(Paper 1 Content Knowledge) 1.3 Cells: Diffusion, Osmosis, Active Transport

Question 1

How do particles in liquids and gases move?

Answer 1

They move continuously and randomly.

Question 2

What is diffusion?

Answer 2

The net movement of particles from a region of higher concentration to a region of lower concentration

Question 3

In diffusion, particles move in which directions?

Answer 3

Particles move in all directions, but there is a net movement from high to low concentration.

Question 4

What happens to particles at the end of diffusion?

Answer 4

They become evenly spread throughout the liquid or gas but continue to move randomly.

Question 5

What causes diffusion?

Answer 5

An imbalanced concentration gradient

Question 6

Define net movement.

Answer 6

Overall movement of particles from higher to lower concentration.

Question 7

How do gases enter and leave a leaf?

Answer 7

By diffusion through stomata.

Question 8

What gas diffuses into leaves for photosynthesis?

Answer 8

Carbon dioxide

Question 9

Which gas diffuses out of leaves during photosynthesis?

Answer 9

Oxygen

Question 10

Why does carbon dioxide diffuse into a leaf?

Answer 10

Because its concentration is lower inside the leaf (used up in photosynthesis) than outside.

Question 11

Why does oxygen diffuse out of a leaf during photosynthesis?

Answer 11

Because oxygen concentration is higher inside the leaf (produced during photosynthesis) than outside.

Question 12

Through which structure do gases diffuse in leaves?

Answer 12

The Stomata

Question 13

What controls the opening and closing of stomata?

Answer 13

Guard Cells

Question 14

Where in the lungs does gas exchange occur?

Answer 14

The alveoli

Question 15

How does oxygen move into the blood from the lungs?

Answer 15

By diffusion, from high concentration (alveoli) to lower concentration (blood).

Question 16

How does carbon dioxide move from the blood into the lungs?

Answer 16

By diffusion, from high concentration (blood) to lower concentration (alveoli).

Question 17

What feature of alveoli makes diffusion efficient?

Answer 17

They have a large surface area, thin walls, and good blood supply.

Question 18

Why do alveoli have thin walls?

Answer 18

To shorten the diffusion distance for gases.

Question 19

Why must alveoli be surrounded by capillaries?

Answer 19

To maintain a steep concentration gradient for efficient diffusion.

Question 20

Which gas diffuses from alveoli into the bloodstream?

Answer 20

Oxygen (O₂).

Question 21

Which gas diffuses from the bloodstream into alveoli?

Answer 21

Carbon dioxide (CO₂).

Question 22

Where is urea produced in the body?

Answer 22

The liver

Question 23

By which process does urea move out of liver cells?

Answer 23

Diffusion

Question 24

Why does urea diffuse from liver cells into the blood?

Answer 24

Because there’s a higher concentration of urea inside liver cells than in the surrounding blood.

Question 25

After diffusing into the blood, where does urea go next?

Answer 25

To the kidneys, where it is filtered out and excreted in urine.

Question 26

What maintains the concentration gradient for urea diffusion out of liver cells?

Answer 26

Blood continuously carrying urea away to the kidneys.

Question 27

In a solution, what is the solute?

Answer 27

The substance that dissolves (e.g., potassium manganate).

Question 28

In a solution, what is the solvent?

Answer 28

The liquid in which the solute dissolves (e.g., water).

Question 29

Define solution.

Answer 29

A mixture formed when a solute dissolves in a solvent.

Question 30

What is a concentration gradient?

Answer 30

The difference in concentration between two areas.

Question 31

How do particles move along a concentration gradient?

Answer 31

From high concentration to low concentration (down the gradient).

Question 32

Name three factors affecting the rate of diffusion.

Answer 32

1. Concentration gradient 2. Temperature 3. Surface area

Question 33

How does the concentration gradient affect diffusion rate?

Answer 33

The greater the difference in concentration, the faster the rate of diffusion.

Question 34

How does temperature affect the rate of diffusion?

Answer 34

Higher temperatures increase particle kinetic energy, increasing diffusion rate.

Question 35

How does surface area affect the rate of diffusion?

Answer 35

A larger surface area increases the rate of diffusion.

Question 36

Why is diffusion sufficient for substances to move in bacteria?

Answer 36

They are very small, so substances diffuse short distances quickly.

Question 37

How do simple multicellular organisms (e.g., mosses) take in substances?

Answer 37

By diffusion and osmosis over their surfaces.

Question 38

Why do larger organisms need more complex transport systems than just diffusion?

Answer 38

Their surface area to volume ratio decreases as they grow, making diffusion alone insufficient.

Question 39

What happens to the surface area to volume ratio as an organism increases in size?

Answer 39

It decreases.

Question 40

What is osmosis?

Answer 40

The diffusion of water molecules from an area of higher water concentration to an area of lower water concentration, across a partially permeable membrane.

Question 41

What type of membrane is needed for osmosis?

Answer 41

A partially permeable membrane.

Question 42

What is a partially permeable membrane?

Answer 42

A membrane that allows some substances, such as water molecules, to pass through but not others.

Question 43

Define dilute solution.

Answer 43

A solution with a high concentration of water molecules (low concentration of solute).

Question 44

Define concentrated solution.

Answer 44

A solution with a low concentration of water molecules (high concentration of solute).

Question 45

What happens when the water concentration is equal on both sides of a membrane?

Answer 45

Water molecules move equally in both directions; there is no net movement.

Question 46

What happens to a plant cell in pure water?

Answer 46

It becomes turgid (firm), as water moves in by osmosis and the cytoplasm pushes against the cell wall.

Question 47

Why don't plant cells burst in pure water?

Answer 47

Because they have a strong cellulose cell wall.

Question 48

What happens to plant cells in concentrated solutions?

Answer 48

They lose water, become flaccid, and may become plasmolysed.

Question 49

Define plasmolysis.

Answer 49

When the cell contents shrink and pull away from the cell wall due to water loss.

Question 50

How does osmosis affect animal cells placed in dilute solutions?

Answer 50

They gain water, swell, and may burst (lysis).

Question 51

How does osmosis affect animal cells placed in concentrated solutions?

Answer 51

They lose water and shrink (crenation).

Question 52

Why must the concentration of body fluids (like blood plasma) be strictly controlled in animals?

Answer 52

To prevent cells from gaining or losing too much water, which would stop them from functioning efficiently.

Question 53

How do root hair cells take up water from moist soil?

Answer 53

By osmosis, moving water from high concentration (soil) into lower concentration (cell).

Question 54

What happens to freshwater plants placed in seawater?

Answer 54

They lose water by osmosis and become plasmolysed.

Question 55

Define active transport.

Answer 55

The movement of molecules from a lower concentration to a higher concentration (against a concentration gradient), using energy.

Question 56

Does active transport require energy?

Answer 56

Yes, it requires energy from respiration.

Question 57

In which direction does active transport move substances?

Answer 57

From a low concentration to a high concentration (against a concentration gradient).

Question 58

Give an example of active transport in plants.

Answer 58

The uptake of mineral ions from dilute soil solutions into root hair cells.

Question 59

Why is active transport important for plants?

Answer 59

It allows plants to absorb essential mineral ions from the soil, even when the concentration in the soil is low.

Question 60

Give an example of active transport in animals.

Answer 60

Absorption of glucose molecules from the intestine into the blood.

Question 61

Why might glucose need to be absorbed by active transport in animals?

Answer 61

When glucose concentration in the intestine is lower than in the blood.

Question 62

What provides the energy for active transport?

Answer 62

Energy released from respiration.