Transport in cells

Question 1

Define diffusion.

Answer 1

The net movement of particles from an area of high concentration to an area of low concentration down a concentration gradient across a semi-permeable membrane.

Question 2

Name three substances which move by diffusion within animal cells.

Answer 2

1. Oxygen 2. carbon dioxide in gas exchange, 3. Urea out of cells to be excreted from the body.

Question 3

Name three factors which affect the rate of diffusion.

Answer 3

1. The difference in concentrations (concentration gradient)
2. Temperature
3. Surface area of the membrane.

Question 4

Does a single-celled organism have a high or low surface area:volume ratio?

Answer 4

High.

Question 5

How do single-celled organisms get enough oxygen without having lungs?

Answer 5

Due to its small size, and therefore its high SA:vol, diffusion across its membrane allows sufficient gas exchange

Question 6

Why do multicellular organisms tend to need exchange surfaces and transport systems?

Answer 6

Low SA:vol, therefore cannot rely on diffusion across cell membranes.

Question 7

Name two common features that aid the exchange of substances in the small intestine, lungs and fish gills but also a plant roots and leaves.

Answer 7

1. Large surface area, 2. Thin membrane to provide a short diffusion path.

Question 8

Define osmosis.

Answer 8

The diffusion of water from a dilute solution to a concentrated solution through a partially permeable membrane.

Question 9

If an animal cell loses a lot of water, what happens?

Answer 9

It crenates (shrivels) and cellular reactions are slowed or stopped.

Question 10

If an animal cell gains a lot of water, what happens?

Answer 10

It can lyse (burst) and die.

Question 11

If a plant cell loses a lot of water, what happens?

Answer 11

It becomes plasmolysed (cell membrane shrinks away from the cell wall).

Question 12

If a plant cell gains a lot of water, what happens?

Answer 12

It becomes turgid (cell membrane pushes up against the cell wall).

Question 13

Define active transport.

Answer 13

The movement of substances from a low concentration to a high concentration (against a concentration gradient).

Question 14

What two things does active transport require that diffusion doesn’t?

Answer 14

1. A transport protein (found in the cell membrane)
2. Energy.

Question 15

From what reaction does the energy required for active transport come?

Answer 15

Respiration.

Question 16

Where does active transport happen within a cell?

Answer 16

The mitochondria.

Question 17

Give two examples of where active transport is used in Biology. (1 plant, 1 animal)

Answer 17

1. Plant root hair cells absorbing mineral ions from the soil, 2. Glucose absorption from the small intestine into the blood.

Question 18

Why does active transport require extra energy?

Answer 18

Goes against the concentration gradient.