Photosynthesis (SL IB Environmental Systems & Societies (ESS))

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