4.1.3.1 Diffusion

Question 1

What is diffusion?

Answer 1

• gradual movement of particles from an area of higher concentrations to an area of lower concentrations

Question 2

Where does diffusion happen and why?

Answer 2

• in solutions and gases
• particles in the substances are free to move

Question 3

What is the simplest type of diffusion?

Answer 3

• different gases diffuse through each other

Question 4

What is a concentration gradient?

Answer 4

• the difference in concentration

Question 5

What does a bigger concentration mean for the rate of diffusion?

Answer 5

• the diffusion rate is faster

Question 6

What a higher temperature mean for the rate of diffusion?

Answer 6

• the diffusion rate is faster because the particles have more energy

Question 7

What do cell membranes do?

Answer 7

• they hold the cell together
• they let dissolved substances move in and out of the cell by diffusion

Question 8

What small molecules can diffuse through cell membranes?

Answer 8

• oxygen
• glucose
• amino acids
• water

Question 9

What does it mean if there a lot more particles on one side?

Answer 9

• there is a net (overall) movement from that side

Question 10

What does a large surface area mean for the rate of diffusion?

Answer 10

• the diffusion rate is faster because more particles can pass through at once

Question 11

What is exchange surfaces?

Answer 11

• how easily something moves between an organism and its environment depending on its surface area to volume ratio

Question 12

Why can enough substances be exchanged across a membrane in a single-celled organism?

Answer 12

• it has a large surface area compared to volume

Question 13

Why can’t enough substances be exchanged across a membrane in multicellular organisms?

Answer 13

• they have a smaller surface area compared to volume

Question 14

What does a multicellular organism do for efficient diffusion?

Answer 14

• exchange surface

Question 15

How are exchange surfaces adapted to maximise effectiveness?

Answer 15

• thin membrane so substances have a short distance to diffuse
• large surface area so lots of substances can diffuse at once
• exchange surfaces in animals have lots of blood cells to get things into and out of the blood quickly
• gas exchange surfaces in animals (alveoli) are often ventilated

Question 16

What are alveoli specialised for?

Answer 16

• to maximise the diffusion of oxygen and carbon dioxide

Question 17

How are alveoli adapted to do their function?

Answer 17

• an enormous surface area (around 75 meters squared)
  -moist lining for dissolving gases
• very thin walls
• good blood supply

Question 18

What is a villi’s function?

Answer 18

• to absorb digested food quicker into the blood

Question 19

How are villi adapted to do their funtion?

Answer 19

• single layer of surface cells
• good blood supply to assist quick absorption
• large surface area

Question 20

What are the exchange surfaces of a leaf?

Answer 20

• the underneath of the leaf as it is covered in stomata which carbon dioxide diffuses through
• walls of the cells inside as the air spaces inside increase the area of the surface so there is more chance for carbon dioxide to get into the cell

Question 21

What are the gills’ function in a fish?

Answer 21

• gas exchange surface
• water enters the fish through mouth and passes through the gills, oxygen diffuses into the blood and carbon dioxide diffuses into the water

Question 22

What are the adaptations of gills?

Answer 22

• gills made up of gill filaments which increase surface area for exchange of gases
• gill filaments covered in lamellae which increases surface area even more
  lamellae have lots of blood capillaries to speed up diffusion
• lamellae have a thing surface layer of cells to minimise distance
• blood flows through lamellae in one direction and water in the other for a large concentration gradient
• concentration of oxygen in water is higher than blood so as much oxygen diffuses into blood