Photosynthesis

Question 1

what is the importance of photosynthesis

Answer 1

• for plants to make their own food to gain energy
• energy for metabolic reactions

Question 2

what is the equation of photosynthesis

Answer 2

Carbon Dioxide + Water = Glucose + oxygen

Question 3

what is the need for energy

Answer 3

• metabolic reactions

Question 4

what is a metabolic pathway

Answer 4

series of small reactions controlled by enzymes

Question 5

what is phosphorylation

Answer 5

• adding a phosphate to a molecule
• ADP is phosphorylase to ATP

Question 6

what is photophosphorylation

Answer 6

• using light to add a phosphate to a molecule

Question 7

what is photolysis

Answer 7

splitting of a molecule using light energy

Question 8

what is hydrolysis

Answer 8

splitting of a molecule using water

Question 9

what is decarboxylation

Answer 9

removal of carbon dioxide

Question 10

what is dehydrogenation

Answer 10

removal of hydrogn

Question 11

what is chemiosmosis

Answer 11

• diffusion of protons from high to low concentration
• movement of protons down the gradient releases energy that is used in the attachment of and inorganic phosphate to ADP to create ATP
• energy to do this comes from excited electrons

Question 12

what are excited electrons

Answer 12

• excited in pigment molecules when absorbing light energy
• high energy electrons released when chemical bonds are broken in respiratory substrate molecules
• excited electrons pass into electron transport chain and used to generate a proton gradient

Question 13

what is the electron transport chain

Answer 13

• made of electron carriers
• electrons move down the gradient from one carrier to another and release energy
• pumps protons across creating a concentration difference and a gradient

Question 14

what is the structure of a chloroplast

Answer 14

Chloroplast envelope = double membrane

Thylakoids = stacked up into grana and linked by thylakoid membranes called lamellae

Photosynthetic pigments = coloured substances that absorb light energy, in thylakoid membranes attached to a protein

Stroma = fluid-filled membrane, contains starch grains, oil droplets, DNA + Ribosomes, light-independent stage

Question 15

what are photosystems

Answer 15

• contains primary and secondary pigments
• photosystem 1 and 2

Question 16

what is chlorophyll what colours do each pigment represent

Answer 16

Chlorophyll A = yellow/green (Primary)
Chlorophyll B = blue/green
Carotene = yellow/ orange
Xanthophyll = yellow

Question 17

what is the light dependent stage

Answer 17

• needs light energy
• in thylakoid membranes
• energy absorbed by photosynthetic pigments and converted to chemical energy

Question 18

what are the 4 stages of non-cyclic phosphorylation

Answer 18

• light energy excites electrons
• photolysis of water
• energy makes ATP
• energy generates reduced NADP

Question 19

how does light energy excite electrons

Answer 19

• light energy absorbed by PSII
• light energy excites electrons in chlorophyll
• electrons move to a higher energy level
• high energy electron move along the electron transport chain to PSI

Question 20

what happens in the photolysis of water

Answer 20

• as excited electrons leave PSII to move along the ECT they must be replaces
• light energy splits water into protons, electrons and oxygen

Question 21

how does energy from excited electrons create ATP

Answer 21

• excited electrons lose energy as they move along the ETC
• energy used to transport protons into the thylakoid via proton pumps
• thylakoid has a higher concentration of protons than the stroma
• proton gradient formed across membrane
• protons move down the concentration gradient into the stroma via ATP synthase
• energy combined ADP and Pi to form ATP

Question 22

how does energy from the excited electrons generate reduced NADP

Answer 22

• light energy absorbed by PSI
• excites electrons to a even higher level
• electrons are transferred to NADP with a proton (H+ ion) from the stroma
• reduced NADP formed (NADPH)

Question 23

What is cyclic photophosphorylation

Answer 23

• only uses PSI
• electrons from the chlorophyll aren’t passed onto NADP
• passed back to PSI via electron carriers
• electrons are recycled and repeatedly flow through PSI
• doesn’t produce NADPH or oxygen only small amounts of ATP

Question 24

what is the light independent reaction

Answer 24

• calvin cycle
• doesn’t use light energy directly
• relies on the products from the light independent reaction
• takes place in the stroma

Question 25

what is the first stage of the calvin cycle

Answer 25

- carbon dioxide enters the leaf through the stomata and diffuses into the stroma - CO2 combined with RuBP (5 carbon compound) - unstable 6 carbon compounds which break down into 2 molecules of 3 carbon compounds called GP - RuBisCO catalyses the reaction between CO2 and RuBP

Question 26

what is the second stage of the Calvin cycle

Answer 26

- ATP from light dependent reaction provides energy to turn 3GP to 3 TP - reaction requires H+ ions from reduced NADP in LDR - reduced NADP recycled to NADP - TP converted to several organic compounds

Question 27

what is the third stage of the Calvin cycle

Answer 27

- 5 out of every 6 molecules of TP produced used to regenerate RuBP which used the rest of the ATP produced by LDR

Question 28

what organic substances are made from the Calvin cycle

Answer 28

Carbohydrates - hexose sugars made by joining 2 TP molecules together Lipids - made using glycerol synthesised from TP and fatty which are synthesised from GP Amino acids - made from GP

Question 29

how many times does the calvin cycle need to turn to make a hexose sugar

Answer 29

- three turns produce 6 TP molecules - 5/6 TP molecules are used to regenerate RuBP - three turns produces 1 TP to make a hexose so two TP molecules needed - 6 turns are needed - 6 turns need 18 ATP and 12 NADH from LDR

Question 30

What are limiting factors of photosynthesis

Answer 30

- light - temperature - carbon dioxide

Question 31

how can light be a limiting factor

Answer 31

high light intensity = high energy to excite electrons Very high light intensity = photosynthetic pigments are damaged low = products of LDR are in short supply - conversion of GP to TP and RuBP is slow - level of GP rises and levels of TP and RuBP fall

Question 32

how can temperature be a limiting factor

Answer 32

- too high (above 45) - too low (below 10) - denaturing of enzymes - all reactions in the Calvin cycle are catalysed by enzymes - levels of RuBP, TP, GP fall + denature

Question 33

how can carbon dioxide levels be a limiting factor

Answer 33

- low concentrations conversion of RuBP to GP is slow - level of RuBP rises and GP and TP fall