● `color{Brown}"Photosynthesis"` takes place in the `color{violet}"green leaves of plants"` but it does so also in `color{violet}"other green parts"` of the plants.

● The `color{violet}"mesophyll cells"` in the leaves, have a `color{violet}"large number of chloroplasts."`

● Usually the `color{violet}"chloroplasts align"` themselves along the `color{violet}"walls of the mesophyll cells"`, such that they get the
`color{violet}"optimum quantity"` of the `color{violet}"incident light"`.

● Within the chloroplast there is the `color{Brown}"membranous system"`consisting of `color{violet}"grana"`, the `color{violet}"stroma lamellae"`, and the `color{violet}"fluid stroma."`

● There is a `color{violet}"clear division of labour"` within the chloroplast.

● The `color{Brown}"membrane system"` is responsible for `color{violet}"trapping the light energy"` and also for the `color{violet}"synthesis of ATP and NADPH"`.

● In `color{Brown}"stroma,"` `color{violet}"enzymatic reactions"` incorporate `CO_2` into the plant leading to the `color{violet}"synthesis of sugar"`, which in turn `color{violet}"forms starch"`.

● The `color{violet}"former set of reactions"`, since they are `color{violet}"directly light driven"` are called `color{Brown}"light reactions"`.

● The latter are `color{violet}"not directly light driven"` but are dependent on the products of light reactions (`color{violet}"ATP and NADPH"`).

● Hence, to `color{violet}"distinguish the latter"` they are called, by convention, as `color{Brown}"dark reactions."`

● However, this should `color{violet}"not be construed"` to mean that they `color{violet}"occur in darkness"` or that they are `color{violet}"not light dependent"`.

● We can look for an answer for `color{violet}"why and how"` there are so many `color{violet}"shades of green"` in their leaves – even in the same plant, by trying to `color{violet}"separate the leaf pigments"` of any green plant through `color{violet}"paper chromatography"`.

● A `color{Brown}"chromatographic separation"` of the leaf pigments shows that the colour that we see in leaves is `color{violet}"not due to a single pigment"` but due to `color{Brown}"four pigments"`:

`star` `color{Brown}"Chlorophyll a"` (`color{violet}"bright or blue green"` in the chromatogram),

`star` `color{Brown}"Chlorophyll b"` (`color{violet}"yellow green"`),

`star` `color{Brown}"Xanthophylls"` (`color{violet}"yellow"`)

`star` `color{Brown}"Carotenoids"` (`color{violet}"yellow to yellow-orange"`).

● Pigments are `color{violet}"substances"` that have an `color{violet}"ability to absorb light"`, at `color{violet}"specific wavelengths"`.

● It is known that the `color{violet}"wavelength of the visible spectrum"` of light as well as the `color{violet}"VIBGYOR"`.

● Now look at the figure showing the `color{violet}"wavelengths"` at which `color{violet}"maximum photosynthesis occurs"` in a plant.

● The wavelengths at which there is `color{violet}"maximum absorption by chlorophyll a"`, i.e., in the `color{Brown}"blue and the red regions"`, also shows `color{violet}"higher rate of photosynthesis"`.

● Hence, we can conclude that `color{violet}"chlorophyll a"` is `color{violet}"the chief pigment"` associated with photosynthesis.

● These `color{violet}"graphs"`, together, show that `color{violet}"most of the photosynthesis"` takes place in the `color{violet}"blue and red regions"` of the spectrum; some photosynthesis does take place at the `color{violet}"other wavelengths"` of the visible spectrum.

● This is because that though `color{violet}"chlorophyll is the major pigment"` responsible for trapping light, other `color{violet}"thylakoid pigments"` like `color{violet}"chlorophyll b, xanthophylls"` and `color{violet}"carotenoids"`, which are called `color{Brown}"accessory pigments"`, also `color{violet}"absorb light"` and `color{violet}"transfer the energy"` to chlorophyll a.

● Indeed, they not only enable a `color{violet}"wider range of wavelength"` of incoming light to be `color{violet}"utilized for photosynthesis"` but also `color{violet}"protect chlorophyll a:"` from `color{Brown}"photo-oxidation"`.