Size and Surface Area

Question 1

What do cells need to exchange with their environment?

Answer 1

Cells need to take in oxygen and nutrients. Cells need to excrete waste products like carbon dioxide and urea. Most organisms need to stay at roughly the same temperature, so heat needs to be exchanged too

Question 2

How easy an organism exchanges substance depends on what?

Answer 2

The organisms surface area to volume ratio

Question 3

What has a higher surface area to volume ratio, smaller or larger animals?

Answer 3

Smaller animals

Question 4

What is the diffusion rate like in single-celled organisms?

Answer 4

In single-celled organisms, substances can diffuse directly into (or out of) the cell across the cell-surface membrane. The diffusion rate is quick because of the small distances substances have to travel

Question 5

What is the diffusion rate like in multicellular organisms?

Answer 5

In multicellular organisms, diffusion across the outer membrane is slow because of two reasons:

1. Some cells are to deep within the body - there is a big distance between them and the outside environment
2. Larger animals have a large surface area to volume ratio - it is difficult to exchange enough substances to supply a large volume of animal through a small outer surface

Question 6

What do multicellular organisms need to absorb and excrete substances?

Answer 6

Specialised exchange organs

Question 7

What is mass transport?

Answer 7

Mass transport is a system to carry substances to and from their individual cells

Question 8

How is mass transport used in mammals?

Answer 8

In mammals, mass transport usually refers to the circulatory system, which uses blood to carry glucose and oxygen around the body. It also carries hormones, antibodies and waste

Question 9

What does mass transport in plants involve?

Answer 9

Mass transport involves the transport of water and solutes in the xylem and phloem

Question 10

How does body size affect heat exchange?

Answer 10

The rate of heat loss depends on its surface area. If an organism has a large volume, its surface area is relatively small. This makes it harder to lose heat. If an organism is small, its surface area is relatively large, so heat is lost more easily. This means smaller animals need a high metabolic rate in order to generate enough heat to stay warm

Question 11

How does body shape affect heat exchange?

Answer 11

Animals with a compact shape have a small surface area relative to their volume - minimising heat loss. Animals with a less compact shape have a larger surface area relative to their volume - increasing heat loss. Whether an animal is compact or not depends on the temperature of its environment