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Scales in space and time
Scales in space and time

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2.10 Glucose

The following video introduces glucose molecules and their size. It describes how glucose stores energy, in some cases by forming more complex molecules that can be stored for longer. Plants and animals obtain glucose in different ways, but use it in the same way. Here you will consider the size of a glucose molecule and the timescales over which plants and animals use it.

While watching the video, record the following information to use in the questions that follow:

  • the length of the linear form of the glucose molecule
  • the amounts of glucose used by an oak leaf for growth and maintenance per day
  • definition of autotroph and heterotroph
  • a description of the solubility of glucose and starch
  • the uses of energy listed (e.g. growth).
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Glucose: a molecule that stores energy
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Question 1

How big is a glucose molecule? Give your answer in scientific notation.

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Question 2

How much glucose is needed to maintain a gram of oak leaf each day? Give your answer in scientific notation.

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The English oak, Quercus robur, is a deciduous species that loses its leaves over winter. The following graph (Figure 11) shows the amount of sugars (including glucose) and starch – both of which are carbohydrates – in English oak twigs during the year. Three specific time periods are shown: just before leaves are lost, when the tree has no leaves, and just before bud break (which is when the leaf buds begin expanding into leaves). The columns are the mean values of 10 twigs, each from a different plant.

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Figure 11  Sugar (including glucose) and starch content in twigs of Quercus robur at three time periods (adapted from Morin et al., 2007).

Question 3

Use your notes from the video together with Figure 11 to describe the graph and interpret its significance in terms of how a plant uses glucose and starch to store energy. Select the most appropriate terms from the drop-down lists to complete the following paragraph.

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A very simple food chain was shown in the video. It involved a bird (great tit) obtaining its energy (and protein) by eating the caterpillar (hairstreak butterfly larvae), which in turn obtained glucose by eating the oak leaf. You can measure the blood glucose concentrations in birds in order to compare them with other species.

Table 7 shows the average blood sugar levels of 14-day-old blue tit and great tit chicks (both of which can feed on caterpillars on oak leaves). For comparison, it also contains the levels of a healthy adult human both before and after eating.

Table 7 Average blood glucose concentrations in blue tit and great tit chicks in an oak woodland in Poland (Kaliński et al., 2015) and for an adult human after fasting and two hours after eating (Diabetes UK, n.d.).
Animal Average blood glucose concentration/mg ml−1
Blue tit chick 2.503
Great tit chick 2.684
Fasting adult human 0.900
Adult human 2 h after eating 1.400

Question 4

Use your list of the functions of glucose in an animal from the video to comment on the relative amounts of glucose in the bloodstream of tits and humans. Specifically, consider the age of the animals and what types of activity (work) the adult animals listed in the table do that might account for the differences. (Your answer should be between 50 and 100 words.)

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Answer

The tit chicks have two to three times the concentration of glucose in their blood compared to adult humans. Glucose is used to power growth, reproduction, work, generate heat, maintain cells and some is lost in waste. As the tits are just 14 days old they are likely to be growing quickly. Growth requires lots of energy in comparison to maintaining cells, so this could be one reason for the high blood glucose levels in the chicks, compared to the human.

Alternatively, flying uses a lot of energy, so perhaps birds have higher blood glucose levels in general than animals that do not fly.

Summary

Here you learned about a molecule, glucose, which stores energy in both plants and animals. It takes energy to synthesise glucose and when glucose is broken down into CO2 and water again, that energy is released (through cellular respiration). Your calculations and interpretation of graphs and tables of data allowed you to consider how plants and animals use glucose over time and at different stages in their development.

Next: Now look at even smaller scales by examining a carbon atom, which you can do with the ‘Next >’ button, or you can return to the size–time explorer [Tip: hold Ctrl and click a link to open it in a new tab. (Hide tip)] to choose a level for yourself.