ThatBioTutor's Content Notes (Pure Bio 2025)

1. Cells Learning Outcomes: Identify and state the functions of plant and animal cell organelles State the relationship between cell structure and function (w.r.t. RBC, root hair cell, muscle cell) 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 Component/OrganelleFunction Visible underLightMicroscope? Nucleus  Contains DNA (in the form of chromatin) Controlscellular activities Y Nuclear envelope Separates nucleus from cytoplasm Y Rough EndoplasmicReticulum  Studded with ribosomes Ribosomessynthesise proteins (for transport out of thecell) N Smooth EndoplasmicReticulum  Synthesises fats and steroids **Pro Tip: A class of molecules, including sexhormones Carries outdetoxification: where harmful substances areconverted to harmless ones N Cytoplasm  Place where most cellular activities occur Containsorganelles Y 1. Cells 1

 Site ofanaerobic respiration Vacuole Animals: Severalsmall and temporary vacuoles Store food and water Plants: Have alarge central vacuole Storescell sap (water + dissolved substances such as:sugars, amino acids, mineral salts) Y (plants)N (animals) Golgi body/apparatus• Modifies, Sorts and Packages substances intovesicles for secretion out of cellN Mitochondria  Site of aerobic respiration, where foodsubstances (such as glucose) are broken downto release energy N Chloroplast (plants only)  Site of photosynthesis Y Cell surfacemembrane/plasmamembrane • Partially permeable Controls movement of substances in and outof the cell Y Cell wall (plants only)  Fully permeable Made ofcellulose Gives cell its shape Y 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 Cell Structure Red Blood Cell How it is adapted to its function 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 1. Cells 2

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 Muscle Cell Elongated, cylindrical shape Contains many nuclei Have many mitochondria to generate a lot of energy via aerobic respiration for muscular contractions 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 Need personalised guidance for O Level Pure Bio? Learn more here: www.thatbiotutor.com © 2025 ThatBioTutor Pte. Ltd. All Rights Reserved. 1. Cells 3

Example 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 *Pro Tip: When explaining these processes in contexts of questions, replace' substances' with the molecule in the question, e.g. CO2 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. 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 2. Movement of Substances Learning Outcomes: 1. Definitions 2. Movement of substances in nutrient uptake and gas exchange Process Type of molecule Partially permeable membrane needed? Energy needed? Direction w.r.t. Concentration gradient Diffusion Any No No Down (higher to lower) Osmosis Water molecules Yes No Down (higher to lower) Active transport Dissolved molecules/ions Yes Yes Against (lower to higher) 2 . M o v e m e n t o f S u b s t a n c e s

Effect on Plant Cell Water Potential of Solution Effect on Animal Cell Turgid High Bursts/Lysed Flaccid Low Crenated Very Low Crenated Plasmolysed 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 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 molecules flows in by osmosis 3. Effects of osmosis on plant and animal tissues 2 . M o v e m e n t o f S u b s t a n c e s

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 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) © 2025 ThatBioTutor Pte. Ltd. All Rights Reserved. Need personalised guidance for O Level Pure Bio? Learn more here: www.thatbiotutor.com *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. 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. 4. Bonus: Factors affecting rate of diffusion 2 . M o v e m e n t o f S u b s t a n c e s

3. Biomolecules Learning Outcomes: Formation If you're our student: Biomolecules Crash Course Clips Keywords: Single sugars, double sugars, complex carbohydrates Amino acid, polypeptide Glycerol, fatty acid, triglyceride, solvent Carbohydrate, starch, glycogen, cellulose Reducing sugar, precipitate, cloudy white emulsion Carbohydrates, fats, and proteins: Their chemical elements, and the smaller molecules that make them up