3.5 - 3.5.1 Photosynthesis (A-level only) Flashcards
In what cell of a plant does photosynthesis take place?
Chloroplasts.
True or false?
Chloroplasts are flattened organelles surrounded by a double membrane.
True.
What are thylakoids?
They are fluid-filled sacks and are stacked up in the chloroplast into grand (singular = granum). These grana are linked together by bits of the thylakoid membrane called lamellae (singular = lamella).
What pigments do chloroplasts contain?
Photosynthetic pigments.
What are examples of the photosynthetic pigments?
Chlorophyll a, chlorophyll b and carotene.
What are photosynthetic pigments?
Coloured substances that absorb the light energy needed for photosynthesis.
Where are the photosynthetic pigments found? + What are they attached to? + What are they called together?
In the thylakoid membranes.
They are attached to proteins.
They are called a photosystem.
What are the two photosystems used by plants to capture light energy called?
Photosystem I (or PSI) and photosystem II (or PSII).
Does photosystem I or photosystem II absorb light best?
Photosystem I (PSI) absorbs light best at a wavelength of 700nm compared to photosystem II (PSII) which absorbs light at 680nm.
What is the stroma in a chloroplast?
It is a gel-like substance which is contained within the inner membrane of the chloroplast and surrounds the thylakoids.
What does stroma contain?
Enzymes, sugars and organic acids.
What are carbohydrates which are produced during photosynthesis stored as, as they are not stored straight away?
Starch grains located in the stroma.
How many stages can photosynthesis be split into? and what are the stages called?
Two.
The light-dependant reaction and the light-independent reaction.
Which reaction in photosynthesis needs light energy?
The light-dependant reaction.
Where does the light-dependant reaction take place?
and where does the light-independent reaction take place?
LDR - Thylakoid membranes.
LIR - Stroma.
What happens during the light-dependant reaction of photosynthesis?
The light energy is absorbed by chlorophyll in the photosystems. This light energy excites the electrons in the chlorophyll which leads to their release from the molecule. Therefore, the chlorophyll has been photoionised.
Some of the energy from the released electrons is used to photophosphorylate ATP and some are used to reduce NADP to reduced NADP.
What is the role of ATP?
Transfer energy to the LIR.
What is the role of reduced NADP?
Transfers hydrogen to the LIR.
During the LDR, what is H2O oxidised to?
O2.
What is the LIR also called?
Calvin cycle.
What happens during the light-independent reaction of photosynthesis?
The ATP and reduced NADP from the light-dependant reaction supply the energy and hydrogen to make simple sugars from CO2.
By what process is ATP made in the LIR?
Photophosphorylation.
What 3 things is the energy resulting from the photoionisation of chlorophyll in the LDR used for?
1) Photophosphoroylation (making ATP from ADP and inorganic phosphate).
2) Making reduced NADP from NADP.
3) Photolysis (splitting water into protons, electrons and oxygen).
What are hydrogen ions also called?
Protons.
What are protons also called?
Hydrogen ions.
What are the photosystems in the thylakoid membranes linked by?
Electron carriers.
What forms an electron transport chain?
The photosystems and electron carriers.
What is an electron transport chain?
A chain of protons through which excited electrons flow.
What is chemiosmosis?
The process of electrons flowing down the electron transport chain and creating a proton gradient across the membrane to drive ATP synthesis.
What theory is chemiosmosis described by?
The chemiosmosis theory.
What is the light-independent reaction also called?
The Calvin cycle.
What does the Calvin cycle (light-independent reaction) make?
A molecule called triode phosphate from carbon dioxide and ribulose bisphosphate (5 carbon compound).
What can triose phosphate be used to make?
Glucose and other useful organic substances.
What are two things the Calvin cycle needs to keep it going?
ATP and hydrogen ions.
What is the starting compound in the Calvin cycle?
Ribulose bisphosphate (RuBP).
What is the Calvin cycle also known as?
(Answer not light-independent reaction)
Carbon dioxide fixation.
What are the three main stages of the Calvin cycle?
1) Carbon dioxide is combined with ribulose bisphosphate to form two molecules of glycerate 3-phosphate.
2) ATP and reduced NADP are required for the reduction of GP to triose phosphate.
3) Ribulose bisphosphate is regenerated.
What molecules are made with triose phosphate and glycerine 3-phosphate?
Carbohydrates, lipids and amino acids.
Carbohydrates are hexose sugars, how are they made?
By joining two triode phosphate molecules together and larger carbohydrates are made by joining hexose sugars together ion different ways.
What are lipids made from?
Glycerol, which is synthesised from triode phosphate, and fatty acids, which are synthesised from glycerate 3-phosphate.
What are amino acids made from?
Glycerate 3-phosphate.
How many times does the Calvin cycle need to turn to make one hexose sugar?
SIx.
How many turns of the Calvin cycle produces 6 molecules of triose phosphate? Because 2 molecules of TP are made for every one CO2 molecules used.
3 turns.
How many out of the 6 TP molecules are used to regenerate ribulose bisphosphate?
5.
For three turns of the Calvin cycle how many out of the 6 TPs are used to make a hexose sugar?
1.
A hexose sugar has 6 carbons so how many TP molecules form 1 hexose sugar?
2.
How many times does the Calvin cycle need to turn to produce 2 molecules of TP that can be used to make 1 hexose sugar?
2.
How many ATP and reduced NADP molecules are needed for 6 turns of the Calvin cycle?
18 ATP.
12 reduced NADP.
