Download What is osmosis?

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How does diffusion create equilibrium?
Molecules move constantly and randomly. You might smell perfume when you walk past someone
who is wearing it. The perfume molecules move freely throughout the air. This random movement of
molecules from an area where there are more of them into an area where there are fewer of them is
called diffusion. Diffusion is a type of passive transport. Molecules will keep moving from one area to
another until the number of these molecules is equal in the two areas. When this occurs, equilibrium is
reached and diffusion stops.
All cells in your body use oxygen. Oxygen is taken in as you breathe. Then the oxygen moves
through your body in the red blood cells. When your heart pumps blood to your lungs, your red blood
cells contain few oxygen molecules. Your lungs have many oxygen molecules. Oxygen molecules move, or
diffuse, from your lungs into your red blood cells. The blood continues its journey through your body.
When the blood reaches your big toe, there are more oxygen molecules in your red blood cells than in
the cells of your big toe. The oxygen diffuses from your red blood cells to your big toe’s cells. Once the
oxygen is in the cells the mitochondria use it to break down glucose and release energy. The
mitochondria give off carbon dioxide as a waste product which is carried by the blood cells back the
lungs and as we breathe out we release the carbon dioxide into the air.
Put the following steps of cellular respiration in order from 1 - 8.
_____ You breathe oxygen into your lungs.
_____ You breathe out Carbon dioxide as waste.
_____ Oxygen diffuses from your lungs into your blood.
_____ The Carbon dioxide diffuses into your blood.
_____ Cellular respiration releases Carbon dioxide.
_____ The red blood cells carry the Carbon dioxide to your lungs.
_____ The mitochondria in your cells use the oxygen to break down
glucose and release energy.
_____ Your red blood cells carry oxygen to the rest of your cells.
What is osmosis?
Remember that water makes up a large
part of living matter. Water molecules move by
diffusion in and out of cells. The diffusion of
water through the cell membrane is called
osmosis.
What happens when you do not water
plants? As a plant cell loses water, its cell
membrane pulls away from the cell wall. This
reduces pressure against the cell wall, and the
plant cell becomes limp, as shown on the left in
the figure below. The plant wilts because more
water leaves the plant’s cells than enters them.
When you water the plant, the water
moves through the cell membranes and fills the cells with water. The plant’s cell membranes push against
their cell walls, and the cells become firm.
Osmosis in Animal Cells
Osmosis also takes place in animal cells. If animal
cells were placed in pure water, they too would swell up.
However, animal cells are different from cells. Just like an
overfilled balloon, animal cells will burst if too much water
enters the cell and if they don’t have enough water they will
shrivel up.
Determine if the following statements are showing DIFFUSION or OSMOSIS (circle the answer)
1. Leftover salad wilting in the refrigerator.
2. Making a cup of tea. DIFFUSION
3. Smoke escaping from a chimney.
DIFFUSION
OSMOSIS
OSMOSIS
DIFFUSION
OSMOSIS
4. You spilled soda on your shirt so you soak it in water to get the stain out. DIFFUSION
OSMOSIS
5. After soaking celery sticks in red water you see the red dye has moved through the celery.
DIFFUSION
OSMOSIS
6. The smell of a candle spreading through the room.
7. You put raisins in a glass of water and they plump up.
DIFFUSION
OSMOSIS
DIFFUSION
OSMOSIS
8. Oxygen being released from plant cells as a waste product. DIFFUSION
OSMOSIS
9. While running you begin to sweat (a lot) and you begin to feel thirsty.
DIFFUSION
OSMOSIS
10. In order to keep your cookies from going stale you put a piece of bread in with them to keep them
moist.
DIFFUSION
OSMOSIS