Lesson 2 – Energy Flow in Ecosystems

The Source of Energy The Sun is the source of almost all the energy living things need to survive Most of the Sun’s energy is radiant energy, which travels through empty space About 30 % of the Sun’s energy is reflected by clouds or Earth’s surface

The Source of Energy About 70 % is absorbed by the atmosphere, water, and land, and is converted into thermal energy A very small amount is absorbed by living organisms ~ 0.023 %

The Source of Energy 30 % reflected 19 % absorbed by clouds and atmosphere 70 % absorbed 0.023 % absorbed by plants 51 % absorbed by land and oceans

Photosynthesis Some organisms use light to make their own food An organism that makes its own food is called a producer – plants are producers The process of converting light energy into chemical energy is called photosynthesis Plants are green because they contain chlorophyll, the chemical that absorbs light energy

Photosynthesis Light energy is used to convert two chemicals (carbon dioxide and water) to a different chemical (sugar) which is stored in the plant During photosynthesis, plants release oxygen We use a word equation to describe photosynthesis: carbon dioxide + water sugar + oxygen light energy Photosynthesis Video

Cellular Respiration Many organisms do not produce their own food and must obtain energy from other sources These organisms are called consumers, e.g. humans Consumers obtain energy by eating other organisms that contain stored energy As food is digested, the energy is released through a process called cellular respiration

Cellular Respiration In cellular respiration, the sugar and oxygen are changed into carbon dioxide and water As this occurs, energy is released We use a word equation to describe cellular respiration: sugar + oxygen carbon dioxide + water + energy

Complementary Processes Photosynthesis and cellular respiration are opposite reactions Both processes need to happen in order to sustain life