Summary
Highlights
All life consists of cells. Electron microscopes offer higher resolution than light microscopes, revealing subcellular structures. Cell size can be calculated using magnification principles. Cells are categorized as eukaryotic (with a nucleus, e.g., plant and animal cells) or prokaryotic (without a nucleus, e.g., bacteria). Key cell structures include the semi-permeable cell membrane, cytoplasm (site of chemical reactions), mitochondria (respiration), and ribosomes (protein synthesis). Plant cells also have a cellulose cell wall, chloroplasts (photosynthesis), and a permanent vacuole.
Enzymes are biological catalysts that break down large molecules. Examples include amylase (starch to glucose), carbohydrases (carbohydrates to simple sugars), proteases (proteins to amino acids), and lipases (lipids to glycerol and fatty acids). Enzymes are specific, operating on a lock-and-key principle where the substrate binds to the active site. Enzyme activity increases with temperature until denaturation occurs at the optimum temperature or pH. A practical to investigate enzyme activity involves mixing amylase with starch at varying temperatures/pH and tracking starch breakdown with iodine solution.
Food tests identify nutrients: iodine for starch (orange to black), Benedict's for sugars (blue to brick red), Biuret reagent for proteins (blue to purple), and cold ethanol for lipids (cloudy). Diffusion is the passive movement of molecules from high to low concentration. Active transport uses energy to move substances against the concentration gradient via carrier proteins. Osmosis is the specific movement of water across a semi-permeable membrane. Factors increasing diffusion/osmosis include higher concentration differences, higher temperature, and larger surface area (e.g., villi, alveoli, root hair cells). A potato osmosis practical demonstrates water movement based on sugar solution concentration.
Eukaryotic DNA is stored in chromosomes within the nucleus (humans have 23 pairs in diploid cells, 23 in haploid gametes). Mitosis produces new identical cells for growth and repair, involving DNA duplication and cell division. Cells differentiate or specialize for specific functions (e.g., nerve, muscle). Stem cells are unspecialized cells found in embryos, plant meristems, and bone marrow. They have therapeutic potential for conditions like diabetes and paralysis. Cloning plants and animals also involves stem cells or manipulating early developmental stages.
The nervous system includes the Central Nervous System (brain, spinal cord) and Peripheral Nervous System (nerves). Receptors detect stimuli, sending electrical signals via sensory and relay neurons to the CNS. Neurotransmitters bridge synapses between neurons. Signals return via relay and motor neurons to effectors (muscles, glands). Reflexes are rapid, bypassing the brain. Reaction times can be investigated using a ruler drop test. The brain has specialized regions: cerebral cortex (higher functions), cerebellum (motor skills), and medulla (unconscious actions). The eye accommodates by changing lens shape for focus: ciliary muscles and suspensory ligaments work to adjust the lens. Key eye parts include the cornea, sclera, pupil, iris, and retina (containing rods for intensity and cones for color). Myopia and hyperopia are vision defects corrected by lenses or laser surgery.
Sexual reproduction (e.g., meiosis for gametes) introduces variation, aiding adaptation. Asexual reproduction (e.g., mitosis for clones) only requires one parent. The genome is an organism's total genetic material. DNA is a double helix with nucleotide bases (A-T, C-G) that code for amino acids, forming proteins. Mutations can alter protein function. Gene expression can be influenced by epigenetics. Traits are controlled by genes (alleles); dominant alleles are expressed over recessive ones. Punnett squares predict phenotype probability. Inherited disorders like polydactyly (dominant) and cystic fibrosis (recessive) are examples. Sex is determined by XX (female) or XY (male) chromosomes. Darwin's theory of evolution by natural selection explains adaptation and survival. Lamarck's ideas, once dismissed, find some truth in epigenetics. Antibiotic resistance in bacteria is a prime example of rapid evolution. Organisms producing fertile offspring belong to the same species. Selective breeding and genetic engineering allow manipulation of traits, such as creating insulin-producing bacteria or nutrient-enhanced crops (e.g., golden rice).
Diseases are either non-communicable (internal causes, e.g., cardiovascular disease, type 2 diabetes, cancer) or communicable (caused by pathogens like viruses, bacteria, fungi, or protists). Carcinogens increase cancer risk. BMI assesses weight health. Viruses infect cells to reproduce; bacteria release toxins. Our bodies defend against pathogens: skin, mucus, acid/enzymes. White blood cells (lymphocytes) produce antitoxins and antibodies, while phagocytes ingest pathogens. Immunity is gained when the immune system 'remembers' specific antigens. Vaccines introduce inactive pathogens to stimulate antibody production. Bacterial growth can be studied on agar in petri dishes using aseptic techniques and assessing zones of inhibition for antibiotics. Antibiotics kill bacteria but not viruses; their overuse leads to resistance. Drugs, originally plant-derived, are now synthesized and undergo rigorous trials (lab, animal, blind/double-blind human trials) to test efficacy and safety. Monoclonal antibodies, produced from hybridoma cells, offer targeted therapies for diseases and diagnostic tools, though side effects can be a concern.