Energy Transfers in and between Organisms Flashcards
(123 cards)
1
Q
what is an ecosystem?
A
an ecosystem includes all the organisms living in a particular area and all the non-living conditions.
2
Q
what is biomass?
A
the total mass of living material in a specific area at a specific time
3
Q
how can biomass be measured?
A
biomass can be measured in terms of the mass of carbon that an organism contains or the dry mass of its tissue per unit area.
4
Q
what is dry mass?
A
dry mass is the mass of the organism with the water removed.
5
Q
how is dry mass measured?
A
a sample of the organism is dried, often in an oven set to a low temperature.
the sample is then weighed at regular time intervals. once the mass becomes constant you know that all the water has been removed.
the mass of carbon present is generally taken to be 50% of the dry mass.
6
Q
how can we calculate the amount of chemical energy stored in biomass?
A
using a calorimeter.
a sample of dry biomass is burnt and the energy released is used to heat a known volume of water.
the change in temperature of the water is used to calculate the chemical energy of the dry biomass.
7
Q
what is gross primary production (GPP)?
A
the total amount of chemical energy converted from light energy by plants, in a given area.
8
Q
what is respiratory loss (R)?
A
where approximately 50% of the gross primary production is lost to the environment as heat when the plants respire.
9
Q
what is net primary production (NPP)?
A
the remaining chemical energy once respiratory loss has taken place.
this is the energy available to the plant for growth and reproduction, stored in the plant’s biomass, as well as the energy available to organisms at the next stage in the food chain.
10
Q
what is the formula for NPP?
A
NPP = GPP - R
11
Q
how do consumers get chemical energy to store in their biomass?
A
consumers get their energy by ingesting plant material, or animals that have eaten plant material.
12
Q
why does biomass decrease along a food chain?
A
energy is lost in waste (urine) and faeces.
not all of the food is eaten.
energy is lost to surroundings as heat.
13
Q
what is the consumers’ net production?
A
the energy that’s left, after around 90% of energy is lost, is stored in the consumers’ biomass and is available to the next trophic level.
14
Q
how can the net production of consumers be calculated?
A
N = I - (F + R)
I : chemical energy from ingested food
F : chemical energy lost in faeces and urine
R : energy lost through respiration
15
Q
how are food chains able to show how energy is transferred between organisms?
A
food chains show simple lines of energy transfer. each of the stages in a food chain are called trophic levels.
16
Q
how are food webs able to show how energy is transferred between organisms?
A
food webs show lots of food chains in an ecosystem and how they overlap.
17
Q
how do most farming practices aim to increase the amount of energy that is available for human consumption?
A
by reducing the energy lost to other organisms.
by reducing the energy lost through respiration.
18
Q
explain how simplifying food webs reduces energy loss to other organisms. use ‘pests’ example.
A
pests are organisms that can reduce the amount of energy available for crop growth and therefore the NPP. this ultimately reduces the amount of energy available for humans.
by simplifying the food web, i.e getting rid of food chains that don’t involve humans, energy losses will be reduced and the NPP of the crop will increase.
19
Q
how can farmers get rid of pests, in order to simplify the food web?
A
farmers can reduce pest numbers using chemical pesticides.
for example, insecticides kill insect pests that eat and damage crops. killing insect pests means less biomass is lost from crops, so they grow larger, which means NPP is greater.
herbicides kill weeds. killing weeds can remove direct competition with the crop for energy from the Sun. it can also remove the preferred habitat or food source of the insects pests, helping to remove further numbers and simplify the food web.
20
Q
what else helps to reduce the number of pests?
A
biological agents.
e.g. parasites live in or lay their eggs on a pest insect. parasites either kill the insect or reduce its ability to function. .
21
Q
explain how reducing respiratory losses means energy is transferred more efficiently. use an example which can help reduce respiratory losses.
A
farmers increase the net production of their livestock by controlling the conditions that they live in, so that more of their energy is used for growth and less is lost through respiration as well as activities that increase the rate of respiration. this means that more biomass is produced and more chemical energy can be stored, increasing net production and the efficiency of energy transfer to humans.
e.g movement increases the rate of respiration, so animals may be kept in pens where their movement is restricted. the pens are often indoors and kept warm, so less energy is wasted by generating body heat.
22
Q
what is a natural ecosystem?
A
this is an ecosystem that hasn’t been changed by human activity. in natural ecosystems, nutrients are recycled through the food webs.
23
Q
what important role do fungi have in nutrient recycling?
A
some fungi form symbiotic relationships with the roots of plants. these relationships are known as mycorrhizae.
24
Q
how are some fungi able to form symbiotic relationships with the roots of plants?
A
the fungi are made up of long, thin strands called hyphae, which connect to the plant’s roots.
the hyphae greatly increase the surface area of the plant’s root system, helping the plant to absorb ions from the soil that are usually scarce. hyphae also increases the uptake of water by the plant.
in turn, the fungi obtain organic compounds, such as glucose, from the plant.
25
what are saprobionts?
they are a type of decomposer; they feed on the remains of dead plants and animals and on their waste products, breaking them down. this allows important chemical elements in the remains to be recycled.
26
what is extracellular digestion?
where saprobionts secrete enzymes and digest their food externally, then absorb the nutrients they need. during this process, organic molecules are broken down into inorganic ions.
27
what is saprobiotic nutrition?
obtaining nutrients from dead organic matter using extracellular digestion.
28
what does the nitrogen cycle show?
it shows how nitrogen is converted into a usable form and then passed on between different living organisms and the non-living environment.
29
why can't organisms use nitrogen directly from the atmosphere?
nitrogen is very stable due to the strong covalent triple bond so it can't be broken down as easily.
30
name the 4 main stages of the nitrogen cycle.
nitrogen fixation
ammonification
nitrification
denitrification
31
explain nitrogen fixation.
nitrogen fixation is when nitrogen gas in the atmosphere is turned into nitrogen-containing compounds. biological nitrogen fixation is carried out by bacteria such as Rhizobium. they turn nitrogen into ammonia, which goes on to form ammonium ions in solution that can then be used by plants.
Rhizobium are found inside root nodules of plants such as peas, beans and clovers. they form a mutualistic relationship with the plants; they provide the plant with nitrogen compounds and the plant provides them with carbohydrates.
32
explain ammonification.
ammonification is when nitrogen compounds from dead organisms are turned into ammonia by saprobionts, which goes on to form ammonium ions.
animal waste also contains nitrogen compounds. these are also turned into ammonia by saprobionts and go on to form ammonium ions.
33
explain nitrification.
nitrification is when ammonium ions in the soil are changed into nitrogen compounds that can then be used by plants (nitrates).
the first nitrifying bacteria change ammonium ions into nitrites.
then other nitrifying bacteria change nitrites into nitrates.
34
explain denitrification.
denitrification is when nitrates in the soil are converted into nitrogen gas by denitrifying bacteria; they use nitrates in the soil to carry out respiration and produce nitrogen gas.
this happens under anaerobic conditions, e.g in waterlogged soils.
35
what are the other ways nitrogen is able to get into an ecosystem?
by lightning which fixes atmospheric nitrogen or by artificial fertilisers, produced from atmospheric nitrogen on an industrial scale in the Haber process.
36
why do plants and animals need phosphorus?
they need phosphorus to make biological molecules such as phospholipids, DNA and ATP.
37
where is phosphorus found?
phosphorus is found in rocks and dissolved in the oceans in the form of phosphate ions. phosphate ions dissolved in water in the soil can be assimilated by plants and other producers.
38
what does the phosphorus cycle show?
it shows how phosphorus is passed through an ecosystem.
39
explain the phosphorus cycle. (7 points)
-phosphate ions in rocks are released into the soil by weathering.
-phosphate ions are taken into the plants through the roots. mycorrhizae greatly increases the rate at which phosphorus can be assimilated.
-phosphate ions are transferred through the food chain as animals eat the plants and are in turn eaten by other animals.
-phosphate ions are lost from the animals in waste products.
-when plants and animals die, saprobionts are involved in breaking down the organic compounds, releasing phosphate ions into the soil for assimilation by plants. these microorganisms also release the phosphate ions form urine and faeces.
-the weathering of rocks also releases phosphate ions into seas, lakes and rivers. this is taken up by aquatic producers, such as algae, and passed along the food chain to birds.
-the waste produced by sea birds is known as guano and contains a high proportion of phosphate ions. guano returns a significant amount of phosphate ions to soils. it is often used as a natural fertiliser.
40
how are nutrients lost when crops are harvested?
crops take in minerals from the soil as they grow and use them to build their own tissues.
when crops are harvested, they're removed from the field where they've grown rather than being allowed to die and decompose there. this means the mineral ions that they contain are not returned to the soil by decomposers in the nitrogen or phosphorus cycles.
41
how are phosphates and nitrates lost when animals or animal products are removed from the land?
animals eat grass and other plants, taking in their nutrients. when they are taken elsewhere for slaughter or transferred to a different field, the nutrients aren't replaced through their remains or waste products.
42
why are fertilisers added to soils?
adding fertilisers replaces the lost minerals, so more energy from the ecosystem can be used for growth, increasing the efficiency of energy transfer.
43
what are the 2 types of fertilisers?
artificial
natural
44
what are artificial fertilisers?
these are inorganic; they contain pure chemicals as powders or pellets.
45
what are natural fertilisers?
they are organic matter; they include manure, composted vegetables, crop residues and sewage sludge.
46
how does using fertilisers raise environmental issues?
-sometimes more fertiliser is applied than the plants need or are able to use at a particular time.
-this can lead to the fertilisers leaching into waterways.
-this can lead to eutrophication.
-inorganic ions in chemical fertilisers are relatively soluble. this means that excess minerals that are not used immediately are more likely to leach into waterways.
-in natural fertilisers, the nitrogen and phosphorus are still contained in organic molecules that need to be decomposed by microorganisms before they can be absorbed by plants. this means that their release into the soil for uptake by plants is more controlled, and leaching is less likely.
-the leaching of phosphates is less likely than the leaching of nitrates because phosphates are less soluble in water.
47
what is leaching?
leaching is when water-soluble compounds in the soil are washed away. they're often washed into nearby ponds and rivers.
leaching is more likely to occur if the fertiliser is applied just before heavy rainfall.
48
what is eutrophication caused by?
excess nutrients
49
what is the process of eutrophication?
-mineral ions leached from fertilised fields stimulate the rapid growth of algae in ponds and rivers.
-large amounts of algae block light from reaching the plants below in the ponds and rivers.
-eventually the plants die because they're unable to photosynthesise enough.
-bacteria feeds on the dead plant matter. the increased numbers of bacteria reduce the oxygen concentration in the water by carrying out aerobic respiration.
-fish and other aquatic organisms die because there isn't enough dissolved oxygen.
50
what specific properties does ATP have that makes it a good energy source?
-ATP stores or releases only a small, manageable amount of energy at a time, so no energy is wasted as heat.
-it's a small, soluble molecule so it can be easily transported around the cell.
-it's easily broken down, so energy can be easily released instantaneously.
-it can be quickly remade.
-it can make other molecules more reactive by transferring one of its phosphate groups to them.
-ATP can't pass out of the cell, so the cell always has an immediate supply of energy.
51
define metabolic pathways
a series of small reactions controlled by enzymes
52
define phosphorylation
adding phosphate to a molecule
53
define photophosphorylation
adding phosphate to a molecule using light
54
define photolysis
the splitting of a molecule using light (photo) energy
55
define photoionisation
when light energy 'excites' electrons in an atom or molecule, giving them more energy and causing them to be released. the release of electrons causes the atom or molecule to become a positively charged ion
56
define hydrolysis
the splitting of a molecule using water
57
define decarboxylation
the removal of carbon dioxide from a molecule
58
define dehydrogenation
the removal of hydrogen from a moleculedef
59
define redox reactions
reactions that involve oxidation and reduction
60
what is a coenzyme?
a molecule that aids the function of an enzyme.
they work by transferring a chemical group from one molecule to another
61
what coenzyme is used photosynthesis?
NADP. this transfers hydrogen from one molecule to another; this means it can reduce (give hydrogen to) or oxidise (take hydrogen from) a molecule
62
what are chloroplasts?
they are flattened organelles surrounded by a double membrane. they are found in plant cells.
63
what features are in chloroplasts?
-double membrane
-thylakoids
-grana
-stroma
-starch grains
-photosynthetic pigments
64
what are thylakoids?
they are fluid-filled sacs which are stacked up in the chloroplast into structures called grana. the grana are linked together by the thylakoid membrane called lamellae.
65
what is the stroma?
a gel-like substance contained within the inner membrane of the chloroplast, that surrounds the thylakoids.
the stroma contains enzymes, sugars and organic acids
66
what are starch grains?
carbohydrates produced by photosynthesis but are not used straight away are stored as starch grains in the stroma.
67
what are photosynthetic pigments? and list 3 examples
these are coloured substances that absorb light energy needed for photosynthesis. the pigments are found in the thylakoid membranes; attached to the proteins.
e.g chlorophyll a, chlorophyll b and carotene
68
what is a photosystem?
the attachment of a protein and pigment. they are used by plants to capture light energy.
69
what are the two photosystems?
photosystem I
photosystem II
70
at what wavelengths do the photosystems absorb light best?
photosystem I - 700nm
photosystem II - 680nm
71
what two stages make up photosynthesis?
the light-dependent reaction and the light-independent reaction
72
where does the light-dependent reaction take place?
it takes place in the thylakoid membranes of the chloroplasts
73
what occurs in the light-dependent reaction?
light energy is absorbed by chlorophyll and other photosynthetic pigments in the photosystems.
the light energy excites the electrons in the chlorophyll, leading to their eventual release from the molecule. the chlorophyll has been photoionised.
some of the energy from the released electrons is used to add a phosphate group to ADP to form ATP, and some is used to reduce NADP to form reduced NADP.
ATP transfers energy and reduced NADP transfers hydrogen to the light-independent reaction
during the process H2O is oxidised to O2.
74
what is the light-independent reaction also known as?
the Calvin cycle.
75
where does the light-independent reaction take place?
it takes place in the stroma of the cholorplast.
76
what occurs in the light-independent reaction?
the ATP and reduced NADP from the light-dependent reaction supply the energy and hydrogen to make simple sugars from CO2.
77
what is the energy, resulted from the photoionisation of cholorphyll in the light-dependent reaction, used for?
making ATP from ADP and inorganic phosphate. this reaction called photophosphorylation.
making reduced NADP from NADP.
splitting water into protons (H+ ions), electrons and oxygen. this is called photolysis.
78
what are the two types of photophosphorylation?
non-cyclic and cyclic
79
what is involved in non-cyclic photophosphorylation? and what 3 substances does it produce?
it involves photosystem I (PSI) and photosystem II (PSII).
and it produces ATP and reduced NADP and oxygen
80
explain stage 1 in the process of non-cyclic photophosphorylation
stage 1 is the photoionisation of chlorophyll in PSII.
chlorophyll in photosystem II absorbs light energy. this energy causes an electron in the chlorophylll to be excited. the electron is emitted/lost from the chlorophyll molecule. the excited electron is captured by an electron acceptor and it moves along the electron transport chain to PSI.
the cholorphyll molecule is oxidised and becomes positively charged.
81
explain stage 2 in the process of non-cyclic photophosphorylation
stage 2 is the photolysis of water
photoionisation of chlorophyll results in the photolysis of water into oxygen, hydrogen ions and electrons.
the electron lost form the chlorophyll molecule can now be replaced by a reduced chlorophyll molecule.
82
explain stage 3 in the process of non-cyclic photophosphorylation
stage 3 is the electron transport chain and photophosphorylation (chemiosmosis)
as the electron is passed from carrier to carrier along the electron transport chain in a series of redox reactions, energy is released at each stage.
the energy is used to move hydrogen ions from the stroma into the thylakoid space against their concentration gradient creating an electrochemical gradient.
the hydrogen ions pumped into the thylakoid space move down their concentration gradient through the enzyme ATP synthase which is embedded in the thylakoid membrane. the energy from this movement combines ADP + inorganic phosphate to form ATP.
83
explain stage 4 in the process of non-cyclic photophosphorylation
stage 4 is the photoionisation of chlorophyll in PSI
at the exact same time as photoionisation of chlorophyll in PSII: chlorophyll in PSI also absorbs light energy.
an electron gets excited and is emitted/lost from the chlorophyll molecule.
the excited electron is captured by an electron acceptor. the electron lost from the molecule in PSI is replaced by electron that passed down the electron transport chain lost from the chlorophyll in PSII.
84
explain stage 5 in the process of non-cyclic photophosphorylation
stage 5 is the reduction of NADP to reduced NADP
the excited electron from the chlorophyll molecules in photosystem I is passed along a series of electron carriers across another electron transport chain to the final acceptor molecule NADP.
the hydrogen ions from the photolysis of water also combine with NADP to form reduced NADP (NADPH).
85
what is involved in cyclic photophosphorylation? and what substance does it produce?
it involves only PSI.
it only produces ATP.
86
why is cyclic photophosphorylation called 'cyclic'?
it is called 'cyclic' because the electrons from the chlorophyll molecule aren't passed onto NADP, but are passed back to PSI via electron carriers.
87
what are the three stages of the calvin cycle?
stage 1: fixation of carbon dioxide from an inorganic molecule into an organic molecule
stage 2: reduction of GP using reduced NADP and ATP
stage 3: regeneration of RuBP using ATP so the cycle can continue
88
explain stage 1 of the calvin cycle
carbon dioxide reacts with ribulose bisphosphate (RuBP), a 5C compound, in a reaction catalysed by the enzyme Rubisco.
the resulting 6C compound is unstable and immediately breaks down into two molecules of a 3C compound called glycerate-3-phosphate (GP).
89
explain stage 2 of the calvin cycle
the GP is reduced to two molecules of triose phosphate (TP), a 3C compound, using hydrogen (H+)/electrons from reduced NADP and energy from ATP.
TP is then converted to complex organic molecules e.g glucose, sucrose, starch, cellulose, amino acids etc.
90
explain stage 3 of the calvin cycle
five out of every six molecules of TP produced in the cycle are used to regenerate RuBP in a series of enzyme catalysed reactions. this uses energy from ATP.
91
why does the calvin cycle need to turn six times to make one hexose sugar?
-three turns of the calvin cycle produces six molecules of TP because two molecules of TP are made for every one carbon dioxide molecule used.
-five out of six of these TP molecules are used to regenerate RuBP.
-this means that for three turns of the cycle only one TP is produced that's used to make a hexose sugar.
-a hexose sugar has six carbons though, so only two TP molecules are needed to form one hexose sugar.
-this means the cycle must turn six times to produce two molecules of TP that can be used to make one hexose sugar.
-six turns of the cycle need 18 ATP and 12 reduced NADP.
92
what are the three factors that limit the rate of photosynthesis?
light intensity
temperature
carbon dioxide concentration
93
what are the ideal conditions for light intensity in photosynthesis?
-high light intensity of a certain wavelength.
the higher the intensity of the light, the more energy it provides.
only certain wavelengths of light are used for photosynthesis.
the photosynthetic pigments only absorb red and blue in sunlight.
94
what are the ideal conditions for temperature- in photosynthesis?
-temperature around 25 degree celsius.
photosynthesis involves enzymes (e.g ATP synthase, rubisco).
if the temperature falls below 10 degrees the enzymes become inactive, but if the temperature is more than 45 degrees they may start to denature.
also at high temperatures stomata close to avoid losing too much water. this causes photosynthesis to slow down because less CO2 enters the leaf when the stomata are closed.
95
what are the ideal conditions for carbon dioxide concentration in photosynthesis?
-carbon dioxide at 0.4%.
carbon dioxide makes up 0.04% of the gases in the atmosphere.
increasing this to 0.4% gives a higher rate of photosynthesis, but any higher and the stomata start to close.
96
explain the light intensity graph on its approach on limiting the rate of photosynthesis
the graph increases at first and then levels off.
when the graph increases the rate of photosynthesis is limited by light intensity. so as the light intensity increases, so can the rate of photosynthesis.
the point where the graph begins to level off is known as the saturation point, where increasing light intensity after this point makes no difference because something else has become the limiting factor. and so the graph now levels off.
97
explain the temperature graph on its approach on limiting the rate of photosynthesis
the graph levels off when light intensity is no longer the limiting factor. however the graph levels off at a higher point where the rate of photosynthesis was at 25 degrees. this shows that the temperature must have been a limiting factor because it increases the rate of photosynthesis, rather than levelling off at the same area of the light intensity graph.
the temperature graph shows that the point of 15 degrees is where light intensity stopped being the limiting factor and instead temperature kicked in.
98
explain the carbon dioxide concentration graph on its approach on limiting the rate of photosynthesis
the graph, again, levels off when light intensity is no longer the limiting factor. however when this occurs the carbon dioxide concentration is at 0.04%. at 0.4% the line graph is at a higher point, showing that the rate of photosynthesis has increased. at 0.04% the line graph levels off at a lower point and so it shows that CO2 conc. became a limiting factor at 0.04%.
in this case the limiting factor wouldn't be temperature as they're both at 25 degrees. instead it's the CO2 conc. that's leading to the change of the rate of photosynthesis.
99
how do agricultural growers use information about limiting factors to increase plant growth?
agricultural growers know the factors that limit photosynthesis and therefore limit plant growth. this means they try to create an environment where plants get the right amount of everything that they need, which increases growth and increases yield.
they create optimum conditions in glasshouses.
100
what are the optimum conditions of the limiting factors that agricultural growers make in glasshouses?
carbon dioxide concentration: CO2 is added to the air by burning a small amount of propane.
light: light can get in through the glass. lamps provide light at night-time.
temperature: glasshouses trap heat energy from sunlight, which warms the air. heaters and cooling systems can also be used to keep a constant optimum temperature.
101
what are the two types of respiration?
aerobic (requires oxygen)
anaerobic (doesn't require oxygen)
102
what do both types of respiration have in common?
they both produce ATP
they both start with the process of glycolysis.
103
what are the four stages of respiration?
stage 1: glycolysis
stage 2: link reaction
stage 3: krebs cycle
stage 4: oxidative phosphorylation
104
what is glycolysis?
glycolysis involves splitting one molecule of glucose into two smaller molecules of pyruvate.
this process happens in the cytoplasm of cells.
there are 2 stages in glycolysis: phosphorylation and oxidation.
105
explain stage 1 of glycolysis
glucose is phosphorylated using a phosphate from a molecule of ATP. this creates 1 molecule of glucose and 1 molecule of ADP.
ATP is then used to add another phosphate, forming hexose biphosphate.
hexose biphosphate is then split into 2 molecules of triose phosphate.
106
explain stage 2 of glycolysis
triose phosphate is oxidised (loses hydrogen), forming 2 molecules of pyruvate.
NAD collects the hydrogen ions, forming 2 reduced NAD.
4 ATP are produced, but 2 were used up in stage one, so there's a net gain of 2 ATP.
107
what are the products of glycolysis in aerobic respiration and where do the products go?
2 reduced NAD- goes to stage 4 (oxidative phosphorylation)
2 pyruvate- actively transported into the mitochondrial matrix for use in the link reaction
2 ATP (net gain)- used for energy
108
what are the products of glycolysis in anaerobic respiration and where do the products go?
pyruvate- converted into ethanol (alcoholic fermentation) in plants and yeast.
pyruvate- converted to lactate in lactate fermentation in animal cells and some bacteria.
109
what is the benefit of the production of lactate and ethanol in anaerobic respiration?
production of lactate or ethanol regenerates oxidised NAD. this means glycolysis can continue even when there isn't much oxygen around.
110
what happens in the link reaction stage?
pyruvate is decarboxylated (one carbon is removed from pyruvate in the form of CO2).
pyruvate is oxidised to form acetate and NAD is reduced to form reduced NAD.
acetate is combined with coenzyme A (CoA) to form acetyl coenzyme A (acetyl CoA).
no ATP is produced in this reaction.
111
how often does the link reaction occur for every glucose molecule?
twice. this is because two pyruvate molecules are made for every glucose molecule that enters glycolysis.
112
what are the products of link reaction in aerobic respiration and where do the products go?
2 acetyl coenzyme A- goes to the Krebs cycle
2 carbon dioxide- released as a waste product
2 reduced NAD- goes to oxidative phosphorylation
113
what is the krebs cycle?
it involves a series of oxidation-reduction reactions, which take place in the matrix of the mitochondria. the cycle happens once for every pyruvate molecule, so it goes round twice for every glucose molecule.
114
explain the process of the krebs cycle.
1) acetyl coA from the link reaction combines with a four-carbon molecule (oxaloacetate) to form a six-carbon molecule (citrate).
coenzyme A goes back to the link reaction to be used again.
2) the 6C citrate molecule is converted to a 5C molecule.
decarboxylation occurs, where CO2 is removed.
dehydrogenation also occurs, where hydrogen is removed.
the hydrogen is used to produce reduced NAD from NAD.
3) the 5C molecule is then converted to a 4C molecule. during this conversion there are some intermediate compounds formed.
decarboxylation and dehydrogenation occur, producing one molecule of reduced FAD and two of reduced NAD.
ATP is produced by the direct transfer of a phosphate group from an intermediate compound to ADP. when a phosphate group is directly transferred from one molecule to another it's called substrate-level phosphorylation. citrate has now been converted into oxaloacetate.
115
what are the products of the krebs cycle in aerobic respiration and where do the products go?
1 coenzyme A- reused in the next link reaction
oxaloacetate- regenerated for use in the next krebs cycle
2 CO2- released as a waste product
1 ATP- used for energy
3 reduced NAD- to oxidative phosphorylation
1 reduced FAD- to oxidative phosphorylation
116
what is oxidative phosphorylation?
it is the process where energy is carried by electrons, from reduced coenzymes, is used to make ATP.
oxidative phosphorylation involves the electron transport chain and chemiosmosis.
117
how does oxidative phosphorylation actually work?
- hydrogen atoms are released from reduced NAD and reduced FAD as they've oxidised to NAD and FAD. the H atoms split into protons and electrons.
- the electrons move down the electron transport chain losing energy at each carrier.
- this energy is used by the electron carriers to pump protons from the mitochondrial matrix into the intermembrane space.
- the conc. of protons is now higher in the intermembrane space than in the mitochondrial matrix; this forms an electrochemical gradient (a concentration gradient of ions).
- protons then move down the electrochemical gradient, back across the inner mitochondrial membrane and into the mitochondrial matrix, via ATP synthase. this movement drives the synthesis of ATP from ADP and inorganic phosphate.
- this process of ATP production driven by the movement of H+ ions across a membrane is called chemiosmosis.
- in the mitochondrial matrix, at the end of the transport chain, the protons, electrons and oxygen combine to form water. oxygen is said to be the final electron acceptor.
118
how much ATP is made from one glucose molecule and how?
32 ATP. this is because 2.5 ATP is made from each reduced NAD and 1.5 ATP is made from reduced FAD, so when multiplied and added, it all sums to 32
119
how can mitochondrial diseases affect ATP production?
mitochondrial diseases affect the functioning of mitochondria. they can affect how proteins are involved in oxidative phosphorylation or the Krebs cycle function, reducing ATP production.
this may cause anaerobic respiration to increase, to try and make up some of the ATP shortage.
this results in lots of lactate being produced, which can lead to muscle fatigue and weakness.
some lactate will also diffuse into the bloodstream, leading to high lactate concentrations in the blood.
120
what other respiratory substances can be used in aerobic respiration?
fatty acids from lipids
amino acids from proteins
121
Exam Q:
State why dry biomass is a more accurate measurement than wet biomass. (2)
Organisms contain different amounts of water in their tissues (1)
Dry biomass enables comparisons to be made between different organisms that are due to tissue water content (1)
122
Exam Q:
The simple calorimeter does not produce a completely accurate estimate of the energy stored inside the plant tissue sample.
Suggest two reasons why the estimate may not be completely accurate. (2)
Heat energy escapes through the lid/draught excluder (1)
The sample may not be completely burned up (1)
123
