Energy Transfers (3.5) Flashcards
This topic covers: photosynthesis, respiration, energy transfers and nutrient cycles.
AS Recap (Gas Exchange)
Explain the relationship between stomatal opening and photosynthesis (2 marks).
- Stomata allow uptake of carbon dioxide;
- Carbon dioxide is required for photosynthesis
AS Recap (Gas Exchange)
Describe how carbon dioxide in the air outside a leaf reaches mesophyll cells inside the leaf (3 marks).
- Carbon dioxide enters via stomata;
- (Stomata opened by) guard cells;
- Diffuses through air spaces (in the spongy mesophyll layer);
- Down diffusion/concentration gradient;
AS Recap (Cells)
Which of the below plant cell organelles has stacked membranes arranged in parallel and contains DNA. (1 mark).
Cell Wall
Chloroplast
Nucleus
Mitochondrion
Golgi apparatus
Chloroplast
AS Recap (Cells)
Give one feature of the chloroplast that allows protein to be synthesised inside the chloroplast and describe one difference between this feature in the chloroplast and similar features in the rest of the cell (2 marks).
Mark in pairs, 1 and 2 OR 3 and 4
- Feature: DNA;
- Difference: Is not associated with protein/histones but nuclear DNA is;
OR Is circular but nuclear DNA is linear
OR Is shorter than nuclear DNA;
- Ribosomes;
- Are smaller than cytoplasmic ribosomes;
Accept: 70S ribosomes in chloroplast, but 80S ribosomes in cytoplasm
AS recap (Cells)
Where is chlorophyll located in a plant mesophyll cell (1 mark)?
Thylakoid membrane (of granum) found in chloroplasts.
A2 (Photosynthesis AO1)
What process do photoautotrophic organisms use to convert carbon dioxide into organic molecules (1 mark)?
Photosynthesis
A2 (Photosynthesis AO1)
Which reaction comes first in photosynthesis (1 mark)?
Light-dependent
A2 (Photosynthesis AO1)
What molecule’s electrons are elevated to a higher energy state during photoionisation (1 mark)?
Chlorophyll
A2 (Photosynthesis AO1)
Where does the light-dependent reaction take place within the plant mesophyll cell (1 mark)?
Thylakoid membrane
A2 (Photosynthesis AO1)
What is the term for the splitting of water into H+, e- and oxygen (1 mark)?
Photolysis
A2 (Photosynthesis AO1)
What waste product is generated as a result of photolysis of water (1 mark)?
Oxygen
A2 (Photosynthesis AO1)
Which chemicals are needed for the light-dependent reaction? (1 mark)
NADP, ADP, Pi and water
A2 (Photosynthesis AO1)
Describe what happens during photoionisation in the light-dependent reaction (2 marks).
- Chlorophyll absorbs light energy
OR Light excites/moves electrons in chlorophyll;
- Electron/s are lost
Accept electrons go to electron transport chain for ‘electrons lost’.
A2 (Photosynthesis AO1)
What are the products of the light-dependent reaction? (1 mark)
NADPH and ATP
Reduced NADP is accepted.
A2 (Photosynthesis AO1)
Energy enters most ecosystems through the light-dependent reaction of photosynthesis.
Describe what happens during the light-dependent reaction (5 marks).
- Chlorophyll absorbs light energy;
- Excites electrons / electrons removed (from chlorophyll);
- Electrons move along electron transport chain releasing energy;
- Energy used to join ADP and Pi to form ATP;
- Photolysis of water produces protons, electrons and oxygen;
- NADP reduced by electrons and protons
A2 (Photosynthesis AO1)
Describe the role of chlorophyll in photolysis (3 marks).
Absorbs light energy;
Loses electrons;
Accepts electrons from water
A2 (Photosynthesis AO1)
Describe how NADP is reduced in the light-dependent reaction of photosynthesis (2 marks).
by electrons;
from chlorophyll / photolysis
A2 (Photosynthesis AO1)
What molecule is a nitrogen-containing biological molecule, a type of nucleotide, and has two phosphate groups? (1 mark)
NADP
A2 (Photosynthesis AO1)
What process involves the movement of protons down their gradient to produce ATP? (1 mark)
Chemiosmosis
A2 (Photosynthesis AO1)
Where does the Calvin cycle take place? (1 mark)
Stroma
Therefore the enzyme rubisco is located in the stroma.
A2 (Photosynthesis AO1)
Describe one function of NADPH in the light-independent reaction (1 mark).
Provides H / electrons for the reduction of GP to triose phosphate
You must say triose phosphate in full!
A2 (Photosynthesis AO1)
Describe one function of ATP in the light-independent reaction (1 mark).
Provides energy for the reduction of GP to triose phosphate;
Provides Pi to convert triose phosphate to RuBP;
A2 (Photosynthesis AO1)
Describe the light-independent reaction of photosynthesis (6 marks).
- Carbon dioxide combines/reacts with ribulose bisphosphate/RuBP;
- Produces two GP molecules using (enzyme) Rubisco;
- GP reduced to triose phosphate;
- Using reduced NADP / NADPH;
- Using energy from ATP hydrolysis;
- Triose phosphate converted to glucose/hexose/RuBP/ribulose bisphosphate/named organic substance;
A2 (Photosynthesis AO2)
Heat stress is a condition that often occurs in plants exposed to high temperatures for a prolonged period of time. Heat stress is a major factor in limiting the rate of photosynthesis.
Heat stress decreases the light-dependent reaction of photosynthesis.
Explain why this leads to a decrease in the light-independent reaction (2 marks).
- Less ATP;
- Less reduced NADP / NADPH;
A2 (Photosynthesis AO2)
Atrazine is a herbicide used to reduce the growth of weeds.
Atrazine binds to proteins in the electron transfer chain in chloroplasts of weeds, reducing the transfer of electrons down the chain.
Explain how this reduces the rate of photosynthesis in weeds (4 marks).
- Reduced transfer of protons across thylakoid membrane
OR
Reduced chemiosomotic gradient / proton gradient across thylakoid membrane;
- (So) less ATP produced;
- (So) less reduced NADP / NADPH produced;
- (So) less reduction of GP to triose phosphate.
OR
(So) light-independent reaction slows / stops;
A2 (Photosynthesis AO2)
Iron deficiency reduces electron transport. Use this information and your knowledge of photosynthesis to explain the decrease in production of triose phosphate in the iron-deficient plants (4 marks).
- ATP and reduced NADP produced during light-dependent reaction;
(In the case of iron deficiency)
- Less ATP produced;
- Less reduced NADP produced;
- Less GP to triose phosphate;
A2 (Photosynthesis AO2)
Some bacteria use hydrogen sulfide, H2S, to produce organic compounds. The hydrogen sulfide has a similar role to that of water in photosynthesis.
A simple equation for this process in bacteria is shown below:
hydrogen sulfide + carbon dioxide → glucose + sulfur + water
Suggest what the hydrogen sulfide is used for in these bacteria (2 marks).
- (Provides) hydrogen/protons/H+ and electrons/e-;
- For reduction (of NADP);
- Source of electrons for chlorophyll / electron transfer chain;
A2 (Photosynthesis AO2)
Another effect of heat stress is a decrease in the activity of the enzyme rubisco. A decrease in the activity of an enzyme means that the rate of the reaction it catalyses becomes slower.
A decrease in the activity of the enzyme rubisco would limit the rate of photosynthesis.
Explain why (2 marks).
- Less carbon dioxide (reacts) with RuBP;
- Less GP;
A2 (Photosynthesis AO2)
Plants produce ATP in their chloroplasts during photosynthesis. They also produce ATP during respiration.
Explain why it is important for plants to produce ATP during respiration in addition to during photosynthesis (5 marks).
- In the dark no ATP production in photosynthesis in leaves;
- Some tissues (e.g. roots) unable to photosynthesise / produce ATP;
- ATP cannot be moved from cell to cell / stored
(as it is an immediate energy compound); - Plant uses more ATP than produced in photosynthesis;
- For example, ATP required for active transport / protein synthesis;
A2 (Photosynthesis AO2)
An investigation was carried out into the effect of carbon dioxide concentration and light intensity on the rate of photosynthesis in a species of plant.
The temperature was kept constant during this investigation. Explain why (2 marks).
Temperature affects photosynthesis;
because it affects enzyme activity;
So that any change in photosynthesis rate is result of carbon dioxide / light intensity;
A2 (Photosynthesis AO1)
List potential limiting factors for photosynthesis
Temperature
Carbon dioxide concentration
Light intensity
Wavelength of light
AS Recap (Cells)
Identify organelles S and T
S = Vacuole
T = Chloroplast
AS Recap (Cells)
Identify structures D and E
D = Grana/granum/thylakoid
E = Starch/lipid
AS Recap (Cells)
B;
A;
E;
AS Recap (ATP)
Describe how an ATP molecule is formed from its component molecules (4 marks).
- and 2. Accept for 2 marks correct names of three components adenine, ribose, three phosphates;;
- Condensation (reaction);
- (catalysed by) ATP synthase;
A2 (Photosynthesis AO2)
Data from an investigation showed that mutant plants producing more chlorophyll b grow faster than normal plants in all light intensities.
Explain how (4 marks).
- Have faster production of ATP and reduced NADP;
- (So) have faster / more light-independent reaction;
- (So) produce more sugars that can be used in respiration;
- (So) have more energy for growth;
- Have faster / more synthesis of new organic materials (e.g. amino acids).
A2 (Photosynthesis AO2)
During an investigation into the rate of photosynthesis.
Explain why scientists measured the rate of production of oxygen in this investigation (2 marks).
Oxygen is produced in the light dependent reaction
The faster the oxygen produced, the faster the light dependent reaction.
AS Recap (ATP)
Draw out and label a single molecule of ATP
P = phosphate, not phosphorus.
Which organelle is shown in the below TEM?
Mitochondrion
Singular, plural = mitochondria
AS Recap (ATP)
ATP is useful in many biological processes. Explain why (4 marks).
- Releases energy in small / manageable amounts;
- (Broken down) in a one step / single bond broken OR immediate energy compound / makes energy available rapidly;
- Phosphorylates / adds phosphate makes (phosphorylated substances) more reactive / lowers activation energy;
- Do not accept phosphorus or P on its own
- Rapidly reformed / made again;
- Is not lost from / does not leave cells.
AS Recap (Cells)
Identify X
Cristae
Part of the folds of the inner mitochondrial membrane
AS Recap (Cells)
AS Recap (Cells)
Give the function of a mitochondrion.
The site of aerobic respiration (reactions)
OR
ATP is made / ADP is phosphorylated;
A2 (Respiration AO1)
Respiration produces ………………………
ATP
A2 (Respiration AO1)
TRUE OR FALSE:
Glycolysis is the first stage of anaerobic AND aerobic respiration
TRUE
A2 (Respiration AO1)
Where does glycolysis take place?
Cytoplasm
A2 (Respiration AO1)
Describe the process of glycolysis (4 marks).
1. Phosphorylation of glucose using ATP;
2. Oxidation of triose phosphate to pyruvate;
3. Net gain of (2) ATP (molecules);
4. NAD reduced/ NADH produced;
A2 (Respiration AO1)
If respiration is aerobic, pyruvate from glycolysis enters the mitochondrial matrix by…………………….
active transport
Pyruvate therefore crosses the double membrane of mitochondria
A2 (Respiration AO1)
Where does the link reaction take place?
(Mitochondrial) matrix
A2 (Respiration AO1)
Pyruvate is oxidised to ……………….. during the link reaction.
Acetate
This produces carbon dioxide and NADH
A2 (Respiration AO1)
Describe how acetylcoenzyme A is formed in the link reaction (2 marks)
1. Oxidation of / hydrogen removed from pyruvate AND carbon dioxide released;
2. Addition of coenzyme A (to 2C acetate).
A2 (Respiration AO1)
What are the reactants needed for the link reaction?
Pyruvate
NAD
CoenzymeA
A2 (Respiration AO1)
Acetylcoenzyme A reacts with a four-carbon molecule, releasing coenzyme A and producing a six-carbon molecule that enters the ……………………..
Krebs cycle
A2 (Respiration AO1)
Where does the Krebs cycle take place?
(Mitochondrial) matrix
A2 (Respiration AO1)
The Krebs cycle is a series of oxidation-reduction reaction that produces………
Products through oxidation-reduction:
Reduced NAD / NADH
Reduced FAD / FADH
other products:
ATP by substrate-level phosphorylation
Carbon dioxide
A2 (Respiration AO1)
What is the name of the enzyme that helps to produce NADH and FADH?
Dehydrogenase
A2 (Respiration AO1)
What is the name of the enzyme that helps to produce carbon dioxide during the link reaction and Krebs cycle?
Decarboxylase
A2 (Respiration AO1)
A2 (Respiration AO1)
TRUE OR FALSE:
FADH is produced during the link reaction and Krebs cycle
FALSE
FADH is only produced during the Krebs cycle
A2 (Respiration AO1)
Malonate inhibits a reaction in the Krebs cycle.
Explain why malonate would decrease the uptake of oxygen in a respiring cell.
- Less/no reduced NAD/ reduced FAD OR
Fewer/no hydrogens/electrons removed (and passed to electron transfer chain);
- Oxygen is the final/terminal (electron) acceptor;
Less NADH/FADH = less electron transfer, so less oxygen required.
A2 (Respiration AO1)
Describe how ATP is made in mitochondria (6 marks).
Substrate level phosphorylation
- ATP produced in Krebs cycle;
Oxidative phosphorylation
- Krebs cycle and link reaction produces NADH;
Krebs cycle produces FADH
- Electrons released from NADH / FADH;
- (Electrons) pass along carriers / through electron transport chain / through series of redox reactions;
- Energy released;
- Protons move into intermembrane space (electrochemical / proton gradient forms);
(Protons move down electrochemical gradient and release energy used to combine)
- ADP / ADP + Pi;
- ATP synthase
A2 (Respiration AO1)
What do NADH and FADH bring to the electron transport chain?
(High energy) electrons
A2 (Respiration AO1)
Where is the electon transport located in the mitochondria?
In the cristae (the folds of the inner mitochondrial membrane)
A2 (Respiration AO1)
What is advantage of the cristae during oxidative phoshorylation?
Large surface area, so more inner membrane to embed more electron transport chain (e.g. proton pumps) and ATP synthase.
A2 (Respiration AO1)
What are the 4 stage of aerobic respiration?
- Glycolysis
- Link reaction
- Krebs cycle
- Oxidative phosphorylation
A2 (Respiration AO1)
Explain why oxygen is needed for the production of ATP on the cristae of mitochondria (3 marks)?
1. ATP formed as electrons pass along transport chain (ETC);
2. Oxygen is final electron acceptor / accepts electrons from electron transport chain;
3. Forms H2O (accepts H+ from reduced NAD/FAD / oxidises reduced NAD/FAD);
4.. Electrons cannot be passed along electron transport chain if there is no O2 to accept them;
A2 (Respiration AO1)
Describe how oxidation takes place in glycolysis and in the Krebs cycle (4 marks).
1. Removal of hydrogen;
2. By enzymes/dehydrogenases;
3. H accepted by NAD / reduced NAD formed;
(Triose phosphate is oxidised)
4. In Krebs cycle, FAD (used as well);
A2 (Respiration AO1)
List alternative respiratory substrates
Amino acids
Fatty acids
Glycerol
A2 (Respiration AO1)
TRUE OR FALSE:
Fatty acids, glycerol and amino acids can also enter the Krebs cycle to contribute to the generation of ATP
TRUE
A2 (Respiration AO2)
- Less / no malonyl-CoA produced;
- More fatty acids transported / moved into mitochondria;
- Respiration / oxidation of fatty acids provides ATP;
A2 (Respiration AO1)
Which organisms produce carbon dioxide AND ethanol during anaerobic respiration
Yeast
Bacteria
Some plants
A2 (Respiration AO1)
In which animal cells does anaerobic respiration mainly take place?
Muscle cells
Specifically fast-twich muscle fibres
A2 (Respiration AO1)
What are the products of anaerobic respiration in animal cells?
Lactate / lactic acid
ATP (net yield of 2 ATP)
NAD
A2 (Respiration AO1)
What are the 2 main phases of anaerobic respiration?
- Glycolysis
- Regeneration of NAD
A2 (Respiration AO1)
Where does anaerobic respiraiton take place?
Cytoplasm
A2 (Respiration AO1)
Pyruvate is ____________ to ethanol and carbon dioxide in some plants and yeast.
reduced
A2 (Respiration AO1)
Pyruvate is ________________ to lactate in animal cells.
reduced
A2 (Respiration AO1)
Reduction of pyruvate
A2 (Respiration AO1)
Explain why converting pyruvate to lactate allows the continued production of ATP during anaerobic respiration (2 marks).
-
Regenerates NAD
(accept oxidises reduced NAD); - NAD used in glycolysis.
A2 (Respiration AO2)
In muscles, some of the lactate is converted back to pyruvate when they are well supplied with oxygen.
Suggest one advantage of this.
Pyruvate used in aerobic respiration / can enter the link reaction
OR
Less lactate so less cramp / muscle fatigue.
A2 (Respiration AO1)
Humans synthesise more than their body mass of ATP each day.
Explain why it is necessary for them to synthesise such a large amount of ATP.
- ATP cannot be stored / is an immediate source of energy;
- ATP only releases a small amounts / packets of energy at a time;
A2 (Respiration AO1)
Aerobic respiration produces more ATP per molecule of glucose than anaerobic respiration.
Explain why ( 2 marks).
- Oxygen is final/terminal (electron) acceptor /
- (This allows aerobic respiration) oxidative phosphorylation / electron transfer chain;
- Anaerobic (respiration) only glycolysis occurs
(so some ATP produced via substrate level phosphorylation)
A2 (Respiration AO2)
- Fewer cristae/smaller surface area (of cristae);
- So less electron transport/oxidative phosphorylation;
- (So) not enough ATP produced
OR Not enough energy to keep neurones alive;
A2 (Respiration AO1)
During anaerboc respiration, a build up of ethanol in yeast cells is ____________ .
toxic
This may lead to some yeast cells dying
A2 (Respiration AO1)
A2 (Respiration AO1)
1. Oxygen used by seeds (aerobic respiration);
2. Carbon dioxide produced is absorbed by potassium hydroxide;
3. Decrease in pressure/volume (of air inside);
A2 (Respiration AO1)
In an experiment using a respirometer, apart from time, give two measurements the student would have to make to determine the rate of aerobic respiration of these seeds in cm3 hour–1.
- Distance liquid moves;
- Diameter/radius of the tubing/lumen
A2 (Respiration Maths)
A2 (Respiration AO1)
- Equilibrium reached / allow to equilibrate
- Allow for pressure change in apparatus;
- Allow respiration rate of seeds to stabilise.
A2 (Respiration AO2)
Prevents oxygen being taken up / entering / being absorbed
A2 (Respiration AO2)
- Affects enzymes;
- Affects respiration;
OR
- Affects volume / pressure of gases;
- Affects readings;
Energy transfers (AO1)
In any ecosystem, plants synthesise ________________ compounds from atmospheric, or aquatic, carbon dioxide.
organic
Organic means the molecule contains c-c or c-h bonds
Energy transfers (AO1)
Most of the sugars synthesised by plants are used by the plant as respiratory substrates. The rest are used to make other groups of biological molecules. These biological molecules form the ______________ of the plants.
biomass
Energy transfers (AO1)
Producers are _______________ organisms that manufacture their own organic compounds using light energy, water and carbon dioxide.
photosynthetic
Energy transfers (AO1)
Primary consumers obtain their energy by feeding on ___________.
producers
Energy transfers (AO1)
____________________ are a group of organisms that break down the organic materials in dead organic matter and faeces into simple ones.
Saprobionts / decomposers
Energy transfers (AO1)
In natural ecosystems, most of the light energy falling onto producers is NOT used in photosynthesis. Explain why (2 marks).
- Light being reflected
- Pigments may not absorb the wavelength of light received
- Light may miss the chlorophyll
- There is another limiting factor that means that the light cannot be used e.g. carbon dioxide concentration
Energy transfers (AO1)
Farming cattle for humans to eat is less efficient than farming crops because of energy transfer. Explain why (2 marks).
- Energy lost during transfer between trophic levels;
(Humans eating cattled adds a trophic level)
- Energy lost via respiration / heat loss / maintaining temperature / muscle contraction / movement
Also accept: excretion / faeces / parts of food not eaten e.g. roots/bones;
Energy transfers (AO1)
What is the equation for energy efficiency?
Energy transfers (Maths)
0.155%
Energy transfers (AO1)
Definition of biomass
Total mass of carbon per given area per given time
OR
Total dry mass of tissue per given area per given time
Energy transfers (AO1)
Give three reasons for the low efficiency of energy transfer from secondary consumers to tertiary consumers in an ecosystem.
1. Heat (loss) from respiration;
2. (Food) not digested
OR Not all eaten;
3. Excretion;
Energy transfers (AO1)
The chemical energy stored in dry biomass can be estimated using _____________.
calorimetry
Energy transfers (AO2)
Suggest how you could determine the dry mass of a sample of plant material (2 marks).
- Heat at 100°C to evaporate water;
(Or value which would not burn material)
- Weigh and heat until no further change in mass
Energy transfers (AO2)
What is the advantage of using dry mass and not fresh mass to compare the yield of plants (2 marks).
- Water content present will vary in fresh mass;
- This issue will not affect dry mass;
Energy transfers (AO1)
Gross primary production (GPP) is the ____________ energy store in plant biomass, in a given area or volume.
chemical
Energy transfers (AO1)
The higher GPP, the higher the rate of ______________
photosynthesis
Energy transfers (AO1)
What is the equation for Net Primary Production (NPP)?
NPP = GPP-R
Where:
GPP = Gross primary production
R = respiratory losses
Energy transfers (AO1)
This NPP is available for _____________
plant growth and reproduction
Energy transfers (AO1)
What is the equation for the net production of consumers (N)?
N = I - (F+R)
Energy transfers (AO1)
In the below equation, what does I represent?
N = I - (F+R)
I = Chemical energy/store of ingested/consumed food
Energy transfers (AO1)
In the below equation, what does F represent?
N = I - (F+R)
(energy loses due to)
F = faeces and urine
Energy transfers (AO1)
In the below equation, what does R represent?
N = I - (F+R)
R = Respiratory losses
(due to heat loss / maintaining temperature / movement)
Energy transfers (AO1)
In the below equation, what does N represent?
N = I - (F+R)
N = net production of consumers
Energy transfers (Maths)
Energy transfers (AO1)
What are suitable units for the energy stored in biomass?
Energy transfers (AO1)
What are suitable units for net primary or secondary productivity?
Energy transfers (AO1)
Describe how calorimetry can estimate the energy stored in biomass.
Sample of (dry) biomass is combusted;
This releases heat energy;
This warms the surrounding water;
The larger the temperature increases of water, the more energy stored in the biomass;
Water is used because it has a high specific heat capacity
(we know much energy is required to heat 1cm3 of water by 1oC).
Energy transfers (AO1)
- Stirrer distributes heat energy;
- Insulation by air spaces reduces heat loss
- Water has a high specific heat capacity
Energy transfers (Maths)
Energy transfers (AO1)
To increase the net productivity of domestic livestock, farmers aim to decrease energy losses due to ________.
Respiration / heat loss / maintaining body temperature / movement;
Energy transfers (AO1)
- Organic
- Respiration
- Carbon
Accept tissue(s)/plant(s)/animal(s)/organism(s)
- Calorimetry;
Energy transfers (AO2)
- Low respiration;
Accept less energy lost in respiration
- More growth/biomass
Energy transfers (AO1)
Explain why farmers try to reduce respiratory losses (e.g. by keeping animals indoors during the winter).
More energy is available for growth/biomass
Energy transfers (AO1)
Explain why simplifying food webs reduces energy losses to non-human food chains (2 marks).
- Insecticides/pesticides/fungicides are used to exclude competitors who may feed on crops;
- This means a higher N (net production of consumers) / more energy available for growth/biomass of crops
Nutrient Cycles (AO1)
Nitrogen cycle stages
Nitrogen fixation
Nitrification
Ammonification
Denitrification
Nutrient Cycles (AO1)
What is the name of the microorganism involved in nitrogen fixation?
Nitrogen fixing bacteria
Nutrient Cycles (AO1)
Where are nitrogen fixing bacteria found?
Root nodules
OR
Free in the soil
Nutrient Cycles (AO1)
What reaction do nitrogen fixing bacteria undertake?
Convert atmospheric nitrogen into ammonia
Nutrient Cycles (AO1)
Describe nitrification
Ammonia into nitrites;
Nitrites into nitrates;
By nitrifying bacteria
Nutrient Cycles (AO1)
What is the name of the microorganism that returns nitrogen to the atmoshphere?
Denitrifying bacteria
Nutrient Cycles (AO1)
What reaction do denitrifying bacteria undertake?
Convert nitrates in the soil into atmospheric nitrogen
(in anerobic / waterlogged conditions)
Nutrient Cycles (AO1)
In what chemical form is nitrogen absorbed into the plant roots.
Nitrates
Nutrient Cycles (AO1)
After nitrates have been absorbed from the soil via the plant roots. This nitrogen is _________ into the plant’s tissues.
assimilated
Nutrient Cycles (AO1)
What is the name of the microorganism that will use enzymes to hydrolyse nitrogen-containing molecules such as proteins in faeces and dead remains.
Saprobionts
Nutrient Cycles (AO1)
Describe the role of saprobionts in the nitrogen cycle (Ammonification stage) (2 marks).
- (They use enzymes to) decompose proteins/DNA/RNA/urea;
Accept digest/breakdown/hydrolyse for decompose
- Producing/releasing ammonia/ammonium ions;
Nutrient Cycles (AO1)
Describe how the action of microorganisms in the soil produces a source of nitrates for crop plants (5 marks).
(Nitrogen fixation)
Nitrogen into ammonia;
By nitrogen-fixing bacteria;
(Nitrification)
3. (oxidation of) ammonia into nitrite;
4. Nitrite into nitrate;
5. By nitrifying bacteria;
(Ammonification)
6. protein / amino acids / DNA into ammonia
7. (use enzymes to decompose) by saprobionts;
Nutrient Cycles (AO1)
Give two examples of biological molecules containing nitrogen that would be removed when a crop is harvested.
Any two from:
1. amino acid / protein / polypeptide / peptide;
- nucleic acid / nucleotide / base;
- DNA;
- RNA;
- ATP / ADP;
- NAD / NADP (reduced or not);
- Cyclic AMP / cAMP;
- Chlorophyll;
Nutrient Cycles (AO1)
After harvesting, the remains of crop plants are often ploughed into the soil.
Explain how microorganisms in the soil produce a source of nitrates from these remains (5 marks).
(Ammonification)
1. Protein/amino acids/DNA/urea into ammonia;
2. By saprobionts
(Nitrification)
3. Ammonia into nitrite;
4. Nitrite into nitrate ;
5. By nitrifying bacteria;
Note: there are no marks for the role of nitrogen-fixing bacteria as the question refers to producing a source of nitrates from the remains of crops.
Nutrient Cycles (AO1)
How can a farmer replace the nitrates and phosphates lost from the soil following the harvest of crops?
Add natural (e.g. manure / compost) AND/OR
artificial (e.g. liquid ammonia) fertilisers
Nutrient Cycles (AO2)
Freshwater marsh soils are normally waterlogged. This creates anaerobic conditions.
Use your knowledge of the nitrogen cycle to suggest why these soils contain relatively high concentrations of ammonium compounds and low concentrations of nitrite ions and nitrate ions (2 marks).
- Less nitrification
OR Fewer/less active nitrifying bacteria;
OR Nitrifying bacteria require oxygen/aerobic conditions;
- (Less) oxidation/conversion of ammonia to nitrite (ions) and to nitrate (ions);
- More denitrification
OR More/more active denitrifying bacteria
OR denitrifying bacteria require anaerobic conditions;
- (So more) nitrate (ions) reduced/converted to nitrogen (gas);
Nutrient Cycles (AO1)
What is the role of mycorrhizae?
Increase uptake of water and inorganic ions by plants.
Nutrient Cycles (AO1)
TRUE OR FALSE
Mycorrhizal networks can connect the roots of plants growing next to each other so the plants can exchange biological molecules.
TRUE
Nutrient Cycles (AO1)
Explain how mycorrhizae networks can increase plant growth?
Increase surface area;
For absorption of water and mineral ions;
Which are used for growth/protein synthesis/respiration/photosynthesis
Nutrient Cycles (AO1)
Describe the phosphorus cycle
(5 marks).
- Phosphate ions in rocks are eroded by water/weather
- Dissolve into water systems and soil
- Absorbed by plants and assimilated into compounds such as nucleic acids and phospholipids
- These can be passed on during feeding to higher trophic levels
- Excretion of phosphate ions in waste and decomposition of remains by saprobionts
- Deposition of these phosphate ions leads to phosphate held in rocks
OR
Sedimentation of phosphate ions in water leads to phosphates in rocks
Nutrient Cycles (AO2)
Nitrogenase catalyses the reduction of nitrogen during nitrogen fixation. The reaction requires 16 molecules of ATP for each molecule of nitrogen that is reduced.
When ammonia inhibits nitrogenase activity, nitrogen-fixing bacteria may benefit.
Explain how (2 marks).
- Less/no ATP/energy required/used
OR More ATP/energy available;
- ATP/energy can be used for growth/synthesis/replication
OR Lower (rate of) respiration required
OR ATP for phosphorylation;
Nutrient Cycles (AO1)
Suggest one way in which arbuscular mycorrhiza fungi may benefit from their association with plants.
Receive a carbon-containing biological compound e.g. glucose / carbohydrate / amino acid;
Nutrient Cycles (AO1)
Arbuscular mycorrhiza fungi (AMF) are fungi which grow on, and into, the roots of plants. AMF can increase the uptake of inorganic ions such as phosphate.
Suggest one way in which an increase in the uptake of phosphate could increase plant growth.
Used to produce named phosphate compound in cells;
e.g. ATP / ADP / phospholipids / DNA / RNA / RuBP / Triose Phosphate /GP.
Nutrient Cycles (AO1)
R
Nutrient Cycles (AO2)
One farming practice used to maintain high crop yields is crop rotation. This involves growing a different crop each year in the same field.
Suggest two ways in which crop rotation may lead to high crop yields.
1. Grow crops / plants with nitrogen-fixing (bacteria);
Accept: grow legumes / named example e.g. peas, beans, clover
Accept: fallow year
2. (Different crops use) different minerals / salts / nutrients / ions (from the soil);
3. (Different crops have) different pests / pathogens / diseases.
Nutrient Cycles (AO1)
Nitrate from fertiliser applied to crops may enter ponds and lakes. Explain how nitrate may cause the death of fish in fresh water (5 marks).
(Eutrophication)
1. Growth of algae / surface plants / algal bloom blocks light;
- Reduced / no photosynthesis so (submerged) plants die;
- Saprobionts (microorganisms / bacteria);
- Aerobically respire / use oxygen in respiration;
- Less oxygen for fish to respire / aerobic organisms die;
Nutrient Cycles (AO1)
As fertiliser use increases and soil quality decreases, excess Nitrogen, Phosphorus (and potassium) used on farmlands can be picked up by rainfall in a process known as ________________.
leaching
Nutrient Cycles (AO1)
P = Nitrification
Q = Denitrification
Nutrient Cycles (AO1)
Name the process by which some bacteria oxidise ammonia to nitrate.
Nitrification
