Plant Processes: Gas Exchange and Photosynthesis

8SCIENCE Mon. Feb. 14, 2011

What is gas exchange in plants?• When we inhale, we breathe in a mixture of gases we

need for survival• When we exhale, we breathe out the waste products• In plants, CO₂ and H₂O are two substances needed for

survival– CO₂ enters through the stomata – H₂O is absorbed through roots of

the plant and released as water vapor through the stomata

Gas Exchange

• Light, H₂O and CO₂ all affect the opening and closing of stomata

• Stomata are usually open during the day and close at night – When stomata closes, less

CO₂ can enter and less H₂O can escape

• When plants lose water vapor through stomata, this is called transpiration

Photosynthesis

• Photosynthesis is the process in which plants use light energy to make food– Chlorophyll is a chemical in plants that helps to

capture this light energy• Other than light, plants also need H₂O and CO₂• These molecules combine to form an organic

compound, a carbohydrate (sugar) called glucose

Process of Photosynthesis

6CO₂ + 6H₂O + light energy C₆H₁₂O₆ + 6O₂ Carbon dioxide + water + light (and chlorophyll) produces glucose and oxygen

• A plant needs 6 molecules of carbon dioxide (CO₂) and 6 molecules of water (H₂O) to make one molecule of glucose (C₆H₁₂O₆)

• The chemical bonds in glucose contain the energy the plant needs for growth and survival and is the main source of food for plants

• Oxygen is also produced during photosynthesis and released through plant stomata