Topic 1b- Transport in cells

Question 1

What is diffusion?

Answer 1

Diffusion is the net movement of particles from an area of high concentration to an area of lower concentration. It is a passive process.

Question 2

What factors affect the rate of diffusion?

Answer 2

1. Concentration gradient
2. Temperature
3. Surface area

Question 3

Define osmosis.

Answer 3

Osmosis is the net movement of water molecules across a partially permeable membrane from a region of higher water concentration to a region of lower water concentration. It is a passive process.

Question 4

Define active transport.

Answer 4

Active transport is the movement of particles against a concentration gradient using energy transferred during respiration.

Question 5

Why do root hair cells need to use active transport to absorb mineral ions from the soil.

Answer 5

The concentration of minerals is usually higher in the root hair cell than in the soil.

Question 6

Give an example of when active transport occurs in the human body?

Answer 6

When there’s a higher concentration of glucose and amino acids in the blood than in the gut, meaning that active transport must be used to prevent diffusion of nutrients from the blood into the gut and allow glucose and amino acids to continuously be absorbed into the blood.

Question 7

Where does gaseous exchange occur in humans?

Answer 7

Lungs –> alveoli

Question 8

Explain gaseous exchange in the human lung.

Answer 8

• The alveoli are surrounded by a network of capillaries (tiny blood vessels).
• There is a higher concentration of oxygen in the air in the alveolus than in the blood.
• Therefore, oxygen diffuses out of the air in the alveolus into the blood in the capillaries.
• Carbon dioxide diffuses in the opposite direction (into the alveolus)
• The air exits the body via bronchioles.

Question 9

What are adaptations of the alveoli?

Answer 9

• Enourmous surface area
• Moist lining for dissolving gases
• Very thin walls
• Good blood supply

Question 10

How is the small intestine adapted to better absorb nutrients?

Answer 10

• large surface area due to villi that are covered in microvilli
• single layer of surface cells
• very good blood supply

Question 11

Explain gaseous exchange in leaves.

Answer 11

1. Underneath each leaf is an exchange surface covered in stomata.
2. Carbon dioxide diffuses into the leaf through the stomata.
3. The carbon dioxide then diffuses into the cells from the spaces within the leaf.
4. Oxygen and water diffuse out of the leaf and are lost from the stomata.

Question 12

Explain how a plant retains and looses water.

Answer 12

• Most water is lost through the stomata
• If the plant is loosing water faster through its leaves than can be replaced, the stomata can be closed by guard cells.

Question 13

Explain gaseous exchange in fish.

Answer 13

1. The gaseous exchange surface is the gills.
2. Water enters the fish through its mouth and passes out through the gills.
3. Oxygen diffuses from the water into the blood in the gills and carbon dioxide diffuses from the blood into the water.

Question 14

How are a fish’s gills adapted for gaseous excahnge?

Answer 14

• gill fillaments in the gill create a large surface area and in turn, increase the rate of diffusion.
• the gill fillaments are further covered with lamellae which further increase the surface area.
• thin surface layer of cells to minimise the distance that gases have to diffuse.
• blood flows through the lamellae in one direction while water flows in the other maintaining a large concentration gradient.

Question 15

How is urea extracted in blood cells by the body?

Answer 15

Diffuses from cells into the blood plasma for removal from the body by the kidneys.