COAS B1 Ch04
Chapter 4
Exchange
Background
e-Learning
Objectives
Exchange surfaces
All of the cells in your body need constant supplies of oxygen and nutrients, and need to get rid of waste materials, such as carbon dioxide, that are produced in their metabolic reactions. These substances are obtained from, or released to, the external environment, through your body’s surface.
Cells and organisms have problems of scale to solve as they get bigger. As an organism gets
Cube with 1 cm sides
bigger, both its surface area and its volume increase. However, its surface area does not increase as much as its volume (Figure 4.1). So a large organism such as yourself must find ways of increasing surface area, to provide enough surface to ensure that exchanges with your environment can take place rapidly enough to supply all of your cells with their needs.
Cube with 10 cm sides
The large object is, in effect, made up of 1000 small cubes.
surface area of one small cube = 6 cm2 volume of one small cube
= 1 cm3 surface area surface area : volume ratio
= __________ volume =6
= 600 cm2
= 1000 cm3 surface area
= __________ volume = 0.6
surface area of large object volume of large object surface area : volume ratio
The large object has much less surface area for each ‘unit’ of volume; it has a much lower surface area to volume ratio.
Figure 4.1 Size and surface area : volume ratio.
SAQ
1 Draw a table like this, with seven more empty rows in it.
Length of one side of a cube / cm
Total surface area / cm2 Volume / cm3
Surface area divided by volume 1
6
1
6
2
24
8
3
a Complete your table for cubes with sides up to 10 cm. b Describe what happens to the surface area : volume ratio as the side length of the cube increases. c Explain the relevance of this to living organisms.
50
Hint
Answer
Chapter 4: Exchange
Properties of exchange surfaces
In this chapter, we will look at how oxygen and carbon dioxide are exchanged with your
environment,
Exchange
Background
e-Learning
Objectives
Exchange surfaces
All of the cells in your body need constant supplies of oxygen and nutrients, and need to get rid of waste materials, such as carbon dioxide, that are produced in their metabolic reactions. These substances are obtained from, or released to, the external environment, through your body’s surface.
Cells and organisms have problems of scale to solve as they get bigger. As an organism gets
Cube with 1 cm sides
bigger, both its surface area and its volume increase. However, its surface area does not increase as much as its volume (Figure 4.1). So a large organism such as yourself must find ways of increasing surface area, to provide enough surface to ensure that exchanges with your environment can take place rapidly enough to supply all of your cells with their needs.
Cube with 10 cm sides
The large object is, in effect, made up of 1000 small cubes.
surface area of one small cube = 6 cm2 volume of one small cube
= 1 cm3 surface area surface area : volume ratio
= __________ volume =6
= 600 cm2
= 1000 cm3 surface area
= __________ volume = 0.6
surface area of large object volume of large object surface area : volume ratio
The large object has much less surface area for each ‘unit’ of volume; it has a much lower surface area to volume ratio.
Figure 4.1 Size and surface area : volume ratio.
SAQ
1 Draw a table like this, with seven more empty rows in it.
Length of one side of a cube / cm
Total surface area / cm2 Volume / cm3
Surface area divided by volume 1
6
1
6
2
24
8
3
a Complete your table for cubes with sides up to 10 cm. b Describe what happens to the surface area : volume ratio as the side length of the cube increases. c Explain the relevance of this to living organisms.
50
Hint
Answer
Chapter 4: Exchange
Properties of exchange surfaces
In this chapter, we will look at how oxygen and carbon dioxide are exchanged with your
environment,