Define photosynthesis
The process whereby light energy is transformed into chemical energy, and used to synthesise both organic and inorganic molecules
Define autotroph
Organisms that use light energy or chemical energy to synthesise complex organic molecules
Define heterotroph
Organisms that ingest and digest complex organic molecules, releasing the chemical potential energy stored in them
What were the first lifeforms on Earth
Chemoautotrophs
What are organisms that can photosynthesise called
Photoautotrophs
Why does respiration in autotrophs and heterotrophs depend on photosynthesis
The products of photosynthesis are the reactants of respiration. (and vv)
Where does photosynthesis take place
In the chloroplasts
What type of membrane does a chloroplast have
Double membrane
What is the difference between the two membranes
The outer one is permeable to small ions, the inner one is less permeable and has transport proteins embedded in it.
What is the inner membrane folded into
Lamellae, which are stacked up like pancakes. Each stack is a granum
What are the two regions of a chloroplast
Stroma and grana
What is the stroma
A fluid filled matrix, where the reactions of the light independent stage take place
What are photosynthetic pigments
Molecules that absorb light energy. They absorb a range of wavelengths in the visible region
What are the photosynthetic pigments organised into
Photosystems
Where are the enzymes needed to catalyse light-independent reactions held
The stroma
Which membrane are the photosystems held in
The thykaloid membrane
What type of chlorophyll is in the PPRC
A
What type of chlorophyll is in the accessory pigments
B (and cartenoids)
What is an accessory pigment
Light-absorbing compounds, found in photosynthetic organisms. They absorb wavelengths not well absorbed by chlorophylls and pass the energy to the PPRC
What is the structure of chlorophyll
Long phytol (hydrocarbon) chain and a porphyrin group
What are the two forms of chlorophyll
P680 and P700
What is photophosphorylation
The making of ATP from ADP and Pi in the presence of light
What are electron carriers
Molecules that transfer electrons
What are electron acceptors
Chemicals that accept electrons from another compound. They are reduced whilst acting as oxidising agents
Where does the light dependent stage of photosynthesis occur
On the thykaloid membrane
PS1 occurs mainly on…
… the intergranal lamellae
PS11 occurs mainly on…
… the granal lamellae
What is the process of splitting water with light called
Photolysis
In which photosystem does photolysis occur
PS11
What is the equation for photolysis
2H2O –> 4H+ + 4e- + O2
What is the oxygen produced by photolysis used for
Plant aerobic respiration
Human aerobic respiration (leaves through stomata)
Where do H+ and e- come from
Water
What process uses H ions to produce ATP
Chemiosmosis
What is NADPH used for
The reduction of carbon dioxide
Why is water needed in plants (other than source of H and e)
It is used to keep plant cells turgid
What is the word for light travelling in particles
A photon
What is the Endosymbiotic Theory
Photosynthetic bacteria were acquired, by endocytosis, by early eukaryotic cells.
Describe the process of non-cyclic photophosphorylation
- Light strikes PSII
- 2 electrons become excited and leave the chlorophyll molecule
- Electrons pass along electron carriers and release energy
- H+ passes through ATP synthesise and forms ATP
- These electrons, along with the protons from photolysis of water join NADP
- NADPH formed
Describe the process of cyclic photophosphorylation
- Light strikes PSI and 2 electrons are excited and pass to an electron acceptor/carrier
- Electron carrier moves down the ETC
- Small amounts of ATP are made.
- Electrons return to the PS1
What is a light dependent reaction
Takes place in the thylakoid membrane, use light energy to make ATP and NADPH
What is the light independent stage
The photosynthesis is where carbon dioxide is fixed and used to build complex organic molecules
What is the Calvin Cycle
The set of chemical reactions that take place in chloroplasts during the light independent stage of photosynthesis
Describe the Calvin Cycle
- CO2 diffuses through the stomata into the stroma
- CO2 combines with Ribulose Bisphosphate (enxzyme is rubisco)
- Glycerate-3-phosphate is created
- GP is reduced and phosphorlyated to Triose Phosphate (TP)- ATP and NADPH are used
- 5/6 molecules of TP are recycled by phosphorylation using ATP to three molecules of RuBP
What is a limiting factor
A factor that is present at the lowest or least favourable value
Name three limiting factors
Light
Water
Temperature
Chlorophyll presence
What are the three main effects that light has on a plant?
Light causes stomata open to increase carbon dioxide diffusing in.
Light is trapped by chlorophyll and excited electrons.
Light splits water to produce protons.
What stage of photosynthesis does temperature have an effect on?
The enzyme controlled reactions of the Calvin Cycle
What is used to measure the rate of photosynthesis
Photosynthometer
What are the three methods of measuring photosynthesis
- Volume of oxygen production per minute.
- Rate of uptake of carbon dioxide.
- Rate of increase in dry mass.
