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Biology
Study Notes
All notes follow the official WAEC and JAMB approved syllabus. Study a topic first, then take the practice quiz โ after the test, come back here to see which topics you need to improve.
Cell Structure & Organelles
Plant vs animal cells, organelle functions
Cell Division
Mitosis and meiosis โ stages and significance
Transport Across Membranes
Diffusion, osmosis, active transport
Photosynthesis
Light and dark reactions, chlorophyll, factors
Animal Nutrition & Digestion
Alimentary canal, enzymes, absorption
Food & Nutrients
Carbohydrates, proteins, fats, vitamins, deficiencies
Respiration
Aerobic, anaerobic, ATP, equation
Gaseous Exchange
Breathing mechanism, alveoli, lungs, gills
Excretion
Kidneys, liver, skin โ organs and waste products
Mendel's Laws
Monohybrid, dihybrid crosses, Punnett square
DNA & Chromosomes
DNA structure, genes, sex determination
Variation & Evolution
Natural selection, adaptation, mutation
Ecosystem & Habitat
Population, community, biotic and abiotic factors
Food Chains & Energy Flow
Trophic levels, producers, consumers, pyramids
Ecological Relationships
Mutualism, parasitism, commensalism, predation
Circulatory System
Heart, blood vessels, blood composition, groups
Nervous System & Senses
Brain, spinal cord, neurons, reflex arc, sense organs
Skeleton, Muscle & Hormones
Skeletal system, endocrine glands, hormones
Cell Structure & Organelles
A cell is the smallest structural and functional unit of all living organisms. Robert Hooke discovered cells in 1665. There are two main types: prokaryotic (no membrane-bound nucleus โ e.g. bacteria) and eukaryotic (with a membrane-bound nucleus โ e.g. plant and animal cells).
| Organelle | Function | Found In |
|---|---|---|
| Nucleus | Controls cell activities; contains DNA and chromosomes | Both |
| Cell membrane | Controls what enters and leaves the cell; selectively permeable | Both |
| Cell wall | Rigid outer layer; provides shape, support and protection | Plants only |
| Mitochondria | Site of aerobic respiration; produces ATP (energy) | Both |
| Chloroplast | Site of photosynthesis; contains chlorophyll | Plants only |
| Ribosome | Site of protein synthesis | Both |
| Golgi body/apparatus | Modifies, packages and secretes proteins and lipids | Both |
| Endoplasmic reticulum | Rough ER: transports proteins. Smooth ER: lipid synthesis | Both |
| Lysosome | Contains digestive enzymes; breaks down waste and foreign material | Animals mainly |
| Vacuole | Large central vacuole in plants stores water, sap; maintains turgor | Both (large in plants) |
| Centriole | Helps in cell division (forms spindle fibres) | Animals only |
Most tested differences โ plant vs animal cells: Plants have cell wall, chloroplast, and large central vacuole. Animals have centrioles and lysosomes. Both have nucleus, mitochondria, ribosome, Golgi body, ER, cell membrane and cytoplasm.
Cell Division: Mitosis & Meiosis
| Feature | Mitosis | Meiosis |
|---|---|---|
| Purpose | Growth, repair, asexual reproduction | Sexual reproduction (gamete formation) |
| Number of divisions | 1 | 2 (meiosis I and II) |
| Daughter cells produced | 2 | 4 |
| Chromosome number | Same as parent (diploid: 2n) | Half of parent (haploid: n) |
| Genetic variation | No (genetically identical) | Yes (crossing over creates variation) |
| Where it occurs | Somatic (body) cells | Gonads (testes and ovaries) |
| Result in humans | 46 chromosomes in each daughter cell | 23 chromosomes in each gamete |
Prophase โ chromosomes condense and become visible.
Metaphase โ chromosomes line up at the cell equator.
Anaphase โ sister chromatids are pulled to opposite poles.
Telophase โ two new nuclei form; cell divides (cytokinesis).
Exam trick: MITosis = Making Identical Two. Meiosis produces gametes for sexual reproduction. Meiosis gives genetically different cells; mitosis gives identical cells.
Transport Across Membranes
| Type | Definition | Energy needed? | Example |
|---|---|---|---|
| Diffusion | Movement of particles from high to low concentration | No | COโ leaving the lungs into blood |
| Osmosis | Movement of water molecules across a semi-permeable membrane from high water potential to low water potential | No | Water entering root hair cells |
| Active transport | Movement of particles from low to high concentration (against the concentration gradient) | Yes (ATP) | Absorption of glucose in the gut; mineral uptake by roots |
Turgid (plant cell in water): vacuole full, cell firm โ cell wall prevents bursting.
Plasmolysed (plant cell in salt solution): vacuole shrinks, membrane pulls away from wall.
Haemolysis (animal cell in water): cell swells and bursts (no cell wall).
Crenation (animal cell in salt solution): cell shrivels.
Osmosis is a special type of diffusion โ only water moves, and only through a semi-permeable membrane. Active transport is the ONLY type that requires energy (ATP).
Photosynthesis
Photosynthesis is the process by which green plants use sunlight, water, and carbon dioxide to produce glucose and oxygen. It takes place mainly in the chloroplasts of leaf cells, which contain the pigment chlorophyll.
Carbon dioxide + Water โ Glucose + Oxygen
6COโ + 6HโO โ CโHโโOโ + 6Oโ (in the presence of light and chlorophyll)
| Factor | Effect when increased | Limiting factor? |
|---|---|---|
| Light intensity | Rate increases up to a point, then levels off | Yes โ at low light levels |
| COโ concentration | Rate increases up to a point | Yes โ at low COโ levels |
| Temperature | Rate increases up to optimum (~25โ30ยฐC), then enzymes denature | Yes โ at low temperatures |
| Water availability | Needed as a raw material and for stomata to remain open | Yes โ at severe shortage |
Chlorophyll absorbs red and blue light most strongly. It reflects green light โ which is why leaves appear green. WAEC tests leaf adaptations: thin, flat, large surface area, veins, stomata, chloroplasts.
Animal Nutrition & Digestion
| Region | Enzyme(s) | Substrate โ Product |
|---|---|---|
| Mouth (salivary glands) | Salivary amylase | Starch โ Maltose |
| Stomach (gastric glands) | Pepsin (in gastric acid) | Protein โ Peptides |
| Small intestine (pancreas) | Pancreatic amylase, trypsin, lipase | Starch โ maltose; protein โ amino acids; fats โ fatty acids + glycerol |
| Small intestine (wall) | Maltase, sucrase, lactase, peptidase | Disaccharides โ monosaccharides; proteins fully broken down to amino acids |
Bile is produced by the liver, stored in the gall bladder, and released into the small intestine. Bile does NOT contain enzymes. Its function is to emulsify fats โ breaking large fat droplets into smaller ones to increase surface area for lipase to act on.
Absorption: Most digested food is absorbed in the small intestine via villi and microvilli (increase surface area). Water is mainly absorbed in the large intestine. Movement of food is by peristalsis.
Food & Nutrients
| Nutrient | Function | Sources | Deficiency Disease |
|---|---|---|---|
| Carbohydrates | Main energy source | Rice, yam, bread, cassava | Marasmus (severe energy deficiency) |
| Proteins | Growth, repair, enzyme and hormone production | Meat, fish, eggs, beans, milk | Kwashiorkor (protein deficiency) |
| Fats & Oils | Energy reserve, insulation, fat-soluble vitamins | Palm oil, butter, groundnut | Deficiency rare; excess โ obesity |
| Vitamin A | Vision, healthy skin and immune system | Carrots, liver, dairy | Night blindness, xerophthalmia |
| Vitamin Bโ (thiamine) | Energy metabolism, nerve function | Cereals, nuts, meat | Beriberi |
| Vitamin C | Wound healing, immune function, iron absorption | Citrus fruits, vegetables | Scurvy |
| Vitamin D | Calcium absorption; bone and teeth formation | Sunlight, fish, dairy | Rickets (children), osteomalacia (adults) |
| Calcium (mineral) | Bone and teeth formation, muscle contraction | Milk, fish, vegetables | Rickets, osteoporosis |
| Iron (mineral) | Part of haemoglobin; oxygen transport | Liver, meat, spinach | Anaemia |
| Water | Solvent, transport medium, temperature regulation | Fruits, vegetables, drinks | Dehydration |
Most tested: Kwashiorkor (protein) vs Marasmus (energy/calories); Scurvy (Vitamin C); Rickets (Vitamin D/calcium); Beriberi (Vitamin B1); Night blindness (Vitamin A). Know the deficiency disease for each nutrient โ this appears every year.
Respiration (Aerobic & Anaerobic)
| Feature | Aerobic | Anaerobic |
|---|---|---|
| Oxygen required | Yes | No |
| Site | Mitochondria | Cytoplasm |
| Products (animals) | COโ + HโO + ATP (energy) | Lactic acid + small amount of ATP |
| Products (plants/yeast) | COโ + HโO + ATP | Ethanol + COโ + small amount of ATP (fermentation) |
| Energy yield | High (36โ38 ATP) | Low (2 ATP) |
Glucose + Oxygen โ Carbon dioxide + Water + Energy
CโHโโOโ + 6Oโ โ 6COโ + 6HโO + ATP
Glucose โ Lactic acid + small amount of ATP
Lactic acid causes muscle fatigue โ "oxygen debt" is repaid during recovery.
ATP (adenosine triphosphate) is the energy currency of the cell. All respiration produces ATP. Aerobic yields far more. The mitochondria is the "powerhouse of the cell" because aerobic respiration occurs there.
Gaseous Exchange & Breathing
| Organism | Respiratory Organ |
|---|---|
| Mammals (including humans) | Lungs |
| Fish | Gills |
| Insects | Trachea / Spiracles |
| Earthworm | Moist skin (cutaneous respiration) |
| Amphibians (e.g. frog) | Skin + lungs (both) |
| Stage | Diaphragm | Intercostal muscles | Chest volume | Air movement |
|---|---|---|---|---|
| Inhalation (breathing in) | Contracts and flattens | Contract (ribs move up and out) | Increases | Air rushes IN |
| Exhalation (breathing out) | Relaxes and domes up | Relax (ribs move down and in) | Decreases | Air pushed OUT |
Alveoli are tiny air sacs in the lungs. Adaptations: thin walls (one cell thick), moist lining, rich blood supply, large surface area. Oxygen diffuses from alveoli โ blood. COโ diffuses from blood โ alveoli.
Breathing (mechanical) is NOT the same as respiration (chemical). Breathing moves air in and out. Respiration releases energy from glucose inside cells. WAEC and JAMB test this distinction every year.
Excretion in Animals
Excretion is the removal of metabolic waste products from the body. Do NOT confuse with egestion (removal of undigested food as faeces).
| Organ | Waste Product Excreted |
|---|---|
| Kidneys | Urea, excess water and salts (as urine) |
| Lungs | Carbon dioxide and water vapour |
| Skin | Water, salts and small amounts of urea (as sweat) |
| Liver | Produces urea (by deamination of excess amino acids); also breaks down old red blood cells |
Filtration: Blood is filtered at the glomerulus in Bowman's capsule โ produces filtrate containing water, salts, glucose, urea.
Reabsorption: Useful substances (glucose, water, salts) are reabsorbed back into blood in tubules.
Secretion: Remaining waste (urea, excess salts) passes to collecting duct โ forms urine โ stored in bladder.
Urea is made in the LIVER (not kidneys). The kidneys FILTER urea from the blood and excrete it in urine. This distinction is tested almost every year in WAEC and JAMB.
Mendel's Laws of Inheritance
| Term | Definition |
|---|---|
| Gene | A unit of heredity that controls a characteristic; located on a chromosome |
| Allele | Different forms of the same gene (e.g. tall T and short t) |
| Dominant | Allele expressed even when only one copy is present (written in CAPITALS) |
| Recessive | Allele only expressed when two copies are present (written in lowercase) |
| Genotype | The genetic makeup of an organism (e.g. TT, Tt, tt) |
| Phenotype | The observable trait (e.g. tall, short) |
| Homozygous | Two identical alleles (TT or tt) โ pure breeding |
| Heterozygous | Two different alleles (Tt) โ hybrid |
Parent genotypes: TT ร tt
Fโ generation: all Tt (tall) โ 100% tall phenotype
Fโ ร Fโ: Tt ร Tt
Fโ Punnett Square: TT : Tt : tt = 1:2:1 genotype ratio
Phenotype ratio: 3 Tall : 1 Short โ Mendel's 3:1 ratio
Gregor Mendel is the Father of Genetics. His two laws:
1. Law of Segregation: alleles separate during gamete formation.
2. Law of Independent Assortment: genes on different chromosomes are inherited independently.
DNA, Chromosomes & Genes
- DNA (deoxyribonucleic acid) is the molecule that carries genetic information.
- DNA is a double helix โ two strands twisted together, like a twisted ladder.
- The "rungs" are base pairs: Adenine (A) pairs with Thymine (T); Guanine (G) pairs with Cytosine (C).
- DNA is found mainly in the nucleus, wound around proteins called histones to form chromosomes.
- Humans have 46 chromosomes (23 pairs) in every somatic cell.
- Gametes (sperm and egg) have 23 chromosomes (haploid).
Sex is determined by the sex chromosomes: XX = female, XY = male. The father determines the sex of the child, since mothers always contribute X.
Mother (XX) ร Father (XY):
Offspring: 50% XX (female) : 50% XY (male)
Each pregnancy has a 50% chance of being male or female.
Sex-linked traits (like colour blindness and haemophilia) are carried on the X chromosome. Since males have only one X, they show the trait even with one recessive allele. Females need two copies to be affected โ they can be carriers with one copy.
Variation & Evolution
| Type | Definition | Examples | Cause |
|---|---|---|---|
| Continuous variation | Shows a range of values with no distinct categories | Height, weight, skin tone | Many genes + environment |
| Discontinuous variation | Distinct categories with no intermediate forms | Blood groups (A, B, AB, O), tongue rolling, sex | Single gene; little environmental influence |
- Organisms produce more offspring than can survive (overproduction).
- There is variation among individuals in a population.
- There is a struggle for existence โ competition for limited resources.
- Those best adapted to their environment survive and reproduce ("survival of the fittest").
- Favourable traits are inherited by the next generation โ over time, the population changes (evolution).
A mutation is a sudden change in the DNA sequence โ the source of new genetic variation. Mutations can be beneficial (rare โ e.g. antibiotic resistance in bacteria), harmful (most), or neutral. Caused by radiation, chemicals (mutagens), or errors during DNA replication.
Ecosystem & Habitat
| Term | Definition | Example |
|---|---|---|
| Habitat | The physical place where an organism lives | A pond, a forest, a desert |
| Population | All organisms of the same species living in an area | All the frogs in a pond |
| Community | All populations of different species living in an area | All plants and animals in a forest |
| Ecosystem | A community of organisms plus their physical environment (biotic + abiotic) | A rainforest, a coral reef |
| Biosphere | All ecosystems on Earth โ the global sum of all ecosystems | The entire Earth's living zone |
| Biotic factors | Living components of an ecosystem | Plants, animals, bacteria, fungi |
| Abiotic factors | Non-living components of an ecosystem | Temperature, light, water, pH, soil |
| Niche | The role or function of an organism in its habitat | A bee's niche: pollinator + honey producer |
Ecosystem = Community + Environment. Nigeria's major biomes include tropical rainforest in the south and savanna in the north. A biome is a large geographic area with similar climate and organisms.
Food Chains & Energy Flow
| Trophic Level | Organism Type | Example |
|---|---|---|
| 1st โ Producers | Green plants (autotrophs) โ make own food by photosynthesis | Grass, algae, trees |
| 2nd โ Primary consumers | Herbivores โ eat producers | Grasshopper, rabbit, cow |
| 3rd โ Secondary consumers | Omnivores/carnivores โ eat primary consumers | Frog, small fish, lizard |
| 4th โ Tertiary consumers | Top carnivores โ eat secondary consumers | Hawk, eagle, lion |
| Decomposers | Break down dead organic matter | Bacteria, fungi |
Grass โ Grasshopper โ Frog โ Snake โ Eagle
Only about 10% of energy is transferred from one trophic level to the next. The other 90% is lost as heat, used in respiration, or in waste. This is why food chains rarely have more than 4โ5 links.
Pyramids: Pyramid of numbers can be inverted (e.g. one tree supporting many caterpillars). Pyramid of biomass is usually upright. Pyramid of energy is ALWAYS upright โ energy always decreases at each level.
Ecological Relationships
| Relationship | Species A | Species B | Example |
|---|---|---|---|
| Mutualism | Benefits (+) | Benefits (+) | Rhizobium bacteria in legume roots; oxpecker bird on buffalo |
| Commensalism | Benefits (+) | Not affected (0) | Epiphytic plants on tree trunks; barnacles on whale |
| Parasitism | Benefits (+) | Harmed (โ) | Tapeworm in gut; mosquito and human; mistletoe on host plant |
| Predation | Predator benefits (+) | Prey is harmed (โ) | Lion and zebra; hawk and mouse; spider and fly |
| Competition | Harmed (โ) | Harmed (โ) | Two plant species competing for light and water; weeds and crops |
Mutualism vs Commensalism: In mutualism BOTH benefit. In commensalism only ONE benefits and the other is unaffected (not harmed). This distinction is tested very frequently. Parasitism: one benefits, one is harmed but not killed immediately โ the parasite needs the host alive.
Circulatory & Blood System
| Blood Vessel | Function | Key feature |
|---|---|---|
| Arteries | Carry blood AWAY from the heart | Thick muscular walls; high pressure; no valves |
| Veins | Carry blood TOWARDS the heart | Thinner walls; lower pressure; have valves to prevent backflow |
| Capillaries | Exchange substances between blood and body tissues | One cell thick; very narrow; no muscle layer |
Pulmonary circuit: Right heart โ lungs (to pick up Oโ) โ left heart.
Systemic circuit: Left heart โ body tissues (deliver Oโ) โ right heart.
The pulmonary artery is the only artery that carries deoxygenated blood. The pulmonary vein is the only vein carrying oxygenated blood.
| Component | Function |
|---|---|
| Red blood cells (erythrocytes) | Contain haemoglobin; carry oxygen; no nucleus (in mammals) |
| White blood cells (leucocytes) | Fight infection (phagocytosis and antibody production) |
| Platelets (thrombocytes) | Blood clotting; prevent excessive blood loss |
| Plasma | Liquid part; transports dissolved substances (glucose, COโ, hormones, waste) |
ABO Blood Groups: Group O = universal donor. Group AB = universal recipient. Always know which groups are compatible for transfusion. WAEC tests this regularly.
Nervous System & Senses
The nervous system coordinates body activities by transmitting electrical impulses.
| Division | Components | Function |
|---|---|---|
| Central Nervous System (CNS) | Brain + spinal cord | Processes and integrates information |
| Peripheral Nervous System (PNS) | Nerves connecting CNS to body | Carries impulses to and from CNS |
Sensory neuron: carries impulses FROM sense organs TO CNS.
Motor neuron: carries impulses FROM CNS TO muscles/glands (effectors).
Relay (interneuron): connects sensory and motor neurons in the CNS.
Stimulus โ Receptor โ Sensory neuron โ Spinal cord (relay neuron) โ Motor neuron โ Effector (muscle/gland) โ Response. Reflexes are AUTOMATIC โ they do not require conscious thought.
Sense organs and their stimuli: Eye (light), Ear (sound and balance), Nose (smell/chemicals), Tongue (taste/chemicals), Skin (touch, pain, temperature, pressure). The eye's lens is controlled by the ciliary muscles for focusing (accommodation).
Skeleton, Muscle & Hormones
- Support โ gives the body shape and supports soft tissues
- Protection โ skull protects brain; ribcage protects heart and lungs; vertebral column protects spinal cord
- Movement โ bones act as levers; muscles attached to bones enable movement
- Blood cell formation โ red bone marrow produces blood cells (haematopoiesis)
- Mineral storage โ stores calcium and phosphorus
Joints: Ball-and-socket (hip, shoulder) โ movement in all directions. Hinge (knee, elbow) โ movement in one plane only.
| Gland | Hormone | Function |
|---|---|---|
| Pituitary (master gland) | FSH, LH, GH, ADH | Controls other glands; growth; water reabsorption by kidneys |
| Thyroid | Thyroxine | Controls metabolic rate; deficiency โ goitre |
| Pancreas | Insulin (ฮฒ cells) / Glucagon (ฮฑ cells) | Insulin lowers blood glucose; glucagon raises it. Diabetes = insulin deficiency |
| Adrenal glands | Adrenaline | "Fight or flight" response โ increases heart rate, breathing, blood sugar |
| Ovary | Oestrogen, Progesterone | Female secondary sexual characteristics; menstrual cycle control |
| Testes | Testosterone | Male secondary sexual characteristics; sperm production |
Hormones vs nerves: Hormones are chemical messengers carried in blood โ slow, long-lasting. Nerve impulses are electrical โ fast, short-lived. WAEC asks you to compare these two coordination systems almost every year.
You've now covered all major WAEC and JAMB Biology topics. Try the past questions first to see how WAEC/JAMB phrase their questions, then take the 60-question timed CBT practice to get your full score breakdown.