Lecture 15-16: Photosynthesis

Question 1

photosynthesis:

Answer 1

builds reduced molecules from CO2 and H2O (anabolic)

Question 2

photosynthesis is done by?

Answer 2

photoautotrophs (the producers of the biosphere)

Question 3

what kind of reaction is photosynthesis?

Answer 3

endergonic (requires energy from sunlight)

Question 4

where does photosynthesis take place?

Answer 4

chloroplast

Question 5

a typical mesophyll cell has how many chloroplasts?

Answer 5

30-40

Question 6

what is fluid inside the chloroplast called?

Answer 6

stroma

Question 7

where does the calvin cycle occur?

Answer 7

the stroma -> inside the chloroplast

Question 8

how many layers does the membrane of the chloroplast have?

Answer 8

2

Question 9

what is the third membrane system inside the chloroplast called?

Answer 9

thylakoids

Question 10

how do thylakoids form grana?

Answer 10

by being stacked inside the chloroplast

Question 11

what is the lumen?

Answer 11

the thylakoid intermembrane space, where light reactions occur

Question 12

what is chlorophyll?

Answer 12

the pigment that absorbs and transforms photon energy

Question 13

where is chlorophyll found?

Answer 13

the thylakoids

Question 14

what do pigments absorb?

Answer 14

wavelengths of light

Question 15

what happens when pigments don’t absorb wavelengths of light?

Answer 15

its reflected, giving off “colour”

Question 16

why are plant leaves green?

Answer 16

they don’t absorb green light!

Question 17

what is the absorption spectrum?

Answer 17

the pigments light absorption versus wavelength

Question 18

what happens when a photon is absorbed by a molecule?

Answer 18

an electron is converted to a higher-energy state (excited state)

Question 19

what happens when an excited electron falls back to ‘ground state’?

Answer 19

1. energy can be dissipated as heat
2. energy can be re-emitted in form of less energetic and longer wavelength photon called fluorescence
3. energy can be transferred to another molecule

Question 20

when will chlorophyll fluoresce?

Answer 20

when its isolated from the chloroplast because it isn’t organized by the chloroplast!

Question 21

why does the chloroplast have many types of pigments?

Answer 21

allows it to absorb many different wavelengths of energy from sunlight

Question 22

three main types of chlorophyll:

Answer 22

chlorophyll a
chlorophyll b
carotenoids

Question 23

what are photosystems composed of?

Answer 23

reaction centre complex surrounded by many light-harvesting complexes

Question 24

what chlorophyll molecules are in the reaction centre?

Answer 24

P680 and P700
(P: pigment, ###: wavelength absorbed best)

Question 25

where does the reaction centre pass on electrons to?

Answer 25

primary electron acceptor

Question 26

can photoexcited electrons bypass photosystem II into photosystem I?

Answer 26

sometimes! it’s like a short circuit

Question 27

what is the advantage and disadvantages of photoexcited electrons skipping to photosystem I?

Answer 27

advantage: supplements ATP synthesis
disadvantage: no NADPH production and no O2

Question 28

mitochondria and chloroplasts both utilise ______ to generate ATP

Answer 28

chemiosmosis

Question 29

both the mitochondria and chloroplasts utilize chemiosmosis to pump H+ across a membrane from a region of ___ H+ to ____ H+

Answer 29

low -> high

Question 30

where does photosyntheiss occur in a “normal” C3 plant

Answer 30

mesophyll cells

Question 31

where does the gas exchange take place in a C3 plant?

Answer 31

the stromata

Question 32

how do the sugars get transported in a C3 plant?

Answer 32

the veins of the leaf

Question 33

chemical formula for photosynthesis:

Answer 33

energy + 6CO2 + 6H2O -> C6H12O6 + 6O2

Question 34

C4 plants have extra cells called _____ associated with the veins

Answer 34

bundle sheaths

Question 35

where does the calvin cycle occur in C4 plants?

Answer 35

only in the chloroplasts of the bundle sheaths

Question 36

difference between C3 and C4 plants?

Answer 36

majority of plants are C3 (first carbon compound produced in photosynthesis has 3 carbons), C4 plants have adapted to be able to bind carbon dioxide when it enters the leaf and produce a 4-carbon compound

Question 37

_____ are products of ancient photosynthesis

Answer 37

fossil fuels