Photosynthesis 5.6 Flashcards
What is photosynthesis?
The process where an organism converts light energyfrom the sun into sugar and other organic molecules so it can use and store them as chemical energy
two step process
What does a chloroplast consist of?
- outer membrane
- inner membrane
- granum (thylakoid stack)
- stroma
- thylakoid (lamellae)
Where do the two main stages of photosynthesis happen?
- light dependent stage happens in the thylakoid membrane
- calvin cycle happens in the stroma
What are autotrophs?
Organisms that use light or chemical energy to synthesise larger organic molecules from smaller inorganic ones
What are heterotrophs?
Organisms that obtain large organic molecules from autotrophs
What are chemoautotrophs?
Organisms that synthesise larger organic molecules urging energy from chemicals
What are photoautotrophs?
Organisms that synthesise larger organic molecules using energy from light
What are the compensation points on the graph?
When the rate of photosynthesis is working at the same rate as respiration so there is not net gain or loss
What are the adaptations of the chloroplast to increase rate of photosynthesis?
- inner membrane
- many grana
- photosynthetic pigments
- fluid filled stroma
- DNA and ribosomes
How does the inner membrane of a chloroplast help with photosynthesis?
Controls transport of molecules across the membrane with transport proteins
How does having many grana in a chloroplast help with photosynthesis?
- creates a large SA for photopigments
What are photosystems?
They are funnel shaped structures made of photosynthetic pigment molecules that are arranged in light harvesting clusters that carry out the absorption of light
What are the two types of photosystems?
- photosystem I (PS1) 700nm
- Photosystem II (PS2) 680nm
Why are photosynthetic pigments important?
- they are found in photosystems
- absorb specific wavelengths of light
- energy captured and funnelled to the primary pigment reaction centre by the light harvesting systems
How does the fluid filled stroma in a chloroplast help with photosynthesis?
Contains enzymes needed to catalyse reactions of the LDS, starch, ribosomes and DNA
How does the DNA and ribosomes of a chloroplast help with photosynthesis?
Makes proteins for photosynthesis
What is chlorophyll?
Light capturing photosynthetic pigments that funnel the energy into primary pigment reaction centres
What are the different types of chlorophyll?
- chlorophyll a
- chlorophyll b
- carotenoids
- xanothophylls
What wavelength does chlorophyll a absorb?
blue - green wavelengths
What wavelength does chlorophyll b absorb?
yellwo - green wavelengths
What wavelength does carotenoids absorb?
Blue wavelengths
What wavelength does xanothophylls absorb?
Blue - green wavelengths
What are the different stages of the light dependent stage?
- light harvesting
- photolysis of water
- photophosphorylation
- formation of NADH from NAD
What happens during light harvesting?
Energy from the light is harvested and is used to drive the production of chemicals as a source of energy
to split water
What happens during photolysis?
Water molecules are split into protons and electrons in the presence of light
What is photophosphorylation?
It is the name for the overall process of using light energy and electron transport chain to phosphorylate ADP to ATP
What happens during cyclic photophosphorylation?
- Cyclic photophosphorylation uses only PSI and happens in the thylakoid membrane
- Light energy excites two e- (photonised) and they escape the chlorophyll molecule and are captured by an e- carrier
- the e- pass down a chain of e- carriers and lose energy and are then passed back to PSI
What happens during non cyclic photophosphorylation?
- non cyclic photophosphorylation uses both PSI and PSII and happens in the thylakoid membrane
- Light energy excites two e- (photonised) and they escape the chlorophyll molecule and are captured by an e- carrier
- the e- pass down a chain of e- carriers and lose energy
- H+ ions produced by photolysis are pumped into the thylakoid lumen using the energy provided by the e-
- this sets up an electrochemical concentration gradient across the membrane
- The H+ ions are free to move and diffuse through the ATP synthase allowing it to reduce ADP + Pi into ATP
- this is chemiosmosis
- The H+ ions along with the e- that reached PSI are accepted by NAD to be reduced into NADH
What happens during the calvin cycle?
- CO2 combines with RuBP which is a 5 carbon sugar
- this is catalysed by rubisco enzyme
- This results in a 6 carbon compound which is unstable and splits into two three carbon molecules known as GP
- energy from ATP and hydrogen from NADPH reduce GP into another pair of three carbon molecules known as TP
- 1/6 of the TP molecule (1 carbon) is used to produce the hexose sugar
- the rest of the TP molecule is used to regenerate RuBP
- this process requires ATP
- cycle is repeated
- 12 TP lead to 2TP being produced which is a glucose molecule
When does the calvin cycle happen?
When light is present (daylight hours)
How many times does the calvin cycle have to be repeated to form one hexose sugar?
6
What happenes when rubisco acts as a carboxylase?
It binds to the CO2 and combines with RuBP giving two molecules of triosephosphate
What causes rubisco to act as an oxygenase?
At low levels of CO2 rubisco binds to O2 and combines with RuBP to form 1 molecule of GP
What happens when rubisco acts as an oxygenase?
It releases CO2 in photorespiration
How do ions create an optimum condition for rubisco?
H+ ions are pumped into thylakoid space which increases the pH to 8 which is the optimum pH for rubisco
What happens to the Mg+ ion concentration during the calvin cycle?
It increases
How does light intensity and CO2 concentration affect TP?
Increased light intensity increases TP production and increased CO2 conc. increases TP production
How does light intensity and CO2 concentration affect GP?
Increased light intensity decreases GP production and increased CO2 conc. increases GP production
How does light intensity and CO2 concentration affect RuBP?
Increased light intensity increased RuBP production and increased CO2 conc. decreases RuBP production
How does temperature affect GP?
Increased temperature increases GP production up to about 30 degrees and then the rate of production begins to decrease due to enzymes denaturing
How does temperature affect TP?
Increased temperature increases TP production up to about 30 degrees and then the rate of production begins to decrease due to enzymes denaturing
How does temperature affect RuBP?
Increased temperature increases RuBP production up to about 30 degrees and then the rate of production begins to decrease due to enzymes denaturing
What is water stress?
When there is not enough water for a plant to function normally
What are the effects of water stress?
- cells lose water and become plasmolysed
- roots produce abscidic acid which causes the tomata to close, reducing gaseous exchange
- tissue becomes flaccid and leaves wilt
- rate of photosynthesis decreases
What is a photosynthometer?
A set of of capillary tubing and equipment which is used to calculate the rate of photosynthesis
How does a photosynthometer work?
Gis given off by the plant over a period of time is collected in a flared end of a capillary tube and is then measured and divided by time to calculate the rate of photosynthesis
How do you calculate rate of photosynthesis from a photosynthometer?
Volume of the air bubble/ time
