What is Photosynthesis? | The Openbook

The word photosynthesis can be separated to make two smaller words:
“photo” which means light
“synthesis” which means putting together
Photosynthesis is the process by which plants make their own food.
To make food, plants need not just one but all of the following:
• carbon dioxide
• water
• sunlight

Let’s take a look at how these are collected by plants.
• Carbon dioxide from the air passes through small pores (holes) in the leaves. These pores are called stomata.

• Water is absorbed by the roots and passes through vessels in the stem on its way to the leaves.

• Sunlight is absorbed by a green chemical in the leaves.

The photosynthesis process takes place in the leaves of plants. The leaves are made up of very small cells. Inside these cells are tiny structures called chloroplasts. Each chloroplast contains a green chemical called chlorophyllwhich gives leaves their green color.
• Chlorophyll absorbs the sun’s energy.
• It is this energy that is used to split water molecules into hydrogen and oxygen.
• Oxygen is released from the leaves into the atmosphere.
• Hydrogen and carbon dioxide are used to form glucose or food for plants.

Some of the glucose is used to provide energy for the growth and development of plants while the rest is stored in leaves, roots or fruits for later use by plants.

Photosynthesis occurs in two stages commonly known as Light dependent Reactions and the Calvin Cycle.
Light dependent reactions occur in the thylakoid membrane of the chloroplasts and take place only when light is available. During these reactions light energy is converted to chemical energy.
• Chlorophyll and other pigments absorb energy from sunlight. This energy is transferred to the photosystems responsible for photosynthesis.
• Water is used to provide electrons and hydrogen ions but also produces oxygen.

• The electrons and hydrogen ions are used to create ATP and NADPH. ATP is an energy storage molecule. NADPH is an electron carrier/donor molecule. Both ATP and NADPH will be used in the next stage of photosynthesis.

The Calvin Cycle
The Calvin Cycle reactions occur in the stroma of the chloroplasts. Although these reactions can take place without light, the process requires ATP and NADPH which were created using light in the first stage. Carbon dioxide and energy from ATP along with NADPH are used to form glucose. #theopenbook #Education #Educationalvideos #Studyiq #learn #Cbse #icse #ssc #generalknowledge