B1-B8 Biology Study Topics
B1: Cell Structure and Transport
Cell Types and Classification * Eukaryotic Cells: These are cells that contain their genetic material (DNA) enclosed in a nucleus. Examples include all animal and plant cells. * Prokaryotic Cells: These are significantly smaller than eukaryotic cells (). Their genetic material is not enclosed in a nucleus; instead, it consists of a single DNA loop and may include small rings of DNA called plasmids. Bacterial cells are the primary example.
Organelles and Their Functions * Nucleus: Contains genetic material and controls the activities of the cell. * Cytoplasm: A jelly-like substance where most chemical reactions happen. It contains enzymes that control these reactions. * Cell Membrane: Controls the passage of substances into and out of the cell (e.g., glucose and mineral ions in, urea and hormones out). * Mitochondria: The site of aerobic respiration, where energy is released for the cell. * Ribosomes: The site of protein synthesis. * Chloroplasts (Plants only): Contain chlorophyll to absorb light for photosynthesis. * Permanent Vacuole (Plants only): Filled with cell sap to keep the cell turgid. * Cell Wall (Plants and Algae): Made of cellulose, which strengthens the cell and provides structural support.
Transport Processes * Diffusion: The spreading out of the particles of any substance in solution, or particles of a gas, resulting in a net movement from an area of higher concentration to an area of lower concentration. Factors affecting the rate include the concentration gradient, temperature, and surface area of the membrane. * Osmosis: The diffusion of water from a dilute solution (high water potential) to a concentrated solution (low water potential) through a partially permeable membrane. * Active Transport: Moves substances from a more dilute solution to a more concentrated solution (against a concentration gradient). This process requires energy released from respiration. Examples include mineral ions being absorbed into plant root hairs and sugar molecules being absorbed from the lower concentrations in the gut into the blood.
B2: Cell Division
Chromosomes and the Cell Cycle * The nucleus of a cell contains chromosomes made of DNA molecules. Each chromosome carries a large number of genes. In body cells, chromosomes are normally found in pairs. * Cells divide in a series of stages called the cell cycle. During the cell cycle, the genetic material is doubled and then divided into two identical cells.
Mitosis * Stage 1 (Interphase): The cell grows and increases the number of sub-cellular structures such as ribosomes and mitochondria. The DNA replicates to form two copies of each chromosome. * Stage 2 (Mitosis): One set of chromosomes is pulled to each end of the cell and the nucleus divides. * Stage 3 (Cytokinesis): The cytoplasm and cell membranes divide to form two identical daughter cells. * Function: Mitosis is essential for growth and development of multicellular organisms and for repairing damaged tissues.
Differentiation and Stem Cells * Differentiation: The process by which a cell changes to become specialized for its job. Most animal cells differentiate at an early stage, whereas many plant cells retain the ability to differentiate throughout life. * Stem Cells: An undifferentiated cell of an organism which is capable of giving rise to many more cells of the same type, and from which certain other cells can arise from differentiation. * Stem Cell Sources: * Embryonic Stem Cells: Can be cloned and made to differentiate into most different types of human cells. * Adult Stem Cells (Bone Marrow): Can form many types of cells including blood cells. * Meristem Tissue (Plants): Can differentiate into any type of plant cell throughout the life of the plant, allowing for the production of clones quickly and economically.
B3: Organisation and the Digestion System
Levels of Organisation * Tissues: A group of cells with a similar structure and function (e.g., muscular tissue, glandular tissue). * Organs: Aggregations of tissues performing specific functions (e.g., the stomach contains muscular, glandular, and epithelial tissues). * Organ Systems: Groups of organs that work together to perform a specific function (e.g., the digestive system).
The Digestive System and Enzymes * The digestive system is an organ system in which several organs work together to digest and absorb food. * Enzymes: Biological catalysts that speed up chemical reactions in living organisms. They have a specific active site that fits a specific substrate (the "lock and key" theory). * Amylase (Carbohydrase): Produced in the salivary glands and pancreas. It breaks down starch into simple sugars. * Protease: Produced in the stomach, pancreas, and small intestine. It breaks down proteins into amino acids. * Lipase: Produced in the pancreas and small intestine. It breaks down lipids (fats) into glycerol and fatty acids. * Bile: Made in the liver and stored in the gall bladder. It is alkaline to neutralize hydrochloric acid from the stomach and emulsifies fat to form small droplets which increase the surface area for lipase to work.
Food Tests (Qualitative Reagents) * Starch: Use Iodine solution. A positive result turns from browny-orange to blue-black. * Sugars: Use Benedict's solution and heat in a water bath. Higher concentrations of sugar turn the solution from blue to green, yellow, or brick-red. * Proteins: Use Biuret solution. A positive result turns from blue to purple/lilac. * Lipids: Use Sudan III stain or the ethanol emulsion test. Sudan III forms a red-stained oil layer on the surface.
B4: Organising Animals and Plants
The Heart and Blood Vessels * The heart is an organ that pumps blood around the body in a double circulatory system. The right ventricle pumps blood to the lungs; the left ventricle pumps blood to the rest of the body. * Structure: Includes the aorta, vena cava, pulmonary artery, pulmonary vein, and coronary arteries (which supply oxygenated blood to the heart muscle itself). * Blood Vessels: * Arteries: Carry blood away from the heart under high pressure; have thick muscular walls. * Veins: Carry blood back to the heart; have thinner walls and valves to prevent backflow. * Capillaries: Tiny vessels with walls one cell thick to allow for efficient exchange of substances.
Blood Composition * Plasma: The liquid portion transporting $CO_{2}$, digested food, urea, and hormones. * Red Blood Cells: Transport oxygen using haemoglobin; biconcave shape for large surface area. * White Blood Cells: Part of the immune system; defend against pathogens. * Platelets: Small fragments of cells that help blood to clot at wound sites.
Gas Exchange in the Lungs * The lungs are optimized for gas exchange. Air enters via the trachea, travels through bronchi and bronchioles to the alveoli. Alveoli have a large surface area, thin walls, and a good blood supply to maximize diffusion of oxygen into the blood and carbon dioxide out.
Plant Organisation * Leaf Structure: Includes the epidermis, palisade mesophyll (where most photosynthesis occurs), spongy mesophyll (with air spaces for gas exchange), and guard cells which open/close the stomata. * Xylem: Transports water and mineral ions from the roots to the stems and leaves. It is composed of hollow tubes strengthened by lignin adapted for the transpiration stream. * Phloem: Transports dissolved sugars from the leaves to the rest of the plant for immediate use or storage. This process is called translocation.
B5: Communicable Disease
Pathogens * Pathogens are microorganisms that cause infectious (communicable) disease. They may be viruses, bacteria, protists, or fungi. * Bacteria: May produce toxins that damage tissues and make us feel ill. * Viruses: Live and replicate inside cells, causing cell damage.
Specific Diseases and Symptoms * Measles (Viral): Symptoms include fever and a red skin rash. * HIV (Viral): Initially causes a flu-like illness; attacks the body's immune cells. Late-stage HIV is known as AIDS. * Tobacco Mosaic Virus (Viral): Gives a 'mosaic' pattern of discoloration on plant leaves, affecting growth due to lack of photosynthesis. * Salmonella (Bacterial): Food poisoning spread by bacteria in food; causes fever, abdominal cramps, vomiting, and diarrhoea. * Gonorrhoea (Bacterial): STD with symptoms of a thick yellow/green discharge and pain on urinating. * Rose Black Spot (Fungal): Purple or black spots develop on leaves, which then turn yellow and drop early. * Malaria (Protist): Spread by mosquitoes; causes recurrent episodes of fever and can be fatal.
Human Defence Systems * Non-specific Defences: Skin, nose (hair and mucus), trachea/bronchi (mucus and cilia), and stomach (hydrochloric acid). * Immune System (White Blood Cells): Work via phagocytosis (engulfing pathogens), antibody production (targeting specific antigens), and antitoxin production (neutralizing bacterial toxins).
B6: Preventing and Treating Disease
Medical Treatments * Vaccination: Involves introducing small quantities of dead or inactive forms of a pathogen into the body to stimulate the white blood cells to produce antibodies. If the same pathogen re-enters the body, the white blood cells respond quickly to produce the correct antibodies. * Antibiotics: Medicines (e.g., penicillin) that help to cure bacterial disease by killing infective bacteria inside the body. They cannot kill viral pathogens. * Painkillers: Used to treat the symptoms of disease but do not kill pathogens.
Drug Development and Testing * Traditionally, drugs were extracted from plants (e.g., digitalis from foxgloves, aspirin from willow) and microorganisms (e.g., penicillin from Penicillium mould). * Stages of Testing: 1. Preclinical Testing: Done in a laboratory using cells, tissues, and live animals to test for toxicity, efficacy, and dose. 2. Clinical Trials: Use healthy volunteers and patients. * Low doses are used initially to check for safety. * If safe, further trials are carried out to find the optimum dose. * Double-blind Trials: Some patients are given a placebo. Neither the doctor nor the patients know who has received the real drug.
B7: Non-Communicable Disease
Lifestyle Factors and Risk * Non-communicable diseases cannot be passed from person to person. Risk factors are linked to an increased rate of a disease. * Correlation vs. Causation: A risk factor may be correlated with a disease, but scientists must look for a causal mechanism (e.g., the effect of smoking on lung cancer).
Impact of Specific Factors * Diet, Smoking, and Exercise: Linked to cardiovascular disease. * Obesity: A strong risk factor for Type 2 diabetes. * Alcohol: Can cause liver disease and affect brain function. Alcohol consumption by pregnant women can cause fetal alcohol syndrome. * Smoking: Highly linked to lung disease and lung cancer. It also affects the development of unborn babies. * Carcinogens: Ionising radiation and certain chemicals are risk factors for various cancers.
B8: Photosynthesis
The Photosynthesis Equation * Photosynthesis is an endothermic reaction in which energy is transferred from the environment to the chloroplasts by light. * Word Equation: Carbon dioxide + water $\rightarrow$ glucose + oxygen * Chemical Equation:
Factors Affecting the Rate * Temperature: Low temperatures limit the kinetic energy of enzymes; high temperatures denature enzymes. * Light Intensity: As light intensity increases, the rate increases until another factor becomes limiting. * Carbon Dioxide Concentration: Increasing concentration increases the rate until it levels off. * Amount of Chlorophyll: If leaves are variegated or diseased, they have less chlorophyll to absorb light.
Uses of Glucose * The glucose produced in photosynthesis may be: * Used for respiration to release energy. * Converted into insoluble starch for storage. * Used to produce fat or oil for storage. * Used to produce cellulose, which strengthens the cell wall. * Used to produce amino acids for protein synthesis (plants also need nitrate ions from the soil for this).