Photosynthesis (C1)

Question 1

Role of chloroplasts

Answer 1

act as TRANSDUCERS converting the energy of light PHOTONS into the CHEMICAL energy of
ATP

Question 2

Name the primary photosynthetic pigment

Answer 2

chlorophyll a :
absorbs BLUE and RED wavelengths of light
(reflect green)

Question 3

Name the accessory photosynthetic pigments

Answer 3

chlorophyll b :
absorbs BLUE and RED wavelengths of light
(reflect green)

carotenoids i.e xanthophyll and carotene :
absorb violet/blue light
(reflect orange- think carrot)

Question 4

What is the ABSORPTION spectra/spectrum?

peaks? dips?

Answer 4

a graph that shows the amount of light absorbed by each photosynthetic pigment at each wavelength

• peaks mean more absorbents of that wavelength
• those with no peak are the wavelengths reflected, the colour we see

Question 5

Advantage of plants having more than one pigment in their leaves

Answer 5

the accessory pigments can absorb WIDE RANGE of wavelengths

Question 6

What is the ACTION spectra/spectrum?

Answer 6

a graph that shows the rate of photosynthesis at different wavelengths of light

Question 7

Describe the relationship between the absorption and action spectra graphs

Answer 7

CLOSE CORRELATION between the two, suggesting that the pigments are responsible for absorbing the light used in photosynthesis

Question 8

What is the chromatography experiment used for?

Answer 8

• used to separate photosynthetic pigments

Question 9

Chromatography method

Answer 9

1. tear up leaves, grind with acetone (this dissolves the phospholipid membrane to extract pigments) forming a pigment
2. use capillary tube to spot pigment on chroma. paper
3. place paper into solvent i.e acetone/petroleum (this dissolves solute to carry pigment up paper)
4. remove paper once solvent reaches the top strip, observe different distances pigments travelled (moved further = more soluble)
5. calculate Rf values and compare to known values

Question 10

What is the Rf calculation?

Answer 10

distance travelled by solvent

Question 11

Photosystems: where? role?

Answer 11

• found on thylakoid membrane of chloroplast

- transducers; light energy to high energy electrons which can fuel proton pumps thus synthesis of ATP

Question 12

The process of light harvesting in the photosystem reaching the reaction center

Answer 12

The accessory pigment group with associated proteins forming an ANTENNA COMPLEX which harvests light energy and passes the excitation to the REACTION CENTRE (from one pigment molecule to another). At the reaction centre, two excited chlorophyll a molecules can each emit one electron to a higher energy level

Question 13

Light dependent reaction: occur? required? produced?

Answer 13

• light dependent reactions occur in the THYLAKOID MEMBRANES and thylakoid CAVITY
• require light energy and water (photolysis)
• light energy is transformed to chemical energy in ATP and NADPH (oxygen as a by-product of photosynthesis)
• photophosphorylation of ATP can be cyclic or non-cyclic

Question 14

Adaptations of leaves for photosynthesis

Answer 14

stoma - allows gas exchange
large surface area - max amount of light absorbed
thin - light penetrates all layers of leaf
air spaces in spongy mesophyll - co2 can diffuse in to photosynthesizing cells

Question 15

What’s an antenna complex?

Answer 15

accessory pigments grouped to associated proteins which absorb photons of light energy and funnel this energy downwards

Question 16

Explain Non-cyclic photophosphorylation (aka the Z scheme)

Answer 16

• photons of light energy are absorbed by a pigment molecule of the antenna complex of PS II; the excitation is passed to the pair of chlorophyll a molecules in the reaction centre;
• each has one of their many electrons boosted from their ground state, to an excited state;
• the excited electrons pass to electron acceptors, leaving the chlorophyll a molecules oxidised, they then pass via a series of electron carriers/ETC (e- energy levels lower and released fueling the proton pumps)
• electron transfer is linked to proton pumping (via one proton pump) from the stroma into the thylakoid space, raising its proton/h+ concentration in thylakoid cavity and lowering the pH, electrochemical gradient is formed
• protons then flow down their gradient, through ATP synthetase, releasing energy to form ATP;
• photons of light energy are absorbed by a pigment molecule of the antenna complex of PS I and the energy is passed to the pair of chlorophyll a molecules in the reaction centre;
• each has one of their many electrons boosted from their ground state, to an excited state;
• the excited electrons can each reduce an electron acceptor, which pass an electron to oxidised NADP, reducing it. Each NADP receives two electrons and picks up two hydrogen ions from the stroma to become reduced NADP (NADPH + H+) - final electron acceptor
• photolysis (splitting of water using light) creates two h+ and two e- and by product water, these e- replace those lost at PSll

Question 17

Explain the process of cyclic phosphorylation

Answer 17

In cyclic photophosphorylation
• only PSl involved: excited electrons from PSI can pass from the electron acceptor to the electron carriers and back, via the proton pump, to PS I therefore ATP is produced through chemiosmosis but no reduced NADP

Question 18

Explain the photolysis of water

Answer 18

• molecules of water within thylakoid spaces are split into hydrogen ions, electrons, oxygen and reformed water;
• the electrons replace those lost by the chlorophyll a of photosystem II;
• light is responsible only indirectly for splitting water

Question 19

Where do light independent reactions (Calvin cycle) occur?

Answer 19

light independent reactions (Calvin cycle) occur in the

STROMA of the chloroplast

Question 20

What does the Calvin cycle consume (use/fix) to produce?

Answer 20

the Calvin cycle consumes CO2 and energy from ATP and reduced NADP so organic chemicals e.g. carbohydrates/glucose are produced

Question 21

Name the 3 stages of the light independent reaction

Answer 21

1. co2 fixation
2. reduction
3. regeneration

Question 22

Name the steps that occur in the light-independent reactions (Calvin Cycle)

Answer 22

• uptake and fixation of carbon dioxide by 5C (RuBp) ribulose bisphosphate (using the enzyme, Rubisco) to form 6C unstable compound which forms 2 x 3C glycerate-3-phosphates (GP);
• utilisation of ATP (to ADP) and reduced NADP (becomes oxidized) from the light dependent reactions to reduce glycerate-3- phosphate to the 3C carbohydrate, triose phosphate (TP);
• out of the 6 carbons left ( two times 3C triose phosphate) one is used to produce organic molecules i.e glucose therefore 5 carbons remain
• then ribulose bisphosphate (5C)is regenerated, via ribulose phosphate (requires ATP)

Question 23

Factors affecting the rate of photosynthesis and why?

Answer 23

1. TEMPERATURE - affects enzyme activity thus the Calvin cycle is only affected: more KE, more successful collisions, increase in rate unless surpassing optimum temp which denatures enzyme (LID is more affected and reactions speed up more than the LDS creating a lag)
2. CONCENTRATION OF CO2 - during phs co2 is fixed to form organic molecules, co2 makes up a small % of the atmosphere therefore can be a limiting factor (if concentrations become to high, co2 will dissolve in water forming carbonic acid, lowering the ph making the leaf more acidic)
3. LIGHT INTENSITY - essential for excitation of electrons and for photolysis in LDR, as light intensity increases the rate of cyclic and non cyclic phosphorylation does too, ATP and NADPH are produced faster, entering the Calvin cycle, thus increasing rate pf phs

Question 24

Roles of nitrogen (nitrates) and magnesium (magnesium ions/ Mg2+) in plants

Answer 24

• nitrogen - synthesis of proteins, nucleic acids and
chlorophylls - associated proteins (nitrogenous bases in these molecules)
• magnesium - constituent of chlorophyll

*may become limiting factors to metabolism, if in short supply

Question 25

In the Calvin cycle what can be produced from the triose phosphate when 1C is removed?

Answer 25

• carbohydrates i.e glucose - actually fructose bisphosphate
• lipids
• amino acids {with the addition of nitrogen obtained
from nitrates}