Size matters IBill Indge

Size matters

Knowledge and understanding

Application and analysis

How science works

Size matters

Knowledge and understanding

Application of knowledge and understanding

Analysis and interpretation

Size matters

1 cm

1 cm

1 cm

Surface area = 1×1×6 = 6 cm2

Volume = 1×1×1 = 1 cm3

Surface area = 6 = 6Volume 1

Size and surface area to volume ratio

Size matters

0 1 2 3 4 5 6Side length

6

5

43210

Surface area to volume ratio

Size matters

0 1 2 3 4 5 6

6

5

43210

Small organisms have a large surface area to volume ratio

Large organisms have a small surface area to volume ratio

Surface area to volume ratio

Side length

Size matters

The formula for finding the surface area of a sphere is 4πr2.The formula for finding the volume of a sphere is (4/3) × πr3.(a) Explain how the surface area to volume ratio of a sphere may be calculated from the expression:

surface area to volume ratio = 3/r (3 marks)

Size matters

Answer: (a) The surface area to volume ratio of a sphere is calculated by dividing the surface area by its volume:

4πr2

(4/3) × πr3

Simplify by cancelling, in other words, dividing the top line and the bottom line by 4, π and r2. This gives:

1 (1/3)r

Multiplying the top and the bottom lines by 3 gives:3/r (3)

Size matters

Radius of sphereSurface area to

volume ratio1 3.023456 0.5

(b) Use this simplified expression to complete the table.(1 mark)

Size matters

Radius of sphereSurface area to

volume ratio1 3.02  1.53 1.04 0.85 0.66 0.5

(c) Assume that a cell is spherical. Use the data in the table to describe the relationship between the size of a cell and its surface area to volume ratio. (1 mark)

Answer (b) (1)

Size matters

The southern elephant seal is a very large mammal. Fully grown male elephant seals may reach a length of almost 5 m and have a mean body mass of 3200 kg. Elephant seals spend much of their lives in the cold waters around the sub-Antarctic islands.

Read the information in the stem. You will need this to answer the question.

Seals

Size matters

Explain the advantage of a large size to a mammal that lives in cold water. (3 marks)

• Seals are mammals and have a high body temperature;• Will lose less heat to the surrounding water;• Because they have a small surface area to volume ratio; (3)

Size matters

Many species of earthworms burrow through the soil. Earthworms of one particular species may be up to 200 mm in length although their diameter is only 6 mm.

Again start by reading the information in the stem. You will need this.

(a) Explain the advantage to an earthworm of being covered in mucus. (2 marks)Answer (a)•Acts as a lubricant;•Enables the worm to move easily through the soil when burrowing; (2)

Earthworms

Size matters

(b) The oxygen that earthworms require for respiration diffuses through their body surface into the blood vessels in the skin. Explain how the shape of a burrowing earthworm aids diffusion.

(2 marks)Answer (b)•The rate of diffusion is directly proportional to surface area;•Earthworm has large surface area to volume ratio; (2)

(c) In dry conditions, soil-dwelling earthworms curl into a ball. Explain the advantage of this behaviour to an earthworm in dry conditions. (2 marks)Answer (c)•Provides a smaller surface area to volume ratio;•From which to lose water/for evaporation; (2)

Size matters

Elephants

Signposts

• Where questions are based on a passage, start by reading it through quickly.

• Underline one or two words in each paragraph. These words should indicate what the passage is about and will help you to find your way around.

Size matters

African elephants are the largest of all land mammals. Although geographically variable in size, fully mature males average over 3 m at the shoulder and have a mean body mass of around 5000 kg. Mature females are smaller and have corresponding measurements of 2.5 m and 3000 kg. Elephants formerly occurred throughout sub-Saharan Africa, wherever water and trees were found.

Signposts

Size matters

• African elephants – size• Ear flapping• Thermal windows• Dust bathing

This should enable you to find your way round the passage and locate the information you want quickly.

You can then read the paragraph you want more carefully, when you want it.

Signposts

Size matters

(a) The features of the blood vessels in the ears of an elephant described in the passage could result in heat loss (lines 8–9). Explain how. (3 marks)

Answer (a) •Dense capillary bed provides large surface area;•Large diameter of arteries ensures delivery of large volume of blood;•Blood at core temperature/at higher temperature than that of the environment. (3)

Size matters

(b) If ear flapping plays an important role in heat loss, explain why you would expect its frequency to:(i) increase as the ambient temperature rose (lines 10–11)

(2 marks)(ii) be inversely related to wind velocity (lines 11–12) (2 marks) Answer (b) (i)•Flapping will increase airflow over the ears/will increase heat loss by convection;•Temperature gradient between body surface and surroundings lower/less heat can be lost to surroundings from body surface; (2)Answer (b) (ii)•As wind speed/velocity increases, more heat is lost;•Ear flapping requires expenditure of energy by the elephant;(2)

Size matters(c) Explain what is meant by a ‘thermal window’ (line 14).

(3 marks)Answer (c)•An area of increased blood flow;•On skin/surface of animal;•Associated with heat loss; (3)(d) Explain how ‘restriction of areas of enhanced blood flow to thermal windows’ might enable an elephant to ‘react more flexibly to its needs regarding heat loss’ (lines 16–18).

(2 marks)Answer (d) •The use of thermal windows allows heat loss from small discrete areas;•Which can be recruited independently;•Allows finer control than from the whole body surface; (2)

Size matters(e) The researchers investigating dust bathing concluded that its function was not related to thermoregulation. Identify and explain the evidence in the passage that supports this conclusion. (3 marks)

Answer (e) •Frequency of dust bathing independent of body mass;•Larger elephants have a smaller surface area to volume ratio;•Larger elephants generate more metabolic heat;•Expect frequency to increase with body mass; (3)