8.2 :Multicellular animals (e.g. gas exchange in worms)

Question 1

How does the diffusion process differ between larger and smaller organism?

Answer 1

in larger organisms many cells are aggregated together.

they have a lower surface area to volume ratio than smaller organisms.

so diffusion across thier surfaces is not effecient enough for their gas exchange.

Question 2

What does terrestrial mean?

Answer 2

An organism that lives on land

Question 3

what is metabolic rate?

Answer 3

The rate of energy expenditure by the body

Question 4

What type of oranism is a flat worm

Answer 4

an aquatic organism.

Question 5

What are the 3 benefit of a flatworm being flat

Answer 5

1. they have a much larger surface area to volume ratio relative to spherical organisms of the same volume.
2. The large surface area to volume ratio has overcome the problem of size.
3. This means the diffusion pathways are short

Question 6

What type of organism is an earth worm

Answer 6

• A terrestial organism.

Question 7

How does the surface area of a earthworm compare to a flatworm

Answer 7

• It is cylindrical
• Which means that the suface to volume ratio is smaller than a flatworm
• However it is larger than a compact organism of the same volume

Question 8

What is the earthworms respiratory surface

Answer 8

• Its skin

Question 9

How does an earthworm keep its skin moist and what implications does this have for its habitat?

Answer 9

• It keeps its skin moist by secreting mucous, It is found in damp soil.

Question 10

Why does an EW have a low oxygen requirement?

Answer 10

• It is slow moving
• Has a low metabolic rate
• Therefore does not require high levels of oxygen for respiration

Question 11

What are the 7 features of an earthworm?

Answer 11

1. An EW is a Terrestrial organism.
2. It is cylindrical and so its surface area to volume ratio is smaller than a flatworm’s
   
   1. but larger than that of a compact organism of the same volume
3. Its skin is the respiratory surface which it
   
   1. (keeps moist by secreating mucus)
   2. It need to keep its body moist so is most commonly found in damp soil
4. There has a low oxygen requirement because it is slow moving and has a low metabolic rate
   
   1. Enough oxygen diffuses accross its skin into the blood capilliaries beneath
5. Haemoglobin is present in the blood, carrying oxygen around the body in blood vessels
6. Carrying oxygern away fropm the surface maintains a diffusion gradient at the respiratopry surface
7. Carbon dioxide is also carried in the blood and diffuses out accross the skin down a diffusion gradient

Question 12

How does an EW maintain an oxygen concentration gradient?

Answer 12

• Haemoglobin is present in the red blood cells
• This allows the blood to carry oxygen around the body in blood vessels
• The blood carries oxygen away from the surface creating a diffusion gradient