- Summary list for 8.3 Photosynthesis
- Mindmaps
- Exam style question about photolysis
- Model answer
- Exam style question on the light-independent reactions of photosynthesis
- Model answer
- Model answer
- Multiple choice questions
- 8.3 Photosynthesis 1/1
Learn and test your biological vocabulary using these 8.3 Photosynthesis HL flashcards
Summary list for 8.3 Photosynthesis
Light-dependent reactions
- Located on the thylakoid membranes and in the space inside them.
- Reduced NADP (NADPH) and ATP are produced in the light-dependent reactions.
- Light absorbed by photosystems generates excited electrons.
- Photolysis of water generates electrons for use in the light-dependent reactions.
- Excited electrons are transferred between carriers in the thylakoid membranes.
- Excited electrons from Photosystem II are used to generate a proton gradient.
- ATP synthase in the thylakoids generates ATP using the proton gradient.
- Excited electrons from Photosystem I are used to reduce NADP to NADPH.
Light-independent reactions
- Take place in the stroma.
- RuBP carboxylase enzyme catalyses the carboxylation of ribulose bisphosphate (RuBP).
- Glycerate 3-phosphate is reduced to triose phosphate using "reduced NADP" (NADPH) and ATP.
- Triose phosphate is used to regenerate RuBP and produce carbohydrates.
- Ribulose bisphosphate (RuBP) is regenerated using ATP.
Chloroplast structure
- The structure of the chloroplast is adapted to its function in photosynthesis.
Skills
- to recognise details of Calvin’s experiment to elucidate the carboxylation of RuBP.
- to be able to annotate a diagram showing the adaptations of a chloroplast to its function.
Mindmaps
This diagram summaries the main sections of topic 8.3
Test if you can draw something like these concept maps from memory.
Exam style question about photolysis
Explaining the control of gene expression, methylation and promoter regions is an important skill from this topic.
Answer the question below on a piece of paper, then check your answer against the model answer below.
Outline the process of photolysis in the light dependent reactions of photosynthesis. [3]
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Multiple choice questions
This is a self marking quiz containing questions covering the topic outlined above.
Try the questions to check your understanding.
START QUIZ!
Light-dependent reactions happen in the thylakoid membranes and in the space inside them.
In the light dependant reactions what happens to water molecules?
Photolysis splits water into hydrogen ions, electrons and oxygen.
In the light dependant reactions what happens to NADP molecules?
Reduced NADP (NADPH2) is one of the products of the light dependent reactions.
Hydrogen reduces the NADP.
NADP is a hydrogen carrier.
In the light dependant reactions reduced NAD, and oxygen are produced.
What other important molecule is also synthesised?
ATP is also produced in the light-dependent reactions by ATP synthase and chemiosmosis.
The diagram below shows photosystem II
Light energy is harvested by the large collection of chlorophyll molecules in the photosystem and to excite an electron. How is this electron replaced?
Light absorbed by photosystem II generates excited electrons.
Photolysis of water produces H+ ions, oxygen atoms and electrons which replace those excited in the light-dependent reactions.
What is the role of electron carriers in the thylakoid membrane
Excited electrons produced by photosystem II are transferred to photosystem I in the thylakoid membranes. They ultimately continue to be passed between membrane proteins until they participate in the reduction of NADP.
Excited electrons carry energy which can be used to generate a proton gradient or to reduce NADP as shown in this diagram.
Where do these two reaction happen?
Excited electrons from Photosystem II (on the left of the diagram) are used to generate a proton gradient in B of the diagram as they pass through the electron carriers.
Excited electrons from Photosystem I (on the right of the diagram) are used to reduce NADP in D..
Which enzyme structure generates ATP using chemiosmosis?
ATP synthase in the thylakoids generates ATP using the proton gradient.
The diagram shows the structure of a chloroplast.
In which structure do the light independent reactions take place?
Light-independent reactions take place in the stroma.
The diagram below shows the Calvin cycle.
At which stage does carboxylation occur?
RuBP carboxylase enzyme (RuBisCO) catalyses the carboxylation of ribulose bisphosphate (RuBP).
How is the structure of the chloroplast membranes an adaptation to help it's function?
The structure of the chloroplast is adapted to its function in photosynthesis
There are many membranes because this enables the chloroplast to have many chlorophyll molecules, important in the light dependant reactions of photosynthesis.
A famous 'lollipop' experiment was performed by Calvin and Benson in the 1950s.
Radioactive carbon dioxide was introduced into the "lollipop" and photosynthesis allowed to continue for just a few seconds, then repeated for longer and longer periods.
The products of photosynthesis were separated by two way chromatography.
What did Calvin and Benson find out using this technique?
- Algae cells were exposed to 14CO2 and light in "lollipop"-shaped flask.
- 14C is radioactive.
- Any molecules containing the 14CO2 carbon atoms will become radioactive and can be detected.
Results of Calvin's work
- When light exposure was only 7 seconds, 12 compounds were radioactively labeled.
- When light exposure was reduced to 2 seconds, most of the radioactive carbon was in just one compound, 3-PGA
- It was concluded PGA must be the first molecule CO2 is fixed to.
The diagram below shows the Calvin cycle.
Which molecule is oxidised during the reduction of a 3-C molecule?
Glycerate 3-phosphate is reduced to triose phosphate using "reduced NADP" and ATP.
A triose phosphase molecule (GP) is used to produce carbohydrates in the Calvin cycle.
What is the other role of GP in the Calvin cycle?
Triose phosphate is used to regenerate RuBP and produce carbohydrates.
Ribulose bisphosphate (RuBP) is regenerated using ATP.
Drag and drop activities
Test your ability to construct biological explanations using the drag and drop questions below.
The light independent reaction is an important concept in this topic.
Drag and drop the correct word or phrase into the gap to make a summary of the light-independent reaction of photosynthesis.
light-dependent glycerate-3-phosphate Pyruvate regenerate triose phosphate pentose NADP carbohydrates hexose ATP carboxylase Calvin Cycle Krebs NAD
The light-independent reaction uses and reduced from the reaction.
RuBP enzyme catalyses the addition of a carboxylation of the ribulose biphosphate to form an unstable which breaks down to form two molecules of .
Reduced NADP and ATP are used to reduce glycerate phosphate to .
Triose phosphate can be utilised to form or to RuBP in the using ATP.
Examiner hint. This is an outline, more detail is neccessary for complete knowledge of this concept. See the preceeding question on this concept.
Everyone needs a bit of fun while they revise. Try this Photosynthesis card matching game.
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