Myanmar Matriculation Biology key terms

The net movement of water molecules through a partially permeable membrane from a region of higher water potential to one of lower water potential, without energy input from the cell.

A measure of the tendency of water to move from one place to another, expressed in pressure units; pure water at atmospheric pressure has a value of zero, and solutions have negative values.

The shrinking and pulling away of the protoplast from the cell wall when a plant cell loses water by osmosis in a more concentrated surrounding solution.

Nuclear division producing two daughter nuclei genetically identical to the parent nucleus, usually followed by cytokinesis; it underlies growth, repair and asexual reproduction in eukaryotes.

Two successive nuclear divisions that follow one round of chromosome replication, halving the chromosome number and generating four haploid cells with new allele combinations through crossing over and independent assortment.

A pair of chromosomes, one inherited from each parent, that carry the same genes at the same loci but may hold different alleles and pair during prophase I of meiosis.

The exchange of corresponding segments between non-sister chromatids of a homologous pair at chiasmata during prophase I, producing recombinant chromatids with new allele combinations.

A microtubule structure that forms between the poles of a dividing cell and attaches to centromeres or kinetochores, moving chromosomes apart during anaphase.

A globular protein that acts as a biological catalyst, lowering activation energy by forming a temporary enzyme-substrate complex at its active site; it is not used up in the reaction.

The small region of an enzyme molecule, formed by a few specific amino acid residues, that binds substrate molecules and where catalysis takes place.

Loss of an enzyme's three-dimensional shape, and therefore its catalytic function, caused by heat, extremes of pH or heavy metal ions breaking hydrogen and ionic bonds.

A model explaining enzyme specificity in which the rigid active site has a shape complementary to only one substrate, like a key fitting a lock.

A chemical reaction in which two molecules join with the loss of a small molecule such as water, for example forming a glycosidic bond between two monosaccharides or a peptide bond between amino acids.

A reaction in which a large molecule is split into smaller ones by the addition of water, catalysed by enzymes such as carbohydrases, proteases and lipases during digestion.

The covalent bond formed by a condensation reaction between the carboxyl group of one amino acid and the amino group of another, linking amino acids in a polypeptide chain.

One of two or more alternative forms of a gene occupying the same locus on homologous chromosomes and differing slightly in base sequence, giving rise to variation in a characteristic.

The genetic constitution of an organism with respect to a particular gene or set of genes, usually written as pairs of letters showing the alleles present.

The observable characteristics of an organism resulting from the interaction between its genotype and the environment, such as flower colour or blood group.

An allele that expresses its effect in the phenotype even when only one copy is present, masking the expression of a recessive allele in a heterozygote.

A cross between an individual showing a dominant phenotype and a homozygous recessive individual, used to determine whether the dominant individual is homozygous or heterozygous.

The synthesis of a messenger RNA molecule from a DNA template strand, catalysed by RNA polymerase, in which uracil replaces thymine and the sugar-phosphate backbone contains ribose.

The process at ribosomes in which the base sequence of messenger RNA is decoded into a specific sequence of amino acids, with transfer RNA delivering amino acids according to codon-anticodon pairing.

A sequence of three consecutive bases on messenger RNA that specifies one amino acid or acts as a start or stop signal during protein synthesis.

A single-stranded RNA molecule transcribed from DNA that carries the genetic code from the nucleus to the ribosomes, where it directs the order in which amino acids are assembled.

A change in the amount or arrangement of DNA bases, such as substitution, insertion or deletion, which may alter the amino acid sequence of a protein and produce a new phenotype.

The process by which individuals with inherited characteristics better suited to their environment survive and reproduce more successfully, so their alleles increase in frequency over generations.

The formation of one or more new species from an existing species when populations become reproductively isolated and diverge genetically over many generations.

The loss of water vapour from the aerial parts of a plant, mainly through stomata, which pulls water up the xylem and cools the leaves.

A pore in the leaf epidermis, bounded by two guard cells, that allows gaseous exchange and the loss of water vapour; it opens when guard cells are turgid.

Vascular tissue of dead, hollow vessel elements and tracheids that transports water and dissolved mineral ions upward from the roots to the leaves and provides mechanical support.

The outward pressure exerted by cell contents against the cell wall when water enters a plant cell by osmosis, keeping non-woody tissues firm and stiff.

The maintenance of a relatively constant internal environment within narrow limits, such as blood glucose concentration, body temperature and water balance, despite changes outside the body.

A control mechanism in which a deviation from the normal level triggers responses that reduce the deviation and restore the set point, as in insulin and glucagon control of blood glucose.

The functional unit of the kidney, consisting of a Bowman's capsule, glomerulus and tubule, where blood is filtered and useful substances are selectively reabsorbed.

A feature of flowering plants in which one male gamete fuses with the egg to form a zygote and a second fuses with two polar nuclei to form triploid endosperm.

The transfer of pollen grains from the anther of a flower to the stigma of the same or another flower, brought about by wind, insects, water or other agents.

A fertilised ovule containing an embryo, stored food and a protective testa, capable of surviving unfavourable conditions and germinating when conditions become suitable.

A sequence of organisms in which each feeds on the one before it, showing the direction of energy transfer from producer through primary and secondary consumers.

The position an organism occupies in a food chain, such as producer, primary consumer or secondary consumer, each level containing less energy than the one below it.

An organism, usually a bacterium or fungus, that breaks down dead organic matter and wastes, releasing mineral ions and carbon dioxide back into the environment.

The anaerobic breakdown of glucose by microorganisms or muscle cells, producing substances such as ethanol and carbon dioxide in yeast or lactate in muscle.

The technique of growing cells or small pieces of tissue on a sterile nutrient medium under controlled conditions to produce many genetically identical plantlets or cell products.