Role of the Sun as Energy Source

The Sun is the principal source of energy input into biological systems.
It provides the light and heat necessary for photosynthesis, influencing the distribution and diversity of life.

Photosynthesis

Photosynthesis is the process by which green plants, algae, and some bacteria absorb light energy and use it to convert carbon dioxide and water into glucose and oxygen.
This solar energy absorbed by plants is transformed into chemical energy, stored as glucose, which is used for respiration or converted into other substances such as cellulose, proteins or fats.
In this way, solar energy flows from the Sun into the ecosystem and is converted into edible energy.

The energy flow in ecosystems begins with the energy from the Sun.
Producers, like plants, transform this solar energy into chemical energy during photosynthesis.
This energy is then transferred to the primary consumers (herbivores) when they eat the plants, and onwards to secondary and tertiary consumers (carnivores and omnivores) as they eat other animals.
Each transfer of energy involves a significant loss, mostly as heat, which is why this is a one-way flow, from the Sun and ultimately out of the ecosystem.

Energy loss occurs at each link in the food chain due to the second law of thermodynamics, which states that whenever energy changes form, some of the energy is lost as heat.
Approximately 90% of the energy consumed at each trophic level is lost as heat with only 10% being transferred to the next level.
This loss of energy is the reason why food chains are typically short and explains the pyramid shape of the energy flow in ecosystems. This is known as an ecological pyramid.

Without the Sun, there would be no primary production, and hence no herbivores, carnivores, decomposers and minimal life on Earth.
Thus, the Sun is a vital element in the balance and sustainability of all ecosystems on Earth.