5.1 Photosynthesis Flashcards
What is the word and symbol equation for photosynthesis?
Carbon dioxide + Water -> Glucose + Oxygen
6CO2 + 6H2O -> C6H12O6 + 6O2
(With light over the arrow)
How is CO2 and H2O acquired for photosynthesis?
CO2 - diffuses into the plant from the atmosphere through the stomata
H2O - moves via osmosis from the soil into the root hair cells, eventually moving through the xylem in transpiration
How is a leaf adapted for carrying out photosynthesis?
Large surface area
Minimal leaf overlapping
Palisade cell is long and narrow absorbing more light
Spongy mesophyll with air gaps allow for a short diffusion distance
Guard cells on stomata all to open and close
Transparent cuticle to let light through
Network of xylem
What is involved in the structure of a chloroplast?
Inner/outer membrane Thylakoid membrane Granum (stack of thylakoid membrane) Intergranal lamella Stroma Starch grains DNA
What are the three stages of photosynthesis?
Capturing light energy
Light dependent reaction
Light independent reaction
What takes place in the grana (thylakoid membrane)?
Site of light dependent reaction
What takes place in the stroma?
Site of light independent reaction
How do we remember redox?
OIL RIG
Oxidation is loss
Reduction is gain
(Of electrons)
What is the aim of the light dependent reaction?
To add an inorganic phosphate molecule to ADP to form ATP
To split water into H+ ions (protons) in photolysis
Describe the first stage of the light dependent reaction?
Light energy (photon) is absorbed by chlorophyll 2 (II)
Chlorophyll II is oxidised as the light energy excites the electrons (raising to a higher energy state) therefore losing 2 electrons - photoionisation
The primary acceptor gains the 2 electrons from the chlorophyll and is therefore reduced
To keep the reaction going photolysis of water takes place where the light splits water into: 2 electrons (to reduce the chlorophyll), 2 H+ and oxygen - which diffuses back out
Describe the second stage of the light dependent reaction?
From the primary acceptor 2 electrons are transferred along many electron carriers, which releases energy used to create ATP leading to each carrier being at a lower energy level therefore the electrons lose energy
(The electron carriers undergo redox)
Light energy is absorbed by chlorophyll 1 (I) and it also gains the 2 electrons
Chlorophyll I loses 2 electrons to another primary acceptor which is reduced
The 2 electrons combine with the 2H+ (from photolysis of water) and NADP to form NADPH2
What are all the products of the light dependent reaction?
NADPH2
Oxygen
ATP
How are chloroplasts adapted for the light dependent reaction?
Thylakoid membrane provides a large surface area for attachment of chlorophyll, electron carriers and enzymes
Network of proteins hold the chlorophyll precisely
Granal membranes have ATP synthase channels to catalyse ATP
Contains DNA and ribosomes to quickly manufacture proteins involved in the reaction
What is the light independent reaction also called?
The Calvin cycle
Describe the first 2 stages of the Calvin cycle/light independent reaction?
CO2 is added to RuBP called carboxylation catalysed by rubisco
A 6 carbon unstable molecule is produced and quickly broken down into 2 x 3 carbon molecules called GP
GP is reduced by reduced NADP and energy supplied from ATP (both from light dependent reaction)
NADP - back to the first photosynthesis stage
GP is reduced to 2 x 3 carbon molecules called TP
Describe the last stage of the Calvin cycle/light independent reaction?
1/6 of TP goes to form glucose (used to make starch, amino acids etc…)
5/6 of TP is involved in regeneration
ATP (from the light dependent reaction) is hydrolysed and the Phosphate group (Pi) is used to make RuBP
How is the second stage of photosynthesis linked to the first?
The second doesn’t need light but it needs the products from the light dependent reaction
Where does the CO2 come from in the light independent reaction?
Diffuses through the stomata of the leaf from the atmosphere
It dissolves in water around the walls of the mesophyll cells
It diffuses through the cell surface membrane, cytoplasm, chloroplast membrane and into the stroma
How are chloroplasts adapted for the light independent reaction?
The fluid stroma contains a high concentration of enzymes
Stroma surrounds the grana therefore the products of the first stage can readily diffuse into the stroma
Contains DNA and ribosomes to quickly manufacture proteins involved in the reaction
In a question what does adding CO2 into the reaction do? (Potentially via hydrogen carbonate)
Acts as an immediate source of CO2
Can often be tracked (radioactively labelled) by the carbon from the CO2 into it’s products i.e glucose
What is significant about RuBP?
It’s not very efficient as it also has an affinity for oxygen
What are some factors affecting photosynthesis?
Light intensity
Carbon dioxide concentration
Temperature
Presence of chlorophyll
What is a limiting factor?
The factor in shorter supply which limits the maximum rate of photosynthesis and growth
On a rate of photosynthesis graph what tends to be the initial limiting factor?
The one along the bottom
How does increasing light affect the rate of photosynthesis?
More water is split in photolysis and excites the electrons quicker
How does increasing CO2 concentration affect the rate of photosynthesis?
More RuBP is turned into GP using the CO2 with rubisco in carboxylation
How does increasing temperature affect the rate of photosynthesis?
The heat energy excites the electrons
Keeps enzymes working at optimum conditions
What is the light compensation point?
Where the volume of oxygen produced and carbon dioxide absorbed in photosynthesis
Is exactly balanced by
The volume of oxygen absorbed and the carbon dioxide produced in respiration
No net exchange of gases
