SLE132 Prac 4 Part 2: Photosynthesis Report on Light Reactions

This document presents a completed lab report for SLE132 Prac 4 Part 2, focusing on photosynthesis. The report includes answers to questions about the light reactions, identifying key chemical species and energy-rich compounds involved. It details an experiment using DCPIP to substitute for cytochrome c, with a graph of absorbance against time. The results section describes the observed trends, including the behavior of dark control, chloroplast, and control samples. The conclusion links the observed trends with the functioning of light reactions in plants, discussing how the amount of light affects photosynthesis. The report also examines the impact of blocking electron flow between photosystems II and I. Desklib provides a platform for students to access similar past papers and solved assignments.

SLE132 Prac 4 Part 2: Photosynthesis Report Template
Complete this template on your own, and then convert to a PDF file before uploading to the
assignment folder. This is an individual assignment.
The assignment is marked out of 50 and will be converted to /10% of your final assessment for this
unit.
Refer to the following concept map of the photosynthetic light reactions to answer the following
questions. Figure 10.14 of your text will help you. (1 mark for each question on this page)
1. What is the chemical species that is transferred through the light reactions? (Box A)
Answer: Electrons
2. What energy-rich compound is produced by the actions of the cytochrome complex? (Box B)
Answer: Adenosine Triphosphate
3. What is the compound formed from water? (Box C)
Answer: Oxygen
4. What energy is used to energise the light reactions? (Box D)
Answer: Light energy
5. What is the product of the reaction that is occurring at NADP+ reductase? (Box E)
Answer: Nicotinamide adenine dinucleotide phosphate (NADPH)
6. Provide names for structures i and ii? (0.5 mark for each correct answer)
Answer: Photosystem II and Photosystem I respectively
7. The electron-accepting dye, DCPIP, substitutes for which compound in your prac 4, part B
experiment?
Answer: cytochrome c (cyt c)

Results
Results 1. Using the data your group collected in prac 4, produce a graph of absorbance against time
using Excel. Label the x and y axes with appropriate units, and have a line of best fit between your
data points. Provide a figure legend which concisely describes the graph, and the experiment that
underlies the measurements. The first sentence should be a descriptive title of the figure. A figure
legend does not reproduce the entire experimental procedures in detail, but rather puts the shown
result into an experimental context. (15 marks for graph, 7 marks for legend)
1 2 3 4 5 6 7 8
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
Absorbance vs Time graph
C (no DCPIP) E (chloroplasts) DC (dark control)
Tme (minutes)
Absorbance
This graph is a representation of the absorbance against time (minutes) with a control setup

Results 2. In 100 words or less, describe the trend observed in your results. Do not provide a
conclusion. (5 marks)
Conclusion. In one paragraph (150 words or less) provide a conclusion linking your observed trend
with the functioning of the light reactions in plants. How does the amount of light received affect the
light reactions of photosynthesis? (12 marks)
The graph shows particular trend in the data interpretation. The Dark control showed a
uniform absorbance irrespective of the time. Chloroplasts showed decreasing trend in
absorbance, the mote the time the less the exposure. While the control showed very minute
variance in the absorbance. The bars produced by the control is similar all throughout the
data.
The test tube that contained the chlorophyll showed decreased absorbance as the time
progressed because the DPIP gets oxidised as the time progresses and the solution becomes
clearer which reduces the photosynthetic activity and reduced absorbance. At the beginning
of the experiment the concentration of DPIP is high and thus it showed elevated
photosynthetic activity. In the photosynthesis, the rate of the reaction occurring inside the
chloroplast is dependent on the pigment and this pigment is responsible for the elevated
level of photosynthesis. The type of pigment also plays a role in the rate of photosynthesis
and the wavelength of the light absorbed. Thus, in the control setup the levels of
absorbance are similar throughout the experiment due to the lack of any photosynthetic
pigment.

In 50 words or less, describe what would happen, and why, to the change in absorbance of an
experimental system (assume that it is the same set up as in the prac), if a compound was added to
the assay which blocked the flow of electrons between photosystem II and photosystem I. Two
sentences would be enough to answer this question. (4 marks)
In photosynthesis, electrons in the pigment absorb energy and energy level of the electrons gets
increased and this electron helps in the transport of the high energy molecules (ATP) from the
photosystem II to photosystem I. If a compound is placed that will the block the movement of
electrons, then photosynthetic reaction will stop.