Topic 5: Photosynthesis Flashcards
What is the ultimate source of energy?
The Sun
Give the equation for photosynthesis
Carbon dioxide + water –> glucose + oxygen
Where does photosynthesis take place?
The chloroplasts
What substances do you find in the stroma of the chloroplast?
Lipid globules Starch molecules Circular DNA Ribosomes Grana Thylakoid Lamellae
What is chlorophyll?
A mixture of photosynthetic light-capturing pigments
Name the types of chlorophyll
Chlorophyll a
Chlorophyll b
Carotenoids
What colour is chlorophyll a?
Blue-green
What colour is chlorophyll b?
Yellow-green
Name some carotenoids and their colours
Carotene - orange
Xanthophyll - yellow
Phaeophytin - grey
What is the advantage of a plant have lots of different types of chlorophyll?
The plant can absorb a wider range of wavelengths of light so more light can be used
What wavelengths of light does chlorophyll a absorb?
Red-orange
Blue-violet
Which is the most abundant pigment?
Chlorophyll a
What is the purpose of accessory pigments?
Broaden the range of light that a plant can use - don’t take part in the light dependent reaction
What is an absorption spectrum?
Shows the wavelengths of light that a particular pigment absorbs as a graph of wavelength (x) against relative absorption of light (y)
What is an action spectrum?
Shows the wavelengths of light which bring about photosynthesis in a particular plant
What method can be used to identify which pigments are in a leaf?
Chromatography
Explain how chromatography can be used to identify which pigments are in a leaf
Grind up leaf and mix with propanone
Use capillary tube to spot a drop of the mixture onto a piece of paper with a pencil line
Dip it into solvent
Spots should separate
Calculate Rf values and compare to data book values
What are photosystems?
Complex arrangements of chlorophyll a and accessory pigments which can capture light to energise electrons
Where is PS 1 found?
Lamellae
Where is PS 2 found?
Grana
Which wavelengths of light does PS I absorb?
700nm
Which wavelengths of light does PS II absorb?
680nm
What are the two stages of photosynthesis?
Light dependent reaction
Light independent reaction
Were does the light dependent reaction take place?
Thylakoid membrane
What is the purpose of the LDR?
To produce ATP and to produce H+ ions to form NADP
In which part of the LDR is ATP produced?
Cyclic and non-cyclic
In which part of the LDR is NADH produced?
Non-cyclic
Describe what happens when a photon of light hits PSII
An electron is promoted to a higher energy level where it can leave the chlorophyll and pass onto another molecule
What is photolysis?
The splitting of water due to light
What happens in photolysis?
Water is split into 2H+. O- and 2e-
Why is photolysis needed in photosynthesis?
Because when an electron is excited and leaves PS II, the photosystem is positive so electrons are added to make it neutral again.
How are the products of photolysis used?
Electrons go into the photosystem
H+ ions used to reduce NADP
O2 let off as a waste gas
Summarise what happens in non-cylic phosphorylation
Light hits PSII
Electrons excited and leave PS
Get accepted by the primary electron acceptor
Passed down ETC where energy is released and ATP is produced
Goes into PSI. Light hits and electron excited and removed. Accepted by primary acceptor. Passed down ETC to the final electron acceptor NADP+
What is the ETC and how does it work?
Electron transport chain
Made up of a chain of electron carrier molecules, each with a greater affinity for electrons than the last which keeps electrons moving
Electrons are passed down in a series of redox reactions
What process forms ATP?
Photophosphorylation
How is ATP formed in the light dependent reaction?
Electrons move down ETC, releasing energy as they do
Energy used to drive a protein pump
Protons pumped across thylakoid membrane into the lumen
H+ conc builds up creating a proton gradient
Protons flow through ATP synthase by chemiosmosis down a proton gradient
Explain the differences between cyclic and non-cylic photophosphorylation
In cyclic, only PSI is used but in non-cyclic, both photosystems are used
In cyclic, only ATP is produced, but in non-cyclic ATP and NADPH are formed
Where does the light independent reaction occur?
Stroma
What is another name for the light independent reaction?
Calvin cycle
What is carbon fixation?
When RuBP reacts with carbon dioxide through the enzyme RUBISCO, forming an unstable 6 carbon compound
Summarise the Calvin cycle
RuBP + CO2 (+RUBISCO) to make a 6 carbon compound
6 carbon compound breaks down into two molecules of G3P
G3P reduced to GALP
2 molecules of GALP form a molecule of glucose
Explain how G3P is converted to GALP
NADPH loses a hydrogen which is picked up by the G3P
ATP is also used in the reduction
How many times does the Calvin cycle go around and what are the products
6 times
12 GALP molecules
6 glucose molecules
How is the glucose from the LIR used?
Used to make:
- lipids
- carbohydrates
- amino acids
Name the limiting factors of photosynthesis
Light intensity
Temperature
CO2 concentration
Why is light a limiting factor?
Affects amount of chlorophyll that’s excited
Affects amount of NADPH and ATP so less used in the LIR
Why is CO2 a limiting factor?
Affects carbon fixation
Why is temperature a limiting factor?
Photosynthesis is an enzyme controlled reaction
Temp will either denature enzymes or not provide enough energy for the enzymes to function
