Download The Cycling of Matter – Answers

The Cycling of Matter – Answers
THE CARBON CYCLE Understanding Concepts p. 65
1. In your own words explain why photosynthesis and respiration are considered reverse
processes.
Respiration and photosynthesis are considered to be complimentary because the
raw materials of one process are the products of the other and vice versa.
2. Explain the importance of decomposers in the carbon cycle.
Decomposers are important in the carbon cycle because they release carbon from
dead organisms.
3. The oceans are often described as a carbon reservoir. In what ways is carbon held within
the oceans?
The oceans are carbon sinks because carbon dioxide reacts with water to form
carbonic acid, allowing more CO2 to dissolve. Organisms remove carbon from the water
to produce the calcium carbonate in their shells, and carbon also precipitates and forms
sedimentary rocks such as limestone.
4. Explain how the burning of fossil fuels by humans affects the carbon cycle.
Burning fossil fuels releases carbon that has been locked up in peat, coal, natural
gas, or petroleum since they were formed by the death and compression of organic
materials from prehistoric plants and animals.
5. Carbon cycles more quickly through some ecosystems than others.
a) Explain why carbon is cycled more slowly in northern ecosystems than in the tropics.
Carbon is cycled more slowly in northern ecosystems than in the tropics
because there are fewer plants and their rate of photosynthesis is much slower than in
the tropics. In addition, most plants in northern ecosystems lie dormant for part of the
year. Some northern plants have needles that are not as efficient as deciduous leaves.
b) Explain why carbon is cycled more rapidly in grassland communities than in peat
bogs and swamps.
Carbon is cycled more rapidly in grassland communities than in peat bogs and
swamps because there is more biomass in grassland and the plants are replaced more
frequently (many are annuals), with the associated release of carbon from the decaying
plants. In the bogs and swamps, much of the carbon dioxide released from decaying
plants is dissolved in the water.
6. Scientists have expressed concerns about the burning of the rainforests to clear land for
farming.
a) Explain how the burning of the forests could change oxygen levels in the
atmosphere.
Burning the rainforests reduces the oxygen supply in the atmosphere because
much less photosynthesis occurs in the resulting field
b) What impact would the change in oxygen levels have on living things?
Reduced oxygen levels make it more difficult for plants and animals to carry
on respiration
7. a) the amount of carbon dioxide entering the atmosphere each year is 232 x1013 kg.
The amount of carbon dioxide leaving the atmosphere each year is 227 x1013 kg. This
means that the amount of carbon dioxide in the atmosphere is increasing at a rate of:
232 x 1013kg - 227 x 1013 kg = 5 x 1013 kg per year.
c) the oxygen concentration in the atmosphere is also affected by the burning plants
because photosynthesis produces oxygen as a by-product
d) answers could include:
- reduce use of fossil fuels
- reduce burning of forests
- plough straw back into ground rather than burning it
THE NITROGEN CYCLE Understanding Concepts p. 69
1. Explain why nitrogen is important to organisms.
Organisms require nitrogen to produce proteins and nucleic acids
2. If nearly 79% of the atmosphere is nitrogen, howcould there be a shortage of nitrogen in
some soils?
Nitrogen must be convertedin to nitrates before it can be used by organisms. If
the soil lacks nitrogen-fixing bacteria, then it has few nitrates for the plants to take in.
3. How do animals obtain usable nitrogen?
Animals receive the nitrogen they need by consuming living and dead organic
matter.
6. Explain why it is a good practice to aerate lawns.
Aerating lawns exposes denitrifying bacteria to oxygen and so reduces the
breakdown of nitrates to nitrogen. The soil is able to retain the nitrates that would
otherwise be lost.
7. Explain why phosphorous is important to living things.
Phosphorous is important in the process of respiration to form energy-storing
compounds (ADP and ATP). It is part of cell membranes, DNA molecules, and calcium
phosphate molecules in bones.
8. Some farmers alternate crops……Why would farmers plant a crop that provides less
economic value?
Farmers plant less-valuable crops such as alfalfa and clover because they contain
nodules with nitrogen-fixing bacteria in their roots and increase the nitrate concentration
of the soil.
9. Explain why bogs and swamps are usually low in nitrogen.
Bogs and swamps are low in nitrogen because of the lack of nitrogen-fixing bacteria
and earthworms that would aerate the soil.