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How are photosynthesis and respiration

CO, & H,O are the raw materials for
photosynthesis and the products of respiration.
O, & glucose are the raw materials for
photosynthesis and the products of respiration.


Describe the structure of a chloroplast.

Usually disc-shaped.
Double membrane (envelope).

Thylakoids: flattened discs stack to form grana.
Intergranal lamellae: tubular extensions attach thylakoids in adjacent grana

Stroma: fluid-filled matrix with high enzyme & substrate concentration & own loop of DNA.


Where do the light-dependent &
light-independent reactions occur in

Light-dependent: in the thylakoids of
Light-independent: stroma of


What is the role of photosynthetic
pigments? Name the 2 main groups.

Embedded within thylakoid membrane. Absorb different wavelengths of light to maximise rate of photosynthesis.

Primary pigment: chlorophyll (made of chlorophyll a & chlorophyll b) found in photosystems.

Accessory pigments: carotenoids (carotene & xanthophylls) found in light-harvesting systems.


Name the processes in the
light-dependent reaction.

electron transfer chain

non-cyclic only:
reduction of NADP
photolysis of water


Explain the role of light in

Chlorophyll molecules absorb energy
from photons of light.
This 'excites' 2 electrons (raises them to
a higher energy level), causing them to
be released from the chlorophyll.


What happens in the electron transfer
chain (ETC)?

Electrons released from chlorophyll move down a series of carrier proteins
embedded in the thylakoid membrane &
undèrgo a series of redox reactions
which releases energy.


How does chemiosmosis produce ATP in
the light-dependent stage?

Some energy released from the ETC is coupled to active transport of H* ions from stroma into thylakoid space.

H* ions move down concentration gradient from thylakoid space into stroma via transmembrane channel protein AT synthase.

ATP synthase catalyses ADP + Pi -> ATP


Describe non-cyclic

Uses Photosystems I & 2. Excited electrons enter ETC to produce ATP. NADP acts as final electron
acceptor & is reduced. Water is photolysed to release electrons to replace those lost from Photosystem 2

Purpose is to produce ATP & reduced NADP for Calvin cycle to produce biological compounds.


Describe cyclic photophosphorylation.

Uses only Photosystem I. Excited electrons enter ETC to produce ATP then return directly to photosystem (so no reduction of NADP & no water
needed to replace lost electrons)

Purpose is to produce additional ATP to meet surplus energy demands of cell


What happens in photolysis of water?

Light energy splits molecules of water
2H20 -› 4H+ + 4- + 02


What happens to the products of the
photolysis of water?

H* ions: move out of thylakoid space via ATP synthase & are used to reduce the coenzyme NADP.

e-: replace electrons lost from chlorophyll.

O2: used for respiration or diffuses out of leaf as waste gas.


How and where is reduced NADP
produced in the light-dependent

NADP + 2H+ (from photolysis of water) + 2e- (from acting as final electron acceptor in ETC) -> reduced NADP.

Catalysed by dehydrogenase enzymes.
Stroma of chloroplasts.


Name the 3 main stages in the
light-independent reaction.

1. Carbon fixation
2. Reduction
3. Regeneration


What happens during carbon fixation?

Reaction between CO2 & ribulose
bisphosphate (RuBP) catalysed by ribulose bisphosphate carboxylase (RuBisCo).

Forms unstable 6C intermediate that breaks down into 2x glycerate 3-phosphate (GP).


What happens during reduction in the
light-independent reaction?

2 × GP are reduced to 2 x triose phosphate (TP)

Requires 2 x reduced NADP & 2 x ATP
Forms 2 x NADP & 2 x ADP


Outline the roles of TP from the
light-independent reaction.

Raw material: 1C leaves the cycle to produce monosaccharides, amino acids & other biological molecules.

Involved in regeneration of RuBP: After 1C leaves cycle, the 5C compound RuP forms. RuP is converted
into RuBP using 1x ATP. Forms 1x ADP.


State the number of carbon atoms in

RuBP: 5
GP: 3


define limiting factor

Factor that determines maximum rate of
a reaction, even if other factors change
to become more favourable.


Name 4 environmental factors that can
limit the rate of photosynthesis.

Light intensity (light-dependent stage).

CO2 levels (light-independent stage).

Temperature (enzyme-controlled steps).

Mineral/magnesium levels (maintain
normal functioning of chlorophyll)


How does light intensity affect the rate of photosynthesis?

Low light intensity = slower light- dependent reaction = less ATP & NADPH produced to convert GP to TP in light-independent reaction.

GP level rises
TP level falls = RuBP level falls


Describe the implications of water stress.

1. Abscisic acid binds to complementary receptors on guard cell membrane, causing Ca2+ ion channels on tonoplast to open. Ca2+ ions diffuse from vacuole into cytosol.

2.Positive feedback triggers other ion channels to open. Other ions e.g. K* diffuse out of guard cell.

3. Water potential of quard cell becomes more positive. Water diffuses out via osmosis.

4 Guard cells become flaccid so stomata close.


State the purpose and principle of thin
layer chromatography (TLC).

Molecules in a mixture are separated
based on their relative attraction to the
mobile phase (running solvent) vs the
stationary phase (TLC plate, usually
coated in a silicate)


Outline a method for extracting
photosynthetic pigments.

Use a pestle and mortar to grind a leaf
with an extraction solvent e.g.


Outline how TLC can be used to
separate photosynthetic pigments.

1. Use a capillary tube to spot pigment extract onto pencil 'start line' (origin) 1 cm above bottom of plate.

2. Place chromatography paper in solvent (origin should be above solvent level).

3. Allow solvent to run until it almost touches the other end of the paper. Pigments move different distances.


ppq: (i) Describe two ways in which the structure of part C (granum) is adapted to its function.

contains photosystems

contains atp synthase

has a large surface area for light absorption


ppq: A key aspect of photosynthesis is the metabolic pathway involving carbon dioxide. Place a tick (/) in the appropriate box to indicate the part of the chloroplast (A (inner membrane, B (stroma) or C (granum) ) in
which the metabolic pathway involving carbon dioxide is located.

only b (stroma)


ppq: Fig. 1.2
With reference to the biochemistry of photosynthesis, explain why the theoretical rate of
photosynthesis is not achieved at higher light intensities.

at high light intensity. light is no longer the limiting factory e.g temperature becomes a limiting factor ;

idea that temperature becomes limiting as Calvin cycle / light independent reaction, involves enzymes / relies on kinetic energy of molecules ;

idea that CO, (concentration) becomes limiting as it is required for Calvin cycle / light independent reaction / formation of (named) Calvin cycle compound /
reaction with RuBP / fixation by Rubisco ;


ppq: The leaf of a plant that is adapted to living in shade will differ from the leaf of a plant that
is adapted to living in sunlight.
Suggest one way in which the structure of these leaves will differ.

shade leaf will have
1 large(r) / more , chloroplast(s) / (palisade) mesophyll;

2 more , grana / thylakoids (in
chloroplast) ;

3 large(r) surface area (of leaves) ;


ppq: Photosynthesis involves two main stages: the light-dependent stage, which involves photosystems the light-independent stage, which involves the Calvin cycle.

(a) Photosynthetic pigments are arranged in groups known as photosystems I and 2

(i) Name the primary photosynthetic pigment in these photosystems.

chlorophyll A


ppq: name an accessory pigment

chlorophyll b




ppq: state the advantage to the plant of having a range of accessory pigments in photosystems

able to absorb a range of different light wavelengths


ppq: name the compound that is synthesised in the LDR as a result of the generation of an electrical and pH gradient across the thylakoid membrane



ppq: identify the enzyme that catalyses the fixation of carbon dioxide

RuBP carboxylase


ppq: identify the first stable product of carbon dioxide fixation



ppq: identify the compound that is regenerates in the calvin cycle so that more carbon dioxide can be fixed



ppq: name two different polysaccharides that can be synthesises from the end produce of the LIR of photosynthesis


and cellulose


The molecules listed below are all associated with photosynthesis.
amino acid, reduced NADP, ATP
ribulose bisphosphate (RuBP)
carbon dioxide
glycerate-3-phosphate (GP)
From these molecules, identify:
(a) the enzyme.



The molecules listed below are all associated with photosynthesis.
amino acid, reduced NADP, ATP
ribulose bisphosphate (RuBP)
carbon dioxide
glycerate-3-phosphate (GP)
From these molecules, identify:

b) a product of the LDR that is USED in the LIR

ATP / reduced NADP


The molecules listed below are all associated with photosynthesis.
amino acid, reduced NADP, ATP
ribulose bisphosphate (RuBP)
carbon dioxide
glycerate-3-phosphate (GP)
From these molecules, identify:

c) a 3 carbon compound



The molecules listed below are all associated with photosynthesis.
amino acid, reduced NADP, ATP
ribulose bisphosphate (RuBP)
carbon dioxide
glycerate-3-phosphate (GP)
From these molecules, identify:

d) a compound that can be made from TP but is NOT part of the calvin cycle

amino acid


The molecules listed below are all associated with photosynthesis.
amino acid, reduced NADP, ATP
ribulose bisphosphate (RuBP)
carbon dioxide
glycerate-3-phosphate (GP)
From these molecules, identify:

e) a 5 carbon compound



The molecules listed below are all associated with photosynthesis.
amino acid, reduced NADP, ATP
ribulose bisphosphate (RuBP)
carbon dioxide
glycerate-3-phosphate (GP)
From these molecules, identify:

f) a product of the LDR that is NOT USED in the LIR



ppq: (il) The chloroplast contains fat droplets, as shown in Fig. 3.1. These act as a reserve of raw
material for the chloroplast.
Suggest what this raw material might be used for in the chloroplast.

for membrane formation


ppq describe how light is harvested in the chloroplast membranes

primary and accessory pigments are photosystem

photon absorbed by pigment molecules

electron excited and returns to pigment

photon passed from one pigment to another

photon passed to primary pigment chlorophyll a

range of accessory pigments allow range of wavelengths to be absorbed


ppq: Plants treated with triazine herbicide
can, when illuminated under experimental
conditions, be seen to fluoresce (emit light) and give off small quantities of heat.
Suggest how this experimental finding could be explained.

energy given off from excited electron


ppq: One way to determine the rate of photosynthesis is to measure the uptake of carbon
(a) Discuss why measuring carbon dioxide may or may not give a better indication of photosynthetic activity than measuring oxygen production.

oxygen only produced in one stage of
photosynthesis. oxygen produced might be used for respiration

carbon dioxide
CO2 only used in one stage of photosynthesis. CO2 produced during respiration might be used for ,
photosynthesis / light independent reaction / Calvin cycle ;


State the factor that is limiting the rate of photosynthesis at A on the graph.

light intensity


ppq: suggest one factor that may limit the rate of photosynthesis at B

CO2 concentration


ppq: (ili)
Carbon dioxide is given off by the plant when the light intensity is lower than X.
Name the process that produces carbon dioxide in the plant.



ppq: (iV)
With reference to Fig. 4.1, explain the biochemical processes that are occurring in the

as light intensity increases from O (zero) to X.
at light intensity X.
at light intensities greater than X.

at 0, respiration only / no photosynthesis ;

between 0 and X
idea that (rate of) respiration is greater than (rate of) photosynthesis;

at X
idea that (rate of) respiration equals (rate of) photosynthesis /
at compensation point

after X
idea that (rate of) photosynthesis is greater than (rate of) respiration


ppq: name the products of the LDR of photosynthesis

reduced NADP


ppq: Paraquat is a weedkiller. It binds with electrons in photosystem I.
Suggest how paraquat results in the death of a plant.

prevents photophosphorylation;
cyclic and non-cyclic;

no/less, ATP / reduced NADP, for ,
light-independent stage / Calvin cycle /
GP to TP :

no (named) substrate made for respiration ;



(b) The table below contains statements that refer to the light-dependent stage of photosynthesis.

Complete the table, indicating with the letters C, N or B, whether each statement applies to:

cyclic photophosphorylation only (C)
non-cyclic photophosphorylation only (N)
both cyclic and non-cyclic photophosphorylation (B)

a) atp is produced
b) an electron leaves photosystem I
c) electrons are passed along an electron carrier chain
d) electrons leave both photosystem I and photosystem II
e) an electron from a water molecule replaces the electron lost from the photosystem
f) the same electron returns to the photosystem

a) B

b) B

c) B

d) N

e) N

f) C


ppq) state what additional info would be required to calculate the volume of gas produced

use pie r squared


ppq) suggest how the student supplied the aquatic plant with a source of carbon dioxide

sodium hydrogen carbonate


ppq) b) Certain assumptions are made when using the apparatus shown in Fig. 2.1 to measure th
rate of photosynthesis.
One of these assumptions is that all of the oxygen produced by the plant durin
photosynthesis is collected.
Suggest why not all of the oxygen produced by the plant is collected.

idea that some of the oxygen
would dissolve in the water;

used in , respiration / oxidative phosphorylation ;

may escape the collection apparatus;

trapped in, a bubble attached to / air spaces in ,


ppq) (i) Another assumption is that all of the gas collected is oxygen.
Analysis of the gas collected reveals that it has the following composition:
oxygen 50%
nitrogen 44%
carbon dioxide 6%
Suggest a reason for the presence of nitrogen in the gas collected.

nitrogen was present in the air spaced in the leaf

nitrogen leaves the plant with the oxygen

idea that nitrogen comes out of solution


ppq) (c) Some aquatic photosynthetic organisms, for example seaweeds, contain pigments such as
fucoxanthin and phycoerythrin, in addition to chlorophyll. These pigments give seaweeds a brown or red color and are produced in larger quantities in those seaweeds that live in deeper water.

Suggest why the presence of these pigments is an advantage to seaweeds that live in deeper water.

in deeper water there is, less / lower, light intensity ;
(these pigments) can absorb what (little) light there is;

not all wavelengths of light can penetrate
mainly shorter wavelengths can penetrate
(mostly) blue light (450 - 520 nm) penetrates ;
(these pigments) can absorb
wavelengths of light that can penetrate
(deeper water) ;


ppq) name the products of the LDR in calvin cycle


reduced NADP


ppq) discuss the fate of triose phosphate in the calvin cycle

regenerates / produces , ribulose bisphosphate / RuBP;

so cycle can continue / for (further) CO, fixation / to combine with CO2;

formation of (named) , sugar / glucose / hexose / sucrose / starch / cellulose ;

formation of (named) , fat / triglyceride / lipid / fatty acids / glycerol /
amino acids / protein / nucleic acids / nucleotides ;

10x TP for RuBP and 2x TP for production
or most TP used to produce RuBP and the rest for production ;


ppq) describe and explain the likely effect on photosynthesis of an increase in the oxygen concentration

reduces (rate of) photosynthesis /
increases (rate of) photorespiration;

less Rubisco available for CO2 /
more oxygen competing with CO, for Rubisco / more O2 binding to Rubisco
O2 outcompetes CO2 for Rubisco ;

less CO2, fixation / for Calvin cycle ;
CO2 given off ;

less, glycerate 3-phosphate / GP / TP , produced ;
less RuBP, regenerated / formed ;


ppq) (ini)
Some plants, known as C4 plants, use an enzyme called PEP carboxylase, instead of Rubisco, to fix carbon dioxide.

suggest why these plants do not show photorespiration

oxygen not a substrate for / cannot bind to / will not compete for , PEP carboxylase


ppq) (b) In order to maximise production, market gardeners often grow plants in glasshouses.
Light conditions can be controlled along with a number of other factors.

How can factors other than light conditions be controlled to increase the rate of photosynthesis and maximise production?

In your answer you should explain why the rate of photosynthesis is affected by the controlled
factors you have discussed.

photosynthesis / named stage,
is controlled by / needs / involves / uses
(named photosynthetic) enzymes ;

temperature can be,
increased by heater /
reduced by ventilation (or fan)
maintained by air conditioning (or other method) ;

increase CO2 concentration (in environment) by burning,
fuel / gas / paraffin ;
idea that increased / more / higher, CO2 (conc),
so CO2 no longer a limiting factor /
increases COy fixation / (or described)
increases Calvin cycle (or described)

idea that easier to control,
water supply / irrigation (to prevent wilting) / humidity /
minerals / fertiliser;