Biology

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.

Biological molecules Biological molecules are substances made by living organisms. Carbohydrates, fats and oils, and proteins contain different elements and are built from smaller molecules. Food tests identify some of these molecules in a sample. Elements and building blocks Molecule Elements Smaller molecules or units Carbohydrates Carbon, hydrogen, oxygen Starch, glycogen, and cellulose are made from glucose molecules. Fats and oils Carbon, hydrogen, oxygen Made from fatty acids and glycerol. Proteins Carbon, hydrogen, oxygen, nitrogen; sometimes sulfur Made from amino acids. A large molecule made from many repeating smaller units is often called a polymer. The smaller units are monomers. This terminology is useful, but remember the exact syllabus relationships above. ...

Movement into and out of cells Diffusion Diffusion is the net movement of particles from a region of higher concentration to a region of lower concentration, down a concentration gradient. Particles move randomly because they have kinetic energy. The energy for diffusion comes from this kinetic energy, not from respiration or ATP. Diffusion can occur through a cell membrane or through air and water. It is important for: ...

Cells and organisms This guide covers syllabus sections 1 and 2: characteristics and classification of living organisms, organisation of the organism, specialised cells, and magnification. Characteristics of living organisms Use MRS GREN: Movement: an action by an organism or part of an organism. Plants show movements such as phototropism. Respiration: chemical reactions in cells that release energy from nutrients. Sensitivity: detecting and responding to changes in the internal or external environment. Growth: a permanent increase in size and dry mass by an increase in cell number or size. Reproduction: production of offspring, sexually or asexually. Excretion: removal of toxic materials, waste products of metabolism, and substances in excess of requirements. Nutrition: taking in materials needed for energy, growth, and development. A species is a group of organisms that can reproduce with one another to produce fertile offspring. The binomial system gives each species two names: the genus followed by the species name, for example Homo sapiens. ...

Quiz: Coordination and Response Question 1 Define the term ‘reflex action’. [2] Question 2 The diagram below shows a simple reflex arc. Identify the role of the effector in this process. [1] Explain why reflex actions are important for survival. [2] Question 3 Identify the hormone produced by the pancreas that lowers blood glucose levels. [1] Question 4 Plants respond to their environment through growth movements. Define ‘phototropism’. [2] State the name of the plant hormone responsible for controlling phototropism. [1] Question 5 Compare the structure and function of a sensory neuron and a motor neuron. [4] ...