3.2 photosynthesis

write the equation for photosynthesis

6CO2 + 6H20 → C6H12O6 + 6O2

why are chloroplasts known as transducers?

they convert energy in the photons of light into chemical energy

label the chloroplast

where is the main site of photosynthesis in the leaf?

palisade mesophyll cells

how is the feature of the leaf efficient for gas exchange: large surface area?

larger sa = more stomata

how is the feature of the leaf efficient for gas exchange: thin?

short diffusion pathway for gases entering/leaving the leaf

how is the feature of the leaf efficient for gas exchange: air spaces in spongy mesophyll tissue?

allows O₂ and CO₂ to diffuse more easily between stomata and cells

how is the feature of the leaf efficient for gas exchange: stomatal pores?

gas exchange in and out of leaf

in englemann’s experiment why did the bacteria cluster in the red and blue regions of the spectrum?

• wavelengths of light absorbed the most

• higher rate of light dependent stage

• more photolysis of water to release O2

• bacteria need O2 for aerobic respiration

in englemann’s experiment why are there no bacteria present on the green regions?

very little green light absorbed/it is reflected

what is a suitable control for englemann’s experiment?

use white light only

bacteria would distribute evenly across the tube

shows different wavelengths of light are causing the distribution seen in the experiment

what is a pigment?

a coloured substance that absorbs specific wavelengths of light

what are the 2 main classes of photosynthetic pigments?

chlorophylls

carotenoids

what are the different types of chlorophylls?

chlorophyll a - primary pigment

chlorophyll b/c - accessory pigments

what are the different types of carotenoids?

carotenes and xanthophylls - both accessory pigments

how would a lack of Mg result in poor growth in a plant?

• lack of Mg so lack of chlorophyll

• plant cannot absorb as much light energy

• less light dependent stage

• less ATP and NADPH for light independent stage

• rate of photosynthesis decreases

• less glucose for respiration

• less ATP for protein synthesis/cell division

what graph is this?

absorption spectrum

what graph is this?

action spectrum

what does an absorption spectrum show?

how much light energy a particular pigment absorbs at each wavelength

what are the advantages of having multiple pigments?

can absorb a wider range of wavelengths

more light dependent stage

more ATP and NADPH for light independent stage

rate of photosynthesis increases

what does an action spectrum show?

rate of photosynthesis at different wavelengths of light

what does the correlation between action and absorption spectrum suggest?

close correlation

photosynthetic pigments responsible for absorbing light energy in photosynthesis

where are the photosystems located?

thylakoid membranes

what is each photosystem made up of?

antenna complex

reaction centre

what is the antenna complex?

clusters of up to 400 photosynthetic pigments

anchored into phospholipids of thylakoid membrane

allows range of wavelengths to be absorbed

what is the reaction centre?

at base of antenna complex

2 molecules of primary pigment cha

label the photosystem

photosystem I (PSI)?

absorption peak of 700nm

P700

richer in chlorophyll a than b

photosystem II (PSII)?

absorption peak of 680nm

P680

richer in chlorophyll b than a

what are the 2 stages of photosynthesis?

light dependent stage

light independent stage

what is the light dependent stage split into?

non-cyclic photophosphorylation

cyclic photophosphorylation

talk through non-cyclic photophosphorylation

The chlorophyll a in the reaction centre of photosystem II absorbs light energy, which causes 2 high energy electrons to be emitted to a higher energy level

The electrons are received by an electron acceptor

The photolysis of water occurs (H2O -> 2H+ + 2e- + 1/2O2) and the 2 electrons reduce the chlorophyll a in the reaction centre of PSII so it becomes stable

The high energy electrons move along the etc from one electron carrier to another, losing energy to fuel the 1 proton pump so it can pump protons from the stroma into the thylakoid space, setting up an electrochemical gradient

The protons diffuse down an electrochemical gradient through the stalked particle and ATP synthase, releasing energy which is used for ADP + Pi -> ATP by photophosphorylation

The chlorophyll a in the reaction centre of PSI absorbs light energy and emits 2 high energy electrons to a higher energy level

PSI is reduced by the 2 electrons from chlorophyll a in the reaction centre of PSII

2H+ + 2e- + NADP -> NADPH2 (NADP acts as the final electron acceptor)

The NADPH2 is used in the Calvin cycle