5.2.1 Photosynthesis

Question 1

Describe 2 differences between the respiration and photosynthesis reactions

Answer 1

Respiration breaks down glucose whereas photosynthesis produces glucose
Respiration releases energy to use in metabolic processes however photosynthesis uses energy in the form of light photons to fix carbon

Question 2

Explain why the compensation point in plants is only seen at 2 points in a 24 hour period

Answer 2

CP= rate of respiraion= to rate of photosynthesis
During day, more sunlight photosynthesis takes over
During night, respiration is more dominant
Only equal in specfic points during night becoming day,vise versa

Question 3

Explain the importance of ribosomes in the chloroplast

Answer 3

Produce the enzymes required for photosynthesis in the chloroplast

Question 4

Explain the function of the thylakoid membrane

Answer 4

Site of light dependent reaction
Contain chlorophyll pigments which absorb photons to excite electrons
Provide the site of ETC, needed for ATP synthesis

Question 5

Describe the structure,location and function of photosystem in plant cells

Answer 5

Funnel shaped structure in the thylakoid membrane of the chloroplast
Contain photosynthetic pigments,with accessory pigments surrounding the primary pigment reaction centre
Different photosynthetic pigments in the photosystems each absorb specfic wavelenghts and trap energy

Question 6

Explain how the light energy that is harnessed in the light dependent reaction is stored and used in cells (cyclic photophosrylation)

Answer 6

Light energy excites electrons in the chlorophyll molecule of the cell (photoionisation), light energy photolyses water, forming H+ and electrons, which replaces electrons from photoionisation and passes down ETC. Provides energy for ATP synthesis in ATP synthase

Question 7

Summarisenon cyclic photophosrylation

Answer 7

Uses PSII to produce ATP and reduced NADP

Question 8

Explain the role of PSI and PSII in the light dependent reactions of photosynthesis

Answer 8

Energy from light is absorbed in chlorophyll in PSI and PSII which excites chlorophyll electrons, electrons leave chlorophyll and are picked up by electron carriers in the thylakoid membrane . Electrons passed along electron carriers in a series of reduction and oxdation reaction, forms ETC. Energy prod from these reactions pump h+ into the inner membrane space. Photolysis occurs to prod electrons to replace the ps II electrons
Reduced NADP via electrons from PSI chlorphyll

Question 9

Where does the light independent stage occur and explain why the enzyme catalysing the Calvin cycle is described as rate limiting enzyme

Answer 9

Stroma
Carbon fixation of CO2, prod 2 GP molecules that either prodcues glucose or restarts the cycle
Reaction cycle can only occur as fast as the enzyme can work to incorporate CO2 into organic molecule

Question 10

Describe the role of ATP and reduced NADP produced by light dependent stage

Answer 10

Role of NADP provide hydrogen that reduces the GP to TP
energy required to fuel the reaction is ATP
ATP provide 4 TP into RuBP

Question 11

Describe the first stage of the Calvin Cycle, stating the number of carbon atoms in the reactants and product

Answer 11

CO2 combine with RuBP(5C) by the action of RuBisCo to produce a 6 carbin compound which immediatley splits to form two molecules of GP(3C)

Question 12

Describe 3 uses of TP in the body

Answer 12

make a molecule of glucose
Synthesise useful organic molecules like AA, fatty acids and glycerol
TP recycled to regenerate the supply of RuBP

Question 13

State 3 factors that affect the rate of photosynthesis

Answer 13

Temperature
Light intensity
CO2 concentartion

Question 14

Explain how low light intensity affects the rate of photosynthesis

Answer 14

Light energy needed for light dependent stage
Light is used in photolysis, prod H+ and electrons, replacing those that were lost in photoionisation
Light is used in phtoionisation, exciting electrons which produces ATP and NADP required to catalsyse the light independent stage

Question 15

What is a photosynthometer and what formulas required

Answer 15

Measures the rate of photosynthesis using the product oxygen which forms a bubble
LI= 1/d2
Volume gas collected = length of bubble x pie x r2

Question 16

State one factor that must be controlled in the photosynthometers

Answer 16

Temperature
Photosynthesis relies upon catalysed by enzymes, rates affeceted by temperature
Controlling other variables ensures that only light intensity is affecting the rate of photosynthesis

Question 17

Which area do hydrogen ions build up inside a chloroplast

Answer 17

Thylakoid lumen

Question 18

How is light harvested in the chloroplast membrane

Answer 18

Primary and accessory pigments are formed in an antenna compelx
Photon absorbed by pigment moleucle
Energy passed from one pigment to another
Passed to reaction centre

Question 19

Where do light dependent and light independent reactions occur in plants

Answer 19

Light dependent - in the thylakoids of chloroplast

Light independent - stroma of chloroplast

Question 20

Define photosynthetic pigments

Answer 20

Embedded in thylakoid membranes within chloroplast, attached to proteins (photosystem)
E.g chlorophyll a, chlorophyll b, carotene
Variety of pigments to widen the range of wavelengths of light they can absorb
Important in shaded conditions

Question 21

Name the processes in the light dependent reaction

Answer 21

Photoionisation, ETC, chemiosmosis

Non cyclic only: reduction of NADP,photolysis of water

Question 22

Describe the steps in non cyclic photo phosphorylation

Answer 22

Light energy is absorbed by PS2, electrons in PS2 reaction centre are excited, electrons are taken up by electron acceptors, passed along an electron transport chain to PS1,energy is released, ATP synthesised by chemiosmosis, photolysis- water split into protons, electrons, oxygen. Electrons replace the lost electrons in PS2, light energy absorbed by PS1, electrons are taken up by electron acceptors, passed along an ETC to NADP, energy is released, ATP synthesised by chemiosmosis,electrons from PS2 replace the electrons lost at PS1
NADP final electron acceptor, takes up the electrons and H+ ion (in stroma - H+ from photolysis of water) and forms reduced NADP

Question 23

Describe cyclic photophosphorylation

Answer 23

Uses only PS1, excited electrons enter ETC to produce ATP then return directly to phosystem- no reduction of NADP and no water needed to replace lost electrons
Purpose is to produce additional ATP to meet surplus energy demands of cell

Question 24

What happens to the products of the photolysis of water

Answer 24

H+ ion - move out thylakoid space via ATP synthase and are used to reduce the coenzyme NADP
e- replace electrons lost from chlorophyll
O2- used for respiration or diffuse out of leaf as waste gas

Question 25

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

Answer 25

NADP+ 2 H+ + 2e-(from acting as final acceptor in ETC) -> reduced NADP
catalysed by dehydrogenase enzymes
Stroma Of chloroplast

Question 26

Explain the process of ATP synthesis by chemiosmosis

Answer 26

1) excited electrons lose energy as they move along the ETC
2) energy used to actively transport protons (H+) from stroma across the thylakoid membrane into the thylakoid space via proton pumps where they collect
3) thylakoid concentration of protons > stroma
4) proton gradient across the thylakoid membrane
5) protons move down the electrochemical gradient into the stroma via ATP synthase
6) energy from this,combines ADP and inorganic phosphate (Pi) to form ATP

Question 27

What is the light energy absorbed in the photosystem used for in light dependent stage

Answer 27

Photophosphorylation - making ATP from ADP and Pi, using light energy
Making reduced NADP from NADP,h+,2e-
Photolysis - splitting water into protons (H+) , electrons and oxygen

Question 28

What is the purpose of photolysis

Answer 28

Light energy split molecules of water
Products: H+ ions move out of thylakoid space via ATP synthase and are used to reduce coenzyme NADP to reduced NADP
Electrons : replace electrons lost at PS2 reaction centre (p680)
Oxygen - used for respiration or diffuse out of leaf as by product

Question 29

Define the key terms of: metabolic pathway, phosphorylation, photophosphorylation, photolysis, hydrolysis, decarboxylation , dehydrogenation, redox

Answer 29

MP- series of small thread of reactions controlled by enzymes
Phosphorylation - Addition of phosphate group to a molecule
Photo - addition of phosphate group to a molecule, using light
Photolysis - splitting of a molecule using light energy, hydro - using water
Decarboxylation- removal of CO2 from a molecule
Dehydrogenation - removal of hydrogen from a molecule
Redox reaction - reactions that involve oxidation and reduction

Question 30

How are coenzymes involved in photosynthesis

Answer 30

NADP
transfers hydrogen from one molecule to another (can reduce or oxidise a molecule)
Can be reduced to from reduced NADP or NADPH

Question 31

What is the difference between non cyclic and cyclic photophosphorylation

Answer 31

Non cyclic - products are ATP,reduced NADP,O2 ATP and reduced NADP used in Calvin cycle, o2 by product, electrons don’t come back to the same molecule,involves both PS1 and PS2, photolysis involved, first electron donor is water, last electron acceptor is NADP
CYCLIC- products is ATP, Electrons came back to same molecule, involves PS1 only, fist and last electron acceptor is PS1

Question 32

What are the roles of ATP and reduced NADP in the light independent reaction

Answer 32

ATP: reduction of GP - TP

Reduced NADP- coenzyme transport electrons needed for reduction of GP to TP

Question 33

Outline the steps in the light independent reaction

Answer 33

Occurs in the stroma
Carbon fixation - RuBP(5C) combined with CO2, catalysed by RUBISCO, unstable 6C compounds form, quickly broken down to 2 GP (3C) molecule
Reduction - 2 ATP(provides energy) and 2 reduced NADP (provides H+) used to convert 2 gp to 2 TP (3C), reduced NADP is recycled to NADP, used again in light dependent stage,
Regeneration - 5 of every 6 molecules of TP produced, regenerate RuBP,aid of ATP, remaining TP molecules are a starting material of essential organic compounds - lipids etc

Question 34

Outline the importance of photosynthetic pigments in photosynthesis

Answer 34

Pigments absorb photons which makes electrons excited
Accessory pigment pass energy to primary pigments , primary pigments become oxidised and pass electrons to ETC
For light dependent reaction

Question 35

Plan an investigation into the rate of transpiration in 2 species of plant that would allow valid data to be collected

Answer 35

Set up a potometer, submerge leaves underwater and cut the stem at an angle, let leaf acclimatise
Movement of bubble in potometer measured, timing distance travelled by bubble, calculate mean
And control variables: surface area of leaves, wind movement, humidity

Question 36

Give 3 properties of cellulose that makes it suitable as the basis of plant cell walls

Answer 36

Insoluble, high tensile strength, flexible, can form hydrogen bins with neighbouring chains