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Photosynthesis

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Practical 2: Photosynthesis

Introduction: Photosynthesis is a vital process in plants as carbon dioxide is used to form sugars and other complex compounds for growth. There are two basic processes in photosynthesis: light-dependent and light-independent. Light-dependent process, a temperature-independent reaction where light energy is absorbed by the photosynthetic pigments and transformed into chemical energy which is used for water, splitting into oxygen molecule, proton (H+) for driving ATP during phosphorylation, and electron (e-) which is being passed down the electron transport chain to yield NADPH. Light–independent, temperature-dependent reaction occurs to form carbohydrate and water molecule by the assimilation of carbon dioxide, driven by NADPH and ATP from light-dependent reaction. In this practical, DCPIP, a blue dye is used. DCPIP turns into colourless as it is reduced by accepting electrons. The rate of DCPIP turns into colourless indirectly gives an estimation on the rate of electron transport, as well as the rate of photosynthesis.

Aim: To determine the rate of DCPIP turns into colourless/photosynthetic electron transport in isolated chloroplasts from silverbeet leaves under different type of treatments. The rate of DCPIP turns into colourless is indicated by measuring the absorbance using a spectrophotometer.

Hypothesis: The faster the DCPIP turns into colourless, the more rapid is the decrease in absorbance over time, the faster the electron being transported in silverbeet leaves, thus, the higher the rate of photosynthesis.

Methods: First of all, seven test tubes were numbered and solutions A-D were added according to the volumes shown in Table 1. Tube 1 was capped with parafilm and inverted several times. The spectrophotometer (λ=600nm) was calibrated using Tube 1, which contained chloroplasts and

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