Topic 5: Energy Transfers Flashcards
1
Q
What does photoautotrophic mean?
A
Organisms capable of synthesising their own food from inorganic ions using light as an energy source
2
Q
Name 5 uses of ATP
A
- Nerve impulses and muscle contraction
- Activation of molecules
- Synthesis of molecules
- Active transport
- Cell division
3
Q
TRUE OR FALSE?
Phagocytosis requires ATP
A
TRUE
4
Q
What are the 3 main components of ATP?
A
- An adenine nitrogenous base
- A phosphate group
- A ribose 5C sugar
5
Q
What is the equation for the synthesis of ATP?
A
ADP + Pi + energy -> ATP
6
Q
What enzyme catalyses the formation of ATP?
A
ATP synthase
7
Q
What type of reaction of ATP synthesis?
A
A condensation reaction
8
Q
What is the reaction for the release of energy from ATP?
A
ATP + H2O -> ADP + Pi + Energy
9
Q
When ATP is synthesised, is energy used?
A
Yes
10
Q
What enzyme catalyses the conversion of ATP to ADP +Pi?
A
ATP hyrolase
11
Q
What type of reaction is ATP -> ADP + Pi?
A
Hydrolysis
12
Q
Why is ATP used as an intermediate energy source instead of glucose?
A
- ATP hydrolysis releases less energy so it is more manageable
- Only a single reaction, so quicker
- An immediate source of energy
13
Q
What are coenzymes?
A
Molecules that enzymes need to function
14
Q
Give 3 coenzymes used in respiration.
A
- NAD
- FAD
- Coenzyme A
15
Q
What coenzyme is used in photosynthesis?
A
NADP
16
Q
What does OIL RIG stand for?
A
Oxidation Is Loss
Reduction Is Gain
(of electrons)
17
Q
What is oxidation?
A
- Gaining oxygen
- Loosing Hydrogen
- LOSS OF ELECTRONS
18
Q
What is reduction?
A
- Gaining hydrogen
- Lossing oxygen
- GAIN OF ELECTRONS
19
Q
Which of oxidation and reduction causes energy to be released?
A
Oxidation = Energy released
Reduction = Energy taken in
20
Q
Oxidation and reduction are said to be _ reactions?
A
Oxidation and reduction are LINKED REACTIONS
As one molecule becomes oxidised, another becomes reduced
21
Q
LEAF ADAPTATIONS FOR PHOTOSYNTHESIS
Why do leaves have a high surface area?
A
LEAF ADAPTATIONS FOR PHOTOSYNTHESIS
To absorb light
22
Q
LEAF ADAPTATIONS FOR PHOTOSYNTHESIS
Why do leaves have a transparent cuticle and epidermis?
A
LEAF ADAPTATIONS FOR PHOTOSYNTHESIS
Allows light to reach chloroplasts in the palisade mesophyll cells beneath for the light dependent reaction
23
Q
LEAF ADAPTATIONS FOR PHOTOSYNTHESIS
Why are leaves thin?
A
LEAF ADAPTATIONS FOR PHOTOSYNTHESIS
Offers a short diffusion pathway for oxygen through stomata
24
Q
LEAF ADAPTATIONS FOR PHOTOSYNTHESIS]
Why do leaves have lots of stomata?
A
LEAF ADAPTATIONS FOR PHOTOSYNTHESIS
To allow gas exchange and water pressure gradient in plants
25
LEAF ADAPTATIONS FOR PHOTOSYNTHESIS
| Why are there large spaces between spongy mesophyll cells?
LEAF ADAPTATIONS FOR PHOTOSYNTHESIS
| Allows for rapid diffusion of CO2 and O2
26
What is the function of xylem with regards to photosynthsis?
The xylem supplies the leaf cells with water
Water is a reactant in photosynthesis - involved in photolysis
27
What is the function of phloem with regards to photosynthsis?
The phloem carries away the products of photosynthesis
28
Thylakoids (in chloroplasts) have a large surface area. Why is this useful for photosynthesis?
- Large SA for pigments
| - More electron carriers for the light dependent reaction
29
Where does the light dependent reaction of photosynthesis take place?
In the thylakoid membrane
30
What are grana in chloroplasts made up of?
Thylakoids
31
Where does the light independent reaction of photosynthesis take place?
In the stroma of chloroplasts
32
What are photosystems?
- Groups of pigments (chlorophyll) held in thylakoid membranes
- Maximises the absorption of light energy
- Enables the light-dependent reaction of photosynthesis to occur
33
What is the role of ATP synthase channels in thylakoid membranes (chloroplasts)?
- Allow protons to move out of the thylakoid lumen down the electrochemical gradient
- The movement through the ATP synthase channels causes the synthesis of ATP by the phosphorylation of ADP
34
What is the overall equation for photosynthesis?
6CO2 + 6H2O -> C6H12O6 + 6O2
35
What are the two main stages of photosynthesis?
- Light dependent reaction
| - Light independent reaction
36
How do plants absorb light from multiple wavelengths?
Many types of pigment in photosystems in thylakoid membranes
37
Which photosystem is first used in the light dependent reaction of photosynthesis?
PSII
38
What happens to a chlorophyll molecule as it gains light energy?
Electrons gain energy and move to higher energy levels
39
What is it called when chlorophyll becomes oxidised?
Photoionisation
| electron moves to higher energy levels along electron transport chain
40
Where is the energy released from the photoionisation of chlorophyll in photosystems used?
The energy is conserved in the production of ATP and reduced NADP
41
What 2 products of the light dependent reaction are used in the light independent reaction of photosynthesis?
1. ATP
| 2. Reduced NADP
42
What are the 7 steps of the light dependent reaction of photosynthesis?
1. PSII absorbs light energy
2. Electrons are excited and pass along electron carriers to PSI (photoionsiation)
3. Some light energy used in the photolysis of water, releasing electrons, protons and oxygen
4. Energy released by electrons as they pass between electron carriers causes protons to be actively transported into the thylakoid lumen (from the stroma)
5. At the same time as in stage 1, light is absorbed in PSI
6. Electrons excited at PSII travel along electron carriers and join with NADP and H+ ions to produce reduced NADP
7. Photolysis of water and H+ ion active transport creates a proton gradient (higher concentration in the thylakoid lumen compared to stroma)
8. Protons move through ATP synthase channel from high concentration in thylakoid lumen to the stroma by facilitated diffusion
43
What is the photolysis of water?
The use of some light energy to split water into electrons, protons and oxygen
44
What are the electrons released in the photolysis of water used for?
The electrons replace the electrons released by PSII in photoionisation
45
What happens as electrons pass between electron carriers in the light dependent reaction of photosynthesis and in oxidative phosphorylation in respiration?
- Energy is released
- Allows the active transport of H+ ions
- Sets up H+ ion gradient
46
Why do protons have to travel through a protein in light dependant reaction of photosynthesis and in oxidative phosphorylation of respiration?
H+ ions are (+vely) charged so cannot pass through phospholipid bilayers
47
How are leaves arranged to absorb maximum light?
There is minimal overlapping so few leaves are shadowed by another
48
What happens to the oxygen released from the photolysis of water? (2 points)
1. Used for respiration
| 2. Diffuses out of leaf as a waste product
49
How is ATP produced by the movement of H+ ions through ATP synthase channels?
- Protons passing through cause ATP synthase enzyme to change shape
- Catalyses the synthesis of ATP (ADP + Pi)
50
What is the movement of H+ ions through ATP synthase also called?
Chemiosmosis
51
In what part of photosynthesis is water used?
In the light-dependent reaction
52
In what part of photosynthesis is CO2 used?
In the light independent reaction
53
How does CO2 used in the light independent reaction enter the chloroplast?
- Diffuses from atmosphere into leaf via stomata
- Diffuses through water surrounding mesophyll cells
- Diffuses through cell surface membrane, cytoplasm + chloroplast membranes
- Enters the stroma
54
What are the 8 steps of the Kalvin Cycle?
1. CO2 combines with RuBP (5C) and enzyme rubisco
2. Forms 2x GP (3C)
3. ATP hydrolysed into ADP + Pi
4. Reduced NADP to NADP
5. 2x TP (3C)
6. Useful organic substances produced
7. Several enzyme-controlled reactions and ATP hydrolysis
8. RuBP (5C)
Restarts!
55
How many cycles of the Kalvin cycle are required to produce glucose?
6
56
What product of the light dependent reaction is used to reduce GP?
Reduced NADP
| Energy provided by the hydrolysis of ATP
57
After reduced NADP becomes NADP in the Kalvin Cycle what happens to the NADP?
- Returns to the light-dependent reaction
| - Picks up more hydrogen to allow further light dependent reactions to take place
58
What useful "organic substances" does the Kalvin Cycle produce?
- Hexose sugars
- Fatty acids
- Amino acids
(the building blocks for life)
59
Why is it important that chloroplasts contain DNA and ribosomes?
Allows quick and easy manufacture the proteins involved in the light dependent reaction
60
Why is it important that thylakoid membranes are selectively permeable?
Allows the proton gradient to be established in the light dependent reaction of photosynthsis
61
Would the light independent reaction occur in the absence of light?
In theory yes, however it requires reduced NADP and ATP for the Kalvin cycle to work.
Reduced NADP and ATP are both products of the light dependent reaction, so the light dependent reaction will quickly stop without them
62
In which two steps does ATP from the light dependent reaction provide energy in the Kalvin cycle?
1. Reduction of GP to TP
| 2. Regeneration of RuBP
63
What are the 3 main limiting factors that affect the rate of photosynthesis?
1. CO2 concentration
2. Light intensity (and wavelength)
3. Temperature
64
What is the law of limiting factors?
At any given moment, the rate of photosynthesis is limited by the factor that is at its least favourable value
65
How can farming practices overcome some limiting factors?
Greenhouses used
- Artificial light to increase 'daylight hours'
- Artificial heating
- More CO2 added
66
Is the rate of photosynthesis affected by all the factors involved?
No. It is affected by the factor with the least favourable value
67
Why are selectively permeable membranes in mitochondria important for respiration?
Allows pyruvate in, but glucose can't
68
Why is the large SA created by the mitochondrial cristae important for respiration?
Allows for many electron carriers on the inner mitochondrial membrane
69
What is used as an immediate energy source by cells?
ATP
70
How is ATP formed?
ATP is formed from the energy released by the hydrolysis of glucose in cellular respiration (forms ATP from ADP + Pi)
71
What are the two types of cellular respiration?
Aerobic and anaerobic respiration
72
Under what conditions does aerobic respiration occur?
When oxygen is present
73
Under what conditions does anaerobic respiration occur?
When oxygen is absent
74
What is the simple equation for aerobic respiration?
C6H12O6 + 6O2 -> 6CO2 + 6H2O
| ADP + Pi -> ATP in the conversion
75
What is the simple equation for anaerobic respiration in animals?
Glucose -> Lactate
76
What is the simple equation for anaerobic respiration in plants and yeast?
Glucose -> Ethanol + CO2
77
What are the 4 stages of aerobic respiration?
1. Glycolysis
2. Link reaction
3. Kreb's Cycle
4. Oxidative phosphorylation
78
What stage of respiration is involved in both aerobic and anaerobic respiration?
Glycolysis
79
What basically happens in glucolysis? (respiration)
Glucose (6C) is broken down into 2 Pyruvate molecules (3C)
80
Where does Glycolysis take place? (respiration)
In the cell cytoplasm
81
What type of sugar is glucose?
A hexose sugar
82
Of anaerobic and aerobic respiration, which one produces more ATP?
Aerobic respiration
83
Which part of respiration is the ONLY part to USE ATP?
Phosphorylation of glucose in glycolysis
84
Outline what happens in glycolysis (respiration)
1. Glucose is phosphoylated to form glucose phosphate
(2x ATP used)
2. Phosphorylated glucose splits into two TP
3. TP is oxidised and NAD is reduced as hydrogen is transferred (oxidation and reduction are liked reactions)
4. 4x ATP is synthesised
5. TP converts into pyruvate
85
What is NAD?
A coenzyme (a hydrogen carrier)
86
What is activation energy?
The energy required to bring about a reaction (lowered by enzymes)
87
What are the products of glycolysis for every glucose used(resp.)?
2x pyruvate
2x Reduced NAD
2x ATP (net, 2 used, 4 produced)
88
What is the reduced NAD from glycolysis used for?
The production of ATP in oxidative phosphorylation
89
What is the process by which ATP is formed during glycolysis called?
Substrate-level phosphorylation
90
Does glycolysis require oxygen to be present?
No
91
What is the purpose of the phosphorylation of glucose (1st step of glycolysis)?
Makes glucose more reactive, lowering the activation energy for the other enzyme-controlled reactions in glycolysis
92
Where does the link reaction of respiration take place?
In the matrix of the mitochondria
93
How does pyruvate from glycolysis (resp) enter the mitochondria
By active transport
94
What are the 4 steps of the link reaction of aerobic respiration?
1. Pyruvate (3C) is oxidised
2. NAD is reduced (hydrogen acceptor)
3. CO2 is release, togther creating acetate (2C)
4. Acetate (2C) combines with coenzyme A to create acetyl coenzyme A
95
What are the products of the link reaction for every molecule of glucose entering glycolysis?
2x CO2 released
2x Reduced NAD
2x acetyl coenzyme A
96
Where does the Kreb's Cycle take place (aerobic resp.)?
In the mitochondrial matrix
97
What are the steps of the Kreb's cycle?
1. Acetyl coenzyme A (2C) combines with 4C molecule to produce 6C molecule
2. Coenzyme A leaves the cycle to pick up more acetyl in link reaction
3. 6C molecule is first oxidised as NAD takes hydrogen + turns into reduced NAD.
4. CO2 released, forming a 5C molecule
5. Further CO2 is released, 2 NAD reduced, ATP synthesised, FAD reduced to form 4C molecule
Restarts!
98
For each molecule of glucose used in glycolysis, what are the products of the Krebs Cycle (aerobic resp.)?
```
6x Reduced NAD
2x Reduced FAD
2x ATP
4x CO2
(also 2x acetyl coA to be reused in the link reaction)
```
99
Where does oxidative phosphorylation take place?
On electron carriers on the inner mitochondrial membrane
100
What do hydrogen atoms produced in glycolysis, the link reaction and the Kreb's cycle (aerobic resp.) all combine with?
NAD and FAD (latter only in Krebs) to form Reduced NAD and reduced FAD respectively
101
Why do mitochondria in cells that are metabolically active have a more densely packed cristae?
- Densely packed cristae provides greater SA
- So more membrane incorporated enzymes and proteins involved in oxidative phosophorylation
- Ensures that maximum quantity of ATP is produced
102
What are the steps for oxidative phosphorylation?
1. Reduced NAD donates electrons to first molecule in electron transport chain (ETC), reduced FAD donates electrons to the second
2. Electrons pass along ETC, continual oxidation and reduction reactions occur
3. Energy released by electrons as they pass along the ETC used to actively transport H+ ions from mitochondrial matrix to the inner membrane space (through proteins)
4. A proton gradient is created
5. Protons diffuse through ATP synthase channel (from low-high conc)
6. ATP synthase changes shape so ADP + Pi -> ATP
7. H+ ions (having diffused though ATP synth), 4e- (from ETC) and O2 combine to create 2H2O in the matrix
103
What is the role of oxygen in aerobic respiration?
Acts as the final electron acceptor in oxidative phosphorylation
104
What would happen if oxygen was not available in aerobic resp? (4 points)
- No O2 to accept e- from the last electron carrier
- Last carrier cannot take e- from previous carrier etc.
- Reduced NAD and FAD cannot give up e - (or H+)
- No NAD or FAD recycled to pick up H from Krebs etc
Electrons will back up, respiration will stop
105
Why is oxidative phosphorylation given its name?
It involves a series of oxidation-reduction reactions along the ETC. Oxygen is the terminal electron acceptor
106
What are two other respiratory substrates, besides glucose?
1. Lipids
| 2. Amino acids
107
What does the hydrolysis of a lipid result in?
Glycerol and fatty acids
108
What bonds are broken when a lipid is hydrolysed?
Ester bonds
109
What does the hydrolysis of a protein result in?
What bonds are broken?
Amino acids
Peptide bonds are broken
110
How can lipids be used as a respirator substrate?
- Lipids hydrolysed into glycerol + fatty acids
- Glycerol is phosphorylated and converted into TP
- TP enters the rest of glycolysis
- Fatty acids are converted into acetyl coen A
111
How is reduced NAD returned to NAD in anaerobic respiration?
- Pyruvate accepts hydrogen from reduced NAD
112
Why does reduced NAD need to become NAD again in anaerobic respiration?
- The finite supply of NAD will run out as more is reduced
| - No more NAD will be available to take up hydrogen in glycolysis
113
What happens to pyruvate in anaerobic respiration in animals?
Pyruvate is converted to lactate
114
What happens to pyruvate in anaerobic respiration in plants?
Pyruvate is converted to ethanol + CO2
115
Under what conditions do plant cells respire anaerobically?
In waterlogged root cells where oxygen supply is limited
116
When does anaerobic respiration occur in animals?
When there is less O2
- When undergoing strenuous muscle activity
- Aquatic animals
117
What happens when lactate builds up in muscle cells?
Lactate build up causes fatigue and cramps
118
Why does the buildup of lactate cause fatigue and cramps?
Lactate is an acid so it can denature enzymes, affecting metabolic reactions
119
What is substrate-level phosphorylation?
The direct transfer of phosphate from a repiratory intermediate to ADP to produce ATP
Used to create ATP in glycolysis and Krebs
120
What are most sugars used for in plants?
Respiration
121
Apart from carbon dioxide and water, what other INORGANIC molecules are required by plants to make useful organic substances?
Nitrates
| Phosphates
122
How is energy passed between different organisms?
In the molecules within biomass
123
What are the 3 groups organisms are divided into depending on how they obtain energy + nutrients?
- Producers
- Consumers
- Saprobionts (decomposers)
124
What are producers?
Photosynthetic organisms that use light energy, CO2, H2O and mineral ions to manufacture organic substances
125
How do consumers obtain energy?
By eating other organisms
| secondary and tertiary consumers are usually predators but may be scavengers/parasites
126
How can consumers be split up?
Into trophic levels
| Primary, secondary and tertiary consumers
127
What are saprobionts?
- Mostly fungi/bacteria
- Release extra-cellular enzymes
- Hydrolyse large, complex materials in dead organisms into small, simple ones which can be absorbed
- Release minerals in a form usable by plants
128
What are extra-cellular enzymes?
Enzymes that catalyse reactions outside the host cell
129
What is a trophic level?
A stage on a food chain
130
What are chemoautotrophs?
Organisms that use energy from chemical reactions to make food
131
What are food chains used for?
To describe feeding relationships between organisms, joins trophic levels together
132
What do arrows on food chains and webs show?
The direction of energy flows
133
Why do ecologists tend to use food webs instead of food chains to describe energy transfers between organsisms in a community?
Foodwebs show how many food chains are linked together because most animals have multiple food sources
134
What is the disadvantage of using food webs?
Food webs are very complex
135
What makes a stable food web?
- A food web with more interactions between species
| - If one organism is lost the food web will be less likely to collapse
136
What is biomass?
The total mass of living material in a specific areas at a given time
137
How can biomass be measured (2 ways)?
1. Fresh biomass
| 2. Dry biomass
138
Why is measuring fresh biomass unreliable?
The volume of water within plants will vary
139
How can dry biomass be measured?
- Dried in an oven until a constant mass is achieved
| - Temperature below 70C so that water still evaporates but enzymes and non-water structures are not damaged
140
What are the problems with measuring dry biomass?
- All organsims must be killed
| - Only allows a small sample to be taken, unrepresentative of the whole area
141
How can the chemical energy stored in dry biomass be estimated?
Using calorimetry
142
What apparatus is used to calculate calorimetry?
A bomb calorimetry
143
How does bomb calorimetry work? (4 steps)
1. Sample of dry material weighed
2. Sample burnt in pure O2 in 'the bomb'
3. Water in water bath surrounding the bomb warms up
4. The increase in temperature of the water used to calculate energy released from burnt biomass
144
What is the SI unit for energy?
Joules (J)
145
What is the source of energy for ecosystems?
The sun
146
How much energy from the sun is lost due to reflection by dust + clouds?
90%
147
What % of light energy from the sun is captured by plants and thus made available to organisms in the food chain?
As little as 1%
148
Why is light energy lost when it hits leaves (4 reasons)?
1. Energy used to evaporate water from the leaf
2. Some energy is reflected
3. The light energy may not hit chlorophyll
4. Not all light wavelengths used in plants
149
What is Gross Primary Production (GPP)?
The chemical energy store in plant biomass in a given area or volume, at a given time
150
What is Net Primary Production (NPP)?
The chemical energy store in plant biomass after respiratory losses to the environment
151
What is NPP used for by plants?
- Growth + reproduction
| - Available to other trophic levels in the ecosystem
152
Why is a very small proportion (10%) NPP available to primary consumers for THEIR biomass? (4 points)
- Not every part of the plant is eaten
- Some used in respiration (for ATP and heat)
- Some lost in egestion
- Some lost in excretion
153
Why is the transfer of energy from plant to primary consumer lower than from primary to secondary consumer?
Plant material contains cellulose + lignin which cannot be digested (or at least hard to digest as requires several enzymes)
154
What is the equation to represent net production?
N = I - (F+R)
```
N = Net production
I = Chemical energy in ingested food
F = Chemical energy lost to the environment in faeces
R = Respiratory losses to the environment
```
155
Why do food chains only have 4 or 5 trophic levels?
Energy transfers between organisms are inefficient, meaning:
- Insufficient energy to support large breeding pops at higher trophic levels
- Total mass of organisms is less at higher trophic levels
- Amount of energy is less at each higher trophic level
156
Why do farming practices aim to increase the efficiency of energy transfers?
To increase yeilds
157
How does intensive farming increase energy conservation? (4 points)
- Less movement (less energy used in muscle contraction)
- Warm environment reduces heat loss from the body
- Optimum amount + type of food for max growth (so no waste)
- Predators excluded (no loss to other orgaisms)
158
What 5 things do weeds compete with plants for?
Water, mineral ions, CO2, space and light
159
Why is growing crops in a monoculture bad?
It enables insect and fungal pests to spread rapidly
160
What is the aim of pest control?
To simplify the food web in order to limit the effect of pests on production to an acceptable level
161
Why must farmers balance costs with benefits regarding increasing productivity?
Whilst food should be produced cheaply in order to make a living, natural resources need to be conserved so humans can have food in the future
162
What makes an effective pesticide?
A pesticide which biodegrades (doesn't accumulate), is specific and is cost effective
163
Why do pesticides sometimes stop working?
Pests develop genetic resistance
164
What does 'biological control' aim to do?
Controls a pest instead of eradicating it
165
Why is eradicating a pest not a good practise?
- The pest population falls
- Less food for predator
- Predator dies
- Pest population will increase again with no natural predators
166
What is a more sustainable alternative to pest control?
Biological control
167
What are the 3 advantages of biological control?
- Specific as the predator only preys on the pest
- Once introduced the predator can reproduce (only one 'application' required)
- The pests will not become resistant to predators like they do to pesticides
168
What is the aim of integrated control?
Integrates all forms of pest control to reduce pest populations to acceptable levels
169
Why should elements like carbon, nitrogen and phosphorous be recycled?
To ensure that there is a continuous avaliblilty of nutrient ions in a usable form
170
How do saprobionts obtain their nutrients? (4 points)
- Genes activated to make the right enzymes
- Extra-cellular enzymes are secreted
- Enzymes hydrolyse surrounding organic material into simple, soluable compounds (sugars + AAs)
- Compounds are absorbed by saprobionts
171
Name 4 organic compounds in living organisms that contain nitrogen
1. Urea
2. Nucleotides (DNA)
3. ATP
4. Amino acids
172
What from of nitrogen can plants take up?
Nitrate ions (NO3-)
173
How do animals obtain nitrogen-containing compounds?
By eating + digesting plants / other animals
174
What are the 4 stages of the nitrogen cycle?
1. Ammonification
2. Nitrification
3. Nitrogen fixation
4. Denitrification
175
What is ammonification? (N cycle)
- The production of ammonia from organic nitrogen containing compounds (eg. urea, proteins and nucleic acids)
- From urine, faeces + dead organisms
176
What organisms carry out ammonification?
Sprobionts
177
What is the product of ammonification?
Ammonium ions (in soil)
178
What organisms perform nitrification?
Nitrifying bacteria
179
What two reactions are involved in nitrification?
Why type of reaction are these two reactions?
1. Ammonium ions to nitrate ions
2. Nitrate ions to nitrite ions
Both reactants are oxidised
180
Why do farmers have to keep soil structures light and well aerated?
- Nitrifying bacteria require oxygen, so need air spaces
| - Good drainage prevents air spaces becoming filled with water
181
What is Nitrogen fixation?
The process by which nitrogen gas is converted into nitrogen compounds
182
How does nitrogen fixation occur?
- Lightning in the atmosphere
- The Haber process
- Microorganisms
183
What two types of microorganism 'fix' nitrogen?
- Free living-nitrogen fixing bacteria
| - Mutualistic nitrogen-fixing bacteria
184
What do free living-nitrogen fixing bacteria do?
- Reduce gaseous nitrogen to ammonia
- Use ammonia to produce amino acids
- Release nitrogen-rich comounds when they die
- Creates ammonium ions
185
What do mutualistic nitrogen-fixing bacteria do?
- Live in nodules of roots in legumes
- Fix nitrogen from the atmosphere
- Use carbohydrates from plants
- Plants acquires AAs from the bacteria
186
What is denitrification?
- Soils become waterlogged
- Oxygen concentration decreases, so less aerobic nitrifying and fixating bacteria
- More anaerobic denitrifying bacteria present
- Convert soil nitrates into gaseous nitrogen
187
Under what soil conditions does deniftrification occur?
In waterlogged soils, thus low oxygen concentration, so more anaerobic bacteria
188
Why is denifrication bad for plants?
- Denifrifying bacteria convert soil nitrates into gaseous nitrogen
- Less nitrates available to plants by absorption
189
Which 4 organic compounds in living organisms contain phosphorus?
ATP, ADP, phospholipids, nucleic acids
190
What is the main 'reservoir' in the nitrogen cycle?
The atmosphere
191
What is the main 'reservoir' in the phosphorous cycle?
Phosphorous in mineral form (rocks and soils)
192
Does the phosphorous cycle have a gaseous phase?
No
| The nitrogen cycle does
193
What form of phosphorous is cycled in the phosphorous cycle?
Phosphate ions
194
How do phosphate ions become available to plants in the phosphorous cycle?
Naturally with erosion
Also with fertilisers
(both increase phosphate ion concentration in soils)
195
By what process do plants take up phosphate ions?
By active transport
196
How do phosphate ions return to water or soil in the phosphorous cycle?
- Excreted by living animals
| - Decomposition of dead animals + plants by saprobionts
197
How do animals obtain phosphate ions?
By digesting plants
198
What are mycorrhizae?
- The association between certain types of fungi and plants
- Act as extensions to plant roots, increasing SA for absorption
- Can be intreacellular or extracellular
199
Why are mycorrhiza useful for water retention with plants?
- Acts like a sponge
- Holds water near plant roots
- So less difference in water potential
- Plants are more able to resist drought
200
What do plants do to benefit mycorrhizae?
Supply the fungus with organic compounds (sugars + AAs)
201
What sort of relationship do plants and mycorrhizae have?
A mutualistic relationship (symbiotic)
202
Why are fertilisers needed in agricultural ecosystems?
- Plants need mineral ions
- Intense food production means areas of land are repeatedly used so nutrients become deprived
- When plants are harvested, the mineral ions absorbed by them are also removed from the system, so need to be replaced
203
Why are mineral ions taken up by crops in agriculture?
Mineral ions are used for:
- Food (by humans)
- Fodder (animals)
204
Why is intensive food production bad?
- Increases demand on the soil
| - Mineral ions are continually taken up and become deprived
205
Why do fertilisers need to be used in agriculture?
Once plants are harvested for human consumption, they are eaten elsewhere so the excreted substances do not return to the same area of land
The mineral ion concentration falls
Fertilisers replenish it
206
What are the two types of fertiliser?
- Natural fertilisers
| - Artificial fertilisers
207
What are natural fertilisers?
- Legumes (beans) grown in the same spot as other crops
- Refertilises the soil with nitrogen-fixing bacteria
- Manure also added to fields to fertilise the soil
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What are artificial fertilisers?
- A blended mixture of minerals to provide a suitable balance depending on the crop being grown
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How are artifical fertilisers obtained?
- Phosphate ions obtained through mining of rocks
| - Nitrogen fertilises obtained through Haber process
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Why is it important that fertilisers are applied in appropriate quantities?
There is a point when increasing the quantity of a fertiliser no longer increases productivity because the fertilisers become toxic
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Why would farmers not add high concentrations of fertiliser?
- Costs outweigh benefits
- Fertilisers are toxic in very high concs
- Toxicity can reduce crop yields
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What are 2 major advantages of natural fertilisers?
1. Can improve drainage
| 2. Less leaching
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What is a disadvantage of natural fertilisers?
The mixture may contain unwanted weeds/pests
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What are 2 disadvantages of artificial fertilisers?
- Energy consuming
| - Very soluble, so more leaching occurs
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How can nitrogen-containing fertilisers reduce species diversity?
- Nitrogen rich soils favour the growth of rapidly growing species (nettles etc)
- These species out-compete others, so the others dies
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Name 3 deterimental effects of nitrogen-containing fertilisers
1. Reduced species diversity
2. Leaching
3. Eutrophication
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What is leaching?
The process by which nutrients are removed from soils by runoff, entering watercourses
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How does the runoff of fertilisers occur?
- Rainwater dissolves soluble nutrients in soils
| - Nutrients are carried deep into the soil, beyond the reach of plant roots
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What type of fertiliser is most susceptible to leaching? Why?
Artificial because they are more soluble
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What is eutrophication?
The process by which nutrient levels (phosphates and nitrates) increase in bodies of water
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What are the 10 steps of eutrophication
1. Nitrate ion concentration increases due to leaching. Algae grow quickly
2. Algal bloom forms on the surface (very dense)
3. Algae absorbs light, cannot penetrate the lower levels
4. Light becomes LIMITING FACTOR for plants below the surface. These plants die
5. More material for saprobionts to use, so more saprobionts (replicate rapidly)
6. Saprobionts use O2 for aerobic respiration. Water has increase biological oxygen demand
7. O2 conc decreases in the water
8. O2 becomes the limiting factor for aerobic organisms (fish), these too die
9. Less competition for anaerobic organisms, so population increases
10. Anaerobic organisms further decompose dead material, release more nutrients + some toxic waste
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What could eutrophication be considered to be?
A positive feedback loop
