Paper 1 cells 3

Question 1

Define diffusion?

Answer 1

Diffusion is the spreading of particles of any substance in solution (or particles of a gas) resulting in net movement from an area of higher concentration to an area of lower concentration

Question 2

Where can diffusion happen?

Answer 2

It can happen in a gas, liquid, or across a membrane

Question 3

Explain net movement?

Answer 3

Net movement is when movement of particles is random, so some will be moving towards the higher concentration area, but more will be moving towards the lower concentration area.

Question 4

How do you calculate the net movement?

Answer 4

Net movement = particle moving in - particles moving out

Question 5

What determines the rate of net movement?

Answer 5

1. Concentration gradient
2. temperature
3. Surface area

Question 6

Explain what how a concentration gradient helps in diffusion?

Answer 6

The greater the difference in concentration between the two areas, the faster diffusion will be.
We say that diffusion occurs down a concentration gradient

Question 7

Explain why the temperature is affected in diffusion ?

Answer 7

As the gas or solution heats up, the particles gain more kinetic energy and move around faster.
This increases the random movement of the particles and enables them to diffuse more rapidly.

Question 8

Explain why a large surface area is better in diffusion?

Answer 8

• Dissolved substances move into and out of our cells through the cell membrane
• Our membranes allow only some materials to pass through and are called partially permeable
• By increasing the surface area through which the particles can move, diffusion can occur faster

Question 9

Explain the diffusion of oxygen.

Answer 9

Air in lungs (high concentration) —

Question 10

Explain the diffusion of carbon dioxide

Answer 10

CO2 from respiring cells (high concentration)—

Question 11

Explain gaseous exchange

Answer 11

The movement of O2 and CO2 in opposite directions. Also known as respiration

Question 12

Explain the diffusion of glucose

Answer 12

Digested food in intestines (high concentration)—

Question 13

Explain the diffusion of urea

Answer 13

Created by breaking down amino acids in the liver (high concentration)—

Question 14

What’s the relation ship between the size of an organism and the surface area to volume ratio?

Answer 14

The larger the organism, the smaller the surface area to volume ratio

Question 15

Why do we have specialised exchange surfaces?

Answer 15

In order to speed up the transport of oxygen and glucose to respiring cells and removal of waste, specialised exchange surfaces are created to increase the surface area

Question 16

Who exchanges substances faster by diffusion and why, bacteria or animals?

Answer 16

Bacteria, because they’re single cellular so they have a larger surface area to volume ratio

Question 17

Why are animals slow at exchanging substances by diffusion?

Answer 17

Because they’re multicellular organisms so they have a small surface area to volume ratio

Question 18

Give 3 ways to adapt for better diffusion and why?

Answer 18

1. Increase the surface area, so more particles can move at once
2. Have a short diffusion distance the particles have to travel
3. Increase the steepness of the concentration gradient to speed up the net flow of particles

Question 19

Example why the lungs are so good at diffusion (4)

Answer 19

1. A large number of small alveoli, creates a large surface area for rapid diffusion of gases
2. A rich capillary blood supply brings fresh blood to the alveoli to maintain steep diffusion gradient for rapid diffusion
3. Ventilation (breathing) refreshes the air in the lungs to maintain a steep diffusion gradient for rapid diffusion
4. A thin alveolar wall gives the shortest diffusion distance for the gases

Question 20

Give reason the small intestine is good at diffusion? (3)

Answer 20

1. The lining of the intestine is folded into thousands of villi, which in turn have numerous microvilli on their surface. They give the digestive system a huge surface area for absorption
2. They have a rich capillary blood supply to remove absorbed nutrients and maintain a steep concentration gradient
3. The walls are only one cell thick to keep the diffusion distance short

Question 21

Gives reasons why plant roots are good at diffusion compared to other parts of the plant?

Answer 21

• the top of the roots are covered in root hair cells
• these are the only part of the root that actually absorb water and nutrients
  1. Their hair -like projection increases their surface area for absorption
  2. Transpiration in the leaves continuously pulls water up the plant, creating a steep concentration gradient.
  3. There is a short distance from the edge of the root to the xylem in the middle

Question 22

Give reasons why plant leaves are good at diffusion/osmosis? (2)

Answer 22

1. The thin leaf shape minimises the diffusion distance for gases
2. there are pores in the bottom surface of the leaf called stomata to allow carbon dioxide to diffuse into the leaf and oxygen out The air spaces in the spongy layer exposes a large surface area for gaseous exchange

Question 23

Define osmosis

Answer 23

Osmosis is the diffusion of water from a dilute solution (where there is a high concentration of water) to a strong solution (where there is a low concentration of water) across a partially permeable membrane

Question 24

Define partially permeable membrane

Answer 24

Let’s stuff through small holes

Question 25

Define dilute solution

Answer 25

Where there is a high concentration of water