This study guide covers Chapter 5 of the IGCSE Biology (2026-2028) syllabus: Enzymes. It addresses both Core and Extended syllabus requirements covering enzymes as biological catalysts and factors affecting enzyme activity.

Carbohydrates Chemical Composition Carbohydrates consist of three elements: Element Symbol Typical Proportion Carbon C ~44% by mass Hydrogen H ~6.7% by mass Oxygen O ~49% by mass General formula: C(H₂O)n - water to carbon ratio Types of Carbohydrates Simple Carbohydrates (Monosaccharides and Disaccharides) Single sugar units or two joined together Sweet-tasting, soluble in water Examples: glucose, fructose, sucrose Complex Carbohydrates (Polysaccharides) Long chains of monosaccharide units Not sweet-tasting, insoluble in water Examples: starch, glycogen, cellulose ...

Diffusion Diffusion is the net movement of particles from a region of higher concentration to a region of lower concentration due to their random kinetic movement. Fundamental Principles What is Diffusion? Net Movement: Particles move down a concentration gradient (high → low) Random Motion: Driven by kinetic energy - particles possess thermal energy causing constant random movement Equilibrium: Occurs when particles are evenly distributed (concentration gradient eliminated) Passive Process: Does NOT require energy (ATP) from respiration ...

Characteristics of Living Organisms All living organisms share defining characteristics that distinguish them from non-living matter. Understanding these characteristics is fundamental to biological classification and study. MRS GREN - Seven Characteristics of Life Movement All living organisms exhibit some form of movement, either externally visible or internal. Plants show growth movements (tropisms) such as phototropism (toward light) and gravitropism (root down, shoot up). Animals display locomotion through muscles, cilia, or flagella. Respiration All living systems require energy release through respiration. Aerobic respiration: Glucose + Oxygen → Carbon dioxide + Water + Energy Anaerobic respiration: Glucose → Lactic acid/Alcohol + Energy Occurs continuously in all living organisms at cellular level. Sensitivity Organisms can detect stimuli from their environment and respond accordingly. Examples include the pupil reflex, shivering response to cold, and plant responses to light. Nerves relay electrical impulses for animals; hormones act as chemical messengers. Growth Permanent increase in dry mass through cell division. Not simply getting bigger or accumulating food - must be irreversible growth of cells. Involves mitosis to produce more cells. Reproduction Production of new individuals, either sexually or asexually. Asexual reproduction: genetically identical offspring from one parent (bacteria binary fission, plants vegetative propagation). Sexual reproduction: fusion of nuclei from male and female gametes to form a zygote; offspring genetically different. Species defined as a group of organisms that can reproduce to produce fertile offspring. Excretion Elimination of harmful waste products from the body. In humans: kidneys excrete urea, excess water and ions through urine; lungs excrete carbon dioxide and water vapour. Important: removal of toxic nitrogenous compounds (e.g., urea from protein metabolism). Nutrition Uptake and processing of raw materials to build organic molecules for energy and cell structures. Autotrophs make own food via photosynthesis (plants, algae). Heterotrophs ingest or absorb nutrients from other organisms (animals, fungi). Essential for growth, repair, and maintenance of life processes. Classification of Living Organisms The binomial naming system provides a standard method to classify species using Latin/Scientific names: Genus species (e.g., Homo sapiens, Quercus robur). ...

Scatter Diagrams and Correlation 1. Bivariate Data Bivariate data consists of pairs of values for two different variables recorded for the same subject. Example: Height and weight of students. The goal is to determine if there is a relationship (correlation) between the two variables. 2. Scatter Diagrams A scatter diagram plots bivariate data on a Cartesian plane. X-axis: Independent variable. Y-axis: Dependent variable. Each pair $(x, y)$ is plotted as a single point. ...