Module 5 Energy essential notes

Question 1

Describe the processes in the cell that require energy

Answer 1

1. Active transport (carrier proteins, endocytosis and exocytosis) Anabolic reactions (biosynthesis reactions such as DNA replication, transcription and translation)
2. Movement (cilia, flagella, muscle contraction)

Question 2

Describe the structure of ATP (and ADP)

Answer 2

1. ATP is adenosine triphosphate A pentose sugar, ribose
2. Joined by glycosidic bond to an adenine nitrogenous base on C1
3. Joined by ester bond to three phosphate groups on C5

Question 3

Explain how ATP synthesis and hydrolysis are related to its role as an energy storage molecule

Answer 3

1. ATP is synthesised by adding a phosphate group to ADP
2. Adding the third phosphate group requires an energy input
3. The energy to synthesise ATP usually comes from respiration
4. ATP is hydrolysed by removing the third phosphate group This releases energy
5. The energy released can be provided to active cellular processes

Question 4

Explain why respiration is dependent on photosynthesis

Answer 4

1. ATP production requires energy
2. Energy for ATP production comes from respiration
3. Respiration is the breakdown of complex organic molecules to simpler inorganic molecules
4. Photosynthesis is the process of using light energy to convert simple inorganic molecules into complex organic molecules
5. Respiration requires complex organic molecules produced by photosynthesis

Question 5

Compare the molecular requirements and products of photosynthesis and respiration

Answer 5

1. Both involve carbon dioxide, water, oxygen and glucose Respiration uses glucose and oxygen, but photosynthesis uses water and carbon dioxide
2. Respiration produces carbon dioxide and water, photosynthesis produces glucose and oxygen

Question 6

Describe the main structures of the chloroplast and where applicable, where the stages of photosynthesis occur.

Answer 6

Question 7

Describe the structure and role of photosystems in photosynthesis

Answer 7

1. Photosystems are proteins which contain photosynthetic pigments such as chlorophyll at their reaction centre
2. Chlorophyll absorbs light energy
3. This is later used to convert simple inorganic molecules into complex organic molecules
4. There are two photosystems, II and I Each absorbs a slightly different wavelength of light

Question 8

Describe the role of accessory pigments in light harvesting

Answer 8

1. Chlorophyll A is the primary pigment in the reaction centre of PSII, and absorbs red/blue wavelengths of light
2. Other photosynthetic pigments form an antenna complex absorbing other wavelengths of light
3. And transferring the energy to chlorophyll A
4. Increasing the wavelengths of light that can be used for photosynthesis
5. Thus increasing efficiency of energy conversion

Question 9

Describe how thin layer chromatography can be used to separate a mixture of photosynthetic pigments

Answer 9

1. Make a paste of leaf material with (with some alcohol to disrupt cell membranes), using a mortar and pestle
2. Draw a horizontal line near the bottom of the chromatography paper or plate
3. Draw spots to indicate the initial positions of the mixtures
4. Use a capillary tube to spot the mixture onto the paper/plate
5. The bottom of the paper/plate is placed in the solvent
6. The solvent is allowed to move up the paper/plate
7. Another horizontal line is drawn at this level
8. The different colours of the pigments should indicate their position on the chromatogram
9. Rf values are calculated by dividing the distance travelled by the pigment by the distance travelled by the solvent
10. Due to unique solubility in the solvent different pigments travel specific distances and therefore have unique Rf values

Question 10

Summarise the light-dependent stage of photosynthesis

Answer 10

1. Energy of light is absorbed by PSII
2. This is used to carry out the photolysis of water and excite electrons
3. Oxygen is produced as a waste product
4. Energy in excited electrons is used to synthesis ATP (photophosphorylation)
5. Electrons are combined with protons and transferred to NADP, producing NADPH

Question 11

Describe the role of water in photosynthesis

Answer 11

1. PSII absorbs a photon of light which excites electrons in chlorophyll
2. Excited electrons are transferred to the electron carriers (electron transport chain)
3. The loss of electrons from chlorophyll causes the splitting of a water molecule into oxygen, protons and electrons
4. The electrons replace those lost by chlorophyll
5. The protons remain in the thylakoid space
6. The oxygen diffuses out of the chloroplast

Question 12

Describe non-cyclic photophosphorylation

Answer 12

1. The high-energy electrons are transferred through the electron transport chain
2. The electron carriers use the energy of electron transfer to pump protons from the stroma to the thylakoid space
3. This creates a proton gradient
4. Protons diffuse through the ATPsynthase from the thylakoid space into the stroma
5. This results in the phosphorylation of ADP to ATP (chemiosmosis)
6. The electrons are re-energised at PSI by another photon of light
7. They are transferred to NADP along with protons to form NADPH

Question 13

Describe cyclic photophosphorylation

Answer 13

1. Excited electrons from the electron carriers are transferred to PSI A photon of light is absorbed by PSI and used to re-energise the electrons
2. These electrons are transferred back to the electron carriers (instead of passing on to NADP)
3. The electron carriers use the energy of the electrons to pump protons into the thylakoid space
4. This creates a proton gradient which is used to synthesis ATP (chemiosmosis)

Question 14

Summarise the light-independent stage (LIS) of photosynthesis

Answer 14

1. The light-independent stage of photosynthesis is a metabolic pathway called the Calvin-Benson cycle
2. It has three main steps, all carried out by enzymes in the stroma
3. Its three stages are called fixation, reduction and regeneration
4. Carbon dioxide is incorporated
5. ATP and NADPH are converted to ADP and NADP
6. Glucose is produced

Question 15

Describe the fixation step of the LIS

Answer 15

1. Carbon dioxide diffuses into the chloroplast
2. The enzyme RuBisCO combines carbon dioxide with ribulose bisphosphate to produce two molecules of glycerate 3-phosphate (GP)
3. This changes carbon from being in an inorganic molecule to an organic molecule
4. There it is called fixation

Question 16

Describe the reduction step of the LIS

Answer 16

1. Glycerate 3-phosphate (GP) is reduced to triose phosphate The hydrogen from NADPH is used to reduce the GP
2. The energy from ATP hydrolysis is also required
3. The NADPH and ATP used in the reaction were produced in the
4. LDS

Question 17

Describe the fate of triose phosphate

Answer 17

1. Triose phosphate is a three-carbon sugar
2. These molecules can be combined to form six-carbon sugars such as glucose
3. Triose phosphate can also be used to synthesise other types of molecule such as lipids, amino acids (protein) and nucleic acids
4. Triose phosphate must also be used to regenerate ribulose bisphosphate, so that the Calvin-Benson cycle can continue
5. This is done in the regeneration step
6. The energy of ATP hydrolysis is also required for this step

Question 18

Describe how the rate of photosynthesis may be measured

Answer 18

1. Submerge an aquatic plant such as pondweed in water
2. Add sodium bicarbonate as a source of carbon dioxide Use a funnel and measuring cylinder to record the volume of oxygen given off by the plant
3. Use a timer to allow the plant to photosynthesise for a specific length of time
4. Use the volume of oxygen recorded and the length of time to determine/estimate a rate of photosynthesis
5. Repeat the experiment while varying a particular factor, to investigate its effect on the rate of photosynthesis
6. Use a heat shield where appropriate

Question 19

Identify factors which can affect the rate of photosynthesis

Answer 19

1. Light intensity
2. Light wavelength
3. Temperature
4. Water stress (stomatal closure)
5. Carbon dioxide concentration

Question 20

Discuss the concept of limiting factors in relation to the rate of photosynthesis

Answer 20

1. Photosynthesis rate can be affected by a number of factors The principle of limiting factors states that the factor that is least optimal, or in shorted supply will limit the rate So the rate of photosynthesis is dependent on the factor which is least optimal or in shortest supply
2. As the level of that limiting factor is changed, a point may be reached where it is no longer the limiting
3. another factor is then the limiting factor

Question 21

Explain how light intensity can affect the rate photosynthesis, and the levels of GP, RuBP a nd TP

Answer 21

1. If light intensity is limiting, it can limit the energy available for excitation of electrons in the LDS
2. This limits photophosphorylation (ATP production)
3. This also limits the NADPH produced
4. As a result, it will limit the reduction and regeneration steps in the Calvin-Benson cycle
5. This will limit the production of TP and RuBP, and cause an accumulation of GP
6. If ADP and NADP are not regenerated it limit the LDS as well

Question 22

Explain how carbon dioxide concentration c an affect the rate of photosynthesis, and the levels of GP, RuBP a nd TP

Answer 22

1. If carbon dioxide concentration is limiting it limits the fixation step in the Calvin-Benson cycle As RuBisCO will be limited by substrate concentration
2. This will limit GP and TP levels, while RuBP accumulates
3. If ADP and NADP are not regenerated it limit the LDS as well

Question 23

Explain how temperature can affect the rate o f photosynthesis, and the levels of GP, RuBP a nd TP

Answer 23

1. If the temperature is limiting
2. There will not be enough kinetic energy for enzymes and substrates of the Cavin-Benson cycle to collide and form ESC This will limit the rate of the metabolic pathway as a whole
3. And limit the rate of production of Glucose and other biomolecules from TP
4. This will also lower the fixation (consumption) of carbon dioxide into the pathway
5. This will reduce the regeneration of ADP and NADP, and will reduce the rate of the LDS