biology - unit 3 aos 2

3A - enzymes

• enzymes - proteins usually ending in ‘ase’ that catalyse (speed up) biochemical reactions by lowering the activation energy required required to initiate the reaction

• substrate (reactant) binds to active site on enzyme (which has 3d complementary shape), making enzyme-substrate complex, then reaction occurs, and products are released

• substrate specificity - each enzyme only binds to 1 substrate → only catalyse 1 reaction

coenzyme

ATP, NADPH/NADP⁺, NAD⁺/NADH, FAD/FADH₂

• Enzymes catalyse most of the reactions in photosynthesis. For example, in the lightdependent stage, the enzyme ATP synthase catalyses the reaction ADP + Pi → ATP

• Having enzymes regulate each step in photosynthesis ensures reactions are sped up and controlled, so plants can metabolise efficiently.

3B - factors that affect enzymes

• temperature

• pH

• concentration

3B - temperature

• assuming pH is constant

• optimal temp - maximum rate of substrate entering the active site and products leaving

• under optimal temp - particles move slower. substrate enters active site slower + products leave slower

• above optimal temp -

• way too above optimal temp - enzyme denatures. active site changes shape. substarte cannot bind.

3B - pH

• assuming temperature is constant

• denatures if not optimal pH

3B - concentration

• saturation point -

• excess enzyme

• excess substrate

3B - enzyme inhibition

• enzyme inhibitors - molecules that bind to an enzyme, preventing it from performing it’s function.

• competitive inhibitors

  • chemical that binds to active site of enzyme (meaning it has a simialr shape to its’ substrate), and directly blocks the substrate. substrate + inhibitor are ‘competing’.

  • if there are competitive inhibitors, you can increase the substrate concentration, in order to increase the chance of substrate binding rather than inhibitor

• non-competitive inhibitors

  • binds to the enzyme somewhere other than the active site, called an allosteric site. this changes the shape of the active site → substrate can’t bind

  • changing substrate concentration will not change non-competitive inhibition, because they bind to different locations, and aren’t bothered by an increase of something that doesn’t go to the same site.

• irreversible - render an enzyme disfunctional even after enzyme detaches

biochemical pathway

• biochemical pathway - a series of biochemical reactions, where the outputs of one reaction are the inputs of another reaction, and so on. ex, photosynthesis, cellular respiration

5A - photosynthesis

• photosynthesis - the process in which plants (photoautotrophs) convert light energy into chemical energy (stored as glucose), that they can use for their own energy. occurs in two stages - light dependent and light independent.

• equation:

  • 6CO₂ + 12H₂O →(light) → C₆H₁₂O₆ + 6O₂ + 6H₂O

  • 6CO₂ + 6H₂O →(light) → C₆H₁₂O₆ + 6O₂

• primary product is glucose - plants can use glucose immediately as an input for cellular respiration to create energy, or they can store it as starch, or use it to form more complex molecules.

5A - plant structures involved in C3 photosynthesis

• plants mainly perform photosynthesis at the leaves. they typically have a large surface area to maximise the amount of light hitting the surface. there are many cell types in leaves that perform different functions:

• mesophyll cells - contain lots of chloroplasts → main cell type in leaves that photosynthesise.

• sheath bundle cells?

• stomata - tiny pores on the surface of leaves that open and close to regulate gaseous exchange. when open, carbon dioxide in the atmosphere diffuses into the leaf, and oxygen and water are lost, which the plant must regulate by closing the stomata.

5A - chloroplasts

• chloroplast - site of both stages of photosynthesis in plant cells

  • thylakoids - flattened membrane-bound sacs, arranged into grana. thylakoid membrane contains chlorophyll + proteins, + is site of LDS. fluid space inside thylakoid is lumen.

  • granum (pl. grana) - a stack of thylakoids

  • chlorophyll - green pigment in thylakoid. absorbs red + blue wavelengths. responsible for green colour of thylakoids + → whole chloroplast

  • stroma - fluid between grana. contains enzymes for LIS + chloroplast’s DNA, which is stored in a circular chromosome (similar to bacteria → endosymbiotic theory)

  • membrane

5A - light dependent stage

• light dependent stage - light energy splits water molecules into hydrogen and oxygen. also generates high energy coenzymes NADPH and ATP. occurs on the thylakoid membranes of chloroplasts, and only when light is present.

process

1. on the thylakoid membrane, light energy excites electrons in chlorophyll. these electrons leave chlorophyll + move along proteins in the membrane, which powers the pumping of H⁺ ions into the thylakoid lumen. water donates electrons to chlorophyll to replace the electrons that left, causing water to split into oxygen and two H⁺(photolysis).

2. oxygen is released out of the chlorophyll → either diffuses out of stomata into environment or used as input for aerobic cellular respiration

3. H⁺ + e^- from water combine with NADP⁺, which is reduced, generating the high energy coenzyme NADPH. Also, there is now a high concentration of H⁺ inside the lumen and a low conc outside in the stroma → concentration gradient which H⁺ ions want to balance → H⁺ ions leave the lumen through the protein ATP synthase. as H⁺ flows out, their movement provides energy, which converts ADP + Pi into ATP.

4. NADPH + ATP coenzymes are then used in light independent stage

inputs

• 12 H₂O

• 12 NADP⁺

outputs

• 6O₂

• 12 NADPH

• 18 ATP

5A - cycle of coenzymes from LDS to LIS

5B - light independent stage

• light independent stage - using NADPH + ATP produced in LD stage + carbon dioxide, glucose is produced through a cycle of reactions (calvin cycle) occurs in the stroma of chloroplasts, and doesn’t require light.

process

1. carbon fixation - inorganic (doesn’t contain a C-H bond) CO₂ molecules (collected from the stomata in leaves) enter the stroma, and are ‘fixed’ into organic molecules. rubisco enzyme converts CO₂ and RuBP (5C) into 3PGA (3C)

• 3 x CO₂ + 3 x RuBP → 6 × 3PGA

2. reduction - NADPH donates electrons and H+ to 3PGA, reducing it. ATP break down into ADP + Pi, donating energy to 3PGA. through these processes, the 3PGA are then converted into G3P (3C), a higher energy molecule which can be converted into glucose

• 6 × 3PGA → 6 x G3P

3. regeneration - although 6 G3P are produced, 5 are recycled to regenerate RuBP, meaning each cycle produces 1 net G3P. however glucose requires 2 x G3P, so the cycle repeats twice for each 1 glucose made.

• 2 x G3P → 1 glucose

4. some of the oxygen molecules leftover from the breaking of CO2 at the beginning of the cycle combine with hydrogen ions from NADPH to create the output water.

inputs

• 6CO₂

• 12 NADPH

• 18 ATP

outputs

• C₆H₁₂O₆

• 12 NADP⁺

• 18 ADP + Pi

• 6 H₂O

5B - rubisco

• rubisco - rubisco is a key enzyme in the LIS of photosynthesis. during the first stage of the calvin cycle (carbon fixation), it binds to CO₂, and fixes carbon from it. however, sometimes it uses O₂ as a substrate rather than CO₂. this is a major flaw of rubisco, as when this happens, CO₂ cannot bind, and a different reaction called photorespiration occurs instead

  • CO₂ cannot bind - when O₂ binds to rubisco, it acts as a competitive inhibitor, by binding to the active site which CO₂ would’ve binded to.

  • photorespiration - photorespiration is also a wasteful process as it uses energy produced in photosynthesis

  • = by binding O₂ and undertaking photorespiration, CO₂ loses an opportunity to undergo LIS → less glucose produced

• Rubisco has a lower affinity to bind to O₂ over CO₂ when there is low O₂ concentration or when temperatures are normal or cool

5B - adaptations to photorespiration

• there are 3 different types of plants when it comes to adapting to minimise photorespiration:

  • C3 (no adaptation)

  • C4 - LIS seperated spatially

  • CAM - seperated temperally

• in hot + dry environments, stomata close, which prevents CO2 from coming in and prevents O2 from leaving → lower conc CO2 and higher conc O2 → likely for photorespiration to occur → have adaptations

• to minimise photorespiration + increase photosynthesis, rubisco should be exposed to high concentration of CO2 and low concentration of O2.

5B - C3 plants

• C3 plants contain no mechanism to minimise photorespiration.

• photosynthesis occurs within a single mesophyll cell. first stage of LIS, carbon fixation, involves rubisco fixing carbon from CO2 into 3-PGA, which is 3C (hence C3 plants)

• C3 plants are vulnerable to photorespiration in hot dry environments - when C3 plants are in hot, dry environments, stomata may close to reduce water loss. however, this means oxygen produced in LDS cannot escape → builds up, increasing photorespiration.

• examples - 85% of plants, incl rice, wheat, trees, + most fruits, vegetables, nuts’

• better suited to cooler temepratures, lower light intensity

5B - C4 plants

• LDS is exactly the same as C3 plants. however, LIS/calvin cycle is seperated into two different cells - a mesophyll cell and a bundle sheath cell.

  1. in mesophyll cell, CO2 enters. the enzyme PEP carboxylase (not rubisco, bc PEP carboxylase has no affinity to bind to O2) adds the carbon from CO2 to a PEP molecule (3C), fixing it into oxaloacetate (4C).

  2. oxaloacetate (4C) is converted into malate (also 4C, but capable of being transported to bundle sheath cells). → malate transported to bundle sheath cells, creating high concentration of CO2 (in form of malate), meaning photorespiration is minimised.

  3. in bundle sheath cell, rubisco breaks down malate + releases CO2 → this CO2 then enters calvin cycle like C3 plants.

  4. Pyruvate formed from the breakdown of malate is transported back to the mesophyll cell and converted to another molecule, PEP, with the help of ATP

  5. PEP is then ready to contribute to the fixation of CO2 and production of oxaloacetate and the cycle continues all over again.

• example - maize, sugarcane

• higher efficiency in hot, high light intensity environments. however, more ATP is required to convert pyruvate to PEP for the initial carbon fixation → C4 plants use more energy than C3 plants in photosynthesis.

• requires more ATP to cycle PEP

5B - CAM plants

• light independent stage is seperated over time/temperally to minimise photorespiration.

• Separate CO₂ fixation by time (night vs. day) to conserve water.

• Night: Stomata open, CO₂ is fixed into a 4-carbon acid (malate) and stored.

• Day: Stomata close, and the stored malate releases CO₂ for the Calvin cycle.→ controlled release

• Advantage: Survive in arid environments by minimizing water loss.

• example - cacti, pineapples, succulents

• requires more ATP to cycle PEP

5C - factors affecting rate of photosynthesis

• light intensity + wavelength

• temperature + pH

• carbon dioxide concentration

• water availability

• enzyme inhibition

light wavelength

• the greatest rate of photosynthesis occurs in violet or red light

• lowest at green wavelength, because green is reflected (explains why chlorophyll is green)

5D - agricultural applications of CRISPR-Cas9

5

• C3 - plants with no evolved adaptation to minimise photorespiration

• C4 - plants that minimise photorespiration by separating initial carbon fixation and the remainder of the Calvin cycle over space

• CAM plants - plants that minimise photorespiration by separating initial carbon fixation and the remainder of the Calvin cycle over time

photosynthesis and cellular respiration

• photosynthesis and cellular respiration are related, as each process can ‘recycle’ the outputs of the other reaction, using them as inputs

• however, they are very different biochemical pathways, with very different structures and enzymes are involved

• plants + algae can undergo both photosynthesis and cellular respiration → don’t need to source all their photosynthesis and cellular respiration inputs from the environment.

✅6A - cellular respiration

• cellular respiration - all cells undergo cellular respiration, which generates ATP from glucose. ATP is a high energy molecule that all organisms need to grow, produce enzymes and many other things.

• there are 2 biochemical pathways in which ATP is produced from cellular respiration. main difference is presence or absence of oxygen.

  • aerobic cellular respiration - more efficient (produces 30 or 32 ATP)

  • anaerobic fermentation - faster than aerobic respiration, but less efficient (only produces 2 ATP) + produces harmful by-products

• glucose carries too much energy to be useful in most biochemical reactions → cellular respiration breaks down glucose into smaller packages, ATP. DRAW DIAGRAM when the third phosphate is broken off, it releases lots of usable energy

✅6A - aerobic cellular respiration

• aerobic cellular respiration - a form of cellular respiration that occurs when oxygen is present. it is series of enzyme-controlled reactions in which glucose reacts with oxygen to produce carbon dioxide, water and ATP

• overall equation: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O

• however, above is a simplified version. there are many enzyme-controlled reactions involved that occur over 3 stages.

1. glycolysis

2. krebs cycle

3. electron transport chain

• ATP yield per glucose molecule

  • glycolysis - 2

  • krebs cycle - 2

  • ETC - 26 or 28

  • = 30 or 32 ATP in total

✅6A - mitochondria

• the mitochondria is crucial to aerobic respiration as it is the site of the 2nd (krebs cycle) and 3rd (ETC) stages

structure

• intermembrane space - the narrow, small space between the inner and outer membrane

• inner mitochondrial membrane - membrane made of phospholipid bilayer which is the site of ETC.

• cristae - the inner membrane folds into peaks and ridges called cristae

• mitochondrial matrix - the space inside the inner membrane, filled with a dense fluid containing many enzymes and solutes. site of krebs cycle.

• contains it’s own genome of DNA

✅6A - glycolysis

• glycolysis - in the cytosol, 1 glucose (6C) is broken down into 2 pyruvate molecules (3C). during this complicated process, glucose is partially oxidised (loses electrons + H⁺) + loses energy. NAD⁺ is reduced (accepts these electrons + some H⁺), producing 2NADH, and 2 ADP + Pi capture the energy to produce 2 ATP. pyruvate + NADH are then transported and used in other stages to generate more ATP.

• 1 glucose (C₆H₁₂O₆) → 2 pyruvate

  • pyruvate molecules produced then transported to mitochondria matrix for krebs cycle, where they are further broken down and modified.

• 2NAD⁺ + 2H⁺ + 4e^- → 2NADH

  • hydrogen and electrons inputs come from breakdown of glucose

  • NADH produced is then transported to the mitochondria for ETC

• 2 ADP + 2Pi → 2 ATP.

  • ATP produced can then be used for energy.

inputs + outputs (draw as table)

• inputs

  • 1 glucose

  • NAD⁺

  • 2 ADP + 2 Pi

• outputs

  • 2 pyruvate

  • NADH

  • 2 ATP

✅6A - link reaction

• link reaction: pyruvate → acetyl-CoA + CO₂ + NADH

  • pyruvate produced in glycolysis is transported to the mitochondria matrix. it then combines with coenzyme A (CoA) to form acetyl-CoA (2C). during this link reaction, pyruvate is further oxidised (loses electrons), and in order to capture this energy, coenzyme NAD⁺ is reduced (accepts these electrons), producing NADH

  • pyruvate has to be converted immediately because it’s toxic!!

  • this link reaction also releases CO₂ and produces NADH that is later used in the ETC

✅6A - krebs cycle

• krebs cycle - generates lots of high-energy electron and proton carriers, NADH and FADH2, which can be used in the electron transport chain. Carbon dioxide is released, and small amounts of ATP are also produced.

• occurs in the matrix of the mitochondria. loads co-enzymes

• after link reaction, acetyl-coA can now enter the Krebs cycle in the mitochondrial matrix. coenzymes break down acetyl-CoA, extracting its energy, and then CoA is recycled back for use in the link reaction. loaded coenzymes NADH and FADH2 are high energy electron and proton carriers, which are then used in ETC. co2 is also released and 2 ATP

• inputs of krebs cycle

  • 2 acetyl-CoA (derived from pyruvate)

  • unloaded coenzymes

  • 2 ADP + 2Pi

  • NAD⁺ + H⁺

  • FAD + H⁺

• outputs of krebs cycle

  • CO₂

  • loaded coenzymes (→ inner membrane for ETC)

  • 2 ATP

  • NADH

  • FADH₂

✅6A - electron transport chain

• electron transport chain - using NADH and FADH₂ produced in the Krebs cycle, electrons are passed between enzymes in the inner membrane/cristae and H⁺ is pumped from the mitochondrial matrix into the intermembrane space. this sets up a H⁺ gradient that ATP synthase uses to make ATP. oxygen is used when it combines with the electrons and hydrogen ions, forming the by-product water.

1. coenzymes unload - NADH and FADH₂ unload H⁺ ions and electrons at the first and second protein complexes of the ETC on the inner membrane. after unloading H⁺ + e^-, the coenzymes stay in the matrix and are recycled into the Krebs cycle, where they can become loaded again.

• NADH → NAD⁺ + H⁺ + 2e^-

  • NADH from Krebs cycle (8 NADH per glucose) + glycolysis (2 NADH per glucose) unloads H⁺ + e^- at protein complex I. it is oxidised to NAD⁺ → recycled into Krebs cycle.

• FADH₂ → FAD + 2H⁺ + 2e^-

  • FADH₂ from Krebs cycle (2 FADH₂ per glucose) unloads H⁺ + e^- at protein complex II. it is oxidised to FAD → recycled into Krebs cycle.

2. electron movement - when electrons are unloaded into the inner membrane, they enter at protein complex I and II, and are transferred by a mobile electron carrier (nonpolar phospholipid bilayer repels charged things → electrons can’t move freely through membrane) to protein complex III. they then move to complex IV. (before they are accepted by oxygen). the movement of electrons through the ETC (see diagram) is due to oxygen present in the matrix. oxygen is very electronegative, meaning it has a high electron-pulling power. oxygen pulls electrons through the ETC. this movement of electrons powers H⁺ to be actively transported to the intermembrane space from transmembrane protein complexes I, III and IV. this means if oxygen runs out → electrons no longer pulled + H⁺ no longer pumped → ETC stops + less ATP is produced.

3. concentration gradient - this leads to a buildup of H⁺ in the intermembrane space. because this space is narrow and small, concentration of H⁺ quickly increases → creates a steep concentration gradient

4. ATP synthase - to move down their concentration gradient, H⁺ must travel through ATP synthase → causes ATP synthase to spin like a turbine, generating kinetic energy which powers the reaction that synthesises ATP from ADP + Pi. this produces 26 or 28 ATP per glucose molecule.

5. water formation - in order for the ETC to function, electrons must go somewhere, and H⁺/protons flow back to the matrix through ATP synthase. high concentrations of unbound electrons + protons are dangerous for cells, so to prevent a buildup in the matrix, oxygen accepts electrons at complex IV, acting as a terminal acceptor, and then combines with H⁺ to form water, a harmless by-product.

• ½ O₂ + 2H⁺ + 2e^- → H₂O

• inputs

  • 26 or 28 ADP + Pi

  • NADH

  • FADH₂

  • O₂

• outputs

  • 26 or 28 ATP (some cells have the capacity to make 28 bc more efficient, some can only make 26)

  • NAD⁺ + H⁺

  • FAD + H⁺

  • H₂O (H⁺ from NAD⁺ and FAD)

6B - anaerobic fermentation

• anaeorbic fermentation - cellular respiration involving the breakdown of glucose when oxygen is not present. both stages occur in the cytosol. faster than aerobic respiration, but less efficient + produces harmful by-products - these can be disposed of, but accumulation is inevitable → anaerobic fermentation cannot continue indefinitely

• in anaerobic conditions, glycolysis still occurs, but electrons + H⁺ in the ETC can’t bond with oxygen to form water → coenzymes can no longer unload + be recycled into the Krebs cycle. = the oxygen dependent pathways of the Krebs cycle + ETC are disrupted + this key source of ATP is lost. as a result, these two stages happen:

1. glycolysis

2. fermentation

• ATP yield - 2 ATP per glucose molecule (all produced during glycolysis)

6B - glycolysis

• glycolysis in anaerobic conditions is identical to in aerobic conditions

• glycolysis - in the cytosol, 1 glucose (6C) is broken down into 2 pyruvate molecules (3C). during this complicated process, glucose is partially oxidised (loses electrons + H⁺) + loses energy. NAD⁺ is reduced (accepts these electrons + some H⁺), producing NADH, and ADP + Pi capture the energy to produce ATP.

• 1 glucose (C₆H₁₂O₆) → 2 pyruvate

  • pyruvate molecules produced then transported to x

• 2NAD⁺ + 2H⁺ + 4e^- → 2NADH

  • hydrogen and electrons inputs come from breakdown of glucose

  • NADH produced must be converted back to NAD⁺ to be recycled as an input for glycolysis → transported to x for fermentationb

• 2 ADP + 2Pi → 2 ATP.

  • ATP produced can then be used for energy.

  • in anaerobic glycolysis less ATP is produced??

inputs + outputs

• inputs

  • 1 glucose

  • 2 NAD⁺

  • 2 ADP + 2 Pi

• outputs

  • 2 pyruvate

  • 2 NADH

  • 2 ATP

6B - fermentation

• after anaerobic glycolysis, NAD⁺ must be regenerated from NADH for anaeorbic glycolysis. also, the very toxic molecule pyruvate is produced. through the process of fermentation, NAD+ is regenerated + recyced, and pyruvate is converted into less toxic by-products, all done without oxygen.

• fermentation occurs in the cytosol (also where glycolysis occurs), which allows for efficient recycling of NADH and NAD⁺ as the coenzymes can freely diffuse in the cytosol without needing to be transported across a phospholipid membrane. fermentation differs between plants and animals:

• yeasts + plants - alchoholic fermentation

• animals - lactic acid fermentation

6B - lactic acid fermentation

in animals - lactic acid fermentation

• when oxygen availability is insufficient, (ex. from working at high intensities), animals undertake lactic acid fermentation after glycolysis.

• process - 2 x pyruvate (3C) produced from glycolysis is converted into 2 x lactic acid (3C). NAD⁺ is regenerated during the process + recycled back for use in glycolysis.

• however, lactic acid lowers the pH of animals’ cells and blood, and can be toxic in high amounts → anaerobic respiration is not preferred; once oxygen is available, any remaining lactic acid is converted back to pyruvate so it can undergo aerobic respiration (converted into acetyl-CoA instead)

6B - alchoholic fermentation

in yeasts + plants - alchoholic fermentation

• after glycolysis, yeasts + plants undergo alchoholic fermentation when oxygen isn’t present.

• process - 2 x pyruvate (3C) is converted into 2 x ethanol (2C) + 2 x CO₂. NAD⁺ is regenerated during the process + recycled back for use in glycolysis.

• ethanol is a toxic by-product and can’t be converted into anything useful → ethanol easily diffuses out of yeast cells, but can accumulate to toxic levels if in a confined environment

6C - factors affecting rate of cellular respiration

• factors that affect rate of cellular respiration, which therefore affect rate of ATP production:

  • temperature + pH

  • glucose

  • oxygen

  • enzyme inhibition

6C - temperature + pH

• (CRR = cellular respiration rate)

• enzymes are catalysts that speed up reactions and they are essential in cellular respiration → the factors that affect enzyme function also affect CRR

temperature

• enzymes each have an optimal temperature at which their function is maximised. therefore, CRR is highest when the temperature aligns with the enzyme’s optimal temperature

• below optimal temperature - enzymes + substrates have less kinetic energy → less successful collisions → slower CRR

• above optimal temperature - enzymes begin to denature + CRR drops rapidly due to loss of enzyme function

pH

• enzymes also have an optimal pH. in order to function at all, they must be pretty close to this pH, however it’s function is also maximised at the exact optimal pH → CRR is highest at enzymes’ optimal pH

• above + below optimal pH - enzymes begin to denature

6C - glucose

• glucose is the input for glycolysis (which happens in both aerobic + anaerobic respiration) → increase in glucose availability increases CRR

• however, increasing glucose concentration doesn’t increase CRR indefinitely. at some point, CRR will plateu because enzymes involved have reached their saturation point at which they are operating at maximum capacity

6C - oxygen

• aerobic respiration requires oxygen for the ETC to function. when oxygen is not present, the cell switches to anaerobic respiration. as oxygen is increased, the CRR increases, but also only till enzymes are saturated

6C - enzyme inhibition

• there are competitive and non-competitive enzyme inhibitors. there are also reversible and irreversible inhibitors (stop enzyme’s function even when inhibtors is displaced). all inhibitors can slow down CRR.

• the effect of competitive inhibitors can be overcome if the substrate concentration is increased → displaces inhibitors. (only if reversible)

6D - biofuels NOT ON THE SAC

• biofuels - fuels made from biomass (organic material from plant material and animal by-products)

• biofuels are a renewable energy, meaning it can be replenished at the same or a faster rate at which it is consumed. this is because biomass can be sourced indefinitely.

• biofuel production is also a carbon neutral process, as the CO₂ released during production + combustion is equivalent to the CO₂ that was originally captured from the atmosphere. → no net increase in CO₂ in the atmosphere. CO₂ in the atmosphere can then be recaptured, meaning that biofuel production simply utilises the carbon cycle.

  • plant material biomass - during photosynthesis, plants capture CO₂ from the atmosphere, and retains this CO₂ until it is released during biofuel production + combustion.

  • animal by-product biomass - animals eat plants (or other animals that ate plants). this means they consume carbon in plants that was captured from the atmosphere. this is just adding an extra step in the carbon cycle, as the CO₂ released from animal by-product biofuel is equivalent to the CO₂ that the original plants captured.

• biofuels also ‘burn clean’, meaning they undergo complete combustion, and don’t release pollutants upon combustion.

6D - bioethanol

• bioethanol - a biofuel which is produced from the anaerobic fermentation of glucose (from biomass) using yeast, which produces ethanol which can be harnessed to produce bioethanol

process

1. deconstruction

   • biomass is broken down to increase surface area in order to make the fermentation process more efficient. this can be done in many ways, such as the physical grinding of the biomass.

2. digestion by enzymes

   • the starch/cellulose from the broken down biomass is then exposed to enzymes + further broken down and converted into glucose

   • (starch if from first generation biomass, cellulose if from second generation biomass)

3. ethanol fermentation

   • glucose is put in solution with water and the microorganism yeast. yeast cells use glucose as an input, and thus yeast facilitates the anaerobic fermentation of glucose.

   • yeast prefers to undergo cellular respiration through the anaerobic pathway. also, the aqueous environment means that the oxygen (if any) is used up quickly → ensures glucose undergoes anaerobic fermentation (which produces ethanol) rather than aerobic respiration

   • = a large amount of ethanol is produced as a by-product of this anaerobic fermentation. this ethanol diffuses out of the yeast cells + is captured for use as a biofuel.

4. purification and dehydration

   • the ethanol is distilled, removing water, converting it into a usable biofuel. it is then purified + ready to be used as liquid fuel

6D - application of biofuels

• biofuels can be used as a renewable alternative to fossil fuels in many ways.

• transportation - biofuels can replace traditional fuels such as petrol and diesel, as they are able of combusting in most engines. ex. bioethanol is blended with gasoline to cut down on smog-causing emmissions, often 10% bioethanol, 90% gasoline, E10

• more uses include cleaning, heating homes, backup energy generation

6D - first vs second generation biofuels

• the ‘generation’ of a biofuel relates to the type of biomass that it is sourced from

• first generation biofuels - produced directly from food (ex. corn, sugar-cane). starch is broken down.

  • → competes with food crops → can impact food security

  • if more crops grown deliberately for biofuel → can involve land degradation + loss of biodiversity

  • easy conversion into biofuels

• second generation biofuels - produced from cellulose-based non-food crops (ex. straw, waste paper) left over from other crops/processes. cellulose is broken down.

  • → doesn’t compete with food crops

  • more difficult to break down + convert into biofuels

6D - implications + ethics of biofuels

strengths

• climate impact - biofuels are carbon neutral, compared to fossil fuels, which produce lots of CO₂ emissions → excess CO₂ causes enhanced greenhouse effect → climate change + extreme weather events. replacing fossil fuels with biofuels mitigates enhanced greenhouse effect.

• energy security - biofuels are a renewable energy, while fossil fuels are not (take millions of years to form). as our energy demands continue to increase, the finite supply of fossil fuels diminishes. replacing fossil fuels with biofuels decreases our reliance on non-renewable energy → energy security.

• localised energy - biomass can be sourced + farmed all around the world, but fossil fuels cannot, and rely on international imports + exports. replacing fossil fuels with biofuels helps nations rely less on these imports + exports, and rather produce their own fuel, thus increasing energy independence + security of nations, decentralising control over fuel supplies, increasing job opportunities and reducing the risks associated with fossil fuel transport (such as oil spills).

weaknesses

• food vs fuel - first generation biofuels compete with food crops, which can lead to food insecurity.

• second order environmental impacts - 1st and 2nd gen biofuels require farmland, which can lead to deforestation, loss of biodiversity and land degradation. farming can also involve fertiliser, which can pollute waterways + release nitrous oxide

• cost + difficulty of uptake - biofuels are more expensive to produce than fossil fuels, and there is also a lack of infrastructure to support biofuels → difficult to penetrate the market

experimental design

• to create an experient:

• hypothesis

• independent variable

• dependent variable

• constant variables

• control

• expected results

• repeatability - multiple trials under exactly same conditions ex. one person can do experiment multiple times

• reproduceable - same thing but something has been slightly changed. ex. whole class can all do experiment

• validity - show only one independent variable (with control)

• precise - multiple trials

• accuracy - true value to compare it to + it’s similar (most of the time don’t know)