Photosynthesis, Chlorophyll, Chloroplast

Plants are the universal producers of food and leaves of plants are known as “Kitchen of Nature”. Photosynthesis is the initiating step of food production in plants. Photosynthesis requires certain essential components like a site for synthesis – chloroplast, pigments – chlorophyll, raw materials, etc. Algae and some bacteria also follow the photosynthetic pathway for energy production.

Photosynthesis is a physicochemical process in which plant utilize materials like water, carbon dioxide in the presence of sunlight to produce glucose (food).

Plastids: Site of Photosynthesis

Plastids are special organelles which are unique to plant cells. Types of plastids can vary from colorless leucoplasts to yellowish chromoplasts and green-pigmented chloroplasts. The chloroplast is the site of photosynthesis in plants.

A chloroplast is a double-membraned plastid where grana, lamellae, and stroma are enclosed. Grana is a stack of coin-shaped structures and each coined structure is called thylakoid. Thylakoids are functional units of photosynthesis. They trap the light energy and also synthesize ATP and NADPH. Stroma fills the gap between grana and it’s the site of sugar synthesis. The reactions which occur in thylakoid are called light reaction since they are directly dependent on light. While the reaction in stroma depends on products of the light reaction than direct light. So it is called a dark reaction.

Chlorophyll: Pigments 

Pigments are another essential cellular components for photosynthesis. Pigments are molecules that impart color. They absorb light at some specific wavelength and reflect back the unabsorbed light.

Pigments are unique to its absorption spectra and pattern. Photosynthetic plants mainly contain chlorophyll a and accessory pigments such as chlorophyll b and carotenoids. These pigments are present in the thylakoids and help them to entrap the light energy. Chlorophyll a is the main pigment.

Photosynthesis is an essential process and a plant requires certain cellular components for this process to occur. Two of them are plastids and pigments.

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Practise This Question

Of the total incident solar radiation the proportion of PAR is: