unit 3 KA1b - photosynthesis

Question 1

how is light energy absorbed

Answer 1

by photosynthetic pigments to generate ATP and for photolysis

Question 2

what are the three potential fates of light energy

Answer 2

• absorbed
• transmitted
• reflected

Question 3

what are the different pigments that are used in photosynthesis

Answer 3

• chlorophyll a
• chlorophyll b
• carotene
• xanthophyll

Question 4

what is the difference between the different pigments in photosynthesis

Answer 4

they each absorb different ranges of wavelengths of light

Question 5

what do carotenoids do

Answer 5

they extend the range of wavelengths absorbed and pass the energy to chlorophyll for photosynthesis

Question 6

what are the two different spectras in photosynthesis

Answer 6

• absorption spectra

- action spectra

Question 7

how is light energy converted to ATP for photosynthesis

Answer 7

• the absorbed light energy excites electrons in the pigment molecule
• transfer of these electrons through the electron transport chain releases energy to generate ATP by ATP synthase

Question 8

how is the energy made from the light energy used

Answer 8

it is used for photolysis, in which water is split into oxygen, which is evolved, and hydrogen ions, which are transferred to the coenzyme NADP

Question 9

what are the two stages of photosynthesis

Answer 9

• photolysis- the light dependent stage

- the calvin cycle - carbon fixation

Question 10

what happens in the carbon fixation stage (the calvin cycle)

Answer 10

• the enzme RuBisCO fixes carbon dioxide by attaching it to RuBP.
• the 3-phosphoglycerate (3PG) produced is phosphorylated by ATP and combined with hydrogen ions from NADPH to form glyceraldehyde-3-phosphate (G3P)
• G3P is used to regenerate RuBP and for the synthesis of glucose

Question 11

what are the possible fates of glucose

Answer 11

it may be used as a respiratory substrate, synthesised into starch or cellulose, or passed onto other biosynthetic pathways

Question 12

what can the biosynthetic pathways lead to

Answer 12

the formation of a variety of metabolites such as DNA, protein and fat.

Question 13

which colours of light are absorbed by the leaf pigments - ie which are the most important for photosynthesis

Answer 13

blue, violet and red

Question 14

how can the leaf pigments be separated

Answer 14

chromatography

Question 15

what is the most important pigment for photosynthesis

Answer 15

chlorophyll

Question 16

what does an absorption spectrum show

Answer 16

these show the absorption of light of each wavelength by each pigment

Question 17

what does an action spectrum show

Answer 17

these show the rate of photosynthesis at each light wavelength

Question 18

what do xanthophyll and carotene do

Answer 18

they allow the plant to carry out photosynthesis in a wider range of light wavelengths

Question 19

what are the accessory pigments, and why are they named this way?

Answer 19

• xanthophyll and carotene

- they pass the energy they capture onto chlorophyll a and b

Question 20

where does absorption of light and photosynthesis take place

Answer 20

the grana - because this is where the photosynthetic pigments are contained

Question 21

where does carbon fixation take place

Answer 21

the stroma of the chloroplast

Question 22

describe the steps of capture of energy and photolysis

Answer 22

• light energy is absorbed by the chlorophyll, creating high energy electrons
• electrons are passed along the chain, pumping hydrogen ions into grana
• energy is used to split water
• hydrogen ions are picked up by NADP to make NADPH for carbon fixation (the calvin cycle)
• hydrogen ions are used by ATP synthase to make ATP for carbon fixation

Question 23

what is the order of occurrence of molecules in the calvin cycle

Answer 23

• ribulose biphosphate
• 3-phosphoglycerste
• glyceraldehyde-3-phosphate