1. Basic Concepts of Biology

Biology is the branch of science that studies living organisms, their structure, functions, growth, reproduction and interactions with the environment.

• Botany: Study of plants.
• Zoology: Study of animals.
• Microbiology: Study of microorganisms.
• Ecology: Study of relationships between organisms and their environment.
• Genetics: Study of heredity and variation.
• Physiology: Study of the functions of living organisms and their parts.
• Anatomy: Study of the structure of organisms.

2. Cell: The Basic Unit of Life

All living organisms are made up of one or more cells. Cells may be prokaryotic or eukaryotic.

• Prokaryotic cells: Lack a membrane-bound nucleus.
• Eukaryotic cells: Possess a membrane-bound nucleus.
• Mitosis: Cell division generally producing two genetically similar daughter cells.
• Meiosis: Specialized cell division that reduces chromosome number and produces genetic variation.

3. Biomolecules

Biomolecules are chemical substances produced by living organisms and required for life processes.

• Carbohydrates: Important sources of energy; examples include glucose and starch.
• Proteins: Made of amino acids and involved in structure, transport, defence and catalysis.
• Lipids: Include fats, oils, phospholipids and steroids.
• Nucleic acids: DNA and RNA store or help express genetic information.
• Enzymes: Biological catalysts that accelerate biochemical reactions.
• ATP: An important energy-transfer molecule in cells.

4. Plant and Animal Tissues

A tissue is a group of cells that work together to perform a particular function.

• Epithelial tissue: Covers body surfaces and lines organs.
• Connective tissue: Supports, connects and protects body structures.
• Muscular tissue: Produces movement by contraction.
• Nervous tissue: Receives and transmits signals.

5. Plant Kingdom

• Algae: Mostly aquatic, photosynthetic organisms with relatively simple bodies.
• Bryophytes: Non-vascular plants such as mosses and liverworts.
• Pteridophytes: Vascular plants that reproduce through spores, such as ferns.
• Gymnosperms: Seed-producing plants with exposed or “naked” seeds.
• Angiosperms: Flowering plants whose seeds are enclosed within fruits.

6. Photosynthesis

Photosynthesis is the process by which green plants, algae and some microorganisms use light energy to produce organic compounds from carbon dioxide and water.

• Chlorophyll is the principal light-absorbing pigment in green plants.
• Photosynthesis mainly occurs in chloroplasts of plant cells.
• Carbon dioxide enters leaves mainly through stomata.
• Oxygen is released during the light-dependent reactions as water is split.
• Glucose and other carbohydrates are formed through carbon-fixation pathways.

7. Plant Physiology

• Transpiration: Loss of water vapour from plant surfaces, mainly through stomata.
• Respiration: Cellular process that releases usable energy from organic molecules.
• Translocation: Movement of sugars and other organic substances through the phloem.
• Phototropism: Growth response of a plant to light.
• Geotropism: Growth response to gravity.
• Auxins: Plant hormones involved in growth and tropic responses.
• Gibberellins: Plant hormones that influence growth and seed germination.
• Cytokinins: Plant hormones that promote cell division.
• Abscisic acid: Plant hormone involved in stress responses and dormancy.
• Ethylene: Plant hormone involved in fruit ripening and other processes.

8. Animal Kingdom

Animals are multicellular, heterotrophic organisms whose cells generally lack cell walls.

9. Human Digestive System

The digestive system breaks food into simpler substances that can be absorbed and used by the body.

• Mouth: Digestion begins with chewing and the action of salivary enzymes.
• Oesophagus: Transports food to the stomach through peristalsis.
• Stomach: Mixes food with gastric juice and begins substantial protein digestion.
• Small intestine: Main site of digestion and nutrient absorption.
• Liver: Produces bile and performs several metabolic functions.
• Gallbladder: Stores and concentrates bile.
• Pancreas: Produces digestive enzymes and bicarbonate.
• Large intestine: Absorbs water and electrolytes and forms faeces.

10. Human Respiratory System

• The respiratory system brings oxygen into the body and removes carbon dioxide.
• Air generally passes through the nose, pharynx, larynx, trachea and bronchi before reaching the lungs.
• Alveoli: Tiny air sacs where gas exchange occurs.
• Oxygen is transported in blood mainly by haemoglobin.
• Carbon dioxide is transported in several forms, mainly as bicarbonate ions in blood.
• The diaphragm plays a major role in breathing movements.
• Cellular respiration produces ATP from nutrients.

11. Blood and Circulatory System

The human circulatory system transports oxygen, nutrients, hormones and waste products throughout the body.

• The human heart has four chambers: two atria and two ventricles.
• Arteries generally carry blood away from the heart.
• Veins generally carry blood towards the heart.
• Capillaries allow exchange of substances between blood and tissues.
• The pulmonary artery carries deoxygenated blood from the heart to the lungs.
• The pulmonary veins carry oxygenated blood from the lungs to the heart.

12. Excretory System

Excretion is the removal of metabolic waste products from the body.

• The kidneys are the principal organs of urine formation in humans.
• Nephron: Structural and functional unit of the kidney.
• Urine formation involves filtration, reabsorption and secretion.
• The ureters carry urine from the kidneys to the urinary bladder.
• The urinary bladder temporarily stores urine.
• The urethra carries urine out of the body.
• The skin removes some water, salts and urea through sweat.
• The lungs remove carbon dioxide and water vapour.

13. Nervous System and Sense Organs

• Neuron: Basic structural and functional unit of the nervous system.
• Central nervous system: Brain and spinal cord.
• Peripheral nervous system: Nerves and ganglia outside the central nervous system.
• The cerebrum is associated with thinking, memory, sensory processing and voluntary actions.
• The cerebellum helps coordinate movement and maintain balance.
• The medulla oblongata regulates several involuntary functions.
• The retina contains photoreceptor cells that detect light.
• The cochlea is involved in hearing.
• The skin contains receptors for touch, pressure, temperature and pain.

14. Endocrine System

The endocrine system consists of glands that release hormones into the bloodstream.

• Insulin: Helps lower blood glucose levels.
• Glucagon: Helps raise blood glucose levels.
• Thyroxine: Helps regulate metabolic activity.
• Adrenaline: Participates in the fight-or-flight response.

15. Reproduction

• Asexual reproduction: Reproduction involving one parent and generally no fusion of gametes.
• Sexual reproduction: Reproduction involving the formation and fusion of gametes.
• Fertilisation: Fusion of male and female gametes.
• Pollination: Transfer of pollen from anther to stigma in flowering plants.
• Puberty: Developmental stage when reproductive maturity begins.
• In humans, sperm are produced in the testes and ova mature in the ovaries.
• The placenta facilitates exchange of nutrients, gases and wastes between mother and developing foetus.
• DNA replication is essential before cell division.

16. Genetics and Evolution

• Gene: A unit of hereditary information, generally a DNA sequence with a functional role.
• Chromosome: Structure containing DNA and associated proteins.
• Genotype: Genetic constitution of an organism.
• Phenotype: Observable characteristics of an organism.
• Dominant allele: Allele that can determine a phenotype in a heterozygous condition under a particular genetic model.
• Recessive allele: Allele whose effect may be masked in a heterozygous condition under a particular genetic model.
• Gregor Mendel is widely known for foundational work on inheritance in pea plants.
• Mutation: A change in genetic material.
• Natural selection: Differential survival and reproduction associated with heritable variation.
• Evolution is the change in heritable characteristics of populations over generations.

17. Diseases and Immunity

• Pathogen: Disease-causing organism or infectious agent.
• Communicable disease: Disease that can spread from one host to another.
• Non-communicable disease: Disease that does not normally spread through infection between people.
• Vaccine: Preparation that stimulates protective immune responses against a specific pathogen or disease.
• Antibody: Protein produced by certain immune cells that specifically binds an antigen.
• Antibiotics: Substances used to treat certain bacterial infections; they do not treat viral infections.
• Malaria: Disease caused by Plasmodium parasites and commonly transmitted by infected female Anopheles mosquitoes.
• Dengue: Viral disease commonly transmitted by infected Aedes mosquitoes.
• Tuberculosis: Infectious disease caused by Mycobacterium tuberculosis.
• Diabetes mellitus: Group of disorders involving persistently elevated blood glucose levels.

18. Ecology and Environment

• Ecosystem: Community of organisms interacting with their physical environment.
• Biotic components: Living components of an ecosystem.
• Abiotic components: Non-living factors such as light, water, soil and temperature.
• Food chain: Sequence through which energy and nutrients pass as organisms feed on one another.
• Food web: Network of interconnected food chains.
• Producers: Organisms that produce organic matter, usually through photosynthesis or chemosynthesis.
• Consumers: Organisms that obtain energy by feeding on other organisms.
• Decomposers: Organisms that break down dead organic matter.
• Biodiversity: Variety of life at genetic, species and ecosystem levels.
• Conservation: Protection and sustainable management of natural resources and biodiversity.

19. Nutrition and Vitamins

• Carbohydrates: Major source of energy.
• Proteins: Required for growth, repair and many biological functions.
• Fats: Concentrated energy source and important for cell membranes.
• Minerals: Inorganic nutrients needed for body structure and regulation.
• Balanced diet: Diet containing appropriate amounts of essential nutrients and energy.

20. Quick Revision Facts