Chapter 2 Transport in Cells

Question 1

Give the definition of diffusion.

Answer 1

Diffusion is the spreading out of the particles of a substance. This results in the net movement of particles from an area of high concentration to an area of lower concentration.

Question 2

What does passive mean?.

Answer 2

Diffusion is passive. This means it does not require any energy.

Question 3

Why is diffusion important?

Answer 3

Diffusion is important because it allows substances to enter and leave cells.

Question 4

What does partially permeable mean?

Answer 4

The cell membrane is partially permeable. This means that only some substances can enter and leave the cell.

Question 5

List 5 substances able to enter and leave the cell by diffusion.

Answer 5

Substances able to enter and leave the cell by diffusion include oxygen, carbon dioxide, glucose, amino acids and water.

Question 6

Give 2 molecules that cannot pass through the cell membrane by diffusion.

Answer 6

Large molecules like starch and proteins cannot pass through the cell membrane by diffusion.

Question 7

Which cells does oxygen diffuse into? Which cells do they diffuse out of?

Answer 7

Oxygen diffuses into red blood cells in the lungs and then diffuses out of red blood cells and into body cells.

Question 8

Describe the diffusion of carbon dioxide in animal cells.

Answer 8

Carbon dioxide diffuses from body cells into red blood and travels to the lungs where it diffuses into the lungs and is breathed out.

Question 9

Give 3 factors that affect the rate of diffusion.

Answer 9

Factors that affect the rate of diffusion include:
The concentration gradient - the bigger the difference in concentration the higher the rate of diffusion

Temperature - the rate of diffusion increases with temperature

Surface area of the membrane - the rate of diffusion increases as surface area increases.

Question 10

Give the full definition of osmosis.

Answer 10

Osmosis is a special case of diffusion where water molecules move from an area of high water concentration to an area of lower water concentration through a partially permeable membrane like a cell membrane.

Question 11

What is a dilute solution?

Answer 11

A dilute solution has very few dissolved particles.

Question 12

What is a concentrated solution?

Answer 12

A concentrated solution has many dissolved particles.

Question 13

Describe visking tubing? WHat is it a model of?

Answer 13

Visking tubing models a cell membrane because it is partially permeable. Only some substances can pass through.

Question 14

What is an isotonic solution?

Answer 14

An isotonic solution has the same concentration of solutes as the cell.

Question 15

What is a hypotonic solution?

Answer 15

A hypotonic solution has a lower concentration of solutes than the cell has. Water will move into the cell.

Question 16

What is a hypertonic solution?

Answer 16

A hypertonic solution has a higher concentration of solutes than the cell has. Water will move out of the cell.

Question 17

Draw a diagram to represent what happens to animal cells when placed in hypertonic, isotonic and hypotonic solutions.

Answer 17

The diagram below represents what happens when animal cells are placed in different solutions.

Question 18

Describe what will happen to an animal cell when placed in a hypertonic solution.

Answer 18

When animal cells are placed in hypertonic solutions (high solute concentration) they will shrink and become shrivelled.

Question 19

Describe what will happen when animal cells are placed in a hypotonic solution.

Answer 19

When animal cells are placed in hypotonic solutions (low solute concentration / high water concentration) they will swell and burst.

Question 20

Draw a diagram to represent what happens when plant cells are placed in hypertonic, isotonic and hypotonic solutions.

Answer 20

The diagram below represents what happens when plant cells are placed in different solutions.
Hypertonic Isotonic Hypotonic

Question 21

Describe what happens to a plant cell when placed in a hypertonic solution.

Answer 21

When plant cells are placed in hypertonic solutions (high solute concentration) the vacuole shrinks and the cell membrane pulls away from the cell wall. We describe a cell like this as plasmolysed.

Question 22

What name is given to plant tissue made up of plasmolysed cells?

Answer 22

Plant tissue made up of plasmolysed cells can be described as flaccid.

Question 23

Describe what happens when plant cells are placed in a hypotonic solution.

Answer 23

When plant cells are placed in hypotonic solutions (low solute concentration / high water concentration) they gain water and become turgid. They do not burst because the cell wall protects them from bursting.

Question 24

How can we investigate osmosis?

Answer 24

Osmosis can be investigated by placing potato cylinders in different concentrations of sucrose solutions.

Question 25

Describe an investigation into osmosis.

Answer 25

Potato cylinders are weighed before the investigation then after submersion in the different solutions. The % change in mass is then calculated.

Question 26

Why is % change in mass used in osmosis investigations?

Answer 26

We use % change in mass because it is difficult to get the starting masses the same.

Question 27

What is the formula for calculating % change?

Answer 27

The formula for calculating % change is:

Question 28

Why must we blot potato cylinders dry before weighing?

Answer 28

Potato cylinders must be blotted dry before weighing to remove any water on the outside so it is not included in the mass.

Question 29

What happens to the mass of potato cylinders when placed in hypertonic solutions?

Answer 29

Potato cylinders placed in hypertonic solutions will lose mass.

Question 30

What happens to the mass of potato cylinders when placed in hypotonic solutions?

Answer 30

Potato cylinders placed in hypotonic solutions will gain mass.

Question 31

What happens to the mass of potato cylinders when placed in isotonic solutions?

Answer 31

Potato cylinders placed in isotonic solutions will remain the same mass.

Question 32

Give the definition of active transport.

Answer 32

Active transport involves substances moving from an area of low concentration to an area of high concentration against the concentration gradient. Active transport requires energy.

Question 33

Where does the energy for active transport come from?

Answer 33

The energy for active transport comes from breaking down food by respiration.

Question 34

What does the rate of active transport depend on?

Answer 34

The rate of active transport depends on the rate of respiration. If the rate of respiration is low then active transport is low because there is not enough energy available to move the substances.

Question 35

Describe how active transport is used in plant root hair cells.

Answer 35

Plant root hairs use active transport to get mineral ions the plant needs into the cells from the soil against a concentration gradient.

Question 36

What happens to the surface area to volume ratio as objects get bigger?

Answer 36

As objects get bigger their surface area to volume ratio decreases.

Question 37

Do single celled organisms have a large or small surface area to volume ratio?

Answer 37

Single celled organisms have a large surface area to volume ratio so can exchange all substances across their membranes.

Question 38

How do multicellular organisms overcome the issue of low surface area to volume ratio?

Answer 38

Multicellular organisms have organs with specialised cells for the exchange of materials. For example, gas exchange takes place in the air sacs of the lungs where there is a large surface area.

Question 39

Give 3 features of airs sacs that make them good for gas exchange.

Answer 39

Airs sacs have a large surface area, very thin walls so gases don’t have far to travel and a rich blood supply to carry the gases away to body cells.