B4 Diffusion and Osmosis

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How do Substances move in and out of cell membranes?
by diffusion
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What is diffusion?
Diffusion is the movement of a substance from a region of high, concentration to a region of low concentration.
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What is random movement (in diffusion)?
Particles move about in lots of different directions.
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What is net overall movement?
Diffusion is the net (overall) movement of particles from an area of high concentration to an area of low concentration.
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What are the three things the rate of diffusion is increased by?
1. there's a greater surface area of the cell membrane 2.there's a greater difference between concentrations (a steeper concentration gradient) 3. the particles have a shorter distance to travel.
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What moves in and out of plants through their leaves?
carbon dioxide and oxygen
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In plants during the day how is carbon dioxide used up?
in photosynthesis
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What happens to the concentration as carbon dioxide is used during the day through photosynthesis?
The concentration inside the leaves is lower than the concentration outside the leaves.
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How does carbon dioxide diffuse into plants during the day?
Through the stomata (tiny pores) on the bottom of their leaves
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How does oxygen diffuse from plants during the day?
oxygen, a product of photosynthesis, diffuses from the plant into the atmosphere.
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At night what happens to photosynthesis?
it stops
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What does oxygen and carbon dioxide do at night?
Oxygen diffuses into leaf cells and carbon dioxide diffuses out of leaf cells.
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How are the stomata on the underside of leaves specially adapted to do?
open — to help increase the rate of diffusion of carbon dioxide and oxygen • close — to prevent excessive water loss in drought conditions.
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What is osmosis?
Osmosis is the diffusion of water from high concentration of water (dilute solution) to low concentration of water (concentrated solution); through a partially-permeable membrane
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What is partially-permeable membrane
(a membrane that allows the passage of water molecules but not solute molecules).
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What is osmosis a special type of?
diffusion involving water molecules.
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Plant cells are surrounded by what?
a cell membrane
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What does a membrane allow?
water to move in and out of the cells
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How do Water and solute molecules move (osmosis)?
Water and solute molecules move freely through the cellulose cell wall.
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What is The function of the cell wall?
The function of the cell wall is to provide support — it doesn't affect the movement of substances in or out of the cell.
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Whilst the water particles move randomly in osmosis what do they do?
collide with eachother whilst passing through the membrane in both directions
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What is the net movement?
net movement of molecules is from the area of high water concentration to the area of low water concentration. This gradually dilutes the solution.
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How can you predict the direction of water movement?
You can predict the direction of water movement if you know what the concentration of the water is,
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What molecules can't pass through the membrane?
solute
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What molecules can pass through the membrane?
water
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Movement of water is always what?
Movement of water is always from high to low water concentration.
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What does water also do in an animal cell?
Water also diffuses in and out of animal cells through the cell membrane by osmosis.
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What do animal cells not have?
a cell wall
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What problem could animal cells not having a cell wall cause?
animal cells don't have a cell wall, so too much water entering a cell could cause the cell to burst.
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When do red blood cells retain their ideal shape?
When red blood cells are in solutions with the same concentration as their cytoplasm, they retain their shape.
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When do red blood cells become swollen?
When in a weaker solution, they absorb water, swell up, and may burst.
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When do red blood cells become shrivelled?
When in a more concentrated solution, they lose water and shrivel up,
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What do animal cells not have unlike plant cells?
Animal cells, unlike plant cells, don't have an inelastic cell wall.
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What is iysis?
Blood cells in a pure water solution will gain water by osmosis. Without a cell wall to prevent water entering the cell, they absorb more and more water until eventually they burst. This is called lysis.
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What happens to blood cells in a concentrated solution (very little water)?
Blood cells in a concentrated solution (very little water) will lose water by osmosis.
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Without a cell wall to prevent water loss what can animal cells do?
Without a cell wall to prevent water loss, they can shrivel up and become crenated (have rough edges).
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What walls do plant cells have?
inelastic cell walls
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What is essential for the support of young non-woody plants?
Plant cells have inelastic cell walls which, together with the water inside the cells, are essential for the support of young non-woody plants.
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What does the cell wall do in plant cells?
prevents cells from bursting due to excess water • contributes to rigidity.
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What is turgor pressure?
The pressure of the water pushing against the cell wall is called turgor pressure.
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What can a lack of water cause plants to do?
A lack of water can cause plants to droop (wilt).
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Why does A lack of water can cause plants to droop (wilt)?
As the amount of water inside the cells reduces, the cells become less rigid due to reduced turgor pressure.
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As water moves into plant cells by osmosis what happens?
As water moves into plant cells by osmosis, the pressure inside the cell increases.
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Why does the (plant) cell become very turgid(rigid)?
As water moves into plant cells by osmosis, the pressure inside the cell increases. The inelastic cell walls can withstand the pressure and the cell becomes very turgid (rigid).
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What happens to the plant when all cells are fully turgid?
When all the cells are fully turgid, the plant is firm and upright.
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What happens to a plant when water is in short supply?
if water is in short supply, cells will start to lose water by osmosis. They lose turgor pressure and become flaccid (not rigid), and the plant begins to wilt.
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What is plasmolysis?
When cells lose a lot of water, the inside of the cell contracts. This is called plasmolysis.
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Card 2

Front

What is diffusion?

Back

Diffusion is the movement of a substance from a region of high, concentration to a region of low concentration.

Card 3

Front

What is random movement (in diffusion)?

Back

Preview of the front of card 3

Card 4

Front

What is net overall movement?

Back

Preview of the front of card 4

Card 5

Front

What are the three things the rate of diffusion is increased by?

Back

Preview of the front of card 5
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