Osmosis And Tonicity

Question 1

Define osmosis

Answer 1

The movement of water molecules from an area of high concentration to low concentration across a semi permeable membrane

Question 2

Why is osmosis needed/why is it important?

Answer 2

We need osmosis to balance the water and amount of solute in the cells.

Question 3

What exactly do we mean by high concentration to low concentration (concentration of what?)

Answer 3

When the body or a plant loses water, the amount of water drops outside a cell. However, there are still the same amount of ions and other particles that remain outside the cell. This means the cell increases in solute and that’s the concentration that increases.

Question 4

How does osmosis work to balance water and solute amount in a cell?

Answer 4

The water or solute will move from the place where concentration of ions and other particles are high to where the concentration of those ions and particles are low, this will balance the water or solute in the cell and outside the cell and it will be equalised in concentration

Question 5

How does it affect osmosis that the membrane is semi permeable?

Answer 5

The semi permeable membrane only allowed certain things through (it has tiny holes that bigger molecules can’t fit through). For example: water, ions can fit but sucrose and other big molecules can’t

Question 6

What does it mean by “steady net flow” of water

Answer 6

Having a steady net flow of water means that even though the water movement is random and will travel both ways (in and out of the membrane), overall movement is where there is more water is to less

Question 7

What’s the difference between diffusion and osmosis?

Answer 7

Osmosis only transports certain particles to balance water and ions whereas diffusion is particles in general and unlike osmosis, can travel through a membrane that’s isn’t semi permeable

Question 8

What’s one similarity of osmosis and diffusion?

Answer 8

Both transport particles or molecules down the concentration gradient

Question 9

List minimum of two examples of osmosis occurring in either animals or plants

Answer 9

Plant: when water moves from soil to root of the plant
Animal: in the kidneys, water moves in and out to balance salt and pH levels

Question 10

What experiment do we use to test for osmosis? How does it work?

Answer 10

The potato cylinder experiment- potato cylinders are put into a concentration of sugar/salt. If the potatoes have drawn in water they increase in mass and the opposite happens when they lose water.

Question 11

For plants, what is turgor pressure? In what context involving turgor pressure will it mean that a plant wilts?

Answer 11

When a plant wilts, water moves out from the cells so the cells’ internal pressure decreases. This pressure normally supports the plants and is called turgor pressure. It’s the pressure that pushes plasmic membrane and cytoplasm into the cell wall to keep it rigid and give the cell its structure. Without this pressure, a plant would wilt.

Question 12

What is tonicity? What terms are used to describe it?

Answer 12

It’s the ability of extra cellular solutions (any fluid outside the cell) to make water moves into or out of a cell by osmosis. The terms hyper-hypo-iso-tonic are used to describe tonicity

Question 13

What does hypertonic mean for a solution and for a cell?

Answer 13

If a cell is placed in a hypertonic solution, there will be a net flow of water OUTSIDE of the cell and the cell loses volume. A solution is only hypertonic is the solution’s solute concentration is higher than the concentration in the cell and if the solutes cannot cross the membrane

Question 14

The term plasmolyed/plasmolysis can ONLY BE USED FOR PLANTS. What does it mean?

Answer 14

It’s the process in which cells lose water in a hypertonic solution. When water leaves, the cytoplasm shrinks, pulling the membrane and cytoplasm away from the cell wall- making the cell flaccid

Question 15

What does it mean for the cell and solution if the solution is hypotonic?

Answer 15

If a cell is placed in a hypotonic solution there’ll be a net flow of water INTO the cell. The cell will gain volume. If the solute concentration outside the cell is lower than inside the cell than the solute can’t cross the membrane, the solution is hypotonic to the cell

Question 16

The term turgid IS ONLY USED TO PLANTS. What does it mean?

Answer 16

Turgid- plant cell’s vacuole swell and becomes hard. Pressure in the cell rises so high they no more water can enter the cell. Cell may burst.

Question 17

What does an isotonic solution mean for the cell and the solution?

Answer 17

No net flow of water either in nor out of cells and the cell’s volume will remain stable. If the solute concentration outside is the same as inside the cell and solutes cannot cross the membrane then the solution is isotonic to the cell

Question 18

Both Amoeba and Paramecium do osmoregulation with their contractile vacuoles because of their living conditions. The vacuole expels excess water. Explain how it works and why it happens?

Answer 18

Both of these organisms live in fresh water so this so this process is necessary as freshwater has a lower concentration of solutes than the amoeba and paramecium’s own solutes. Because of this, the water is hypotonic to them. So the cell could burst. The vacuole expels excess water so the water is transported out by the contractile vacuole otherwise the cell might burst.

Question 19

Marine amoeba don’t need contractile vacuoles. Why?

Answer 19

Because the concentration of solutes within the cell is in balance to the concentration outside the cell so the water is isotonic in respect to the cell