Question

20. Write the differences between light and dark
reactions of photosynthesis?​

Answer 1

Explanation:

Light Reaction

The light reaction is a light-dependent process which includes a series of events such as light absorption, hydrolysis, the release of oxygen, formation of ATP and NADPH.

The light reaction of photosynthesis initiates only when it is supplied with light energy.

The photosystem is the arrangement of pigments including chlorophyll within thylakoids.

There are two photosystems in plants:

Photosystem I (PS-I)

Photosystem II (PS-II)

Photosystem I absorbs light at a wavelength of 700 nm, whereas Photosystem II absorbs light at a wavelength of 680 nm.

The light reaction occurs in the thylakoids of the chloroplast. When the light hits, chlorophyll a get excited to higher energy state followed by a series of reactions. This energy is converted into energy molecules ATP and NADPH by using PS I and PS II. Also, hydrolysis occurs and releases oxygen.

Also Read: Cyclic and non-cyclic photophosphorylation

Dark Reaction

Dark reaction is also called carbon-fixing reaction. It is a light-independent process in which sugar molecules are formed from the carbon dioxide and water molecules.

The dark reaction occurs in the stroma of the chloroplast where they utilize the products of the light reaction.

Plants capture the carbon dioxide from the atmosphere through stomata and proceed to the Calvin cycle.

In the Calvin cycle, the ATP and NADPH formed during light reaction drives the reaction and convert 6 molecules of carbon dioxide into one sugar molecule i.e. glucose.

Also Refer: Photosynthesis in Higher plants

Difference between Light and Dark Reaction

Following are the important difference between light and dark reaction:

Light Reaction

Dark Reaction

It takes place only in the presence of light.

It can take place in the presence or absence of sunlight.

It is a photochemical phase.

It is a biochemical phase.

It takes place in the grana of the chloroplast.

It takes place in the stroma of the chloroplast.

NADP utilizes H+ ions to form NADPH.

The hydrogen of NADPH combines with CO2

The end products are ATP and NADPH.

Glucose is the end product. ATP and NADPH help in the formation of glucose.

The water molecules split into hydrogen and oxygen.

Glucose is produced. Co2 is utilized in the dark reaction.

Photolysis occurs in PS-II.

Photolysis does not occur.