Comprehensive Biology Paper 1 Study Notes

Cell Biology: Eukaryotes, Prokaryotes, and Sub-cellular Structures

• Cells are the basic unit of all forms of life. The structural differences between various types of cells enable them to perform specific functions within the organism.
• These differences in cells are controlled by genes in the nucleus.
• Eukaryotic Cells:     - Plant and animal cells are eukaryotic cells.     - They possess a cell membrane, cytoplasm, and genetic material enclosed in a nucleus.
• Prokaryotic Cells:     - Bacterial cells are prokaryotic cells and are much smaller in comparison to eukaryotic cells.     - They have cytoplasm and a cell membrane surrounded by a cell wall.     - The genetic material is not enclosed in a nucleus.     - It consists of a single DNA loop and there may be one or more small rings of DNA called plasmids.
• Sub-cellular Structures in Animal Cells:     - Nucleus: Controls the activities of the cell.     - Cytoplasm: The site where most chemical reactions take place.     - Cell membrane: Controls the passage of substances into and out of the cell.     - Mitochondria: Where most energy is released in respiration.     - Ribosomes: The site where protein synthesis occurs.
• Sub-cellular Structures in Plant Cells:     - Plant cells often contain additional structures to those found in animal cells:     - Chloroplasts: These absorb light energy to make food.     - Permanent vacuole: Filled with cell sap.     - Cell wall: Made of cellulose, which serves to strengthen the cell (also found in algal cells).
• Cell Specialisation:     - Cells may be specialised to carry out a particular function:     - Animal examples: Sperm cells (carry half genetic info, tails for swimming), nerve cells (long up to $2\,m$ to carry messages), and muscle cells (change length to help movement).     - Plant examples: Root hair cells (large surface area to take in water), xylem cells, and phloem cells.     - Ciliated Epithelial Cells: Found in tubes leading to the lungs and in the oviduct; hairs (cilia) move dirt out of lungs and move eggs.     - Palisade Cells: Contain chloroplasts to help the plant make food via photosynthesis.

Cell Division and Stem Cell Technology

• For an organism to grow, cells must divide by mitosis, producing two new identical cells.
• Chromosomes:     - The nucleus contains chromosomes made of coiled DNA molecules.     - Each chromosome carries a large number of genes.     - In body cells, chromosomes are normally found in pairs.
• The Cell Cycle and Mitosis:     - Cells divide in a series of stages called the cell cycle.     - Before a cell can divide, it must grow and increase the number of sub-cellular structures such as ribosomes and mitochondria.     - The DNA replicates to form two copies of each chromosome.     - In mitosis, one set of chromosomes is pulled to each end of the cell and the nucleus divides.     - Finally, the cytoplasm and cell membranes divide to form two identical cells (daughter cells).     - Cell division by mitosis is essential for the growth and development of multicellular organisms.
• Stem Cells:     - A stem cell is an undifferentiated cell of an organism which is capable of giving rise to many more cells of the same type.     - Embryonic stem cells: Can be cloned and made to differentiate into most different types of human cells.     - Adult stem cells: From bone marrow; can form many types of cells including blood cells.     - Plant Meristem tissue: Can differentiate into any type of plant cell throughout the life of the plant.     - Applications: Treatment with stem cells may help conditions such as diabetes and paralysis.     - Therapeutic cloning: An embryo is produced with the same genes as the patient, so stem cells are not rejected.     - Risks: Transfer of viral infection and ethical/religious objections.     - Plant cloning: Meristems allow for quick, economical cloning to protect rare species from extinction or to produce large numbers of identical crop plants with disease resistance.

Transport in Cells: Diffusion, Osmosis, and Active Transport

• Diffusion:     - The spreading out of 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.     - Examples: Oxygen and carbon dioxide in gas exchange; urea from cells into blood plasma for excretion in the kidney.     - Factors affecting rate: Concentration gradient, temperature, and membrane surface area.     - Single-celled organisms have a large surface area to volume ratio, allowing sufficient transport of molecules.
• Osmosis:     - The diffusion of water from a dilute to a more concentrated solution through a partially permeable membrane.     - Water moves into or out of cells based on concentration differences between the inside and outside.
• Active Transport:     - Moves substances from a more dilute solution to a more concentrated solution (against a concentration gradient).     - Requires energy from respiration.     - Examples:         - Mineral ions being absorbed into plant root hairs from dilute solutions in the soil (required for healthy growth).         - Sugar molecules absorbed from lower concentrations in the gut into the blood (required for cell respiration).

Principles of Organisation and the Human Digestive System

• Cells are basic building blocks; tissues are groups of cells with similar structures/functions; organs are aggregations of tissues; organ systems work together to form organisms.
• Tissues in Animals:     - Muscular tissue: Contracts for movement.     - Epithelial tissue: Covers some parts of the body.     - Glandular tissue: Produces enzymes and hormones.
• The Stomach (as an organ):     - Contains muscular tissue (to churn contents), glandular tissue (to produce digestive juices), and epithelial tissue (to cover inside and outside).
• The Human Digestive System:     - Salivary glands and pancreas: Produce digestive juices.     - Stomach and small intestine: Where digestion occurs.     - Liver: Produces bile.     - Small intestine: Where absorption of soluble food occurs.     - Large intestine: Where water is absorbed from undigested food, producing faeces.
• Enzymes:     - Biological catalysts that increase the rate of chemical reactions.     - Enzymes are proteins with a specific active site; high temperatures denature them by changing the active site shape.     - Amylase: Produced in salivary glands, pancreas, and small intestine; breaks down starch into sugars.     - Protease: Produced in stomach, pancreas, and small intestine; breaks down proteins into amino acids.     - Lipase: Produced in pancreas and small intestine; breaks down lipids (fats and oils) into fatty acids and glycerol.     - Stomach Acid: Hydrochloric acid provides the acidic conditions for stomach enzymes to work effectively.     - Bile: Produced in liver, stored in gall bladder; neutralises stomach acid and emulsifies fats to increase surface area for lipase.

Chemistry of Food and Testing

• Carbohydrates: Made of units of sugar.     - Simple sugars (one or two units) turn Benedict's solution brick red on heating (original color blue).     - Complex carbohydrates (long chains) like starch turn yellow-red iodine solution blue-black.
• Lipids: Consist of one molecule of glycerol and three molecules of fatty acids; Ethanol test indicates presence.
• Proteins: Long chains of amino acids; Biuret reagent turns blue to purple in their presence.

The Cardiovascular and Respiratory Systems

• Lungs and Gaseous Exchange:     - Located in the thorax, protected by the ribcage, separated from the abdomen by the diaphragm.     - Ventilated by the ribcage moving out and up and the diaphragm flattening to move air in.     - Oxygen diffuses from the alveoli into red blood cells; carbon dioxide diffuses from blood plasma into the air.
• The Heart:     - A double circulatory system pumping blood to the lungs and the rest of the body.     - Four chambers: Left and right atria (receive blood), left and right ventricles (pump blood).     - Right ventricle pumps to lungs; left ventricle (thicker wall) pumps to the rest of the body.     - Valves prevent backflow.     - Natural heart rate is controlled by a pacemaker group of cells in the right atrium; artificial pacemakers can correct irregularities.
• Blood Vessels:     - Arteries: Thick walls with muscle and elastic fibres; carry blood under high pressure.     - Veins: Thinner walls with valves to prevent backflow; carry blood under low pressure.     - Capillaries: Narrow, thin-walled (single cell) for substance exchange between blood and tissues.
• Blood Composition:     - Plasma: Transports $CO_2$, soluble digestion products, and urea.     - Red Blood Cells: No nucleus; contains haemoglobin ($\text{Haemoglobin} + \text{oxygen} \rightleftharpoons \text{oxyhaemoglobin}$).     - White Blood Cells: Have a nucleus; part of the immune system.     - Platelets: Fragments of cells; no nucleus; assist blood clotting at wounds.

Disease and Health Issues

• Health: State of physical and mental well-being. Major causes of ill health include communicable/non-communicable diseases, diet, stress, and life situations.
• Coronary Heart Disease (CHD):     - Layers of fatty material build up in coronary arteries, reducing oxygen to the heart muscle.     - Stents: Used to keep arteries open.     - Statins: Reduce blood cholesterol levels to slow fatty deposit rates.     - Valves: Faulty valves replaced with biological or mechanical versions.     - Transplants: Donor hearts or artificial hearts (used while waiting or for recovery).
• Non-communicable Diseases and Risk Factors:     - Lifestyle factors: Diet, alcohol, and smoking.     - Proven causal mechanisms: Smoking (lung disease/cancer), Obesity (Type 2 diabetes), Alcohol (liver/brain function).     - Effects on unborn babies: Smoking and alcohol.     - Carcinogens: e.g., ionising radiation.
• Cancer:     - Caused by uncontrolled growth and division due to cell changes.     - Benign: Growth contained in one area, usually a membrane; does not invade other parts.     - Malignant: Cancers that invade neighboring tissues and spread via blood to form secondary tumours.
• Communicable Diseases:     - Caused by pathogens: Viruses, bacteria, protists, or fungi.     - Measles (Viral): Fever, red rash, spread by inhalation of droplets; serious/fatal.     - HIV (Viral): Flu-like illness; attacks immune cells; leads to AIDS if uncontrolled; spread by body fluids/needles.     - TMV (Viral): Discoloration on plant leaves (mosaic pattern), reduces photosynthesis.     - Salmonella (Bacterial): Food poisoning from unhygienic conditions; symptoms include cramps, vomiting, fever.     - Gonorrhoea (Bacterial): STD with discharge and pain on urinating; treated with penicillin (though resistance is high) and prevented by condoms.     - Rose black spot (Fungal): Purple/black spots on plant leaves; leaves turn yellow and drop; spread by wind/water; treated with fungicides.     - Malaria (Protist): Life cycle includes mosquito vector; causes recurrent fever; controlled by mosquito nets and preventing breeding.

Human Defence Systems and Treatment

• Non-specific Defenses: Skin, trachea/lung mucus, stomach hydrochloric acid, ear wax, tears, nostril hairs.
• Internal Defenses (White Blood Cells):     - Phagocytosis: Ingesting pathogens.     - Antibody production: Destroy specific bacteria/viruses.     - Antitoxin production: Counteract toxins.
• Vaccination: Introducing dead or inactive pathogens to stimulate antibody production; provides rapid response if the pathogen re-enters.
• Antibiotics and Painkillers:     - Antibiotics (e.g., Penicillin): Kill bacterial pathogens; specific bacteria require specific antibiotics. They DO NOT kill viruses.     - Antibiotic Resistance: Strains like MRSA develop via natural selection. Doctors avoid prescribing for minor infections/viruses.     - Painkillers: Treat symptoms but do not kill pathogens.
• Drug Discovery:     - Traditionally from plants/microorganisms: Digitalis (foxgloves), Aspirin (willow), Penicillin (Alexander Fleming from Penicillium mould).     - Most new drugs are synthesised by chemists after starting with plant chemicals.     - Testing: Preclinical (cells, tissues, live animals) followed by Clinical trials (healthy volunteers, then patients).     - Clinical Trials: Start with very low doses to check safety, then find optimum dose. Double-blind trials use placebos.

Plant Tissues, Organs, and Systems

• Plant Tissues: Epidermal (covers plant), Mesophyll (photosynthesis), Xylem and Phloem (transport), Meristem (growing tips).
• Transport SystemAdaptations:     - Root hair cells: Uptake water by osmosis and mineral ions by active transport.     - Xylem: Hollow tubes strengthened by lignin; transports water and mineral ions (the transpiration stream).     - Phloem: Elongated cells with pores in end walls; transports dissolved sugars (translocation) from leaves to the rest of the plant.     - Stomata and guard cells: Control gas exchange and water loss.
• Transpiration: The movement of water from roots through xylem and out of leaves. Affected by temperature, humidity, air movement, and light intensity.

Bioenergetics: Photosynthesis and Respiration

• Photosynthesis:     - Endothermic reaction: Energy transferred from environment to chloroplasts by light.     - Equation: $6CO_2 + 6H_2O + \text{Light energy} \rightarrow C_6H_{12}O_6 + 6O_2$     - Absorbed by chlorophyll in chloroplasts.     - Limiting factors: Shortage of light, low temperature, shortage of $CO_2$.     - Uses of Glucose: Respiration, converted to insoluble starch (storage), making fat/oil (storage), making cellulose (cell wall strength), making amino acids (protein synthesis with nitrate ions from soil).
• Cellular Respiration:     - Exothermic reaction continuously occurring in living cells to transfer energy.     - Aerobic Respiration: Using oxygen.     - Equation: $C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O (+ \text{energy})$     - Anaerobic Respiration in Muscles: No oxygen; glucose incompletely oxidised.     - Equation: $\text{Glucose} \rightarrow \text{lactic acid}$     - Less energy transferred than aerobic.     - Anaerobic Respiration in Plant/Yeast:     - Equation: $\text{Glucose} \rightarrow \text{ethanol} + \text{carbon dioxide}$     - In yeast, called fermentation; important for bread and alcoholic drinks.
• Response to Exercise:     - Increased demand for energy causes increased heart rate, breathing rate, and breath volume to supply oxygenated blood.     - Anaerobic respiration occurs if oxygen is insufficient, causing lactic acid build-up and oxygen debt.     - Lactic acid is transported by blood to the liver and converted back to glucose.     - Oxygen debt is the extra oxygen needed after exercise to react with and remove lactic acid.
• Metabolism:     - Sum of all reactions in a cell or body.     - Includes: Conversion of glucose to starch/glycogen/cellulose; forming lipids from glycerol and three fatty acids; forming amino acids from glucose and nitrate ions; respiration; breakdown of excess proteins to form urea for excretion.

Microscopy and Culturing Microorganisms

• Microscopy:     - Electron microscopes have higher magnification and resolving power than light microscopes.     - Calculation: $\text{Magnification} = \frac{\text{size of image}}{\text{size of real object}}$     - Prefixes: centi ($10^{-2}$), milli ($10^{-3}$), micro ($10^{-6}$), nano ($10^{-9}$).
• Culturing Microorganisms:     - Bacteria multiply via binary fission as often as every 20 minutes.     - Cultures grown in nutrient broth or agar gel plates.     - Techniques: Sterilise petri dishes and media; sterilise inoculating loops via flame; tape lid; store upside down.     - Incubation in schools: Maximum $25\,^{\circ}\text{C}$ to avoid human pathogen growth.     - Area of colony or clear zone calculated using $\pi r^2$ to measure antibiotic effectiveness.