Summary

Summary CONCEPT- Photosynthesis

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Course
BIO130

Institution
University Of Toronto (U Of T )

It is a detailed typed word document about one of the most important topics - photosynthesis. this note includes simple conceptual diagrams and conceptual points .

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Uploaded on August 23, 2022
Number of pages 13
Written in 2022/2023
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What is photosynthesis?
 The process of synthesis with the assistance of light is termed
as photosynthesis.
 It is the mechanism by which sunlight is used by green plants to produce food
from simple molecules like CO2 and H2O.
 Often called carbon assimilation, photosynthesis is expressed by the following
equation;
 6CO2 + 6H2O——— > C6 H12 O6 + 6O2
 The light energy is transformed into chemical energy during the
photosynthesis process and is stored into the organic matter, which is
normally carbohydrates, and O2 is a by-product of photosynthesis.
 The raw materials for this process are CO2 and H2O.
 CO2 from the air and H2O from the soil are absorbed.
 The following points make photosynthesis essential to humanity:
 It preserves the atmospheric equilibrium of O2.
 It provides food either directly as vegetables or indirectly as animal meat or
milk which, in turn, is fed to plants.

Where does photosynthesis takes place?
 The photosynthesis occurs in chloroplasts in case of plants and blue-green
algae.
 When microscopic observation of a leaf section is done, chlorophyll is not
uniformly distributed in the cell.
 However, it is confined to organelles termed as chloroplasts.
 In plants, chloroplasts lie mainly in the cells of mesophyll, a layer that includes
several air spaces and a very high concentration of water vapor.
 The exchange of gases takes place between interior of the leaf and the outside
through microscopic pores, termed as stomata.
 Each mesophyll cell consists of 20-100 chloroplasts.
 The chloroplast is enclosed by outer and inner membranes.
 The inner membrane encloses a fluid filled region termed as stroma.
 Stroma consists of most of the enzymes needed to produce carbohydrate
molecules.
 The third system of membranes is suspended in the stroma.
 This system forms an interconnected set of flat, disc like sacs called thylakoids.
 A fluid-filled internal space, the thylakoid lumen, is enclosed by the thylakoid
membrane.
 Thylakoid sacs are arranged in stacks called grana (sing., granum) in some
regions of the chloroplast.
 Each granum is identical to a coin stack, with a thylakoid being each “coin.”

,  Some thylakoid membranes extend from one granum to another.
 Thylakoid membranes are involved in ATP synthesis.

Photosynthetic pigments:
 There are major three photosynthetic pigments. They are:
 Chlorophylls
 Carotenoid
 Phycobillins

i. Chlorophylls:

 Chlorophylls are present in thylakoid membranes.
 Thylakoid membranes consist of several kinds of pigments that absorb visible
light.
 Various pigments absorb light from various wavelengths.
 Chlorophyll is the dominant photosynthesis pigment and it absorbs light
mainly in the visible spectrum’s blue and red areas.
 Green light is not appreciably absorbed by chlorophyll.
 Some of the green light that strikes the plant is either scattered or reflected
and hence the plants typically appear to be green in colour.
 There are two principal parts of a chlorophyll molecule, a complex ring and a
long side chain.
 A porphyrin ring is ring structure that comprises of smaller rings made of
carbon and nitrogen atoms.
 The porphyrin ring absorbs light energy.
 The chlorophyll porphyrin ring is remarkably similar to the red pigment
hemoglobin component of the heme in red blood cells.
 However, unlike heme, that holds an atom of iron in the center of the ring,
chlorophyll consists of an atom of magnesium in that position.
 The chlorophyll molecule also contains a long, hydrocarbon side chain that
makes the molecule extremely nonpolar and ties up the chlorophyll in the
membrane
 All chlorophyll molecules in the thylakoid membrane are associated with
specific chlorophyll-binding proteins
 Each thylakoid membrane is filled with accurately oriented chlorophyll
molecules and chlorophyll-binding proteins that facilitate the transfer of
energy from one molecule to another.
 There are many kinds of chlorophyll.
 The chlorophyll ‘a’ is the most essential pigment that starts the light-
dependent reactions of photosynthesis.
 Chlorophyll ‘b’ is the accessory pigment which also takes part in
photosynthesis.

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