5.17 - Energy for biological processes (+ photosynthesis)

Question 1

What is the word equation for photosynthesis?

Answer 1

carbon dioxide + water = glucose + oxygen

Question 2

What is the balanced symbol equation for photosynthesis?

Answer 2

6CO2 + 6H2O = C6H12O6 = 6O2

Question 3

What is metabolism?

Answer 3

The sum of all chemical reactions within an organism or cell

Question 4

What are anabolic reactions?

Answer 4

The synthesis of smaller molecules into larger molecules.
Endothermic as energy is absorbed
E.g. photosynthesis

Question 5

What are catabolic reactions?

Answer 5

The breakdown of larger molecules into smaller molecules
Exothermic as energy is released
E.g. respiration

Question 6

What is ATP?

Answer 6

Adenosine triphosphate
- Adenine and 3 phosphates attached to ribose
- Short term energy store
- The universal energy currency in cells.

Question 7

How are photosynthesis and respiration related?

Answer 7

Carbon dioxide and water are the reactants for photosynthesis and the products of respiration. Oxygen and glucose are the reactants for respiration and the products or photosynthesis

Question 8

Describe the structure of a chloroplast

Answer 8

• thylakoids membranes that form flattened sacs stacked into grana
  Linked by intergranal lamellae
  Inner and outer membrane
  Stroma (aqueous environment) containing ribosomes, DNA, starch and enzymes

Question 9

How is ATP synthesised through photophosphorylation?

Answer 9

1. Electrons in chlorophyll are excited by absorbing photon from the sun
2. The high energy electron moves through electron transport chain in the thylakoid membrane.
3. Energy released by electron is used to pump protons across the membrane into the thylakoid
4. Protons move back down chemiosmotic gradient through hydrophilic protein channel ATP synthase. The flow of protons provide energy to phosphorylate ADP into ATP

Question 10

What are the adaptations of chloroplasts?

Answer 10

• Stroma provides aqueous solution for chemical reactions
• Grana provide large SA:V
• DNA, ribosomes, enzymes, self-sufficient, able to manufacture more proteins
• double membrane maintains internal environment, ability to exchange substances
• different pigments e.g. chlorophyll to absorb different wavelengths of light

Question 11

Where do the light dependent and light independent reactions happen in photosynthesis?

Answer 11

light-dependent = thylakoid membrane
light-independent = stroma

Question 12

Why are leaves different shades?

Answer 12

Specific pigment molecules absorb specific wavelengths of light and reflect others. Different combinations of pigment cause leaves to appear different colours. Leaves are orange in autumn because chlorophyll is not produced when there is little sunlight, leaving the carotenoid pigments that causes the leaves to appear orange

Question 13

Outline how thin layer chromatography (TLC) can be used to separate different photosynthetic pigments

Answer 13

1. use pestle and mortar to grind leaf with an extraction solvent e.g. propanone
2. use a capillary tube to spot pigment extract onto the pencil start line 1cm above the bottom of TLC plate
3. place chromatography plate in solvent
4. allow solvent to diffuse up until it almost touches end of plate
5. pigments should separate and move different distances up the plate
6. pigments can be identified using colour or Rf value

Question 14

What is the Rf value (chromatography)

Answer 14

distance travelled by component (solute)
/ distance travelled by solvent

Question 15

What is the antennae complex in a photosystem

Answer 15

Where light energy travels through accessory pigments and then chlorophyll a to maximise the absorbance of light energy

Question 16

What are the processes in the light-dependent reaction

Answer 16

1. Photoionisation
2. electron transport chain
3. chemiosmosis
   (photophosphorylation)
   Non-cyclic:
   -photolysis of water
   -reduction of NADP

Question 17

What is the photolysis of water

Answer 17

water molecules split into protons electrons and oxygen in the presence of light
H2O = 2H+ +2e- +1/2O2

Question 18

What happens to the products of photolysis?

Answer 18

• oxygen is used for respiration or diffused out of stomata as waste gas
• electrons replaces electrons lost from chlorophyll
• protons are released into thylakoid lumen to drive ATP formation then return to combine with NADP and two electrons to make NADPH in stroma

Question 19

What happens in non-cyclic photophosphorylation

Answer 19

Photosystem II:
Sun energy excites an electron, which moves down ETC, movement of protons synthesise ATP. Electrons lost from PSII replaced by photolysis of water.
Photosystem I:
ETC, chemiosmosis
Electrons lost from PSI replaced by electrons from PSII.
Electrons from PSI ETC accepted along with H+ ion from photolysis of water by NADP, forming (reduced) NADPH

Question 20

What is the difference between photosystem I and II?

Answer 20

PSI follows PSII, but both occur at the same time.
PSII absorbs a lower wavelength of light (680nm)
PSI absorbs higher wavelength of light (700nm)

Question 21

What happens in cyclic photophosphorylation?

Answer 21

Only uses photosystem I
- Excited electrons enter ETC to produce ATP, then return directly to PSI
- No reduction of NADPH and no water required to replace electrons
- purpose is to produce ATP to meet short term surplus energy requirements of the cell

Question 22

What are the adaptations of ATP?

Answer 22

• good immediate short term energy store
• small so moves easily between cells
• water soluble as reactions take place in aqueous environments
• releases energy in small quantities
  (large enough for cellular reactions but no energy is lost as heat)
• easily regenerated as reaction is reversible and easily recharged with energy

Question 23

What are the 3 stages in the light independent stage?

Answer 23

1. Fixation
2. Reduction
3. Regeneration

Question 24

What happens during fixation? (the Calvin cycle)

Answer 24

1. 6CO2 is diffused into the stroma of the chloroplast from stomata in the leaf
2. 6CO2 is combined with 6RuBP, a 5C molecule (carbon fixation). This is catalysed by RuBisCO
3. Creates 6 unstable intermediate 6C molecules
4. These immediately break down into 12 3C GP molecules

Question 25

What happens during reduction?

Answer 25

1. The 12 3C GP molecules are rearranged using energy from ATP (ATP = ADP + P)
   2.