Photosynthesis

By Naomi Keddy

Photosynthesis is the production glucose in plants with sunlight, carbon dioxide and water and they can do this because they contain the green pigment called chlorophyll which able to absorb all the required things for this process.

Role of photosynthesis:

-Plants use it to make their own food

-Animals get their food from plants

-Plants produce oxygen which is needed for most living things

-Photosynthesis was responsible for forming fossil fuels

Photosynthesis is divided into two stages, which are light stage and dark stage.

Light stage:

1. Light is absorbed

2. Water is split

3. The products of the splitting of water

Light: 

Light is absorbed by the sun. The light is trapped by the pigment chlorophyll. Chlorophyll is found in the organelle called chloroplasts. Only green plants contain chlorophyll pigments. Sunlight that is absorbed by the plant provides energy to the plant.

Water:

Some of the trapped sunlight provides energy and some of that energy is used to split water into four protons (4H+), four electrons (4e-) and Oxygen (02)

Products:

The three products from the splitting of water go to:

-The electrons are passed to the chlorophyll

-Protons are released into a storage pool in the chloroplast

-Oxygen is passed into the chloroplast into the cytoplasm and then into the atmosphere. 

Light stage is divided into two pathways: 

-Pathway 1-Cyclic electron flow

-Pathway 2-noncyclic electron flow

Pathway 1-Cyclic electron flow:

-The light stage occurs in the grana of the chloroplast

-The high-energised electrons pass from the reaction centre chlorophyll to an electron acceptor.

-They pass from the electron acceptor to a series of other electron acceptors and back to the chlorophyll.

-when the electrons return to the chlorophyll they lose energy.

-The energy they release is trapped by ADP and a phosphate to form ATP

Pathway 2-non-cyclic electron flow:

-Two high energised electrons leave the chlorophyll.

-They pass to an electron acceptor and along another series of electron acceptors

-This time the energised electrons do not return to the chlorophyll.

-They lose some energy.

-The energy released is used to form more ATP

-The electrons lost from chlorophyll 1 molecule are picked up by the NADP+ and combine with protons from the proton pool to form NADPH.

𝑵𝑨𝑫𝑷+ + 𝟐𝒆_ + 𝑯+ −→𝑵𝑨𝑫𝑷𝑯

-This NADPH is used in the dark stage

-The chlorophyll is now short of electrons. It gains new electrons from the splitting of water.

Dark stage:

-The dark stage takes place in the stroma of the chloroplast.

-The dark stage is controlled by enzymes. 

-This means it is affected by temperature. 

-Carbon dioxide from the atmosphere or from respiration enters the chloroplast.

-The hydrogen ions are released from NADPH to convert carbon dioxide into Glucose.

. The energy for this process comes from the breakdown of ATP that was formed in the light stage.

-NADP+ and ATP are recycled back into the light stage.

Light stage: 

-Occurs in the Grana of the cell

-Requires Light

-ATP is produced

-Oxygen is produced

-NADPH is produced

Dark Stage:

-Occurs in the stroma

-Doesn’t require light

-ATP is used

-NADPH is used

-Carbon dioxide is converted into glucose