DP Biology: Light Independent Reactions

InThinking Revision Sites

INTHINKING REVISION SITES

Own your learning

Why not also try our independent learning self-study & revision websites for students?

We currenly offer the following DP Sites: Biology, Chemistry, English A Lang & Lit, Maths A&A, Maths A&I, Physics, Spanish B

"The site is great for revising the basic understandings of each topic quickly. Especially since you are able to test yourself at the end of each page and easily see where yo need to improve."

"It is life saving... I am passing IB because of this site!"

Basic (limited access) subscriptions are FREE. Check them out at:

www.StudyIB.net

Light Independent Reactions

  • /
  • Additional HL/
  • HL Metabolism Activities for Learning/
  • Light Independent Reactions

The reactions of the Stroma of the Chloroplast are known as the light independent reactions and also the Calvin cycle. This activity introduces some of the molecules to students and some steps of the reactions then asks the students to link their ideas using a set of SOLO hexagons to answer an IB style question. A final activity includes an excellent animation of the whole process of photosynthesis and a summative task to assemble all the cards from both light dependent and light independent reactions of photosynthesis. This could be used as assessment.

Lesson Description.

Guiding Questions

  • How does the chloroplast trap CO2 from the air?
  • Which 'carbohydrates' do the light independent reactions make?
  • Which products from the light dependent reactions are used in the light independent reactions?

Activity 1 - Introduction to the reactions

Study the following slides to learn the names of the important molecules and some of their reactions

  

Activity 2: Construct an explanation using hexagons

Match the images to the statements in the  Light independent reactions SOLO hexagons below to create a multimedia answer to the IB style question.

1.       Outline the three main stages of the Calvin cycle:

  • fixation of carbon  dioxide by combination with ribulose bisphosphate (RuBP),
  • the reduction of Glyceraldehyde-3-phosphate
  • the regeneration of ribulose  bisphosphate (RuBP) using ATP

(Total 8 marks)

Activity 3 - Summary of the whole of photosynthesis

This is a summary activity to tell the whole story about photosynthesis

Watch the following short video which summarises the whole process of photosynthesis, both light dependent and light independent reactions in just 5 minutes.  (Don't worry about the names of the individual electron carriers)

Combine all the hexagons from both the light independent and the light independent reactions of photosynthesis to link these ideas about photosynthesis together. Try to tell the whole story. 

Click the eye icon to see a summary of all the points.

Photosynthesis key points

Light dependent reactions

•The light dependent reactions take place in the thylakoid membrane.
•Thylakoid membranes of the chloroplast provide a large surface area.
•Chlorophyll is located in the membrane in groups of molecules called photosystems.
•Photolysis of water occurs in thylakoid space and generates electrons for Photosystem II.
•Absorption of light in the photosystems gives “excited electrons”.
•Excited electrons from photosystem II are passed to electron carriers.
•Electron carriers are embedded in the thylakoid membrane.
•Excited electrons from photosystem I are  used to reduce NADP+.
•NADP+ accepts two high energy electrons and an H+ ion (proton) to form NADPH.
•Electron flow through electron carriers causes H+ to be pumped into the thylakoid space
•A proton concentration gradient is formed in the space between thylakoids.
•ATP synthase is embedded in the thylakoid membrane
•H+ ions flow back through ATP synthase channels to produces ATP by chemiosmosis.
•ATP and NADPH (reduced NADP) are produced in the light dependent reactions

Light independent reactions

1.ATP and NADPH produced in the light dependent reactions are used in the light independent reactions.
2.The light independent reactions occur in stroma of chloroplast.
3.The enzyme ribulose bisphosphate carboxylase (Rubisco) catalyses attachment of CO2 to ribulose bisphosphate (RuBP).
4.This briefly forms an unstable six-carbon intermediate compound.
5.The six carbon compound splits to form two glycerate-3-phosphate molecules.
6.Each (of the two) glycerate-3-phosphate then receives one phosphate from ATP;
7.Each (of two) phosphorylated glycerate-3-phosphate is reduced by NADPH + H; 
8.The result is two molecules of triose phosphate (TP).
9.for every six molecules of triose phosphate one goes to form glucose.
10.The five remaining TP molecules are reorganised to reform RuBP.
11.The reorganisation of TP into RuBP (for the regeneration of RuBP) requires ATP.

Once you have finished take a photo of your work and tweet it to a friend or

Teachers notes

This lesson follows on from the light dependent reactions lessons and so the style is similar.

This enables students to combine their hexagons to try to summarise the whole process at the end.  This final arrangement of hexagons could make a good assessment to conclude this section on photosynthesis.  Taking photos of the diagrams would be a nice way to simplify the marking.

There is a nice video explanation of photosynethsis from HNMI. which would complement the SOLO activity well.

Revision activity

I have also made a Photosynthesis 'theatre' molecule cards which are a great way to involve the whole class, and break down some of the difficult ideas into manageable parts. In lessons I cut out the words and give one to each student as they enter the room.  Then I structure the activity into these stages:

  1. Group yourselves into two groups, those molecules used in the Light-dependent and Light-independent reactions.
  2. Discuss with each other what is the role of the molecule on your card, until you can explain it in one sentence.
  3. Line up in the class starting from water, in the order of photosynthesis.
  4. Explain the whole process, one sentence from each student, (each student represents one molecule)
  5. Can we improve anything? Repeat the explanation a couple of times.
  6. Students write down five sentences from this explanation. (or a class could write the whole process on a colaborative page / Google doc.)

    It would be good to ask students to read about the lollipop experiment used by Melvin Calvin to identify the sequence of chemicals in the Calvin-Benson cycle.   Read his Nobel speech from 1962

    To illustrate the use of practical work to establish reactions there is Hill´s method. This experiment demonstrates electron transfer in chloroplasts by observing DCPIP reduction in the lab. There are some good practical instructions here and from Nuffield here