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Y13 Biology > 5. Energy Transfers > Flashcards

5. Energy Transfers Flashcards

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1
Q

What are the stages of photosynthesis and where do they occur?

A
  1. Light dependent reaction
    - thylakoid membrane of chloroplast
  2. Light independent reaction
    - stroma of chloroplast
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2
Q

Describe the structure of a chloroplast (4)

A
  • double membrane
  • stroma, containing:
    > 70s ribosomes
    > thylakoid membrane
    > circular DNA
    > starch granules/lipid droplets
  • lamella (thylakoid linking grana)
  • grana (stacks of thylakoid)
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3
Q

Describe photoionisation in the LDR

A
  • Chlorophyll absorbs light energy which excites its electrons (jump to a higher energy level)
  • So electrons are released from chlorophyll (chlorophyll becomes positively charged)
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4
Q

Describe what happens after photoionisation in the LDR

A

Some energy from electrons released in photoionisation is conserved in the production of ATP/reduced NADP (chemiosmotic theory):
1. Electrons move along the electron transport chain (electron carriers), releasing energy
2. This energy is used to actively pump protons from the stroma into the thylakoid across the thylakoid membrane
3. Protons move by facilitated diffusion down their electrochemical gradient back into the stroma via ATP synthase
4. Energy used to join ADP and Pi to form ATP (photophosphorylation)
5. NADP accepts a proton and an electron to become reduced NADP

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5
Q

Describe photolysis of water in the LDR

A

Water splits to produce protons, electrons and oxygen
H2O —> 1/2 O2 + 2e- + 2H+ )
- Electrons replace those lost from chlorophyll

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6
Q

Describe the LIR of photosynthesis (Calvin cycle)

A
  1. CO2 reacts with ribulose bisphosphate (RuBP)
    > catalysed by the enzyme rubisco
  2. Forming 2x glycerate-3-phosphate (GP) molecules
  3. GP reduced to triose phosphate (TP)
    > using products from LDR (reduced NADP and energy from ATP)
  4. Some TP converted to useful organic substances (e.g glucose)
  5. Some TP used to regenerate RuBP in the Calvin cycle (using energy from ATP)
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7
Q

Describe and explain how temperature affects the rate of photosynthesis

A
  1. As temperature increases, rate increases
    - enzymes e.g rubisco gain kinetic energy
    - so more E/S complexes form
  2. Above an optimum temperature, rate decreases
    - enzymes denature as hydrogen bonds in tertiary structure break
    - so fewer E/S complexes form (no longer complementary)
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8
Q

Describe and explain how light intensity affects the rate of photosynthesis

A
  1. As light intensity increases, rate increases
    - LDR increases (more photoionisation of chlorophyll) so more ATP and reduced NADP produced
    - so LIR increases as more GP reduced to TP and more TP regenerates RuBP
  2. Above a certain light intensity, rate stops increases
    - another factor is limiting, e.g temperature/CO2 concentration
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9
Q

Describe and explain how CO2 concentration affects rate of photosynthesis

A
  1. As CO2 concentration increases, rate increases
    - LIR increases
    - as more CO2 combines with RuBP to form GP
    - more GP reduced to TP
    - so more TP converted to organic substances and more RuBP regenerated
  2. Above a certain CO2 concentration, rate stops increasing
    - another factor is limiting, e.g temperature, light intensity
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10
Q

Explain the key consideration when evaluating data relating to agricultural practices used to overcome the effect of limiting factors

A
  • Agricultural practices should increase the rate of photosynthesis, leading to an increased yield
    > as more glucose produced for faster respiration
    > so more ATP to release energy for growth, e.g cell division, protein synthesis
  • But profit from extra yield should be greater than costs
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11
Q

Why is respiration important?

A
  • Respiration produces ATP (to release energy)
  • For active transport, protein synthesis etc
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12
Q

Describe the structure of a mitochondria

A
  • outer membrane
  • cristae (folded inner membrane)
  • matrix, containing:
    > 70s ribosomes
    > circular DNA
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13
Q

Summarise the stages of aerobic and anaerobic respiration and where each occurs

A

AEROBIC:
1. Glycolysis - cytoplasm (anaerobic process)
2. Link reaction - mitochondrial matrix
3. Krebs cycle - mitochondria matrix
4. Oxidative phosphorylation- inner mitochondrial membrane

ANAEROBIC:
1. Glycolysis- cytoplasm
2. NAD regeneration - cytoplasm

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14
Q

Describe the process of glycolysis

A
  1. Glucose is phosphorylated to glucose phosphate
    > using inorganic phosphates from 2 ATP
  2. Hydrolysed (splits) to 2 x triose phosphate
  3. TP is oxidised to 2 x pyruvate
    > reduces 2 NAD (1 per TP molecule)
    > 4 ATP regenerated (net gain of 2 ATP)
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15
Q

Explain what happens after glycolysis if respiration is anaerobic

A
  1. Pyruvate is converted to lactate (animals and some bacteria) or ethanol (plants & yeast) —> (remove CO2 to form ethanal, then oxidise NADH to form ethanol)
  2. Oxidising reduced NAD —> regenerating NAD
  3. So glycolysis can continue (which requires NAD) allowing continued production of ATP
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16
Q

Suggest why anaerobic respiration produces less ATP per molecule of glucose than aerobic respiration

A
  • Only glycolysis involved which produces little ATP (2 molecules)
  • No oxidative phosphorylation which forms majority of ATP (around 34 molecules)
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17
Q

What happens after glycolysis if respiration is aerobic?

A

Pyruvate is actively transported into the mitochondrial matrix

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18
Q

Describe the link reaction

A
  1. Pyruvate is oxidised and decarboxylated to acetate
    > CO2 produced
    > reduced NAD produced (picks up H)
  2. Acetate combines with coenzyme A, forming acetyl coenzyme A

Products per glucose molecule:
- 2x acetyl CoA
- 2x CO2
- 2x reduced NAD

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19
Q

Describe the Krebs cycle
Products per glucose molecule?

A
  1. Acetyl CoA (2C) reacts with a 4C molecule
    > releasing CoA
    > producing a 6C molecule that enters the Krebs cycle
  2. In a series of redox reactions, the 4C molecule is regenerated and:
    - 2x CO2 lost
    - 3x NAD molecules are reduced to NADH
    - x1 FAD molecule is reduced to FADH
    - Substrate level phosphorylation (direct transfer of Pi from intermediate compound to ADP) —> produces 1 molecule of ATP

Products per glucose molecule:
- 6x NADH
- 2x FADH
- 2x ATP
- 4x CO2

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20
Q

Describe the process of oxidative phosphorylation

A
  1. Reduced NAD/FAD (coenzymes) are oxidised to release H atoms —> split into protons and electrons
  2. Electrons transferred down the ETC, by redox reactions
  3. Energy released by electrons using in the production of ATP from ADP + Pi (chemiosmotic theory):
    - energy used by electron carriers to actively pump protons from the matrix through the IMM into the IMS
    - protons diffuse into the matrix down an electrochemical gradient, via ATP synthase (embedded)
    - releasing energy to synthesis ATP from ADP + Pi
  4. In the matrix at the end of ETC, oxygen is the final electron acceptor (electrons cant pass along otherwise)
    - so protons, electrons and oxygen combine to form water
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21
Q

Give examples of other respiratory substrates

A

Breakdown products of lipids and amino acids, which enter the Krebs cycle, e.g:
- Fatty acids from hydrolysis of lipids —> converted to acetyl CoA
- Amino acids from hydrolysis of proteins —> converted to intermediates in Krebs cycle

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22
Q

Describe how biomass is formed in plants

A
  • During photosynthesis, plants make organic (carbon) compounds from atmospheric or aquatic CO2
  • Most sugars synthesised are used by the plant as respiratory substrates
  • Rest are used to make other groups of biological molecules (e.g carbs, lipids & proteins) —> form biomass
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23
Q

How can biomass be measured?

A

mass of carbon or dry mass of tissue per given area

24
Q

Describe how dry mass of tissue can be measured

A
  1. Sample dried in an oven, e.g at 100ºC (avoid combustion)
  2. Sample weighed and reheated at regular intervals until mass remains constant (all water evaporated)
25
Q

Explain why dry mass is more representative than fresh (wet) mass

A

water volume in wet samples will vary but will not affect dry mass

26
Q

Describe how the chemical energy stored in dry biomass can be estimated

A

Using calorimetry:
1. Known mass of dry biomass is fully combusted (burnt)
2. Heat energy released heats a known volume of water
3. Increase in temperature of water is used to calculate chemical energy of biomass

27
Q

Explain how features of a calorimeter enable valid measurement of heat energy released

A
  • Stirrer —> evenly distributes heat energy in water
  • Air/insulation —> reduces heat loss & gain to and from surroundings
  • Water —> has a high specific heat capacity
28
Q

What is gross primary production (GPP)?

A

Chemical energy store in plant biomass, in a given area or volume, in a given time
> total energy transferred into chemical energy from light energy during photosynthesis

29
Q

What is net primary production (NPP)?

A

chemical energy store in plant biomass after respiratory losses to environment have been taken into account

30
Q

State the formula for NPP

A

NPP = GPP - R
R —> respiratory losses to the environment

31
Q

Explain the importance of NPP in ecosystems

A
  • NPP is available for plant growth and reproduction
  • NPP is also available to other trophic levels in the ecosystem, such as herbivores and decomposers
32
Q

What is primary or secondary productivity?

A

The rate of primary or secondary production, respectively.

33
Q

State the units used for primary or secondary productivity

A

kJ ha^-1 year^-1 (unit for energy, per unit area, per year/time)

34
Q

Explain why the units for primary and secondary productivity are used

A

Per unit area —> takes into account that different environments vary in size, standardising results to enable comparison between environments
Per year —> takes into account effect of seasonal variation (temperature etc) on biomass, more representative and enables comparison between environments

35
Q

Explain why most light falling on producers is not used in photosynthesis

A
  • Light is wrong wavelength or reflected
  • Light misses chlorophyll/chloroplasts
  • CO2 concentration or temperature is a limiting factor
36
Q

State the formula for net production of consumers (N)

A

N = I - (F + R)

I = chemical energy store in ingested food
F = chemical energy lost to the environment in faeces and urine

37
Q

State the formula for efficiency of energy transfer

A

Energy or biomass available after transfer / energy or biomass available before transfer (x100 if a %)

38
Q

Explain why energy transfer between trophic levels in inefficient

A
  • heat energy is lost via respiration
  • energy lost via parts of an organism that aren’t eaten (e.g bones)
  • energy lost via food not digested —> lost as faeces
  • energy lost via excretion e.g urea in urine
39
Q

Explain how crop farming practices increase efficiency of energy transfer

A
  • Simplifying food webs to reduce energy/biomass losses to non-human food chains e.g
    > herbicides kill weeds : less competition so more energy to create biomass
    > pesticides kill insects : reduce loss of biomass from crops
    > fungicides : reduce fungal infections, more energy to create biomass
  • Fertilisers e.g nitrates to prevent poor growth due to lack of nutrients
40
Q

Explain how livestock farming practices increase efficiency of energy transfer

A
  • Reducing respiratory losses within a human food chain (so more energy to create biomass):
    > restrict movement and keep warm : less energy lost as heat from respiration
    > slaughter animal while still growing/young, when most of their energy is used for growth
    > treated with antibiotics : prevent loss of energy due to pathogens
    > selective breeding to produce breeds with higher growth rates
41
Q

Explain the role of saprobionts in recycling chemical elements

A
  • Decompose (break down) organic compounds e.g proteins/urea/DNA in dead matter/organic waste
  • by secreting enzymes for extracellular digestion (saprobiotic nutrition)
  • absorb soluble needed nutrients and release mineral ions (form of ammonium ions into soil)
42
Q

What are mycorrhizae?

A

symbiotic association between fungi and plant roots

43
Q

Explain the role of mycorhizzae

A
  • Fungi (hyphae) act as an extension of plant roots to increase surface area of root system
  • to increase rate of uptake/absorption of water and inorganic ions
  • in return, fungi receive organic compounds e.g carbohydrates
44
Q

Give examples of biological molecules that contain nitrogen

A

amino acids
proteins or enzymes
urea
DNA or RNA
chlorphyll
ATP or ADP
NAD or NADP

45
Q

Name the key stages of the nitrogen cycle

A
  1. Nitrogen fixation (N2 gas to ammonia)
  2. Ammonification (nitrogen-containing compounds to ammonia)
  3. Nitrification (ammonium ions to nitrites, then nitrates)
  4. Denitrification (nitrates into N2 gas)
46
Q

Describe the role of bacteria in nitrogen fixation

A
  • N2 gas is converted into ammonia (NH3), which forms ammonium ions (NH4+) in the soil
  • by nitrogen-fixing bacteria (may be found in root nodules)
47
Q

Describe the role of bacteria in ammonification

A
  • Nitrogen-containing compounds e.g proteins/DNA/urea from dead organisms/waste are broken down/decomposed
  • converted into ammonia, which forms ammonium ions in the soil
  • by saprobionts —> secrete enzymes for extracellular digestion
48
Q

Describe the role of bacteria in nitrification

A
  • Ammonium ions in soil converted into nitrites (NO2-) then nitrates (NO3-), via a 2-step oxidation reaction
    > for uptake by plant root hair cells by active transport
  • by nitrifying bacteria in aerobic conditions (oxygen)
49
Q

Describe the role of bacteria in denitrification

A
  • Nitrates in soil converted into nitrogen gas (reduction)
  • By denitrifying bacteria in anaerobic conditions (no oxygen, e.g waterlogged soil)
50
Q

Suggest why ploughing (aerating) soil increases its fertility

A
  • More ammonium converted into nitrite and nitrate/more nitrification/more active nitrifying bacteria
  • Less nitrate converted to nitrogen gas/less denitrification/fewer active denitrifying bacteria
    (aerobic conditions)
51
Q

Give examples of biological molecules that contain phosphorus

A

Phospholipids
DNA/RNA
ATP/ADP
NADP
TP/GP
RuBP

52
Q

Describe the phosphorus cycle

A
  1. Phosphate ions in rocks released (into soils/oceans) by erosion/weathering
  2. Phosphate ions taken up by producers/plants/algae and incorporated into their biomass —> rate of absorption increased by mycorrhizae
  3. Phosphate ions transferred through food chain e.g as herbivores eat producers
  4. Same phosphate ions lost from animals in waste products (excretion)
  5. Saprobionts decompose organic compounds e.g DNA in dead matter/organic waste, releasing phosphate ions
53
Q

Explain why fertilisers are used

A
  • To replace nitrates/phosphates lost when plants are harvested and livestock are removed
    > those removed from soil and incorporated into biomass can’t be released back into the soil through decomposition by saprobionts
  • So improve efficiency of energy transfer —> increase productivity/yield
54
Q

Describe the difference between artificial and natural fertilisers

A

Natural: organic, e.g manure, compost, sewage —> ions released during decomposition by saprobionts
Artificial: contain inorganic compounds of nitrogen, phosphorus and potassium

55
Q

Explain the key environmental issue arising from use of fertilisers

A
  • Phosphates/nitrates dissolve in water, leading to leaching of nutrients into lakes/rivers/oceans
  • this leads to eutrophication:
    1. rapid growth of algae in pond/river (algal bloom) so light blocked
    2. so submerged plants die as they cannot photosynthesise
    3. So saprobionts decompose dead plant matter, using oxygen in aerobic respiration
    4. so less oxygen for fish to respire aerobically, leading to their death
56
Q

Explain the key advantage of using natural fertiliser over artificial fertiliser

A
  • Less water soluble so less leaching —> eutrophication less likely
  • Organic molecules require breaking down by saprobionts —>slow release of nitrate/phosphate etc
57
Q

Why is aerobic respiration only 32% efficient?

A
  • some protons leak across the mitochondrial membrane during oxidative phosphorylation
  • ATP is used to actively transport pyruvate and NADH into the mitochondrial matrix
  • some energy is lost as heat

Y13 Biology (4 decks)

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