- Slides: 21
Size matters I Bill Indge
Size matters How science works Knowledge and understanding Application and analysis
Size matters Analysis and interpretation Knowledge and understanding Application of knowledge and understanding
Size matters Size and surface area to volume ratio 1 cm Surface area = 1× 1× 6 = 6 cm 2 Volume = 1× 1× 1 = 1 cm 3 1 cm Surface area = 6 Volume 1 1 cm
Size matters 6 5 Surface area to volume ratio 4 3 2 1 0 0 1 2 3 4 Side length 5 6
Size matters 6 Surface area to volume ratio 5 Small organisms have a large surface area to volume ratio 4 3 2 1 Large organisms have a small surface area to volume ratio 0 0 1 2 3 4 Side length 5 6
Size matters The formula for finding the surface area of a sphere is 4πr 2. The formula for finding the volume of a sphere is (4/3) × πr 3. (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: 4πr 2 (4/3) × πr 3 Simplify by cancelling, in other words, dividing the top line and the bottom line by 4, π and r 2. This gives: 1 (1/3)r Multiplying the top and the bottom lines by 3 gives: 3/r (3)
Size matters (b) Use this simplified expression to complete the table. (1 mark) Radius of sphere 1 2 3 4 5 6 Surface area to volume ratio 3. 0 0. 5
Size matters Answer (b) (1) Radius of sphere 1 2 3 4 5 6 Surface area to volume ratio 3. 0 1. 5 1. 0 0. 8 0. 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)
Size matters 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.
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 rati o; (3)
Size matters Again start by reading the information in the stem. You will need this. Earthworms 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)
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 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 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.
Size matters 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.
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)