Photosynthesis 8.3 HL

This topic covers the tricky details of the light dependent and light independent reaction of photosynthesis. This includes photolysis and oxidative phosphorylation as well as chemiosmosis where ATP synthase enzyme generates ATP.  Photolysis begins the process by splitting water into hydrogen ions and oxygen while rubisco fixes carbon dioxide to RuBP in the Calvin cycle leading to the production of carbohydrates at the end.

Key concepts

Learn and test your biological vocabulary using these 8.3 Photosynthesis HL flashcards

Essentials

These slides summarise the essential understanding and skills in this topic. 
They contain short explanations in text and images - great revision.

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Summary

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 questions

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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Extra exam style question on photosynthesis.   Click to open.

Exam style question on the light-independent reactions of photosynthesis

The link between the light-dependent and light-independent reactions is an important concept.

You might like to do the drag and drop activity on the light-independent reaction before you attempt this question

Answer the question below on a piece of paper, then check your answer against the model answer below.

Outline the role of each of the following in the light-independent reaction of photosynthesis.

I Carboxylase enzyme. (2 marks)



II NADPH+H+. (2 marks)



III ATP. (2 marks)



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Extra exam question on limiting factors of photosynthesis.     Click to open.

Various environmental factors can limit the rate of photosynthesis. You should be able to explain these factors and be able to link them to the process of photosynthesis and an experimental or natural situation.

Answer the question below on a piece of paper, then check your answer against the model answer below.

Describe three limiting factors of photosynthesis and how these may affect the growth of a crop in a field. (6 marks)

Examiner hint: Describe needs a detailed explanation, credit is not given for naming the limiting factor but for giving the reason.





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Extra exam question on the adaptations of the chloroplast to its function. Click to open.

Structure/function relationships are an important concept in biological systems. The chloroplast is a good example of this, both as an organelle and in the importance of membranes in metabolic processes.

Describe how the structure of the chloroplast is related to its function (6 marks).





Hint: Link structure and function in each sentence.
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Test yourself

Multiple choice questions

This is a self marking quiz containing questions covering the topic outlined above.
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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.

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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.


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