Size and Surface Area

Question 1

Why does every organism exchange substances with its environment?

Answer 1

• Cells need to take in nutrients oxygen (for aerobic respiration).
• Organisms need to excrete waste products like carbon dioxide and urea.
• Heat needs to be exchanged as most organisms need to stay at roughly the same temperature.

Question 2

What affects how quickly organisms exchange substances with the environment?

Answer 2

The organisms surface area:volume ratio

Question 3

What surface area:volume ratio do small organisms have compared to large organisms?

Answer 3

A higher ratio.

Question 4

How do you calculate the volume of a cylinder?

Answer 4

πr²h

Question 5

How do you calculate the volume of a sphere?

Answer 5

4/3 πr³

Question 6

How do single-celled organisms exchange substances?

Answer 6

The substances can diffuse directly into or out of the cell across the cell-surface membrane.

Question 7

What happens to diffusion when substances are exchanged by single-eclled organisms?

Answer 7

The diffusion rate is quick because of the small distances the substances have to travel.

Question 8

How do multicellular organisms echange substances?

Answer 8

• They use specialised exchange organs e.g. lungs
• They also need efficient systems to carry substances to and from their individual cells (mass transport).

Question 9

Why can’t multicellular organisms exchange by diffusion across their outer membrane?

Answer 9

This is too slow because;

• Some cells are deep within the body, so the distance is too large.
• Larger animals have a low surface area:volume ratio, so it is difficult for enough substances to supply a large animal, through a relatively small outer surface.

Question 10

mass

Answer 10

transport

Question 11

mass

Answer 11

transport

Question 12

What does the rate of an organisms heat loss, to maintain a constant internal environment, depend on?

Answer 12

• Body size
• Body shape
• Adaptations for heat exchange

Question 13

Why does an organisms rate of heat exchange depend on their body size?

Answer 13

Because it is harder to lose heat from a large organism with a small surface area:volume ratio. Whereas smaller organisms with a high surface area:volume ratio lose heat more easily.

Question 14

What do some smaller organisms have to have regarding heat exchange due to their large surface area:volume ratio?

Answer 14

A relatively high metabolic rate, in order to generate enough heat to stay warm.

Question 15

Why does an organisms rate of heat exchange dpend on its body shape?

Answer 15

• Having a compact shape gives a smaller surgace area:volume ratio, minimising heat loss from their surface.
• Whereas animals with a less compact shape (sticky out bits) have a larger surface area:volume ratio, increasing heat loss from their surface.

Question 16

What does an organisms body shape depend on?

Answer 16

The environment it habitates, meaning the organisms body shape is adapted to its environment.

Question 17

What are some examples of organisms with adaptations to their environment?

Answer 17

All having body temps of 37ºc

• Artic fox (outside temp 0ºc).
• African bat-eared fox (outside temp 25ºc)
• European fox (outside temp 12ºc)

Question 18

How is the Artic fox adapted to its environment?

Answer 18

It has small ears and a round head to reduce its surface area:volume ratio, thus reducing heat loss.

Question 19

How is the African bat-eared fox adapted to its environment?

Answer 19

It has large ears and a more pointed nose to increase its surface area:volume ratio, thus increasing heat loss.

Question 20

How is the european fox adapted to its environment?

Answer 20

It is the intermediate of the two, matching the temperature of its environment.

Question 21

What are other adaptations organsisms have to suit their environment?

Answer 21

• Some high surface area;volume ratio desert mammals produce less urine to compensate for their water loss.
• Small mammals have thick layers of fur and hibernate when it is cold to reduce heat loss.
• Elephants have large flat ears, increasing their surface area:volume ratio, increasing heat loss.
• Hippos are always in the water, a behavioural adaptation to increase heat loss.