17.3 Photosynthesis

Question 1

define photosynthesis

Answer 1

the process by which energy (in the form of sunlight) is used to build complex organic molecules (e.g. glucose)

Question 2

define autotrophic

Answer 2

an organism that can photosynthesise

e.g. plants and algae

Question 3

define heterotrophic

Answer 3

an organism that obtains complex molecules by eating other organisms

Question 4

what is the equation for photosynthesis

Answer 4

carbon dioxide + water –> glucose + oxygen

Question 5

where does photosynthesis take place

Answer 5

chloroplasts

Question 6

where are complex pigments such as chlorophyll found

Answer 6

embedded in the thylakoid membranes

Question 7

describe the inner membrane of chloroplasts

Answer 7

controls travelling between the cells cytoplasm and the stroma

Question 8

describe the grana

Answer 8

many grana provide large SA for photosynthetic pigments, electron carriers and ATP synthase

Question 9

describe the photosynthetic pigments

Answer 9

arranged in photosystems which allows maximum absorption of light

Question 10

function of proteins embedded in the grana

Answer 10

hold the photosystems in place

Question 11

describe the stroma

Answer 11

• fluid-filled

- contains enzymes needed for LIS

Question 12

why do chloroplasts contain their own DNA and ribosomes

Answer 12

can make their own proteins for photosynthesis

Question 13

why do different pigments have different colours

Answer 13

they absorb and reflect different wavelengths

Question 14

what makes up the light harvesting system

Answer 14

• proteins

- pigments embedded in the grana

Question 15

what does the light harvesting system do

Answer 15

absorb light energy of different wavelengths and transfers this energy quickly and efficiently to he reaction centre

Question 16

what makes up a photosystem

Answer 16

• light harvesting system

- reaction centre

Question 17

describe chlorophyll a

Answer 17

• primary pigment reaction centre
• 2 forms (PSI and PSII)
• appears yellow/green
• absorbs red (=blue at 450nm)
• not made when there is little light
• destroyed by intense light
• contains a Mg atom

Question 18

what is the purpose of the Mg atom in chlorophyll a

Answer 18

light hits the Mg atom and excites electrons

Question 19

describe chlorophyll b

Answer 19

• absorbs light at wavelengths between 500-640nm
• appears blue/green
• accessory pigment

Question 20

describe carotenoid

Answer 20

• absorbs blue
• reflects yellow and orange
• absorbs light not normally absorbed by chlorophyll and passes on energy
• present through growing season

Question 21

describe anthocyanins

Answer 21

• appears red/purple
• made when sugar conc = high
• more made in high light intensities
• absorb blue/green and UV light so inhibits destruction of chlorophyll

Question 22

what happens in the LDS

Answer 22

• sunlight energy is absorbed and used to form ATP

- hydrogen (from water) reduces coenzyme NADP to reduced NADP

Question 23

what happens in the LIS

Answer 23

• hydrogen from reduced NADP and CO2 are used to build organic molecules
• ATP supplies energy

Question 24

outline non-cyclic photophosphorylation

Answer 24

1. light energy is absorbed by PSII
2. energy excites electrons in chlorophyll so they move to a higher energy level
3. electrons move along the ETC to PSI
4. photolysis of H2O (light energy splits water into H+, electrons and O2) to replace electrons that left PSII
5. energy lost by electrons moving down the ETC is used to transport protons into the thylakoid to increase conc an form a proton gradient (chemiosmosis)
6. protons move down a conc gradient into storm via ATP synthase (energy from this combines ADP and Pi to form ATP)
7. light absorbed by PSI excites electrons so they get transferred to NADP along with a H+ ion to make reduced NADP

Question 25

what does non-cyclic photophosphorylation produce compared to cyclic photophosphorylation

Answer 25

• non-cyclic photophosphorylation = ATP+reduced NADP+O2

- cyclic photophosphorylation = ATP

Question 26

outline cyclic photophosphorylation

Answer 26

• only uses PSI

- electrons from chlorophyll aren’t passed onto NADP but are passed back to PSI via electron carriers

Question 27

where does the Calvin cycle take place

Answer 27

in the stroma

Question 28

outline the LIS

Answer 28

1. CO2 diffuses into the stroma and combines with RuBP (catalyst by RuBisCO)
2. an unstable 6-carbon compound is formed which quickly breaks down into 2 GP molecules
3. ATP provides energy to turn GP–>TP
4. reduced NADP provides H+ ions and is recycled into NADP
5. TP is converted to useful organic compounds
6. 5/6 molecules of TP are used to regenerate RuBP (uses remaining ATP)

Question 29

what are TP and GP molecules used to make

Answer 29

• carbohydrates (2 TP molecules = hexose sugar)
• lipids (TP synthesises glycerol, GP synthesises fatty acids)
• amino acids (some made from GP)

Question 30

give the equation for photolysis

Answer 30

H2O –> 2H+ + 2e- + 1/2 O2

Question 31

summarise the Calvin cycle

Answer 31

• fixation (CO2 is fixed)
• reduction (GP–>TP by addition of hydrogen from reduced NADP using ATP)
• regeneration (RuBP is regenerated from recycled TP)

Question 32

describe the regeneration of RuBP

Answer 32

• 6 turns of the Calvin cycle = 1 hexose sugar
• 3 turns = 6 TP (5 used to regenerate RuBP and 1 used to make a hexose sugar)
• 2 TP = hexose sugar
• 6 turns need 18 ATP and 12 reduced NADP

Question 33

describe chromatography for photosynthetic pigments

Answer 33

• used to separate the pigments in the plant
• mobile phase = solution containing pigment mixture
• stationary phase = silica gel or TLC paper
• the solubility of the pigment affects interactions with the stationary phase and therefore affects Rf value