Biology End of Year Exam Revision Guide PDF

Cell Structure Prokaryotic vs. Eukaryotic Cells ​ Prokaryotic Cells: ○​ Size: 1-10 μm. ○​ No nucleus; DNA is in a nucleoid region (single circular chromosome). ○​ Plasmids: Small circular DNA, often carry antibiotic resistance genes. ○​ Ribosomes: 70S ribosome...

Cell Structure Prokaryotic vs. Eukaryotic Cells ​ Prokaryotic Cells: ○​ Size: 1-10 μm. ○​ No nucleus; DNA is in a nucleoid region (single circular chromosome). ○​ Plasmids: Small circular DNA, often carry antibiotic resistance genes. ○​ Ribosomes: 70S ribosomes for protein synthesis. ○​ Cell wall: Made of peptidoglycan (murein). ○​ Flagella: Simple structure for movement. ○​ Pili: For attachment or conjugation. ​ Eukaryotic Cells: ○​ Size: 10-100 μm. ○​ DNA within a membrane-bound nucleus (linear chromosomes). ○​ Ribosomes: 80S ribosomes in cytoplasm; 70S in mitochondria and chloroplasts. ○​ Organelles are compartmentalized by membranes. Organelles and Their Functions 1.​ Nucleus: ○​ Double membrane with nuclear pores; contains nucleolus (site of rRNA synthesis). ○​ Controls cell activities via transcription. 2.​ Mitochondria: ○​ Site of ATP synthesis through aerobic respiration. ○​ Inner membrane forms cristae; the matrix contains enzymes for the Krebs cycle. 3.​ Ribosomes: ○​ Free in cytoplasm (proteins for internal use) or attached to rough ER (proteins for secretion). 4.​ Rough ER: ○​ Processes and folds proteins synthesized by bound ribosomes. 5.​ Smooth ER: ○​ Synthesizes lipids, steroids, and detoxifies harmful substances. 6.​ Golgi Apparatus: ○​ Modifies, packages, and sorts proteins and lipids into vesicles. ○​ Forms lysosomes. 7.​ Lysosomes: ○​ Contain hydrolytic enzymes for digestion (autophagy, autolysis). 8.​ Chloroplasts (plant cells): ○​ Photosynthesis occurs in the thylakoid membranes and stroma. 9.​ Vacuole (plant cells): ○​ Contains cell sap (storage of ions, sugars). ○​ Maintains turgor pressure for structural support. 10.​Cytoskeleton:  ○​ Microtubules: Shape, intracellular transport, spindle formation. ○​ Microfilaments: Cell movement, cytokinesis. ○​ Intermediate filaments: Mechanical strength. Microscopy 1.​ Light Microscope: ○​ Magnification: x1500; resolution ~200 nm. ○​ Can observe live specimens. 2.​ Electron Microscopes: ○​ Transmission Electron Microscope (TEM): High resolution, observes internal details. ○​ Scanning Electron Microscope (SEM): 3D images of surfaces. 1.1 Cells are the Basic Units of Life ​ Definition: Cells are the smallest structural and functional units of life. ​ Cell Theory: ○​ All living organisms are made of cells. ○​ Cells arise from pre-existing cells. ○​ The cell is the basic unit of structure and function. ​ Types of Organisms: ○​ Unicellular: Single-celled (e.g., bacteria, protozoa). ○​ Multicellular: Organisms made of many specialized cells (e.g., plants, animals). 1.2 Cell Biology and Microscopy ​ Microscopy is essential to studying cell structure. ​ Light Microscopy: ○​ Magnification: Up to x1500. ○​ Resolution: ~200 nm (cannot resolve most organelles). ○​ Stains enhance contrast (e.g., iodine for plant cells). 1.3 Plant and Animal Cells as Seen with a Light Microscope ​ Plant Cells: ○​ Visible structures: Cell wall, plasma membrane, nucleus, cytoplasm, chloroplasts, large central vacuole. ​ Animal Cells:  ○​ Visible structures: Plasma membrane, nucleus, cytoplasm (organelles not visible unless stained). Comparison: Feature Plant Cells Animal Cells Cell wall Present (cellulose) Absent Chloroplasts Present in photosynthetic cells Absent Vacuole Large, central, permanent Small, temporary if present 1.4 Measuring Size and Calculating Magnification ​ Magnification Formula:​ Magnification=Image sizeActual size\text{Magnification} = \frac{\text{Image size}}{\text{Actual size}}Magnification=Actual sizeImage size​​ Ensure units are consistent (e.g., convert mm to μm: 1 mm = 1000 μm). ​ Micrometer Measurements: ○​ 1 mm = 1000 μm. ○​ 1 μm = 1000 nm. ​ Using an Eyepiece Graticule: ○​ Calibrate using a stage micrometer. ○​ Measure specimen size directly. 1.5 Electron Microscopy ​ Advantages over Light Microscopy: ○​ Higher resolution (~0.1 nm). ○​ Greater magnification (up to x500,000). ​ Limitations: ○​ Specimens must be dead (vacuum environment). ○​ Time-consuming preparation and staining (e.g., heavy metals). Plant and Animal Cells as Seen with an Electron Microscope ​ Visible organelles include: ○​ Nucleus: Double membrane, nucleolus visible. ○​ Mitochondria: Cristae and matrix visible. ○​ Chloroplasts: Grana (stacks of thylakoids) and stroma visible. ○​ Endoplasmic Reticulum: Rough (with ribosomes) and Smooth.  ○​ Golgi Apparatus: Series of flattened sacs. ○​ Lysosomes: Membrane-bound vesicles. ○​ Ribosomes: Smaller dots (80S). Bacteria ​ Structure: ○​ Cell wall: Peptidoglycan. ○​ Plasma membrane: Regulates entry and exit. ○​ Cytoplasm: Contains 70S ribosomes and enzymes. ○​ Nucleoid: Circular DNA, no nucleus. ○​ Plasmids: Small, additional DNA molecules. ○​ Flagella: For motility. ○​ Pili: Attachment and conjugation. ​ Reproduction: Binary fission (asexual). Comparing Prokaryotic Cells with Eukaryotic Cells Feature Prokaryotic Cells Eukaryotic Cells Size 1-10 μm 10-100 μm Nucleus Absent Present DNA Circular, naked, in nucleoid region Linear, associated with histones Organelles Non-membrane-bound only (e.g., ribosomes) Membrane-bound (e.g., nucleus, ER) Ribosomes 70S 80S Cell Wall Peptidoglycan Cellulose (plants), absent in animals Viruses ​ Non-cellular Structure: ○​ Size: 20-300 nm (smaller than bacteria). ○​ Protein coat (capsid) surrounds nucleic acid (DNA or RNA). ○​ Some have a lipid envelope derived from the host cell. ​ Examples: ○​ DNA viruses: Adenoviruses. ○​ RNA viruses: Influenza, HIV. ​ Reproduction: ○​ Obligate intracellular parasites (cannot replicate without a host). ○​ Lifecycle: Attachment → Entry → Replication → Assembly → Release. Biological molecules: Biochemistry ​ Definition: Biochemistry studies chemical processes within and relating to living organisms. ​ Biomolecules are essential for life and include carbohydrates, lipids, proteins, nucleic acids, and water. ​ Importance: ○​ Provide structural components (e.g., cellulose, phospholipids). ○​ Act as energy stores (e.g., starch, glycogen). ○​ Serve functional roles (e.g., enzymes, hormones, DNA replication). The Building Blocks of Life ​ Elements in Biomolecules: 1.​ Carbon, hydrogen, oxygen, nitrogen, phosphorus, sulfur (CHONPS). 2.​ Carbon’s ability to form four covalent bonds enables diverse structures like chains, rings, and branched molecules. ​ Four Key Biomolecules: 1.​ Carbohydrates: Energy storage and structural roles. 2.​ Lipids: Energy storage, membrane structure, insulation. 3.​ Proteins: Enzymes, structural components, transport. 4.​ Water: Universal solvent, participates in metabolic reactions. Monomers, Polymers, and Macromolecules ​ Monomers: Small, basic molecular units. ○​ Examples: Glucose (monosaccharide), amino acids, nucleotides. ​ Polymers: Large molecules made of repeating monomer units, formed by condensation reactions. ○​ Examples: Starch, proteins, DNA. ​ Macromolecules: Large, complex molecules (e.g., proteins, polysaccharides). ​ Condensation Reaction: Forms covalent bonds between monomers, releasing water. ​ Hydrolysis Reaction: Breaks covalent bonds, using water. Carbohydrates ​ Structure: Contain carbon (C), hydrogen (H), and oxygen (O) in a 1:2:1 ratio (general formula: (CH2O)n(CH_2O)_n(CH2​O)n​). ​ Monosaccharides: Single sugar units. ○​ Examples: Glucose, fructose, galactose. ○​ α-glucose vs. β-glucose: Differ in the orientation of the -OH group on carbon 1. ​ Disaccharides: Two monosaccharides joined by a glycosidic bond. ○​ Examples: ​ Maltose: Glucose + Glucose. ​ Sucrose: Glucose + Fructose. ​ Lactose: Glucose + Galactose. ​ Polysaccharides: Long chains of monosaccharides. ○​ Starch: Energy storage in plants. ​ Amylose: Unbranched, helical structure. ​ Amylopectin: Branched, more easily hydrolyzed. ○​ Glycogen: Energy storage in animals, highly branched for rapid energy release. ○​ Cellulose: Structural component in plant cell walls; β-glucose chains linked by hydrogen bonds to form microfibrils. Lipids ​ Structure: Contain carbon, hydrogen, and oxygen but have a lower proportion of oxygen than carbohydrates. ​ Types: ○​ Triglycerides: ​ Glycerol + 3 fatty acids (joined by ester bonds through condensation reactions). ​ Saturated fatty acids: No double bonds, solid at room temperature (e.g., butter). ​ Unsaturated fatty acids: One or more double bonds, liquid at room temperature (e.g., olive oil). ○​ Phospholipids: ​ Glycerol, 2 fatty acids, and a phosphate group. ​ Hydrophilic head (phosphate) and hydrophobic tails (fatty acids). ​ Major component of cell membranes (phospholipid bilayer). ○​ Steroids: ​ Four fused carbon rings (e.g., cholesterol, hormones like estrogen and testosterone). ​ Functions: ○​ Long-term energy storage. ○​ Insulation and protection. ○​ Components of membranes. ○​ Signaling molecules (e.g., hormones). Proteins ​ Structure: Contain carbon, hydrogen, oxygen, nitrogen, and sometimes sulfur. ​ Monomer: Amino acids. ○​ General structure: Central carbon atom bonded to an amino group (-NH2), carboxyl group (-COOH), hydrogen atom, and an R group (variable side chain). ​ Formation: ○​ Amino acids joined by peptide bonds through condensation reactions. ​ Levels of Protein Structure: ○​ Primary: Sequence of amino acids in a polypeptide chain. ○​ Secondary: Folding into α-helices or β-pleated sheets (stabilized by hydrogen bonds). ○​ Tertiary: 3D folding due to interactions between R groups (hydrogen bonds, ionic bonds, disulfide bridges). ○​ Quaternary: Association of multiple polypeptide chains (e.g., hemoglobin). ​ Functions: ○​ Enzymes (e.g., amylase). ○​ Structural (e.g., collagen, keratin). ○​ Transport (e.g., hemoglobin). ○​ Immune response (e.g., antibodies). Water ​ Structure: Two hydrogen atoms covalently bonded to an oxygen atom. The molecule is polar due to the uneven distribution of charge. ​ Properties and Importance: 1.​ Solvent: ​ Dissolves polar molecules and ions (e.g., glucose, salts). ​ Medium for biochemical reactions. 2.​ High Specific Heat Capacity: ​ Absorbs large amounts of heat without a significant temperature change. ​ Stabilizes aquatic environments and body temperature. 3.​ High Latent Heat of Vaporization: ​ Evaporation of water (e.g., sweat) cools organisms. 4.​ Cohesion and Adhesion: ​ Water molecules stick together (cohesion) and to surfaces (adhesion). ​ Enables capillary action in plants. 5.​ Density: ​ Ice is less dense than liquid water, allowing it to float and insulate aquatic life. What is an Enzyme? ​ Definition: Enzymes are biological catalysts that speed up chemical reactions without being consumed. ​ Structure: ○​ Globular proteins with a specific 3D shape. ○​ The active site is a region where substrates bind, complementary in shape to the substrate. ​ Importance: ○​ Lower activation energy, enabling reactions to proceed at a faster rate and under milder conditions (e.g., body temperature). ○​ Highly specific to substrates due to their unique active sites. Mode of Action of Enzymes 1.​ Formation of Enzyme-Substrate Complex: ○​ Substrate binds to the enzyme's active site. ○​ Binding is specific and follows the lock-and-key model or the induced fit model: ​ Lock-and-Key Model: The active site is a perfect fit for the substrate. ​ Induced Fit Model: The active site molds to the substrate for a better fit. 2.​ Catalysis: ○​ Enzymes catalyse the reaction, breaking or forming bonds. ○​ Products are released from the active site. 3.​ Reusability: ○​ Enzymes remain unchanged after the reaction and can be reused. ​ Example: Catalase catalyzing the decomposition of hydrogen peroxide into water and oxygen. Investigating the Progress of an Enzyme-Catalyzed Reaction ​ Measure how quickly substrate is consumed or product is formed over time. ​ Key Techniques: 1.​ Measuring Gas Production: Collect oxygen released during the catalysis of hydrogen peroxide by catalase. 2.​ Color Change: Use colorimetric assays (e.g., starch breakdown by amylase monitored with iodine). 3.​ Mass Loss: Record the loss of mass in reactions producing gaseous products. ​ Reaction Phases: 1.​ Initial rate: Rapid due to a high concentration of substrate. 2.​ Plateau: Reaction rate decreases as substrate is consumed and fewer enzyme-substrate complexes form. Factors that Affect Enzyme Action 1.​ Temperature: ○​ Optimal Temperature: Maximum enzyme activity. ○​ Too high: Enzymes denature (loss of 3D structure). ○​ Too low: Reduced kinetic energy slows reactions. 2.​ pH: ○​ Enzymes have an optimal pH (e.g., pepsin in the stomach: pH 2; amylase in saliva: pH 7). ○​ Deviation from optimal pH disrupts ionic bonds, altering the active site. 3.​ Substrate Concentration: ○​ Increases reaction rate up to a saturation point where all active sites are occupied. 4.​ Enzyme Concentration: ○​ Directly proportional to reaction rate, provided substrate is not limiting. 5.​ Presence of Cofactors: ○​ Non-protein molecules or ions (e.g., zinc, magnesium) that assist enzyme activity. Comparing Enzyme Affinities ​ Enzyme Affinity: Refers to how strongly an enzyme binds to its substrate. ​ Michaelis-Menten Constant (KmK_mKm​): ○​ Represents the substrate concentration at which the enzyme works at half its maximum velocity (VmaxV_{max}Vmax​). ○​ Low KmK_mKm​: High affinity (enzyme binds substrate strongly). ○​ High KmK_mKm​: Low affinity (enzyme binds substrate weakly). ​ Using Lineweaver-Burk Plot: Double reciprocal graph to determine KmK_mKm​and VmaxV_{max}Vmax​. Enzyme Inhibitors 1.​ Competitive Inhibitors: ○​ Compete with substrate for binding to the active site. ○​ Can be overcome by increasing substrate concentration. ○​ Example: Malonate inhibits succinate dehydrogenase. 2.​ Non-Competitive Inhibitors: ○​ Bind to an allosteric site (not the active site), changing the enzyme’s shape and reducing its activity. ○​ Cannot be overcome by increasing substrate concentration. ○​ Example: Cyanide inhibits cytochrome c oxidase. 3.​ Irreversible Inhibitors:  ○​ Form covalent bonds with the enzyme, permanently disabling it. ○​ Example: Nerve gas inhibits acetylcholinesterase. Immobilizing Enzymes ​ Definition: Enzymes are fixed to a solid support or trapped in a gel to restrict movement. ​ Methods: ○​ Adsorption onto inert surfaces (e.g., glass beads). ○​ Entrapment in alginate beads or a cellulose matrix. ○​ Covalent bonding to a carrier. ​ Advantages: ○​ Enzymes can be reused. ○​ Products are enzyme-free (easier separation). ○​ Increased stability and resistance to denaturation. ​ Applications: ○​ Industrial Processes: Lactase to hydrolyze lactose in milk. ○​ Biosensors: Glucose oxidase immobilized in blood sugar monitors. The Importance of Membranes ​ Definition: Membranes are selectively permeable barriers that control the movement of substances into and out of cells and organelles. ​ Functions: 1.​ Compartmentalization: ​ Separate cellular environments (e.g., cytoplasm from the extracellular environment). ​ Maintain conditions for specific biochemical reactions (e.g., enzymes in lysosomes). 2.​ Communication: ​ Facilitate cell signaling through receptors and recognition. 3.​ Transport: ​ Regulate entry and exit of nutrients, waste, and signaling molecules. 4.​ Site of Biochemical Reactions: ​ Provide surfaces for reactions (e.g., ATP synthesis in mitochondria). Structure of Membranes  ​ Fluid Mosaic Model (proposed by Singer and Nicolson, 1972): 1.​ Phospholipid Bilayer: ​ Hydrophilic (polar) heads face outward. ​ Hydrophobic (nonpolar) tails face inward. 2.​ Proteins and lipids are embedded within the bilayer, forming a dynamic structure. ​ Key Components: 1.​ Phospholipids: ​ Form the bilayer; provide flexibility and create a hydrophobic barrier. 2.​ Proteins: ​ Integral (embedded) and peripheral (on the surface). ​ Involved in transport, signaling, and enzymatic activity. 3.​ Cholesterol: ​ Embedded within animal cell membranes. ​ Provides stability, reduces fluidity at high temperatures, and prevents solidification at low temperatures. 4.​ Glycolipids and Glycoproteins: ​ Lipids or proteins with carbohydrate chains. ​ Involved in cell recognition and signaling. Roles of the Molecules Found in Membranes 1.​ Phospholipids: ○​ Form a semi-permeable barrier. ○​ Allow passage of small, nonpolar molecules (e.g., oxygen, carbon dioxide). 2.​ Proteins: ○​ Channel Proteins: Facilitate diffusion of specific ions or molecules. ○​ Carrier Proteins: Involved in active transport and facilitated diffusion. ○​ Receptor Proteins: Bind signaling molecules and initiate cellular responses. 3.​ Cholesterol: ○​ Modulates membrane fluidity and mechanical stability. 4.​ Glycoproteins and Glycolipids: ○​ Serve as antigens for immune recognition. ○​ Facilitate cell adhesion and communication. Cell Signaling ​ Definition: The process by which cells communicate to coordinate responses and activities. ​ Process: ○​ Reception: ​ A signaling molecule (ligand) binds to a specific receptor on the membrane. ​ Examples: Hormones, neurotransmitters. ○​ Transduction:  ​ The receptor undergoes a conformational change, triggering a cascade of intracellular events. ​ Example: Activation of secondary messengers like cAMP. ○​ Response: ​ A specific cellular activity is triggered (e.g., gene expression, enzyme activation). ​ Types of Signaling: ○​ Autocrine: Signal acts on the same cell that produced it. ○​ Paracrine: Signal acts on nearby cells. ○​ Endocrine: Signal travels through the bloodstream to distant cells. ​ Receptor Examples: ○​ Ion Channel Receptors: Open or close in response to a ligand. ○​ G-Protein Coupled Receptors: Activate intracellular pathways via G-proteins. ○​ Enzyme-Linked Receptors: Activate enzymatic activity upon ligand binding (e.g., tyrosine kinases). Movement of Substances Across Membranes 1.​ Passive Transport (does not require energy): ○​ Diffusion: Movement of molecules from a high to low concentration gradient. ​ Examples: Oxygen, carbon dioxide. ○​ Facilitated Diffusion: ​ Involves channel or carrier proteins for polar molecules (e.g., glucose). ○​ Osmosis: Diffusion of water across a semipermeable membrane from low solute to high solute concentration. 2.​ Active Transport (requires energy in the form of ATP): ○​ Moves substances against their concentration gradient. ○​ Involves carrier proteins. ​ Example: Sodium-potassium pump. 3.​ Bulk Transport: ○​ Transport of large molecules or particles. ​ Endocytosis: ​ Phagocytosis: Engulfing solid particles (e.g., bacteria by white blood cells). ​ Pinocytosis: Engulfing liquids or small solutes. ​ Exocytosis: Vesicles fuse with the membrane to release contents outside the cell (e.g., secretion of enzymes). 4.​ Factors Affecting Transport: ○​ Membrane permeability. ○​ Concentration gradient. ○​ Temperature. ○​ Surface area to volume ratio. Growth and Reproduction ​ Importance: ○​ Growth: Increase in cell number through mitosis to build tissues and organs. ○​ Reproduction: Single-celled organisms reproduce via mitosis to produce genetically identical offspring. ○​ Tissue repair: Replacement of damaged or dead cells (e.g., skin regeneration). ​ Asexual Reproduction: ○​ Mitosis produces offspring without genetic variation (e.g., binary fission in bacteria). Chromosomes ​ Structure: ○​ DNA is tightly coiled around histone proteins, forming chromatin. ○​ During cell division, chromatin condenses into visible chromosomes. ​ Composition: ○​ Each chromosome consists of two sister chromatids joined at a centromere. ○​ Telomeres are repetitive sequences at the ends of chromosomes that protect genetic material. ​ Ploidy Levels: ○​ Diploid (2n2n2n): Two sets of chromosomes (e.g., somatic cells in humans). ○​ Haploid (nnn): One set of chromosomes (e.g., gametes in humans). ​ Human Chromosome Count: 46 chromosomes (23 pairs). The Cell Cycle ​ Definition: The sequence of events that a cell undergoes from one division to the next. 1.​ Interphase (90% of the cycle): ○​ G1 Phase (Gap 1): Cell growth, organelle production, and protein synthesis. ○​ S Phase (Synthesis): DNA replication occurs, doubling the genetic material. ○​ G2 Phase (Gap 2): Preparation for mitosis; synthesis of spindle proteins. 2.​ M Phase (Mitotic Phase): ○​ Includes mitosis and cytokinesis. 3.​ Checkpoints: Ensure accuracy: ○​ G1 Checkpoint: Verifies cell size, nutrients, and DNA integrity. ○​ G2 Checkpoint: Ensures DNA replication is complete and accurate. ○​ M Checkpoint: Confirms correct spindle attachment before anaphase. Mitosis  ​ Definition: Division of the nucleus resulting in two genetically identical daughter cells. ​ Stages: ○​ Prophase: ​ Chromosomes condense and become visible. ​ Nuclear envelope breaks down. ​ Spindle fibers form and attach to centromeres. ○​ Metaphase: ​ Chromosomes align at the metaphase plate (center of the cell). ○​ Anaphase: ​ Sister chromatids are pulled apart by spindle fibers to opposite poles. ○​ Telophase: ​ Chromosomes decondense into chromatin. ​ Nuclear envelopes reform around each set of chromosomes. ​ Cytokinesis: ○​ Division of the cytoplasm. ○​ In animal cells: Cleavage furrow forms. ○​ In plant cells: A cell plate forms, leading to new cell walls. The Role of Telomeres ​ Definition: Telomeres are repetitive DNA sequences at the ends of chromosomes. ​ Functions: ○​ Protect chromosomes from degradation and fusion with other chromosomes. ○​ Prevent loss of essential genes during DNA replication. ​ Telomere Shortening: ○​ Occurs with each cell division; associated with aging and the Hayflick limit (maximum number of divisions). ○​ Telomerase enzyme extends telomeres in certain cells (e.g., stem cells, cancer cells). The Role of Stem Cells ​ Definition: Undifferentiated cells capable of self-renewal and differentiation into specialized cell types. ​ Types: ○​ Embryonic Stem Cells: ​ Pluripotent: Can differentiate into any cell type in the body. ○​ Adult Stem Cells: ​ Multipotent: Limited to differentiating into specific cell types (e.g., hematopoietic stem cells for blood cells). ​ Functions: ○​ Regeneration and repair of tissues. ○​ Used in medical therapies (e.g., bone marrow transplants). ​ Applications:  ○​ Research on treating diseases like Parkinson’s, diabetes, and spinal cord injuries. Cancers ​ Definition: Uncontrolled cell division resulting in abnormal growths (tumors). ​ Causes: ○​ Mutations: Changes in genes that regulate the cell cycle (e.g., proto-oncogenes to oncogenes, tumor suppressor gene loss). ○​ Carcinogens: Environmental factors like tobacco smoke, radiation, and certain chemicals. ○​ Genetic Predisposition: Inherited mutations (e.g., BRCA1/BRCA2 in breast cancer). ​ Types of Tumors: ○​ Benign: Non-invasive, do not spread to other tissues. ○​ Malignant: Invasive, metastasized to other parts of the body via blood or lymph. ​ Treatments: ○​ Surgery: Removal of tumors. ○​ Chemotherapy: Drugs to kill dividing cells. ○​ Radiation: Targets and destroys cancer cells. ○​ Immunotherapy: Boosts the immune system to target cancer cells.