gas exchange, transport, muscles

Actin

a thin protein that forms (together with myosin) the contractile filaments of muscle cells; contains binding sites for the myosin heads.

Active transport

movement of particles from lower to higher concentration, using energy from ATP that has been created during respiration. Movement is through carrier proteins.

Adenosine diphosphate (ADP)

a nucleotide, present in every living cell, made of adenosine and two phosphate groups bonded in a linear sequence; it is important in energy-transfer reactions of metabolism.

Adenosine triphosphate (ATP)

a nucleotide, present in every living cell, formed in photosynthesis and respiration from ADP and Pi; it functions in metabolism as a common intermediate between energy-requiring and energy-yielding reactions.

Aerobic respiration

respiration requiring oxygen, involving the oxidation of glucose to carbon dioxide and water.

Alveolus (plural, alveoli)

air sac in the lung.

Anaerobic respiration

respiration in the absence of oxygen, producing either lactic acid (humans) or ethanol and carbon dioxide (plants and yeast).

Antagonistic muscle

a muscle that works as one of a pair: as one muscle contracts, the other muscle relaxes/lengthens. The muscle that is contracting is called the agonist and the muscle that is relaxing/lengthening is called the antagonist.

Aorta

main artery that carries blood away from the heart to the rest of the body.

Apoplast pathway

the pathway (e.g. of water) through the non-living part of a cell, e.g. cell walls and spaces between cells.

Arteriole

a very small artery.

Atherosclerosis

deposition of plaque (cholesterol derivative) in the inner wall of blood vessels.

Atrioventricular node

mass of specialized cardiac muscle cells in the wall of the right atrium.

Atrioventricular valve

heart valve that opens to allow the passage of blood into a ventricle; it closes to prevent the backflow of blood into the atrium.

Atrium (plural, atria)

upper chambers of the heart from which blood is passed to the ventricles.

Bicuspid valve

atrioventricular valve on the left side of the heart.

Bohr effect

the decrease in the oxygen affinity of haemoglobin in response to decreased blood pH, resulting from increased carbon dioxide concentration in the blood.

Bronchiole

small terminal branch of a bronchus.

Bronchus (plural, bronchi)

a tube connecting the trachea with the lungs.

Capillary action

the tendency of a liquid to move up against gravity when confined within a narrow tube (capillary). Also known as capillarity.

Capillary tubes

channels with a very small internal diameter.

Cardiac cycle

the sequence of events of a heartbeat, by which blood is pumped all over the body.

Casparian strip

a band of cells containing suberin, a waxy substance impermeable to water, found in the endodermal cell walls of plant roots.

Endothelium

the innermost lining layer of arteries and veins, and the layer of cells that comprise the capillary; also lines the inside of the heart.

Cilium (plural, cilia)

motile, hair-like outgrowth from the surface of certain eukaryotic cells, which move rhythmically to propel objects such as mucus in the trachea and eggs in oviducts.

Closed circulation

blood is contained inside blood vessels, circulating in one direction from the heart through the circulatory system before returning to the heart again.

Cohesion

force by which individual molecules of the same type attract and associate ('stick together').

Concentration gradient

the difference in concentration of a substance between one area and another.

Adhesion

the force by which individual molecules stick to surrounding materials and surfaces.

Diaphragm

sheet of tissues, largely muscle, separating thorax from abdomen in mammals.

Diastole

relaxation of heart muscle.

Diffusion

the free passage of molecules (and atoms and ions) from a region of their higher concentration to a region of lower concentration.

Double circulation

in which the blood passes twice through the heart (pulmonary circulation, then systemic circulation) in any one complete circuit of the body.

Endoskeleton

an internal skeleton, such as the bony or cartilaginous skeleton of vertebrates.

Epidermis

outer layer(s) of cells.

Epithelium

sheet of cells, bound strongly together, covering internal or external surfaces of multicellular organisms.

Excretion

the removal from the body of the waste products of cell metabolism.

Exoskeleton

skeleton secreted external to the epidermis of the body.

Expiratory reserve

difference between the maximum expiratory level and the tidal volume.

Flagellum (plural, flagella)

a long, thin structure occurring singly or in groups on some cells and tissues; used to propel unicellular organisms and to move liquids past anchored cells (flagella of prokaryotes and eukaryotes have a different internal structure).

Gas exchange

exchange of respiratory gases (oxygen, carbon dioxide) between cells/organism and the environment.

Hydrostatic pressure

mechanical pressure exerted on or by liquid (e.g. water), also known as pressure potential.

Inspiratory reserve

difference between the maximum inspiratory level and the tidal volume.

Intercalated discs

link cardiac cells together and define their borders, and facilitate cell-to-cell communication, which is needed for coordinated muscle contraction.

Intercostal muscles

muscles between the ribs involved in ventilation.

Lignin

complex polymer in which cellulose microfibrils are embedded, giving great strength and rigidity to xylem.

Lumen

the hollow interior of a blood vessel, through which the blood passes.

Lymph

fluid that flows through the lymphatic system.

Lymph node

a kidney-shaped organ in the lymphatic system, part of the body's defences against disease.

Lymphatic system

network of fine capillaries throughout the body of vertebrates, which drain lymph and return it to the blood circulation.

Mass flow

the movement of fluids down a pressure or temperature gradient.

Meristem

a group of cells in plants that retains the ability to divide by mitosis and form new cells and tissues throughout the life of a plant.

Mesophyll tissue

parenchyma cells containing chloroplasts.

Motile

capable of locomotion (whole organism movement).

Motor neuron

nerve cell that carries impulses away from the central nervous system to an effector (e.g. muscle, gland).

Mucous membranes (mucosa)

the inner lining of some organs and body cavities (e.g. the nose, mouth, lungs, and intestines). Glands in the mucous membrane make mucus.

Mucus

a watery solution of glycoprotein with protective and lubrication functions.

Multinucleate

a cell that has two or more nuclei.

Myofibril

contractile protein filament from which muscle is composed.

Myogenic

originating in heart muscle cells themselves, as in the generation of the heartbeat.

Myosin

a thick protein that forms (together with actin) the contractile filaments of muscle cells; it can convert chemical energy in the form of ATP to mechanical energy.

Neuromuscular junction

a specialized synapse between a motor neuron nerve terminal and its muscle fibre, responsible for converting electrical impulses generated by the motor neuron into electrical activity in the muscle fibres.

Osmosis

diffusion of free water molecules from a region where they are more concentrated (low solute concentration) to a region where they are less concentrated (high solute concentration) across a partially permeable membrane.

Oxygen dissociation curve

graph of percentage saturation (with oxygen) of haemoglobin against concentration of available oxygen.

Palisade mesophyll

columnar (oblong-shaped) cells containing many chloroplasts found beneath the upper epidermis in leaves.

Partial pressure

the pressure of a specific gas in a mixture of gases.

Pericardium

a tough membrane surrounding and containing the heart.

Plasma

the clear, yellowish, liquid part of the blood that carries blood cells.

Platelets

tiny cell fragments found in the blood that lack a nucleus; involved in the blood-clotting mechanism.

Pleural membrane

lines lungs and thorax cavity; it secretes the pleural fluid.

Pneumocyte

specialized cells that occur in the alveoli of the lungs.

Pulmonary circulation

the blood circulation to the lungs in vertebrates having a double circulation.

Respiratory centre

region of the medulla of the brain concerned with the involuntary control of breathing.

Root pressure

force generated in the roots that helps to drive water upwards into xylem vessels.

Sarcolemma

membranous sheath around a muscle fibre.

Sarcomere

unit of a skeletal (voluntary) muscle fibre, between two Z lines.

Semilunar valve

half-moon shaped valves, preventing backflow in a tube (e.g. a vein).

Sessile

fixed in one place; immobile.

Single circulation

blood passes through the heart once in each complete circuit of the body; blood is pumped by the heart to the gills, after which the blood flows to the rest of the body and back to the heart.

Sink

location in a plant where sucrose is transported to, either to be converted to glucose for storage as starch or for use in respiration.

Sinoatrial node (pacemaker)

structure found on right atrium of heart that is the origin of the myogenic heartbeat.

Source

location in a plant where glucose is produced or stored (cotyledons, potato tubers, carrots) and converted into sucrose for transport.

Spongy mesophyll

rounded cells in the leaf that are loosely packed, creating air spaces where air circulates, providing a large surface area for gas exchange; contains chloroplasts but fewer than palisade mesophyll.

Stoma (plural, stomata)

pore in the epidermis of a leaf, surrounded by two guard cells.

Striated

muscle tissue that is marked by alternating dark and light bands.

Surface tension

property of the surface of a liquid that allows it to resist an external force, due to the cohesion between water molecules.

Surfactant

a detergent secreted by cells in the wall of alveoli which breaks surface tension and stops alveoli walls from sticking together, keeping the alveoli open.

Symplast pathway

the pathway (e.g. of water) through the cell membrane and plasmodesmata (the living contents of the cell).

Synovial fluid

lubricates the joint, nourishes the cartilage and removes any (harmful) detritus from worn bone and cartilage surfaces.

Synovial joint

joint where a very thin layer of viscous synovial fluid separates and lubricates the two cartilage-covered bone surfaces.

Systemic circulation

the blood circulation to the body (not the pulmonary circulation).

Systole

contraction of heart muscle.

Tendon

fibrous connective tissue connecting a muscle to bone.

Tension

the force that is transmitted through a substance when it is pulled tight by forces acting from opposite ends.

Thorax

in mammals, the upper part of the body separated from the abdomen; in insects, the region between head and abdomen.

Tidal volume

volume of air normally exchanged in breathing.

Tissue fluid

a mixture of water and solutes, forced out of the blood by ultrafiltration, which surrounds body cells.

Titin

a large mechanical protein in muscle cells; its main function is to act as a molecular spring in the sarcomeres.

Trachea

windpipe

Transpiration

the evaporation of water from the spongy mesophyll tissue and its subsequent diffusion through the stomata.