Download Microscopic Life – Revision Pack (B6) Advantages and

Microscopic Life – Revision Pack (B6)
Advantages and Disadvantages of Living in Water:
There are a number of advantages of living in water:
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There is NO risk of water shortage or dehydration
The temperature of the water varies less than air temperature
Water helps to provide support
Waste products are easily disposed of into the water
There are also some disadvantages of living in water:
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The water content of the body can vary and needs to be controlled
Water is denser than air so resists movement
If the water is freshwater, then organisms can take up too much water by osmosis. In
salt water, the opposite happens and organisms may lose too much water to the
surroundings by osmosis.
Organisms such as amoeba have a contractile vacuole. The contractile vacuole
can store excess water. The vacuole can then fuse with the cell membrane and
empty the water to the outside.
Variation of Numbers:
Phytoplanktons are tiny aquatic plants and zooplanktons are tiny aquatic animals.
The population of these two aquatic organisms varies at different depths and
seasons.
One reason for this is because factors that affect the photosynthesis of
phytoplankton will vary:
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There is less light deeper in the water and during winter
The temperature will be lower deeper down and during winter
Minerals are used up towards the end of summer
Food webs of marine organisms can provide useful information. The webs rely on
different types of food:
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Most rely directly on green plants
Others, deeper in the ocean, feed on dead material known as marine snow
which floats down
Some rely on bacteria, deep in the ocean, acting as producers
Water Pollution:
Sewage and fertilisers run off into rivers, and often cause eutrophication. The
fertilisers cause algal bloom on the surface of the water. This blocks sunlight off to
photosynthesising plants at the bottom of the water. This means that these plants
die, and as such the oxygen levels in the water decrease. Aerobic bacteria then
Microscopic Life – Revision Pack (B6)
feed on the decaying material and use up the remaining oxygen in the water. Other
organisms in the water will also die because there is no oxygen for respiration.
Some species of organisms can be used as biological indicators. Some organisms
are sensitive to pollution, so their absence could indicate high pollution levels in the
water. Other organisms can ONLY live in polluted conditions so their presence could
be used to indicate pollution levels (which involve pH and oxygen levels of water).
Some chemicals such as PCBs and DDT will kill organisms higher up the marine food
chains; this is because:
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These chemicals are toxic
The chemicals do NOT break down so accumulate and become more
concentrated higher up the food chain
The chemicals affect animals with long life-spans, e.g. whales
Microscopic Life – Revision Pack (B6)
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