photosynthesis Flashcards
what is photosynthesis?
process by which organisms convert solar energy into chemical energy
what are the layers of the leaf top to bottom?
- waxy cuticle
- upper epidermis
- palisade mesophyll
- spongy mesophyll
- lower epidermis
- waxy cuticle, guard cells and stomata
give 3 ways the leaf is adapted for photosynthesis
- xylem that bring water to leaf cells
- phloem that carry sugars produced in photosynthesis
- leaves arranged in a way to minimise overlapping and increase light exposure
- lots of stomata that open and close in response to light
- transparent cuticle and epidermis that allows light to penetrate and reach photosynthetic cells
- large SA to collect max sunlight
- air spaces in lower mesophyll for allow diffusion of CO2 and O2
- long and narrow upper mesophyll cells that have many chloroplasts
where in the chloroplasts is chlorophyll found?
thylakoids
what are the three stages of photosynthesis?
- capturing of light/ energy
- light dependant reaction
- light independent reaction
how is light captured for photosynthesis?
absorbed by the pigment, chlorophyll, in chloroplasts
what happens in the light dependant reaction?
- light energy converted to chemical energy
- electron flow created
- photolysis of water in P, E and o2
what is ultimately produced by the light dependant reaction of photosynthesis?
- reduced NADP
- ATP
- oxygen
what happens in the light independent reaction?
- protons used to reduce co2
- sugars and organic molecules produced
what are the three ways of explaining oxidation?
- gain of oxygen
- loss of hydrogen
- loss of electrons
what are the three ways of explaining reduction?
- loss of oxygen
- gain of hydrogen
- gain of electrons
where does the light dependent reaction occur?
thylakoid
what are the two purposes of the solar energy in the LDR?
- combine ADP and Pi to form ATP —> photo phosphorylation
- to split 2 water molecules to form 4 electrons, 4 protons and oxygen —-> photolysis
what is part 1 of the LDR?
making of ATP
what are the 4 stages of making ATP in the LDR?
- photoionisation (electron boosting)
- boosted electrons taken up by electron carrier
- chain of redox reactions begins
- electron transport chain and energy used to actively transport protons
what is the way of making ATP in the LDR called?
photophosphorylation
describe the process of photoionisation and photo-phosphorylation
- protons actively transported into thylakoid lumen via proton pump
- this is carried out with the energy released from electron transport chain
- photolysis of water causes more hydrogen ions in the thylakoid
- a concentration gradient is formed between the thylakoid and stroma due to high concentration of protons in thylakoid
- protons move out of thylakoid via facilitated diffusion through ATP synthase
- ATP synthase changes shape which catalyses the reaction between ADP and Pi to form ATP
what is the equation for photosynthesis?
- 6CO2 + 6H2O —-> C6H12O6 + 6O2
how big are chloroplasts?
- 2-10um long
- 1um in diameter
what is the grana of a chloroplast?
- stacks of up to 100 disc like structures called
thylakoids - where the LDR takes place
what is the stroma of a chloroplast?
- fluid filled matrix
- where LIR takes place
what is the role of the electrons released from the photolysis of water in the LDR?
to replace the electrons, by reducing the chlorophyll molecule, that were lost from the chlorophyll molecule and allow it to regenerated so it can absorb more light
what are the products of photolysis of 2 molecules of water in the LDR?
- 4 protons
- 4 electrons
- one oxygen molecule
what is the role of the oxygen molecule released from the photolysis of water in the LDR?
- by product
- used in respiration
- or leaves cell and then leaf via stomata
what is the role of the protons released by the photolysis of water in the LDR?
- taken up by NADP which acts as the final electron acceptor of the ETC
- this reduced the NADP
- reduced NADP enters the LIR taking the electrons with it from the chlorophyll molecules
what is the main product of the LDR?
reduced nadp
give 2 ways chloroplasts are structurally adapted for the LDR
- thylakoid membrane provides large SA for attachment of chlorophyll, electron carriers and enzymes
- network of proteins in grana hold chlorophyll in a way that allows max absorption of light
- granal membranes have ATP synthase channels in then which catalyse ATP production
- chloroplasts contain DNA and ribosomes so quickly and easily manufacture proteins
where are electron carriers located for the LDR?
on thylakoid membrane of the grana
what is another name for the LIR?
the calvin cycle
what happens in the first stage of the light independent reaction?
- carbon dioxide diffuses into leaf from atmosphere through stomata
- dissolves in water around walls of mesophyll cells
- then diffuses through plasma membrane, cytoplasm and chloroplast membrane into the stroma of the chloroplast
- carbon dioxide binds to ribulosebiphosphate (RuBP) using rubisco
- this produces two molecules glycerate 3-phosphate which are “activated”
what happens in the second stage of the light independent reaction?
- reduced NADP from the LDR provides reducing power to reduce the 2 GPs
- this creates 2 triose phosphate molecules
- ATP from the LDR provides energy for this
- ADP and Pi return to thylakoid membrane for recycling
what happens in the third stage of the light independent reaction?
- most triose phosphate molecules continues through a series of reactions to regenerate the RuBP and complete the cycle
- the hydrolysis of ATP provides phosphate required to regenerate RuBP
what happens in the fourth stage of the light independent reaction?
- some triose phosphate leave the cycle
- two triose phosphate combine to form one glucose molecule
what happens in the fifth stage of the light independent reaction?
- glucose molecules are combined through condensation reactions to synthesis biological molecules like starch
- also used in respiration to produce ATP needed in the LIR for formation of glucose
how many carbons does RuBP have?
5
how many carbons does GP have?
3
how many carbons does TP have?
3
where does the LIR take place?
the stroma of the chloroplast
give 2 ways the chloroplast is adapted for the LIR
- stroma fluid contains enzymes needed for LIR, and is membrane bound which means a chemical environment with a high concentration of enzymes and substrate can be maintained
- stroma fluid surrounds grana so products of LDR can easily diffuse into stroma
- contains DNA and ribosomes so can easily manufacture proteins needed
explain why oxygen production can be used to measure the rate of photosynthesis?
- oxygen produced in LDR in photolysis
- amount of oxygen can be how fast it’s happening
what is a limiting factor in reference to photosynthesis?
- a factor that limits the rate that the process of photosynthesis can take place
- light intensity
- carbon dioxide concentration
- light intensity
what is the compensation point in reference to photosynthesis?
the point where rate of photosynthesis is equal to rate of respiration
explain light intensity as a limiting factor for photosynthesis
- as light intensity increases, rate of photosynthesis increases
- when it levels out, something else has become the limiting factor
