Dependence on Other Organisms
This lesson covers:
- What an ecosystem is and how its organisms are interdependent
- Why almost all life depends on plants
- How plants capture light energy and release oxygen
- How plants depend on insects for reproduction
What is an ecosystem?
An ecosystem consists of all the living organisms in one area, along with non-living parts like soil, water and air.
The organisms within an ecosystem depend on each other and interact in various ways. If one organism is removed, it affects the whole system.

For example:
- Plants depend on light energy, typically from the sun, to provide energy for photosynthesis.
- Herbivores depend on plants as a food source.
- Carnivores depend on other animals, either herbivores or other carnivores, as prey.
How plants capture the sun's energy
Plants, algae, and some bacteria can perform photosynthesis using energy from sunlight.

- Plants use light energy, typically from sunlight, carbon dioxide and water to produce glucose (food) and oxygen.
- The glucose is used to build molecules like carbohydrates and proteins that store chemical energy.
- When animals eat plants, this stored energy is passed on and used by the animals.
So almost all energy entering ecosystems starts with photosynthesis capturing light energy from sunlight.
Plants provide oxygen which is used in respiration
All living organisms, including plants, carry out respiration to release energy from food.

- To respire, organisms take in oxygen from the air to break down food like glucose.
- This releases energy, carbon dioxide and water.
- Plants help provide the oxygen needed for respiration and remove carbon dioxide through photosynthesis.
This cycling of gases allows both photosynthesis and respiration to occur.
Dependence on insects
Many flowering plants depend on insects for pollination and reproduction.

- Insect pollinators carry pollen between plants as they collect nectar.
- This allows fertilisation and reproduction in plants.
- Many plants depend completely on insect pollinators to be able to set seed and bear fruit.
- Without this, both natural plant populations and human food crops would decline dramatically.
- So both plants and humans depend on insects for our survival.