Summary
Highlights
Plants have organs like leaves for photosynthesis and transpiration, and roots for water and mineral absorption. Xylem transports water unidirectionally, while phloem translocates sugars and sap bidirectionally. Transpiration rate increases with temperature, decreased humidity, and increased air movement. The leaf's cross-section features a waxy cuticle, upper epidermis, palisade mesophyll (major photosynthesis site), spongy mesophyll (gas exchange), vascular bundles, and lower epidermis with stomata controlled by guard cells.
Photosynthesis, an endothermic reaction in chloroplasts, produces glucose for respiration, storage (starch/fat), cellulose (cell walls), and amino acids (proteins). Its rate is affected by temperature (optimal range), light intensity, and CO2 concentration; one can be a limiting factor. The rate can be measured by observing oxygen production in pondweed with varying light intensity, an inverse square relationship.
Gibberellins promote seed germination, flowering, and fruit size. Ethene induces fruit ripening. Auxins control shoot and root growth; they accumulate on the shaded side of shoots, causing them to bend towards light (phototropism), and inhibit root growth, causing them to grow downwards (geotropism). Auxins are also used as weed killers, rooting powders, and in tissue cultures.
Homeostasis is the body's ability to maintain stable internal conditions, crucial for enzyme function. The body regulates blood glucose, temperature, and water levels. Thermoregulation, controlled by the brain, involves mechanisms like sweating (evaporation cools) and vasodilation (increased blood flow to skin) when hot, and vasoconstriction (reduced blood flow) and shivering (muscle heat production) when cold.
The endocrine system consists of glands secreting hormones into the blood, slower than the nervous system. The pituitary gland is the 'master gland'. Examples include the pancreas (insulin/glucagon), thyroid (metabolic rate, growth), and adrenal glands (adrenaline). The pancreas regulates blood glucose: insulin lowers high levels (glucose to cells/glycogen storage in liver), glucagon raises low levels (glycogen to glucose). Type 1 diabetes involves insufficient insulin, Type 2 involves cell insensitivity.
The kidneys regulate water balance by removing excess water from the blood, mixing it with urea to form urine. Too much water can cause cells to burst, too little causes them to become flaccid. Kidneys also filter blood, reabsorbing useful substances like glucose. ADH (anti-diuretic hormone) from the pituitary gland controls water reabsorption in the kidneys. Negative feedback ensures levels return to normal. Kidney failure requires dialysis to prevent urea buildup.
In females, FSH from the pituitary matures eggs and stimulates estrogen production, which thickens the uterus lining and inhibits FSH. LH causes egg release. Progesterone maintains the uterus lining. Contraception includes pills/injections/implants (inhibiting hormones), condoms/diaphragms (barriers), IUDs (prevent implantation), and surgical methods (tying tubes, cutting sperm ducts). Infertility, often due to hormone imbalances, can be treated with injections or IVF, though IVF has a low success rate and risk of multiple births.
The heart is central to the double circulatory system, pumping blood twice per circuit. Deoxygenated blood enters the right side (vena cava to right atrium, then right ventricle), goes to the lungs via the pulmonary artery, gets oxygenated, returns to the left side (pulmonary vein to left atrium, then left ventricle), and is pumped to the body via the aorta. The left side has thicker walls for greater pumping strength. Electrical pulses regulate heartbeats; pacemakers assist if needed. Arteries carry blood away from the heart (thick walls, narrow lumen), veins carry it towards (thinner walls, valves). Capillaries are tiny, one-cell thick for efficient diffusion.
The heart muscle needs its own blood supply via the coronary artery. Blockages from fatty deposits cause coronary heart disease (CHD) and heart attacks. Stents keep blood vessels open, and statins reduce cholesterol. Faulty heart valves can be replaced. Blood contains plasma, red blood cells (oxygen transport), white blood cells (fight infection), and platelets (clotting).
Breathing delivers oxygen for respiration. Air travels down the trachea, bronchi, bronchioles, to alveoli where gas exchange occurs due to a large surface area. Oxygen binds to hemoglobin in red blood cells. CO2 dissolves in plasma and is exhaled. Respiration (aerobic with oxygen) in mitochondria produces energy. During exercise, heart and breathing rate increase. Anaerobic respiration (without oxygen) produces lactic acid, causing an oxygen debt. Plant and yeast cells respire anaerobically to produce ethanol and CO2 (fermentation), used in baking and alcoholic drinks.
Metabolism is the sum of all chemical reactions in an organism, including respiration, conversion of glucose (starch, glycogen, cellulose), synthesis of amino acids/proteins, and breakdown of excess proteins to urea. Organisms compete for resources (food, water, space, light/CO2, shelter, mates). Interdependence describes how organisms rely on each other, forming communities. Abiotic factors are non-living (light, temperature, pH, gases); biotic factors are living (food, predators, pathogens).
Quadrats estimate population size; transects show distribution changes. Food chains illustrate biomass/energy flow: producers (plants/algae) are eaten by primary (herbivores/omnivores), then secondary (carnivores/omnivores), and tertiary consumers, with apex predators at the top (trophic levels). Carbon and water are recycled in ecosystems. Farmers use decomposition for natural fertilizers and to produce methane. Potable water is safe to drink, treated from fresh sources (filtration, sterilization) or desalinated from sea water (distillation, reverse osmosis). Pure water is dangerous in large amounts.
The nitrogen cycle converts atmospheric N2 into nitrates by nitrogen-fixing bacteria. Decomposers convert proteins into ammonia, which nitrifying bacteria turn into nitrates for plant absorption. Denitrifying bacteria convert nitrates back to N2 gas. Excessive man-made fertilizers can lead to eutrophication: runoff into water bodies causes algal blooms, blocking light, killing underwater plants, and leading to oxygen depletion by bacteria, harming aquatic life.
Biodiversity is the variety of organisms in an ecosystem; high biodiversity promotes stability but human development reduces it. Waste management (sewage, chemicals, pollution) is a growing problem. Land use for building, farming, and waste disposal (e.g., peat bog destruction) damages habitats and releases CO2. Deforestation reduces biodiversity and provides farmland. The pyramid of biomass shows biomass loss at each trophic level (not all consumed/absorbed, lost in living processes, waste). Food security is threatened by population growth, changing diets, transport costs, environmental changes, and conflicts. Sustainable fishing methods (e.g., nets with larger holes to allow young fish to escape) are vital to prevent species depletion.