Definitions topic 2 biology

• Cell-Surface Membrane – A phospholipid bilayer with embedded proteins that controls the movement of substances into and out of the cell.

• Nucleus – The organelle containing genetic material (DNA) in the form of chromosomes, surrounded by a nuclear envelope.

• Mitochondrion – The site of aerobic respiration, providing ATP for cellular functions.

• Golgi Apparatus – An organelle responsible for modifying, packaging, and transporting proteins and lipids.

• Lysosomes – Membrane-bound vesicles containing hydrolytic enzymes that break down cellular waste.

• Ribosomes – Organelles responsible for protein synthesis, found in the cytoplasm or attached to the rough endoplasmic reticulum.

• Rough Endoplasmic Reticulum (RER) – A membrane system covered with ribosomes involved in the synthesis and transport of proteins.

• Smooth Endoplasmic Reticulum (SER) – A membrane system involved in lipid synthesis and detoxification.

• Chloroplast – An organelle found in plant and algae cells, responsible for photosynthesis.

• Cell Wall – A rigid structure made of cellulose (plants), chitin (fungi), or other polysaccharides, providing support and protection.

• Cell Vacuole – A membrane-bound organelle in plant cells that contains cell sap, aiding in maintaining turgor pressure.

Prokaryotic Cells

• Plasmids – Small, circular DNA molecules in bacteria that can replicate independently of the chromosomal DNA.

• Binary Fission – The method of asexual reproduction in prokaryotic cells, involving replication of circular DNA and division of the cytoplasm.

• Flagella – Tail-like structures in bacterial cells that aid in movement.

Viruses

• Human Immunodeficiency Virus (HIV) – A virus that infects T cells, leading to AIDS by weakening the immune system.

• Viruses Replication – Viruses are acellular and replicate by injecting their genetic material into host cells, using the host’s cellular machinery to produce new virus particles.

Microscopy & Cell Fractionation

• Magnification – The ratio of an image’s size to the actual size of the specimen.

• Resolution – The ability to distinguish between two separate points in an image.

• Fluid-Mosaic Model – The model describing the structure of the plasma membrane as a flexible bilayer with embedded proteins.

Cell Cycle & Mitosis

• Cell Cycle – The sequence of phases (interphase, mitosis, cytokinesis) that prepare a cell for division.

• Mitosis – The process by which a eukaryotic cell divides to produce two genetically identical daughter cells.

• Cytokinesis – The division of the cytoplasm, following mitosis, to form two separate daughter cells.

Immune System & Immunity

• Antigen – A marker molecule on the surface of a pathogen that triggers an immune response.

• Antibody – A protein produced by plasma cells that binds to specific antigens.

• Agglutination – The clumping of pathogens by antibodies, aiding in their destruction.

• Phagocytosis – The process by which phagocytes engulf and destroy pathogens.

• Helper T Cells – A type of white blood cell that activates other immune cells.

• Active Immunity – Immunity developed when the body produces its own antibodies in response to a pathogen.

• Passive Immunity – Immunity gained through the introduction of external antibodies (e.g., from breast milk or injections).

• Herd Immunity – Protection from disease achieved when a large portion of the population is vaccinated.

• Primary Immune Response – The immune system’s first response to a pathogen, typically slower as memory cells are not yet present.

• Secondary Immune Response – A faster, stronger immune response due to memory cells recognising a previously encountered pathogen.

• Monoclonal Antibodies – Identical antibodies produced from a single cloned plasma cell, often used in medical diagnostics and treatments.

• Clonal Selection – The process of selecting the correct B or T lymphocyte with receptors that match the pathogen’s antigens.

• Clonal Expansion – The rapid multiplication of the selected lymphocytes to fight the infection.

Membrane Transport

• Simple Diffusion – The passive movement of molecules from an area of high concentration to low concentration.

• Facilitated Diffusion – The passive movement of molecules across a membrane via transport proteins.

• Osmosis – The diffusion of water molecules from a region of high water potential to low water potential through a selectively permeable membrane.

• Active Transport – The movement of molecules against a concentration gradient using ATP and transport proteins.

• Co-Transport – A type of membrane transport where two molecules move together, often involving a concentration gradient.