Photosynthesis

Question 1

What does photosynthesis do?

Answer 1

• Uses energy from light to convert carbon dioxide into sugar.

Question 2

What is the major source of chemical energy for most organisms?

Answer 2

• Carbohydrate in the form of glucose.

Question 3

What is Light?

Answer 3

• A form of electromagnetic radiation.
• Travels as a wave
• Behaves as particles (photons).

Question 4

What are Pigments?

Answer 4

• Molecules that absorb wavelengths in the visible

spectrum.

Question 5

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Answer 5

• The electromagnetic spectrum shows the wide range of wavelengths / energy levels that photons can have.
• Spectrum ranges from short
  wavelength/high energy gamma
  rays to long wavelength/low
  energy radio waves

Question 6

What happens when a photon meets a molecule? (B.P.A)

Answer 6

• 1: The photon can BOUNCE of the molecule.
• 2: The photon may PASS through the molecule.
• 3: The photon may be ABSORBED by the molecule.

: 1+2 no changes made to molecule
: 3: Photon disappears but not its energy, because energy is
neither created nor destroyed.

Question 7

What do photons do a molecule?

Answer 7

• Add energy to the molecule.

Question 8

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Answer 8

• The molecule moves from

ground state to an excited state and possess more energy.

Question 9

What is Chlorophyll? (green pigment)

Answer 9

• Absorbs red + blue light but reflects Green light, making plants appear green.

Question 10

What are the 2 Chlorophylls that absorb light energy?

Answer 10

• Chlorophyll a

- Chlorophyll b

Question 11

What are Carotenoids also called?

Answer 11

• Accessory Pigments

Question 12

What are Carotenoids?

Answer 12

• Absorb wavelengths between red + blue and transfer some of that energy to the chlorophylls

Question 13

Where does Photosynthesis occur?

Answer 13

• In Chloroplasts

Question 14

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Answer 14

• Chlorophyll was once free-living bacteria that got swallowed up by ENDOSYMBIOSIS.
• In other parts of the plant, chloroplasts get used for storage of food or other pigments.

Question 15

What are Chromoplasts?

Answer 15

• Have many pigments e.g. yellow, orange +red (like in flowers &
  fruits) .

Question 16

Look at structure of Chloroplast.

Answer 16

• Double membrane (inner + outer)
• Stroma (a semifluid interior)m’nd
• Grana (made of thylakoids)
• Thylakoids ( membranous disks interconnected w/ each other + inner membrane).

Question 17

What photosynthetic pigments do thylakoids contain?

Answer 17

• Chlorophyll a + b

Question 18

What is the Photosynthesis equation?

Answer 18

6 CO2 + 6 H2O → C6 H12 O6 + 6 O2

Question 19

What are the 2 stages/parts of Photosynthesis?

Answer 19

• Light Reactions/

- Calvin cycle/

Question 20

Describe the light reaction stage.

Answer 20

• occurs ONLY in light.
• location Thylakoid Membrane.
• Light energy is captured by chlorophyll + used to extract electrons from water, which converts it to oxygen.
• Solar energy is converted to chemical energy:
  solar energy → chemical energy (ATP, NADPH)

Question 21

What are the 2 photosystems utilized by the Light Reactions stage?

Answer 21

-Photosystem I (PS I)→ P700(molecules of chlorophyll a)
• absorbs light energy @ 7oonm
• non cyclic pathway produces NADPH
• cyclic pathway is N.B to produce ATP

-Photosystem II (PS II) )→ P680 (molecules of chlorophyll b)
• only participates in the non cyclic pathway
• produces ATP
• hydrolysis of water → O2

organized in the way they were discovered.

Question 22

What do are the photosystems composed of?

Answer 22

• a Pigment Complex ( PS 1 + PS 11)
• Electron acceptor molecule.

the pigment complexes act as antenna to gather solar energy.

Question 23

Describe the non - cyclic pathway of the light reactions. (part 1+2)

Answer 23

1 - Begins w/ PS II. The pigment complex (P680) absorbs solar energy, which gets passed from one pigment to the other until it is concentrated in a particular pair of chlorophyll b molecules, called the RXN CENTRE.

2 - Electrons (e-) in the RXN CENTRE become so energized that they ESCAPE from the rxn center and move to nearby electron acceptor molecules.

Question 24

Describe the non - cyclic pathway of the light reactions. (part 3+4)

Answer 24

3 - W/ out replacement electrons PS II would disintegrate, and these are removed from water, which splits, releasing oxygen (O2) to the
atmosphere.

4 - An electron acceptor sends energized electrons down the E.T.C, a series of carriers that pass electrons from one to the other. As the electrons pass from one carrier to the next, energy is captured & ATP is produced. ATP will be used in the Calvin cycle.

Question 25

Describe the non - cyclic pathway of the light reactions. (part 5+6)

Answer 25

5 - When the PS I pigment complex (P700) absorbs solar energy, energized electrons leave the rxn centre + are captured by electron acceptors. Low-energy electrons from the ETC replace those lost by PS I.

6 - The electron acceptors in PS I pass their electrons to NADP+ molecules to become a reduced to NADPH. This NADPH will be used by the Calvin cycle reactions in the stroma.

Question 26

Describe the cyclic pathway of Light Reactions.

Answer 26

• Electrons leave P700 & then return back to it, instead of reacting with NADP+.
• Before they return to P700 they pass ETC and ATP
  is produced.

Question 27

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Answer 27

• Cyclic electron flow common in cell with especially high ATP needs (such as the sugar-synthesizing)
• Cyclic electron flow may play a photoprotective role, preventing excess light from damaging photosystem.

Question 28

Where does the Calvin cycle occur?

Answer 28

• The stroma of the chloroplast.

Question 29

How does the Calvin cycle produce sugars?

Answer 29

• By using CO2 from the atmosphere.

Question 30

What 3 portions is the calvin cycle divided into?

Answer 30

1) CO2 fixation
2) CO2 reduction
3) regeneration of ribulose-1,5-bisphosphate (RuBP)

Question 31

What happens in the fixation of CO2?

Answer 31

• CO2 + ribulose-1,5-bisphosphate (5 carbon sugar)

- = 6 carbon molecule, that splits into two 3-carbon molecules.

Question 32

What happens during the reduction of CO2?

Answer 32

• The two 3-carbon molecules are called 3PG (3-phosphoglycerate).
• The two 3PG molecules undergo reduction
• Turning to G3P (glyceraldehyde 3-phosphate)

This rxn uses the ATP and NADPH from the light rxn.

Question 33

What happens during the regeneration of RuBP?

Answer 33

• 5 molecules of G3P become 3 moles of RuBP.
• Only after 3 turns of the Calvin cycle can 1 G3P exit.

This rxn uses ATP produced by light.

Question 34

What is the end product of photosynthesis?

Answer 34

• It is considered to be Glucose

Two G3Ps are needed to form
glucose phosphate;

Question 35

What role does sucrose have in plants?

Answer 35

• The transport sugar in plants.

Question 36

what role does starch have in plants?

Answer 36

• The storage form of glucose.

Question 37

What role does cellulose play in plants?

Answer 37

• Helps structurally to the plant cell wall

Question 38

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Answer 38

• Plants capture solar energy and store it in carbon-based organic nutrients that are passed to other organisms when they feed on plants and/or on other organisms.

– Plants are called autotrophs because they make their own
organic food.
– Heterotrophs are organisms that take in preformed organic
food.

• Therefore all life is dependent on the ability of plants to capture solar energy and produce carbohydrate molecules.