2. Cell Structure: Definitions (AQA A-Level Biology): Revision Notes
2. Cell Structure: Definitions
Active immunity: A type of immunity that develops when the body's immune system responds to a pathogen by producing specific antibodies and memory cells.
Active transport: The movement of substances against their concentration gradient from areas of low concentration to high concentration, requiring energy from ATP.
Agglutination: The process where cells or particles clump together when antibodies bind to them, making phagocytosis more effective.
Antibody: A Y-shaped protein molecule produced by plasma cells that specifically binds to antigens as part of the immune response.
Antigen: Foreign molecules or markers that can be recognised by antibodies and stimulate an immune response in the body.
Binary fission: A method of asexual reproduction in prokaryotic cells where the circular DNA replicates before the cell divides into two identical daughter cells.
Cell cycle: The sequence of events that prepare a cell for division, including interphase (growth and DNA replication) and mitosis.
Cell-surface membrane: A phospholipid bilayer containing embedded proteins that encloses cells and controls what enters and leaves the cell.
Cell vacuole: A membrane-enclosed compartment in plant cells that stores cell sap and helps maintain structural support.
Cell wall: A rigid outer layer made of polysaccharides that surrounds plant, algae, and fungal cells, providing structural strength and protection.
Chloroplast: A membrane-bound organelle in plant and algal cells where photosynthesis occurs, containing chlorophyll pigments.
Clonal expansion: The rapid multiplication of specific B or T lymphocytes after they have been activated by antigen recognition.
Clonal selection: The mechanism by which specific lymphocytes are chosen and activated when their receptors match antigens presented by antigen-presenting cells.
Clonal selection and expansion work together - first specific immune cells are selected based on antigen recognition, then those selected cells multiply rapidly to mount an effective immune response.
Co-transport: A transport mechanism where two different substances are moved across a membrane simultaneously, either in the same or opposite directions.
Cytokinesis: The final stage of cell division where the cytoplasm splits to form two separate daughter cells.
Facilitated diffusion: The passive movement of substances down their concentration gradient through specific transport proteins, without requiring energy.
Flagella: Long, whip-like projections from bacterial cells that rotate to enable cell movement and locomotion.
Fluid-mosaic model: The current model describing cell membrane structure as a flexible layer of phospholipids with embedded proteins that can move laterally.
Golgi apparatus: A stack of flattened membrane sacs in eukaryotic cells responsible for modifying, packaging, and dispatching proteins from the endoplasmic reticulum.
Helper T cell: A type of white blood cell that coordinates immune responses by activating other immune cells including cytotoxic T cells, B cells, and phagocytes.
Herd immunity: Protection from disease that occurs when a high percentage of a population is vaccinated, preventing disease transmission to unvaccinated individuals.
Human Immunodeficiency Virus (HIV): A retrovirus that specifically targets and destroys T helper cells, potentially leading to acquired immunodeficiency syndrome (AIDS).
Lysosomes: Membrane-bound organelles containing digestive enzymes called lysozymes that break down waste materials and worn-out cell components.
Magnification: The degree to which an image appears larger than the actual object, calculated using: .
Mitochondrion: A double-membraned organelle in eukaryotic cells that carries out aerobic respiration to produce ATP.
Mitosis: The stage of the cell cycle where a eukaryotic cell nucleus divides to produce two genetically identical daughter cells.
Monoclonal antibodies: Identical antibodies produced by cloned immune cells that all originate from a single parent cell.
Nucleus: The membrane-bound control centre of eukaryotic cells that houses chromosomes and is surrounded by the nuclear envelope
Osmosis: The passive movement of water molecules through a selectively permeable membrane from a region of high water potential to low water potential.
Passive immunity: Temporary immunity gained by receiving ready-made antibodies rather than producing them through one's own immune response.
Phagocytosis: The process by which phagocytes engulf and digest foreign particles, pathogens, or cellular debris.
Plasmids: Small, circular pieces of DNA found in bacterial cells that exist independently of the main chromosome.
Primary immune response: The initial, slower immune reaction when the body encounters a specific pathogen for the first time.
Resolution: The ability of a microscope to distinguish between two separate points that are close together in a specimen.
Ribosomes: Small organelles found free in the cytoplasm or attached to membranes that synthesise proteins by translating messenger RNA.
Rough endoplasmic reticulum (RER): A membrane system studded with ribosomes that synthesises and packages proteins for secretion or membrane incorporation.
Secondary immune response: The faster, more intense immune reaction when the body encounters a previously encountered pathogen, mediated by memory cells
Simple diffusion: The passive movement of substances from high to low concentration directly through cell membranes without requiring energy or transport proteins.
Smooth endoplasmic reticulum (SER): A ribosome-free membrane system involved in lipid synthesis and detoxification processes.
Vaccine: A preparation containing dead, weakened, or inactive pathogens that stimulates immunity and provides long-term protection against disease.
Key Points to Remember:
- Cell membranes control transport through various mechanisms - simple diffusion, facilitated diffusion, active transport, and osmosis each work differently
- Organelles have specific functions - mitochondria for respiration, chloroplasts for photosynthesis, ribosomes for protein synthesis
- The immune system has two main types of responses - active immunity (body produces its own antibodies) and passive immunity (receives ready-made antibodies)
- Cell division involves the cell cycle, with mitosis producing identical daughter cells and cytokinesis splitting the cytoplasm
- Transport proteins enable substances to cross membranes, with some requiring energy (active transport) and others working passively