3.5.1 Photosynthesis

Question 1

Movement of chloroplast in dim and intense light

Answer 1

In the night, chloroplast to aggregate at the top service of the cell, and to orientate themselves to display a large proportion of their service area to the incoming light rays

In intense light, chloroplast aggregate at the lower end of the cell and orientate themselves in a vertical position reduce the chance of damage to the chloroplast through bleaching

Question 2

The type of microscope for observing organelles, why?

Answer 2

TEM
Internal structure shown, high resolution
2D

Question 3

Method of studying internal structure in cell

Answer 3

Physically get out chloroplast by ultrifurcation
Tem microscope

Question 4

Internal structure of chloroplast

Answer 4

Inner and outer membrane (envelope)
Stroma
Ribosome
Lamellae
Granum/ Grana (p)
Thylakoids
Circular dna molecule
Lipid Droplets

Question 5

Leaf structure inside adaptation

Answer 5

Microscopic adaptations
● Transparent cuticle and epidermis to allow light through & waxy layer to reduce water loss
● Palisade cells packed with chloroplasts to absorb sunlight
● Numerous stomata for gas exchange (so that every mesophyll cell is only a short diffusion pathway from a stomata)
● The stomata open and close in response to light intensity
● Many air spaces to allow rapid diffusion
● Xylem that brings water to the leaf and phloem that carries away the sugars produced

Question 6

Leaf adaptation

Answer 6

● Large surface area to absorb as much sunlight as possible
● Leaf arrangement on the plant to minimise overlapping to avoid shadowing
● Thin - short diffusion pathway for gases

Question 7

Why iron deficient plant have a reduced growth rate, with less thylakoid membrane

Answer 7

1. Less (thylakoid) membrane OR Fewer/smaller grana;
2. Smaller surface area (of membrane in chloroplast)/less chlorophyll;
3. (Less chlorophyll so) reduced light absorption;
4. (So) slower rate of photosynthesis;
   Accept reduced rate of any named biochemical process in photosynthesis; eg. reduced production of ATP/reduced NADP

Question 8

Describe how a sample of chloroplasts please could be isolated from leaves

Answer 8

1. Break open cells/tissue and filter
   OR
   Grind/blend cells/tissue/leaves and filter; Accept homogenise and filter
2. In cold, same water potential/concentration, pH controlled solution;
   Accept for ‘same water potential/ concentration’, isotonic Accept for ‘pH controlled’, buffered
3. Centrifuge/spin and remove nuclei/cell debris;
4. (Centrifuge/spin) at high(er) speed, chloroplasts settle out;

Question 9

Describe the function of chloroplast

Answer 9

Absorb light
for photosynthesis
Produce carbonhydrate/ sugar/ lipid / protein

Question 10

Stages of photosynthesis

Answer 10

Capturing of light energy - by chloroplast pigments
The light-dependent reaction (LDR) - some of the light energy that was absorbed is conserved in chemical bonds (takes place in the thylakoid membranes)
The light-independent reaction (LIR) - sugars and other organic molecules are produced (takes place in the stroma)

Question 11

Redox reaction involved in photosynthesis

Answer 11

Hydrogen
reduce = gain electron, gain hydrogen ,lost oxygen
Oxidised = Lost electron ,lost hydrogen ,gain oxygen

Question 12

Coenzyme work, and name in photosynthesis

Answer 12

Transferring a chemical group from one molecule to another
NADP transfer hydrogen, it can be reduced ( carry h) or oxidised (not carrying h)

Question 13

Photosynthetic pigments - light absorbing molecules (location, characteristic and 2 types) (5)

Answer 13

Chloroplast pigments, located on the membranes of the thylakoids, absorb
light. These pigments have hydrophobic (lipophilic properties).
In flowering plants, there are two major groups of chloroplast pigments:
1. Chlorophylls
- Chlorophyll a is the commonest and is found in all photosynthetic organisms (blue Green)
- Chlorophyll b is found in flowering plants (yellow green)
- Phaeophytin, a breakdown product of chlorophyll a molecule (grey)
2. Carotenoids
- Carotenes: α- and β-carotene are orange (but lycopene, found in tomatoes is bright red)
- Xanthophylls, such as lutein and zeaxanthin, appear yellow

Question 14

One other molecule that absorb light other than pigment

Answer 14

Magnesium ion absorbs light of specific wavelengths

Question 15

Definition of absorption and action spectrums

Answer 15

The absorption spectrum indicates the wavelengths of light absorbed by each pigment (e.g. chlorophyll)
The action spectrum indicates the overall rate of photosynthesis at each wavelength of light

Question 16

Why red and blue light are more effective for photosynthesis?

Answer 16

Chlorophylls absorb wavelengths in the blue-violet and red regions of the light spectrum
They reflect green light, causing plants to appear green

Carotenoids absorb wavelengths in the blue-violet of the light spectrum

Question 17

The advantage of having five Pigment

Answer 17

Each pigment absorbs a different wavelength of light
Plants are adapted to the environment of having different proportion of each pigment
To maximise the absorption of sunlight
Increase the variation of wavelength of light absorption
Increase the rate of photosynthesis

Question 18

Photoionisation

Answer 18

Light energy is absorbed it by chlorophyll
Light energy excite the electron in the chlorophyll
Electron gains energy and move to higher orbit
Eventually released from chlorophyll molecule (oxidation)
Chlorophyll molecule is now a positively charged ion

Question 19

Procedure to separate biological compounds using thin layer/paper chromatography

Answer 19

Describe the procedure
1. Draw line/origin on chromatography paper or TLC plate (using ruler and pencil)
2. Use a pipette /dropper/ paint brush to add the pigment extract (chlorophyll) on the origin
3. Add solvent making sure it is below line/origin;
4. Remove/ the TLC plate / paper from glassware before the solvent reaches end of chromatography paper
OR
Mark the position of the solvent front (where it reach)

Analysis
Measure the distance travelled by the pigment and the distance travelled by the solvent to calculate an Rf value for each pigment.

Question 20

Explain why the student makred the origin usnig pencil rather than usnig pen in chromatography

Answer 20

Ink and (leaf) pigments would mix OR
(With ink) origin/line in different position OR
(With pencil) origin/line in same position/ visible

Ink from the pan with dissolve in the solvent and run

Question 21

Describe the method the student used ot separate the pigments after the solution of pigments had been applied to the origin in chromatography

Answer 21

.1 Level of solvent below origin/line;
.2 Remove/stop before (solvent) reaches top/end;

Question 22

The pigments ni leaves are different colours. Suggest and explain the advantage of having different coloured pigments ni leaves.

Answer 22

Absorb more different wavelength of light for photosynthesis

Question 23

Describe what happens during photoionisation in the light-dependent reaction.

Answer 23

Chloro view absorb light energy
Light energy excite the electron to higher orbit
Eventually, electron is lost
Chlorophyll become positively charged it

Question 24

In chromatography experiment, why should you measure the RF value from the middle of the pigment Mak?

Answer 24

Pigment mark his spread out by measuring from the position each time it is a way to standardised to measure you are taking to allow for comparison

Question 25

In chromatography experiment, why should you draw a line where the servant reach immediately?

Answer 25

Dissolvent evaporate rapidly so the end position is not visible shortly after the experiment

Question 26

In chromatography experiment, why should you make sure your chrotography paper is vertical is stripped?

Answer 26

So the pigment moves straightup the paper to avoid them running off the side of the paper or being washed off

Question 27

Why lowering the temperature has very lead to effect on the light dependent reaction but it slow down the light independent reaction

Answer 27

Light dependent reaction
Light is the main source for photochemical reaction , citation of electron is not related to temperature only related to light intensity

Light independent reaction
Rely on enzyme in stroma
Lower temperature , less kinetic energy, less collision, less enzymes substrate complex, lower rate of further synthesis

Question 28

Explain what caused the amount of radioactively labelled glucose to decrease after the light was switched off

Answer 28

Respiration
Making cellulose, sucrose, starch

With last TP, have less glucose still increase

Question 29

In the experiment of cell use in photosynthesis were supplied with radioactive label ,explain why

Answer 29

Follow carbon pathway through photosynthesis process / use in photosynthesis s and detect product

Question 30

Explain why after the light source is switch off GP increase and RuBP decreased?

Answer 30

➔ Light dependent reaction stops when the light is turned off.
➔ Therefore no ATP and NADPH is made.
➔ This means that GP cannot be converted into TP, so GP accumulates, increasing in concentration.
➔ TP levels decrease, therefore less TP is available to be recycled back through the Calvin cycle to RuBP, therefore less RuBP is made and the concentration decreases.

Question 31

Abiotic factor of photosynthesis

Answer 31

Light intensity and duration
Carbon dioxide concentration
Temperature

Water (close stomata)
Quality of soil (making organic molecule)

Question 32

Abiotic factor of photosynthesis

Answer 32

Light intensity and duration
Carbon dioxide concentration
Temperature

Water (close stomata)
Quality of soil (making organic molecule)

Question 33

Describe limiting factor graphs

Answer 33

As x increase , y increase
Until (a point ), above that point x increase y do not increased, other is limiting factor
[Light intensity\ carbon dioxide]

Above optimum temperature x increased y do not increased, other is limiting factor

Question 34

Definition of limiting factor

Answer 34

A factor that has the least favourable value and therefore limits the rate of a process
As it increased the rate of photosynthesis increased

Question 35

Explain the graph of light intensity as limiting factor of photosynthesis

Answer 35

As slight intensity increased more energy is available and the rate of photosynthesis increased

Common dioxide level began to limit the reaction

No further increase can occur without more common dioxide

Question 36

Chloroplast adaptations

Answer 36

Thylakoid membranes provide a large surface area for chlorophyll, ETC proteins and enzymes.
Thylakoid membranes have ATP synthase channels, which use the hydrogen ion gradient to catalyse the formation of ATP.
They have DNA and ribosomes to synthesise some of the proteins involved in the LDR and LIR.
The stroma contains enzymes needed for the LIR.
The stroma surrounds the grana, so the products of the LDR can readily diffuse into it for use in the LIR

Question 37

Suggest why the teacher said, studying the date her with her student that no definite conclusion could be drawn when comparing the main value in the graph of bar chart

Answer 37

There’s no standard deviation and error bar show
If there’s overlap of Error bar , there is no significant difference between mean value, any difference is due to chance

Question 38

Atrazine bind to protein in electron transfer train in chloroplast of wheat, reducing the transfer of electrons down the chain. Why the weeds will give off small amount of heat

Answer 38

Heat energy is released from high energy/ excited electrons that were lost from chlorophyll

Question 39

Using solvent A student separate five pigment she then repeats her method using a different solvent B using solvent B she separate six pigment explained the difference between these result

Answer 39

Two pigments have same solubility in a the difference B
Or
One pigment is soluble in B but not in A

Question 41

Light dependent reaction

Answer 41

Chlorophyll absorbs light energy.
Electrons in chlorophyll are excited and move from chlorophyll into the electron transfer chain (photoionisation of chlorophyll).
Electrons release energy as they move through the electron transport chain.
The release of energy is used to create a proton (H+) gradient across the thylakoid membrane. The energy stored in the proton gradient is used to join ADP to Pi to form ATP.
Photolysis of water occurs, releasing electrons, protons and oxygen (which diffuses out through the stomata). The electrons replace those lost by the excitation of chlorophyll.
The electrons are transferred from the electron transport chain to NADP forming reduced NADP (NADPH).
ATP and NADPH are used in the Light Independent Stage (LIR)

Question 42

Light independent reaction

Answer 42

❏ Carbon dioxide reacts with a 5 carbon acceptor molecule (RuBP)
❏ The reaction is catalysed by Rubisco.
❏ The products are two 3 carbon acids called GP.
❏ 2GP is reduced to two 3 carbon sugars called Triose Phosphate (TP).
❏ Reduced NADP/NADPH (made in the LDR) provides the
hydrogen/electrons to reduce GP to Triose Phosphate.
❏ The conversion of GP to Triose phosphate also requires energy from
the hydrolysis of ATP (made in the LDR).
❏ One sixth of the TP molecules are used to make glucose (and other
organic molecules)
❏ 5⁄6 of the TP is used to regenerate RuBP (5C acceptor) molecules.
❏ ATP is also required to transfer a phosphate group during the
regeneration of RuBP