Biology

Human nutrition Balanced diet A balanced diet contains suitable amounts of carbohydrates, fats and oils, proteins, vitamins, minerals, fibre, and water for health, growth, energy, and repair. Requirements vary with age, activity, pregnancy, and health. Nutrient Sources Importance Carbohydrates Bread, rice, potatoes, pasta, cereals Energy for respiration Fats and oils Butter, oils, meat, nuts, seeds Energy store, insulation, and part of cell membranes Proteins Meat, fish, eggs, milk, beans, nuts Growth and repair; making enzymes and other proteins Vitamin C Citrus fruits, berries, peppers, green vegetables Healthy skin and gums; deficiency causes scurvy Vitamin D Sunlight, oily fish, eggs, fortified foods Helps calcium absorption and healthy bones; deficiency causes rickets Calcium ions Milk, cheese, yoghurt, leafy vegetables Strong bones and teeth; deficiency can contribute to rickets Iron ions Meat, liver, beans, leafy vegetables Needed to make haemoglobin; deficiency can cause anaemia Fibre Whole grains, fruits, vegetables, beans Adds bulk and helps food move through the alimentary canal Water Drinks, fruits, vegetables, soups Solvent for digestion; transport; temperature control; raw material in reactions The digestive system The alimentary canal is a tube through which food passes: ...

Plant nutrition Photosynthesis Photosynthesis is the synthesis of carbohydrates from raw materials using light energy. Word equation: carbon dioxide + water → glucose + oxygen Balanced chemical equation: $$6CO_2 + 6H_2O \rightarrow C_6H_{12}O_6 + 6O_2$$ Chlorophyll is a green pigment in chloroplasts. It transfers light energy to the photosynthesis reactions. Carbon dioxide enters through stomata and water arrives through xylem. Uses and storage of carbohydrates Starch: storage carbohydrate in plants. Cellulose: makes strong plant cell walls. Glucose: used in respiration to release energy. Sucrose: transported in phloem to other parts of the plant. Nectar: contains sugars that attract pollinators. Leaf structure and adaptations Leaves are thin and have a large surface area. These features give a short diffusion distance and allow absorption of much light. ...

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: ...