Size matters I Bill Indge

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Size matters IBill Indge
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Knowledge and understanding
How science works
Application and analysis
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Knowledge and understanding
Analysis and interpretation
Application of knowledge and understanding
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Size and surface area to volume ratio
1 cm
Surface area 116 6 cm2
Volume 111 1 cm3
1 cm
Surface area 6 6 Volume 1
1 cm
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6 5 4 3 2 1 0
Surface area to volume ratio
0 1 2 3 4 5 6
Side length
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6 5 4 3 2 1 0
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
0 1 2 3 4 5 6
Side length
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The formula for finding the surface area of a
sphere is 4pr2. The formula for finding the
volume of a sphere is (4/3) pr3. (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)
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Answer (a) The surface area to volume ratio of a
sphere is calculated by dividing the surface area
by its volume 4pr2 (4/3)
pr3 Simplify by cancelling, in other words,
dividing the top line and the bottom line by 4, p
and r2. This gives 1 (1/3)r Multiplying
the top and the bottom lines by 3
gives 3/r (3)
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(b) Use this simplified expression to complete
the table. (1 mark)
Radius of sphere Surface area to volume ratio
1 3.0
2
3
4
5
6 0.5
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Answer (b) (1)
Radius of sphere Surface area to volume ratio
1 3.0
2  1.5
3 1.0
4 0.8
5 0.6
6 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)
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Read the information in the stem. You will need
this to answer the question.
Seals
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.
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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)

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

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(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)

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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.

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Signposts
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.
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Signposts

• 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.
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(a) The features of the blood vessels in the ears
of an elephant described in the passage could
result in heat loss (lines 89). 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)

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(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 1011) (2 marks) (ii)
be inversely related to wind velocity (lines
1112) (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)

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(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 1618). (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)

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(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)