High School Physics

Photosynthesis – class 11 revision notes

Last updated on February 5th, 2022 at 04:48 am

Photosynthesis is a series of reactions in which energy transferred as light is transformed into chemical energy. In this post, we have presented important information and facts on the Photosynthesis process. This post is apt for class 11 students of different boards (like ISC board, CBSE board, etc.) and NEET aspirants.

Important: This post is spanned across a few pages.
Links to the next pages are available at the bottom of each page of this photosynthesis series.

Fundamentals of photosynthesis process

Energy from light is trapped by chlorophyll, and this energy is then used to:

  1. split apart the strong bonds in water molecules to release hydrogen
  2. produce ATP
  3. reduce a substance called NADP

NADP stands for nicotinamide adenine dinucleotide phosphate, which is a coenzyme.

The ATP and reduced NADP are then used to add hydrogen to carbon dioxide, to produce carbohydrate molecules such as glucose (see Figure 1). – These complex organic molecules contain some of the energy that was originally in the light.

The oxygen from the split water molecules is a waste product and is released into the air.

There are many different steps in photosynthesis, which can be divided into two main stages —
(1) the light-dependent stage &
(2) the light-independent stage.

figure 1: An overview of photosynthesis

Photosynthesis takes place inside chloroplasts.

The light-dependent stages take place in grana. (specifically on the thylakoid membrane)

*All the chlorophyll in the chloroplast is contained in the membranes of the thylakoid vesicles

The thylakoid membranes contain light-absorbing pigments, such as chlorophyll and carotenoids, arranged in groups called photosystems. There are two kinds of photosystems, PSI and PSII, each of which contains slightly different kinds of chlorophyll.

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There are enclosed spaces between pairs of membranes, forming fluid-filled sacs called thylakoids. These are involved in photophosphorylation — the formation of ATP using energy from light.

Thylakoids are often arranged in stacks called grana (singular: granum).

The ‘background material’ of the chloroplast is called the stroma, and this is where the light-independent stage takes place.

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