Lab 2 Photosynthesis assignment 2020 online version (3) PDF

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Download Lab 2 Photosynthesis assignment 2020 online version (3) PDF

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Name: Mariam Baissy

2020 Assignment Sheet for BIOSCI 101 LABORATORY 2 Photosynthesis Bench number: 44

UPI: mbai990

Stream Number: 17

Graphs (6 marks) Complete following instructions given on Canvas page for Lab 2 online and upload to Lab 2 Graphs assignment.

Questions 1. Why does the reduction of the dye DCPIP work best using the chloroplasts whose outer envelopes have been damaged during preparation?

2. What colour is light of 620 nm wavelength? 3. Why is this wavelength used to estimate DCPIP?

4. Absorbance readings may be affected by conditions on the surface of the cuvette or by factors within test solutions. Give an example of each.

Answer (enter in space provided) The reduction of the dye DCPIP works best using the chloroplasts whose outer envelopes have been damaged during preparation because it means that the DCPIP can access the thylakoid membranes directly, without having to pass through the outer membranes, to accept electrons directly from the electron transport chain. Therefore, since DCPIP normally cannot fully get across the membrane, damaging the membranes enhances access of the DCPIP to the thylakoid membranes. red

Mark allocation

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(1 mark) This wavelength is used because since DCPIP is a blue dye, that means the blue light wavelengths are the wavelengths that are reflected by the dye. Hence since the dye appears blue, the spectrophotometer must be set to the opposite wavelength of the colour that is reflected. Therefore, the wavelength that is absorbed by DCPIP will be around 620 nm (absorbance maximum for DCPIP) which is the wavelength for red light. Therefore, since DCPIP appears/reflects blue, it must be absorbing red light (wavelength of 620 nm). on the surface of the cuvette = liquid or condensation, fingerprints, or dirt on the surface of the cuvette may affect absorbance readings. factors within test solutions = factors within test solution that may affect absorbance readings is how well the reagents are mixed together, where if the test solution is not homogenous or if there is insufficient mixing of the solution being measured, this may affect the absorbance readings. Other factors within test solution could also include

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bubbles and turbidity which may also affect absorbance readings. 5.

a) Which molecule is the electron donor for the reaction you have studied? b) Is this the natural electron donor? 6. Which molecule is the electron acceptor in the experimental reaction, and in the intact chloroplast? 7. Someone asks you the following question: Which wavelength(s) of light are the most effective in photosynthesis? What is your explanation / hypothesis?

(a) DCPIPH2 (b) No. Chlorophyll is the natural electron donor (1 mark) in the experimental reaction = DCPIP in the intact chloroplast = NADP+ (2 marks) The wavelengths of light that are most effective in photosynthesis are wavelengths of red light at about (580-750 nm) and wavelengths of blue light at around (400-500 nm). These red and blue wavelengths of light are the most effective in photosynthesis because they have exactly the right amount of energy to energize, or excite, chlorophyll electrons and boost them out of their orbits to a higher energy level. Furthermore, the rate of photosynthesis measured by release of oxygen by the leaf, is greatest for wavelengths that correspond to wavelengths of light absorption by chlorophyll pigments (chlorophyll a and b) where the chlorophyll molecules of chloroplasts absorb blue and red light. This is because since chloroplasts appear/reflect green light, they must be absorbing red and blue light.

(2 marks)

Total mark (15 marks)...