Osmosis, active transport

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Osmosis and animal cells
When animal cells are placed in solutions with water potentials higher or
lower than the water potential of the cytoplasm inside the cells.
Higher water potential outside:
Cell swells, bursts and dies
Equal water potential outside and inside:
No change
Low water potential outside:
Cell shrinks significantly
Osmosis and plant cells
Water moves in or out of the cell, down its water potential gradient
(like an animal cell)
The cell wall does not affect this movement, as it is fully permeable to
Water enters the cell by osmosis
The water has to push up against the cell wall, the wall resists the
expansion of the cell (force called pressure potential) and becomes
If the plant cell is put into a concentrated solution, then the water
leaves it by osmosis.
If the plant cell is put into a concentrated solution, water then leaves
by osmosis
The cell will then shrink
If a lot is lost, the contents won't press up against the cell wall and the
cell becomes FLACCID
The cell membrane is usually damaged in the process (plasmolysed)
The cell then usually dies

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Active Transport
Happens when a cell needs to take up, or get rid of, substances whose
concentration gradient is in the `wrong' direction (usually sodium ions
and potassium ions)
Requires energy input from the cell Active Transport
Carried out by transporter proteins, working with ATP
ATP used to change the shape of the transporter proteins
Exocytosis and endocytosis (part of Active Transport)
Moving substances out of a cell in bulk substances is called exocytosis
The substance is contained in a tiny membranebound sac (vesicle)
Vesicle…read more

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Cell Division and Cellular Organisation
The Cell Cycle
You begin your life as a single cell, this is called a zygote (a cell that
forms when 2 gametes fuse)
After it was formed the zygote divides to form two cells, which then
divide to form four cells
The division continued until it made millions of cells (make up your
The cell cycle is made up of two main phases, interphase and mitosis
A cell cycle lasts about 24 hours, 95% of this time…read more

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Significance of mitosis
Mitosis occurs in many parts of the body
Mitosis is the type of cell division that occurs in a developing embryo
and throughout the growth of a human being
Mitosis also comes into play when part of the body is damaged and
needs repair
Mitosis is also used for reproduction (Asexual reproduction)
Singlecelled organisms can also reproduce by mitosis
The specialisation of a cell to carry out a particular function
Once a human cell is differentiated, it cannot change into another…read more

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Xylem vessels
Thick, strong cell walls containing cellulose and lignin help support a
plant.…read more

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System: Collection of organs with particular functions
Exchange Surfaces
Your body needs constant supplies of oxygen and nutrients and need to
get rid of waste materials such as CO2
As an organism gets bigger, both its surface area and its volume
A large organism must find ways of increasing surface area, so there is
enough surface to ensure that exchanges with environment can take
place rapidly enough to supply cells with all they need
Surface area: volume ratio
Surface area
Properties of…read more

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Smooth muscle is found in the walls of the trachea, bronchi and
bronchioles. It contracts slowly and steadily and can remain contracted
for long periods of time. It is an involuntary muscle.
Elastic Fibres are found in the walls of the airways. Important around the
alveoli, when you breathe in, the alveoli expand, stretching out like
elastic fibres. When you breathe out, the fibres recoil, helping to
decrease the volume in the lungs.…read more


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