Photosynthesis

Question 1

What is a coenzyme?

Answer 1

• Coenzymes are organic non-protein compounds that binds with enzymes to catalyse reactions

Question 2

What is an electron transport chain? What do they form?

Answer 2

• The electron transport chain is a cluster of proteins/ electron carrier molecules that transfer electrons through a (thylakoid) membrane
• forms a gradient of protons involved in the synthesis of ATP (adenosine triphosphate)

Question 3

What is an enzyme?

Answer 3

Enzymes are biological catalysts (speed up chemical reactions by lowering activation energy)

Question 4

What is a granum (grana plural)? What takes place in it?

Answer 4

• A granum is a stack of thylakoids in the chloroplast
• wherein the production of starch/ aka photosynthesis takes place

Question 5

What is the grana?

Answer 5

• the grana (plural) are the stacks of thylakoids embedded in the stroma of a chloroplast

Question 6

What is the definition of palisade? What is it the site of?

Answer 6

• palisade is a layer of plant cells containing chloroplasts right below the cuticle and upper epidermis in plants
• palisade cells are the primary site of photosynthesis

Question 7

What are photosystems?

Answer 7

Photosystems are complex structures within the chloroplasts of plants that capture light energy and use it to generate ATP and NADPH

Question 8

What is the stroma? Where is it?

Answer 8

• is a protein-rich, alkaline, aqueous fluid present within the inner membrane of the chloroplast
• it is the fluid that the thylakoids are sitting in

Question 9

What is the thylakoid membrane?
What is it the site of? What are found on the thylakoid membrane?

Answer 9

• the thylakoid membrane is a sheet-like membrane-bound structure found in the chloroplasts and cyanobacteria.
• It is the site of the light-dependent photosynthesis
• photosystems are found on the thylakoid membrane

Question 10

Where does the light dependent reaction take place? Where does the light-independent reaction take place?

Answer 10

• LDR takes place in the thylakoid membrane
• the LIR takes place in the stroma

Question 11

What does the Light dependent reaction produce?

Answer 11

LDR produces:
- ATP
- reduced NADP
- O2 (oxygen, a waste product)

Question 12

What is photophosphorylation?

Answer 12

• the process in which light energy/ energy lost from electrons are used to produce ATP

Question 13

What is the splitting of water known as? What does it require?

Answer 13

• the splitting of water into hydrogen and oxygen requires energy. Photosynthesis uses energy from sunlight to split water. This is known as photolysis of water

Question 14

What is the first part of the LDR?

Answer 14

• energy from light raises 2 electrons in each chlorophyll by 2 energy levels. Electrons are now excited (chlorophyll molecules are now excited)

Question 15

What is the second part of the LDR? What happens to the electrons leaving PSII? What do they loose? What is this used to synthesise?

Answer 15

• electrons leave the excited chlorophyll molecules and pass along a series of electron carrier molecules (forming an electron transport chain)
• electrons from PSII chlorophyll pass from one carrier to the next via a series of oxidation and reduction reactions, loosing energy in the process
• the energy is used to synthesis ATP, (process of photophosphorylation)

Question 16

What is the third part of the LDR? What do the electrons from PSII replace? What happens within the thylakoid space? What is produced?

Answer 16

• the electrons from PSII replace those lost from PSI chlorophyll
• within the thylakoid space, an enzyme catalyses the splitting of water by photolysis to produce oxygen, hydrogen ions and electrons. The electrons replace those lost by PSII

Question 17

What is the fourth part of the LDR? What do the electrons from PSI combine with?

Answer 17

• electrons from PSI chlorophyll that have passed on the electron transport chain combine with the co-enzyme NADP and hydrogen ions from the water to produce reduced NADP (or NADPH2)

Question 18

What is photolysis?

Answer 18

• photolysis is a chemical reaction in which light energy is used to split water molecules into hydrogen ions (protons) (H+), electrons and oxygen

Question 19

What is the Calvin cycle?

Answer 19

• the Calvin cycle is a process that converts carbon dioxide into glucose using the energy from sunlight
  (plants cant eat food for energy so they make their own glucose - the glucose provides energy)

Question 20

Where does the light-independent reaction take place?

Answer 20

• The LIR takes place in the stroma (the fluid that the thylakoids are sitting in)

Question 21

What is RuBisCO?

Answer 21

• RuBisCO is an enzyme that catalyses the reaction that fixes carbon dioxide in the Calvin cycle

Question 22

What are the different stages of the Calvin cycle? What order do they come in?

Answer 22

• (Carbon) fixation
• reduction
• regeneration

Question 23

What products of the LDR are needed to start the LIR?

Answer 23

• the products needed from the LDR for the LIR are:
• ATP
• reduced NADP

Question 24

What is the enzyme called that catalyses the reaction of carbon dioxide with RuBP?

Answer 24

• RuBisCO

Question 25

What is the order of the organic compounds in the Calvin cycle? How many carbons does each compound have? Where do the three stages fit in?

Answer 25

1. carbon dioxide (1C) - fixation 2. x2 GP (3C) - reduction 3. x2 GALP (3C) - regeneration 4. RuBP (5C)

Question 26

Summarise the parts of the Calvin cycle? How many are there of each compound? How many carbons are there throughout the cycle? Where are the different stages? When is ATP and reduced NADP used and is it an endothermic or exothermic reaction?

Answer 26

1. 6 RuBP (5C) (30C) 2. 6 CO2 (1C) (36C) - fixation (RuBisCO combines CO2 and RuBP, it fixes CO2) 3. 12 GP (3C) (36C) - reduction (reduced NADP broken down into NADP) (ATP broken down into ADP + Pi) (endothermic reaction) 4. 10 GALP (3C), 12 GALP (3C) (2 GALPS gone to make glucose (6Cs), so lost 6Cs) Regeneration (ATP broken down into ADP + Pi) (the carbons get remixed by ATP to make RuBP) 5. RuBP (36C)

Question 27

What does the reaction between carbon dioxide and RuBP produce? What does the answer to this get turned into? By what process does it get turned into this?

Answer 27

- the reaction produces x2 GP (Glycerate phosphate) - GP gets turned into GALP by the process of reduction

Question 28

Who was the scientist who worked out the sequence of the LIR?

Answer 28

- calvin

Question 29

How would a decrease in carbon dioxide concentration be a limiting factor in the production of ATP?

Answer 29

- if carbon concentration is low, conversion of RuBP to GP in the Calvin cycle is limited. - less ATP will be produced - rate of photosynthesis decreases

Question 30

How would low light intensity impact photosynthesis?

Answer 30

- less light to excite electrons - less energy for electrons to go down electron transport chain - less ATP

Question 31

Why does NADP become reduced?

Answer 31

- NADP becomes reduced because it accepts electrons - reduction is a gain in electrons

Question 32

Give the name of the process that provides electrons to replace those lost by chlorophyll

Answer 32

- photolysis