[3.5] Energy Transfers In & Between Organisms Flashcards
Photosynthesis, Respiration, Energy and Ecosystems & Nutrient Cycles.
What are the stages of photosynthesis and where do they happen?
-
Light dependant reaction.
- Thylakoid membrane of chloroplast.
-
Light independent reaction.
- Stroma of chloroplast.
Describe photoionisation in the light-dependant reaction (LDR).
- Chlorophyll absorbs light energy which excites its electrons (higher energy level).
- So electrons are released from chlorophyll (chlorophyll becomes positively charged).
Describe what happens after photoionisation in the LDR.
- Some energy from electrons released in photoionisation is conserved in the production of ATP / reduce NADP (chemiosmotic theory).
- Electrons move along electron transfer chain (electron carriers), releasing energy.
- This energy is used to actively pump protons from stroma into thylakoid.
- Protons move by facilitated diffusion down electrochemical gradient intro stroma via ATP synthase.
- Energy used to join ADP and Pi to form ATP (photophosphorylation).
- NADP accepts a proton and an electron to become reduced NADP.
Describe the photolysis of water in the LDR.
- Water splits to produce protons, electrons and oxygen (H₂O -> 1/2 O₂ + 2e⁻ + 2H⁺).
- Electrons replace those lost from chlorophyll.
Describe the light-independent reaction of photosynthesis (Calvin cycle).
- CO₂ reacts with ribulose bisphosphate (RuBP) which is catalysed by the enzyme rubisco.
- Forming 2x glycerate 3-phosphate (GP).
- GP reduced to triose phosphate (TP) using products from light-dependant reaction (reduced NADP & energy from ATP)
- Some TP converted to useful organic substances (e.g. glucose).
- Some TP used to regenerate RuBP in the Calvin cycle (using energy from ATP).
Describe and explain how temperature affects rate of photosynthesis.
- As temperature increases, rate increases.
- Enzymes e.g. rubisco gain kinetic energy.
- So more enzyme-substrate (E-S) complexes form.
- Above an optimum temperature, rate decreases.
- Enzymes denature as H bonds in tertiary structure break.
- So fewer enzyme-substrate (E-S) complexes form.
Describe and explain how light intensity affects rate of photosynthesis.
- As light intensity increases, rate increases.
- Light-dependant reaction increases (e.g. more photoionisation of chlorophyll) so more ATP and reduced NADP produced.
- So light-independent reaction increases as more GP reduced to TP and more TP regenerates RuBP.
- Above a certain light intensity, rate stops increasing.
- Another factor is limiting e.g. temperature / CO₂ concentration.
Describe and explain how CO₂ concentration affects rate of photosynthesis.
- As CO₂ concentration increases, rate increases.
- Light-independent reaction increases.
- As more CO₂ combined with RuBP to form GP.
- So more GP reduced to TP.
- So more TP converted to organic substances and more RuBP regenerated.
- Above a certain CO₂ concentration, rate stops increasing.
- Another factor is limiting e.g. temperature / light intensity.
Explain the key consideration when evaluating data relating to agricultural practices used to overcome the effect of limiting factors.
- Agricultural practice should increase rate of photosynthesis, leading to 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 (money & environmental costs).
Why is respiration important?
- Respiration produces ATP (to release energy).
- For active transport, protein synthesis etc.
Summarise the stages of aerobic and anaerobic respiration.
Aerobic Respiration
- Glycolysis - cytoplasm (anaerobic).
- Link reaction - mitochondrial matrix.
- Krebs cycle - mitochondrial matrix.
- Oxidation phosphorylation - inner mitochondrial matrix.
Anaerobic Respiration
- Glycolysis - cytoplasm.
- NAD regeneration- cytoplasm.
Describe the process of glycolysis.
- Glucose phosphorylated to glucose phosphate.
- Using inorganic phosphates from 2 ATP.
- Hydrolysed to 2x triose phosphate.
-
Oxidised to 2x pyruvate.
- 2 NAD reduced.
- 4 ATP regenerated (net gain of 2).
Explain what happens after glycolysis if respiration is anaerobic.
- Pyruvate converted to lactate (animals & some bacteria) or ethanol (plants & yeast).
- Oxidising reduced NAD -> NAD regenerated.
- So glycolysis can continue (which needs NAD) allowing continued production of ATP.
Suggest why anaerobic respiration produces less ATP per molecule of glucose than aerobic respiration.
- Only glycolysis invovled which produces little ATP (2 molecules).
- No oxidative phosphorlyation which forms majority of ATP (around 34 molecules).
What happens after glycolysis if respiration is aerobic?
- Pyruvate is actively transported into the mitochondrial matrix.
Describe the link reaction.
- Pyruvate oxidised (and decarboxylated) to acetate.
- CO₂ produced.
- Reduced NAD produced (picks up H).
- Acetate combined with coenzyme A, forming Acetyl Coenzyme A.
Describe the Krebs cycle.
- Acetyl coenzyme A reacts with a 4C molecule.
- Releasing coenzyme A
- Producing a 6C molecule that enters the Krebs cycle.
- In a series of oxidation-reduction reactions, the 4C molecule is regenerated and:
- 2x CO₂ lost.
- Coenzymes NAD & FAD reduced.
- Substrate level phosphorylation (direct transfer of Pi from intermediate compound to ADP) which produces ATP.
Describe the process of oxidative phosphorylation.
- Reduced NAD/FAD oxidised to release H atoms -> split into protons (H⁺) and electrons (e⁻).
- Electrons transferred down electron transfer chain (chain of carriers at decreasing energy levels).
- By redox reactions.
- Energy released by electrons used in the production of ATP from ADP + Pi (chemiosmotic theory):
- Energy used by electron carriers to actively pump protons from matrix -> intermembrane space.
- Protons diffuse into matrix down an electrochemical gradient, via ATP synthase (embedded).
- Releasing energy to synthesise ATP from ADP + Pi.
- In matrix at the end of electron transfer chain, oxygen is the final electron acceptor (electrons can’t pass along otherwise).
- So protons, electrons and oxygen combine to form water.
Give examples of other respiratory substrates.
- Breakdown of products of lipids and amino acids, which enter the Krebs cycle. For example:
- Fatty acids from hydrolysis of lipids -> converted to Acetyl Coenzyme A.
- Amino acids from hydrolysis of proteins -> converted to intermediates in Krebs cycle.
Describe how biomass is formed in plants.
- During photosynthesis, plants make organic (carbon) compounds from atmospheric or aquatic CO₂.
- Most sugars synthesised are used by the plant as respiratory substrates.
- Rest used to make other groups of biological molecules (e.g. carbs, lipids & proteins) -> form biomass.
How can biomass be measured?
- Mass of carbon or dry mass of tissue per given area.
Describe how dry mass of tissue can be measured.
- Sample dried in an oven e.g. 100°C (avoid combustion).
- Sample weighed and reheated at regular intervals.
- Until mass remains constant (all water evaporated).
Explain why dry mass is more represenantive than fresh (wet) mass.
- Water volume in wet samples will vary but will not affect dry mass.
Describe how the chemical energy stored in dry biomass can be estimated.
Using calorimetry:
- Known mass of dry biomass is fully combusted (burnt).
- Heat energy released heats a known volume of water.
- Increase in temeprature of water is used to calculate chemical energy of biomass.
Explain how features of a calorimeter enable valid measurement of heat energy released.
- Stirrer -> evenly distributes heat energy (in water).
- Air/insulation -> reduces heat loss & gain to & from surroundings.
- Water -> has a high specific heat capacity.
What is gross primary production (GPP)?
-
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.
What is net primary production (NPP)?
- Chemical energy store in plant biomass after respiratory losses to enivronment taken into account.
State the formula for NPP.
NPP = GPP = R
R = respiratory losses to the environment.
Explain the importance of NPP in ecosystems.
- NPP is available for plant growth and reproduction.
- NPP is also available to other trophic levels in the ecosystem, such as herbivores and decomposers.
What is primary or secondary productivity?
- The rate of primary or secondary production, respectively.
State the units used for primary or secondary productivity.
KJ ha⁻¹ year⁻¹ (unit for energy, per unit area, per year)
Explain why these units for primary or secondary productivity are used.
- Per unit area -> takes into account that different envrionments 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.
Explain why most light falling on prodcuers is not used in photosynthesis.
- Light is reflected or wrong wavelength.
- Light misses chlorophyll / chloroplasts / photosynthetic tissue.
- CO₂ concentration or temperature is a limiting factor.
State the formula for net production of consumers (N).
N = I - (F + R)
I = the chemical energy store in ingested food.
F = the chemical energy lost to the environment in faeces and urine.
State the formula for efficiency of energy transfer.
Energy or biomass available after transfer / energy or biomass available before transfer (x100 if %)
Explain why energy transfer between trophic levels is inefficient.
- Heat energy is lost via respiration.
- Energy lost via parts of 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.
Explain how crop farming practices increase energy transfer efficiency.
-
Simplifying food webs to reduce energy / biomass losses to non-human food chains. For example:
- Herbicides kill weeds -> less competition (e.g. for light) so more energy to create biomass.
- Pesticides kill insects (pests) -> 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.
Explain how livestock farming practices increase energy transfer efficiency.
-
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.
Explain the role of saprobionts in recycling chemical elements.
- 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 e.g. phosphate ions.
Explain the role of mycorrhizae.
Mycorrhizae = symbiotic association between fungi and plant roots.
- 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.
Give examples of biological molecules that contain nitrogen.
- Amino acids / proteins or enzymes / urea / DNA or RNA / chlorophyll / ATP or ADP / NAD or NADP.
Draw a diaram to show the key stages of the nitrogen cycle.
Describe the role of bacteria in nitrogen fixation.
- Nitrogen gas (N₂) converted into ammonia (NH₃), which forms ammonium ions (NH₄⁺) in soil.
- By nitrogen-fixing bacteria (may be found in root nodules).
Describe the role of bacteria in ammonification.
- Nitrogen-containing compounds e.g. proteins / urea from dead organisms / waste are broken down / decomposed.
- Converted to ammonia, which forms ammonium ions in soil.
- By saprobionts - secrete enzymes for extracellular digestion.
Describe the role of bacteria in nitrification.
-
Ammonium ions in soil converted into nitrites then nitrates, via a two-step oxidiation reaction.
- For uptake by plant root hair cells by active transport.
- By nitrifying bacteria in aerobic conditions (oxygen).
Describe the role of bacteria in denitrification.
- Nitrates in soil converted into nitrogen gas (reduction).
- By denitrifying bacteria in anaerobic conditions (no oxygen, e.g. waterlogged soil).
Suggest why ploughing (aerating) soil increases its fertility.
- More ammonium converted into nitrite and nitrate / more nitrification / more (active) nitrifying bacteria.
- Less nitrate converted to nitrogen gas / less dentrification / fewer (active) denitrifying bacteria.
Give examples of biological molecules that contain phosphorus.
- Phospholipids / DNA or RNA / ATP or ADP / NADP / TP or GP / RuBP.
Describe the phosphorus cycle.
- Phosphate ions in rocks released (into soils/oceans) by erosions / weathering.
- Phosphate ions taken up by producers / plants / algae and incorporated into their biomass.
- Rate of absorption increased by mycorrhizae.
- Phosphate ions transferred through food chain e.g. as herbivores eat producers.
- Some phosphate ions lost from animals in waste products (excretion).
- Saprobionts decompose organic compounds e.g. DNA in dead matter / organic waste, releasing phosphate ions.
Explain why fertilisers are used.
- To replace nitrates / phosphate 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.
Describe the difference between artifical and natural fertilisers.
NATURAL
- Organic, e.g. manure, compost, sewage.
- Ions released during decomposition by saprobionts.
ARTIFICAL
- Contain inorganic compounds of nitrogen, phosphorous and potassium.
Explain the key environmental issue arising from use of fertilisers.
- Phosphates / nitrates dissolve in water, leading to leaching of nutritents into lakes / rivers / oceans.
- This leads to eutrophication.
- Rapid growth of algae in pond / river (algal bloom) so light blocked.
- So submerged plants die as they cannot photosynthesis.
- So saprobionts decompose dead plant matter, using oxygen in aerobic respiration.
- So less oxygen for fish to aerobically respire, leading to their death.
Explain the key advantages of using natural fetiliser over artifical fertiliser.
- Less water soluble so less leaching -> eutrophiciation less likely.
- Organic molecules require breaking down by sapriobionts -> slow release nirate / phosphate etc.
