AS & A Level Biology: Immunity, Transport in Mammals, Gas Exchange, and Infectious Disease

Vocabulary practice flashcards covering Chapter 11 (Immunity), Chapter 8 (Transport in Mammals), Chapter 9 (Gas Exchange), and Chapter 10 (Infectious Disease).

Antigen

A substance that is foreign to the body and stimulates an immune response.

Self

Substances produced by the body that the immune system does not recognise as foreign, so they do not stimulate an immune response.

Non-self

Any substance or cell that is recognised by the immune system as being foreign and stimulates an immune response.

Antibody

A glycoprotein (immunoglobulin) produced by specialised lymphocytes in response to the presence of a specific antigen, with variable regions complementary in shape to that specific antigen.

Immune response

The complex series of responses of the body to the entry of a foreign antigen, involving the coordinated activity of lymphocytes and phagocytes.

Neutrophil

A short-lived phagocytic white blood cell that forms about $60\%$ of white blood cells in the blood, characterized by a lobed nucleus and granular cytoplasm containing hydrolytic enzymes.

Macrophage

A large, long-lived phagocytic cell that develops from a monocyte, settles inside organs, and cuts up engulfed pathogens to display antigens to lymphocytes.

Chemotaxis

The directed movement of cells (such as phagocytes) towards a chemical stimulus released by damaged cells or pathogens.

Clonal selection

The activation of only those individual lymphocytes that possess cell surface receptors specific and complementary to the antigens of an invading pathogen.

Clonal expansion

The repeated division by mitosis of an activated lymphocyte to produce large numbers of identical cells during an immune response.

Plasma cell

A short-lived, activated B-lymphocyte produced during clonal expansion that secretes antibody molecules into the blood or lymph at rates up to several thousand per second.

Memory B cell

A long-lived, activated B-lymphocyte that remains circulating in the body and differentiates rapidly into antibody-secreting plasma cells upon subsequent exposure to the specific antigen.

Primary immune response

The initial, relatively slow immune response following the first exposure to a specific antigen, during which few specific B cells are initially present.

Secondary immune response

The faster and much larger immune response that occurs upon repeated encounter with a specific antigen, mediated by memory cells.

Immunological memory

The capacity of the immune system to mount a larger and more rapid response to an antigen that has been previously encountered.

Variable region

The region of an antibody molecule composed of parts of both light and heavy polypeptide chains whose amino acid sequence forms an antigen-binding site complementary to a specific antigen.

Antitoxin

A specialized group of antibodies that bind directly to and neutralise toxins released by bacteria, preventing damage to host cells.

Antigen presentation

The process whereby a host cell (such as a macrophage or infected body cell) cuts up a pathogen and displays its antigens on the cell surface membrane for recognition by T-lymphocytes.

T-helper cell

A type of T-lymphocyte that coordinates the immune response by secreting cytokines to stimulate B cells to divide and macrophages to perform phagocytosis more vigorously.

T-killer cell

A type of T-lymphocyte (also called a T-cytotoxic cell) that attaches to infected host cells displaying foreign antigens and secretes toxic substances such as hydrogen peroxide to destroy them.

Cytokine

Any signalling molecule released by cells to influence the growth, division, or differentiation of the same or another cell during an immune response.

Active immunity

Long-term immunity acquired when an antigen enters the body, an immune response occurs, and antibodies and memory cells are produced by the host.

Passive immunity

Temporary immunity gained without an immune response or memory cell formation, provided by pre-formed antibodies introduced from outside the body.

Vaccine

A preparation containing whole live, dead, or attenuated microorganisms, toxoids, or surface antigens used to stimulate an immune response artificially.

Herd immunity

Protection conferred upon unvaccinated individuals when a high proportion of the population is immune, interrupting the pathogen transmission cycle.

Ring immunity

The strategy of vaccinating all people in direct contact with an infected individual to establish a zone of immunity and stop local disease spread.

Monoclonal antibody (Mab)

An antibody produced by a single clone of hybridoma cells, resulting in identical molecules with identical variable regions specific to a single antigen.

Hybridoma

A cell formed by the fusion of an antibody-producing plasma cell and an indefinitely dividing cancer cell.

Closed blood system

A circulatory system in which blood is continually confined within a continuous network of blood vessels.

Double circulation

A circulatory system in which blood passes through the heart twice during one complete circuit of the body.

Systemic circulation

The portion of the circulatory system that pumps oxygenated blood from the left ventricle through the aorta to body tissues and returns deoxygenated blood to the right atrium via the vena cava.

Pulmonary circulation

The portion of the circulatory system that carries deoxygenated blood from the right ventricle to the lungs via pulmonary arteries and returns oxygenated blood to the left atrium via pulmonary veins.

Endothelium

The smooth, single inner layer of flat epithelial cells (squamous epithelium) lining the lumen of all blood vessels to minimize frictional resistance.

Elastic arteries

Large arteries situated near the heart (such as the aorta) that contain high proportions of elastic fibres in their middle layer to stretch under systolic pressure and recoil during diastole.

Muscular arteries

Arteries located further from the heart whose middle layer has a high proportion of smooth muscle fibres capable of altering vessel diameter to regulate blood flow.

Vasoconstriction

The narrowing of the lumen of an arteriole or muscular artery caused by the contraction of smooth muscle in its wall.

Vasodilation

The widening of the lumen of an arteriole or muscular artery caused by the relaxation of smooth muscle in its wall.

Capillary

A tiny blood vessel with a diameter of about $7\,\mu\text{m}$ and a wall composed of a single layer of endothelial cells, serving as the site of exchange between blood and tissues.

Semilunar valve

A half-moon shaped pocket valve found in veins and at the exits of the ventricles that closes to prevent the backflow of blood.

Plasma

The pale yellow liquid component of blood, consisting of about $95\%$ water, dissolved nutrients, wastes, and plasma proteins in which blood cells are suspended.

Tissue fluid

The almost colourless intercellular fluid formed from blood plasma that leaks through capillary walls into the spaces between body cells.

Oedema

The abnormal accumulation of excess tissue fluid within body spaces, frequently caused by excessively high blood pressure forcing fluid out of capillaries.

Haemoglobin

A globular protein with quaternary structure made of four polypeptide chains, each containing an iron-containing haem group capable of binding one molecule of oxygen ($\text{Hb} + 4\text{O}_2 \rightarrow \text{HbO}_8$).

Bohr shift

The decrease in the affinity of haemoglobin for oxygen in the presence of elevated partial pressures of carbon dioxide, shifting the oxygen dissociation curve downwards and to the right.

Carbonic anhydrase

An enzyme found within the cytoplasm of red blood cells that catalyses the reversible hydration of carbon dioxide to carbonic acid ($\text{CO}_2 + \text{H}_2\text{O} \rightleftharpoons \text{H}_2\text{CO}_3$).

Chloride shift

The movement of chloride ions ($\text{Cl}^-$) from plasma into red blood cells to balance the outward diffusion of hydrogencarbonate ions ($\text{HCO}_3^-$) and maintain electrical neutrality.

Carbaminohaemoglobin

The chemical compound formed when carbon dioxide binds directly to terminal amine groups ($-\text{NH}_2$) of haemoglobin, accounting for about $10\%$ of transported carbon dioxide.

Myogenic

Muscle tissue that naturally contracts and relaxes rhythmically on its own without requiring nervous stimulation, characteristic of cardiac muscle.

Sinoatrial node (SAN)

A patch of myogenic cardiac muscle in the wall of the right atrium that generates rhythmic electrical excitation waves to establish the heart rate; the pacemaker.

Atrioventricular node (AVN)

A patch of conducting tissue in the septum that picks up the excitation wave from the atria, delays it for about $0.1\,\text{seconds}$, and transmits it to the Purkyne tissue.

Purkyne tissue

Specialised conducting muscle fibres in the interventricular septum that rapidly conduct electrical excitation waves to the base of the ventricles, triggering contraction from the bottom upwards.

Atrial systole

The phase of the cardiac cycle in which the thin muscular walls of the atria contract, raising atrial pressure and forcing blood through atrioventricular valves into the ventricles.

Ventricular systole

The phase of the cardiac cycle lasting about $0.3\,\text{seconds}$ during which the ventricular walls contract, closing atrioventricular valves and forcing blood through open semilunar valves into the arteries.

Diastole

The resting phase of the cardiac cycle during which heart muscle relaxes, allowing blood from the veins to flow into the atria and trickle into the ventricles.

Gas exchange surface

A specialised boundary in an organism where gas molecules diffuse between the body and the external environment (e.g., alveoli in mammals).

Alveolus

A tiny lung sac composed of a single layer of squamous epithelium surrounded by pulmonary capillaries, providing a thin surface for gas diffusion.

Trachea

The windpipe airway leading from the larynx to the bronchi, reinforced by regular C-shaped rings of cartilage and lined by ciliated epithelium.

Cartilage

A strong, flexible skeletal tissue that supports the trachea and bronchi, preventing them from collapsing or bursting during pressure changes in ventilation.

Goblet cell

A specialised epithelial cell shaped like a drinking goblet that synthesizes and secretes droplets of mucin to trap inhaled particles and pathogens.

Mucin

A sticky glycoprotein containing many carbohydrate chains that dissolves in water to form mucus.

Ciliated epithelium

A layer of cells featuring surface cilia that beat in synchrony to move mucus up the airways toward the larynx at a rate of approximately $1\,\text{cm}\,\text{min}^{-1}$.

Elastic fibres

Protein bundles composed of elastin present in alveolar walls that stretch during inspiration and recoil during expiration to help expel air.

Pathogen

A biological agent, such as a protoctist, bacterium, or virus, that causes disease.

Infectious disease

A communicable disorder caused by a pathogen that can be transmitted from an infected host to an uninfected individual.

Disease carrier

An infected person who exhibits no clinical symptoms of a disease but can serve as a reservoir and source of infection for others.

Transmission cycle

The repeated sequence of events and mechanisms by which a pathogen transfers from an infected host to new, uninfected hosts.

Endemic disease

A disease that is constantly maintained at a regular baseline level within a particular geographic region or human population.

Epidemic

A sudden, marked increase in the number of cases of an infectious disease within a specific community or region.

Pandemic

An extensive increase in the global incidence of an infectious disease that spreads across multiple continents or worldwide.

Incidence

The number of newly diagnosed cases of a disease within a specific population over a designated timeframe.

Prevalence

The total number of individuals in a population who have a particular disease at a given point in time.

Mortality rate

The number of deaths resulting from a specific disease within a designated population over a set period of time.

Vibrio cholerae

The flagellated, water-borne Gram-negative bacterium that acts as the causative pathogen of cholera.

Choleragen

The enterotoxin produced by Vibrio cholerae in the small intestine that causes massive watery diarrhea and severe electrolyte loss.

Oral rehydration therapy

A treatment for cholera involving drinking a balanced solution of salts and glucose to replenish fluid loss and restore osmotic equilibrium.

Plasmodium

The genus of parasitic protoctists (P. falciparum, P. vivax, P. ovale, P. malariae) that cause malaria.

Disease vector

An organism (such as the female Anopheles mosquito) that transfers a pathogen from one host to another without being harmed itself.

Human immunodeficiency virus (HIV)

An enveloped retrovirus carrying RNA that specifically infects and destroys T-helper lymphocytes, leading to severe immunodeficiency.

Acquired immunodeficiency syndrome (AIDS)

A collection of opportunistic infections and rare cancers resulting from severe destruction of the immune system caused by HIV infection.

Opportunistic infection

An infection caused by pathogens that take advantage of a host whose immune system has become severely compromised.

Reverse transcriptase

An enzyme present in retroviruses such as HIV that uses viral single-stranded RNA as a template to synthesize complementary viral DNA inside host cells.

Mycobacterium tuberculosis

A slow-growing bacterium with an impermeable cell wall that causes pulmonary and systemic tuberculosis in humans.

DOTS (direct observation treatment, short course)

A WHO-promoted scheme in which healthcare workers or designated family members observe TB patients taking their antibiotics daily for $6\text{ to }8\,\text{months}$.

Multiple-drug-resistant TB (MDR-TB)

Strains of Mycobacterium tuberculosis that have evolved genetic resistance to at least isoniazid and rifampicin, the two main first-line anti-TB drugs.

Extensively drug-resistant TB (XDR-TB)

Strains of Mycobacterium tuberculosis that are resistant to first-line drugs (isoniazid and rifampicin) and to second-line drugs used to treat MDR-TB.

Antibiotic

A substance derived from a living organism (or synthesized) that kills or inhibits the growth of bacteria without harming eukaryotic host cells.

Peptidoglycan

The structural macromolecule forming bacterial cell walls, composed of polysaccharide chains cross-linked by short peptide bridges.

Autolysins

Enzymes secreted by growing bacteria that create small openings in peptidoglycan cell walls to allow wall stretching and incorporation of new cross-links.

Beta-lactamase

An enzyme (also known as penicillinase) produced by resistant bacteria that catalyses the breakdown of the beta-lactam ring in penicillin, rendering it ineffective.

Conjugation

The horizontal transfer of genetic material (frequently plasmids carrying antibiotic-resistance genes) between bacteria via direct contact through a conjugation tube.

Minimum inhibitory concentration (MIC)

The lowest concentration of an antimicrobial substance required to prevent visible growth of a bacterium under laboratory testing conditions.