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9.9 Biochemistry: 1. Why study
photosynthesis?
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1. Photosynthesis is one of the most
important biochemical reactions that can be studied
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Students learn to:
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Students:
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Extract from Biology Stage 6 Syllabus (Amended October
2002) © Board of Studies, NSW.
[Edit:18 June 09]
Prior learning: Stage 4, Structures and
Systems 4.8.2 (c), 4.8.4 (d) Interactions 4.10 (c); Stage 5,
Interactions 5.11.2 (b), Structures and Systems 5.8.4 (b)
Preliminary module 8.2 (subsection 2) module 8.3 (subsection 4)
Students studying Chemistry will recognise knowledge from
Module 9.2: The Production and Identification of Materials.
Students not studying Chemistry may wish to access a Chemistry
textbook for research into the potential uses of
photosynthesis.
Background: Photosynthesis is one of the
most important biochemical reactions that can be studied.
Photosynthesis is the process in green plants that captures
light energy from the sun. It therefore is the basis of most
life on Earth.
gather, process and summarise information from secondary sources to identify the products of photosynthesis and describe the function of these compounds in living organisms
- Gather information from various sources such as a textbook or Internet site, evaluate the information and choose the relevant details. Summarise and collate the information to identify the products of photosynthesis and describe the function of these compounds in living things.
- Process the information by evaluating the accuracy of the data in relation to the area of investigation.
Here is a starting point.
Products of photosynthesis 
University of Michigan,
Michigan, USA.
Sample information
Identify the products of photosynthesis.
The products of photosynthesis are oxygen gas, water and
glucose. The glucose is stored as starch in the plant. The
reaction can be summarised by the equation:
6CO2(g) + 6H2O
light→
C6H12O6 + 6O2(g)
Describe the function of these compounds in living
organisms.
Oxygen gas and glucose are required for aerobic (oxygen requiring) respiration in all living things. Aerobic respiration is the process in which cells break down glucose to provide energy for metabolic processes to support growth, movement and reproduction. The energy is stored in the chemical bonds in the glucose. It is released when the glucose is oxidised and stored as ATP (adenosine triphosphate) for use by the cell. Respiration can be summarised by the equation :
C6H12O6 + 6O2(g) → 6CO2(g) + 6H2O + energy as ATP (~30 ATP in eucaryotic cells)
Water is the medium in which all cellular reactions take
place because it is the main constituent (part) of the
cytosol (cytoplasm). It also provides structure for cells by
creating pressure against the cell membrane to retain the
shape of the cell. Movement of water provides a way in which
substances can be transported around the cell and through the
organism. For example, water carries dissolved substances in
the blood in mammals and dissolved substances in the xylem of
plants.
analyse information from secondary sources to discuss and evaluate the potential uses of photosynthesis in replacing materials presently obtained from other non-renewable resources
- Analyse information you have gathered from popular scientific journals and the Internet by making generalisations and use the information to justify your statements.
Some sources of information are:
Biomass Program
Plant Oils
Sample information: Potential uses of
photosynthesis in replacing materials presently obtained from
other non-renewable resources.
Fuels
Fuels produced from biomass (a general term for carbon based matter from plants produced by photosynthesis) provide energy for use in cars in some parts of the world. Ethanol produced by the fermentation of sugars and starches is used alone or added to petrol. There is potential to develop this source of energy to replace or prolong the use of petrol made from non-renewable petroleum resources. At present large amounts of land would have to be used to support the production of sufficient biomass to meet the world’s current need for petroleum products. Large amounts of energy in farming methods (fertilisers, petrol for harvesting machinery) would be needed and the process is not viable at present.
Plastics
Plastics and various polymers are made from non-renewable petroleum resources. It is currently possible to produce plastics (PLA, PHAs and PHBs) from biomass materials using the action of micro-organisms. The development of these plastics has two advantages: the earth’s limited reserves of oil will be preserved and the plastics are biodegradable, reducing pollution and maintaining the cycle of raw materials.
Electricity
Most electricity used in homes and industries comes from burning fossils fuels. It could be possible in the future to harvest trees to replace fossils fuels. At the moment such large quantities would be required that this is not viable, except on a small scale. Problems associated with burning wood for energy (pollution from particulates, carbon dioxide and sufficiently rapid replacement of trees) are yet to be solved. In the USA biogas made from biomass by partial combustion, is used to produce electricity in a gas turbine. There is potential to develop this use of energy provided by photosynthesis on a larger scale.
Fibres
Fibres produced from plants could replace synthetic fibres produced from petroleum. Rayon is produced from the biopolymer cellulose (the main constituent of plant cells walls). Rayon is produced commercially at present and could replace other fabrics like nylon made from fossil fuels.
Ethene
Ethene is an important raw material for the manufacture of
plastics, including polyethene and PVC, and halogenated
hydrocarbons for refrigerants and solvents. If sufficient
glucose could be produced by bacterial digestion from
cellulose and then fermented to produce alcohol, it is
chemically a simple process to produce ethene by dehydration.
The same problems of land usage and energy inputs to produce
the biomass by photosynthesis do not make this a viable
process at present but it is a direction for future research.
discuss reasons for studying photosynthesis, including:
- its production of food resources and the need to increase crop yields
- understanding of photosynthesis may lead to better methods of harvesting solar energy
- photosynthesis can provide raw materials for a range of human needs
- the importance of reducing carbon dioxide levels in the atmosphere given its possible effects as a ‘greenhouse’ gas
- the importance of generating oxygen
- All animals depend on photosynthesis, either directly or
indirectly, for their energy needs. Plants are the producers
of energy for all ecosystems. Only about 1 – 2% of the
sun’s energy is captured by photosynthesis.
Manipulating the process of photosynthesis could increase the
efficiency rate of converting light energy to chemical energy
and selective breeding of more efficient crops could produce
enough food to meet the world’s food needs.
Harvesting solar energy is one answer to the world's energy supply problem. By studying photosynthesis it may become possible to duplicate the reactions and improve on solar harvesting techniques.
Plants store the glucose made in photosynthesis as starch and cellulose in cells walls. Cellulose can be converted to glucose by bacterial action and then to ethanol by fermentation. Ethanol can be used instead of petrol and converted to ethane to provide the raw materials for the production of plastics, fabrics, solvents and refrigerants.
Burning fossil fuels produces carbon dioxide that accumulates in the atmosphere and contributes to global warming by retaining heat that would otherwise be radiated out to the stratosphere. Plants convert carbon dioxide to oxygen, required for respiration by all plants and animals. Large forests and the photosynthetic plankton in the oceans maintain levels of oxygen by photosynthesis for use in respiration.
Oxygen is needed by all living things for respiration.
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