Ch. 10 Photosynthesis

Question 1

what are photosynthetic autotrophs?

Answer 1

organisms that obtain nutrients from non-organic molecules - the sun

Question 2

what are chemosynthetic autotrophs?

Answer 2

organisms that make their food from inorganic compounds: H2S, CH4, NH3, etc

Question 3

what are heterotrophs?

Answer 3

organisms that get their food from organic molecules or other organisms: fungi, animals, plants, protists, bacteria, archaea

Question 4

what is the structure of a chloroplast?

Answer 4

-double membrane enclosing the stroma
-stroma contains grana, which are stacks of thylakoid membranes
-chlorophyll is within the thylakoid membrane

Question 5

where are chloroplasts located?

Answer 5

within the mesophyll cells of leaves

Question 6

what are the 3 pigments involved in photosynthesis?

Answer 6

chlorophyll = green [primary]
fucoxanthin = brown
phycoerythrin = red

Question 7

what is the summary equation for photosynthesis?

Answer 7

6CO2 + 6H20 -> C6H12O6 + 6O2

-H2O gets oxidized
-CO2 gets reduced

Question 8

how does light travel?

Answer 8

light travels in waves and in packets of particles called photons

Question 9

what colours does chlorophyll absorb and reflect?

Answer 9

chlorophyll is green, so it absorbs all colours but green and reflects green

Question 10

what is the absorption spectrum?

Answer 10

the wavelengths of light that a pigment absorbs:
chlorophyll b absorbs around 400-500nm (blue) and 600-660nm (red)

Question 11

what is an action spectrum?

Answer 11

the effects of wavelengths of light on a specific PROCESS, ie , what wavelengths are useful to the organism
ex - wavelengths between 300-500 & 600-700nm stimulate photosynthesis

Question 12

how do the electrons of pigmented molecules work?

Answer 12

-electrons of pigment molecules absorb photons corresponding to a specific wavelength
-this energizes them, causing them to jump to another orbital

Question 13

what 2 things can happen when a pigment electron jumps orbitals?

Answer 13

1. electron loses energy and returns to its original position, giving off light and heat
   OR
2. energy is converted to chemical energy = photosynthesis

Question 14

what are photosystems?

Answer 14

-light harvesting units located in the thylakoid membranes

Question 15

what are photosystems composed of?

Answer 15

1. light harvesting center = collection of accessory pigment molecules
2. reaction centers = light energy is transformed to energized electrons, accepted by the primary electron acceptor

Question 16

what are the two main photosystems in photosynthesis? what is their function?

Answer 16

-photosystem [PS] I and II
-absorb different wavelengths of light and function in light reactions of photosynthesis
-PS II starts the process

Question 17

what is the flow of electrons through photosystem II?

Answer 17

1. light enters PS II and is harvested
2. “chlorophyll a” uses harvested light to excite electrons
3. electrons are taken in by the primary electron acceptor
4. ETC occurs, H+ pumped into thylakoid space, ATP is generated
5. electrons used up are replaced by splitting H2O
6. ATP created is used in calvin cycle

Question 18

what is the flow of electrons through photosystem I?

Answer 18

1. energy from photon hits PS I
2. light is used to excite electrons, which eventually meet the primary electron acceptor
3. ETC undergoes like normal, but
4. no H+ gradient is made. instead, NADPH is made using NADPH reductase

Question 19

how does the electron transport chain in photosystem I differ from photosystem II?

Answer 19

-PS I does not generate a H+ gradient
-instead it uses the electron energy to convert NADP+ to NADPH by using the enzyme NADPH reductase

Question 20

what is the function of cyclic electron flow?

Answer 20

to produce ATP without the synthesis of NADPH in photosystem I

Question 21

why do plant cells need to use cyclic electron flow?

Answer 21

-the calvin cycle needs 9 ATP for every 6 NADPH
-but NADPH and ATP are made in the photosystems in a 1:1 ratio
-therefore, extra ATP needs to be synthesized

Question 22

what are the products of the calvin cycle?

Answer 22

-3 Carbon sugar
-9x ADP + Pi
-6x NADP+

Question 22

what are the reactants of the calvin cycle?

Answer 22

-6x NADPH
-9x ATP
-3x CO2

Question 23

what is the 2nd phase of the calvin cycle?

Answer 23

-reduction: carbon compounds gain energy [reduction]
-NADPH and ATP lose energy [oxidization]

Question 23

what is the 1st phase of the calvin cycle?

Answer 23

-carbon fixation: CO2 must be changed from a gas to an organic molecule
-done through binding to RuBP and being catalyzed by the enzyme rubisco

Question 24

what is the 3rd phase of the calvin cycle?

Answer 24

-regeneration of the CO2 acceptor (RuBP = ribulose biphosphate)

Question 25

what is photorespiration?

Answer 25

a process in which plants use oxygen for the calvin cycle instead of CO2, generating no sugar and essentially wasting NADPH/ATP

Question 26

why does photorespiration occur?

Answer 26

when plants keep their stomata closed to save water, CO2 can’t enter and O2 builds up, eventually binding to RuBP and entering the calvin cycle

Question 27

what are the three types of carbon fixating plants?

Answer 27

C3, C4, and CAM

Question 28

what are C3 plants? where do they fix carbon?

Answer 28

-plants, usually crops, that fix carbon in the mesophyll of their leaves
-these plants are most affected by photorespiration

Question 29

what are C4 plants? how do they combat photorespiration?

Answer 29

-C4 plants allow their CO2 to be fixed and stored as malic acid in the mesophyll of their leaves
-calvin cycle occurs in bundle-sheath cells

Question 30

what are CAM plants?

Answer 30

-plants that open their stomata at night and close them during the day
-CO2 is taken in at night and fixed as organic acids for use during the day