B1.3- Transport in cell

Question 1

Name the process whereby substances move in and out of a cell across the cell membrane.

Answer 1

Diffusion.

Question 2

Define “diffusion”.

Answer 2

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 3

Name three substances which move by diffusion within animal cells.

Answer 3

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

Question 4

Name three factors which affect the rate of diffusion.

Answer 4

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

Question 5

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

Answer 5

High.

Question 6

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

Answer 6

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

Question 7

An organism has a surface area of 50m2 and a volume of 20m3. What is its surface area to volume ratio?

Answer 7

2.5:1

Question 8

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

Answer 8

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

Question 9

Name two common features that aid the exchange of substances in animal small intestine & lungs; fish gills; plant roots and leaves.

Answer 9

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

Question 10

Name two further features that aid the exchange of substances in animals but NOT plants.

Answer 10

1. An efficient blood supply, 2. The ability to ventilate (to allow air to move in and out of the organism).

Question 11

Define osmosis.

Answer 11

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

Question 12

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

Answer 12

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

Question 13

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

Answer 13

It can lyse (burst) and die.

Question 14

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

Answer 14

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

Question 15

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

Answer 15

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

Question 16

Define active transport.

Answer 16

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

Question 17

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

Answer 17

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

Question 18

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

Answer 18

Respiration.

Question 19

Where does active transport happen within a cell?

Answer 19

The mitochondria.

Question 20

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

Answer 20

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