4.9

4.9 Describe the stages in the carbon cycle, including respiration, photosynthesis, decomposition and combustion

1)    Photosynthesis

Carbon dioxide (0.03% of atmosphere) combined with water using chlorophyll traps light energy. This forms organic molecules such as glucose. This is responsible for reducing atmospheric carbon dioxide.

2)    Feeding

Carbon molecules are passed along various trophic levels. When primary consumers eat producers, carbon is passed along and as a result the consumers grow. Since each organism carries out respiration, they all send out carbon dioxide into the air.

3)    Respiration:

Oxygen is broken down by enzymes through aerobic respiration. This releases energy and produces carbon dioxide. This adds carbon dioxide to the atmosphere.

4)    Decomposition

Producers and consumers all die in the end. Then, organic molecules that remain are broken down by decomposer organisms, such as, bacteria and fungi. This releases carbon dioxide back into the air.

5)    Combustion:

Fossil fuels are formed over millions of years as animal and plant materials are compressed. This forms oil and coal, which are combusted to release carbon dioxide. The best known examples are industrial factories and motor vehicles like cars and airplanes. However, this can also occur naturally. If a lightning strikes the vegetation, it can cause forest or grassland fires. 

4.14

4.14 Understand how an increase in greenhouse gases results in an enhanced greenhouse effect and this may lead to global warming and its consequences

Pollution: greenhouse gases concentration increases. à more infrared light re-emitted rather than escaping à raise average global temperature à GLOBAL WARMING

Consequences: difficult to predict.

- Melting of ice caps in the polar regions

- Raised sea levels

- Change in ocean currents

- Change the ways in which winds are generated

CHANGE IN DISTRIBUTION OF BIOMES (ecosystem, major vegetation)

Ice caps melt, Deserts expand, deciduous forest, coniferous forest distribution change. 

4.13

4.13 Understand how human activities contribute to greenhouse gases

1) Burning of fossil fuels: industrial factories, vehicles and domestic homes burning coals

2) Farming: animals like cows digest crops. They emit methane gas to the atmosphere (9%).

3) Evaporation of water produces water vapour. Clouds are significant contributors.

4) Refrigeration, solvents and propellants from CFCs. 

4.12

4.12 Recall that water vapour, carbon dioxide, nitrous oxide, methane and CFCs are greenhouse gases

a) UV light / sunlight: short waves and high energy

b) 50% of the light is reflected back out into the space

The main cause is the clouds.

c) Absorption on the earth’s surface. The UV light is converted

into infrared.

d) Infrared light (longer wave)

e) Some being emitted back outwards.

Some of this is lost to space as heat.

f) The greenhouse gases hit by infrared à absorb energy

à re-emits in all directions including downwards

à raises surface temperature

Enhanced greenhouse effect

If we raised the levels of gluten gases like carbon dioxide and methane, they will absorb more of the escaping infrared radiation and re-emit them back to the earth à high temperature à climate change

CFCs chlorofluorocarbons:

CCl₃F broken down by sunlight à CCl₂F^- + Cl^-

They affect the ozone layer (O₃) by catalysing them to break down into O₂. This is very different to chlorine gas. O₃ is better at absorbing UV light. We are removing the protection of ozone layer. 

4.11

4.11 Understand the biological consequences of pollution of air by sulphur dioxide and carbon monoxide

1) Sulphur dioxide – SO₂ gas

ü  It is released into the atmosphere by combustion of fossil fuels, vehicles and oil/petrol.

ü  SO₂ + H₂O à sulphuric acid

ü  The acid condenses as clouds and rains.

Effects

- Trees/ plants are ‘burned’ by the sulphuric acid (e.g. ends of conifers)

- Acid rain enters the soil and leaches Ca²⁺ and Mg²⁺ out of the soil. This results in yellowing of leaves.

- Acid rain turns into precipitation and enters streams and lakes. This reduces the pH; however, it releases Al³⁺. This affects the fish because aluminium thickens the mucus at the lining of the gills. This reduces the fish’s ability to take oxygen from water.

2) Carbon monoxide – CO gas

It is produced by fossil fuels (coal and gas) burnt with insufficient oxygen. Carbon monoxide combines with haemoglobin inside the red blood cells and forms carbaminohaemoglobin. It prevents RBC from carrying oxygen and reduces oxygen circulation. It is toxic and once the carbaminohaemoglobin is formed, it is difficult to reverse the process.