Unit 3

Question 1

What is diffusion?

Answer 1

Diffusion is the net movement of molecules and ions from a region of high concentration to a region of lower concentration down a concentration gradient, as a result of their ramdom movement.

Question 2

Why is diffusion important?

Answer 2

Diffusion allows molecules and ions like food materials and oxygen to enter the cell. It also allows things like salts and water to enter the cell and get rid of substances like carbon dioxide and other things that would negatively affect the cell.

Question 3

Give examples of how diffusion occurs?

Answer 3

When a cell uses oxygen for aerobic respiration, the concentration of oxygen inside the cell falls, so oxygen molecules diffuse into the cell again until the concentration is raised. The opposite happens with carbon dioxide, during respiration CO2 is produced in the cell so the concentration increases, molecules move out of the cell to a lower concentration.

Question 4

What are some of the variables in the rate of diffusion of something?

Answer 4

1. Temperature
2. The distance it has to diffuse
3. The difference in concentration inside and outside the cell
4. The size of the molecules and ions
5. The surface area across which the diffusion is occurring.

Question 5

How does the rate of diffusion depend on the surface area of a cell (eg. the shape of the cell)?

Answer 5

If the surface area is increased, this should lead to a greater rate of diffusion. Eg. If the surface area is doubled, the rate of diffusion usually will approximately be doubled. Some cells are better at diffusion than others, even if they have the same volume, this is due to surface area.

Question 6

What do microvilli do?

Answer 6

They increase the surface area across which molecules and ions can be diffused in cells.

Question 7

What does an increase in temperature do?

Answer 7

The kinetic energy of the molecules and ions is sped up, leading to the rate of diffusion speeding up.

Question 8

How does the concentration gradient affect the rate of diffusion?

Answer 8

The difference in concentration of molecules and ions on each side of the cell is called the concentration gradient. The larger the concentration gradient/diffusion gradient. The higher the rate of diffusion usually.

Question 9

How does the distance the molecules and ions have to travel affect diffusion?

Answer 9

Cell membranes are all about the same thickness. However, plant cell walls can vary in thickness. The thinker the cell wall, the slower the rate of diffusion generally.

Question 10

How does the size of molecules and ions affect the rate of diffusion?

Answer 10

In general, molecules and ions that are larger will diffuse more slowly. Kind of an exception though.

Question 11

What is osmosis?

Answer 11

Osmosis is the diffusion of water across a partially permeable membrane to make a concentrated solution and a dilute solution equally concentrated.

Question 12

What is active transport?

Answer 12

Active transport is the movement of particles through a cell membrane from a region of lower concentration to a region of higher concentration using the energy from respiration.

Question 13

What do cells need food materials for?

Answer 13

Cells need food materials which they can oxidise for energy or use to build up their cell structures.

Question 14

What are salts and water needed for in a cell?

Answer 14

Salts and water are a part chemical reactions in the cell.

Question 15

Which two ways can substances pass through a cell membrane?

Answer 15

Through diffusion or by some form of active transport.

Question 16

How does decompression sickness ‘the bends’ occur and how can it be overcome?

Answer 16

When a diver descends the water pressure increases, this raises the pressure in a divers air tank or lungs. This raises the nitrogen pressure, which in turn, cause more nitrogen to diffuse into the the diver’s tissues. The body has no use for nitrogen so it builds up. When the diver ascends to the surface to quickly, the pressure decreases, this can cause the nitrogen to come out of solution and form bubbles which can block blood flow and become lodged in joints. This can only be overcome by rapid recompression.

Question 17

What is controlled diffusion?

Answer 17

Controlled diffusion refers to the fact that, the rate of diffusion for any one substance is often faster or slower than expected. This is because the ions or molecules which are diffusing may only pass through the cell membrane by special means, such as through pores, these pores may be few in number or open or closed in different conditions. In other cases, the movement of a substance may be sped up by an enzyme working in the cell membrane.

Question 18

What will happen more often in a cell, controlled diffusion or simple diffusion?

Answer 18

Controlled diffusion, simple diffusion is unlikely to play a very significant part in the movement of ions and molecules.

Question 19

How can osmosis affect the amount of water inside and outside of a cell?

Answer 19

When water diffuses from a dilute solution to a concentrated solution to make them equally concentrated, this should cause the amount the amount of water in the concentrated solution to rise and the amount of water in the dilute solution to fall.

Question 20

What is a partially permeable membrane?

Answer 20

A partially permeable membrane is porous but allows water to pass through more rapidly than dissolved substances.

Question 21

What can happen to a cell if there is excessive uptake or loss of water by osmosis?

Answer 21

It could swell and become damaged or then burst if there is an excessive uptake of water by osmosis. On the other hand, if there is an excessive loss of water by osmosis, the cell may shrink and become damaged.

Question 22

Why are the cells in an animal’s body surrounded by tissue fluid?

Answer 22

To make sure that the concentration of liquid inside the cell and the liquid outside the cell are the same.

Question 23

What does the concentration of the tissue fluid depend on?

Answer 23

The concentration of the tissue fluid depends on the concentration of the blood.

Question 24

How in the concentration of the blood controlled in vertebrates?

Answer 24

In vertebrates the concentration of the blood is monitored by the brain and adjusted by the kidneys.

Question 25

What does the cytoplasm and vacuoles in plant cells contain?

Answer 25

Salts, sugars and proteins.

Question 26

What happens when water diffuses into a plant cells vacuole?

Answer 26

The vacuole will expand until it is stopped when it reaches the cell wall. The cell wall of a mature plant cell cannot be stretched so the inflow of water will be resisted by the cell wall. When cell walls have absorbed a maximum amount of water by osmosis, they become very rigid, this gives plants their skeleton. If the cell loses any water, the water pressure will be decreased which should cause the plant to become limp and wilt.

Question 27

What is water potential?

Answer 27

The water potential of a solution is a measure of whether a particular solution is likely to lose or gain water molecules from another solution. A dilute solution is said to have a high water potential as it will lose water molecules to another solution. This is the opposite to a concentrated solution.

Question 28

What is a plant cell with a vacuole pushing out on the cell wall called?

Answer 28

It is called turgid, the vacuole itself is said to be exerting turgor pressure on the inelastic cell wall. This will result in a firm and upright stem with leaves held out straight.

Question 29

What is a plant cell with low turgor pressure (or just turgor) on the plant cell wall called?

Answer 29

Flaccid. If a plant has flaccid cells it will be limp and it’s stem will droop. The plant will be said to be wilting.

Question 30

What is the process where animal cells swell up called?

Answer 30

Haemolysis in red blood cells.

Question 31

What happens to cells when you exercise?

Answer 31

During physical activity the body may sweat to keep a constant temperature, if the water loss is not compensated for the body may become dehydrated. This causes the plasma to become more concentrated which causes water to be drawn out of red blood cells by osmosis. The red blood cells become plasmolysed.

Question 32

What happens when red blood cells are plasmolysed?

Answer 32

The red blood cells surface area is decreased making it less effective at carrying oxygen.

Question 33

What does isotonic mean?

Answer 33

Having the same water potential as body fluids. Athletes sometimes drink isotonic sports drinks in order not to cause osmotic problems to cells. Drinking isotonic sports drinks can cause weight-gain if the person doesn’t exercise vigorously.

Question 34

What is active transport?

Answer 34

Active transport is the movement of particles through a cell membrane from a region of lower concentration to a region of higher concentration using energy from respiration.

Question 35

Can substances diffuse against their concentration gradient?

Answer 35

Yes.

Question 36

Is controlled diffusion the same as active transport?

Answer 36

I don’t know.

Question 37

What do carrier molecules do?

Answer 37

Carrier molecules allow molecules to move into a cell against the concentration gradient.

Question 38

What type of molecule is a carrier molecule?

Answer 38

Carrier molecules are protein molecules.

Question 39

How do some single-celled organisms avoid bursting?

Answer 39

They possess a contractile vacuole.

Question 40

What is a contractile vacuole?

Answer 40

A contractile vacuole is a vacuole which collects water as it enters the cell and periodically releases it through the cell membrane.

Question 41

What is the shape of a plasmolysed red blood cell known as?

Answer 41

The shape of the cell is called crenated.

Question 42

What is an organism which has a contractile vacuole?

Answer 42

Amoeba which live in freshwater have contractile vacuoles.

Question 43

What is the energy change in active transport?

Answer 43

Chemical energy (from respiration) is converted into kinetic energy.