3.3 Topic 3 - 3.3.1 Surface to volume ratio

Question 1

Why do cells need to take in oxygen?

Answer 1

For aerobic respiration and nutrients.

Question 2

What are examples of waste products cells need to excrete?

Answer 2

Carbon dioxide and urea.

Question 3

True or false? A mouse has a bigger surface area relative to its volume than a hippo

Answer 3

True.

Question 4

Why do organisms need to supply everyone of its cells with substances like glucose and oxygen?

Answer 4

For respiration.

Question 5

Why do organisms need to remove waste products from all of its cells?

Answer 5

To avoid damaging itself.

Question 6

In single-celled organisms, how are substances exchanged?

Answer 6

Through diffusion. directly into or out of the cell across the cell-surface membrane.

Question 7

In single-celled organisms, is the diffusion rate slow or quick and why?

Answer 7

Quick because of the small distances the substances have to travel.

Question 8

In multicellular animals, is the diffusion rate slow or quick and why?

Answer 8

The diffusion rate is slow across the outer membrane. This is because some cells are deep within the body meaning there is a big distance between the and the outside environment. Larger animals have a low surface area to volume ratio meaning it is difficult to exchange enough substances to supply a large volume of animal through a relatively small outer surface.

Question 9

What do multicellular animals need to absorb and excrete substances?

Answer 9

Specialised exchange organs.

Question 10

What is mass transport?

Answer 10

An efficient system to carry substances to and from their individual cells.

Question 11

What does mass transport in mammals normally refer to?

Answer 11

… the circulatory system, which uses blood to carry glucose and oxygen around the body as well as hormones, antibodies and waste such as CO2.

Question 12

What does mass transport in plants involve?

Answer 12

… the transport of water and solutes in the xylem and phloem.

Question 13

What are two factors which affect heat exchange?

Answer 13

Body size and shape.

Question 14

What is an example of something in which metabolic activity inside cells creates?

Answer 14

waste products and heat.

Question 15

What does the rate of heat loss from an organism depend on?

Answer 15

Its surface area.
If an organism has a large volume, its surface area is relatively small = harder for it to lose heat from its body.
If an organism has a small volume, its surface area is relatively large = heat is lost more easily from its body.
Therefore, smaller organisms need a relatively high metabolic rate in order to generate enough heat to stay warm.

Question 16

Animals with a compact shape have a small surface area relative to their volume …

Answer 16

… minimising heat loss from their surface.

Question 17

Animals with a less compact shape have a larger surface area relative to their volume …

Answer 17

… increasing heat loss from their surface.

Question 18

What does whether an animal is compact or not, depend on?

Answer 18

The temperature of its environment.

Question 19

What are two types of adaptations organisms have to aid exchange?

Answer 19

Behavioural or physiological adaptations.

Question 20

Animals with a high surface area : volume ratio tend to lose more water? true or false? + why?

Answer 20

True as it evaporates from their surface.
[some small desert mammals have kidney structure adaptations so that they produce less urine to compensate]

Question 21

What do small mammals living in cold climates need to eat to support their high metabolic rates?

Answer 21

High energy foods.
[e.g. nuts and seeds]

Question 22

Why may smaller mammals have thick layers of fur or hibernate?

Answer 22

To protect themselves when the weather gets really cold.

Question 23

Why do larger organisms living in hot regions find it hard to keep cool?

Answer 23

Their heat loss is relatively slow.

Question 24

What have elephants developed to increase their surface area, allowing them to lose more heat?

Answer 24

Large flat ears.

Question 25

What is an adaptation hippos have which has helped them lose heat and what type of adaptation is it?

Answer 25

They spend most of the day in the water and this is a behavioural adaptation.