated with salt.
Water will move from your bloodstream
to your cells to balance things out. This
triggers a reaction causing you to
become thirsty.
Fluid Movement in Plants
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Vascular tissue in plants connects
roots to the leaves. It is involved in the
transportation of water and sugar
(food/energy).
There are two types of vascular tissue.
Phloem Tissue
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Transports sugars created in the
leaves through photosynthesis DOWN
to the rest of the rest of the plant.
These sugar particles move through
diffusion.
Xylem Tissue
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Transports water UP from the roots to
the rest of the plant. This is done
through osmosis of water from an area
of lots of water (wet soil) to an area of
less water (roots then vascular tissue
and then plant cells)
Root hairs are made up of epidermal
cells (the skin of the cell)
Photosynthesis
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Occurs in specialized cells called
palisade cells. These cells make up
the green leaves of a plant.
They are designed flat and thin so they
can soak up as much sunlight as
possible.
They are full of chloroplasts.
Stomata
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Cells in leaves that open up and allow
gases to enter and leave the cell according
to diffusion.
During photosynthesis plants take in as
much carbon dioxide as possible. When
they are changing their sugar into energy,
they are take in as much oxygen as
possible.
Stomata cells’ opening and closing are
controlled by specialized ‘Guard Cells’.
Transpiration
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Is the loss of water from a plant
through evaporation, usually from the
leaves.
Transpiration is not a problem as long
as the supply of water is replenished
by the roots. If no water comes into the
plant, it dies.
Water Particles, Attraction, and
Life
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Water particles are attracted to each
other. It is this attraction that allows
water to pull itself up a plant through
the xylem tissue.
This pushing (osmosis) and pulling
(attraction) of water molecules is what
has allowed life to occur on Earth.