Topic 5: Energy Transfers Flashcards
Describe the structure of a chloroplast and how its structure relates to its function. (4)
- Starch grains / lipid droplets : store products of
photosynthesis; - double membrane - provides large surface for light absorption.
- Thylakoids: flattened discs stack to form grana; contain photosystems with chlorophyll.
- Intergranal lamellae: tubes attach thylakoids in adjacent grana.
- Stroma: fluid-filled matrix.- vesicular plastid
- Permeable membrane allows diffusion of gases /carbon dioxide;
- Stacking / arrangement of grana/thylakoids maximises
light catchment.
Define photolyis and photoisonisation.
- photolysis: Light energy is used to breakdown water producing hydrogen ions , electrons and oxygen.
- photoioinisation: excitation of electrons by the absorption of light energy.
Outline the equation for photolysis
H2O → 2H+ + 2e- + ½O2
Where do the light independent and light dependent reactions occur
LDR: Thylakoid membranes
LIR: the stroma
Describe the photoionisation of chlorophyll
- light energy is absorbed by chlorophyll in PSII . This Excites electrons; to a higher energy level.
- electrons are removed/released from chlorophyll
LDR process
Describe chemiosmosis
- The excited electrons move along a series of electron channel proteins embedded within the thylakoid membrane.
- As they move along the ETC, via a series of oxidation and reduction reactions they release energy.
- This energy is used to actively transport H+ ions from the stroma into the thylakoid lumen , creating an elctrochemical gradient.
- Protons than flow back into the stroma through ATP synthase , which provides energy needed for ATP synthesis
Describe the production of ATP and reduced NADP in the LDR
- Energy from the electron transfer chain is used to join ADP and Pi to form ATP using ATP synthase through phosphorylation.
- At the end of the electron transport chain, NADP accepts electrons, forming reduced NADP (NADPH)
- these are used in the Calvin Cycle.
D
Outline the difference between oxidation and reduction reactions
oxidation: loss of electrons, increases the oxidation state
reduction: gain of electron , decreases the oidation state
Describe what happens during photoionisation in the light-dependent reaction. (2)
- Chlorophyll absorbs light
OR
Light excites/moves electrons in chlorophyll; - Electron/s are lost
OR
Chlorophyll becomes positively charged
Describe what happens during the light-dependent reaction (5)
1. Chlorophyll absorbs light energy;
Accept light energy ‘hits’ chlorophyll
2. Excites electrons / electrons removed (from chlorophyll); to a higher energy level
3. Electrons move along carriers / electron transport chain releasing energy;
Accept movement of H+ / protons across membrane releases energy
4. Energy used to join ADP and Pi to form ATP;
5. Photolysis of water produces protons, electrons and oxygen;
6. NADP reduced by electrons / electrons and protons / hydrogen;
In photosynthesis, which chemicals are needed for the light-dependent reaction?
- NADP
- ADP
- Pi
- and water
The light absorbed by chlorophyll is used in the light-dependent reaction.
Name the two products of the light-dependent reaction that are required for the light-independent reaction. (2)
- ATP
- Reduced NADP
Accept NADPH
Atrazine binds to proteins in the electron transfer chain in chloroplasts of weeds, reducing the transfer of electrons down the chain.
Explain how this reduces the rate of photosynthesis in weeds. (4)
- Reduced transfer of protons across thylakoid membrane. OR Reduced chemiosomotic gradient / proton gradient across thylakoid
membrane. - (So) less ATP produced;
- (So) less reduced NADP produced;
- (So) light-independent reaction slows / stops;
OR Less reduction of GP to triose phosphate.
Crops use light energy to produce photosynthetic products.
Describe how crop plants use light energy during the light-dependent reaction.
- Excites electrons / electrons removed (from chlorophyll); to a higher energy level
- Electrons move along carriers/electron transfer chain releasing energy through redox reactions
- Energy used to join ADP and Pi to form ATP;
Accept: energy used for phosphorylation of ADP to ATP - Photolysis of water produces protons, electrons and oxygen;
- NADP reduced by electrons / electrons and protons / hydrogen;
Accept: NADP to NADPH (or equivalent) by addition of
electrons/hydrogen.
Reject: ‘produces energy’ for either mark but not for both.
Do not accept NADP reduced by protons on its own.
What role do photosynthetic pigments play in chloroplasts?
- Photosynthetic pigments absorb different wavelengths of light within the thylakoids of chloroplasts, facilitating the process of photosynthesis.
How are pigment molecules arranged in a photosystem?
- pigment molecules are arranged in funnel-like structures within the thylakoid membrane.
- The funnel-like structure helps in passing energy from one pigment molecule to the next until it reaches the primary pigment reaction center, where it is collected and used in LDR.
Name the primary pigments in Photosystem I and Photosystem II
Photosystem I: Chlorophyll a
Photosystem II: Chlorophyll b
Explain the role of chlorophyll and carotenoids in photosynthesis.
- **Chlorophylls (a and b) **are primary pigments that absorb light in the blue-violet and red regions of the spectrum, reflecting green light.
- **Carotenoids **(β carotene and xanthophyll) are accessory pigments that absorb light in the blue-violet region.
https://cdn.savemyexams.com/cdn-cgi/image/w=960,f=auto/uploads/2021/03/Absorption-spectra-of-chlorophylls-and-carotenoids_1.png
Outline the required practical.
Where does the LIR occur?
- occurs in the stroma
What dooes the Calvin Cycle use?
uses:
- carbon dioxide
- reduced NADP and ATP to form a hexose sugar.
- The ATP is hydrolysed to provide energy for this reaction and the reduced NADP donates the hydrogen to reduce molecules GP in the cycle.
Outline the key stages of the calvin cycle
- Carbon Fixation
- Reduction of Glycerate 3-Phosphate
- Regeneration of Ribulose Bisphosphate
Describe the calvin cycle
- Carbon dioxide combines with ribulose bisphosphate (RuBP), a 5-carbon (5C) molecule.
- Rubisco enzyme catalyzes this reaction, forming an unstable (6C) compound which splits into two 3C molecules of glycerate 3-phosphate (GP).
- Energy from ATP and Hydrogen fromm Reduced NADP are used to reduce GP, to a phosphorylaated 3C sugar, triose phosphate.
- 1/6 of TP are used to produce useful organic molecules such as lipids and amino acids and carbohydrates.
- 5/6 of the TP are used to regenerate RuBp which requires ATP
Name the external factors that affect the rate of photosyntheis
- light intensity
- carbon dioxide concentration
- temperature
- these are known as the limiting factors of photosynthesis reducing the rate.
Describe and explain how light intensity affects the rate of photosynthesis
- As light intensity increases the rate of photosynthesis.
- the LDR increases e.g. more photoionisation of chlorophyll so more ATP and reduced NADP for the Calvin Cycle.
- So LDR increases and more GP reduced to TP and more TP regenerates RuBP.
- Abve a certain LI , rate stops increasing.
https://cdn.savemyexams.com/cdn-cgi/image/w=960,f=auto/uploads/2020/01/The-effect-of-light-intensity-on-the-rate-of-photosynthesis.png
Describe and explain how temperature affects rate of photosynthesis
- As temp increases , rate increases.
- Enzymes e.g. rubisco gain kinetic energy.
- So more enzyme-substrated (E-S) complexes form.
- Above the optimum temperature , rate decreases as enzymes denature as H bonds in tertiary structure break.
- So fewer ES complexes form.
Describe and explain how CO2 concentration affects the rate of photosynthesis
- As CO2 concentration increases , rate increases
- LIR increases
- As more CO2 combines with RuBP to form GP
- So more GP is reduced to TP , where more Tp is then converted to organic substances and more RuBP regenerated.
- Above a certain conc , rate stops increasing and it becomes the limiting factor.
Explai the key consideration when evaluating data relating to agriculural practices used to overcome the effect of limiting factors.
- Such practices should increase rate of photosyntheis, leading to increased yield.
- as more glucose is produced for faster respiration.
- so more ATP to release energy for growth e.g. cell dividsion , protein synthesis.
- but profit from extra yield should be greater than costs ( money + environmental costs)
REQUIRED PRACTICAL.
(a) Crops use light energy to produce photosynthetic products.
Describe how crop plants use light energy during the light energy during the light-dependent reaction (5)
1. Excites electrons / electrons removed (from chlorophyll); to a higher energy level
2. Electrons move along carriers/electron transfer chain releasing energy;
3. Energy used to join ADP and Pi to form ATP;
Accept: energy used for phosphorylation of ADP to ATP
Do not accept P as Pi but accept phosphate.
4. Photolysis of water produces protons, electrons and oxygen;
5. NADP reduced by electrons / electrons and protons / hydrogen;
Accept: NADP to NADPH (or equivalent) by addition of electrons/hydrogen.
Reject: ‘produces energy’ for either mark but not for both.
The stomata close when the light is turned off. Explain the advantage of this to the plant (2)
- (Because) water is lost through stomata;
- (Closure) prevents / reduces water loss;
- Maintain water content of cells.
e.g. reduce wilting,
During the light-independent reaction of photosynthesis, carbon dioxide is converted into organic substances. Describe how. (Total 6 marks)
- Carbon dioxide combines with ribulose bisphosphate / RuBP;
- Produces two glycerate (3-)phosphate / GP; from one RuBP.
- GP reduced to triose phosphate / TP;
Must have idea of reduction. This may be conveyed by stating m.p. - Using reduced NADP;
- Using energy from ATP;
Must be in context of GP to TP. - Triose phosphate converted to glucose / hexose / RuBP / ribulose bisphosphate /
named organic substance;
Iron deficiency reduces electron transport.
a) Use this information and your knowledge of photosynthesis to explain the decrease in production of triose phosphate in the iron-deficient plants. (4)
b) Iron deficiency results in a decrease in the uptake of carbon dioxide. Explain why.
(
- (Less) ATP produced;
- (Less) reduced NADP produced;
- ATP / reduced NADP produced during light-dependent reaction;
- (Less) GP to triose phosphate.
b) answer: - less TP converted to RuBP
- CO2 combines with RuBP
Few species of plant can live below large trees in a forest.
Use the information in Figure 1 and Figure 2 to suggest why.
1) Less (light) energy passes through leaves / reaches ground;
2) Smaller range of wavelengths passes through leaves;
Accept reference to only green (and yellow) light pass through.
3) Little light for chlorophyll to absorb;
Accept carotenoids can absorb this light
4) So insufficient photosynthesis (for growth);
5) Photosynthesis unlikely to exceed respiration;
In leaves at the top of trees in a forest, carbon dioxide is often the limiting factor for
photosynthesis.
Use your knowledge of photosynthesis to suggest and explain one reason why. (2)
1) Light not limiting / lots of light (as no shading);
2) Light-dependent reaction not limiting / fast;
1) Temperature not limiting / Warm (as no shading);
2) Fast reactions of enzymes in light-independent reaction;
1) High use of CO2;
2) Light-independent reaction is limiting;
Mark as a pair
only one pair needed
During photosynthesis, oil-palm trees convert carbon dioxide into organic substances. Describe how. (6)
- Carbon dioxide combines with ribulose bisphosphate / RuBP;
- Produces two molecules of glycerate (3-)phosphate / GP.
- Reduced to triose phosphate / TP;
- Using reduced NADP.
- Using energy from ATP.
- Triose phosphate converted to other organic substances / named organic substances / ribulose bisphosphate.
- in light independent reaction / Calvin cycle.
6 max
In the light-independent reaction of photosynthesis, the carbon in carbon dioxide becomes carbon in triose phosphate. Describe how. (5)
1. Carbon dioxide combines with ribulose bisphosphate / RuBP;
2. To produce two molecules of glycerate 3-phosphate / GP;
3. Reduced to triose phosphate / TP;
4. Requires reduced NADP;
5. Energy from ATP;
Describe how the structure of mitochondria relates to its function
Name the four stages in aerobic respiration and where they occur.
- Glycolysis: cytoplasm
- Link Reaction: mitochondrial matrix
- Krebs Cycle: mitochondrial matrix
- Oxidative phosphorylation: cristae membrane
Describe the process of glycolysis.
- Glucose phosphorylated to glucose phosphate , using inorgnaic phosphates from 2 ATP.
- Hydrolysed to 2 x Triose phosphate (TP)
- Oxidised to 2 pyruvate with 2 NAD reduced/
- 4 ATP regenerated.
- net gain of 2.
Describe the link reaction
- Pyruvate oxidised and decarboxylated to acetate.
- This leaves CO2 and Reduced NAD.
- Acetate combines with Coenzyme A , forming Acetyl Coenzyme A.
Give the products of the link reaction
- 2x Acetyl Coenzyme A
- 2x Reduced NAD
- 2X CO2
per glucose molecule
Describe the Krebs Cycle
- Acetyl Coenzyme A (2C) reacts with oxaloacetate (4C) molecule, releasing Coenzyme A. This produced citrate a 6c molecule) that enters the Krebs Cycle.
- In a series of oxidation-reduction reations , the 4C molecule is regenerated and:
- 2x CO2 lost.
- Coenzymes NAD & FAD reduced.
- Substrate-level phosphorylation
- ATP is produced
Describe the process of oxidative phosphorylation
- Reduced NAD/FAD oxidised to release H atoms. This splits into protons and electrons.
- Electrons are transferred down ETC by redox reactions.
- Energy released by electrons used in the production of ATP from ADP + Pi chemiosmotic theory)
- This energy is used by electron carriers to actively pump protons from matrix to the intermembrane space.
- Protons diffuse into matrix down an electrochemmical gradient via ATP synthase, releasing energy to synthesise ATP from ADP+ Pi.
- In matrix at the end of the ETC , O2 is the final electron acceptor so protons, eletrons and oxygen combine to form water.
Name 2 types of molecule that can be used as alternative respiratory substrates.
- amino acids from proteins
- glycerol and fatty acids from lipids
How can lipids act as an alternative respiratory substrate?
lipid - glycerol + fatty acids
1) phosphorylation of glycerol - TP for glycolysis.
2) Fatty acids- acetate
3) Acetate enters link reaction
4) H atoms produced for oxidative phosphorylation.
How can amino acids act as an alternative respiratory substrate?
Deamination produces:
1. 3C compounds - pyruvate for link reaction
2. 4C/5C compounds - intermediates in the Krebs Cycle.
Name the stages in respiration that produce ATP by
substrate-level phosphorylation.
· Glycolysis (anaerobic)
. Krebs cycle (aerobic)
Describe what happens during anaerobic respiration in animals?
- only glycolysis continues reduced NAD + pyruvate.
- Oxidised NAD + lactate
What happens to the lactate produced in anaerobic respiration?
- transported to liver via bloodstream where it is oxidised to pyruvate.
- can enter link reaction in liver cells or be converted to glycogen.
What happens during anaerobic respiration in some microorganisms e.g. yeast and some plant cells?
- only glycolysis continues
- pyruvate is decarboxylated to form ethanal.
- Ethanal is reduced to ethanol using reduced NAD to produced oxidised NAD for further glycolysis.
Suggest why anaerobic respiration produces less ATP per molecule of glucose than aerobic respiration
- only glycolysis involved which produces little ATP (2 molecules)
- No oxidative phosphorylation which forms majority of ATP ( around 34 molecules)
outline disadvantages of both types of anaerobic respiration
producing ethanol: cells die when ethanol conc. is above 12%, which dissolves cell membranes.
producing lactate: Acidic, so decreases pH. Results in muscle fatigue.
RP9
Describe how biomass is formed in plants.
- During photosyntheisis, plants make organic compounds from atmospheric or aquatic CO2.
- most sugars synthesised are used by the plant as respiratory substrate.
- the rest used to make other groups of biological molecules e.g. carbs, lipids and proteins.
What is biomass? And give units.
- total dry mass of tissue or mass of carbon measured over a given time in a specific area.
- when an area is being sampled : gm2
- when a volume is being sampled: gm-3
Describe how dry mass of tissue can be measured.
- Sample dried in an oven e.g. at 100oC (to avoid combustion)
- Sample weighed and reheated at regular intervals until mass remains constant. (all water evaporates).
How can the chemical energy store in dry biomass be estimated?
- using calorimetry.
- known mass of dry biomass is fully combusted (burnt)
- heat energy released heats a known volume of water.
- increase in temperature of water is used to calculated chemical energy of biomass.
- Energy released= specific heat capacity of water x volume of water (cm3) x temperature increase of water.
Explain how features of a calorimeter enable valid measurement of heat energy released.
- stirrer: evenely distributes heat energy ( in water)
- Air/Insulation: reduces heat loss & gain to & frm surroundings.
- Water: has a high specific heat capacity.
Define 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 enenergy store in plant biomass after respiratory losses to environment 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 avaialble to other tropic levels in the ecosystem , such as herbivores and decomposers.
define:
- primary productivity
- secondary productivity
primary: the rate at which organisms create biomass.
secondary: the rate at which consumers convert the chemical energy from their food into their biomass
State the units used for primary or secondary productivity
Explain why these units for primary and secondary productivtiy are used?
-** per unit area **- takes into account that different environemnts 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 producers is not used in photosynthesis
- light is relfected or wrong wavelength
- light misses chlorophyll/ chloroplasts / photosynthetic tissue.
- CO2 concentration or temperature is a limiting factor.
why is most of the sun’s energy not converted to organic matter?
- most solar energy is absorbed by atmosphere or relfected by clouds.
- photosynthetic pigments cannot absorb more waelengths of light
- not all light falls directly on a chlorophyll molecule.
- energy lost as heat during respiration/photosynthesis.
How can the net production of consumers be calculated?
- N= I - ( F+R)
- I : chemican energy from ingested food.
- F: energy lost as faeces and urine
- R: respiratory losses.
State the formula for effiency of energy transfer
- energy of biomass available after transfer / energy or biomass available before transfer. x 100
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.
what is a pyramid of biomass? + why is it preferable to a pyramid of numbers?
- diagram that shows the biomass at each trophic level.
- shape of pyramid of numbers may be skewed since a small number of producers an support many consumers.
Explain how crop farming practices increase efficiency of energy transfer
- simplifying food webs to reduce energy/ biomass losses to non-human food chains e.g:
- herbicides kill weeds which lead to less compeitition e.g. for light so more enrgy to create biomass.
- pesticides kill pests which reduces 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 efficiency of energy transfer.
- 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 whilst young when most of their energy is used for growth
- treated with antibiotics- precent loss of energy due to pathogens.
- selective breeding to produce breeds with higher growth rates.
Explain the role of sapribionts in recycling chemical elements
- decompose organic compounds e.g. proteins/urea/DNA in dead matter /organic waste.
- By secreting enzymers for exracellular digestion (sapribiotic nutrition)
- Absorb soluble needed nutrients and release mineral ions e.g. phosphate ions
Explain the role of mychorrhizae
- have a symbiotic relationship between fungi and plant roots.
- fungi (hyphae) acts as an extension of plant roots to increase surface area of root system.
- to increase the rate of uptake / absorpttion of water and inorganic ions
- in return, fungi recieve organic compounds e.g. carbohydrates.
Give examples of biological molecules which contain nitrogen.
- amino acids
- proteins
- enzymes
- DNA / RNA
- chlorophyll
- ATP / ADP
- NAD/NADP
Order the key stages of the nitrogen cycle
- Nitrogen Fixation
- Ammonification
- Nitrification
- Dentrification
Describe the role of bacteria in nitrogen fixation
- nitrogen gas converted into ammonia (NH3) which forms ammonium ions (NH4+) in soil
- by nitrogen fixing bateria ( found in root nodules)
Describe the role of bacteria in ammonifcation
- nitrogen contaning compounds e.g. proteins/urea from dead organisms / waste are broken down / decomposed
- converted to ammonia , which forms ammonium ion sin soil
- by sapribionts - secrete enzymes for extracelluar digestion
Describe the role of bacteria in nitrification
- Ammonium ions in soil converted into nitrites then nitrates , via an oxidation reaction. For uptake by plant root hair cells by active transport.
- By nitrifying bacteria in aerobic conditions (oxygen)
Describe the role of bacteria in dentrification
- nitrates in soil converted into nitrogen gas (reduction).
- By dentrifying bacteria in anaerobic conditions ( no oxygen, e.g. waterlogged soil).
Suggest why ploughing soil increases its fertility.
- more ammonium converted into nitrite and nitrate / more nitrification / more active nitrifying bacteria.
- less nitrate converted to nitrogen gas / less denitrification / fewer active nitrifying bacteria.
Give examples of biological molecules which contain phosphorous
- phospholipids
- DNA or RNA
- ATP or ADP
- NADP
- TP or GP
- RuBP
Describe the phosphorous cycle
- Phosphate ions in rocks released (into soils/oceans) by erosion/weathering
- Phosphate ions taken up by producers / plants / algae and incorporated into their biomass
- Rate of absorption is increased by mychorrhizae
- Phosphate ions transferred through food chain
- Some phosphate ions lost from animals in waste products
- Sapribionts decompose organic compounds e.g. DNA in dead matter / organic waste releasing phosphate ions.
Explain why fertilisers are used
- to replace nitrates / phosphates lost when plants are harvested and livestock are removed
- Those remove from soil and incroporated into biomass can’t be released back into the soil through decomposition by sapribionts.
- so imporves efficiency of energy transfer by increasing productivity/yield.
Describe the difference between artificial and natural fertilisers
natural: contain inorganic compounds of nitrogen, phosphorous and potassium
Aritficial: Organic, e.g. manure, compost, sewage - ions released during decomposition by sapribionts.
Explain the key environmental issues arising from use of fertilisers.
- phosphates / nitrates dissolve in water , leading to leeching of nutrienets into lakes/rivers/oceans
- this leads to eutoriphication.
Describe eutrophication
- Rapid growth of algae in pond / river (algal bloom) so light blocked.
- so submerged plants die as they cannot photosynthesise
- so sapribionts decompose dead plant matter , using oxygen in aerobic respiration
- so less oxygen for fish to aerobically respire, leading to their death
Explain the key advantage of using natural fertiliser over aritifical fertiliser.
- less water soluble so less leaching - eutrophication is less likely
- organic molecules require breaking down by sapribionts - slow release of nitrate/ phosphate.
