RBSE SS Biology key terms

The process in flowering plants where one male gamete fuses with the egg to form a zygote and a second male gamete fuses with two polar nuclei to form triploid endosperm.

The female gametophyte inside an ovule, typically with eight nuclei in seven cells, including the egg cell and a central cell with two polar nuclei that receives a male gamete.

The nutritive tissue of a seed, usually triploid in angiosperms, formed from the fusion of a male gamete with two polar nuclei and used by the developing embryo.

A tough, chemically resistant polymer forming the outer wall of pollen grains, protecting the male gametophyte from desiccation and decay and aiding its dispersal.

The male gametophyte of seed plants, a small structure with a resistant outer wall that is released from the anther and delivers male gametes to the ovule.

The formation of female gametes in the ovary, in humans producing one large haploid ovum and small polar bodies from each primary oocyte through meiosis.

The production of sperm in the seminiferous tubules of the testis, beginning with spermatogonia and ending with motile haploid sperm after meiosis and maturation.

A cap-like vesicle at the tip of a sperm head containing enzymes that digest the egg's outer layers, allowing the sperm to penetrate and fertilise the ovum.

A glycoprotein layer surrounding a mammalian egg that sperm must cross; after fertilisation it hardens to block further sperm and prevent polyspermy.

A temporary gland formed from the follicle after ovulation that secretes progesterone, maintaining the uterine lining and supporting early pregnancy.

A repeating hormonal cycle in human females of about 28 days in which the uterine lining thickens, an egg is released, and the lining is shed if pregnancy does not occur.

The release of a mature egg from an ovarian follicle, triggered by a surge of luteinising hormone and occurring near the middle of the menstrual cycle.

A steroid hormone secreted mainly by the corpus luteum and placenta that prepares and maintains the uterine lining for implantation and helps sustain pregnancy.

One of two or more alternative versions of a gene at the same locus on a chromosome, which may produce different traits such as different flower colours.

The genetic makeup of an organism at one or more loci, described by the alleles it carries, such as homozygous dominant, heterozygous, or homozygous recessive.

The observable characteristics of an organism, produced by the interaction between its genotype and the environment; examples include seed shape and blood group.

A relationship between alleles in which both are fully expressed in the heterozygote, as when the AB blood group shows both A and B antigens on red cells.

The tendency of genes located close together on the same chromosome to be inherited together, reducing the recombination frequency below the independent assortment expectation.

The exchange of corresponding segments between homologous chromosomes during prophase I of meiosis, producing new combinations of alleles on the resulting chromatids.

The generation of new allele combinations in offspring, arising from independent assortment of chromosomes and from crossing over between linked genes.

The process by which individuals with heritable traits that improve survival and reproduction leave more offspring, gradually changing the frequency of those traits in a population.

Random change in allele frequencies in a population from one generation to the next, especially strong in small populations, independent of any effect on survival.

The relative ability of an individual to survive and produce viable offspring that themselves reproduce, measured against other genotypes in the same population.

A form of genetic drift in which a small group splits from a larger population and establishes a new one, carrying only a subset of the original allele frequencies.

The rapid evolution of many divergent species from a single ancestral lineage that colonises a new habitat or gains a new way of life, such as Darwin's finches.

Body parts in different species that share a common structural plan and ancestry but may differ in function, such as the forelimbs of humans, bats, and whales.

Structures in unrelated organisms that perform similar functions but differ in origin and internal design, such as insect and bird wings, showing convergent evolution.

A Y-shaped protein made by plasma cells that binds specifically to an antigen, marking pathogens for destruction and neutralising toxins.

Any molecule, usually a protein or polysaccharide on a pathogen or foreign cell, that is recognised by the immune system and triggers an antibody response.

Protection against a pathogen provided by antibodies received from another source rather than made by the body, such as maternal antibodies or antiserum, and it fades quickly.

A preparation of weakened, killed, or fragmentary pathogen material that stimulates an immune response and creates long-lasting protective memory without causing the disease.

A small circular DNA molecule separate from the main chromosome in bacteria, widely used as a vector to carry foreign genes into host cells during genetic engineering.

A bacterial protein that cuts DNA at a specific recognition sequence, producing fragments with defined ends and used to insert genes into vectors.

A DNA molecule assembled in the laboratory by joining DNA from two different sources, such as a human gene inserted into a bacterial plasmid.

A technique that copies a chosen DNA segment many times in repeated cycles of heating and cooling, using primers and a heat-stable DNA polymerase.

A feeding position in a food chain, such as producer, primary consumer, or secondary consumer, defined by the number of energy-transfer steps from the sun.

A network of interconnected food chains in an ecosystem, showing how energy and matter pass between organisms through multiple feeding pathways.

A diagram representing numbers, biomass, or energy at each trophic level of an ecosystem, usually broad at the base and narrowing upward.

The gradual development of a community on bare ground with no existing soil or seeds, beginning with pioneer species such as lichens and mosses.

Nutrient enrichment of a water body, often by fertiliser or sewage runoff, that causes algal blooms, oxygen depletion, and death of aquatic animals.

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

The shrinking of a plant cell's protoplast away from its cell wall when water leaves by osmosis in a strongly hypertonic solution, causing wilting.

The outward pressure of cell contents against the cell wall when a plant cell is full of water, giving non-woody tissue its rigidity and driving cell expansion.

A double-membraned organelle where aerobic respiration and ATP synthesis occur, containing its own DNA and folded inner membranes called cristae.

A green double-membraned plant organelle containing thylakoid stacks and chlorophyll, where light energy is captured and converted into chemical energy in photosynthesis.

The splitting of water molecules by light energy in the light reactions of photosynthesis, releasing oxygen and supplying electrons and protons for ATP and NADPH formation.

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

The movement of sugars and other organic solutes through the phloem from sources such as leaves to sinks such as roots, fruits, and growing tips.

The response of plants to the relative lengths of day and night, controlling flowering in short-day and long-day plants and other seasonal changes.

The functional unit of the kidney, a tubule with a capillary tuft that filters blood and then reabsorbs useful materials and secretes wastes to form urine.

A tuft of capillaries inside the kidney's Bowman's capsule where high pressure forces water and small solutes out of the blood to begin urine formation.

The control of water and dissolved-salt balance in body fluids, achieved mainly by the kidneys under the influence of hormones such as ADH and aldosterone.

A rapid, self-propagating reversal of electrical charge across a neuron's membrane, caused by ion channels opening and used to carry nerve impulses.

The junction between a neuron and another neuron or effector cell, across which a signal passes by release of a chemical transmitter rather than by direct electrical contact.

A chemical released from the end of a neuron into a synapse that binds receptors on the next cell and excites or inhibits it, transmitting the nerve signal.

The iron-containing red protein in red blood cells that binds oxygen in the lungs and releases it in tissues, also carrying some carbon dioxide.