Secondary School Biology Notes

No. Topic 1 Biological Molecules (Enzymes) 2 Biological Molecules (Nutrition) 3 Cell Division 4 Cell Structure & Organisation 5 Ecology 6 Excretion 7 Heredity 8 Homeostasis 9 Hormones 10 Molecular Genetics 11 Nutrition in Human 12 Nutrition in Plants 13 Our Impact on the Ecosystem 14 Reproduction in Humans 15 Reproduction in Plants 16 Respiration in Humans 17 The Human Eye 18 The Nervous System 19 Transport Across Membranes 20 Transport in Man 21 Transport in Plants

a-a Amino acid Amt Amount b/w Between DNA Deoxyribonucleic acid EA Activation energy Fa Fatty acids H+ Hydrogen ions KE Kinetic energy mRNA Messanger RNA RBC Red blood cells RNA Ribonucleic acid rxn Reaction Temp Temperature tRNA Transfer RNA SA:V Surface Area to V olume Ratio SA Surface area +ve(ly) Positive(ly) -ve(ly) Negative(ly)

Biological Molecules (Enzymes)  Catalysts: Substances that can alter/speed up a chemical reaction w/o itself being chemically changed at the end of the reaction  Activation energy (EA) - All chemical reactions involve breaking & forming of bonds - Energy is required to break existing bonds in order to form new ones - Transition state: unstable state reached when existing bonds are strained - EA is the energy required to bring reactant molecules to their transition state - New bonds form after existing bonds break - Enzymes  Biological catalysts that are mostly protein-based  Speed up rate of rxns by lowering EA, w/o being chemically changed at the end of the rxn  Required in minute amounts during rxns → Efficient molecules – same enzyme can catalyse rnx many times → No. of substrate molecules that one enzyme can react on in a given span of time is the turnover number  Specific in action → Each chemical rxn in a cell is catalysed by a unique enzyme → Most enzymes can only catalyse one specific rxn due to the specific 3D shape of its active site  Enzyme-substrate complex: temporary structure formed when enzyme and substrates bind [Lock-and-Key Hypothesis] Overall change in energy is –ve: energy content of products lower than that of reactants Overall energy change might be +ve sometimes (opp of everything in –ve)

[Induced Fit Hypothesis]  Active site of enzyme: part where enzyme comes into contact with substrate  Amino acid chain folded into complex 3D shapes  Catalytic amino acids may be far from each other along the chain, but brought together after folding to form the active site  High temperatures denature proteins (proteins loses its 3D structure and active site changes shape – substrate can no longer bind to it) Anabolic Reaction Catabolic Reaction  Reactions that build up complex substances A-A  Polypeptides  Proteins  Reactions that break down complex substances 2H2O2  O2 + 2H2O - Factors affecting Enzyme Activity  pH  temperature → each enzyme has its optimum temp where it’s most active → low temps: enzymes are inactive (K.E. of both enzyme & substrates are low low chances of effective collision between enzyme & substrate) → high temps: enzymes may denature at ~60ºC (K.E of enzyme is high bonds that maintain shape of enzyme break) → Increasing temp from low to optimum: increase in enzyme activity – K.E of both enzyme & substrate increases  chances of effective collision b/w enzyme & substrate increases 1. Measure of H+ concentration 2. H-bonds of 3D shape of enzymes may break depending on H+ concentration 3. Each enzyme functions at its optimum pH 4. Changes in pH  enzymes denature, enzyme activity decrease, eventually stop

 Enzyme Concentration → Low concentration of enzyme can catalyse a large amt of substrate → Limiting factor: amt of substrates available (addition of more enzyme would not increase rate of rxn if substrate concentration is low as there is not enough substrates to fill up active sites) → If all conditions are optimum, & excess substrates are available, rate of rxn is directly proportional to concentration of enzymes  Substrate Concentration → Rate of rxn increase with increasing substrate concentration, up to a certain point → Limiting factor: amt of enzymes available (addition of more substrates will not increase rate of rxn is enzyme concentration is low as all available active sites are filled)  Class of enzymes Class of Enzymes Eg of Enzymes Substrates Products Carbohydrases (digest carbohydrates) Amylase Maltase Sucrase Lactase Starch Maltose Sucrose Lactose Maltose Glucose + Glucose Glucose + Fructose Glucose + Galactose Proteases Pepsin Trypsin Erepsin Proteins Polypeptides Polypeptides Shorter Polypeptides Amino Acids Amino Acids Lipase - Fats Glycerol + 3 Fatty Acids A: enzyme less active at low temp B: enzyme activity increases with increasing temp (on average, rate doubles with every 10ºC rise) C: Optimum temp – enzyme is most active; rate of rxn at its peak (~40ºC for most enzymes) D: Enzymes start denaturing at temps above optimum temp; activity decreases rapidly E: Enzyme completely denatures; unable to catalyse any rxns

Biological Molecules (Nutrition)  7 classes of nutrients - Carbohydrates - Fats - Proteins - Dietary Fibre: a type of carbohydrate that cannot be digested by us. Helps to bulk up faces & in egestion - Vitamins - Water - Minerals (Fe2+,K+, Ca2+, Zn2+)  Water - Functions  Solvent for chemical reactants  Key component of tissues  Controls body temperature: evaporation of water in sweat removes latent heat  Transports dissolved substances to/for/from: digested products (small intestine to other parts), removal of waste products from cells, photosynthesis, maintaining cell turgidity, mineral salts, food substances  Carbohydrates - Organic molecules - Composed of carbon, hydrogen, oxygen (H:O is always 2:1) - Functions  Substrate for respiration (provides energy for cell activities)  Forms supporting structure  Converted to other organic compounds (e.g. a-a, fats)  Formation of nucleic acids  Synthesize lubricants (e.g. mucus)  Synthesize nectar - General formula: CnH2mOm - Isomers: molecules same chemical formula but have different atom arrangements (monosaccharides, disaccharides) - Glycosidic bond is present between two sugars Monosaccharides (Simple Sugars) • Glucose (G) • Fructose (F) • Galactose (Ga) • Chemical Formula: C6H12O6 Disaccharides (Double Sugars) • Maltose (G + G) • Sucrose (G + F) • Lactose (G + Ga) • Chemical Formula: C12H22O11 Polysaccharides (Complex Sugars) • Starch (plant) • Cellulose (plant) • Glycogen (animal) • No definite formula Complex substances (need to be digested) No need to be digested (can be absorbed as they are small enough)

- Monosaccharide: Glucose - Disaccharides  Union of 2 monosaccharides (condensation reaction: loss of one water molecule) – glycosidic bond formed (H-O-H)  Splitting of disaccharides (hydrolysis: addition of one water molecule) – forms its initial monosaccharides - Reducing sugars: all monosaccharides and disaccharides, except sucrose - Benedict’s Test for reducing sugars  Blue precipitate (ppt): no reducing sugar (sucrose)  Green ppt: traces of reducing sugar  Yellow/orange ppt: moderate amounts of reducing sugar  Brick-red ppt: large amounts of reducing sugar - Polysaccharides  Many monosaccharides joined together, formed by many condensation reactions  Cellulose: made up of ~10 000 glucose molecules, sheet-like structure with long, unbranched glucose chains  Starch: made up of thousands of glucose molecules, storage form of glucose in plants, helical structure, identified using iodine solution (turns blue-black), mixture of 2 polysaccharides  Amylose: unbranched polysaccharide, 20-20 000 glucose units  Amylopectin: branched polysaccharide, short side chains of up to 30 glucose units

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