Summary
Highlights
All life consists of cells. Electron microscopes offer higher resolution and better resolving power than light microscopes, allowing for detailed viewing of subcellular structures. The actual size of a cell can be calculated using the formula: Magnification = Image size / Object size. Cells are categorized into eukaryotic (with a nucleus, e.g., plant and animal cells) and prokaryotic (without a nucleus, e.g., bacteria).
The cell membrane is selectively permeable. Plant cells have an additional cell wall made of cellulose for rigidity; bacterial cell walls are not cellulose. Cytoplasm is the liquid where most chemical reactions occur. Mitochondria are the site of respiration, releasing energy. Ribosomes are where proteins are synthesized. Plant cells also have chloroplasts for photosynthesis (containing chlorophyll) and a permanent vacuole for sap storage.
Bacteria multiply by binary fission. A practical involves culturing bacteria on agar in a petri dish using aseptic techniques to prevent contamination. The dish is sealed partially to allow aerobic respiration and incubated at 25°C. After growth, the size of the culture or zones of inhibition (by antibiotics) can be calculated using the area formula: πr² or πd²/4.
Eukaryotic cells have DNA in chromosomes (humans have 23 diploid pairs in somatic cells, 23 haploid in gametes). Mitosis is the process of cell division for growth and repair, producing two identical daughter cells after genetic material duplication. Cells specialize or differentiate to fulfill specific functions (e.g., nerve, muscle, root hair cells). Stem cells are unspecialized, found in embryos and plant meristems, and can be used to treat conditions like diabetes and paralysis or for plant cloning.
Diffusion is the passive movement of molecules from high to low concentration down a concentration gradient. Osmosis is the specific movement of water across a semi-permeable membrane. Rates of diffusion and osmosis increase with higher concentration differences, temperature, or surface area (e.g., villi, alveoli, root hair cells). Active transport uses energy to move substances against a concentration gradient, via carrier proteins (e.g., mineral ions into root hair cells).
A practical for osmosis involves placing equal-sized potato cylinders in varying sugar solutions, weighing them before and after. Percentage change in mass is calculated, and plotting this against sugar concentration allows identification of the potato's internal concentration where no mass change occurs (no osmosis).
Similar cells form tissues, tissues form organs, and organs work together in organ systems. The digestive system breaks down food. Bile from the liver (stored in the gallbladder) neutralizes stomach acid and emulsifies fats, increasing surface area for enzyme action. Enzymes are biological catalysts, specific to their substrates (lock and key principle).
Amylase breaks down starch, proteases break down proteins, and lipases break down lipids. Enzyme activity increases with temperature until denaturation occurs at the optimum temperature. pH also affects enzyme activity, with denaturation at extreme values. A practical for enzyme activity involves testing starch breakdown with amylase at various temperatures or pH using iodine solution. Food tests include iodine for starch (orange to black), Benedict's for sugar (blue to brick red), Biuret for protein (blue to purple), and cold ethanol for lipids (cloudy).
Breathing delivers oxygen for respiration. Air travels down the trachea, bronchi, bronchioles to alveoli where gas exchange occurs due to their large surface area. Oxygen binds to hemoglobin in red blood cells. The heart is a double circulatory system. Deoxygenated blood enters the right side, goes to the lungs for oxygenation via the pulmonary artery, returns to the left side via the pulmonary vein, and is pumped to the body via the aorta. The left ventricle has thicker walls for systemic circulation, while the right ventricle pumps to the lungs. A natural pacemaker in the right atrium regulates heartbeats; artificial pacemakers can be used if necessary.
Arteries carry blood away from the heart (thick walls, high pressure), veins carry it towards (thinner walls, lower pressure, with valves), and capillaries are tiny, one-cell thick for efficient diffusion. Coronary arteries supply the heart muscle; blockage leads to coronary heart disease (CHD). Stents keep vessels open, statins reduce cholesterol. Faulty heart valves can be replaced. Blood contains plasma, red blood cells, white blood cells (for infection), and platelets (for clotting).
Cardiovascular disease (CVD) is a non-communicable disease. Other examples include allergic reactions and cancer. Communicable diseases are caused by pathogens (viruses, bacteria, fungi, protests). Lifestyle factors like diet, smoking, and lack of exercise increase disease risk. Cancer involves uncontrolled cell division leading to tumors; carcinogens increase risk. Benign tumors don't spread, malignant ones do. BMI indicates healthy weight relative to height.
Leaves are sites of photosynthesis (food production) and transpiration (water diffusion out of the plant). The rate of transpiration increases with temperature, decreased humidity, and increased air movement. Roots absorb water and mineral ions. Meristems are growth regions. Phloem transports sugars and sap throughout the plant (translocation). Nitrate deficiency stunts growth by impairing protein synthesis. Magnesium deficiency causes chlorosis (yellowing of leaves) due to reduced chlorophyll production.
A leaf has a waxy cuticle (prevents water loss), an upper epidermis (transparent, allows light), a palisade mesophyll (main site of photosynthesis), a spongy mesophyll (gaps for gas exchange), and a lower epidermis with stomata (pores for gas exit/entry) controlled by guard cells.
Pathogens (viruses, bacteria, fungi, protests) reproduce in the body and cause damage. Viruses inject genetic material into cells to replicate (e.g., Measles, HIV). Bacteria release toxins (e.g., Salmonella, Gonorrhea). Fungi (e.g., athlete's foot) and protests (e.g., Malaria, spread by mosquitoes) also cause infections. Plants are susceptible to fungal infections (rose black spot) and viruses (tobacco mosaic virus). The body's defenses include skin, mucus, acid, enzymes, and white blood cells (lymphocytes produce antitoxins and antibodies, phagocytes engulf pathogens). Vaccines expose the immune system to inert pathogens to build immunity.
Antibiotics kill bacteria but not viruses. Overuse leads to antibiotic resistance due to bacterial mutation. Drugs are screened through lab trials (cell tissue), animal trials, and human trials (blind and double-blind to prevent bias). Monoclonal antibodies are clones producing specific antibodies, made by fusing mouse lymphocytes with tumor cells. They are used in treating diseases, diagnosis, and detecting molecules, but have potential side effects.
Photosynthesis (endergonic reaction) occurs in chlorophyll in chloroplasts, producing glucose (used for respiration, stored as starch/fat, or converted to cellulose/amino acids). Rate of photosynthesis is increased by higher temperature (up to optimum), light intensity, and CO2 concentration. Any of these can be a limiting factor. A practical measures oxygen production from pondweed at varying light intensities.
Respiration, occurring in mitochondria, provides energy. Aerobic respiration (with oxygen) is the opposite of photosynthesis. During exercise, heart and breathing rate increase to supply more oxygen. Anaerobic respiration (without oxygen) produces lactic acid (in animals, causing muscle ache and oxygen debt) or ethanol and carbon dioxide (in plants/yeast, called fermentation). Metabolism is the sum of all chemical reactions in an organism.