Worksheet on Photosynthesis and Respiration – The Answers are in Italics

A. Photosynthesis

1. Ecosystems contain plants, animals, fungi and bacteria. In which of these groups does photosynthesis occur? Plants and some bacteria

2. The main product of photosynthesis is sugar . A by-product is oxygen.

3. In plants, photosynthesis occurs in organelles called chloroplasts.

4. The two main regions of the chloroplast are the stroma and the thylakoid.

5. During photosynthesis, the light-dependent reaction occurs in the thylakoid.

6. During photosynthesis, the light-independent reaction occurs in the stroma.

7. During the light-dependent reactions, solar energy is absorbed by chlorophyll molecules.

8. During the light-dependent reactions, water molecules are split, producing protons, electrons, and oxygen.

9. The transfer of electrons from carrier molecule to carrier molecule in the thylakoid membrane is called electron transport.

10. During the light-dependent reactions, protons accumulate in the thylakoid compartment.

11. During the light-dependent reactions, energy released by the movement of protons through ATPase proteins embedded in the thylakoid membrane is used to make ATP.

12. During the light-dependent reactions, energized electrons and hydrogen ions (protons) ultimately end up on molecules of water.

13. The two main products of the light-dependent reactions are ATP and NADPH. A by-product is oxygen.

14. For the first step of the light-independent reaction (Calvin cycle), the enzyme RUBISCO (ribulose bisphosphate carboxylase) attaches a molecule of carbon dioxide to a molecule of a sugar which contains 5 carbon atoms.

15. During the Calvin cycle, energy from the molecule ATP and electrons and hydrogen ions from the molecule NADPH are used to convert a 3-carbon sugar precursor to a 3-carbon sugar.

16. Some of the 3-carbon sugar produced during the Calvin cycle is exported by the chloroplast and some is retained and used to male more ribulose bisphosphate (the acceptor molecule).

B. Cellular Respiration

17. Ecosystems contain plants, animals, fungi and bacteria. In which of these groups does cellular respiration occur? All of them.

18. The purpose of respiration is to transfer chemical bond energy from molecules of sugar to molecules of ATP.

19. The three main stages of respiration are glycolysis, TCA (Krebs) cycle, and electron transport.

20. Glycolysis takes place in the cytoplasm and the TCA (Krebs) cycle and electron transport take place in the mitochondrial matrix.

21. During glycolysis 6-carbon compounds (glucose) are broken down to 3- carbon compounds. As chemical bonds are broken, their energy is transferred to ATP.

22. A mitochondrion contains 2 membranes.

23. The two main regions of a mitochondrion are the intermembrane compartment and the inner compartment, or matrix.

24. The TCA (Krebs) cycle takes place in the inner compartment, also called the matrix.

25. For the first step of the TCA (Krebs) cycle an enzyme attaches a molecule of a 2-carbon compound to a molecule of a 4-carbon compound to produce a 6-carbon compound.

26. As carbon compounds break down during the TCA (Krebs) cycle, carbon is released as CO₂.

27. As carbon compounds break down during the TCA (Krebs) cycle, some of the energy released is transferred to ATP.

28. As carbon compounds participating in the TCA (Krebs) cycle are oxidized, their electrons are transferred to the molecules NAD+ and FAD.

29. So, to sum up, the main products of the Krebs cycle are ATP, NADH, FADH2 and CO2. Note – one of these is best considered a “by-product.”

30. The electron transport phase of mitochondrial respiration takes place in the inner membrane.

31. To begin electron transport, electrons are transferred from the molecules NADH and FADH2 to carrier molecules embedded in the inner membrane.

32. As electrons are passed from carrier molecule to carrier molecule, protons accumulate in the inner compartment.

33. These escape to the intermembrane compartment by passing though channels in ATPase enzymes embedded in the inner membrane.

34. The energy of their motion is used to make molecules of ATP from ADP and P_i (phosphate).

35. "Spent" electrons end up on atoms of oxygen. These are joined by protons to produce molecules of water.

36. The main product of respiration is ATP.

C. Photosynthesis and Respiration Compared

37. Photosynthesis occurs in cells of plants, algae and some bacteria. Respiration occurs in all cells.

38. The processes of photosynthesis and respiration take in and release the gasses CO₂ and O₂. During photosynthesis, cells take in CO₂ and release O₂. During respiration, cells take in O₂ and release CO₂ .

39. Carbon atoms in carbon dioxide end up in sugar molecules during photosynthesis.

40. Carbon atoms in sugar end up in CO₂ molecules during respiration.

41. During photosynthesis, electrons are (removed/added) (to/from) water molecules.

42. During respiration, electrons are (removed/added) (to/from) oxygen atoms.