Summary
Highlights
Homeostasis is the body's ability to maintain stable internal conditions despite external changes, crucial for enzyme function. The nervous system, comprising the Central Nervous System (brain and spinal cord) and Peripheral Nervous System, uses electrical signals via neurons to respond to stimuli. Reflexes are rapid, bypassing the brain. Reaction times can be investigated using a ruler drop test, influenced by stimulants or depressants.
Key brain parts include the cerebral cortex (higher functions), cerebellum (motor skills), and medulla oblongata (unconscious actions). MRI scans visualize brain activity. The eye uses accommodation to focus light on the retina by changing lens shape; for distant objects, ciliary muscles relax, suspensory ligaments tighten, lens thins; for near objects, muscles contract, ligaments slacken, lens thickens. The pupil, cornea, sclera, and retina (with rods for light intensity and cones for color) are also critical parts. Myopia (short-sightedness) and hyperopia (long-sightedness) can be corrected with glasses or laser surgery.
Thermoregulation, controlled by the brain, involves nervous and hormonal signals to maintain body temperature. Sweating and vasodilation cool the body, while shivering and vasoconstriction warm it. The endocrine system consists of glands producing hormones that travel via blood, a slower process than nervous signals. The pituitary gland is the master gland, controlling others like the pancreas (insulin/glucagon for blood glucose), thyroid (metabolic rate), adrenal glands (adrenaline), and ovaries/testes (sex cells).
The pancreas regulates blood glucose: insulin lowers high levels (glucose to glycogen in liver), and glucagon raises low levels (glycogen to glucose). Type 1 diabetes is insufficient insulin, Type 2 is cell resistance, often linked to diet/weight. Kidneys maintain water balance and filter blood, reabsorbing useful substances. ADH (antidiuretic hormone) from the pituitary gland controls water reabsorption in kidneys. This is a negative feedback loop; kidney failure requires dialysis.
The menstrual cycle involves FSH (matures egg, produces estrogen), estrogen (thickens uterus lining, inhibits FSH, produces LH), LH (releases egg), and progesterone (maintains lining). Contraception methods include pills (inhibit FSH), injections/implants (stop egg release), barriers (condoms/diaphragms), IUDs (prevent implantation), rhythm method, and sterilization (clamping oviducts, cutting sperm duct). Infertility can be treated with hormone injections or IVF (in vitro fertilization).
Plants have hormones like gibberellins (seed germination, flowering, fruit size), ethene (fruit ripening), and auxins (shoot and root growth). Auxins concentrate on the shaded side of shoots, causing them to bend towards light (phototropism). In roots, auxins inhibit growth, causing them to grow downwards (geotropism). Auxins are also used as weed killers and rooting powders.
Sexual reproduction involves gametes made by meiosis (producing varied haploid cells). Asexual reproduction, by mitosis, creates genetically identical offspring (clones). Sexual reproduction provides variation, aiding survival, while asexual reproduction only requires one parent. The genome is all genetic material, stored in DNA (double helix polymer). Genes code for specific proteins. The Human Genome Project mapped genes, helping identify disease causes. Genotype (genetic code) determines phenotype (expressed characteristics). DNA nucleotides (A, T, C, G) code for amino acids, which form proteins. Mutations can alter proteins. Epigenetics shows how DNA influences gene expression.
Traits are controlled by genes with different alleles. Dominant alleles are expressed over recessive ones. Homozygous (BB, bb) and heterozygous (Bb) describe allele pairs. Punnett squares predict inheritance probabilities. Genetic disorders like polydactyly (dominant) and cystic fibrosis (recessive) are inherited. Sex is determined by XX (female) or XY (male) chromosomes. Variation comes from inherited genes and environmental factors. Darwin's theory of evolution states that suited organisms survive and reproduce. Lamarck suggested acquired traits are inherited. Bacterial resistance to antibiotics is evidence of Darwinian evolution; completing antibiotic courses is crucial to prevent resistant strains.
Organisms are of the same species if they produce fertile offspring. Selective breeding enhances desired characteristics. Genetic modification directly alters an organism's genes for specific traits, e.g., bacteria producing insulin, golden rice with vitamin A, disease-resistant crops. Genetic engineering involves cutting a gene with enzymes, inserting it into a vector (plasmid/virus), and then into an early-stage embryo to ensure the gene is in all cells.
Fossils are preserved remains or traces of ancient organisms. Cloning plants is easy with cuttings or tissue culture. Animal cloning can be done by splitting embryo cells (creating identical twins) or somatic cell nuclear transfer (transferring a nucleus from an adult cell into an enucleated egg). Linnaeus classified organisms into kingdom, phylum, class, order, family, genus, and species. The binomial name uses genus and species. Three domains (Archaea, Bacteria, Eukaryota) are a higher classification level.
Organisms compete for resources and form a community through interdependence. Abiotic factors are non-living (light, temperature, pH, CO2), while biotic factors are living (food, predators, pathogens). Quadrat sampling estimates population size. Food chains show biomass and energy flow: producers (plants/algae) are eaten by primary consumers (herbivores/omnivores), then secondary/tertiary consumers (carnivores/omnivores). Apex predators are at the top. Carbon and water cycles demonstrate resource recycling. Farmers use decomposition for natural fertilizers and methane fuel.
Biodiversity refers to the variety of organisms in an ecosystem; high biodiversity promotes stability. Human development (building, quarrying, farming) often reduces biodiversity. Waste disposal (sewage, fertilizers, chemicals, pollution) impacts the environment. Peat bog destruction and deforestation reduce habitats and release CO2. Food chains are represented by pyramids of biomass, showing energy loss at each trophic level. Food security is threatened by population growth, changing diets, transport, environmental changes, farming costs, and conflicts. Sustainable farming and fishing practices are crucial, such as using nets with larger holes to allow young fish to escape and breed.