Biogeochemical cycles Flashcards
Explain the role of photosynthesis in the carbon cycle.
The capture of light energy by pigments such as chlorophyll. It converts carbon dioxide and water into sugars which may be converted into other substances such as proteins and lipids. Oxygen is a by-product. Before being moved from plants to animals through the food chain
Explain how the carbon cycle exists in a dynamic equilibrium.
Carbon moves back and forth between the atmosphere and living things. The transfers cancel each other out so there is no set change. Photosynthesis removes CO2 from the atmosphere and converts it into plant leaves, stems and roots. Respiration returns CO2 to the atmosphere by oxidising sugars. Photosynthesis and respiration are in balance.
Explain the role of respiration in the carbon cycle.
The release of energy from high-energy substances, such as carbohydrates (to drive metabolic processes). Aerobic respiration can break down organic compounds more fully and release much more energy than anaerobic respiration. Anaerobic respiration allows some organisms to survive and use food sources in oxygen-deficient environments.
Explain the role of food chains in the carbon cycle.
Organic compounds are passed as food between organisms.
Explain the role of fossilisation in the carbon cycle.
Incomplete combustion of organisms leading to deposition of fossil fuels. The absorption of carbon dioxide by marine organisms is stored in their skeleton and subsequent sedimentation of limestone and chalk on the seabed.
Explain the role of combustion in the carbon cycle.
The release of carbon dioxide by the burning of organic substances such as wood and fossil fuels
Explain the role of volcanoes and decomposition in the carbon cycle.
Volcanoes: Releases carbon dioxide from fossil fuels or carbonate rocks in the ground
Decomposition: The breakdown of organic matter by microorganisms, releasing gases such as carbon dioxide under aerobic conditions and methane in anaerobic conditions.
Name the sources and sinks in the carbon cycle
Photosynthesis, respiration, food chains, fossilisation, combustion, volcanoes, decomposition.
Explain how humans effect photosynthesis in terms of the carbon cycle (4 ways)
1) Deforestation: Reduces the movement of carbon from the atmosphere into biomass
2) Afforestation: Increases the movement of carbon from the atmosphere from the biomass.
3) Marine pollution: Toxic materials can reduce phytoplankton populations. This reduces the absorption of dissolved carbon dioxide. Some phytoplanktons naturally sinks to the seabed when it dies, increasing the amount of carbon in marine sediments.
Explain how humans effect aerobic respiration in terms of the carbon cycle.
Ploughing increases the oxygen supply to decomposes living in the soil so aerobic decomposition takes place more rapidly. The amounts of carbon in the soil in the soil dead organic matter store is reduced and the amount in the atmosphere is increased.
Explain how humans effect anaerobic respiration in terms of the carbon cycle.
In the absence of oxygen, respiration by anaerobic soil organisms release methane gas. If the methane is released into the atmosphere, it is gradually oxidised to CO2. Anaerobic environments produced by humans activities: rice paid fields, landfill sites, anaerobic sediments in reservoirs, livestock intestines.
Explain how humans effect methane in terms of the carbon cycle
Methane may be released into the atmosphere during coal mining and from the extraction of crude oil and natural gas. Also by anaerobic fermentation in cattle and peat bogs.
Give two suitable management methods of the carbon cycle and explain them.
Conservation of biomass carbon stores. Habitats, such as peat bogs and forests, contain huge amounts of carbon. Protecting these from exploitation, or damaging land-use change, is important to prevent even higher CO2 releases.
Two methods that may be used for
the sustainable management of the
carbon cycle are:
1) carbon sequestration
2) carbon capture and storage (CCS).
Describe ONE similarity and TWO
differences between these two methods.
both reduce/store atmospheric carbon (dioxide)
1) carbon sequestration removes carbon (dioxide) from the atmosphere, CCS stops carbon (dioxide) being released into atmosphere/stops carbon release at source
* carbon sequestration stores short term, CCS stores long term
* carbon sequestration is a natural process eg photosynthesis, CCS
has been developed by humans
Give TWO OTHER methods for the
sustainable management of the carbon
cycle. [2 marks]
- use of alternatives to fossil fuels/use of renewable energy
- energy conservation eg insulation
- sources/use of nuclear power
- afforestation / reforestation
- increasing soil organic matter / mulching / cover crops
- conserving peat bogs
- reduced tillage / long term crops
- solid waste management
- plant based diets for humans / low methane diets for livestock
How has carbon in the biosphere changed?
Biosphere:
* less carbon in living organisms because of deforestation
* less carbon in dead organic matter because of increased
decomposition/peat removal/crop harvesting/soil erosion
How has carbon in the Hydrosphere changed?
Hydrosphere:
* more carbon as dissolved/stored carbon dioxide/(hydrogen)
carbonate ions/carbonic acid because of increased dissolving from
increased carbon dioxide in atmosphere
How has carbon in the Lithosphere changed?
Lithosphere:
* less carbon as carbonates in rocks because of mining/use in
industry/construction
* less carbon in fossil fuels because of combustion
Why is nitrogen essential for living organisms?
All living things need nitrogen to build proteins and other important body chemicals.
What are the main reservoirs of nitrogen?
The major reservoir of nitrogen is the atmosphere
Explain the Nitrogen cycle
nitrogen fixation, nitrification, assimilation, and denitrification. In the nitrogen fixation step, nitrogen is converted from nitrogen gas in the atmosphere into a form that can be used by plants. In the nitrification step, the nitrogen is converted into nitrates.
How do agricultural practices affect the nitrogen cycle?
Each time plants are harvested, the nitrogen contained in them is carried far away from the plot of soil where it came from. So, to avoid soil depletion, nitrogen taken away from the soil – whether through harvesting or environmental loss – has to be put back in the soil in one way or another.
Explain the Phosphorus cycle
Describe how one natural process increases the ammonium ion concentration of soil (1 mark)
nitrogen fixation by root nodule bacteria
