Starter

• Sequence light dependent reaction cards

reduced

The Light-Independent Reactions

AQA book p.38-40

Specification Reference: 3.4.3

Syllabus

• The light-independent reaction in such detail as to show that

• carbon dioxide is accepted by ribulose biphosphate (RuBP) to form two molecules of glycerate 3-phosphate (GP)

• ATP and reduced NADP are required for the reduction of GP to triose phosphate (TP)

• RuBP is regenerated in the Calvin cycle• Triose phosphate is converted to useful

organic substances

Objectives

• How is the carbon dioxide absorbed by plants incorporated into organic molecules?

• What are the roles of ATP and reduced NADP in the light-independent reaction?

• What is the Calvin Cycle?

Light independent reactions - introduction

• Needs ATP and reduced NADP to work so even though these reactions are independent of light in practice they don’t work for long without light

• Worked out by Melvin Calvin so called the Calvin cycle

Location of the reaction

The light-independent reaction can also be called the “dark reactions”, or the Calvin Cycle.

The light-independent reaction takes place in the stroma of the chloroplasts.

The reaction consists of a cycle of enzyme-controlled processes making complex molecules such as carbohydrates.

stroma

The light-independent reaction

Diagram

• Unfortunately your book has chosen to record the events of the cycle in an anticlockwise direction. You may well see the reactions in an exam clockwise!

• Therefore we have given you a clockwise version to work from

• Eventually you need to have learned all this off by heart anyway, so you should be able to apply your knowledge in both directions!

Annotations for diagram1. Put a title ‘The Calvin cycle’2. Read the text and then

pencil in the numbers on your diagram in the correct place

3. Add on that the carbohydrates are organic molecules

4. Add the Number of C atoms at each stage in red

5. Add the Number of phosphate groups at each stage in blue

6. Put a dotted line around each thing from light dependent reactions

7. Copy the numbered notes 1-7 under the diagram

Extra points to add• 2 RuBP acts as a CO2

acceptor• 2 Most important

enzyme = RuBP carboxylase (RUBISCO)

• Each stage controlled by enzymes

• To make 1 new molecule of glucose needs 6 turns of the cycle

Products of the Calvin cycleProducts of the light-independent reaction that pass back into the light-dependent reaction:

Products of the light-independent reaction that are used in other processes:

NADP

ADP

triose phosphate – used to build complex carbohydrates, amino acids and lipids.

inorganic phosphate

Making complex molecules

Pairs of TP molecules combine to form hexose sugars, such as glucose, some of which may isomerize to form fructose.

Triose phosphate is a three-carbon sugar that can be used to make a variety of complex biological molecules.

TP can be converted to glycerol and this may be combined with fatty acids to make lipids.

These monosaccharides can combine to form disaccharides such as sucrose, and polysaccharides such as cellulose and starch.

How much can you remember?

Summary of photosynthesis

light- dependent reactions

light- independent

reactions

light

carbohydrates, other complex molecules

Photosynthesis: true or false?

Objectives

• How is the carbon dioxide absorbed by plants incorporated into organic molecules?

• What are the roles of ATP and reduced NADP in the light-independent reaction?

• What is the Calvin Cycle?

Plenary

• Photosynthesis triominoes