z All organisms need energy to do work. z Organisms get their energy from food. z Metabolism is all the chemical reactions that take place in the cells of organisms.
z Enzymes are biological catalysts. This means that they speed up the chemical reactions in cells.
z Organisms strive to stay the same to make sure that enzymes will work properly. This is called homeostasis.
z Organisms that can make their own food are called producers.
z The way plants make their food is called photosynthesis.
z The word equation for photosynthesis is: sunlight
Carbon dioxide + water chlorophyll → glucose + oxygen
z Farmers can boost production by controlling the factors that affect photosynthesis in glasshouses and polytunnels.
z Photosynthesis is a building reaction. This means that it temporarily stores energy.
z Organisms that must eat food because they cannot make their own are called consumers.
z The release of energy from food is called respiration.
z The word equation for respiration is: →
Glucose + oxygen mitochondria energy +
carbon dioxide
+ water
z Respiration is a breaking reaction. This means that it releases stored energy.
z Photosynthesis and respiration help control the balance between carbon dioxide and oxygen in the atmosphere.
The BIGChallenge
In the 1640s, the Dutch scientist Jan Baptist van Helmont suggested that a willow tree grown in a pot gained 74 kg in mass. Curiously, the mass of the soil in the pot decreased by only 57 g. Van Helmont believed that the increase in mass was due to regularly adding water to the pot over the five years.
Working in small groups, design a similar investigation that may be completed over a period of between one month and six months. (Hint: van Helmont seemed to be aware of water but what other substances should he also have tracked? Consider both sides of the equation for photosynthesis and respiration.) Best of luck – hopefully it won’t take you five years!
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Go to your Portfolio to check what you have learned in this chapter.
