cell transport

Question 1

What is diffusion?

Answer 1

The net movement of particles from an area of high concentration to an area of low concentration

Question 2

What is a concentration gradient?

Answer 2

difference in the concentration of a substance from one location to another

Question 3

How does the concentration gradient affect the rate of diffusion?

Answer 3

The greater the concentration gradient the greater the rate of diffusion

Question 3

How does temperature affect the rate of diffusion?

Answer 3

The higher the temperature, the faster the rate of diffusion. This is because the particles have more energy so they move around faster

Question 4

How do cells/tissues maximise diffusion?

Answer 4

Folded membranes for larger surface area
Thin surfaces for faster diffusion rate

Question 5

How do Alveoli and Villi maintain a concentration gradient?

Answer 5

Large blood supply to removed diffused substances, this maintains a high concentration gradient

Question 6

What do living cells use diffusion for? (3)

Answer 6

Getting raw materials for respiration (dissolved substances and gases)
Removing waste products (e.g. from respiration)
Photosynthesis in plants (raw materials in, waste products out)

Question 7

How are exchange surfaces adapted to maximise effectiveness?

Answer 7

as they are in specialised exchange organs they are adapted:
- they are thin - so substances have a short distance to travel
- they have folded membranes for a larger surface area, so lots of substance can move at once
- in animals- they have lots of blood vessels to get stuff in and out of the blood quickly and to maintain a steep concentration gradient
- gas exchange in animals (alveoli) are often ventilated too- air moves in and out

Question 8

What do cells absorb?

Answer 8

Oxygen, glucose, amino acids

Question 9

What do cells excrete?

Answer 9

Carbon dioxide and urea

Question 10

How can diffusion be increased?

Answer 10

Increasing temperature - this provides more kinetic energy for particles so they move faster
Larger surface area of membrane/cell - this means more particles can cross the membrane at once
Short diffusion distance - this means particles don’t have to diffuse as far
Steeper concentration gradient - the bigger the difference between two concentrations the faster the particles diffuse

Question 11

Examples of diffusion (6)

Answer 11

Oxygen diffuses from alveoli to capillary
Oxygen diffuses from water into gills
Glucose diffuses from bloodstream into respiring cells
Carbon dioxide diffuses from respiring cells into bloodstream
Water vapour diffuses out of leaves through stomata
Carbon dioxide diffuser into leaves through stomata

Question 12

Why do small organisms not need specialised exchange surfaces?

Answer 12

Why do small organisms not need specialised exchange surfaces?
They have a larger surface area to volume ratio
They can get substances like oxygen in and carbon dioxide out by relying on diffusion alone

Question 13

What is osmosis?

Answer 13

What is osmosis?
The net movement of water molecules across a partially permeable membrane from a dilute solution to a concentrated solution

Question 14

Define partially permeable

Answer 14

Define partially permeable
allows some substances through but not others

Question 15

What is the difference between animal and plant cells when too much water enters?

Answer 15

What is the difference between animal and plant cells when too much water enters?
Animal cells may burst
Plants cells will not burst because of rigid cell walls

Question 16

Why is the percentage change used rather than the actual change in mass?

Answer 16

Why is the percentage change used rather than the actual change in mass?
The substances may not all have same starting mass. Percentage change allows easier comparison.

Question 17

When will water enter cells by osmosis?

Answer 17

When will water enter cells by osmosis?
If the cells are in a solution that is more dilute than inside of the cell

Question 18

When will water leave cells by osmosis?

Answer 18

When will water leave cells by osmosis?
If the cells are in a solution that is more concentrated than the inside of the cells

Question 19

What will happen if the concentration of the solution matches the inside of the cell?

Answer 19

What will happen if the concentration of the solution matches the inside of the cell?
There will be no NET movement of water

Question 20

What is the equation for percentage change?

Answer 20

What is the equation for percentage change?
change/original x 100

Question 21

What is active transport?

Answer 21

What is active transport?
The net movement of particles from a low concentration to a high concentration (against a concentration gradient) which requires energy

Question 22

Why is active transport necessary?

Answer 22

Why is active transport necessary?
In order for all of a substance to be completely absorbed it has to be done by active transport (after initial diffusion)

Question 23

Name two cells that carry out active transport

Answer 23

Name two cells that carry out active transport
Root hair cells
Cells in the intestine

Question 24

What adaptations do cells that perform active transport have?

Answer 24

What adaptations do cells that perform active transport have?
Many mitochondria

Question 25

What is released from glucose during respiration?

Answer 25

What is released from glucose during respiration?
Energy that is used for active transport

Question 26

Describe an experiment to investigate osmosis

Answer 26

Cut four cylinders of potato using the borer, use a glass cylinder to push out the core
Using the scalpel, tile and ruler ensure that the cylinders are all the same length
Place four boiling tubes in a rack
Using a measuring cylinder put an equal volume of different sucrose concentrations
Use a marker to record what concentrations are in each tube
With a paper towel pat the cylinders dry and then using a mass balance weigh one of the potato cylinders
Record the starting mass
Repeat for the rest of the cylinders