Syllabus Edition
First teaching 2015
Last exams 2025
Photosynthesis
Written by: Alistair Marjot
Reviewed by: Bridgette Barrett
Photosynthesis
What is photosynthesis?
Primary producers in the majority of ecosystems convert light energy into chemical energy in the process of photosynthesis
The photosynthesis reaction is:
Photosynthesis Equation
Where does photosynthesis take place?
The inputs and outputs are:
Inputs: sunlight as energy source, carbon dioxide, and water
Processes: inside chloroplasts, chlorophyll captures certain visible wavelengths of sunlight energy and stores this as chemical energy
Outputs: glucose and oxygen
Transformations: light energy is transformed into stored chemical energy (in organic matter e.g. carbohydrates, fats and proteins)
Photosynthesis produces the raw material for producing biomass
The glucose produced during photosynthesis is used as an energy source for the plant but also as the basic starting material for other organic molecules (e.g. cellulose and starch)
The process of photosynthesis transfers light energy to chemical energy in biological molecules
In ecosystems where sunlight and water is available, the process of photosynthesis enables plants to synthesise organic compounds (glucose and other sugars) from carbon dioxide
Most of these sugars synthesised by plants are used by the plant as respiratory substrates
A respiratory substrate is a molecule (such as glucose) that can be used in respiration, to release energy for growth
The remaining sugars (not used in respiration) are used to make other groups of biological molecules, such as:
Starch - a complex carbohydrate molecule (formed from many glucose molecules) that acts as a short-term energy storage molecule
Cellulose - another complex carbohydrate molecule (also formed from many glucose molecules) that acts as a structural component of plant cell walls
Lipids - plant cells can convert the sugars produced during photosynthesis into lipids, which act as another type of (longer-term) energy storage molecule
Proteins - plant cells can also combine the sugars produced during photosynthesis with nitrates to make amino acids, which can then be used to produce proteins
These different groups of biological molecules (all formed from the sugars synthesised by plants during photosynthesis) make up the biomass of the plants
The biomass is the mass of living material
The biomass can also be thought of as the chemical energy that is stored within the plant
The sugars synthesised during photosynthesis can be used in respiration or the creation of other biological molecules needed by plants
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