Maharashtra HSC Biology key terms

The tendency of genes located close together on the same chromosome to be inherited together, so that their alleles do not assort independently and parental combinations appear more often than expected in offspring.

The production of new allele combinations in offspring, arising from independent assortment of chromosomes or from crossing over between homologous chromosomes during meiosis, measured as recombination frequency.

Exchange of corresponding segments between non-sister chromatids of homologous chromosomes at chiasmata during prophase I of meiosis, breaking linkage and generating new allele combinations.

Synthesis of an RNA molecule from a DNA template catalysed by RNA polymerase, producing mRNA, tRNA or rRNA that carries out or transmits the genetic message.

The process in which ribosomes read mRNA codons and assemble the corresponding sequence of amino acids into a polypeptide, using tRNA and energy from GTP.

The set of rules by which nucleotide triplets (codons) in mRNA specify particular amino acids or stop signals; it is degenerate, non-overlapping and nearly universal.

A bacterial enzyme that cuts DNA at a specific recognition sequence, producing fragments with sticky or blunt ends; used to create recombinant DNA in genetic engineering.

A self-replicating DNA molecule such as a plasmid or bacteriophage that carries a foreign DNA fragment into a host cell, where it is multiplied and expressed.

An enzyme that joins the sugar-phosphate backbones of DNA fragments, sealing nicks and covalently linking an insert to a vector to form recombinant DNA.

An in-vitro technique that amplifies a specific DNA segment through repeated cycles of denaturation, primer annealing and extension by a thermostable DNA polymerase.

A technique that separates charged molecules such as DNA fragments through a gel under an electric field, with smaller fragments migrating farther than larger ones.

Identification of an individual from the pattern of repeated DNA sequences such as VNTRs, which vary between individuals and are detected after amplification and electrophoresis.

The stage between two mitotic divisions during which the cell grows and replicates its DNA, divided into G1, S and G2 phases; chromosomes are not visibly condensed.

Nuclear division producing two daughter nuclei with the same chromosome number as the parent cell, essential for growth, repair and asexual reproduction in eukaryotes.

Two successive nuclear divisions that halve the chromosome number and produce four genetically varied haploid cells, forming gametes or spores in sexually reproducing organisms.

The sequence of events in the testis by which diploid spermatogonia undergo mitosis and meiosis to form haploid spermatids that mature into spermatozoa under hormonal control.

Formation of haploid ova in the ovary from oogonia, producing one large functional ovum and polar bodies, with meiosis arrested at prophase I until puberty.

The temporary endocrine gland formed from the ruptured follicle after ovulation; it secretes progesterone and oestrogen, maintaining the endometrium for possible implantation.

A roughly 28-day cycle of hormonal changes in females involving follicle growth, ovulation, preparation of the uterine lining and its shedding when pregnancy does not occur.

The chemical potential of water relative to pure water at the same temperature and pressure; water moves from regions of higher to lower water potential, and solutes lower it.

The diffusion of water across a selectively permeable membrane from a region of higher water potential to a region of lower water potential, driven by solute concentration differences.

Shrinkage of the protoplast away from the cell wall when a plant cell loses water to a solution of lower water potential, occurring in hypertonic surroundings.

Loss of water vapour from aerial plant parts, mainly through stomata, which pulls water upward through the xylem and cools the leaf.

Pores in the epidermis bounded by guard cells; they open when guard cells become turgid to admit carbon dioxide for photosynthesis and close to limit water loss.

The light-driven synthesis of organic compounds from carbon dioxide and water in chloroplasts, releasing oxygen and storing energy in products such as glucose and ATP.

Formation of ATP from ADP and inorganic phosphate using light energy during the light reactions of photosynthesis, coupled to electron transport in the thylakoid membrane.

The light-independent series of enzyme-controlled reactions in the stroma that fixes carbon dioxide and reduces it to carbohydrate using ATP and NADPH from the light reactions.

The first stage of respiration in the cytoplasm, where one glucose molecule is split and oxidised to two molecules of pyruvate with net gain of ATP and NADH.

A cyclic sequence of reactions in the mitochondrial matrix that oxidises acetyl-CoA to carbon dioxide, generating reduced coenzymes NADH and FADH2 that feed the electron transport chain.

ATP synthesis driven by proton flow through ATP synthase in the inner mitochondrial membrane, powered by electrons transferred along the respiratory chain to oxygen.

Breakdown of glucose without oxygen, yielding only a small amount of ATP and products such as lactate in animals or ethanol and carbon dioxide in yeast.

A rounded mass of chewed food mixed with saliva, formed in the mouth and moved by peristalsis through the oesophagus to the stomach.

Rhythmic waves of muscular contraction in the wall of the alimentary canal that push food along it and mix it with digestive secretions.

An alkaline secretion of the liver stored in the gall bladder that emulsifies fats into small droplets, aiding lipase action and helping absorption of fat-soluble vitamins.

The structural and functional unit of the kidney, comprising a renal corpuscle and tubule, which filters blood and reabsorbs useful materials to form urine.

Pressure-driven movement of water and small solutes from the blood in the glomerulus into the Bowman's capsule, forming an ultrafiltrate free of large proteins and cells.

Arrangement of the loop of Henle and vasa recta in opposite flow directions that concentrates solutes in the medulla and enables production of hypertonic urine.

A rapid reversal of membrane potential in a neuron produced by ion movements, which propagates along the axon and transmits excitation to other cells.

A junction between two neurons or between a neuron and an effector, across which a signal passes by release of a chemical neurotransmitter such as acetylcholine.

An automatic, rapid involuntary response to a stimulus, mediated by a reflex arc of receptor, sensory neuron, spinal cord, motor neuron and effector.

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

Control in which the product or end effect of a process suppresses the activity that produced it, keeping hormone levels and physiological variables within a stable range.

Maintenance of a relatively constant internal environment, such as temperature, pH, glucose and water balance, by coordinated physiological control mechanisms including negative feedback.

Differential survival and reproduction of individuals differing in heritable traits, leading to increased frequency of advantageous alleles in later generations.

Evolution of diverse forms from a single ancestral lineage that colonises different niches or habitats, illustrated by finches of the Galapagos and marsupials of Australia.

Formation of new species when populations become reproductively isolated and diverge genetically, either in geographic separation or within the same area.

A graphical representation of numbers, biomass or energy at successive trophic levels, showing progressive decrease upward because energy is lost at each transfer.

A sequence of organisms in which each feeds on the preceding one, transferring energy and matter from producers through herbivores to carnivores and decomposers.

The rate at which photosynthetic producers convert solar energy into organic matter per unit area and time, forming the energy base of every ecosystem.