Photosynthesis Lakshmi

Definition Photosynthesis is a process by which cells capture the energy of the sun and store it as chemical energy in complex organic molecules. During photosynthesis plants make use of carbon dioxide from air, water from the soil, and convert it into glucose in the presence of sunlight.

Overall equation of Photosynthesis Overall equation

Photosynthesis

Interconnection between photosynthesis and Cellular respiration

Section of a leaf

Structure of Chloroplast

Important Facts The upper and lower surface of the leaf contains a layer of epidermis. The outer layers of both epidermal layers is covered by the cuticle, a waxy waterproof covering that reduces the evaporation of water from the leaf. A leaf obtains carbon dioxide from the air through pores in the epidermis called stomata.

Section of the leaf Layers of cells between the two layers of epidermis is known as mesophyll. These cells contain chloroplasts, and as a result photosynthesis occurs principally in these cells. Vascular bundles, or veins, supply water and minerals to the mesophyll cells and carry the sugars they produce to other parts of the plant.

Structure of Chloroplast Chlorplasts are organelles that consist of a double outer membrane enclosing semi fluid medium, the stroma. Embedded in the stroma are disk-shaped, interconnected membranous sac called thylakoids. In most chloroplasts, the thylakoids are piled in stacks called grana. Grana are connected by stroma lamellae.

Photosynthesis The chemical reactions of photosynthesis that depend on light (light-dependent reactions) occur within the membranes of the thylakoids. The photosynthetic reactions that can continue for a time in darkness (light- independent reactions) occur in the stroma.

Photosynthesis Song

Test for Starch science.co.uk/Starch.htm science.co.uk/Starch.htm

Which wavelength of light is most effective in driving photosynthesis? Read more:

Action Spectrum Light at the blue end of the spectrum contains more energy than light at the red end (though red light is more efficiently absorbed than blue). UV radiation is higher-energy still, but cannot be used. In fact, it causes cell damage and mutations. Chlorophyll is the most important of all photosynthetic pigment

Action Spectrum Range of wavelength of light that can be used in the light-dependent reaction

Light Dependent Reactions Chlorophyll and other molecules embedded in the membranes of the thylakoids capture sunlight energy and convert some of them into chemical energy stored in energy-carrier molecules (ATP and NADPH). Oxygen gas is released as a by-product

Reactions of photosynthesis

Light-independent Reactions Enzymes in the stroma use the chemical energy of the carrier molecules to synthesize glucose or other organic molecules.

Why do leaves turn brown in autumn?

Factors affecting photosynthesis

Light Intensity

Temperature

Factors affecting photosynthesis