Photosynthesis

Question 1

what is the light energy in photosynthesis used for

Answer 1

to split strong bonds in water molecules (H2O), releasing hydrogen and oxygen

Question 2

what is the waste product when splitting water molecules

Answer 2

Oxygen is released into the atmosphere as a waste product

Question 3

state some reasons why organisms may need a constant supply of energy

Answer 3

To move substances across cell membranes in active transport or to move substances within cells

For muscle contraction

Question 4

structure of ATP

Answer 4

type of nucleic acid

It is a phosphorylated nucleotide
consists of a nitrogenous base, a sugar, and three phosphate group hence triphosphate

Question 5

what does the breakdown of glucose in respiration release

Answer 5

energy needed to phosphorylate ADP

Question 6

what does the hydrolysis of ATP release

Answer 6

inorganic phosphate as well as a small amount of energy which can be used by the cell

ATP –> ADP + Pi

Question 7

what is the removal of a phosphate group called and what is it catalysed by

Answer 7

dephosphorylation
catalysed by the enzyme ATPase

Question 8

what 2 processes can ATP go through

Answer 8

is formed during respiration and can be hydrolysed to release energy for processes such as active transport, muscle contraction, and building new molecules

Question 9

what is each chloroplast surrounded by

Answer 9

double-membrane known as the chloroplast envelope

Each of the envelope membranes is a phospholipid bilayer

Question 10

what are chloroplast filled with

Answer 10

cytoplasm-like fluid known as the stroma

Question 11

what does the stroma contain

Answer 11

enzymes and sugars, as well as ribosomes and chloroplast DNA

Question 12

describe membrane system in the stroma

Answer 12

flattened fluid-filled sacs known as thylakoids, each surrounded by a thylakoid membrane

Thylakoids stack up to form structures known as grana

Grana are connected by membranous channels called lamellae which ensure the stacks of sacs are connected but distanced from each other

Question 13

state the structures of a chloroplast

Answer 13

Chloroplast envelopes
Stroma
DNA
Ribosomes
Thylakoid membrane
Grana
Photosystems

Question 14

function chloroplast envelope

Answer 14

double membrane encloses the chloroplast, keeping all of the components needed for photosynthesis close to each other
The transport proteins present in the inner membrane control the flow of molecules between the stroma and cytoplasm

Question 15

function of stroma

Answer 15

The gel-like fluid contains enzymes that catalyse the reactions of photosynthesis

Question 16

function of DNA in chloroplast

Answer 16

genes that code for some of the proteins used in photosynthesis

Question 17

function of ribosomes in chloroplast

Answer 17

enable the translation of proteins coded by the chloroplast DNA

Question 18

function of grana

Answer 18

large surface area, maximising the number of photosystems and allowing maximum light absorption

(granum) is formed from many layers of thylakoid membranes to increase surface area (for absorbing light)
thylakoid membranes contain chlorophyll to absorb light
electron carrier molecules in thylakoid membrane involved in ATP production

Question 19

what does a photosystem do

Answer 19

absorbs light of a different wavelength, maximising light absorption

Question 20

where does the light dependent reaction take place

Answer 20

across the thylakoid membrane

Question 21

where does the light independent reaction take place

Answer 21

in the stroma

Question 22

what enables the splitting of water molecules

Answer 22

Light energy in the light-dependent reactions in a reaction known as photolysis

Question 23

what does photolysis produces

Answer 23

The hydrogen ions and electrons are used during the light-dependent reactions while the oxygen is given off as a waste product

2 hydrogen ions (2H+), also known as protons
2 electrons (2e-)
One atom of oxygen (O)

Question 24

what process occurs in the light dependent reaction

Answer 24

light energy is converted into chemical energy in the form of ATP and reduced NADP

Question 25

what is NADP

Answer 25

coenzyme; its role is to transfer hydrogen from one molecule to another When NADP gains hydrogen, it is reduced and can be known as either reduced NADP or NADPH

Question 26

how can NADPH reduce other molecules

Answer 26

by giving away hydrogen

Question 27

what are the useful products of the light dependent reaction

Answer 27

ATP and NADPH transferred to the light-independent reactions within the chloroplast

Question 28

what is photophosphorylation

Answer 28

photo = light the addition of phosphate; in this case to ADP to form ATP utilizing light energy from photosynthesis to convert ADP to ATP

Question 29

what does non cyclic photophosphorylation produce

Answer 29

This produces both ATP and NADPH

Question 30

what does Cyclic photophosphorylation produce only

Answer 30

This produces ATP only

Question 31

describe electron transport chain

Answer 31

Electrons pass from one protein to another along the electron transport chain, releasing energy as they do so

Question 32

what is chemiosmosis

Answer 32

The energy released as electrons pass down the electron transport chain is used to produce ATP

Question 33

explain non cyclic photophosphorylation also explain what happens to the H+ ions as electrons passed down

Answer 33

Light energy hits photosystem II in the thylakoid membrane Two electrons gain energy and are said to be excited to a higher energy level The excited electrons leave the photosystem and pass to the first protein in the electron transport chain the electrons pass down the electron transport chain Energy is released as the electrons pass down the electron transport chain which enables chemiosmosis to occur H­­+ ions are actively pumped from a low concentration in the stroma to a high concentration in the thylakoid space H­­+ ions diffuse back across the thylakoid membrane into the stroma via ATP synthase enzymes embedded in the membrane The movement of H­­+ ions causes the ATP synthase enzyme to catalyse the production of ATP At the end of the electron transport chain the electrons from photosystem II are passed to photosystem I Light energy also hits photosystem I, exciting another pair of electrons which leave the photosystem The excited electrons from photosystem I also pass along an electron transport chain electrons combine with hydrogen ions from the photolysis of water and the coenzyme NADP to form NADPH The reduced NADP and the ATP pass to the light-independent reactions

Question 34

Explain cyclic photophosphorylation

Answer 34

same as non cyclic Light hits only photosystem I At the end of the electron transport chain the electrons rejoin photosystem I in a complete cycle; hence the term cyclic photophosphorylation The ATP produced enters the light-independent reaction

Question 35

what does the light independent reaction produce

Answer 35

Starch for storage Sucrose for transport Cellulose for making cell walls

Question 36

what does light independent reaction require

Answer 36

ATP and reduced NADP from the light-dependent reactions

Question 37

3 steps of light independent reaction

Answer 37

1) Carbon dioxide is combined with RuBP a 5-carbon (5C) compound; this yields two molecules of GP a 3-carbon (3C) compound 2) GP is reduced to (GALP), another 3C compound, in a reaction involving reduced NADP and ATP 3) RuBP is regenerated from GALP in reactions that use ATP

Question 38

explain step 1 : Carbon dioxide and RuBP are combined

Answer 38

Carbon dioxide combines with a 5C sugar known as RuBP in a reaction catalysed by the enzyme rubisco The resulting 6-carbon (6C) compound is unstable and splits in two This results in two molecules of a 3C GP

Question 39

explain step 2 : Reduction of GP

Answer 39

Energy from ATP and hydrogen from reduced NADP, both produced during the light-dependent reactions, are used to reduce the two molecules of GP to two 3C molecule known as GALP production of useful organic molecules such as glucose, while the rest remain in the Calvin cycle to allow the regeneration of RuBP

Question 40

explain step 3 : Regeneration of ribulose bisphosphate

Answer 40

Five sixths of the GALP molecules are used to regenerate RuBP This process requires ATP

Question 41

what does GP produce

Answer 41

Amino acids which can be used in protein synthesis for building polypeptides Fatty acids which form the tails of lipid molecules such as triglycerides and phospholipids

Question 42

What does GALP produce

Answer 42

Hexose sugars e.g. glucose Glucose can be used by the plant in respiration while other biological molecules are used to build new plant biomass

Question 43

how is NADPH formed

Answer 43

electrons are picked up by the coenzyme NADP along with hydrogen ions from photolysis, forming NADPH

Question 44

why do indicators change colour

Answer 44

indicators accept the electrons instead of NADP

Question 45

what colour does DCPIP and methylene blue go

Answer 45

blue to colourless

Question 46

why may the colour of reduced solution appear green

Answer 46

due to the presence of chlorophyll

Question 47

Method for the Hill reaction

Answer 47

Grind up the leaves with 20 cm3 isolation solution and blend them in a food blender for 10 seconds Filter the resulting liquid into a clean beaker using a funnel and some filter paper Transfer the filtered liquid into a centrifuge tube and centrifuge for 10 minutes Discard the liquid in the centrifuge tube and keep the pellet of chloroplasts Place 2 cm3 fresh isolation medium and the chloroplast pellet into a clean test tube, stirring with a glass rod to re-suspend the chloroplasts in the liquid; this is now the chloroplast extract transfer the chloroplast extract to an ice-cold water bath Place a test tube containing 0.5 cm3 chloroplast extract into a test tube rack set up at a set distance from a lamp Add 5 cm3 DCPIP solution to the chloroplast extract and mix together using a clean glass rod Use a pipette to immediately remove a sample of the DCPIP-chloroplast mixture and place the sample into a clean cuvette Place the cuvette into a colorimeter and take a reading for absorbance Repeat steps

Question 48

why do we grind up leaves and blend them in food blender and put isolation solution

Answer 48

breaks apart the tissues of the leaf isolation medium will prevent cell damage due to osmosis or extreme pH

Question 49

why transfer filtered liquid in centrifuge tube and centrifuge

Answer 49

result in a pellet of chloroplasts forming at the bottom of the tube

Question 50

what is liquid in centrifuge known as

Answer 50

supernatant

Question 51

why ice cold water

Answer 51

The cold temperature of the water bath slows down the activity of the chloroplasts

Question 52

what should happen to absorbance reading of colorimeter

Answer 52

The absorbance reading of the colorimeter should decrease over the 10 minute test period as the DCPIP indicator is reduced by electrons in the chloroplasts

Question 53

what does the removal of one phosphate from ATP form and two phosphates

Answer 53

Removal of one phosphate creates ADP, and removal of two phosphates creates AMP.

Question 54

describe the role of rubisco in the production of GALP in the light independent reaction

Answer 54

reference to RUBISCO as an {enzyme / catalyst}; in the Calvin cycle; involved in {carbon fixation / bonding of CO2 to RuBP / reaction between COz and RuBP / eq} ; to form GP / eg; GP converted to GALP / eg; using ATP and {reduced NADP / NADPH} (COz to GALP / GP to GALP);

Question 55

describe how membranes inside the chloroplast are involved in photosynthesis

Answer 55

site of light-dependent reaction; credit named molecules {within / on / eq} membrane; idea of {ATPase / eq } in (thylakoid) membranes ; idea that (thylakoid) membranes provide a space for accumulation of H*; reference to photophosphorylation;

Question 56

suggest how GALP can be used to synthesise the cellulose in plant cell walls

Answer 56

reference to conversion (of GALP) to glucose / eg; (which is) B glucose; reference to formation of glycosidic bonds; between C1 and Ca / these bonds are 1-4 (glycosidic bonds) ; by condensation; reference to {straight / unbranched} (chains of glucose) ; reference to cellulose as a {polysaccharide / polymer of glucose / eq}

Question 57

describe the roles of the products of the light dependant reactions in the calvin cycle

Answer 57

(the products) ATP and reduced NADP (1) ATP is used (by the enzyme) converting (GP to GALP / GALP to RuBP} (1) reduced NADP used to convert GP to GALP (1)