OCR a Level Biology a Level Learner Resource 2

OCR a Level Biology a Level Learner Resource 2

Learner Resource 2–Biochemistry of respiration –modelling respiration

You will need:

  • bubblewrap
  • plastic sheet or bag
  • plasticine/modelling clay
  • Molymod® molecular building kit
  • match boxes
  • blown up balloons
  • string
  • aluminium foil
  • straws
  • retort stands with clamps
  • paper
  • a hole punch

Stage One – Building a Mitochondrion Tent…

  1. Take a piece of bubblewrap to represent the inner mitochondrial membrane.
  2. Make holes in five adjacent bubbles and plug each one with a coloured ball of plasticine. These represent the electron carrier proteins of the ETC (electron transport chain).
  3. Use a straw and some plasticine of a different colour to make a stalked particle – the ATP synthetase complex.
  4. Make a new hole in the bubblewrap and plug it with the stalked particle.
  5. Add two more ETC lines of electron carriers and two more stalked particles to your bubblewrap.
  6. Stretch the bubblewrap between clamps with the fat ends of the stalked particles facing downwards towards the bench.
  7. Stretch a piece of polythene between clamps held at a taller height, so that the polythene sheet sits a couple of centimetres above the bubblewrap. This sheet is the outer mitochondrial membrane.
  8. Under the two layers of your tent roof is a space representing the matrix of the mitochondrion. Place a piece of white paper on the bench to make the events in the matrix clearer. Above the tent roof is the cytoplasm of the cell.

Stage Two– Making the players

  1. Use the atoms (black = carbon, red = oxygen, white = hydrogen) to make a glucose molecule.
  2. Use small boxes such as matchbox trays to represent NAD hydrogen carriers.
  3. Use sticky tape, coloured tape and chunks of cotton wool to make three three-dimensional different-coloured blobs to represent enzymes.
  4. Use aluminium foil to make a bigger scrunched up ball (ADP) and a smaller scrunched up ball (P) and then scrunch these together loosely, so you can detach the little ball. Make two of these ATPs, and put them on the roof (i.e. in the cytoplasm). Make more big and small foil balls and scatter them in the matrix (under the tent).
  5. Scatter paper circles from the hole punch to represent protons on the white sheet under the tent, i.e. in the matrix.

Stage 3 – The Game – Follow this storyline…

  1. A phosphorylase enzyme approaches glucose with a couple of silver ATPs, and phosphorylates the glucose to hexose biphosphate. (Scrunch the little detachable P bits over the glucose, one at each end).
  2. Enzymes engulf the model glucose molecule, and strip it to two triose phosphates, then to two pyruvic acid molecules. Follow the instructions in your notes/books and remember to strip off the white balls representing hydrogens as required and to put these in pairs into the NAD boxes.
  3. Pass the pyruvic acid molecules and the NAD carts with their hydrogens into the matrix of the mitochondrion. They have to get through the polythene and the bubblewrap, which is impossible, but hey, we’re only pretending, so they can go round the edge.
  4. Attack your pyruvic acid with enzymes stage by stage to model the link reaction and Krebs cycle. Pass the carbon dioxide molecules produced back out of the mitochondrion ‘tent’ and tie them to balloons so they float away…
  5. If you run out of NAD boxes for spare pairs of hydrogens you will need to offload the hydrogen at the inner membrane. Let the hydrogens hop from plasticine ball to plasticine ball till they get to the end. Here join them to a red oxygen atom and pass the resulting water molecule through the two membranes and out to the cytoplasm. Your empty cart can go back to continue the Krebs cycle dehydrogenations.
  6. Whenever you make a water molecule, pass protons (paper circles cut with hole punch) through from the matrix to the intermembrane space and see if you can push some through the straws in the stalked particles…. If you get some H+ through, congratulations, you can join a big and a little silver foil ball together again and you’ve made some ATP.
  7. Count up what you end up with. Hopefully some H2O and CO2 waste products, a fleet of clean empty NAD boxes, and lots of ATP…

Version 11© OCR 2016

Respiration

Evaluation

1. How and where did we simplify the chemiosmosis story?

2. Were the relative sizes of the materials we used to represent atoms, molecules and protons roughly correct?

3. What can you suggest to improve the model?

4. Which parts of the process are made clearer through this modelling?

5. Which details of the process require study and revision to get right?

Version 11© OCR 2016

Respiration

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