3. Photosynthesis Flashcards
What is the overall equation for photosynthesis?
6 CO2 + 6 H2O –> C6H12O6 + 6 O2
What are the adaptations of a leaf for photosynthesis?
- LARGE SURFACE AREA- more light absorption
- ARRANGEMENT OF LEAVES THAT MINIMISES OVERLAPPING- more light absorption
- THIN- short diffusion distance, most light absorbed in the first few millimetres
- TRANSPARENT CUTICLE AND EPIDERMIS-allow light through
- LONG NARROW UPPER MESOPHYLL PACKED WITH CHLOROPLASTS
- NUMEROUS STOMATA- gas exchange
- STOMATA OPEN AND CLOSE- in response to different light intensities
- MANY AIR SPACES IN LOWER MESOPHYLL- diffusion of gases
- NETWORK OF XYLEM- brings water to the leaf cells
- NETWORK OF PHLOEM- carries away sugars produced in photosynthesis
Describe the structure of chloroplasts
- Double membrane
- Grana- stacks of thylakoids. Thylakoids contain chlorophyll. Some thylakoids have tubular extensions which join thylakoids with adjacent grana (called inter-granal lamellae
- Stroma- a fluid filled matrix where the light independent reaction takes place- also contains starch grains
What is the photolysis of water and what is the equation?
It is the splitting of water
2H2O –> 4H+ + 4e- +O2
In which three ways can oxidation be described?
In which three ways can reduction be described?
Oxidation
- Loss of electrons
- Loss of hydrogen
- Gain of oxygen
Reduction
- Gain of electrons
- Gain of hydrogen
- Loss of oxygen
Describe the light dependent reaction and how ATP is formed.
-Light strikes the chlorophyll molecule
-A pair of electrons are excited into a higher energy state and liberated from the chlorophyll
-Electrons pass to an electron carrier
-Passes down a chain of electron carriers forming a transfer chain in the membranes of the thylakoids
-Each new electron carrier is in a lower energy state than the previous one, so the electrons lose energy at each stage
-This energy is used to combine a Pi with an ADP molecule to make ATP
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What is the role of the photolysis of water in photosynthesis?
-It replaces the electrons that were lost by the chlorophyll molecule.
-Protons taken up by an electron carrier called NADP to form reduced NADP
>NADP enters the light independent reaction along with the electrons from the chlorophyll molecules
Why is reduced NADP (produced from protons from the photolysis of water combining with an electron carrier called NADP) important
-It is a further source of potential energy for the plant
How are chloroplasts structurally adapted for their role in photosynthesis?
- Thylakoid membranes provide a larger surface area for the attachment of chlorophyll molecules, electron carriers and enzymes that carry out the L.D reaction
- Network of proteins in the grana hold the chlorophyll in a precise position for maximum absorption of light
- Granal membranes have enzymes attached to them which help in manufacturing ATP
- Proteins for the L.D reaction an be easily and quickly manufactured as chloroplasts contain both DNA and ribosomes
Describe the stages of the calvin cycle.
- CO2 diffuses into the leaf and dissolves in the water (around the walls of the mesophyll cells).
- It then diffuses through the plasma membrane , cytoplasm and chloroplast membranes into the stroma of the chloroplasts
- In the stroma the CO2 combines with RuBP (5C) using an enzyme
- Combination fo RuBP and Co2 splits into two molecules of GP (3C)
- ATP and reduced NADP from the light dependent reaction reduce the activated GP to triose phosphate (TP)
- NADP is reformed and goes back into the light dependent reaction to be reduced again by accepting more hydrogen
- Some TP molecules are converted into useful organic substances such as glucose
- Most TP are used to regenerate RuBP using ATP from the light dependent reaction
Why is the light independent reaction technically not independent of light being present?
The light independent reaction requires products produced in the light dependent reaction.
-ATP and reduced NADP are required to reduce carbon dioxide in the second stage of photosynthesis.
Where does the light independent reaction take place?
In the stroma of chloroplasts
How is the chloroplast adapted to carrying out the light independent reaction?
-Fluid filled stroma contains all the enzymes necessary to complete the reactions that take place in teh L.I reaction (reduction of carbon dioxide)
- Fluid filled stroma surrounds the grana which means that the products of the light dependent reactions in the stroma can easily diffuse from the grana into the stroma
- Contains both DNA and ribosomes so can easily and quickly manufacture proteins needed for the light independent reaction.
Where does the light dependent reaction take place?
In the thylakoid membranes
Describe Melvin Calvin’s lollipop experiment. (How science works application)
- Single celled algae grown in the lollipop under light
- Radioactive hydrogen carbonate injected into the lollipop (supplies radioactive carbon dioxide to the algae)
- At intervals, samples of the photosynthesizing algae are dropped into hot methanol to stop chemical reactions occurring instantaneously
- Compounds in the algae separated by two way chromatography
- Radioactive compounds are identified and pathway determined by when the compound first appears (eg first to appear is in the first pathway)
What are the limiting factors for photosynthesis?
- Light intensity
- Carbon dioxide concentration
- Water
What happens to the rate of photosynthesis as you increase either the light intensity or the carbon dioxide concentration?
Increases at first then plateaus
This is because another factor has become limiting and is limiting the rate of photosynthesis
Define the law of limiting factors.
At any given moment, the rate of a physiological process is limited by the factor that is at its least favorable value
Which factor is photosynthesis limited by the most?
- Temperature
- Carbon dioxide concentration
- Temperature
Carbon dioxide concentration
What are two ways in which the rate of photosynthesis of a plant can be measured? What are the problems in measuring in these ways?
- Volume of oxygen released - some oxygen produced will not be emitted as it will be re-taken up by the plant for use in respiration
- Volume of carbon dioxide taken up - hard to isolate the co2 taken up and teh co2 taken in because the plant is giving out co2 through respiration at the same time that it is taking up co2 through photosynthesis.
What does the term ‘compensation point’ mean?
The point at which there is no net gas exchange into or out of the plant. When the o2 produced and the co2 absorbed in photosynthesis is exactly balanced by the o2 absorbed and the co2 produced in cellular respiration.
How does the rate of photosynthesis vary when light is a limiting factor? (Describe what happens when light intensity is increased when light is a limiting factor)
When light is a limiting factor and the light intensity is increased, the rate of photosynthesis increases proportionally to the increase in light intensity.
What is the optimum concentration of carbon dioxide for a high rate of photosynthesis?
0.1% (compared to 0.04% that naturally occurs in the air)
How does the rate of photosynthesis vary as the temperature is increased if there are no limiting factors?
The rate of photosynthesis varies in direct proportion to the temperature as it is increased up to about 25 degrees Celsius in most plants after which the rate levels off and then declines as the enzymes are denatured.
Which reaction/s in photosynthesis are affected by temperature?
- Light independent reaction is enzyme controlled and so temperature affects the enzyme activity and therefore influences the L.I reaction
- Light dependent reaction is NOT affected by changes in temperature
(4 marks)
Iron deficiency reduces electron transport. Use this information and your knowledge of
photosynthesis to explain the decrease in production of triose phosphate in the
iron-deficient plants.
- (Less) ATP produced;
- (Less) reduced NADP produced;
- ATP/reduced NADP produced
during light-dependent reaction; - (Less) GP to triose
phosphate/TP;
(2 marks)
Photosynthesis in iron deficient plants
Iron deficiency results in a decrease in the uptake of carbon dioxide. Explain why.
- Less triose phosphate converted
to RuBP; - CO2 combines with RuBP;
(6 marks)
During the light-independent reaction of photosynthesis, carbon dioxide is converted
into organic substances. Describe how.
1. Carbon dioxide combines with ribulose bisphosphate/RuBP; 2. Produces two glycerate (3-)phosphate/GP; 3. GP reduced to triose phosphate/TP; 4. Using reduced NADP; 5. Using energy from ATP; 6. Triose phosphate converted to glucose/hexose/RuBP/ ribulose bisphosphate/named organic substance;
(1 mark)
Explain why CO2 uptake is a measure of net productivity
Shows (gross) photosynthesis/productivity minus
respiration / more carbon dioxide used in
photosynthesis than produced in respiration;
(6 marks)
During the light-independent reaction of photosynthesis, carbon dioxide is converted
into organic substances. Describe how.
1. Carbon dioxide combines with ribulose bisphosphate/RuBP; 2. Produces two glycerate (3-)phosphate/GP; 3. GP reduced to triose phosphate/TP; 4. Using reduced NADP; 5. Using energy from ATP; 6. Triose phosphate converted to glucose/hexose/RuBP/ ribulose bisphosphate/named organic substance;
(5 marks)
Energy enters most ecosystems through the light-dependent reaction of
photosynthesis. Describe what happens during the light-dependent reaction.
- Chlorophyll absorbs light energy;
- Excites electrons / electrons
removed (from chlorophyll); - Electrons move along
carriers/electron transport chain
releasing energy; - Energy used to join ADP and Pi
to form ATP; - Photolysis of water produces
protons, electrons and oxygen; - NADP reduced by electrons /
electrons and protons /
hydrogen;
