ThatBioTutor's Pure Bio 2024 Notes (PDF)

1. Cells Learning Outcomes: 1. Identify and state the functions of plant and animal cell organelles 2. State the relationship between cell structure and function (w.r.t. RBC, xylem, root hair cell) 3. Compare structures of plant and animal cells Keywords: Organelle, membrane, cellula...

1. Cells Learning Outcomes: 1. Identify and state the functions of plant and animal cell organelles 2. State the relationship between cell structure and function (w.r.t. RBC, xylem, root hair cell) 3. Compare structures of plant and animal cells Keywords: Organelle, membrane, cellular activities Steroids, detoxification, protein synthesis Small and temporary, large central, cell sap Modifies, sorts and packages Partially permeable, fully permeable Biconcave, surface area to volume ratio, flexible, bell-shaped, long, narrow protrusion If you're our student:Cells Crash Course Clips 1. Identifying structures 14  Visible Component/ under Light Function Organelle Microscope ? Contains DNA (in the form of chromatin) Nucleus Y Controls cellular activities Nuclear envelope Separates nucleus from cytoplasm Y Rough Studded with ribosomes Endoplasmic Synthesises proteins (for transport out of N Reticulum the cell) Synthesises fats and steroids* Smooth *Pro Tip: A class of molecules, including sex Endoplasmic hormones N Reticulum Carries out detoxification: where harmful substances are converted to harmless ones Place where most cellular activities occur Cytoplasm Contains organelles Y Site of anaerobic respiration Animals: Several small and temporary vacuoles Store food and water Plants: Y (plants) Vacuole Have a large central vacuole N (animals) Stores cell sap (water + dissolved substances such as: sugars, amino acids, mineral salts) Golgi Modifies, Sorts and Packages substances N body/apparatus into vesicles for secretion out of cell Site of aerobic respiration, where food Mitochondria substances (such as glucose) are broken N down to release energy 15  Chloroplast Site of photosynthesis Y (plants only) Cell surface Partially permeable membrane/ Controls movement of substances in and Y plasma out of the cell membrane Fully permeable Cell wall Made of cellulose Y (plants only) Gives cell its shape Ribosomes Protein synthesis N [Memory Hacks] Golgi Body: ◦ When receiving vesicles from ER, says "Majulah SingaPura" ◦ Modifies, Sorts and Packages substances into vesicles for secretion out of cell Rough ER: ◦ Proteins --> Meat. When you bite into meat patty, has a rough texture ◦ Rough ER synthesises proteins Smooth ER: ◦ Lipids --> Oil. Oil is smooth and slippery. ◦ Smooth ER synthesises lipids 2. Linking Structure to Function *Pro Tip: These are repeated/explained more in their later respective topics. 16  Cell structure How it is adapted to its function Red Blood Cell Biconcave, increases surface area to volume ratio, so oxygen can diffuse in/out of it faster Lacks a nucleus hence has more space for more haemoglobin, to transport more oxygen Flexible, so it can squeeze through tiny capillaries Can become bell-shaped in capillaries, further increasing surface area to volume ratio Root hair cell Has a long, narrow protrusion (root hair), that increases surface area to volume ratio, for faster absorption of water and mineral salts Have many mitochondria to generate a lot of energy via aerobic respiration ◦ As they need to pump in mineral salts from the surrounding soil into their large central vacuoles via active transport 3. Comparing Plant and Animal Cells Comparison Animal Cell Plant cell Chloroplasts No Yes (sometimes) Cell wall No Yes (always) Mitochondria Yes (mostly) Yes (mostly) Vacuole Small, temporary Large, permanent Size Relatively smaller Relatively bigger 17 Need personalised guidance for O Level Pure Bio? Learn more here: www.thatbiotutor.com 18 1. Cells CAQs RBC vs RHC Q: The table shows comparisons between a human red blood cell and a root hair cell. Red Feature Root Feature blood number hair cell cell 1 takes in oxygen yes yes 2 cytoplasm present no yes large surface area to volume 3 yes yes ratio 4 nucleus present no yes Which comparisons are correct? A) 1, 2 and 3 only B) 1, 3 and 4 only C) 1 and 2 only D) 3 and 4 only (B) 1 correct: RBC takes in O2 to transport it around. RHC also needs O2 for aerobic respiration. O2 diffuses from the air pockets in the soil into RHCs. 2 wrong - Both RBC and RHC have cytoplasm, since they are living cells. 3 correct - RBC has biconcave shape, RHC has an elongated protrusion, increasing the SA:V for both of them respectively. 4 correct - RBC no nucleus, in order to pack in more haemoglobin. Only RHC has nucleus. Organelle Functions 19 Q: Which organelle produces proteins and which organelle provides the energy for this process? organelle provides organelle produces proteins energy A 1 4 B 2 3 C 3 2 D 4 1 (D) Organelle that produces proteins: Proteins are produced by ribosomes, which are either free ribosomes in the cytoplasm or studded onto the Rough Endoplasmic Reticulum (RER). Only the RER is labelled as 4 in the diagram. Organelle that provides energy: Aerobic respiration occurs in mitochondria to release energy, and a mitochondrion is labelled as 1 in the diagram. *Pro Tip: These questions often test on which organelles synthesise proteins (RER and free ribosomes) Related Questions: ◦ Q: Which part of the living cell is the oxygen concentration lowest? (Using the same cell diagram as above) ◦ (1). ◦ O2 is spread out quite equally throughout the cell due to diffusion, except around mitochondria, 20  ◦ because mitochondria use up O2 for aerobic respiration, so the regions around mitochondria have less O2. Pathway Out Of Cell Q: Describe how proteins made in the cell are released to the outside of the cell. The proteins are synthesised by the Rough Endoplasmic Reticulum, then sent via vesicles to the Golgi body. Here, they are modified, sorted and packaged into vesicles that pinch off the Golgi body. The secretory vesicles move to and fuse with the plasma membrane to release the proteins outside the cell. Many Mitochondria *Q: Suggest why root hair cells [cell type] have many mitochondria. Root hair cells [cell type] need to pump in mineral salts from the surrounding soil into their large central vacuoles via active transport [energy-consuming activity]. Hence they need many mitochondria to generate a lot of energy via aerobic respiration. *Pro Tip: This kind of question could be asked about any cell type that has many mitochondria, e.g. muscle cell, companion cell, etc. You will have to replace [cell type] and [energy-consuming activity] accordingly. Cells With High SA:V *Q: What is the advantage of epithelial cells [cell type] having such a shape (having microvilli)? An epithelial cell [cell type] has many microvilli, which increases its surface area to volume ratio, for faster diffusion and active transport [type of movement process] of digested food substances from the lumen of the small intestine into the cell [substance moved]. *Pro Tip: This kind of question could be asked about any cell that has high SA:V, e.g. root hair cell, red blood cell, etc. You will have to replace [cell type], [type of movement process] and [substance moved] accordingly. Animal vs Plant cells *Q: State 3 ways in which the structure of a plant cell differs from an animal cell. Plant cells ______(A)______, while animal cells ______(B)______. 21  A B may have chloroplasts do not have chloroplasts have cell walls do not have cell walls have a permanent large central have small and temporary vacuole vacuoles. 22 2. Movement of Substances Learning Outcomes: 1. Define Diffusion, Osmosis and Active Transport 2. Movement of substances in nutrient uptake and gas exchange 3. Effects of osmosis on plant and animal tissues 4. Bonus: Factors affecting rate of diffusion. Keywords: Diffuse, osmosis, active transport Water potential, down/against concentration gradient, steepness Partially permeable membrane Crenated, lyse/burst Plasmolysed, flaccid, turgid, turgor pressure If you're our student: Movement of Substances Crash Course Clips 1. Definitions 1. Diffusion: The net movement of particles from a region of higher concentration to a region of lower concentration, down a concentration gradient. 2. Osmosis: The net movement of water molecules from a region of higher water potential to a region of lower water potential, through a partially permeable membrane. 3. Active Transport: The movement of particles, using energy, from a region of lower concentration to a region of higher concentration, against a concentration gradient, through a partially permeable membrane. *Pro Tip: When explaining these processes in contexts of questions, replace' substances' with the molecule in the question, e.g. CO2 23  Process Diffusion Osmosis Active transport Type of molecule Any Water Any Partially permeable No Yes Yes membrane needed? Energy needed? No No Yes Direction w.r.t. Concentration Down (higher to Down (higher Against (lower gradient lower) to lower) to higher) 2. Movement of substances in nutrient uptake and gas exchange 24 Example How substances are moving Digested food substances such as glucose, and amino acids diffuse into epithelial cells of villi in the small intestine After diffusion no longer occurs, these substances are transported in via active transport Mineral salts are transported from the soil into root hair cells via active transport, to maintain a high concentration of mineral salts in their vacuoles This creates a region of lower water potential than the surrounding soil, so that water flows in by osmosis O2 dissolves into the thin film of moisture lining the alveolar air space, then diffuses into the blood plasma Conversely, CO2 diffuses from the blood plasma into the alveoli air space O2 diffuses from the intercellular air spaces of the leaf to the surrounding air, through the stomata CO2 diffuses from the surrounding air into the intercellular air spaces of the leaf, through the stomata 25 3. Effects of osmosis on plant and animal tissues Water potential of High Low Very low solution Crenated Bursts/lysed Crenated Effect on Animal cell Turgid Flaccid Plasmolysed Effect on Plant cell How plasmolysed is different from flaccid: During plasmolysis, as a lot of water molecules have left the cell sap from the large central vacuole to the outside of the cell by osmosis, cytoplasm of the plant cell shrinks so much that the plasma membrane pulls away from the cell wall. *Pro Tip: Turgidity in plant cells is important as it allows the plant to remain upright and reach for sunlight, especially if it has a non-woody stem. 4. Bonus: Factors affecting rate of diffusion Surface area to volume ratio: The higher the SA:V, the higher the diffusion rate Temperature: Higher temperature, molecules have more kinetic energy, hence move faster and diffuse down the concentration gradient faster Steepness of concentration gradient: The steeper the gradient, the higher the diffusion rate 26  Distance: The shorter the distance that molecules need to travel/diffusion distance, the higher the diffusion rate Molecule size: Smaller molecules diffuse faster (e.g. glucose diffuses faster than sucrose) Need personalised guidance for O Level Pure Bio? Learn more here: www.thatbiotutor.com 27 2. Movement of Substances CAQs Important Definitions *Q: Define the term diffusion. The net movement of particles from a region of higher concentration to a region of lower concentration, down a concentration gradient. *Q: Define the term osmosis. The net movement of water molecules from a region of higher water potential to a region of lower water potential, through a partially permeable membrane. *Q: Define the term active transport. The movement of particles, using energy, from a region of lower concentration to a region of higher concentration, against a concentration gradient, through a partially permeable membrane. Plant Cell Osmosis Q: The diagram shows a plant cell in a 5% glucose solution. The concentration of the solution in the vacuole is equivalent to a 10% glucose solution. Which row states where osmosis occurs and the direction of water movement? where osmosis occurs direction of water movement A cell wall into the cell B cell wall out of the cell C vacuolar membrane into the cell D vacuolar membrane out of the cell (C) 28  Where osmosis occurs: Cannot be the cell wall, as cell wall is fully permeable, whereas osmosis requires a partially permeable membrane (by definition). In the diagram, the only places for osmosis to occur would be the plasma membrane or the vacuole's membrane (vacuolar membrane). Since there only is an option for vacuolar membrane, has to be C or D. 5% glucose solution has higher water potential than 10% glucose solution, so water will move into the cell, has to be A or C. *Pro Tip: For movement of substances questions, knowing the definitions well is very advantageous. Which Shows Active Transport Q: The diagrams show four identical plant cells. The dots show the concentration of a chemical. The arrows represent the direction of movement of the chemical. Which diagram(s) show a cell where active transport is taking place? A) 1 and 2 B) 2 and 3 C) 2 and 4 D) 3 only (D) 1 wrong - active transport requires substances to move against the concentration gradient. 2 wrong - active transport requires a partially permeable membrane. 3 correct - against concentration gradient and through a partially permeable membrane. 4 wrong - does not show particles moving from low to high concentration. 29 Applying Definitions *Pro Tip: For certain questions, you may need to weave in the definition of these terms into your answer. Eg. Describe the movement of water into a root hair cell. ◦ Water moves by osmosis from a region of higher water potential in the soil to a region of lower water potential in the root hair cell, through a partially permeable membrane. Strip of Cut Stem Bending Q: A leek stem was cut into small strips and placed into 0.1% salt solution. After 20 minutes, it looked like this: Explain the bent appearance of the strip. 0.1% salt solution has a higher water potential than the cell sap of the cells in the stem. Hence, water moved into the cells via osmosis, causing them to swell and become turgid. The epidermal cells/cells of the outermost layer of the stem are lined with a waxy, inflexible cuticle which restricts their expansion, so they cannot expand as much as the inner cells. The difference in expansion causes the stem to curl further outwards. 30 3. Biomolecules Learning Outcomes: 1. Carbohydrates, fats, and proteins: Their chemical elements, and the smaller molecules that make them up 2. Food tests for starch, reducing sugars, fats and proteins Keywords: Monosaccharide, disaccharide, polysaccharide Amino acid, peptide, polypeptide Glycerol, fatty acid, triglyceride, solvent Carbohydrate, starch, glycogen, cellulose Reducing sugar, precipitate, cloudy white emulsion If you're our student: Biomolecules Crash Course Clips 1. Elements making up carbs, fats and proteins 31  Type of Carbohydrate Fats Protein Nutrient C, H, O, N, (S) *Pro Tip: Some proteins have S (the element Atoms C, H, O (1:2:1 ratio) C, H, very few O Sulfur), but not all. If a question tells you the molecule has Sulfur, it is likely to be a protein. Monosaccharides Glucose Triglyceride (glycerol + Basic unit Amino acid Fructose 3 fatty acids) Galactose Disaccharides Maltose (Glucose + Glucose) Sucrose (Glucose Dimer (2 + Fructose) - Dipeptide units) Lactose (Glucose + Galactose) *Highlighted = reducing sugar Many units Polysaccharides - Polypeptide (several thousand) 32  Long-term energy storage Thermal insulation An immediate Protects vital source of organs energy Forms cell Growth and repair Functions (glucose for membranes* of cells (bold = aerobic Solvent for fat- For the production most respiration) soluble vitamins of enzymes, important Energy storage Secreted as oil on antibodies and to give in Structural the skin to reduce some hormones qns) molecules, e.g. water loss Synthesis of new cellulose muscle fibres *Pro Tip: We intentionally do not say plasma membrane here, as fats are part of membranes within cells too. Formation [Memory Hack] How to remember what the 3 disaccharides are made of? ◦ The 3 disaccharides are all made of glucose + 1 of the 3 monosaccharides ◦ Lactose = Glucose + Galactose (galactose has lactose in the name!) ◦ Sucrose = Glucose + Fructose (Fructose is found in Fruits, which are from plants. Plants also convert glucose into sucrose before transporting it in phloem. Therefore, associate sucrose with fructose as they are both linked to plants.) ◦ Maltose = Glucose + Glucose (once you know the other 2, glucose is the only blank option left for maltose) *Pro Tip: There are 2'c's in -saccharides, be careful when spelling Reducing sugars 33  All monosaccharides and disaccharides in our syllabus are reducing sugars, except sucrose. Polysaccharides Polysaccharid Structure Function Found in e Thousands of glucose Cellulose bonded together Structural support Plant cell walls (FYI: straight chained) Thousands of glucose bonded together, Starch bonds are different Energy storage (plants) Leaves/storage organs from those in cellulose (FYI: Branched) More branched Energy storage Glycogen Liver/muscle cells than starch (animals) 2. Food Tests 34  Test Procedure Results Liquid sample: 1. Add 2cm3 of Benedict's reagent to an equal volume of the sample in a test tube and shake. 2. Heat water in a beaker until it starts boiling (bubbles vigorously). *Pro Tip: The water level in the beaker should be higher than that of the test Benedict's test tube. [Reducing 1. Place the test tube into a beaker (-) Solution remains blue sugars] of already boiling water. (+) A brick- 2. Observe for colour change. red/orange/green ppt is formed Solid sample: *Pro Tip: Upon heating with 1. Add 2cm3 of Benedict's reagent acid, sucrose is broken into to a finely cut sample in a test glucose and fructose, which tube and shake. gives a positive result. 2. (Remaining steps are the same as if sample were liquid.) Liquid sample: 1. Place a few drops of the sample on a white tile. 2. Add a few drops of iodine to a sample, observe for colour Iodine test change. [Starch] (-) Solution remains yellow- Solid sample: brown 1. Add a few drops of iodine to a (+) Yellow-brown solution sample, observe for colour turns blue-black change. 35  Liquid sample: 1. Add 2cm3 of sodium hydroxide solution to an equal volume of sample and shake. 2. Add 1% copper (II) sulfate solution, drop by drop (just a few drops), shaking after each drop. 3. Allow the mixture to stand for 5 minutes and observe for the colour change. Biuret test [Proteins] Solid sample: 1. Add 2cm3 of sodium hydroxide solution to a finely cut sample and (-) Remains blue shake. (+) Turns violet/purple 2. (Remaining steps are the same as if sample were liquid.) *Pro Tip: Biuret reagent/solution is an already prepared solution. Adding protein to it turns it violet. Liquid sample: 1. Add 2cm3 of ethanol to equal volume of sample and shake. 2. Add 2cm3 of water to the mixture, shake. Ethanol Emulsion test Solid sample: [Fats] 1. Add 2cm3 of ethanol to finely cut sample, shake and allow solids to settle. (-) Solution remains clear 2. Decant the ethanol into another (+) Cloudy white emulsion test tube containing 2cm3 of formed water, shake. 36 Need personalised guidance for O Level Pure Bio? Learn more here: www.thatbiotutor.com 37 3. Biomolecules CAQs Food Tests Q: Some tests were done on a sample that contains one or more unknown nutrients. Test Colour at start Colour at end Benedict's test blue blue Biuret test blue blue Iodine solution test brown blue-black Ethanol emulsion test clear cloudy white Which of the nutrients are present in the solution? A) protein, reducing sugar and starch B) protein and starch only C) reducing sugar and fats only D) starch and fats only (D) Benedict’s test: Tests for reducing sugar. (+) Green, yellow, orange or brick red. (-) blue Biuret test: Test for protein. (+) violet (-) blue Iodine solution test: Tests for starch. (+) blue-black. (-) yellow-brown ◦ Starch present Ethanol emulsion test: Tests for fats. (+) cloudy white (-) clear ◦ Fats present *Pro Tip: Annotate (+) and (-) beside the columns while doing such questions. It makes it easier to do, and easier to check later on. Elements in Various Biomolecules Q: Which elements are found in all carbohydrates, fats and proteins? A) carbon and oxygen only B) carbon, hydrogen and oxygen C) hydrogen, nitrogen and oxygen 38 D) nitrogen and oxygen only (B) Carbs: C, H, O (in 1:2:1 ratio) Fats: C, H, and very little O Proteins: C, H, O, N, and sometimes S All 3 have C, H, O Functions of Biomolecules (yellow highlight = most important to give in qns) Q: Describe the functions of carbohydrates in living organisms. Glucose is used in aerobic respiration as an immediate source of energy. Energy storage, such as starch in plants and glycogen in animals. As a structural molecule, such as cellulose cell walls of plants, which give cells their shape and prevents them from bursting. As we cannot digest cellulose, it serves as dietary fibre, preventing constipation. Q: Describe the functions of fats in living organisms. Long-term energy storage, which can be broken down to provide energy for aerobic respiration when needed. Thermal insulation to prevent excessive heat loss to the environment. Are a solvent for fat-soluble vitamins to be absorbed by the body. Are used to form cell membranes. Protects vital organs from physical injury/mechanical damage. Secreted as oil on the skin surface to reduce water loss. Q: Describe the functions of proteins in living organisms. For the growth and repair of cells. Synthesis of enzymes, which are needed for many metabolic reactions. Synthesis of hormones, which are needed for coordinating responses from target organs. Synthesis of antibodies, which are made by the immune system to fight off invading micro-organisms. Synthesis of new muscle fibres. (Any valid point, as proteins are so widely used). 39 4. Enzymes Learning Outcomes: 1. Explain the mode of action of enzymes using 'lock and key' hypothesis, including active site, activation energy, enzyme specificity 2. Effect of pH and temperature on enzyme-catalysed reaction 3. Bonus: Benefits of using enzymes Keywords: Biological catalysts, alternative pathway, activation energy, chemically unchanged Substrates, active site, specific three-dimensional structure, complementary Lock and key hypothesis, enzyme-substrate complex, optimum temperature/pH Kinetic energy, chance of collision Weak bonds, denature If you're our student: Enzymes Crash Course Clips 1. Mode of action Enzymes: Biological catalysts that speed up chemical reactions by providing an alternative pathway of lower activation energy, and remain chemically unchanged after the reaction. Activation energy: The energy needed to start a chemical reaction. Lock and Key hypothesis (Mode of Action) 40  According to the lock and key hypothesis, a specific substrate (key) is complementary to and binds to the active site of the enzyme (lock), and bind, forming an enzyme-substrate complex. The enzyme then catalyses the reaction (by breaking/forming the bond in context)* After reaction, products are no longer complementary to the active site, hence they leave the active site. The enzyme remains chemically unchanged and can accept a new substrate. *Pro Tip: If the question was on 'explain the mode of action of sucrase', state here that sucrase catalyses the reaction by breaking the bond between glucose and fructose [Memory Shortcut] Mode of action of enzymes [Be Careful Red Light Unchanged] ◦ B: enzyme and substrate Binds ◦ C: forming an enzyme-substrate Complex ◦ R: Reaction is catalysed ◦ L: products Leave active site ◦ U: enzyme remains chemically Unchanged Characteristics of Enzymes Protein in nature Have a specific three-dimensional (3D) structure, only catalyse one type of reaction Has an active site that the substrate is complementary to Has an optimum temperature and optimum pH where rate of activity is highest *Pro Tip: Each enzyme has its own preferred optimum temperature and pH, depending on its function. 2. Effect of Temperature and pH Effect of increasing temperature on enzyme activity 41  As temperature increases from low until the optimum temperature, kinetic energy of enzyme and substrate molecules increases, increasing their chances of collision. Enzyme-substrate complexes form faster, and rate of reaction increases until the optimum temperature, where rate is highest. As temperature increases beyond optimum temperature, weak bonds within enzymes are broken, causing the enzyme to lose the shape of its active site and become denatured. The substrate can no longer fit into the active site, hence rate of reaction decreases sharply to 0. Effect of pH on enzyme activity 42  At pH 7, reaction rate is maximum as this is the enzyme's optimum pH. As pH moves further from pH 7, reaction rate decreases sharply. When pH moves too far from 7, weak bonds within the enzyme are broken, the enzyme loses the shape of its active site and becomes denatured. The substrate can no longer fit into the active site, hence rate decreases sharply until 0. 3. Bonus: Benefits of using enzymes As catalysts, they speed up reactions that would otherwise take a long time (saves time) Since enzymes remain chemically unchanged after reaction, only a small amount of them is needed (saves money/resources) Enzymes can catalyse reactions at lower temperatures than if they were to be done without enzymes (saves energy) Enzymes are specific, hence only the intended reaction will occur *Pro Tip: Each of these are actually linking a characteristic of enzymes to a benefit Need personalised guidance for O Level Pure Bio? Learn more here: www.thatbiotutor.com 43 4. Enzymes CAQs Important Definitions *Q: Define the term enzyme. Enzymes are biological catalysts that speed up chemical reactions by providing an alternative pathway of lower activation energy, and remain chemically unchanged after the reaction. *Q: Define the term activation energy. The energy needed to start a chemical reaction. Activation Energy Q: The two curves below show energy levels as a reaction progresses, with and without an enzyme. Which arrow represents the total activation energy of the reaction without the enzyme? (A) Concept: Enzymes lower the activation energy of a reaction, so the taller curve is the one without the enzyme. Activation energy without energy must be A. Enzyme Mode of Action *Q: Using the lock and key hypothesis, explain the mode of action of an enzyme. Mode of action of enzymes [Be Careful Red Light Unchanged] ◦ B: enzyme and substrate Binds 44  ◦ C: forming an enzyme-substrate Complex ◦ R: Reaction is catalysed ◦ L: products Leave active site ◦ U: enzyme remains chemically Unchanged According to the lock and key hypothesis, a specific substrate is the 'key'. It is complementary to the active site of the enzyme, which is the 'lock', And binds to it, forming an enzyme-substrate complex. The enzyme then catalyses the reaction. After the reaction, the products are no longer complementary to the active site, hence they leave the active site. The enzyme remains chemically unchanged and can accept a new substrate. *Pro Tip: For the above question, you are required to make reference to the lock and key hypothesis. Related Questions: ◦ Q: Explain the mode of action of sucrase. ◦ *Pro Tip: For questions like the above that specify the enzyme, use the specific names of the enzymes and substrates in your answer. i.e. For this case, sucrase and sucrose. Enzyme Activity and Temperature *Q: Explain how the rate of an enzyme-catalysed reaction may be affected by increasing temperature. As temperature increases from low until the optimum temperature, kinetic energy of enzyme and substrate molecules increases, increasing their chances of collision. Enzyme-substrate complexes form faster, and reaction rate increases until the optimum temperature, where rate is the highest. As temperature increases beyond optimum temperature, weak bonds within enzymes are broken, the enzyme loses the shape of its active site and is denatured. The substrate is no longer complementary to the active site, hence reaction rate decreases sharply to 0. Related Questions: ◦ Q: The temperature of the water bath for an enzyme-catalysed reaction was maintained carefully at 37°C. Explain why (assuming the enzyme is a human enzyme). 45  ◦ *Pro Tip: You would answer that this temperature is near the optimum temperature of this enzyme, and it is not too low (enzyme would be inactive), neither is it too high (enzyme would denature). Enzyme Activity and pH *Q: Explain how the rate of an enzyme-catalysed reaction may be affected by changes in pH (assuming the optimum pH of the enzyme in question is 7). At pH 7, reaction rate is maximum as this is the enzyme's optimum pH. As pH moves further from pH 7, reaction rate decreases sharply. When pH moves too far from 7, weak bonds within the enzyme are broken, the enzyme loses the shape of its active site and becomes denatured. The substrate is no longer complementary to the active site, hence rate decreases sharply to 0. Limiting Factor Questions Q: Explain why the rate of reaction does not increase after point X, despite the substrate concentration increasing. After point X, substrate concentration is no longer the limiting factor, hence increasing it does not increase reaction rate. Biological Washing Powders Q: Biological washing powders (detergents) contain one or more enzymes. Suggest the advantages of using biological washing powders compared to those without enzymes. As biological catalysts, they speed up reactions for breaking down stains that would otherwise take a long time, saving time. Since enzymes remain chemically unchanged after the reaction, only a small amount of them is needed, saving money and resources. 46  Enzymes can catalyse reactions at lower temperatures than if they were to be done without enzymes, saving energy needed to heat clothes up to higher temperatures. Enzymes are specific, hence only the intended reaction of breaking down the stains will occur, instead of any unintended reactions, such as breaking down of the dyes of clothes. 47 5. Nutrition in Humans Learning Outcomes: 1. Main parts of the alimentary canal + related processes 2. Summary: Enzymes Involved in digestion 3. Peristalsis 4. Structure and function of villi 5. Liver functions and its associated blood vessels 6. Effects of excessive alcohol consumption Keywords: Ingestion, digestion, absorption, assimilation, egestion Peristalsis, antagonistic Bile salts, emulsify, fat globules Digested food substances Deamination, detoxification, blood glucose concentration Addictive, depressant, reaction time, cirrhosis, haemorrhage, social responsibilities, dementia, brain volume If you're our student: Nutrition in Humans Crash Course Clips 1. Main parts of the alimentary canal Definitions of processes 1. Ingestion: The intake of food through the mouth. 2. Digestion: The physical or chemical breakdown of larger food molecules into smaller and soluble molecules that can be absorbed by body cells. 3. Absorption: The uptake of digested food substances into body cells. 4. Assimilation: Digested food substances are used to make new cell parts or used for energy. 5. Egestion: The removal of undigested food waste from the body. 48 49  Part Digestive Function pH (Processes) enzymes Teeth: Chews food (mechanical digestion) Breaks food into smaller pieces, increasing SA:V for enzymes to digest it faster Mouth Salivary (Ingestion, Salivary glands: 7 amylase Digestion) Secrete saliva containing salivary amylase, breaks down starch into maltose Tongue: Rolls food into a bolus to be swallowed Mixes saliva with food Pushes food from mouth into the Oesophagus 7 - stomach Gastric glands secrete gastric juice containing hydrochloric acid and protease Protease breaks down protein into short polypeptides Stomach Stomach churns food, breaking up food 2 Protease (Digestion) (mechanical digestion) and mixing it with gastric juice *Pro Tip: There are many types of protease, but for simplicity in our syllabus, they are all referred to as 'protease' 50  Small intestine Is very long, giving more time for digested food substances to be absorbed Has many folds, increasing SA:V Parts of the small intestine [DJI] ◦ Duodenum: Mainly digestion, some absorption Small ◦ Jejunum: Some digestion, some Intestine absorption (Digestion, ◦ Ileum: Some digestion, mainly Absorption, (Epithelial, absorption Assimilation) LiMP): Intestinal [Memory Hack] 7-9 *Pro Tip: Lipase, "Dwayne Johnson and I" for small Absorption Maltase, intestine parts involves both Protease ◦ Duodenum, Jejunum, Ileum diffusion + active Epithelial cells of the small intestine transport secrete LiMP enzymes ◦ Intestinal Lipase: fats -> glycerol + fatty acids ◦ Maltase: maltose -> glucose + glucose ◦ Protease: short polypeptides -> amino acids Small Intestine 51 Gall bladder Stores bile (an alkaline yellow-green liquid) Bile is secreted into the duodenum via the bile duct during digestion Bile salts in bile emulsify large fat droplets into (Pancre smaller ones, increasing as, SA:V for lipase to digest LAP): triglycerides into glycerol Pancrea and fatty acids tic Lipa *Pro Tip: This is physical se, digestion, not chemical 7-9 Pancrea digestion, since fat molecules tic are not being altered. Amylas Pancreas e, Pancreas secretes Proteas pancreatic juice (alkaline) e containing LAP enzymes into duodenum ◦ Pancreatic Lipase: fats -> glycerol + fatty acids ◦ Pancreatic Amylase: starch -> maltose ◦ Protease: Proteins -> short polypeptides Has many folds, increasing SA:V Large intestine absorbs Large Intestine/Colon water and mineral salts 7 - (Absorption) Undigested food (faeces) are temporarily stored in the rectum Anus Faeces is expelled 7 - (Egestion) 52 [Memory Shortcuts] Pancreatic enzymes [LAP] ◦ L: pancreatic Lipase ◦ A: pancreatic Amylase ◦ P: Protease Enzymes secreted by the small intestine's epithelial cells [LiMP] ◦ intestinal Lipase ◦ Maltase ◦ Protease 2. Summary: Enzymes involved in digestion 53  pH of Enzyme Produced by Digests Found in Location Amylase Salivary Starch --> Maltose Saliva (Mouth) 7 (salivary) glands Gastric Proteins --> Short Protease Stomach 2 glands Polypeptides* Lipase Triglycerides --> Alkaline (pancreatic) Glycerol + Fatty acids (>7) Amylase Pancreas Pancreatic Starch --> Maltose (pancreatic) juice Proteins --> Short Protease Polypeptides* Triglycerides --> Lipase (Intestinal) Glycerol + Fatty acids Maltose --> Glucose + Maltase Epithelial cells Small intestine 7-9 Glucose Short Polypeptides* -- Protease > Amino acids *Pro Tip: Short polypeptides is more accurate than just 'polypeptides', since it distinguishes between the length of the polypeptide (undigested proteins are folded polypeptides, hence the ambiguity). 3. Peristalsis 54 Definition (in digestion): Rhythmic, wave-like muscular contractions in the wall of the alimentary canal that moves food forward Peristalsis propels food forward ensuring it moves in the right direction, also mixes food with digestive juices How it works: At the region before the food mass, circular muscles contract while longitudinal muscles relax, narrowing the lumen and pushing food forward At the food mass, circular muscles relax while longitudinal muscles contract, widening the lumen, allowing food to pass through easily The above also applies for the region just in front of the food mass Circular muscles and longitudinal muscles are antagonistic (i.e. when one contracts, the other relaxes) *Pro Tip: Peristalsis occurs throughout the alimentary canal, not just in the oesophagus [Memory Hack] How to remember what circular muscles are doing in peristalsis ◦ Think of circular muscles as 'controlling' the lumen size. At the point where you see it squeezing (contracting), the circular muscles are therefore contracting too. ◦ If lumen is widening (relaxing) at an area, circular muscles are relaxing too. 4. Structure and function of villi 55 Where digested substances are absorbed: Glucose and amino acids move by diffusion + active transport into blood capillaries (red in diagram) of villi to be transported to the liver. Glycerol and fatty acids move by diffusion + active transport into the epithelial cells of villi, where they reform into triglycerides, then enter the lacteal (yellow in diagram) as fat globules. *Pro Tip: Villus is singular, villi is plural. *Pro Tip: Water is also absorbed at villi by osmosis. Adaptations for fast absorption: Villi are finger-like projections in the small intestine, increasing SA:V Are lined with a one-cell-thick layer of epithelial cells, minimising distance digested food substances have to travel Epithelial cells have microvilli, further increasing SA:V Absorbed substances that enter the lacteal and blood capillaries are constantly transported away, maintaining a steep concentration gradient between the lumen and villi to maximise diffusion rate of digested substances into villi. *Pro Tip: After diffusion has reached equilibrium, active transport is needed to further absorb digested substances 5. The Liver 56 What happens to absorbed digested food substances: Hepatic portal vein transports glucose and amino acids from small intestine to the liver Glucose is converted to glycogen and stored in the liver and muscles, or transported around the body for cells to uptake and use for energy Amino acids are transported around the body and taken up by cells during assimilation, to build new cell parts/protoplasm ◦ Deamination: The process where amino groups are removed from excess amino acids and converted into urea, in the liver. ◦ Hence hepatic vein has high urea. Fats are transported around the body to be stored/used for energy 57  Functions of Description liver Detoxification is the process where harmful substances (e.g. Detoxification hydrogen peroxide, alcohol) are converted into harmless ones. Breakdown of Hormones are broken down at the liver after they have served their Hormones purpose. Bile production The liver produces bile, which is stored in the gall bladder. Amino acids The process where amino groups are removed from excess amino (Deamination) acids and converted into urea, in the liver. When blood glucose concentration is too high, liver converts Blood Glucose glucose to glycogen in response to insulin. regulation When blood glucose concentration is too low, liver converts glycogen to glucose in response to glucagon. [Memory Shortcut] Dun Have BAG for functions of the liver ◦ Detoxification ◦ Hormone breakdown Bile production Amino acids --> Urea (Deamination) Glucose regulation 6. Effects of excessive alcohol consumption Short term effects: Alcohol is a depressant, meaning it slows brain functions, increases reaction time Reduces self-control, increasing tendency to make irrational decisions Long term effects: Addictive, leading to neglect of social responsibilities Stimulates acid secretion in stomach, increasing risk of stomach ulcers Liver is overworked, cells start dying, which can lead to liver damage: ◦ E.g. Liver cirrhosis (formation of fibrous tissue), liver failure Causes brain damage: 58  ◦ E.g. Dementia, high consumption during pregnancy may impair foetus' brain development Need personalised guidance for O Level Pure Bio? Learn more here: www.thatbiotutor.com 59 5. Nutrition in Humans CAQs Important Definitions Q: Define the term ingestion. The intake of food through the mouth. Q: Define the term digestion. The physical or chemical breakdown of larger food molecules into smaller and soluble molecules that can be absorbed by body cells. Q: Define the term absorption. The uptake of digested food substances into body cells. Q: Define the term assimilation. The process whereby digested food substances are used to make new cell parts or used for energy. Q: Define the term egestion. The removal of undigested food waste from the body. Q: Define peristalsis (in the context of digestion). Rhythmic, wave-like muscular contractions in the wall of the alimentary canal that moves food forward. Q: Define deamination. The process where amino groups are removed from excess amino acids and converted into urea, in the liver. Q: Define detoxification. The process whereby harmful substances are converted into harmless ones. Peristalsis Muscles Q: The diagram shows a food bolus moving down the oesophagus. 60 Which row identifies the muscles and their actions at region W? muscle X muscle Y muscle type action muscle type action A circular contracting longitudinal relaxing B circular relaxing longitudinal contracting C longitudinal contracting circular relaxing D longitudinal relaxing circular contracting (D) X = longitudinal muscles (as seen from the horizontal muscle fibres within it) Y = circular muscles. When circular muscles contract, lumen also narrows, so Y is contracting. Since X and Y are antagonistic, X is relaxing. *Pro Tip: Think in terms of circular muscles. When circular muscles contract, the lumen also "contracts". Liver Functions Q: Some processes that occur in the body are listed. Which processes occur in the liver? 1 breakdown of hormones 2 breakdown of starch 3 formation of urine 4 storage of glycogen A) 1 and 2 B) 1 and 4 C) 2 and 3 61 D) 3 and 4 (B) Refer to the functions of the liver memory shortcut, Dun Have BAG. ◦ 1 & 4 are correct. 2 is wrong as animals don't store starch, we store glycogen. 3 is wrong, formation of urea occurs in liver, but formation of urine occurs in kidneys. Alcohol Effects Q: Which section of the diagram represents the effects of excessive alcohol consumption on the body? (C) Careless mistake: Alcohol reduces reaction time. Alcohol reduces reaction speed, hence increases reaction time. Digestion of Various Biomolecules *Q: Describe the digestion of protein in the body. Protein is broken down into short polypeptides by protease in the stomach and small intestine. Short polypeptides are further broken down into amino acids by protease in the small intestine. *Q: Describe the digestion of carbohydrates in the body. Starch is broken down into maltose by salivary amylase in the mouth, And by pancreatic amylase in the small intestine. In the small intestine, maltose is further broken down by maltase into glucose. *Q: Describe the digestion of fats in the body. During digestion, bile is secreted from the gall bladder into the duodenum, through the bile duct. 62  Bile salts in bile emulsify large fat droplets into smaller ones, increasing the surface area to volume ratio for pancreatic lipase and intestinal lipase to digest fats into glycerol and fatty acids. Related Questions: ◦ Q: Describe how bile aids in fat digestion. Q: Describe the roles of enzymes in human digestion. Give examples in your answer. *Pro Tip: For such a question, use examples of digestion of some macromolecules, such as protein (pepsin + trypsin + peptidases involved) and starch (amylase + maltase involved). You don't have to talk about every single enzyme, just include enough points to hit the mark allocation. Adaptations of Villi *Q: Villi are found in the digestive system. Describe the structure and function of a villus. Villi are finger-like projections in the small intestine, which increase surface area to volume ratio for faster absorption. Glucose and amino acids diffuse into blood capillaries of villi to be transported to the liver. Glycerol and fatty acids diffuse into the epithelial cells of villi, where they reform into triglycerides, then enter the lacteal as fat globules. Are lined with a one-cell-thick layer of epithelial cells, minimising distance digested food substances have to travel, increasing absorption rate. Epithelial cells have microvilli, further increasing surface area to volume ratio for faster absorption. Absorbed substances that enter the lacteal and blood capillaries are constantly transported away, maintaining a steep concentration gradient between the lumen and villi to maximise diffusion rate of digested substances into villi. Related Questions: ◦ Q: Describe how villi are adapted to absorb digested food. ▪ *Pro Tip: For this question, just go straight to describing the adaptations. Q: Describe how the small intestine is adapted for absorption of digested food substances. It is very long, allowing more time for more digested food substances to be absorbed as they travel through. 63  Has many folds to increase surface area to volume ratio for faster absorption. ◦ *Pro Tip: For the remaining 2 marks, use any 2 points about villi adaptations. Functions of Liver *Q: Describe the functions of the liver. Functions of the liver [Dun Have BAG] ◦ D: Detoxification ◦ H: Hormone breakdown ◦ B: Bile production ◦ A: Amino acids --> Urea (Deamination) ◦ G: blood Glucose regulation The liver carries out detoxification, where harmful substances such as alcohol are converted into harmless ones. The liver breaks down hormones after they have served their purpose. The liver produces bile, which is then stored in the gall bladder. Bile aids in fat digestion. The liver carries out deamination, where amino groups are removed from excess amino acids and converted into urea. The liver aids in blood glucose regulation, converting glucose to glycogen when blood glucose concentration is too high, and vice versa when glucose levels are too low. Effects of Alcohol *Q: State the short term and long term effects of excessive alcohol consumption. Short term: It is a depressant, which slows brain functions and increases reaction time, increasing chances of driving accidents. It reduces self-control, increasing the chances a person makes irrational/reckless decisions. Long term (Choose 2): It stimulates excessive acid secretion in the stomach, which could lead to peptic ulcers. It could lead to death of liver cells and eventually liver failure/liver cirrhosis. It could lead to addiction, and thus leading to overspending on alcohol/neglect of social responsibilities. It could lead to dementia due to alcohol damage, a condition known as 'wet brain'. High consumption during pregnancy may impair the foetus' brain development. Drinking and driving 64 Q: Alcohol is a depressant. Explain why it is dangerous to drive under the influence of alcohol. While driving, the driver needs to react quickly by pressing the brakes or steering to safety when a collision is about to occur. Alcohol is a depressant, which slows brain functions and increases reaction time. Someone under the influence of alcohol may not be able to react in time, increasing the chances of a road accident. 65 6. Transport in Humans Learning Outcomes: 1. Main blood vessels in the body 2. The role of blood (transport, defence) and its components 3. Blood groups and their compatibilities 4. Structure and function of arteries, capillaries and veins 5. Transfer of materials between capillaries, tissue fluid and cells 6. Structure and function of heart 7. Cardiac cycle 8. Coronary artery disease Keywords: Oxygenated, deoxygenated Insoluble, coagulation, clot, universal donor, universal recipient Tissue rejection, antibody, neutralises, antigen, agglutination Biconcave, bell-shaped Arteries, arterioles, capillaries, venules, veins Tissue fluid, one-cell-thick Blood pressure, backflow, atrioventricular, semi-lunar valves, systole, diastole Coronary, atherosclerosis, fatty deposit, lumen If you're our student: Transport in Humans Crash Course Clips 1. Main blood vessels in the body 66 *Pro Tip: Blood from the stomach and intestines does not go back to the heart directly through veins, it passes through the liver first. 2. The role of blood (transport, defence) and its components 67  Structure / Component Function Appearance Carries dissolved substances in the blood such Plasma (55%) Made of 95% water as glucose, amino acids, mineral salts, CO2, waste, hormones, plasma proteins, etc. O2 binds to haemoglobin in red blood cells and is carried around the body When blood passes through oxygen-poor areas, O2 dissociates from haemoglobin and diffuses into body cells FYI: Carbon dioxide is also transported in red blood cells, brought to the Red lungs for removal. Blood Cells Increases SA:V for O2 to diffuse in/out of the Biconcave cell faster Lacks a nucleus More space to pack in more haemoglobin To squeeze through tiny capillaries, in which, it Flexible can become bell-shaped, further increasing SA:V White Blood Phagocytosis: The process where phagocytes Cells - engulf foreign particles and destroy them Phagocytes Can have a lobed nucleus Can have tendril-like protrusions White Blood 68  Produce antibodies, which: Have a large nucleus Cause pathogens to clump together (agglutination), promoting phagocytosis Bind to and neutralises harmful toxins Cells - that pathogens produce Lymphocytes Tissue rejection: When lymphocytes produce antibodies against a transplanted organ to destroy it Promotes blood clotting (coagulation) at the Membrane-bound site of injury, sealing the wound to prevent loss Platelets bodies of blood and preventing the entry of harmful (Not considered cells) microorganisms. [Memory hack] How to remember which is coagulation and agglutination ◦ Agglutination: Due to Antibodies in the blood ◦ Coagulation: blood Clotting How blood clots (Coagulation) When blood vessels are damaged, platelets are activated, which trigger the conversion of soluble fibrinogen into insoluble Fibrin, Forming long insoluble Fibrin threads which trap red blood cells, forming a clot at the site of injury. 3. Blood groups and their compatibilities 69 How to remember intuitively: The body will naturally produce antibodies of the other blood types, except against its own RBC's antigens (or it will kill its own RBCs!) If you transfer blood into a recipient who does not have antibodies against the donor's blood type, the transfusion will be safe. Special blood types: ◦ AB is the universal acceptor - can receive from all, but cannot donate to any ◦ O is the universal donor - can donate to all, but cannot receive from any 4. Structure and function of arteries, capillaries and veins 70  Type of Structure Function vessel Carries blood away from the heart Usually carry oxygenated blood, except for pulmonary artery Have thick elastic and muscular walls to accommodate/withstand and the high Arteries blood pressure exerted by the heart Elastic and muscular walls stretch and recoil to push blood forward in spurts Arteries branch out into arterioles, then into capillaries Are present near almost every cell in the body Made of a wall of one-cell-thick cells, minimising diffusion distance, increasing Capillaries diffusion rate Capillaries branch repeatedly, increasing SA:V, hence increasing rate of diffusion of substances in and out of them Capillaries converge into venules, then into veins Veins carry blood back to the heart Usually carry deoxygenated blood, except for pulmonary vein Have semi-lunar valves to prevent backflow of blood, which is likely due to low blood pressure Veins in veins Larger lumen to reduce resistance to bloodflow Thin elastic and muscular walls as blood pressure is lower Contraction of skeletal muscles exerts pressure on veins, moving blood along more quickly 71 Graph of Blood pressure against location The further from the aorta, the lower the blood pressure due to loss of energy In arteries and arterioles, blood pressure fluctuates as: ◦ Arteries have thick elastic and muscular walls that stretch and recoil, and are directly connected to the left ventricle. ◦ Hence, blood pressure increases during ventricular systole as left ventricle contracts, and decreases during ventricular diastole as left ventricle relaxes. 5. Transfer of materials between capillaries, tissue fluid and cells Capillaries bring nutrients and O2, which diffuse from the blood plasma to the tissue fluid These then diffuse from tissue fluid into cells Conversely, waste products and CO2 diffuse out of the cells into the tissue fluid, then into the blood plasma of capillaries. 6. Structure and function of the heart + types of circulation 72 [Memory hack] How to remember bicuspid valve is on the left side of the heart, tricuspid is on the right ◦ We always read words from Left to Right ◦ Bicuspid valve has 2 flaps (hence "bi-"), tricuspid valve has 3 flaps (hence "tri-") ◦ So remember Left --> 2, Right --> 3. 73  Parts of the heart Function Atria Have thinner walls then ventricles Left ventricle has thicker muscular walls as it has to generate high pressure to quickly pump blood around entire body Right ventricle has thinner muscular walls, as it does not Ventricles need to generate as high of a pressure to pump blood to lungs *Pro Tip: Use ventricle wall thickness to identify which side of the diagram is right/left. Usually, heart diagrams are mirror imaged, meaning the left side of the picture is the right side of the heart. Chordae tendineae Attaches valves to the heart walls Separates left and right sides, so deoxygenated and Medium septum oxygenated blood stay separate 7. Cardiac Cycle (Link for the above GIF to visualise bloodflow in heart: https://media.tenor.com/dO9JYv5q8xsAAAAC/heart-heart-pumping.gif) 74 *Note: Blue = Aorta, Red = Left Ventricle, Yellow = Left Atrium From Graph: (1) Atrioventricular valves close (2) Semi-lunar valves open (3) Semi-lunar valves close (4) Atrioventricular valves open Systole = contraction Diastole = relaxation RA = Right atrium, LA = Left atrium, RV = Right ventricle, LV = Left ventricle Atrial systole (+Ventricular diastole) Both atria contract, pushing blood past the atrioventricular valves into the ventricles ◦ LA pumps blood past the mitral/bicuspid valve to the LV ◦ RA pumps blood past the tricuspid valve to the RV *Pro Tip: AV valves were already open before atrial systole, as they opened near the end of ventricular diastole. Ventricular systole (+Atrial diastole) Ventricles contract ◦ Pulmonary semi-lunar valve is forced open, blood moves from RV to the pulmonary artery, and is sent to the lungs. 75  ◦ Aortic semi-lunar valve is forced open, blood moves from LV to the aorta, and is sent to the rest of the body. At the same time, atrioventricular valves close, preventing backflow of blood from ventricles to the atria. ◦ This causes the first 'lub' sound. Meanwhile, atria relax, ◦ Blood from pulmonary vein flows into LA ◦ Blood from vena cava flows into RA Ventricular diastole (+Atrial diastole) Ventricles relax ◦ Semi-lunar valves close, preventing backflow of blood from the pulmonary artery and aorta back into the ventricles. ◦ This causes the second 'dub' sound. Blood fills the relaxed atria and ventricles again Typical duration of each cardiac cycle: 0.8s = 75 beats per min *Pro Tip: When the heart pumps faster, such as during exercise, the duration of each cardiac cycle will be shorter. 8. Coronary artery disease Atherosclerosis: The disease where fatty deposits accumulate on the inner walls of arteries, narrowing the lumen. Coronary artery: An artery that branches out of the aorta, sending oxygen and nutrients to the heart muscles. Coronary artery disease: When atherosclerosis occurs in a coronary artery. Heart attack If a fatty deposit ruptures in a coronary artery, a blood clot could form, blocking the artery. Blood with oxygen and nutrients cannot reach the heart muscles for them to release energy via aerobic respiration, hence they die, resulting in a heart attack. Preventive measures Adopt a diet low in saturated fats and cholesterol Not smoking ◦ Carbon monoxide in cigarette smoke damages the inner layer of blood vessels, hence increasing the rate fatty deposits accumulate. 76  ◦ Nicotine stimulates adrenaline release, increasing blood pressure, which also increases the rate fatty deposits accumulate Stress management Regular exercise Need personalised guidance for O Level Pure Bio? Learn more here: www.thatbiotutor.com 77 6. Transport in Humans CAQs Important Definitions Q: Define the term atherosclerosis. The disease where fatty deposits accumulate on the inner walls of arteries, narrowing the lumen. Tissue Fluid Q: The diagram shows a capillary and some tissue cells. Which statement about the movement of substances is correct? A) Diffusion of substances occurs at W and Y. B) Diffusion of substances occurs at Y only. C) Fluid only passes out of the capillary at X. D) Tissue fluid passes into the capillary at Z. (A) A: Diffusion occurs at W, X, Y, Z. This includes both W and Y, although it is incomplete, it is technically correct. B: Wrong, see above point. C: Wrong, fluid can exit along any part of the capillary (W, X, Z). D: Looking at direction of bloodflow, fluid will exit the capillary at Z to provide nutrients to cells, and then re-enter at X, removing waste products from cells. Related Questions: ◦ Q: What is present in the tissue fluid formed from the plasma? (Using the same diagram as above) ◦ This is testing on which substances can pass through the capillary walls. 78  ◦ Can pass through (all the small molecules): Glucose, amino acids, water, mineral salts, urea, O2, CO2 ◦ Cannot pass through (large substances): Blood cells, platelets, proteins (e.g. haemoglobin, fibrin, ADH, insulin) Circulatory System Diagram Q: The diagrams represent the circulatory system. Which diagram is correct for an adult human? (D) Diagrams are usually mirror imaged, heart is flipped (left part in this diagram is the right side of the heart in real life, vice versa). Blood is pumped from RV to lungs, so B is out as it shows LV to lungs. Blood then goes from lungs to LA, so C is out. Between A and D, A is inaccurate as it shows a vein connecting intestines back to the heart (this does not exist!). Hence D is the answer. Substance Concentrations Along Circulatory System Q: The diagram represents part of the human circulatory system. 79  Lower CO2 Higher CO2 Number concentration concentration 1 W X 2 Y X 3 X Z 4 V Z Which comparisons of carbon dioxide concentration are correct? A) 1, 2, 3 and 4 B) 1, 3 and 4 only C) 1 and 4 only D) 2 and 3 only (B) The further blood moves from the heart/more tissues it passes through, the lower the O2 and higher the CO2. So lowest to highest CO2 concentration: V, W, X, Y, Z. 1 correct, since W < X. 2 likely wrong, since Y has blood that passed through intestines + liver, probably has more CO2 than X which has only passed through kidneys. 3 correct since X < Z, since Z is blood just before entering lungs, has highest CO2. 4 correct since V < Z. 80  Related Questions: ◦ Which comparisons of urea concentration are correct? (Using the same diagram as above) ◦ Urea will be highest in Y, as urea is produced via deamination in the liver. ◦ Urea will be lowest in X, as urea is filtered out of the blood by the kidneys. Cardiac Cycle Valves Q: The graph shows pressure changes in the left atrium, the left ventricle and the aorta during one complete cardiac cycle. At which points does the valve between the left atrium and left ventricle close and open? close open A 1 4 B 2 3 C 3 4 D 4 1 (A) At 1, pressure in LV jumps, it is contracting -> bicuspid valve needs to close to prevent backflow of blood from LV to LA At 4, pressure in LV drops below pressure of LA -> blood moves from LA to LV -> opens bicuspid valve in the process. 81 Blood Movement (blood pressure explanation) *Q: Describe and explain how blood is pumped from the left atrium to the aorta. During atrial systole, the left atrium contracts, blood pressure rises above that of the left ventricle. Blood moves past the bicuspid valve, entering the left ventricle. During ventricular systole, the left ventricle contracts, blood pressure rises above that of the aorta. Blood pushes past the aortic semi-lunar valve and opens it, entering the aorta. *Pro Tip: When question asks "describe and explain", must explain how blood moves using blood pressure differences. Related Questions: ◦ Q: Describe and explain how blood entering the heart from the body organs reaches the lungs. Route Taken By Blood *Q: Describe the route taken by the blood from the intestine to the kidney. List the major blood vessels and organs involved. Blood travels from the intestine to the liver via the hepatic portal vein, then exits the liver via the hepatic vein. It returns to the right atrium of the heart via the vena cava, and is pumped by the right ventricle to the lungs via the pulmonary artery. It returns to the left atrium via the pulmonary vein, and is pumped by the left ventricle, out the aorta to the kidneys. Finally, it enters the kidney via the renal artery. Related Questions: ◦ Q: Explain how a drug injected into rats was transported to the heart muscle. ◦ Q: Describe how blood from the lungs is forced through the heart into the aorta. Blood Vessel Structures *Q: Explain the differences in the structures of arteries and veins, with reference to their functions. Arteries have _____(A)______, while veins have _______(B)_______. [Choose 3 comparisons below] 82  A B Thick elastic and muscular walls, to Thin elastic and muscular walls, as withstand high blood pressure within blood pressure is lower within them them Thick elastic and muscular walls, to Thin elastic and muscular walls, as it stretch and recoil in order to push does not need to stretch and recoil to blood forward in spurts. push blood forward. Smaller lumen, to maintain high blood Larger lumen, to reduce resistance as pressure blood pressure is low No semi-lunar valves, as high blood Have semi-lunar valves, to prevent pressure ensures blood flows in the backflow of blood, which is likely due to right direction the low blood pressure Capillary Adaptations Q: Explain how capillaries are adapted for their function. Capillaries are made of a one-cell-thick layer of endothelial cells, minimising the diffusion distance, increasing the rate substances diffuse in and out of capillaries. They branch repeatedly, increasing their surface area to volume ratio, increasing the diffusion rate of substances. The capillary wall is partially permeable, allowing small substances such as glucose and CO2 to diffuse in and out, while ensuring big ones such as blood proteins stay within. They have very large total cross-sectional surface area, lowering blood pressure and slowing blood down, for substances to have more time to diffuse in and out. From Capillaries To Cells Q: Describe how substances move between capillaries and cells. Capillaries bring nutrients and oxygen, which diffuse from the blood plasma to the tissue fluid. These then diffuse from tissue fluid into cells. Conversely, waste products and carbon dioxide diffuse out of the cells into the tissue fluid, then into the blood plasma of capillaries. Blood Flow in Veins 83 Q: Blood has near zero pressure when it reaches veins. Explain how blood returns to the heart from the veins. Contraction of skeletal muscles exerts pressure on veins, forcing blood to move along. Semi-lunar valves in veins prevent backflow of blood, ensuring blood moves to heart in the right direction. Red Blood Cells Q: Explain how red blood cells are adapted to their function. They have a biconcave shape, increasing their surface area to volume ratio for faster diffusion of oxygen in and out of them. They lack a nucleus, for more space to pack in more haemoglobin, increasing their capacity for oxygen transport. They are flexible, allowing them to squeeze through tiny capillaries, in which they may become bell-shaped, further increasing their surface area to volume ratio. White Blood Cells Q: Describe the role of white blood cells in protecting the body from disease. Phagocytes engulf foreign particles which can cause disease and destroy them. Lymphocytes produce antibodies that cause foreign particles to agglutinate, promoting phagocytosis. Antibodies also bind to and neutralise any harmful toxins produced by pathogens. Blood Clotting (Coagulation) *Q: Explain how a blood clot is formed. When blood vessels are damaged, platelets are activated, which trigger the conversion of soluble fibrinogen into insoluble fibrin, Forming long insoluble Fibrin threads which trap red blood cells, forming a clot at the site of injury. Blood Type Incompatibility Q: What will happen if a patient with blood group O is given a transfusion of blood type AB? The red blood cells transfused have A and B antigens on their plasma membranes. 84  However, the blood group O patient has anti-A and anti-B antibodies in their blood plasma, Which bind to the transfused red blood cells, causing them to clump together and agglutinate. (This is dangerous as it could lead to the blockage of arteries.) Related Questions: ◦ Q: Explain what causes the incompatibility of blood between certain donors and recipients. ◦ Q: Describe and explain the undesirable consequence to the recipient when the blood type is not compatible. Valve Opening/Closing Q: Explain how the (bicuspid) valve opens. During ventricular diastole, the blood pressure of the left ventricle falls below that of the left atrium, resulting in blood flowing from the atrium to ventricle, forcing open the bicuspid valve. *Pro Tip: For questions on explaining how valves open/close, explain in terms of pressure difference Related Questions: ◦ Q: State what happens when the pressure in the atrium in higher than the pressure in the ventricle. ◦ Q: Describe how blood from the lungs is forced through the heart into the aorta. Fluctuation of Blood Pressure Q: Explain why blood pressure fluctuates in arteries. In arteries and arterioles, blood pressure fluctuates as arteries have thick elastic and muscular walls that stretch and recoil, and are directly connected to the aorta, which is connected to the left ventricle. Hence, blood pressure increases during ventricular systole as left ventricle contracts, and decreases during ventricular diastole as left ventricle relaxes. Coronary Artery Disease/Heart Attack *Q: Explain how a heart attack usually occurs. 85  Fatty deposits accumulate on the inner wall of a coronary artery, narrowing the lumen, atherosclerosis has occurred. If the fatty deposit ruptures, a blood clot could form, blocking the artery. Blood with oxygen and nutrients cannot reach the heart muscles for them to release energy via aerobic respiration, hence they die, resulting in a heart attack. Related Questions: ◦ Q: Sometimes blood clots can form inside a blood vessel and can be carried in the blood to the brain. The arteries in the brain may become blocked by the clot. Suggest how this blockage may affect the brain. ◦ *Pro Tip: In the above case, would lead to the death of brain cells --> stroke 86 7. Respiration Learning Outcomes: 1. Parts of the respiratory system and their roles in breathing 2. Adaptations of alveoli 3. Bonus: Inspired vs Expired air 4. Harmful effects of tobacco smoke 5. Aerobic and anaerobic respiration Keywords: Alveolar air space, one-cell-thick, film of moisture, dissolve Inspiration/inhalation, expiration/exhalation, thoracic volume, air pressure Foreign particles, pathogens, ciliated, hair-like structures Nicotine, addictive, social responsibilities Carbon monoxide, irreversibly Tar, carcinogen, chronic bronchitis, partition walls, emphysema, cancer Aerobic, oxidise, cellular respiration, release energy, cellular activities Anaerobic, lactic acid, additional energy, oxygen debt If you're our student: Respiration Crash Course Clips 1. Parts of the respiratory system and their roles in breathing 87  Structur Function e Cilia are hair-like structures on ciliated cells Found on inner walls of trachea, bronchi and larger bronchioles Mucus secreted by mucosal/gland cells traps dust Cilia and foreign particles Cilia sweeps mucus with the trapped particles up the trachea to be swallowed, neutralising any pathogens due to the stomach's acidic pH C- shaped Structural support: prevents collapse of the trachea, rings keeps the trachea open for unobstructed breathing of cartila ge Breathing process Event Inspiration (Breathing in) Expiration (Breathing out) Contracts and flattens Diaphragm Relaxes upwards downwards Intercostal Internal* Relax Contract muscles External* Contract Relax Ribcage Moves up and out Moves down and in Thoracic Volume Increases Decreases Lower than surrounding air, Higher than surrounding air, Air pressure in lungs causing air to rush in causing air to rush out *Pro Tip: These muscles are antagonistic 88 [Memory Shortcut] Inspiration/expiration process [DIRVA] ◦ D: Diaphragm ◦ I: Intercostal muscles (internal + external) ◦ R: Ribcage ◦ V: thoracic Volume ◦ A: Air pressure in lungs 2. Adaptations of alveoli 89  Feature Function Minimises distance O2 and CO2 have to travel, increasing One-cell-thick diffusion rate Small and numerous Increases their SA:V, increasing diffusion rate Provides continuous blood supply, oxygenated blood is Surrounded by network of quickly carried away to maintain the concentration capillaries gradients* for O2 to diffuse from alveolar air space into blood and CO2 to diffuse out Thin film of moisture lining Gases dissolve in it before diffusing across alveolar air space *Pro Tip: Concentration gradients are also maintained by fresh air being breathed in and old air breathed out 3. Bonus: Inspired vs expired air Component of air Inspired air Expired air Oxygen 21% 16% Carbon Dioxide 0.03% 4% Nitrogen 78% 78% Water Vapour Varies Saturated Dust Particles Present Almost none Temperature Varies ~37°C 4. Harmful effects of tobacco smoke 90  Chemical in Tobacco Negative Effects smoke Addictive, resulting in social problems Increases blood pressure* and heart rate Increases ease of blood clotting, increasing the risk of heart Nicotine attacks *Pro Tip: This increases 'wear and tear' of arteries, hence increasing the rate that fatty deposits accumulate. Binds irreversibly with haemoglobin such that it cannot transport O2 anymore, reducing the ability of blood to transport O2 Carbon Damages the innermost layer of blood vessels, increasing the rate Monoxide that fatty deposits accumulate in arteries, increasing the risk of heart attacks Paralyses cilia, dust particles cannot be expelled, which can result in: ◦ Chronic bronchitis (where the epithelium lining the airways are inflamed + persistent coughing) ◦ Persistent and violent coughing can lead to Emphysema (when Tar partition walls between alveoli break down, making it hard to breathe) Tar is a carcinogen*, increases chances of lung cancer *Pro Tip: Carcinogen = something that causes cancer 5. Aerobic and anaerobic respiration Living things need cellular respiration to release energy for cellular activities, such as: ◦ Muscular contractions, cell division, active transport, etc. Aerobic respiration: The process where food substances are broken down into carbon dioxide and water, in the presence of oxygen, releasing a large amount of energy. 91  ◦ Glucose + oxygen --> carbon dioxide + water + large amount of energy ◦ C6H12O6 + 6O2 --> 6CO2 + 6H2O + large amount of energy Anaerobic respiration (yeasts): The process where food substances are broken down into carbon dioxide and ethanol, in the absence of oxygen, releasing a small amount of energy. ◦ Glucose --> carbon dioxide + ethanol + small amount of energy ◦ This process is also called alcoholic fermentation Anaerobic respiration (mammals): The process where food substances are broken down into lactic acid, in the absence of oxygen, releasing a small amount of energy. ◦ Glucose --> Lactic acid + small amount of energy Oxygen debt: The amount of oxygen needed to remove lactic acid from the body. ◦ During vigorous exercise, muscles demand more energy than can be generated by aerobic respiration. ◦ Additional energy is generated by anaerobic respiration, resulting in lactic acid produced. ◦ An oxygen debt is incurred. ▪ Lactic acid is transported to the liver, where it is broken down, which requires oxygen (this amount of oxygen = oxygen debt) ◦ Immediately after exercise, the person needs to consume more oxygen compared to at rest, to repay the oxygen debt, by: ▪ Fast heart rate: Carries oxygen around the body quickly ▪ Deeper and faster breathing: Intake large amounts of oxygen quickly Need personalised guidance for O Level Pure Bio? Learn more here: www.thatbiotutor.com 92 7. Respiration CAQs Important Definitions *Q: Define the term aerobic respiration. The process where food substances are broken down into carbon dioxide and water, in the presence of oxygen, releasing a large amount of energy. Q: Define the term anaerobic respiration (yeasts). The process where food substances are broken down into carbon dioxide and ethanol, in the absence of oxygen, releasing a small amount of energy. *Q: Define the term anaerobic respiration (mammals). The process where food substances are broken down into lactic acid, in the absence of oxygen, releasing a small amount of energy. Q: Define the term oxygen debt. The amount of oxygen needed to remove lactic acid from the body. Alveoli Blood Capillaries Q: Which row shows the differences in composition between the blood at X and the blood at Y? 93  concentration of substance in the blood at X compared to the blood at Y carbon glucose oxygen dioxide A less more