Photosynthesis - Module 5

Question 1

Components of a chloroplast

Answer 1

-Outer membrane
-inner membrane
-Lamella
-Stroma
-Grana (made of thylakoids) (singular granum)
-Thylakoids

Question 2

stroma

Answer 2

-gel-like substance
-contains sugars, enzymes, organic acids
-Contains circular chloroplast DNA
-Carbs produced by photosynthesis, then stored as starch grains in stroma if not used

Question 3

Photosynthetic pigments

e.g

Answer 3

e.g, Chlorophyll a, chlorophyll b and carotene
Coloured substances, absorb light energy needed for photosynthesis

Question 4

Photosystem

Answer 4

The collective light harvesting system And reaction centre

Question 5

How can Water stress affect photosynthesis

Answer 5

When plants don’t have enough water, what will happen?
Stomata will close to preserve water
Less carbon dioxide will enter the leaf for the Calvin cycle and slow photosynthesis down

Question 6

As light intensity ( at the correct wavelength) increases, The rate of photosynthesis…

Explain why

Answer 6

Increases

As the light intensity increases, more stomata are open. Therefore more carbon dioxide can diffuse into the leaf for the Calvin cycle.

Question 7

As light intensity decreases, rate of photosynthesis ….

explain why

Answer 7

Decreases

As light intensity decreases, stomata close so less carbon dioxide. Less electrons excited in LD reactions.

Question 8

Effect of reduced light intensity on Light dependent reaction

Answer 8

Less ATP and NADPH made-> less electrons excited, less go through ETC, less energy to pump protons, less protons pass through ATP synthase.

Question 9

Effect of reduced light intensity on Light independent reaction:

Effect on GP,TP,RuBP

Answer 9

INITIALLY RuBP still combing with CO2 to make GP.

Levels of RuBP decreasing, levels of GP increasing.

GP can’t be reduced ( using NADPH and ATP) to make TP so level of TP decrease.
TP can’t be used to regenerate RuBP.

Question 10

WHAT HAPPENS TO THE Relative concentrations of GP, RuBP, TP

when there is a reduced light intensity

Answer 10

Relative concentrations:

GP- increasing as still being made

RuBP- decreasing

TP- decreasing

Question 11

Effect of Increased temperature on rate of photosynthesis

explain why

Answer 11

As temperature increases, so does rate of photosynthesis until optimum as molecules gain kinetic energy.

After this it decreases until no photosynthesis can take place.

High temperature – enzymes denature, stomata close and damage could occur to thylakoid membrane, chloroplast membrane and chlorophyll.

Question 12

Effect of lower temperature on rate of photosynthesis

Answer 12

Low temperature – less kinetic energy, reactions slower, enzymes inactive under 10ºC

Question 13

Effects of Low temps on relative conc. of RuBP, GP, TP

why

Answer 13

Low temps- all reactions will be slower
Levels of GP, TP and RuBP will all fall.

Question 14

Effects of extreme high temps on relative conc. of RuBP, GP, TP

why

Answer 14

High temperatures- enzymes denature e.g ATP synthase, RuBisCO.
Less ATP produced to reduced GP to TP and regenerate TP to RuBP
RuBisCO can’t catalyse reaction between CO2 and RuBP, less GP made so less TP made and less TP to regenerate RuBP
Levels of RuBP, GP and TP will fall.

Question 15

Effect of increased carbon dioxide concentration on rate of photosynthesis

Answer 15

As carbon dioxide concentration increases, so does rate of photosynthesis.

After 0.4%, stomata will close.

Question 16

Effect of decreased carbon dioxide concentration on rate of photosynthesis

Answer 16

Decrease- less CO2 for light independent reaction.

Question 17

Effects of decreased carbon dioxide concentration on relative conc. of RuBP, GP, TP

why

Answer 17

Less CO2 to combine with RuBP to form GP -> levels of GP fall.
Less GP to make TP, levels of TP fall.
Some RuBP still being made and not used so increases.

Question 18

What is the compensation point?

Answer 18

When the rate of photosynthesis equals the rate of respiration

Question 19

How would you describe the limits of a limiting factor graph with light intensity plotted against Rate of photosynthesis
(it increases and then plateaus)

(Point A is origin, Point B is where the graph plateaus)

Answer 19

Between A-B, rate of photosynthesis is limited by light intensity.
B= saturation point increasing light intensity at this point has no effect as something else is limiting.

Question 20

Which wavelengths are mainly absorbed by chlorophyll?

Answer 20

chlorophyll absorbs light in the red (long wavelength) and the blue (short wavelength) regions of the visible light spectrum. Green light is not absorbed but reflected, making the plant appear green.

Question 21

Photosystem-

Answer 21

Photosystem- Photosynthetic pigment + protein- found in thylakoid membrane. Funnel shaped

Question 22

Primary pigment

Answer 22

Primary pigment- reaction centres where electrons are excited during light-dependent reaction. Mostly chlorophyll a

Question 23

Accessory pigments

Answer 23

Accessory pigments- Make up light-harvesting systems which surround primary pigments and transfer light energy to them. E.g chlorophyll b, carotenoids

Question 24

Photosystem 1- Absorbs light best at a wavelength of ______

Answer 24

700nm

Question 25

Photosystem 2- Absorbs light best at a wavelength of ____

Answer 25

680nm

Question 26

Chlorophyll a absorbs mainly ____ and ___ light but reflects ______- reason leaves look green

Answer 26

blue red green

Question 27

Chlorophyll is not produced when there is ____ or ___ sunlight e.g _______ This means you can see other pigments in leaves such as __(a colour)____ ________

Answer 27

little no Autumn Orange carotenoids

Question 28

Two stages of photosynthesis

Answer 28

Light Dependent Light independent

Question 29

very Basic summary of Light Dependent Reaction

Answer 29

in thylakoid membrane Light energy is absorbed by photosynthetic pigments in the photosystems and converted to chemical energy Forms ATP and NADPH

Question 30

Basic summary of Light independent Reaction

Answer 30

in stroma - ATP and NADPH supply energy and hydrogen to make glucose from carbon dioxide.

Question 31

Light energy absorbed by photosystems is used for:

Answer 31

Making reduced NADP from NADP Photolysis- Splitting water into protons, electrons and oxygen using light energy. Making ATP from ADP & Pi = photophosphorylation ( adding phosphate to a molecule using light energy)  non-cyclic and cyclic

Question 32

Non-cyclic photophosphorylation

Answer 32

Light energy absorbed by PSII and excites electrons High energy electrons move along ETC to PSI As excited electrons leave PSII, photolysis of water occurs giving protons, electrons and oxygen electrons re-enter PSII Excited electrons lose(transfer) energy at each carrier in the ETC The energy is used to pump protons from stroma to thylakoid space, forming a proton gradient. Protons re-enter the stroma by facilitated diffusion through ATP synthase (chemiosmosis) Energy from this movement combines ADP + Pi to form ATP. This is photophosphorylation Light energy is absorbed by PSI which excites electrons again to a higher energy level Finally electrons are transferred to NADP , alongside a proton from the stroma, to form NADPH.

Question 33

Cyclic photophosphorylation

Answer 33

Only uses PSI Only forms ATP ( no NADPH or oxygen) Electrons aren’t passed on to NADP but are passed back to PSI by electron carriers- cyclic Electrons are recycled so can repeatedly pass back into PSI ATP is still formed by chemiosmosis- less than non-cyclic

Question 34

Basic summary of The light-independent stage ( The Calvin cycle)

Answer 34

Takes place in the stroma of the chloroplasts. Uses CO2 as a raw material. Uses NADPH and ATP from the light-dependent stage. Used to make organic substances.

Question 35

Calvin cycle summary

Answer 35

Carbon dioxide diffuses into stroma and combines with ribulose bisphosphate(5C)- catalysed by RuBisCO. FIXATION (CO2 is incorporated into an organic molecule) Forms a 6C unstable intermediate compound which splits up into 2 x glycerate-3 phosphate (3C). (GP can be used to make amino acids and Fatty acids) The GP is reduced by NADPH to form 2x triose phosphate. Energy from ATP is also used. REDUCTION 1 out of 6 TP molecules is used to form organic substances e.g glucose. (TP can also be used to make Glycerol which combines with Fatty acids made from GP to make Lipids) 5 out of 6 TP molecules are used to regenerate RuBP. REGENERATION

Question 36

What sugars + carbs are made from photosynthesis

Answer 36

-Hexose sugars- e.g Glucose -Starch -Cellulose -Fructose -Sucrose (glucose + fructose)

Question 37

Why would a leaf receiving only green light become more acidic/Lower the PH

Answer 37

-leaf reflects green light -(green light) cannot be used in photosynthesis/no LD reaction -little/no photolysis -little/no CO2 taken up/fixed -Some CO2 produced during respiration -(slight) increase in CO2, increases acidity/decreases pH -Accessory pigments absorb some green light

Question 38

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

Answer 38

-photosynthesis controlled by photosynthetic enzymes. -Temperature maintained via ___ (air con) -Increased Co2 conc, so is not limiting factor -easier to control water supply/irrigation/humidity/minerals/fertiliser -Biological control e.g: pesticides

Question 39

Herbicides interfere with electron transport by accepting electrons suggest how this may cause plants to die

Answer 39

no photophosphorylation, no ATP produced, no NADPH produced, no calvin cycle, no fixation of CO2

Question 40

When plants grow in glasshouse during winter, when natural light intensities are low, temperatures must be kept low too. with reference to respiration and photosynthesis, WHY?

Answer 40

light intensity limiting factor -low rate of photosynthesis -rate of respiration increases at higher temperatures -rate respiration close to/exceeds rate of photosynthesis -Sugars broken down more quickly than formed

Question 41

chromatography is used to

Answer 41

separate dissolved substances

Question 42

Stationary phase of chromatography

Answer 42

Paper

Question 43

Mobile phase of chromatography

Answer 43

Solvent

Question 44

Adsorption - chromatography

Answer 44

interactions with stationary phase -> stronger the adsorption, the slower the molecules move

Question 45

TLC ->

Answer 45

Thin layer chromotography

Question 46

why does the rate pf plant respiration decrease st night

Answer 46

daytime temperature is higher than night time temperature rate of respiration increases with higher temperatures as enzymes are temperature dependant

Question 47

when asked to describe how the student could improve the presentation of their data, what must you discuss

Answer 47

-Units shown -table presentation -headings -graph

Question 48

where does the light independent reaction take place

Answer 48

stroma