Summary
Highlights
All life is made of cells. Light microscopes show basic cell structures, but electron microscopes provide higher resolution for subcellular details. Magnification calculation is explained: Magnification = Image Size / Object Size. Cells are categorized into eukaryotic (with a nucleus, e.g., plant and animal cells) and prokaryotic (no nucleus, e.g., bacteria). Cell membranes are semi-permeable. Plant cells have an additional cellulose cell wall for rigidity. Key organelles include cytoplasm (site of chemical reactions), mitochondria (respiration), ribosomes (protein synthesis), chloroplasts (photosynthesis in plants), and a permanent vacuole (plants).
Bacteria reproduce by binary fission. A practical involves culturing bacteria on agar in a petri dish using aseptic technique to prevent contamination. This includes lifting the lid towards a flame and using sterilized equipment. The culture is incubated at 25°C. The growth can be measured to calculate the initial drop size or the area where antibiotics inhibited growth (using πr² or πd²/4).
The genome is all genetic material in an organism, stored in DNA, a double helix polymer. A gene is a DNA section coding for a specific protein. The Human Genome Project mapped these genes, aiding in identifying disease-causing genes. Genotype is the genetic code, while phenotype is its expression. DNA monomers are nucleotides (A, T, C, G), with A pairing with T and C with G. Three bases code for an amino acid. mRNA copies the sequence, taking it to ribosomes for protein synthesis. Mutations can lead to non-functional proteins. Some DNA regulates gene expression, a field called epigenetics.
Enzymes are biological catalysts that break down larger molecules into smaller ones for absorption. Examples include amylase (starch to glucose), carbohydrases (carbohydrates to sugars), proteases (proteins to amino acids), and lipases (lipids to glycerol and fatty acids). Enzymes are specific due to their active site and the lock-and-key principle. Enzyme activity increases with temperature until the optimum is reached, after which they denature. pH also affects enzyme activity, with denaturation occurring at extreme pH levels.
A practical involves mixing amylase with starch at varying temperatures or pH. Iodine solution is used to test for starch presence; its disappearance indicates starch breakdown. The time taken is plotted against temperature or pH to find the optimum. Respiration, occurring in mitochondria, provides energy. Aerobic respiration (with oxygen) is glucose + oxygen → carbon dioxide + water + energy. During exercise, breathing and heart rates increase to supply more oxygen. Anaerobic respiration (without oxygen) converts glucose to lactic acid (animals) or ethanol and carbon dioxide (plants/yeast), releasing less energy. Lactic acid buildup causes an oxygen debt. Fermentation (anaerobic respiration in yeast) is used in baking and alcoholic drinks.
Metabolism is the sum of all chemical reactions in a cell/organism, including respiration, conversion of glucose to storage forms (starch, glycogen, cellulose), lipid synthesis, and protein breakdown. Photosynthesis in plant chloroplasts (containing chlorophyll) produces food: carbon dioxide + water (+ light energy) → glucose + oxygen. This is an endothermic reaction. Glucose is used for respiration, stored as starch/fat, or converted to cellulose or amino acids. The rate of photosynthesis is affected by temperature, light intensity, and CO2 concentration; one can be a limiting factor. Graphs show how a limiting factor affects the rate.
The rate of photosynthesis can be measured by submerging pondweed and collecting oxygen produced. Light intensity, varied by distance from a light source, affects the rate following an inverse square law. Diffusion is the passive movement of molecules from high to low concentration. Osmosis is the movement of water across a semi-permeable membrane. Factors increasing diffusion/osmosis include concentration difference, temperature, and surface area (e.g., villi, alveoli, root hair cells). Active transport uses energy to move substances against the concentration gradient via carrier proteins (e.g., mineral ions into root hair cells).
An osmosis practical uses potato cylinders in sugar solutions. Percentage change in mass is calculated after a day. A plot of these percentages against sugar concentration shows the potato's internal concentration where the line crosses the x-axis (no mass change). Eukaryotic cells have DNA in chromosomes (23 pairs in human diploid cells). Gametes are haploid (23 chromosomes). Mitosis is cell division for growth and repair: genetic material duplicates, nucleus breaks down, chromosomes separate, new nuclei form, resulting in two identical cells. Cells specialize (differentiate) for specific functions. Stem cells are unspecialized cells found in embryos and plant meristems; they can be used to treat conditions like diabetes and paralysis. Ethical considerations exist for stem cell research.
The heart is central to the double circulatory system. Deoxygenated blood enters the right side (vena cava → right atrium → right ventricle → pulmonary artery → lungs). Oxygenated blood returns to the left side (pulmonary vein → left atrium → left ventricle → aorta → body). The left ventricle has thicker walls due to pumping blood to the entire body. Electrical pulses from the right atrium regulate heartbeat; artificial pacemakers can assist. Arteries carry blood away from the heart (thick walls, high pressure, narrow lumen, except pulmonary artery). Veins carry blood towards the heart (thinner walls, lower pressure, valves to prevent backflow). Capillaries are tiny, thin-walled vessels for fast diffusion. The coronary artery supplies the heart muscle with oxygen; blockages cause coronary heart disease (CHD), leading to heart attacks. Stents and statins are treatments. Faulty heart valves can be replaced. Blood contains plasma, red blood cells, white blood cells (fight infection), and platelets (clotting).
Leaves are sites of photosynthesis and transpiration (water diffusion up the xylem). Transpiration rate increases with temperature, decreased humidity, and increased air movement. Roots absorb water and mineral ions. Meristems are growth regions. Phloem transports sugars (translocation). Nitrate deficiency stunts growth. Magnesium deficiency causes chlorosis (yellowing leaves) due to lack of chlorophyll. A leaf cross-section reveals: waxy cuticle (prevents water loss), upper epidermis (transparent), palisade mesophyll (most photosynthesis), spongy mesophyll (gas exchange, air spaces), vascular bundle (xylem and phloem), and lower epidermis with stomata (gas exchange pores controlled by guard cells). Stomata close at night to reduce water loss.
Homeostasis maintains stable internal conditions. The nervous system (CNS: brain, spinal cord; PNS: rest of body) regulates this. Receptors detect stimuli (e.g., heat), sending electrical signals via sensory and relay neurons to the spine, then to the brain. Neurotransmitters cross synapses between neurons. The brain processes the signal, sending a response via relay and motor neurons to effectors (e.g., muscles, glands). Reflexes bypass the brain for faster responses. Reaction time can be investigated using a ruler drop test, with factors like stimulants or depressants affecting results. Brain parts: cerebral cortex (memory, speech), cerebellum (motor skills, balance), medulla oblongata (unconscious actions, adrenaline release). MRI scans show brain activity. Brain injuries are hard to treat.
Accommodation is the eye's ability to focus light by changing lens shape. For far objects, ciliary muscles relax, suspensory ligaments tighten, lens thins. For near objects, ciliary muscles contract, suspensory ligaments slacken, lens fattens. The pupil (hole in iris) changes size with light intensity. The cornea is the transparent outer layer where light enters. The sclera is the white outer surface. The retina at the back contains rods (light intensity) and cones (color: green, blue, red) to detect light. Signals go to the brain via the optic nerve. Myopia (short-sightedness) and hyperopia (long-sightedness) are corrected with glasses, contact lenses, or laser eye surgery. Thermoregulation (temperature control) is a homeostatic process. When hot, sweat glands release sweat (evaporative cooling), and blood vessels dilate (vasodilation) to increase heat loss. When cold, blood vessels constrict (vasoconstriction), and shivering generates heat.
The endocrine system consists of glands producing hormones that travel via blood (slower than nervous signals). The pituitary gland (master gland) controls other glands. Examples include the pancreas (insulin), thyroid (metabolic rate), adrenal glands (adrenaline), and ovaries/testes (sex hormones). The pancreas regulates blood glucose: high glucose triggers insulin release (glucose to cells/glycogen in liver); low glucose triggers glucagon release (glycogen to glucose). Type 1 diabetes (insufficient insulin) requires insulin injections. Type 2 diabetes (cells don't absorb glucose) is linked to diet and obesity. Hormones like adrenaline (fight or flight) and thyroxine (metabolic rate) regulate body functions.
The body loses water via exhalation, sweat, and urination. Kidneys regulate water levels and filter blood, reabsorbing useful substances. ADH (antidiuretic hormone) from the pituitary gland controls water reabsorption in kidney tubules. Low water causes more ADH, increasing reabsorption; high water causes less ADH, increasing water loss in urine. This is negative feedback. Kidney failure requires dialysis. Menstruation in females involves FSH (matures egg, stimulates estrogen), estrogen (thickens uterine lining, inhibits FSH, stimulates LH), LH (releases egg), and progesterone (maintains uterine lining). Contraception options include pills (inhibit FSH), injections/implants (stop egg release), barrier methods (condoms, diaphragms), IUDs (prevent implantation), and permanent sterilization (vasectomy, tubal ligation). Infertility, sometimes due to hormone imbalances, can be treated with injections or IVF (in vitro fertilization), though success rates are low.
Plant hormones include gibberellins (seed germination, flowering, fruit size) and ethene (fruit ripening). Auxins control shoot and root growth. Auxins are destroyed by sunlight, accumulating on the shaded side of shoots, causing them to bend towards light (phototropism). In roots, auxins inhibit growth; accumulation on the bottom causes roots to grow downwards (geotropism). Auxins are used as weed killers, rooting powders, and for tissue culture. A mini investigation demonstrates geotropism by observing seeds on damp cotton wool in a petri dish turned on its side.