Biology 101: Complete O Level Revision Course for Beginners

Explore ecology and ecosystem components, defining species, habitat, population, and community, then examine three symbiosis types: mutualism, commensalism, parasitism, with concrete examples.

Explore ecological study techniques for estimating species abundance using quadrats, transects, nets, and traps. Learn sampling, density calculations, and mark-recapture to estimate populations across an area.

Explore how sunlight powers photosynthesis and seasonal day length affects flowering, then examine soil as a habitat, nutrient source, water storage, and filter.

Photosynthesis converts light energy into chemical energy via light dependent and light independent stages, forming glucose from water and carbon dioxide with chlorophyll and releasing oxygen.

Explore macronutrients, including carbohydrates, proteins, and fats, and their structures from monosaccharides to polysaccharides, such as starch, cellulose, and glycogen, amino acids, enzymes, and cell membranes, with energy roles.

Explore how minerals like iron, calcium, phosphorus, and sodium support blood, bones, nerves, and metabolism, and examine malnutrition, obesity, diabetes, and starvation.

Enzymes act as biological catalysts, speeding up cellular reactions and remaining unchanged. They are proteins with a specific active site that binds substrates in a lock-and-key model, forming enzyme-substrate complexes.

Explore ruminant digestion in cows and sheep, detailing cud chewing, regurgitation, and cellulose breakdown by symbiotic bacteria from mouth through the rumen, reticulum, and abomasum.

This lecture explains respiration as release from glucose; aerobic respiration uses oxygen in mitochondria to make atp and co2, while anaerobic respiration occurs without oxygen, producing ethanol or lactic acid.

Engage in vigorous exercise to reveal how oxygen debt forms as cells lack oxygen; lactic acid builds up, causing cramps, then lactic acid is oxidized after activity to release energy.

Explore the transport system—blood vessels, blood, and heart—and its link to immunity, including red and white blood cells, plasma, and platelets, and how antibodies fight antigens.

Explore the anatomy and roles of arteries, veins, and capillaries, detailing wall structure, pressure differences, oxygen transport, diffusion, valves, and how circulation returns blood to the heart.

Explore heart structure and function, including four chambers, key valves, and the flow of blood through pulmonary and systemic circulation, plus heartbeat and blood pressure.

This lecture defines atherosclerosis as fatty plaque buildup in arteries that narrows blood flow to the heart and brain, risking heart attack and stroke, with causes and treatments.

Explore phloem translocation of manufactured food through sieve tube elements and companion cells, powered by living cells and mitochondria, with bidirectional systemic transport from source leaves to sink roots.

Explain how water moves from roots to leaves via osmosis, root hairs, mineral uptake, capillary action, cohesion, and transpiration pull in the xylem.

Explore the basics of plant transpiration, including how water moves from roots to leaves and evaporates from stomata. Understand its role in plant water balance and cooling.

Explore how the kidney and nephron filter blood, reabsorb essential substances, and form urine through Bowman's capsule, proximal and distal tubules, loop of Henle, and collecting duct.

Describe the deamination of amino acids into ammonia and urea, liver processing via the hepatic portal vein, and how excretion and homeostasis are maintained in plants and animals.

Explore osmoregulation, showing how the hypothalamus and pituitary use antidiuretic hormone to regulate kidney absorption and urine concentration, and examine food storage as starch and glycogen in plants and animals.

Compare plant responses to stimuli, including phototropism and gravitropism driven by unilateral light and auxins, with invertebrates' touch sensitivity and Venus flytraps closing on touch.

Explore the human nervous system, including brain regions, neuron structure and types, and how neurotransmitters cross synapses to transmit impulses from sense organs to effectors.

Examine reflex action as a rapid, involuntary response via the reflex arc, outlining stimulus, receptors, sensory and motor neurons, spinal and cranial reflexes, and pupil reflex.

Explore how the endocrine system and nervous system coordinate hormones from glands such as pituitary, pancreas, thyroid, ovaries, and testes to regulate metabolism and reproduction.

Explore how accommodation changes lens shape via the ciliary muscle and suspensory ligaments to focus images on the retina. Identify myopia, hypermetropia, glaucoma, and convex or concave lenses correct vision.

Explore how hormone deficiencies contribute to diabetes, detailing type 1 and type 2, insulin's role, symptoms, risk factors, and management with insulin, metformin, exercise, and diet.

An overview of the skeletal system, its protective and supportive roles, how it enables movement with muscles, stores calcium and phosphorus, and produces blood cells, plus axial and appendicular skeleton.

Explore the vertebral column anatomy, including cervical, thoracic, and lumbar vertebrae, and joints from immovable to synovial, with cartilage discs, synovial fluid, and antagonistic muscles driving movement.

Grow organisms by increasing cell number or enlarging existing cells, producing irreversible size changes. Develop complexity through stages like metamorphosis, and measure growth by dry mass, height, and leaf number.

Explore how sexual reproduction in plants involves pollination and fertilization, detailing stigma, style, ovary, pollen, and zygote formation, and compare with vegetative propagation such as grafting and tissue culture.

Explore human reproduction by detailing the male and female reproductive structures, puberty changes, gamete production, menstrual cycle, fertilization, pregnancy, and birth control methods.

Explore the menstrual cycle and its three phases—follicular, ovulation, and luteal—highlighting FSH, estrogen, and the uterine lining. Learn how menstruation marks the cycle start, understand cycle duration, and recognize menopause.

Explore sexually transmitted infections within a beginner biology course designed for an O level revision.

Explore the history of genetics and how inheritance and environment shape living organisms. Trace beliefs from ancient Egypt to Mendel's plant experiments and the discovery of DNA.

Explore genetic inheritance, including DNA structure, genes, and chromosomes, and learn how alleles interact through dominance, recessiveness, and homozygous or heterozygous states with punnett squares.

Explore how blood groups are inherited from A, B, and O alleles, with dominance and recessiveness, and practice predicting genotype and phenotype ratios using Punnett squares.

Define mitosis and show how a diploid somatic cell, after interphase replication, divides into two identical daughter cells with the same number of chromosomes, via sister chromatids and spindle fibers.

Meiosis produces four haploid gametes through two stages, meiosis i and ii, with crossing over between homologous chromosomes creating genetic recombination, followed by separation of sister chromatids.

Variation means differences among organisms caused by genetic differences or environmental influence, with continuous variation lacking limits and discontinuous variation forming distinct groups, driven by crossing over and mutations.

Biotechnology applies biological and engineering principles to improve health and ecosystems. Genetic engineering, a biotechnology branch, manipulates genes via plasmids and DNA vectors to produce insulin and other products.

Explore how dna template guides the transcription of messenger rna in the nucleus and how ribosomes translate rna into a polypeptide chain, forming a protein.