Transport in cells 1.3

Question 1

What is diffusion?

Answer 1

The net movement of particles from an area of higher concentration to an area of lower concentration

Question 2

What three main factors affect the rate of diffusion?

Answer 2

• Concentration gradient - larger gradient, faster diffusion
• Temperature - higher temperature, faster diffusion
• Surface area - larger surface area, faster diffusion

Question 3

Give examples of substances transported by diffusion in the lungs and the kidney

Answer 3

• Lungs: oxygen diffuses into the blood from the lungs and carbon dioxide diffuses into the lungs from the blood, both down their concentration gradient
• Kidney: urea diffuses from cells into blood plasma so it can be excreted in urine

Question 4

How are single-celled organisms adapted for diffusion?

Answer 4

They have a large surface area to volume ratio- maximises the rate of diffusion of molecules to meet the organism’s needs

Question 5

How is surface area to volume ratio calculated?

Answer 5

Surface area = number of sides x (side length x side width)
Volume = length x width x depth
Ratio = surface area : volume

Question 6

What four factors increase the effectiveness of a gas exchange surface?

Answer 6

• Large surface area
• Thin membrane (short diffusion path)
• Efficient blood supply (animals)
• Ventilation (animals)

Question 7

What is osmosis?

Answer 7

The movement of water molecules from a dilute solution to a concentrated solution through a partially permeable membrane

Question 8

What is meant when a solution is isotonic to a cell?

Answer 8

The concentrations of the external and internal (inside cell) solutions are the same

Question 9

What is meant when a solution is hypertonic to a cell?

Answer 9

The concentration of the external solution is high than that of the internal solution (inside cell)

Question 10

What is meant when a solution is hypotonic to a cell?

Answer 10

The concentration of the external solution is lower than that of internal solution (inside cell)

Question 11

What may happen when an animal cell is placed in a very hypotonic solution?

Answer 11

Water moves into the cell, causing it to burst

Question 12

What may happen when an animal cell is placed in a very hypertonic solution?

Answer 12

Water moves out of the cell, causing it to shrivel up

Question 13

How do plant leaves and stems remain rigid?

Answer 13

Turgor pressure - water moves in by osmosis, causing the vacuole to swell and the cytoplasm to press against the cell wall

Question 14

What may happen when a plant cell is placed in a very hypertonic solution?

Answer 14

Water moves out of the cell by osmosis and the vacuole and cytoplasm decrease in size. The cell membrane may pull away from the cell wall, causing the cell to become plasmolysed

Question 15

What is active transport?

Answer 15

The movement of molecules from a more dilute solution to a more concentrated solution against a concentration gradient, using energy from respiration

Question 16

How do plant root hair cells use active transport?

Answer 16

Root hair cells use active transport to take up mineral ions from a more dilute solution in soils. Ions such as magnesium and nitrates are required for healthy growth

Question 17

How is active transport used to absorb the products of digestion?

Answer 17

Active transport is used to transport glucose from a lower concentration in the gut to a higher concentration in the blood. Glucose is then transported to the tissues where it can be used in respiration