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LS Biology Unit 2
| Term | Definition |
|---|---|
| Organelles | Specialized structures inside cells that perform specific jobs such as mitochondrion or ribosome |
| Cells | Basic unit of life that carry out all necessary life functions |
| Tissues | Groups of similar cells working together to perform a specific function |
| Organs | Structures made of multiple tissues that perform particular tasks |
| Organ Systems | Groups of organs that interact to complete major body functions |
| Organism | A whole living individual made up of interacting organ systems |
| Cell membrane | Semi-permeable barrier that separates a cell from its environment and controls what enters and exits |
| Receptor | Membrane protein that recognizes and binds chemical signals by shape‑matching |
| Diffusion | Passive movement of molecules from an area of high concentration to an area of low concentration |
| Osmosis | Diffusion of water across a membrane from high water (low solute) to low water (high solute) |
| Passive transport | Movement of substances across membranes without cellular energy - includes diffusion and facilitated diffusion |
| Active transport | Movement of substances against a concentration gradient that requires cellular energy (ATP) and transport proteins |
| Facilitated diffusion | Passive transport of polar or large molecules through membrane proteins (channels or carriers) |
| Circulatory system | Body system that moves blood, nutrients, gases and wastes around the body |
| Heart | Muscular pump that drives blood through the circulatory system |
| Arteries | Blood vessels that carry blood away from the heart with thick muscular walls |
| Veins | Blood vessels that carry blood toward the heart and often contain valves to prevent backflow |
| Capillaries | Tiny one-cell-thick blood vessels where exchange (diffusion) of gases and nutrients occurs |
| Plasma | Liquid portion of blood that carries cells and dissolved substances |
| Red blood cells | Blood cells that transport oxygen to tissues and carry carbon dioxide to the lungs |
| White blood cells | Immune cells that identify and fight pathogens |
| Platelets | Cell fragments that help blood clot and repair damaged tissue |
| Respiratory system | System that brings in oxygen and removes carbon dioxide from the body |
| Lungs | Primary organs where gas exchange with the blood occurs |
| Alveoli | Small air sacs in the lungs surrounded by capillaries where gas exchange takes place |
| Bronchioles | Small airway branches that lead air to alveoli |
| Trachea | Windpipe that conducts air to the bronchi; held open by cartilage rings |
| Cilia | Tiny hairlike projections that move mucus and trapped particles out of the airways |
| Digestive system | System that breaks down food into absorbable nutrients for the body |
| Stomach | Organ that uses acid and enzymes to begin protein digestion |
| Small intestine | Organ where most digestion and nutrient absorption occur |
| Large intestine | Organ that absorbs water and compacts feces |
| Villi | Fingerlike projections in the small intestine that increase surface area for absorption into capillaries |
| Salivary glands | Accessory glands that secrete saliva to moisten and begin carbohydrate digestion |
| Liver | Accessory organ that produces bile and processes nutrients and toxins |
| Pancreas | Gland that secretes digestive enzymes and hormones such as insulin |
| Gallbladder | Organ that stores and concentrates bile produced by the liver |
| Excretory system | System that removes metabolic wastes and helps regulate water and salt balance |
| Kidneys | Organs that filter blood to form urine and regulate water, salts and waste |
| Nephron | Functional filtering unit inside the kidney |
| Ureter | Tube that carries urine from each kidney to the bladder |
| Bladder | Muscular organ that stores urine until elimination |
| Urethra | Tube that conducts urine out of the body |
| Nervous system | Fast communication system using neurons and neurotransmitters for targeted responses |
| Neuron | Nerve cell that transmits electrical and chemical signals |
| Neurotransmitter | Chemical messenger released at synapses to transmit signals between neurons |
| Endocrine system | Slower chemical communication system using hormones released into the blood |
| Gland | Organ that secretes hormones |
| Hormone | Chemical messenger released into the bloodstream that affects target cells with matching receptors |
| Immune system | Body system that defends against pathogens and maintains internal stability |
| Pathogen | Disease-causing agent such as a virus, bacteria, fungus or parasite |
| Antigen | Molecule on a pathogen that triggers an immune response |
| Antibody | Protein produced by B cells that binds a specific antigen to neutralize or mark it for destruction |
| Macrophage | Immune cell that engulfs pathogens and displays antigens to trigger responses |
| Helper T cell | Immune cell that recognizes presented antigens and activates B cells and killer T cells |
| B cell | White blood cell that produces antibodies specific to antigens |
| Killer T cell | Immune cell that destroys infected body cells |
| Memory cell | Long-lived immune cell that provides faster response on re-exposure to the same antigen |
| Vaccine | Preparation that exposes the immune system to part or a weakened/dead form of a pathogen to generate memory cells and antibodies |
| Homeostasis | Maintenance of a relatively constant internal environment despite external changes |
| Set point | Target value the body maintains for a variable (37°C for body temperature) |
| Negative feedback | Response that reduces deviation from a set point to restore balance |
| Positive feedback | Response that amplifies a change until a specific outcome is reached then stops |
| Thermoregulation | Process of maintaining stable internal body temperature |
| ADH (antidiuretic hormone) | Hormone released by the pituitary that increases kidney water reabsorption to conserve water |
| Enzyme | Biological catalyst, usually a protein that speeds up chemical reactions without being consumed |
| Substrate | Molecule on which an enzyme acts |
| Active site | Region of an enzyme where the substrate binds; shape-specific |
| Denature | Irreversible change in an enzyme’s shape and function due to extreme pH or temperature |
| Optimum | Conditions (pH, temperature or concentration) at which an enzyme functions best |
| Catalyst | Substance that increases the rate of a reaction; enzymes are biological catalysts |
| Independent variable | The factor deliberately changed in an experiment |
| Dependent variable | The measured outcome that responds to changes in the independent variable |
| Control group | Baseline group used for comparison in an experiment |
| Controlled variables | Factors kept constant to ensure a fair test |
| Diabetes (Type 1) | Autoimmune disease where the immune system destroys insulin-producing pancreatic cells preventing blood glucose regulation |
| Autoimmune disease | Condition in which the immune system attacks the body’s own tissues |
| HIV | Virus that attacks helper T cells weakening the immune system and potentially leading to AIDS |
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