Diseases and immunity cover how pathogens cause disease, how the body defends itself, and how vaccines provide protection.

Transport in humans Circulatory system The human circulatory system contains: vessels to carry blood; the heart, a muscular pump; and valves to maintain one-way blood flow. Single and double circulation In a fish, there is single circulation: heart → gills → body tissues → heart Blood passes through the heart once per complete circuit. Pressure falls as blood passes through the gill capillaries. In a mammal, there is double circulation: ...

Transport in plants involves the movement of water, minerals and food substances throughout the plant. This guide covers xylem and phloem function, root hair structure, transpiration and translocation according to IGCSE Biology syllabus (2026-2028).

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. ...