Tamil Nadu HSE First Year Zoology key terms

A flexible rod of cells running along the back of chordate embryos, supporting the body and acting as the axis around which the vertebral column later develops.

The phylum of animals that at some stage possess a notochord, dorsal hollow nerve cord, pharyngeal gill slits and a post-anal tail, including vertebrates and their close relatives.

The chordate subphylum in which the notochord is replaced during development by a segmented vertebral column enclosing the nerve cord, comprising fishes, amphibians, reptiles, birds and mammals.

A body cavity lying between the body wall and the gut, lined completely by mesoderm-derived epithelium, which houses and cushions the internal organs.

A body cavity that is not fully lined by mesoderm, having mesoderm on the body-wall side only, as seen in roundworms such as Ascaris.

Describes an animal whose body cavity is a true coelom, completely lined by mesodermal epithelium, as in annelids, molluscs, arthropods, echinoderms and chordates.

The condition in which the body is built of a linear series of similar repeated segments, each with its own set of structures, as in earthworms.

Stiff bristles of chitin secreted by epidermal cells, used by earthworms and other annelids to grip the substrate during crawling and to anchor the body.

A tubular excretory organ of annelids, open at the internal end as a ciliated funnel, which filters coelomic fluid and discharges urine through an external pore.

A sheet of closely packed cells resting on a basement membrane, covering body surfaces and lining cavities, and specialised for protection, absorption, secretion or sensation.

A thin non-cellular layer of glycoprotein and collagen that anchors epithelial cells to the underlying connective tissue and guides the exchange of materials.

Tissue in which cells are widely separated by an abundant intercellular matrix, binding, supporting, packing and transporting materials within the body.

A strong cord of dense regular connective tissue, rich in collagen fibres, that joins skeletal muscle to bone and transmits the pull of contraction.

The repeating functional unit of a striated muscle fibre lying between two Z lines, where actin and myosin filaments slide past each other during contraction.

A globular contractile protein that assembles into thin filaments of muscle, providing the track along which myosin heads pull during shortening of the sarcomere.

A motor protein forming the thick filaments of muscle; its projecting heads bind actin and, using ATP, swing to slide the filaments and shorten the sarcomere.

Rhythmic waves of contraction and relaxation of smooth muscle in the wall of the alimentary canal that push food onward and mix it with digestive juices.

Finger-like projections of the small-intestine lining that greatly increase the absorptive surface area and contain capillaries and a central lymph vessel.

An alkaline greenish fluid secreted by the liver, stored in the gall bladder and released into the duodenum, where its bile salts emulsify fats into tiny droplets.

The rounded mass of chewed food moistened with saliva that is formed in the mouth and swallowed into the oesophagus.

A minute thin-walled air sac at the end of a bronchiale in the lung, surrounded by capillaries, where oxygen enters the blood and carbon dioxide leaves it.

An iron-containing red respiratory pigment inside red blood cells that binds oxygen loosely in the lungs and releases it in tissues where oxygen concentration is low.

A dome-shaped sheet of skeletal muscle separating the thoracic and abdominal cavities in mammals, whose contraction flattens it and draws air into the lungs.

A hollow muscular organ that contracts rhythmically to pump blood through arteries, veins and capillaries, driving circulation and the transport of gases and nutrients.

The structural and functional unit of the kidney, comprising a malpighian corpuscle and a tubule, which filters blood and modifies the filtrate to form urine.

The active control of the water and dissolved-salt balance of body fluids, keeping their concentration within limits despite changes in the surrounding environment.

The structural and functional unit of nervous tissue, an excitable cell with dendrites, a cell body and an axon that conducts impulses and communicates at synapses.

The junction between two neurons or between a neuron and an effector, across which a chemical transmitter diffuses to pass the impulse in one direction.

The nerve pathway followed by an involuntary response, running from a receptor through a sensory neuron, the spinal cord, a motor neuron and an effector.

A chemical messenger secreted in small amounts by an endocrine gland into the blood, which acts on specific target cells to regulate growth, metabolism or reproduction.

A protein hormone released by the beta cells of the pancreatic islets that lowers blood glucose by promoting its uptake and storage as glycogen in cells.

A bilobed endocrine gland in the neck whose follicles secrete thyroxine, a hormone containing iodine that controls basal metabolic rate, growth and development.

A reduction division in which one diploid cell produces four haploid cells through two successive divisions, generating gametes and creating genetic variation by crossing over.

The exchange of corresponding segments between non-sister chromatids of homologous chromosomes during prophase I of meiosis, producing new combinations of alleles.

A haploid reproductive cell, such as a sperm or an egg, which fuses with another gamete at fertilisation to form a diploid zygote.

The diploid cell formed by the fusion of a male and a female gamete, which divides repeatedly to develop into the embryo of a new individual.

One of two or more alternative forms of the same gene occupying a corresponding position on homologous chromosomes and giving rise to contrasting traits.

The genetic constitution of an organism at a particular locus or set of loci, described by the alleles it carries, which together with the environment determines the phenotype.

The process by which individuals with inherited variations better suited to their environment survive and leave more offspring, gradually changing the frequency of traits in a population.