B2.1 Diffusion, Osmosis, Active Transport

Question 1

Define diffusion.

Answer 1

Diffusion is the net movement of particles from an area of high concentration to an area of low concentration, down a concentration gradient.

Question 2

Why is diffusion a passive process?

Answer 2

Diffusion occurs because of the ordinary motion of the particles, so energy is not transferred.

Question 3

How do particles in a gas or solution move?

Answer 3

Particles move constantly, and randomly.

Question 4

When does diffusion stop?

Answer 4

When the concentration of the particles is equal everywhere, the concentration gradient is zero.

Question 5

Give a example of diffusion in the body.

Answer 5

Oxygen and glucose diffuse into your cells, and carbon dioxide diffuses out.

Question 6

Which factors affect the rate of diffusion?

Answer 6

• Distance
  (Blood capillaries - one cell thick)
• Concentration Gradient
• Surface area
  (Highly folded small intestine)
• (Temperature)
  (Higher kinetic energy of particles)

Question 7

What is osmosis?

Answer 7

Osmosis is the movement of water molecules across a selectively permeable membrane from an area of high water potential to an area of low water potential (down the water potential gradient).

Question 8

How do water molecules behave around solute molecules?

Answer 8

Water molecules cluster around solute molecules, leaving few free water molecules to diffuse.

Question 9

What is water potential?

Answer 9

Water potential is the concentration of free water molecules.

Question 10

What meant by a hypertonic solution?

Answer 10

When a solution has a higher osmotic pull and higher solute concentration (lower water potential) than another solution.

Question 11

What meant by a hypotonic solution?

Answer 11

When a solution has a lower osmotic pull and lower solute concentration (higher water potential) than another solution.

Question 12

What meant by an isotonic solution?

Answer 12

As isotonic solution has the same osmolarity, or solute concentration, as another solution.

Question 13

What happens when a plant cell is placed in a hypotonic solution?

Answer 13

Water moves into the vacuole via osmosis.
Turgor pressure in the cell increases.
The cell becomes turgid/firm.
The cell wall stops cell from bursting.

Question 14

What is does it mean when a plant cell becomes turgid?

Answer 14

When a plant cell is placed in a hypotonic solution, water enters the vacuole which pushes against the cell wall. The cell becomes firm and swollen.

Question 15

What happens when a plant cell is placed in an isotonic solution?

Answer 15

There is no net movement of water.

Question 16

What happens when a plant cell is placed in a hypertonic solution?

Answer 16

Water moves out of the vacuole via osmosis.
Turgor pressure in the cell falls.
The cell becomes flaccid (soft).
The cell contents collapse away from the cell wall.
The cell becomes plasmolysed.

Question 17

What is plasmolysis?

Answer 17

Plasmolysis is the process of a cell losing water when placed in a hypertonic solution, which causes the shrinking of the plasma membrane away from the cell wall. It is reversible.

Question 18

What happens when an animal cell is placed in a hypotonic solution?

Answer 18

Water moves into the cell via osmosis.
The cells takes up water and swells.
The cell could also burst (lysis).

Question 19

What is lysis?

Answer 19

Lysis is the rupture/disintegration of the cell membrane, resulting in the release of cell contents or the subsequent death of the cell.

Question 20

What happens when an animal cell is placed in an isotonic solution?

Answer 20

There is no net movement of water.

Question 21

What happens when an animal cell is placed in an hypertonic solution?

Answer 21

Water moves out of the cell via osmosis.
The cells shrinks and crinkles (crenation).
Crenation is mainly observed in RBCs.

Question 22

What is crenation?

Answer 22

When an animal cell is placed in a hypertonic solution causing too much water to leave the cell by osmosis and the cell to shrink and shrivel.

Question 23

How are the small intestines adapted to maximise diffusion?

Answer 23

Small intestines

Villi & Microvilli - increases surface area, therefore volume that can be absorbed.
Good blood supply – substances diffuse straight into the bloodstream, maintains concentration gradient.

Question 24

How are the lungs adapted to maximise diffusion?

Answer 24

Alveoli

• They are very thin - small distance to diffuse over
• They are covered by a network of fine capillaries so diffusion happens straight into the bloodstream, maintains concentration gradient.
• They are moist.
• They have a large combined surface area.

Question 25

What role does diffusion play in enabling photosynthesis?

Answer 25

• Carbon dioxide diffuses in through the stomata.
• Oxygen and water diffuse out of the stomata
• During photosynthesis, the level of CO2 is low inside the leaf, creating a big concentration gradient so CO2 diffuses into the cell

Question 26

Define active transport.

Answer 26

The transport of particles from an area of low concentration to an area of high concentration, against a concentration gradient using ATP (energy).

Question 27

What are carrier proteins?

Answer 27

• Proteins embedded within the cell surface membrane.
• They bind with useful molecules and then use ATP to rotate or change shape to transport the molecule into the cell.
• Allow the transport of useful molecules against a concentration gradient.

Question 28

Why do cells that carry out active transport contain a lot of mitochondria?

Answer 28

Mitochondria produce energy and energy is required for active transport to take place.

Question 29

State an example of active transport in plants.

Answer 29

Root hair cells - Transport of mineral ions from low concentration in the soil to higher concentration in the root hair cell.

Question 30

State two examples of active transport in animals.

Answer 30

1. Nerve cells - active transport used to pump sodium & potassium ions required to create nerve impulses
2. Digestion - active transport used to transport the final products of digestion into the bloodstream through the villi