PHOTOSYNTHESIS

Fourth Group XII IPA 3 Compiled by :

Nyimas Zihni Badzlina

Photosynthesis

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In Biology dictionary, Photosynthesis can be difinite as a process of making food that happen in the leaf, which done by the chlorophyll and helped by the sun light. There are some factors which influence the photosynthesis process, such as : light, chlorophyll, temperature, carbondioxide, and water.Photosynthesis is also defined as the production of organic compounds from inorganic molecules using light energy trapped by chlorophyll.Green plants use energy from light to combine carbon dioxide and water to make sugar and other chemical compounds.

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PHOTOSYNTHESIS

chlorophyll

Carbon Dioxide + Water + Light    >>   Glucose + Oxygen

chlorophyll

        6CO2 + 6H2O + Light    >>    C6H12O6 + 6O2

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Location of Chlorophyll in Photosynthetic Plant Cells

Chlorophyll is present in the internal green membranes of the chloroplast.

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THE MAIN EVENTS OF PHOTOSYNTHESIS

(lower level)

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The light is absorbed by the leaf’s chloroplasts. The light energy is used to split water molecules. The break up of water releases oxygen, electrons and protons (H+, H ions) : The electrons go to the chlorophyll, The protons are stored in the chloroplast The oxygen passes from the chloroplast. Some will be used by the mitochondria for aerobic respiration and the remainder will be passed into the atmosphere. Some of the light energy is carried to the chlorophyll to form high energy electrons. The high energy electrons and the stored protons combine with carbon dioxide to form glucose. (C6H12O6)

THE MAIN EVENTS OF PHOTOSYNTHESIS (higher level)

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Photosynthesis takes place in two stages; the light stage and the dark stage. The light stage needs light so it is called the light-dependent stage. The dark stage is called the light-independent stage.

Light Reaction

• The light stage takes place in the chloroplast’s thylakoid membranes. Light Absorption: All the colours of white light (except green light) are absorbed by pigments in the chloroplast. Energy Transfer: The energy is transferred to electrons. These electrons become high energy electrons. Within the chloroplasts are electron acceptors. After the electron acceptor receives the high energy electrons the electrons will flow to one of two paths:

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A Pathway 1 (Cyclic Electron Transport)

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• A Pathway 1 (Cyclic Electron Transport): The high energy electrons travel through a series of electron acceptors (electron carrier system) and then back to the chlorophyll molecule. As they travel through the acceptors they lose energy. This energy is in ADP molecules. This is used to combine with 1 more phosphate molecule to form ATP and water. This is a high energy molecule. The addition of a phosphate molecule to ADP is called phosphorylation. Since light is needed this addition of phosphate is called photophophoylation.

B. Pathway 2 (Non-cyclic Electron Transport)

Pathway 2 (Non-cyclic Electron Transport): As in Stage 1 the electron has gained energy from sunlight. The electron moves from acceptor to acceptor but does not return to the chlorophyll. As an electron moves from acceptor to acceptor it is passed to NADP+. This causes the NADP+ to become neutral. This NADP molecule receives another electron and becomes NADP- (negative). The negative NADP- attracts the proton + which was previously released when water was broken up. The molecule now becomes NADPH. • 

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Light Reactions

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DARK REACTIONS DARK STAGE

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The dark stage takes place in the stroma of the chloroplast. Unlike the light stage, the dark stage is controlled by enzymes and therefore affected by temperature. The enzyme is ribulose bisphosphate carboxylase oxygenase (RUBISCO). In this cycle ATP and NADPH, produced in the light stage, provide the energy and electrons to change carbon dioxide (CO2) to carbohydrates (C H O) molecules. Although this stage is called the dark stage it occurs in light and also in darkness as long as the products of the light phase are still available. The dark stage functions if ATP, NADPH and carbon dioxide are present. At the completion of this stage ADP, Phosphorous, and NADP+ are recycled for use in the light stage.

Conclusion• So, photosynthesis is an

important process that produce oxigen as an air which used by living things to breath, and glucose as a energy source in plant. Photosynthesis provides the chemical energy that is needed to produced these compounds. 

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