3.5 Energy transfers in and between organisms (A-level only) Flashcards
1
Q
Location of light dependent reaction
A
- Thylakoid membranes of chloroplast
2
Q
Location of light independent reaction
A
- Stroma of chloroplast
3
Q
Chloroplast structure
A
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4
Q
Thylakoid membranes
A
- Folded membranes containing photosynthetic proteins (chlorophyll)
- embedded with transmembrane electron carrier proteins
- involved in the LDRs
5
Q
Chlorophyll
A
- Located in proteins on thylakoid membranes
- mix of coloured proteins that absorb light
- different proportions of each pigment lead to different colours on leaves
6
Q
Advantage of many pigments
A
- Each pigment absorbs a different wavelength of visible light
- many pigments maximises spectrum of visible light absorbed
- maximum light energy taken in so more photoionisation and higher rate of photosynthesis
7
Q
Light-dependent reaction (LDR)
A
- First stage of photosynthesis
- occurs in thylakoid membranes
- uses light energy and water to create ATP and reduced NADP for LIR
- involves photoionisation of chlorophyll, photolysis and chemiosmosis
8
Q
Photolysis
A
- Light energy absorbed by chlorophyll splits water into oxygen, H+ and e-
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9
Q
Products of photolysis
A
- H+
◦ Picked up by NADP to form reduced NADP for LIR - e-
◦ passed along chain of
electron carrier proteins - oxygen
◦ used in respiration or diffuses out leaf via stomata
10
Q
Photoionisation of chlorophyll
A
- Light energy absorbed by chlorophyll excites electrons so they move to a higher energy level and leave chlorophyll
- some of the energy released is used to make ATP and reduced NADP
11
Q
Chemiosmosis
A
- Electrons that gained energy move along a series of electron carriers in thylakoid membrane
- release energy as they go along which pumps protons across thylakoid membrane
- electrochemical gradient made
- protons pass back across via ATP synthase enzyme producing ATP down their conc. gradient
12
Q
What happens to protons after chemiosmosis?
A
- Combine with co-enzyme NADP to become reduced NADP
- reduced NADP used in LIR
13
Q
Products of LDR
A
- ATP (used in LIR)
- reduced NADP (used in LIR)
- oxygen (used in respiration/diffuses out stomata)
14
Q
Light independent reaction (LIR)
A
- Calvin cycle
- uses CO2, reduced NADP and ATP to form hexose sugar
- occurs in stroma which contains the enzyme Rubisco
- temperature-sensitive
15
Q
Calvin cycle
A
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16
Q
RuBP
A
- Ribulose Bisphosphate
- 5-carbon molecule
17
Q
GP
A
- Glycerate-3-phosphate
- 3-carbon molecule
18
Q
Triose Phosphate
A
- 3-carbon molecule
- GP is reduced to form triose phosphate in the Calvin cycle.
- Triose phosphate is oxidised to form pyruvate in glycolysis.
19
Q
Producing hexose sugar in LIR
A
- Takes 6 cycles
- glucose can join to form disaccharides (sucrose) or polysaccharides (cellulose)
- can be converted to glycerol to combine with fatty acids to make lipids
20
Q
Limiting factor
A
- A factor which, if increased, the rate of the overall reaction also increases.
21
Q
Limiting factors of photosynthesis
A
- Light intensity
- CO2 concentration
- temperature
22
Q
How light intensity limits photosynthesis?
A
- If reduced, levels of ATP and reduced NADP would fall
◦ LDR limited – less photolysis and
photoionisation - GP cannot be reduced to triose phosphate in LIR
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23
Q
How temperature limits photosynthesis?
A
- LIR inhibited – enzyme controlled (Rubisco)
- up to optimum, more collisions and E-S complexes
- above optimum, H-bonds in tertiary structure break, active site changes shape – denatured
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24
Q
How CO2 concentration limits photosynthesis?
A
- If reduced, LIR inhibited
- less CO2 to combine with RuBP to form GP
- less GP reduced to TP
- less TP converted to hexose and RuBP regenerated
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25
Q
Agricultural practices to maximise plant growth
A
- Growing plants under artificial lighting to maximise light intensity
- heating in greenhouse to increase temperature
- burning fuel to release CO2
26
Q
Benefits of agricultural practices for plant growth
A
- Faster production of glucose → faster respiration
- more ATP to provide energy for growth e.g. cell division + protein synthesis
- higher yields so more profit
27
Q
Products of LIR
A
- Hexose sugar
- NADP – used in LDR
28
Q
Stages of aerobic respiration
A
- Glycolysis
- Link reaction
- Krebs cycle
- Oxidative phosphorylation
29
Q
Location of glycolysis
A
- Cytoplasm
30
Q
Glycolysis
A
- Substrate level phosphorylation – 2 ATP molecules add 2 phosphate groups to glucose
- glucose phosphate splits into two triose phosphate (3C) molecules
- both TP molecules are oxidised (reducing NAD) to form 2 pyruvate molecules (3C)
- releases 4 ATP molecules
31
Q
Coenzymes
A
- A molecule which aids/assists an enzyme
- NAD and FAD in respiration both gain hydrogen to form reduced NAD (NADH) and reduced FAD (FADH)
- NADP in photosynthesis gains hydrogen to form reduced NADP (NADPH)
32
Q
Products of glycolysis
A
- Net gain of 2 ATP
- 2 reduced NAD
- 2 pyruvate molecules
33
Q
How many ATP molecules does glycolysis produce?
A
- 2 ATP molecules used to phosphorylate glycose to glucose phosphate
- 4 molecules generated in oxidation of triose phosphate to pyruvate
- net gain 2 ATP molecules
34
Q
Location of the link reaction
A
- Mitochondrial matrix
35
Q
Link reaction
A
- Reduced NAD and pyruvate are actively transported to matrix
- pyruvate is oxidised to acetate (forming reduced NAD)
- carbon removed and CO2 forms
- acetate combines with coenzyme A to form acetylcoenzyme A (2C)
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36
Q
Products of the link reaction per glucose molecule
A
- 2 acetylcoenzyme A molecules
- 2 carbon dioxide molecules released
- 2 reduced NAD molecules
37
Q
Location of the Krebs cycle
A
- Mitochondrial matrix
38
Q
Krebs cycle
A
- Acetylcoenzyme A combines with 4C molecule to produce a 6C molecule – enters cycle
- oxidation-reduction reactions
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39
Q
Products of the Krebs cycle per glucose
A
- 8 reduced coenzymes
◦ 6 reduced NAD
◦ 2 reduced FAD - 2 ATP
- 4 carbon dioxide
40
Q
Location of oxidative
phosphorylation
A
- Cristae of mitochondria
41
Q
Mitochondria structure
A
- Double membrane with inner membrane folded into cristae
- enzymes in matrix
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42
Q
Role of reduced coenzymes in oxidative phosphorylation
A
- Accumulate in mitochondrial matrix, where they release their protons (H+) and electrons (e-)
- regenerate NAD and FAD to be used in glycolysis/link reaction/Krebs cycle
43
Q
Role of electrons in oxidative phosphorylation
A
- Electrons pass down series of electron carrier proteins, losing energy as they move
- energy released actively transports H+ from mitochondrial matrix to inter-membranal space
- electrochemical gradient generated
44
Q
How is ATP made in oxidative
phosphorylation?
A
- Protons move down electrochemical gradient back into matrix via ATP synthase
- ATP created
- movement of H+ is chemiosmosis
45
Q
Role of oxygen in oxidative phosphorylation
A
- Oxygen is the final electron acceptor in electron transport chain
- oxygen combines with protons and electrons to form water
- enables the electron transport chain to continue
46
Q
How would lack of oxygen affect respiration?
A
- Electrons can’t be passed along the electron transport chain
- the Krebs cycle and link reaction stop because NAD and FAD (converted from reduced NAD/FAD as they release their H atoms for the ETC), cannot be produced.
47
Q
Oxidation
A
- Loss of electrons
- when a molecule loses hydrogen
48
Q
Reduction
A
- Gain of electrons
- a reaction where a molecule gains hydrogen
49
Q
Location of anaerobic respiration
A
- Cytoplasm
◦ glycolysis only source of ATP
50
Q
Anaerobic respiration in plants & microbes
A
- Pyruvate produced in glycolysis is reduced to form ethanol and CO2
- pyruvate gains hydrogen from reduced NAD
- reduced NAD oxidised to NAD so can be reused in glycolysis
- 2 ATP produced
51
Q
Anaerobic respiration animals
A
- Pyruvate produced in glycolysis is reduced to form lactate
- pyruvate gains hydrogen from reduced NAD
- reduced NAD oxidised to NAD so can be reused in glycolysis
- 2 ATP produced
52
Q
Other respiratory substances
A
- Fatty acids and amino acids can enter the Krebs cycle for continued ATP synthesis
53
Q
Lipids as respiratory substances
A
- Glycerol from lipid hydrolysis converted to acetylcoenzyme A
- can enter the Krebs cycle
54
Q
Proteins as respiratory substances
A
- Amino acids from protein hydrolysis can be converted to intermediates within Krebs cycle
55
Q
Producers
A
- Plants
- produce their own carbohydrates from carbon dioxide (autotrophs)
- start of a food web
56
Q
Energy transfer between trophic levels
A
- Biomass and its stored energy is transferred through trophic levels very inefficiently
- most energy is lost due to respiration and excretion
57
Q
Consumers
A
- Heterotrophs that cannot synthesise their own energy
- obtain chemical energy through eating
58
Q
Biomass
A
- Measured in terms of:
◦ mass of carbon
◦ dry mass of tissue per given area
59
Q
How is dry mass of tissue estimated?
A
- Sample of organism dried in oven below 100C (avoiding combustion + loss of biomass)
- sample reweighed at regular intervals
- all water removed when mass constant
60
Q
Why is dry mass a representative measure of biomass?
A
- Water content in tissues varies
- heating until constant mass allows standardisation of measurements
- for comparison
61
Q
Calorimetry
A
- Laboratory method used to estimate chemical energy stored in dry biomass
62
Q
Calorimetry method
A
- Sample of dry biomass is burnt
- energy released used to heat known volume of water
- change in temperature of water used to calculate chemical energy
63
Q
Gross primary production
A
- Chemical energy stored in plant biomass, in a given area/volume
- total energy resulting from photosynthesis
64
Q
Net primary production
A
- Chemical energy stored in plant biomass after respiratory losses
- available for plant growth and reproduction – create biomass available to other trophic levels
65
Q
Calculating net primary production
A
- NPP = GPP - R
- R = respiratory losses to the environment
66
Q
Calculating net production of consumers (N)
A
- N = I - (F + R)
- I = chemical energy store in ingested food
- F = chemical energy store in faeces/urine
- R = respiratory losses
67
Q
Units of productivity rates
A
- kJ Ha-1 year-1
- kJ is the unit for energy
68
Q
Why is productivity measured per area?
A
- Per hectare (for example) is used because environments vary in size
- standardises results so environments can be compared
69
Q
Why is productivity measured per year?
A
- More representative of productivity
- takes into account effects of seasonal variation (temperature) on biomass
- environments can be compared with a standardised amount of time
70
Q
Why is energy transfer inefficient from sun → producer?
A
- Wrong wavelength of light – not absorbed by chlorophyll
- light strikes non-photosynthetic region (bark)
- light reflected by clouds/dust
- lost as heat
71
Q
Why is energy transfer inefficient after producers?
A
- Respiratory loss – energy used for metabolism (active transport)
- lost as heat
- not all plant/animal eaten (bones)
- some food undigested (faeces)
72
Q
Farming practices to increase energy transfer for crops
A
- Simplifying food webs to reduce energy/biomass
◦ herbicides kill weeds → less competition
◦ fungicides reduce fungal infections - results in more energy available to use to create biom to create biomassass
- fertilisers such as nitrates to promote growth
73
Q
Farming practices to increase energy transfer for animals
A
- Reducing respiratory losses (more energy to make biomass)
◦ restrict movement
◦ keep warm - slaughter animal when young (most energy used for growth)
- selective breeding to produce breeds with higher growth rates
74
Q
Saprobionts
A
- Feed on remains of dead organisms and their waste products (faeces/urea) and break down organic molecules
- secrete enzymes for extracellular digestion
75
Q
Mycorrhizae
A
- Symbiotic relationship between fungi and roots of plants
- fungi act as extensions of roots
- increase surface area of system – increasing rate of absorption
- mutualistic relationship as plants supply fungi with carbohydrates
76
Q
Importance of nitrogen to organisms
A
- Used to create
◦ amino acids/proteins
◦ DNA
◦ RNA
◦ ATP
77
Q
Nitrogen cycle stages
A
- Nitrogen fixation
- nitrification
- denitrification
- ammonification
78
Q
Nitrogen fixation
A
- Nitrogen fixing bacteria break triple bond between two nitrogen atoms in nitrogen gas
- fix this nitrogen into ammonium ions
79
Q
Nitrogen fixing bacteria
A
- Fix nitrogen gas into
ammonium ions - free living in soil
- or form mutualistic relationship on root nodules of leguminous plants
◦ give plants N in exchange for carbohydrates
80
Q
Nitrification
A
- Ammonium ions in soil are oxidised to nitrite ions
- nitrite ions are oxidised to nitrate ions
- by nitrifying bacteria
81
Q
Denitrification
A
- Returns nitrogen in compounds back into nitrogen gas in atmosphere
- by anaerobic denitrifying bacteria
82
Q
Ammonification
A
- Proteins/urea/DNA can be decomposed in dead matter and waste by saprobionts
- return ammonium ions to soil – saprobiotic nutrition
83
Q
Importance of phosphorus
A
- Used to create:
◦ DNA
◦ RNA
◦ ATP
◦ phospholipid bilayers
◦ RuBP/GP/Triose phosphate
84
Q
Phosphorus cycle
A
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85
Q
Fertilisers
A
-
Replace nutrients (nitrates and phosphates) lost from an ecosystem’s nutrient cycle when
◦ crops are harvested
◦ livestock removed - can be natural (manure) or artificial (inorganic chemicals)
86
Q
Natural fertilisers advantages
A
-
Cheaper than artificial fertilisers
◦ often free if farmer has own animals – recycle manure - organic molecules have to be broken down first by saprobionts so leaching less likely
87
Q
Artificial fertilisers advantages
A
- Contain pure chemicals in exact proportions
- more water-soluble, so more ions dissolve in water surrounding soil
◦ higher absorption
88
Q
Natural fertilisers disadvantages
A
- Exact minerals and proportions
cannot be controlled
89
Q
Artificial fertilisers disadvantages
A
- High solubility means larger quantities can leach away with rain
◦ risking eutrophication - reduce species diversity as favour plants with higher growth rates e.g. nettles
90
Q
Leaching
A
- When water-soluble compounds are washed away into rivers/ponds
- for nitrogen fertilisers, this can lead to eutrophication
91
Q
Eutrophication
A
- When nitrates leached from fields stimulate growth of algae
- algal bloom
- can lead to death of aquatic organisms
92
Q
How does eutrophication lead to death of aquatic organisms?
A
- Algal bloom creates blanket surface of water blocking light
- plants cannot photosynthesise and die
- aerobic bacteria feed and respire on dead plant matter
- eventually, aquatic organisms die due to lack of dissolved oxygen in water
93
Q
Mutualistic relationships
A
- A type of symbiotic relationship where all species involved benefit from their interactions
94
Q
Role of saprobionts in nitrogen cycle
A
- They use enzymes to decompose proteins/DNA/RNA/urea
- releasing ammonium ions
