Chapters 11,12&13 AQA Biology. Photosynthesis, Respiration & Ecosystems

All of section five from the AQA A Level approved revision guide by Glenn and Susan Toole.

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where does the light dependant stage of photosynthesis take place?
the grana/thylakoid membrane
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How is a leaf adapted to bring together water, light and carbon dioxide? (5 adaptations)
1-Large surface area, 2-arrangement of leaves minimises overlapping, 3-thin for short diffusion distance, 4-transparent cuticle, 5- mesophyll packed with chloroplasts, 6- many stomata for gas exchange, 7-network of xylem
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In what organelle does photosynthesis take place?
the chloroplast
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What are grana?
stacks of disk-like structures called thylakoids. thylakoids contain chlorophyll. Some have tubular extensions connecting granum together called lamellae.
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What is the stroma?
The fluid filled matrix within the chloroplast. Starch grains are also in the stroma.
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What is the purpose of photosynthesis?
to create ATP from ADP and Pi, to split water into H+ ions and OH- ions by the process of photolysis
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What happens at photosystem II?
1) Light is absorbed by photosynthetic pigments and the energy is transferred through the molecules where an electron is excited in a molecule of chlorophyll. This is boosted to a higher energy level. Electron replaced by one from H2O splitting.
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What is the electron transfer chain and what is its relation to chemiosmosis?
As the electron is passed by electron carriers, the energy for its transfer is used to pump H+ ions from the stroma to the thylakoid interior, creating a gradient.
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What happens at photosystem I?
Electron is excited once again by light absorption of pigments, and travels down a shorter electron transfer chain. The electrons then reduce NADP which goes to the light independent stage of photosynthesis.
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How is ATP produced in the Light Dependent stage of photosynthesis?
The H+ ions can only cross the membrane of the thylakoid by ATP synthase channel proteins down a diffusion gradient. ATP synthase joins ADP and Pi to form ATP by proton motive force.
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What are the products of the light dependent stage of photosynthesis?
ATP and reduced NADP
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Where does the light independent stage of photosynthesis take place?
The stroma.
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What cycle is the LI stage of photosynthesis called?
The Calvin cycle.
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How is glycerate-3-phosphate formed in the calvin cycle?
CO2 diffuses into the water surrounding mesophyll cells through the stomata. It diffuses through the cell to the chloroplast's stroma. It reacts with RuBP in the presence of rubisco (enzyme) to form 2 glycerate-3-phosphate molecules.
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How is ATP and reducedNADP used in the LI stage of photosynthesis?
ATP is used to form triose phosphate (ATP -> ADP+Pi). ReducedNADP transfers electrons to LI reaction and is oxidised to NADP. These processed form 2 triosephostphate molecules which can form useful organic molecules. ATP is used again to form RuBP.
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How many carbons does a) RuBP have b) glycerate-3-phosphate have c) triose phosphate have?
a) 5 b) 3 c) 3
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How many times does the calvin cycle have to happen to form one molecule of glucose?
6 times.
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Aerobic respiration...
requires O2, produces much ATP, water and CO2
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Anaerobic respiration...
doesn't require O2, produces lactate in animal cells, ethanol in plants and fungi, and only a little ATP
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Where does glycolysis happen? What happens?
In the cytoplasm of all living cells. The splitting of glucose into two pyruvate molecules.
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Phosphorylation and splitting in glycolysis.
two phosphate molecules are added 2 glucose to make it more reactive using 2 ATP molecules. This lowers the activation energy of enzyme controlled reactions. Each phosphorylated glucose is split into 2 triosephosphate molecules.
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Oxidation of triosephosphate and ATP production
Each triosephosphate is oxidised by removing hydrogen to form 2 NADreduced. Triosephosphate is converted to two pyruvate molecules by removing the phosphate from each. This generates two ATP molecules per triosephosphate molecule.
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What is the net production of glycolysis?
2 ATP and one NADreduced.
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Where does the link reaction and the krebs cycle take place?
The matrix of the mitochondria.
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The Link Reaction. Go. DO IT NOW (per pyruvate molecule)
Pyruvate is dehydrogenated to form NADred and decarboxylated to form CO2 and acetate (two carbon molecule) Acetate joins with coenzyme A (CoA) to form acetyl coenzymeA
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How is a four carbon molecule created in the Krebs cycle?
acetyl CoA combines with a four carbon molecule to form a 6 carbon molecule. This is decarboxylated and dehydrogenated twice to form two CO2 and two NADred (continued on next card)
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This forms a four carbon molecule which is then dehydrogenated twice more to form another NADred and an FADred. ATP is also synthesised from ADP and Pi by substrate level phosphorylation.....(continued on other side)
This 4 carbon molecule goes on to begin the cycle again by joining to acetyl CoA.
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What is the net production of the link reaction and the krebs cycle per pyruvate molecule?
1 ATP, 4 NADred, 1 FADred, 2 CO2.
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Where does oxidative phosphorylation take place? What is it?
the cristae of the mitochondria. It is the mechanism by which some of the energy of the electrons within the Hydrogen atoms is conserved in the formation of ATP.
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What role do NADred and FADred have in oxidative phosphorylation?
NADred and FADred donate the electrons to carrier proteins and are oxidised in the process. These carrier proteins are reduced by gaining the electrons.
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Describe the electron transfer chain.
electrons pass along a chain of electron carrier molecules in a series of redox reactions. As the electrons move along the chain, some of their energy is used to pump H+ ions into the inter membrane space from the matrix.
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How is ATP produced?
The H+ ions in the inner membrane space diffuse through the ATP Synthase protein channel to form ATP from ADP and Pi by proton motive force.
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What happens at the end of the chain?
electrons combine with these H+ ions and oxygen to form water. Oxygen is reduced in this reaction.
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what process does anaerobic respiration have in common with aerobic respiration?
glycolysis
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what happens in anaerobic respiration in plant/fungi cells to produce ethanol?
pyruvate from glycolysis loses a CO2 molecule and accepts a hydrogen from NADred to form ethanol and oxidised NAD.
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what happens in anaerobic respiration to produce lactate in animal cells?
each pyruvate molecules takes up the two hydrogen from NADred produced in glycolysis to produce lactate and oxidised NAD.
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how is energy conserved in plants?
chemical energy
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what is biomass?
the dry mass of biological material
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what is a producer?
a photosynthetic organism that can produce organic molecules
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what is a consumer?
an organism that obtains its energy from consuming other organisms
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what are a) primary consumers, b) secondary consumers, c)tertiary consumers?
a) consumers that eat producers/first in the chain of consumers. b) consumers that ear primary consumers. c) consumers that eat secondary consumers.
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what are saprobionts?
decomposers. a group of organisms that break down complex materials of dead organisms.
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what is a food chain?
describes the feeding relationship between organisms
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what is a trophic level?
the position of an organism in a food web/food chain
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what is a food web?
food chains linked together to show all feeding relationships within a habitat
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why is as little as 1% of sunlight captured by plants? (three reasons)
1) over 90% is reflected back into space by clouds/dust/absorbed by atmosphere. 2) nat all wavelengths can be absorbed by pigments. 3) not all light falls on chlorophyll molecule. 4) limiting factors may reduce the rate of photosynthesis.
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What is GPP? what is its relationship with respiratory losses?
GPP= gross primary production which is total quantity of chemical energy of plant biomass over given time. GPP-respiratory losses=NPP (chemical energy of biomass after respiratory losses taken into account).
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why is efficiency for energy transfer between organisms so low? (three reasons)
1) not all of organism consumed. 2) some parts consumed but can't be digested so lost in faeces. 3) energy lost in excretory materials like urea. 4) energy lost as heat and movement by respiration
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How can net production be calculated?
NP= Chemical energy in food -(energy lost through faeces & urine + energy lost through respiration)
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what does the inefficiency of energy transfer between trophic levels explain?
1) why most food chains only have four/five trophic levels. 2) why the total biomass is less at higher trophic levels. 3) why the total energy available going up the trophic levels becomes less.
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How is nitrogen absorbed by plants?
in the form of nitrate ions (NO3-) absorbed by active transport
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How do animals obtain nitrogen containing compounds?
eating and digesting plants
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what are the four stages of the nitrogen cycle?
ammonification, nitrification, nitrogen fixation, denitrification
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how does nitrogen get into the soil?
nitrogen fixation by free living bacteria reduce nitrogen in the atmosphere into ammonium ions. Mutualistic nitrogen fixing bacteria live in root nodules of plants like beans and peas and do the same thing.
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what happens to ammonium ions in the soil? what stage is this?
saprobiotic bacteria oxidise ammonium ions to nitrite ions (NO2-) and then to nitrate ions (NO3-). This is nitrification
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after being absorbed by the plant, what happens to the ammonium containing molecules?
consumers feed on the plants (producers) and digest them to form amino acids. The animals then die or excrete waste and saprobionts then break down the ammonium containing compounds. This releases ammonium into the soil.
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when does denitrification occur and why?
in waterlogged soil in anaerobic conditions as there are fewer aerobic nitrifying bacteria and more anaerobic denitrifying bacteria.
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what does denitrification do?
release nitrogen back into the atmosphere as a gas.
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how does phosphate get from rocks to water sources and soils?
erosion and use of fertilisers.
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how can phosphate ions (PO4 3-) move from the water sources?
absorption into plants. These plants can die, or can be fed on by animals and digested to be excreted as faeces or urea to wash back into oceans and form sediment on rocks.
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what are the paths phosphate can take from being in plants to being in rocks?
Animals who have fed on the plants/eaten other consumers or died deposit phosphate as guano, bones or shells. These can erode back into the ocean and become sediment, or be deposited on rock.
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Other cards in this set

Card 2

Front

How is a leaf adapted to bring together water, light and carbon dioxide? (5 adaptations)

Back

1-Large surface area, 2-arrangement of leaves minimises overlapping, 3-thin for short diffusion distance, 4-transparent cuticle, 5- mesophyll packed with chloroplasts, 6- many stomata for gas exchange, 7-network of xylem

Card 3

Front

In what organelle does photosynthesis take place?

Back

Preview of the front of card 3

Card 4

Front

What are grana?

Back

Preview of the front of card 4

Card 5

Front

What is the stroma?

Back

Preview of the front of card 5
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