[Y2] Energy Transfers In and Between Organisms Flashcards
(109 cards)
1
Q
What adaptations do leaves have to maximise photosynthesis?
A
- a large SA to absorb as much sunlight as possible.
- an arrangement of leaves on the plant that minimises overlapping and so avoids the shadowing of one leaf by another.
- thin, as most light is absorbed in the first few micrometres of the leaf and the diffusion distance for gases is kept short.
- a transparent cuticle and epidermis that let light through to the photosynthetic mesophyll cells beneath.
- long, narrow upper mesophyll cells packed with chloroplasts that collect sunlight.
- numerous stomata for gaseous exchange so that all mesophyll cells are only a short diffusion patheay from one.
- stomata that open and closer in responce to chanegs in light intensity.
- many air spaces in the lower mesophyll layer to allow rapid diffusion in the gas phase of carbon dioxide and oxygen.
- a network of xylem that brings water to the leaf cell, and phloem theat carries away sugars produced during photosythesis.
2
Q
What is the overall equation of photosythesis?
A
6CO₂ + 6H₂O →(light)→ C₆H₁₂O₆ + 6O₂
3
Q
What are the three main stages of photosynthesis?
A
- The capturing of light energy: by chloroplast pigments such as chlorophyll.
- The light-dependent reaction: light energy absorbed is conserved in chemical bonds. During the process, an electron flow is created causing the photolysis of water into protons (NADP), electrons (ATP), and oxygen.
- The light-independent reaction: where protons are used to produce sugars and other organic molecules.
4
Q
Describe the structure of chloroplasts.
A
- Typically disc shaped, 2-10um long, and 1um in diameter.
- They are surrounded by a double membrane.
- Inside the membrane are two distinct regions:
- The grana: stacks of up to 100 disc-like structures called thylakoids.
- Within the thylakoids is the photosynthetic pigment, chlorophyll.
- Some thylakoids join up with thylakoid in adjacent grana, these are called intergranal lamellae.
- The storma: a fluid-filled matrix where the light dependant stage of photosynthesis takes place.
- Within the stroma are a number of other structures such as starch grains.
5
Q
What is the light energy used for in the light-dependant reaction?
A
- To add an inorganic phosphate (Pᵢ) molecule to ADP, making ATP.
- Photolysis of water into H⁺ ions (protons) and OH⁻ ions.
6
Q
Define oxidation and reduction.
What are their energy changes?
A
Oxidation: oxygen added OR hydrogen lost OR electrons lost. (Exothermic)
Reduction: oxygen lost OR hydrogen gained OR electrons gained. (Endothermic)
7
Q
What happens during photoionisation in the light dependant reaction?`
A
- When a chlorophyll molecule absorbs light energy, a pair of electrons are excited, rasing them to a higher energy level.
- Electrons become so energetic that they leave the chlorophyll molecule altogether.
- As a result the chlorophyll molecule becomes ionised.
8
Q
What happened to electrons after photoionisation?
A
- The elections that leave the chlorophyll are taken up by a molecule called an electron carrier.
(Chlorophyll oxidised, Electron carrier reduced.)
- Electrons are passed along a number of carriers in a series of redox reactions. These are located in the membrane of the thylakoids.
- Each new carrier has a slightly lower energy level than the previous one in the chain, so the electrons lose energy at each stage.
- Some of this energy is used to combine an inorganic phosphate with ADP to make ATP.
9
Q
What is the chemiosmotic theory?
A
- Each thylakoid is an enclosed chamber into which protons (H⁺) are pumped from the stroma using protein carriers in the thylakoid membrane called proton pumps.
- Energy to drive this process comes from electrons released by the photolysis of water.
- The photolysis of water also produces protons which further increases their concentration inside the thylakoid space.
- Overall this creates and maintains a concentration gradient of protons across the thylakoid membrane with a high concentration inside the thylakoid space and a low concentration in the stroma.
- Protons can only cross the thylakoid membrane through ATP synthase channel proteins (the rest of the membrane is impermeable to protons). These channels are also known as stalked granules.
- As protons pass through the ATP synthase channels they cause changes to the structure of the enzyme which then catalyses the combination of ADP with inorganic phosphate to form ATP.
10
Q
How do chlorophyll molecules regain electrons lost as a result of photoionisation? Give the equation associated with it.
A
Gain electrons from the photolysis of water.
2H₂O –> 4H⁺ + 4e⁻ + O₂
11
Q
What happens to the products of the photolysis of water during the light-dependant reaction?
A
2H₂O –> 4H⁺ + 4e⁻ + O₂
- Protons: pass out of thylakoid space through ATP synthase and are taken up by an electron carrier (NADP).
- As a result this NADP becomes reduced.
- This reduced NADP is the main product of the light-dependant reaction, carrying with it electrons from the chlorophyll molecules, into the light-independent reaction.
=============================
- Electrons: allows chlorophyll to replace its lost electrons, to allow them to continue to absorb light energy.
=============================
- Oxygen (by-product of photolysis of water): either used in respiration or diffuses out of the leaf as a waste product of photosynthesis.
12
Q
How are chloroplasts structurally adapted to their function of capturing sunlight and carrying out the light-dependent reaction of photosynthesis?
A
- The thylakoid membranes provide alarge SA for the attachment of chlorophyll, electron carriers, and enzymes (that carry out the light-dependent reaction).
- A network of proteins in the grand hold the chlorophyll in a very precise manner that allows maximum absorption of light.
- The granal membranes have ATP sythase channels within them, which catalyse the production of ATP. They are also selectively permeable, allowing for a proton gradient.
- Chloroplasts contain both DNA and ribosomes so they can quickly and easily manufacture some of the proteins involved in the light-dependent reaction.
13
Q
What are the requirements of the light-independant reaction of photosythesis?
A
The products of the light-dependent reation of photosynthesis:
- ATP.
- NADP.
And CO₂
14
Q
Where does the light-independednt reaction take place?
A
The stroma of the chloroplast.
15
Q
Who worked out the details of the light-independent reaction?
A
Melvin Calvin (and his co-workers). Hence the name Calvin Cycle.
16
Q
Describe the Calvin cycle.
A
- CO₂ from the atmosphere diffuses into the leaf through stomata and dissolves in water around the walls of the mesophyll cells.
- It then diffuses through the cell-surface membrane, cytoplasm, and chloroplast membranes into the stroma of the chloroplast.
- In the stroma, the CO₂ reacts with the 5-carbon compound ribulose bisphosphate (RuBP) a reaction catalysed by an enzyme called ribulose bisphosphate carboxylase (rubisco).
- The reaction between carbon dioxide and RuBP produces two molecules of the 3-carbon compound glycerate 3-phosphate (GP).
- Reduced NADP from the light-dependent reaction is used to reduce glycerate 3-phosphate to trios phosphate (TP) using energy supplied by ATP (from the light-dependent reaction).
- The NADP is re-formed and goes back to the light-dependent reaction to be reduced again by accepting more protons.
- Some triose phosphate molecules are converted to organic substrates that the plant requires such as starch, cellulose, lipids, glucose, amino acids, and nucleotides.
- Most triose phosphate molecules are used to regerate ribulose bisphophate using ATP from the light- dependent reaction.
17
Q
How is the chloroplast adapted to carry out the light-independent reaction of photosynthesis?
A
- The fluid of the storma contains all the enzymes needed to carry out the light-independent reaction. Stromal fluid is membrane-bound in the chloroplast which means a chemical environment which has a high concentration of enzymes and substrates can be maintained within it - as distinct from the environment of the cytoplasm.
- The stroma fluid surrounds the grana and so the products of the light-dependent reaction in the grana can readily diffuse into the stroma.
- It contains both DNA and ribosomes so it can quickly and easily manufacture some of the proteins involved in the light-indepenent reaction.
18
Q
What are the two different forms of cellular respiration?
A
- Aerobic respiration: requires oxygen and produces carbon dioxide, water, and much ATP.
- Anerobic respiration: takes place in the absence of oxygen and produces lactate (in animals) or ethanol and carbon dioxide (in plants and fungi) but only a little ATP in both cases.
19
Q
What are the stages of aerobic respiration?
A
- Glycolysis: the splitting of the 6-carbon glucose molecule into 3-carbon pyruvate molecules.
- Link reaction: the 3-carbon pyruvate molecules enter into a series od reactions which lead to the formation of acetylcoenzyme A, a 2-carbon molecule.
- Krebs cycle: the introduction of acetlycoenzyme A into a cycle of oxidation-reduction reactions that yield some ATP and a large quantity of reduced NAD and FAD.
- Oxidative phosphorylation: the use of the electrons, associated with reduced NAD and FAD, released from the Krebs cycle to synthesise ATP with water produced as a by-product.
20
Q
Which stage of aerobic respiration is also part of anerobic respiration?
A
Glycolysis.
21
Q
Where does aerobi respiration start?
A
Cytoplasm (as that is where glycolysis takes place).
22
Q
What are the stages of glycolysis?
A
- Phosphorylation of glucose to glucose phosphate: before being split into two glucose must be made more reactive, through phosphorylation. The phosphate molecules come from the hydrolysis of two ATP molecules into ADP. This provides the energy to activate glucose and lower the activation energy for the enzyme-controlled reactions that follow.
- Splitting of phosphorylated glucose: each glucose molecule is split into two 3-carbon molecules known as triose phosphate.
- Oxidation of triose phosphate: hydrogen is removed from each of the two triose phosphate molecules and transferred to a hydrogen-carrier molecule known as NAD to form reduced NAD.
- The production of ATP: Enzyme-controlled reactions convert each trios phosphate into another 3-carbon molecule called pyruvate. In the process, two molecules of ATP are regerated from ADP.
23
Q
What is the overall yeild of one glucose molecule undergoing glycolysis?
A
- 2 molecules of ATP (four molecules are produce, but two were used up in the initial phosprylation of glucose and so the net increase is two).
- 2 molecules of reduced NAD (these have the potential to provide energy to produce ATP later on).
- 2 molecules of pyruvate.
24
Q
How does Glycolysis indirect evidece for evolution?
A
It is a unversal feature of every living organism.
25
Why must pyruvate be broken down further?
In order to releas the remainder of potential energy stored in the molecules of pyruvate.
26
Why doesn't glycolysis require any organelle or membrane for it to take place?
The enzymes for the glycolytic pathways are found in the cytoplasm of cells.
(It can also take place weather or not oxygen is present - does not require oxygen.)
27
How can pyruvate be broken down further? What must happen first?
Through the Krebs cycle.
It must be oxidised first (in a process known as the link reaction).
28
Where do the link reaction and Krebs cycle take place?
(In eukaryotic cells) exculsivley inside mitochonria.
29
How does pyruvate get to where it needs to be inorder for the next stage of aerobic respiration to take place?
It is activly transported into the matrix of mirtochoria from the cytoplasm of the cell (in eukaryotes).
30
Describe the link reaction.
- The pyruvate is oxidised to acetate. In this reaction the 3-carbon pyruvate loses a carbon dioxide molecule and two hydrogens. These hyrogens are accepted by NAD to form reduced NAD (which is late used to produce ATP).
- The 2-carbon acetate combines with a molecule called coenzyme A (CoA) to produce a compound called acetylcoenzyme A.
31
Give the chemical equation summarising the link reaction.
pyruvate + NAD + CoA → acetyl CoA + reduced NAD + CO₂
32
Who worked out the Krebs cycle's sequence?
British Biochemist, Hans Krebs.
33
Where does the Krebs cycle take place?
The matrix of the mitochondria.
34
Describe the Krebs cycle.
- The 2-carbon acetylcoenzyme A from the link reaction combines with a 4-carbon molecule to produce a 6-carbon molecule.
- In a series of reactions this 6-carbon molecules loses carbon dioxide and hydrogen to give 4 carbon molecules and singe molecules of ATP produced as a result of substrate-level phosphorylation.
- The 4-carbon molecule can now combine with a new molecule of acetylcoenzyme A to begin the cycle again.
35
What is the overall yeild of one pyruvate molecule undergoing the link reaction and Krebs cycle?
- Reduced coenzymes such as NAD adn FAD: these have the potential to provide energy to produce ATP molecules by oxidative phosphorylation and thus the important product of Krebs cycle.
- One molecule of ATP.
- Three molecules of carbon dioxide.
(the yield of a single glucose is double this as two pyruate molecules are produced for each original glucose)
36
What are coenzymes?
NOT ENZYMES.
They are molecules that some enzymes require in order to function.
37
Give examples of important coenzymes.
- NAD: important throughout respiration.
(it works with dehydrogenase enzymes that catalyse the removal of hydrogenatoms from substrates and transfer them to other molecules involved in oxidative phosphorylation.)
- FAD: imporant in the Krebs cycle.
- NADP: important in photosynthesis.
38
What is the significance of the Krebs cycle on the cells of organisms?
- It breaks down macromolecules into smaller ones - pyruvate is broken down into carbon dioxide.
- It produces hydrogen atoms that are carried by NAD to the electron transfer chain and provide energy for oxidative phosphorylation. This leads to the production of ATP that provides metabolic energy for the cell.
- It regenerates the 4-carbon molecule that combines with acetylcoenzyme A, which would otherwise accumulate.
- It is a source of intermediate compounds used by cells in the manufacture of other important substances such as fatty acids, amino acids and chlorophyll.
39
What is oxadative phophorylation?
The mechanism by which some of the energy of the electrons within hydrogen atoms is conserved in the formation of ATP.
40
Where does oxadative phosphorylation take place?
In the mitochondria, within inner folded membrane (cristar) where enzymes and other proteins are found.
41
What adaptation might individual mitochonria have in more metabolically active cells?
More densely packed crisae which provide a greater surface area of membrane incorporating enzymes and other proteins involved in oxidative phosphorylation.
42
What is the electron transfer chain?
A series of electron carrier molecules that can transfer electrons to eachother.
43
Describe the chemiosmotic theory of oxidative phosphorylation.
- Hydrogen produced during glycosis and the krebs cycle combine with the coenzyme NAD and FAD.
- The reduced NAD and FAD donate the electrons of hydrogen atoms they are carrying to the first molecule in the ETC.
- The electrons pass along a chan of electron transfer carrier molecules in a series of oxidation-reduction reactions. As the electrons flow along the chain, the energy they release causes the active transport of protons accross the inner mitochonrial membrane and into inter-membranal space.
- The protons accumulate in the inter-membranal space before they diffuse back into the mitochonrial matrix through ATP sythase channels embedded in the inner mitochonrial membrane.
- At the end of the chain the electrons combine with these protons and oxygen to form water. Oxygen is therefore the final acceptor of elections in the electron transfer chain.
44
What si teh importance of oxygen in respiration?
To act as the final acceptor of the hydrogen atoms produced in glycosis and the krebs cycle.
Without its role of removing the hydrogen atoms at the end of the chain , the protons and electreons would 'back up' along the chain and the process of respiration would come to a halt.
45
Why aren't the electrons carried by NAD and FAD transferred in one explosive step?
The greater the energy that is releasd in a single step, the more of it is released as heat and the leas there is available for more useful purposes.
When energy is released a little at a time, more of it can be harvested for the benefit of the organism.
46
Why are electrons passed fdown a energy gradient on the ETC?
It allows their energy to be release gradually and therefore more usefully.
47
How are lipids used for respiration?
- Lipids are first hydrolysed to glycerol and fatty acids.
- The glycerol is then phosphorylated and converted to triose phosphate which enter the glycosis pathway and subsiquencly the Krebs cycle.
- The fatty acid component is broken down into 2-carbon fragments whcih are converted into acetyl coenzyme A. This then enters the Kerbs cycle.
48
Which macromolecule produces the most amount of energy per unit mass? Why?
(Lipids or Carbohydrates)
Lipids.
- The oxidation of lipids produces 2-carbon fragments of carbohydrate and many hydrogen atoms.
- The hydrogen atoms are used to produce ATP during oxidative phosphorylation.
Therefore lipids release more than double the energy of the same mass of carboydrate.
49
How are proteins used for respiration?
- It is hydrolysed to its constituent amino acids.
- These have their amno group removed (deamination) before entering the respiratory pathway at different points depending on the number of carbon atoms they contain.
- 3-carbon compounds are converted to pyruvate.
- 4- and 5-carbon compounds are converted to intermediates in the Krebs cycle.
50
Why cant the Krebs cycle or the electron transfer chain continue without oxygen?
If ther is no oxygen, soon all the FAD and NAD will be reduced.
No FAD and NAD will be available to take up the H⁺ produced during the krebs cycle and the enzymes stop working.
51
What must happend for glycolysis to continue in the absence of oxygen?
Its products of pyruvate and hydrogen must be removed.
In particular the hydrogen must be released from the NAD in order to regerate NAD.
Without this, the already tiny supply of NAD in cells will be entirely converted into reduced NAD, leaving no NAD to take up the hydrogen newly produced from glycolysis.
Glycolysis will then grind to a stop.
The repelenismen tof AND is achieved by the private molecule from glycosis accepting the hydrogen from reduced NAD.
The oxidised NAD produced can then be used further in glycosis.
52
In which organisms does aneraobic respiration leading to ethanol occur in?
Certain bacteria and fingi (like yeast).
Some cells of higher plants (like root cells under waterlogged conditions).
53
Summarise the anaerobic respiration in certain fungi, bacteria, and cells of higher plants.
The pyruvate molecule formed at the end of glycolysis loses a molecule of carbon dioxide and accepts hydrogen from reduced NAD to produce ethanol.
pyruvate + reduced NAD → ethanol + carbon dioxide + oxidised NAD
54
How has anerobic respiration in yeast been exploited?
In brewing, ethanol is the important product.
Yeast is grown in anerobic conditions in which it fermetns natural carbohydrates in plant products, such as grapes or barley seeds into ethanol.
55
Why is lactate produced during the anerobic preparation in animals?
To overcome a temporary shortage of oxygen.
56
Describe the anerobic repiration in animals.
- In muscles, as a result of strenuous exercise, oxygen may be used up more rapidly than it can be supplied and thus an oxygen debt occurs.
- It is often essential, however, that the muscles continue to work despite the shortage of oxygen (e.g. fleeing from a preditor).
- When oxygen supply is short, NAD from glycolysis can accumulate and must be removed.
- To achieve this, each pyruvate molecule produced takes up the two hydrogen atoms from the reduced NAD produced in glycolysis to form lactate.
pyruvate + reduced NAD → lactate + oxidised NAD
- At some point the lactate produced is oxidised back into pyruvate. This can then either further oxidides to release energy or converted into glycogen.
- This happened when oxygen is once again avalable.
57
What happends if lactate builds up in the muscles?
- It causes cramp and muscle fatigue if it is allowed to accumulate in the muscle tissue.
- As lactate is an acid it also causes pH changes which affects enzymes.
58
Where is lactate converted into glycogen?
In the liver.
59
How is energy derived aerobic respiration?
- Substrate level phophorylation in glycolysis and the Krebs cycle. This is the direct transfer of phosphate from a respiratory intermediate to ADP to produce ATP.
- Oxidative phosphorylation in the electron transfer chain. This is the indirect linking energy from phosphate to ADP to produce ATP involving energy from the hydrogen atoms that are carried on NAD and FAD. Cells produce most of their ATP in this way.
60
How is energy derived anaerobic respiration?
- Pyruvate is converted into either ethanol or lactate.
- Consequently, it is not available for the Krebs cycle, thus neither the Krebs cycle or the electron transfer chain take place.
- The only ATP that can be produced by anaerobic respiration is, therefore, that formed by glycolysis.
61
What is the ultimate source of energy for almost all organisms?
The Sun.
62
What three groups can organisms be divided into based on how that obtain their energy?
- Producers
- Consumers
- Saprobiants
63
What is a characteristic of a producer?
- Photosythetic organism that sythesis chemical energy from solar energy, water, carbon dioxide, and mineral ions
64
What are characteristics of consumers?
- Obtain energy by feeding on other organisms.
- Primary consumers eat producers.
- Secondary consumers eat primary consumers.
- Tertiary consumers eat secondary consumers.
- Secondary and Tertiary are normally preditors but can also be scavengers.
65
What are characteristics of saprobiants?
- Organisms that break down the comples materials in dead organisms into simple ones.
- They release valuable minerals and elements in a form that can be absorbed by plants so contribute to recycling.
- Mostly bacteria or fungi.
66
What is a food chain?
- It describes the feeding relationship in which producers are eaten by primary consumers. These are eaten by secondary consumers (and so on).
- Each stage in this chain is called a trophic level.
- Arrows on food chain represent the flow of energy.
67
What is a food web?
- Within a single habitat there are many food chains that are linked to form a food web.
68
What is biomass?
The total mass of living matter in a specific area at a given time.
69
Why might fresh mass be unreliable?
- Varing amounts of water within organisms.
70
How are the problems of fresh mass overcome?
Dry mass is measured.
- This is the mass of all the biological molecule in an organims without the water.
71
What are the negatives of dry mass?
- Organism must be killed.
| - therefore normally a small sample, which may not be repreasnetative.
72
What are the units of biomass?
(dry) Mass per given area (used for grasslands, seashore etc).
gm⁻²
OR
(dry) Mass per given volume (used for ponds, lakes etc).
gm⁻³
73
How can the chemical energy in dry mass be estimated?
Calorimetry.
- Smaples of dry material is weighed and then burnt in pure oxygen within a sealed chamber.
- The bomb is surrounded by a water bath and the heat of combustion causes a temperature rise in the water.
- As we know the specific heat capacity of water, we can use E = mcΔT.
74
Why is only a small percentage of the sun's energy available used by plants?
- Over 90% of the Sun's energy is reflected back into space by clouds and dust, or absorbed by that atmosphere.
- Not all wavelengths of light can be absorbed and used for photosythesis.
- Light may not fall on a chlorophyll molecule.
- A factor, such as low carbon dioxide levels, may limit that rate of photsythesis.
75
What is GPP?
Gross Primary Production.
- The total quntity of the chemical energy store in plant biomass.
76
What is NPP?
Net Primary Productivity.
- The chemical energy store which is left when losses to respiration have been taken into account.
77
How can u work out NPP (in plants)?
NPP = GPP - R
78
Why is there a low percentage of energy transferred for growth?
- Some of the organisms is not consumed.
- Some parts are consumed but cannot be digested and thus lost as faeces.
- Some of the energy is lost in excretory materials, such as urine.
- Heat losses from respiration. (High in endotherms, as more energy is needed to maintain their body temp when heat is constantly being lost to the environment)
79
How can u work out NPP (in consumers)?
N = I - (F + R)
N: net production.
I: chemical energy store of indested food.
F: energy in faeces and urine.
R: energy in respiration.
80
The relative inefficiency of energy transferred between trophic levels explains why...
- Most food chains have only four/five trophic levels
- as insufficient energy is available to support large enough breeding populations at larger levels.
- The total mass of organisms in particular place (biomass) is less at higher trophic levels.
- The total amount of energy available is less at each level as one moves up a food chain.
81
Why is it important that elements such as carbon, nitrogen, and phosphorus are recycled?
There is a limitted avalability of nutrient ions in a usable form.
Unlike energy there is not an extraterrestrial source.
82
What is the simple sequence of all nutrient cycles?
- Nutrients are taken up by producers as simple inorganic molecules.
- The produced incorporate them into complex organic molecules.
- When the producer is eaten, they pass it on to consumer.
- It passes along the food chain (animals are eaten by other consumers).
- When producers and consumers die, their complex molecules are broken down by saprobiants.
- Saprobiants release the nutrients in its original simple form. And the cycle is complete.
83
Name two nitrogen-containing molecules
- Amino acids (Proteins)
| - Nucleic acids (DNA, RNA, ATP)
84
How do plants get their nitrogen?
- Up take nitrogen in the form of nitrate ions (NO₃⁻) from the soil.
- This is done via active transport by the roots.
85
How do animals obtain nitrogen?
By eating and digesting plants or other animals.
86
What are the four main stages of the nitrogen cycle?
- Ammonification.
- Nitrification.
- Nitrogen fixation.
- Denitrification.
87
What is ammonifiaction?
- The production of ammonia from organic nitrogen-containing compounds.
- Saprobiants feed on faeces and dead organism materials, releasing ammonia, which then forms ammonium ions in the soil.
- Nitrogen returns to the non-living component of the ecosystem.
88
What is nitrification?
- Oxidation of ammonium ions to nitrite ions (NO₂⁻) then to nitrate ions (NO₃⁻).
- Carried out by free-living nitrifying bacteria.
- Must be in areobic conditions as the nitrifying bacteria require oxygen to carry out these conversions.
89
Why can't nitrification happen in water logged soils?
- Waterlogged soild filles air spaces with water.
- Therfore oxygen cannot be there.
- Anerobic conditions are met.
- Nirtifying bacteria cannot work.
90
What is nitrogen fixation?
- Process by which nitrogen gas is converted into nitrogen-containing compounds.
- Can happen when lighting passes through the atmosphere.
- Free-living bacteria reduce nitrogen gas to ammonia, which can be used to make amino acids.
- Mutualsitic bacteria live in noduces of roots and obtain carbohydrates from the plant in exchange for amino acids for the plant.
91
What does mutualistic mean ?
The nutritional relationship between two species that both gain some advantage.
92
What is denitirfication?
- Soils become waterlog so there is a low oxygen conc, this changes the type of microorganism present.
- Fewer aerobic nitrifying and nitrogen-fixing bacteria are found, and more anaerobic identifying bacteria occur.
- They convert soil nitrates into gaseous compounds reducing the availability of nitrogen-containing compounds for plants.
- As a result, productive soils should be kept well aerated.
93
Starting from producers, what are the steps in the nitrogen cycle?
(basic aerobic conditions)
- Produces store nitrogen as ammonium containing molecules (like proteins).
- Consumers feed and digest producers.
- When producers die or excrete waste (or when consumers die) ammonium containing molecules are uptaken by saprobiants.
- These convert them to ammonium ions via ammonification
- Nitrifying bacteria convert them into nitrite ions then nitrate ions in the soil.
- Consumers can now uptake the ions via absorption.
94
Starting with nitrate ions in the soil, what are the steps in the nitrogen cycle?
(additional, initially anaerobic conditions)
- Anaerobic conditions increase the population of denitrifying bacteria.
- They convert nitrate ions into nitrogen in the atmosphere via denitrification.
- Once aerobic conditions are met.
EITHER:
- Mutualistic nitrogen-fixing bacteria can convert them to ammonium containing molecules for consumers.
OR:
- Free-living nitrogen-fixing bacteria can convert nitrogen gas into ammonium ions in the soil.
95
Name two molecules that contian phosphorus?
- Phospholipids.
| - Nucleic acids (DNA, RNA, ATP).
96
What phase does the phosphorus cycle take?
Mieral form.
Phosphorus cycle lacks a gaseous phase.
97
What is the most common form of phosphorus?
Phosphate ions (PO₄³⁻) in the form of sedimentary rock deposists.
98
Describe the phosphorus cycle, starting from phosphates in sedimentary rock deposits.
- Sedimentary rock deposits are brought to the surface by geological uplifting of rocks.
- Weathering and erosion of rocks help phosphate ions become dissolved in oceans, lakes and soils.
(this can also be whereas a result of fertilisers)
- Dissolved phosphate ions either undergo sedimentation to return to rocks or are absorbed by plants which incorporate the into their biomass.
- Phosphate ions pass into animals as they feed and digest them.
- Excess phosphate ions are excreted and are dissolved in oceans lakes and soils.
- When plants and animals die, decomposers can break them down into phosphate ions in waste and remains (like guano, bones, and shells).
- They are either slowly eroded away into dissolved phosphate ions or deposited into rivers, lake and oceans where they reform sedimentary rocks.
- Compleating the cycle.
99
What is mycorrhizae?
The association between certain types of fungi and the roots of the vast majority of plants.
100
How does mycorrizae benefit plants?
- The association extends the root systems and increases the total SA for water and mineral absorbtion.
- They act like a sponge, holding water and mineral s in the neiboirhood of roots.
- As a result the plant can better resist drought and take up inorganic ions more readily.
101
Why is mycorrizae mutualistic?
The association is mutualistic because:
- The plant benefits from improved water and inorganic uptake.
- The fungi recies organic compounds such as sugars and aminoacids from the plant.
102
Why is it necessary to replenish mineral ions in agricultural systems?
- Urine, faeces, and dead matter are rearely returned to the same area of land.
- Their reduced concentration will become a limiting factor to plant growth.
103
What are natural and artificial fertilisers?
Natural (organic):
- Consist of dead and decaying remains of plants and animals.
- As well as animal wastes such as manure, slurry and bone meal.
Artificial (inorganic):
- Mined from rocks and deposits.
- Then converted into different forms and blended together to give the appropriate balanced of minerals for a particular crop.
- Compounds containing NPK are almost always present.
104
Why is it important that fertilisers are added in the appropriate balance of minerals for a particular crop?
Because there is a point at which further increases in the quantity of fertilisers no longer results in increased productivity.
105
How does increasing nitrogen fertilisers improve crop productivity?
- Nitrogen is an essential component of amino acids, ATP, and nucleotides in DNA.
- Both are needed for plant growth.
- Where nitrate ions are readily available, plants are likely to develop earlier, grow taller and have greater leaf area.
- This increases the rate of photosynthesis and improves crop productivity.
106
What are the problems associated with nitrogen-containing fertilisers?
Reduced species diversity:
- As nitrogen-rich soils favour the growth of grasses, nettles, and other rapidly growing species.
- These outcompete other species, which die as a result.
(Species-rich hay meadows, only survive when soil nitrogen concentrations are low enough to allow other species to compete with grasses.)
Leaching:
- may lead to pollution of watercourses.
Eutrophication:
- Caused by leaching of fertiliser into watercourses.
107
What is leaching?
The process by which nutrients are removed from the soil.
108
Describe the process of eutrophication?
- In lakes and rivers there is a naturally low nitrogen conc, therefore nitrate ions are a limiting factor for plants and algal growth.
- Though leaching nitrate conc increases and so ceases to be a limiting factor.
- Algae grow on the surface and the upper layer of water become densly populated with algae. This is call 'algal bloom'
- The dense surface layer absorbs light and prevents it from penetrating to lower depths.
- Light then becomes the limiting factor for the growth of plants and algae at lower depths.
- This leads to their death.
- The lack of dead plant and algae is no longer a limiting factor for the growth of saprobiontic bacteria.
- Their population grows too, using dead organisms as food.
- Saprobiontic bacteria require oxygen for their respiration, creating an increased oxygen demand.
- The conc of oxygen in the water is reduced and nitrates are released from decaying organisms.
- Oxygen becomes a limiting factor for the population of aerobic organisms.
- Theses organisms ultimately die as the oxygen is used up all together.
- Without aerobic organisms, there is less competitions fro anerobic organisms, whose population rises.
- The anaerobic organisms further decompose dead material, releasing more nitrates and some toxic waste.
- This makes the water putrid.
109
Other than fertilisers, what else can lead to eutriphocation (although to a lesser extent)?
- Manure.
- Animal slurry.
- Human sewage.
- Ploughing old grassland.
- Natural leaching.
