Kerala SSLC Biology key terms

Membrane-bound organelle with folded inner cristae where aerobic respiration occurs; it releases energy from glucose as ATP, so cells with high energy demand, such as muscle and sperm cells, contain many of them.

Type of nuclear division producing two daughter nuclei with the same chromosome number and genetic content as the parent cell; it underlies growth, repair, and asexual reproduction in body cells.

Reduction division in which one diploid cell forms four haploid cells with new gene combinations; it occurs in reproductive organs to form gametes and creates variation through crossing over and independent assortment.

Thread-like structure of DNA and protein found in the nucleus, carrying genes in a linear order. Human body cells contain 23 pairs; gametes contain one chromosome from each pair.

A length of DNA that codes for a particular protein or trait and occupies a fixed position on a chromosome. Alternative forms of the same gene are called alleles.

One of two or more alternative forms of a gene occupying the same position on homologous chromosomes. Alleles may be dominant or recessive and determine which form of a trait is expressed.

The genetic makeup of an organism for one or more traits, described by the alleles it carries, for example homozygous dominant, heterozygous, or homozygous recessive. It interacts with the environment to produce the phenotype.

The observable characteristics of an organism resulting from its genotype and its environment, such as flower colour, blood group, or height. Dominant alleles are expressed even when only one copy is present.

An allele that produces its effect in the phenotype even when a different allele is present on the homologous chromosome, so it is expressed in heterozygous individuals and masks the recessive partner.

An allele whose effect appears in the phenotype only when two copies are present, that is in the homozygous state; it is masked in heterozygotes by a dominant allele.

Net movement of particles from a region of higher concentration to a region of lower concentration by their own random motion, without energy input from the cell and without a membrane barrier.

Movement of water molecules through a partially permeable membrane from a dilute solution to a more concentrated solution, that is from higher to lower water potential, without expenditure of metabolic energy.

Movement of ions or molecules across a membrane against a concentration gradient using energy released by respiration, usually through carrier proteins; it allows roots to absorb mineral salts from dilute soil solution.

Protein that speeds up a specific biochemical reaction by lowering its activation energy; its active site is complementary to the substrate, and activity is altered by temperature and pH.

Greenish alkaline fluid made in the liver, stored in the gall bladder, and released into the small intestine; it emulsifies fats into small droplets and neutralises acidic chyme from the stomach.

Finger-like projection of the small intestine lining that greatly increases surface area for absorption; each contains a network of blood capillaries and a lacteal to carry absorbed nutrients away.

Release of energy from glucose in the presence of oxygen, producing carbon dioxide and water; it yields far more ATP per glucose molecule than anaerobic respiration and occurs mainly in mitochondria.

Release of a small amount of energy from glucose without oxygen; in human muscle it forms lactic acid, and in yeast it produces ethanol and carbon dioxide, a process used in brewing and baking.

Adenosine triphosphate, the short-term energy currency of cells; energy released when its terminal phosphate bond is broken drives processes such as active transport and muscle contraction, and it is regenerated during respiration.

Tiny air sac in the lungs where gas exchange occurs; its walls are one cell thick, richly supplied with capillaries, and coated with moisture so oxygen and carbon dioxide diffuse rapidly.

Iron-containing protein pigment in red blood cells that binds oxygen in the lungs to form oxyhaemoglobin and releases it in tissues where oxygen concentration is low, also helping to carry carbon dioxide.

Blood vessel that carries blood away from the heart; it has a thick muscular elastic wall, a narrow lumen, and no valves, and it conducts blood at high pressure, branching into arterioles.

Blood vessel that carries blood towards the heart at low pressure; it has a thin wall, a wide lumen, and pocket valves that prevent backflow, aided by the squeezing action of skeletal muscles.

Microscopic blood vessel with walls only one cell thick that links arterioles and venules; its large total surface area and slow flow allow exchange of gases, nutrients, and wastes with tissue fluid.

Functional filtering unit of the kidney, consisting of a glomerulus, Bowman's capsule, and a tubule; it filters blood and reabsorbs useful substances such as glucose and water, forming urine.

Process in the kidney tubule in which useful substances such as glucose, amino acids, and most water are taken back into the blood by diffusion and active transport, leaving wastes to be excreted as urine.

Control of the water and salt balance of body fluids, mainly by the kidneys under the influence of hormones such as ADH, keeping the internal environment steady despite changes in water intake and loss.

Maintenance of a stable internal environment, such as constant body temperature, blood glucose, and water content, through negative feedback mechanisms involving receptors, control centres, and effectors.

Rapid involuntary response to a stimulus, such as blinking or withdrawing the hand from a hot object, coordinated by a reflex arc through the spinal cord without waiting for a decision from the brain.

Junction between two neurons or between a neuron and an effector, separated by a narrow gap across which a chemical neurotransmitter diffuses to transmit the impulse in one direction only.

Hormone secreted by the beta cells of the pancreas that lowers blood glucose by promoting uptake into cells and conversion of glucose to glycogen in the liver; deficiency causes diabetes mellitus.

Transfer of pollen grains from the anther to the stigma of a flower, by wind, water, insects, or other animals; it precedes fertilisation and may occur within one flower or between different flowers.

Fusion of a male gamete nucleus with a female gamete nucleus to form a diploid zygote. In flowering plants it follows pollination and leads to development of seed and fruit.

Temporary organ in the uterus through which the embryo obtains oxygen and nutrients from the mother's blood and passes out carbon dioxide and urea; maternal and fetal blood do not mix.

A sequence of organisms in which each feeds on the one before it, showing the direction of energy transfer from producer to primary consumer and then to higher consumers, ending with decomposers.

Feeding position occupied by an organism in a food chain, such as producer, primary consumer, or secondary consumer; only about ten per cent of energy passes from one level to the next.

Organism such as bacteria or fungi that breaks down dead organisms and waste materials, releasing mineral nutrients and carbon dioxide back to the environment so that matter can be reused by producers.

Variety of living organisms in an ecosystem or on Earth, measured at genetic, species, and ecosystem levels; it supports ecosystem stability and is threatened by habitat loss, pollution, and overexploitation.

Species found naturally only in one restricted geographical area and nowhere else, such as many plants of the Western Ghats; their narrow range makes them especially vulnerable to habitat destruction.