Biology: Photosynthesis and Food Chain Productivity

Biology: Photosynthesis and Food Chain Productivity


  • Photosynthesis is the process by which plants, algae, and some bacteria convert light energy, usually from the sun, into chemical energy in the form of glucose.

  • This crucial process involves the absorption of light energy by a pigment called chlorophyll found within the chloroplasts of plant cells.

  • The overall equation for photosynthesis is: 6CO2 + 6H2O -> C6H12O6 + 6O2. This reaction converts carbon dioxide and water into glucose and oxygen.

  • Photosynthesis can be split into two stages: the light-dependent reaction which generates ATP (energy) and NADPH (a reducing agent), and the light-independent reaction (also known as the Calvin Cycle) which uses ATP, NADPH, and CO2 to produce glucose.

  • The rate of photosynthesis can be affected by several factors including light intensity, carbon dioxide concentration, and temperature. It typically increases with the increase in these factors to a certain point, after which it levels off.

Food Chain and Energy Transfer

  • A food chain is a linear representation of how energy and matter pass from one organism to another within an ecosystem.

  • Every food chain begins with a producer, which is an organism that generates food energy (usually plants that perform photosynthesis). This is followed by consumers of different levels: primary, secondary, and tertiary consumers.

  • Primary consumers (or herbivores) eat producers, secondary consumers (or carnivores) eat primary consumers, and tertiary consumers (or apex predators) eat secondary consumers.

  • In any food chain, energy and matter are lost at each step. This loss is due to factors such as heat loss in metabolic processes, inefficiencies in digestion, and resources locked within indigestible material.

Productivity in Ecosystems

  • The term productivity in relation to ecosystems refers to the amount of biomass produced by plants (the primary producers).

  • Gross Primary Productivity (GPP) is the total energy that plants capture and assimilate in a given period. Net Primary Productivity (NPP) is what remains after plant respiration (maintenance, growth) is deducted.

  • The energy contained within the NPP is what is available to be passed onto the next trophic level (herbivores).

  • The pyramid of productivity illustrates the energy flow from one trophic level to the next with each level on the pyramid representing a trophic level in an ecosystem. It also highlights the energy loss that happens at each level.

  • Maximising sustainable productivity in ecosystems is key to human food security and can be achieved by managing ecological factors (light, nutrients) and reducing energy loss.