photosynthesis Flashcards
(40 cards)
1
Q
What are the two stages of photosynthesis
A
- light dependent stage
- light independent stage
2
Q
What is the overall equation for photosynthesis
A
6CO2 + 6H2O -> C6H12O6 + 6O2
3
Q
phosphorylation
A
the synthesis of ATP from ADP and Pi (inorganic phosphate) using light energy
4
Q
Give an overview of the light dependent stage
A
where light energy is converted into chemical energy as the photolysis of water releases protons and electrons whcih poduce ATP via phosphorylation and reduce the co enxyme NADP
5
Q
Give an overview of the light independent stage
A
- calvin cycle where ATP and NADPH from the light dependent reaction reduce carbon dioxide to produce glucose
6
Q
How is the leaf adapted for gas exchange and phtosynthesis
A
- havign a large surface area allowing the leaf to capture light and having pores called stomate through which gases diffuse
- the air spaces between cells allow for carbon dioxide to diffuse to the photosynthesising cells
- highest concentration of chloroplasts isfound in the palisade mesophyll on the leafs upper surface
- palisade cells are arranges veritcally which allows more light to be absorbed by chlorplasts than if they were stacked horizontally as light only has to pass through cuticle and epidermal cells and one palisade cell wall
7
Q
Describe adaptation of chloroplast to help with photosynthesis
A
- chloroplasts have a large surface area for the maximum absorption of light
- they are also able to move within palisade cells to maximise the absorption of light
8
Q
transudcers
A
change energy from one form into another
9
Q
Describe how the site of photosynthesis was detected
A
- englemann in 1887
- he shone a light through a prism to seperate the different wavelengths of light and exposed this to a suspension of algae with evenly distributed motile aerobic bacteria
- after a preiod of time he noticed that the bacteria congregated around the algae exposed to blue and red wavelengths
- this was because this algae photsynthesised more and so produced more oxygen attracting the motile bacteria
10
Q
How are chloroplasts act as transducers
A
- as transducer chloroplasts can change energy from one form into another is this case light energy into chemical energy
11
Q
What are the two main pigments in flowering plants and give examples
A
- chlorophylls which absorb red and blue - violet regions of the spectrum - chorophyll a and chlorophyll b
- carotenoids which absorb light energy from the blue violet region of the spectrum b carotene and xanthrophylls and act as accessory pigments
12
Q
What is the advantage of chlorophylls having several photsynthetic pigements
A
- allow the plant to absorb a wider range of wavelengths of light than a single pigment
13
Q
absorption spectrum
A
a graph that shows how much light energy is absorbed at different wavelenghts
14
Q
action spectrum
A
- a graph that shows the rate of photosynthesis at different wavelengths
15
Q
Describe what an absorption spectrum indicates and does not indicate
A
- show how much light energy a particular pigmen absorbs at different wavelengths for example chlorophyll a which absorbs red and blue violet regions of the spectrum
- it does not indicate wether the particular wavelength is used in photosynthesis
16
Q
What does an action spectrum indicate
A
- shows the rate of photoynthesis at different wavelengths by measuring the mass of carbohydrates synthesised by plants
17
Q
antenna complex
A
- an array of protein and pigment molecules in the thylakoid membranes with chlorophyll a at the reaction centre
- it transfers energy from light of a range of wavelenghts to chlorophyll a
18
Q
Where are chlorophylls and accessory pigments found
A
- lying in the thylakoid membranes grouped into structures called antenna complexes
19
Q
What are the two types of reaction centre
A
- photosystem 1 chlorophyll a absorption peak of 700 nm also P700
- photosystem 2 chlorophyll a with an absorption peak of 680nm P680
20
Q
Describe how you can identify different photosynthetic pigments from chloroplasts
A
- pigments can be extracted by grinding plant material in a suitable solvent eg propanone
- and seperated by paper chromatography
- by dividing the distance travelled by the pigment and the distance travelled by the solvent front the rf value can be calculated
21
Q
Where does the light dependednt stage of photosynthesis occur
A
thylakoid membranes
22
Q
What are the two pathways of photophosphorylation
A
- non cyclic
- cyclic
23
Q
What is non cyclic photophosphorylation
A
- involved photosystems 1 and 2 generatig 2 ATP molecules and NADPH
- photolysis generates oxygeen
- the electrons take a linear pathway
24
Q
Describe the steps of non cyclic photophosphorylation
A
- light energy (photons) strikes chlorophyll PS2 exciting its electrons boosting them to a higher energy level
- electrons are accepted by an electron carrier in the thylakoid membrane
- the oxidised chlorophyll removes electrons from water producting protons ad oxygen (photolysis) this occur in the thylakoid space
- as electrons pass from carrier to carrier electron energy is lost which pumps protons from the stroma into the thylakoid space
- as protons flow back throguh the stalked particle ADP is phosphorylated 2ATP are made in total
- electrons enter photosystem ! where light excites them boosting them to an even higher energy level
- electrons enter a final electron carrier
- electrons and protons reduce NADP to NADPH which pass to the calvin cycle with the two ATP made
25
What is cyclic photophosphorylation
* involved only photosystem 1 producing 1 ATP molecule only
* photolysis does not occur
* no oxygen is released
* electrons take a cyclical pathway
26
Describe cyclic photophosphorylation
* if there is no NADP available then the electrons fall back into the electron transport chain (at an intermediate energy level) and generate 1 ATP
* this cycle continues until NADP is available
* the ATP produced can be used in the calvin cycle in the stomatal opening mechanism or for other cellular processes
* ATP is produced in the chloroplast when protons are pumped across the thylakoid membrane uing energy from the electrons and accumulate with protons generated from photolysis of water in the thylakoid space generating and electrochemical (proton) gradient
* The H+ ions diffuse back into the stroma through stalked particles generating ATP
* the protons and electrons reduce NADP which removes H+ ions from the stroma further contrbuting to the H+ gradient
27
What is chemiosmosis
movement of protons
28
Where does the calvin cycle occur
in the stroma
29
Outline the calvin cycle
* ATP and NADPH from the light dependent reaction are used to fix carbon from carbon dioxide with the help of the enzyme RuBisCO
30
How was the calvin cycle figured out
* using a radioactive isotopes of carbon 14 present in hydrogen carbonate
* at regular intervals Calvin removed samples into hot methanol to kill the chlorella algae used and to stop all enzyme reactions
* he then performed chromatography to identfiy the products
* he exposed his chromatogram to a piece of x ray film which would detect radiation emitted from carbon 14 used
* identified products containing carbon 14 in the order they were produced first was hydrogen carbonate ions then glycerate-3-phosphate, triose phosphate, ribulose bisphosphate (RuBP) and finally glucose
31
Describe the steps in the calvin cycle
* carbon dioxide diffuses into leaf via stomata dissolving in the water surrounding palisade mesophyll cells before diffusing into the cells
* carbon dioxide combines with the 5 carbon compound ribulose bisphosphate (RuBP) using the enzyme RuBisCO to form an unstable 6C compound
* unstable 6C compound immediatley breaks down into 2 molecules of glycerate-3-phosphate (GP)
* using one ATP molecule from the light reaction GP is reduced to triose phosphate (TP) using hyrogen atoms from NADPH
* triose phosphate molecules combine in pairs to form hexose sugards
* five out of every six triose phosphate molecules produced are used to regenerate RuBP 9 via intermedicate ribulose phosphate) using ATP from the light dependent reaction to supply energy and phosphate. Allowing the cycle to continue
32
Describe how some of the products of photosynthesis are used by the plants
* plants must produce all the carbohydrates, fats and proteins they need from the products of the calvin cycle
* fructose phosphate formed from the two molecules of triose phosphate can be converted to glucose or combines with glucose to produce sucrose
* sucrose is then translocates in the phloem to the growing regions of the plant
* some alpha glucose is stores as starch beta glucose forms cellulose in cell walls
* fatty acids can be formed from glycerate-3-phosphate and glycerol from triose phosphate the building blocks of triglycerides
* proteins can be formed from glyverate-3-phosphate but the amino group requires nitrogen from nitrate ions
* other compounds eg chlorophyll require additional ions eg Mg2+ and the middle lamella off cell walls needs Ca2+
33
What does a lack of nitrogen result in
* results in stunted growth in plants
* as plants cannot synthesise protins due to the lack of nitrogen
34
What does a lack of magnesium result in
* cholorosis - yellowing of leaves
* chlorphyll cannot be synthesised
35
limiting factor
a factor that limits the rate of a physical process by being in short supply
36
What is the rate of photosynthesis controlled by
* a number of factors including the concentration of carbon dioxide, light intesity and temperature
37
Describe the effect of concentration of carbon dioxide on photosyntheis
* at low concentrations carbon dioxide concentration is limiting
* above 0.5% the rate plateus showing that something else must be limiting
* above 1% the stomata close preventing uptake of carbon dioxide
38
Describe the effect of light intensity on photosynthesis
* as light intensity increates the rate of photosynthesis increases
* when some other factor becomes limiting
* at very high light intesities the rate decreases a chloroplast pigments become blached
* different plants have evolved to be most efficient at light intensities found in their envirnoment eg sun and shade plants
39
Describe the effect of temperature on photosynthesis
* temperature increases the kinetic energy of the reactants and enzymes involved in photosynthesis
* unlike other factor a plateu is ot reached as enzymes eg RuBisCO begin to denature so the rate of photosynthesis decreases above the optimum temperature
* this will be in species atdapted to hot,dry environments
40
Describe a method to measure the rate of photoynthesis
* by using a water bath and controlling hydrogen carbon concentation
* it is easy to collect and accuratley measure oxygen produced in a capillary tube
* volume of the bubble collected is calculated
* an aquatic plant is used
