RBSE SS Agricultural Biology key terms

The process by which green plants use sunlight, water, and carbon dioxide to make sugars and release oxygen. Chlorophyll in chloroplasts captures light energy, which drives the light and dark reactions.

The green pigment in chloroplasts that absorbs light energy for photosynthesis. It absorbs mainly red and blue wavelengths and reflects green light, which is why leaves look green.

Loss of water vapour from plant leaves through small pores called stomata. It pulls water and dissolved minerals upward from roots and cools the leaf surface.

Tiny openings on leaf surfaces, bounded by guard cells, that allow carbon dioxide to enter and water vapour and oxygen to leave. They open and close in response to light, water status, and humidity.

The breakdown of sugars in living cells to release usable energy, carbon dioxide, and water. Aerobic respiration uses oxygen and occurs day and night in all plant tissues.

The response of plants to the relative lengths of day and night, controlling flowering and other developmental changes. Short-day plants flower when nights are long, while long-day plants flower when nights are short.

The promotion of flowering by exposure to a period of low temperature, especially in crops such as wheat and barley. It ensures flowering occurs in the appropriate season.

The proportion of total variation in a trait within a population that is due to genetic differences. High heritability means selection based on appearance is likely to be effective.

The genetic makeup of an organism, including the specific alleles it carries at particular gene loci. It interacts with the environment to produce the observable phenotype.

The observable characteristics of an organism, such as height, grain colour, or yield, resulting from the interaction of its genotype with the environment.

One of two or more alternative forms of a gene occupying the same position on a chromosome. Different alleles produce variations in traits such as flower colour or disease resistance.

Describing an organism that carries two identical alleles for a particular gene. Homozygous lines breed true and are important in producing pure-line varieties.

Describing an organism that carries two different alleles for a particular gene. Heterozygous plants often show hybrid vigour and are used to produce hybrid seed.

The superior growth, yield, or vigour shown by offspring produced by crossing genetically different parents. Also called heterosis, it is exploited in hybrid maize and many vegetable crops.

The deliberate choice of plants or animals with desirable traits to parent the next generation. It may be mass selection, pure-line selection, or progeny testing depending on the breeding goal.

A sudden heritable change in the DNA sequence of a gene or chromosome. Mutations create new alleles and are a source of genetic variation used in mutation breeding.

The resumption of growth by a seed, beginning with water uptake and ending with emergence of the radicle. It requires viable seed, adequate moisture, suitable temperature, and oxygen.

A condition in which viable seeds fail to germinate even when conditions are favourable. It may be caused by hard seed coats, immature embryos, or chemical inhibitors, and can be broken by scarification or stratification.

The quantity of seed sown per unit area, chosen so the resulting plant population matches the crop's optimum density. It depends on seed size, germination percentage, and spacing.

Growing different crops in a planned sequence on the same field over successive seasons. It helps maintain soil fertility, disrupt pest and disease cycles, and reduce soil erosion.

Growing two or more crops together in the same field at the same time, often in alternating rows. It improves land use efficiency and spreads risk for smallholder farmers.

The relative proportions of sand, silt, and clay particles in a soil. Texture strongly influences water-holding capacity, drainage, aeration, and workability.

The arrangement of soil particles into aggregates or clods, creating pore spaces for air and water. Good structure supports root growth and is improved by organic matter.

The ability of a soil to hold positively charged nutrient ions such as calcium, magnesium, and potassium on clay and humus surfaces. Soils with high capacity retain nutrients better.

A measure of the acidity or alkalinity of soil, on a scale from 0 to 14. It affects nutrient availability, microbial activity, and the choice of crops and amendments.

The capacity of a soil to supply essential plant nutrients in adequate amounts and suitable proportions. It is maintained through organic matter, fertilizers, and good management practices.

Living and dead plant and animal material in soil, including humus. It improves structure, water retention, and nutrient supply, and supports beneficial soil organisms.

A strategy that combines biological, cultural, mechanical, and chemical methods to keep pest populations below damaging levels. Chemical pesticides are used only when monitoring shows they are needed.

The pest population density at which control measures should be applied to prevent the pest from reaching the level where economic loss occurs. It guides when to spray.

The use of living organisms, such as predators, parasitoids, or pathogens, to suppress pest populations. Examples include ladybird beetles feeding on aphids and Trichoderma against soil-borne fungi.

An abnormal condition in a plant caused by a pathogen such as a fungus, bacterium, virus, or nematode, or by environmental factors. Symptoms include wilting, spots, blights, and stunting.

A set of criteria used to prove that a specific microorganism causes a particular disease. The organism must be isolated from a diseased host, grown in culture, and reproduce the disease when reinoculated.

The gross income from a crop or enterprise minus its variable costs. It is used in farm planning to compare the profitability of different enterprises.

The total expenditure incurred in producing a crop, including variable inputs and fixed costs. It is expressed per unit of output and used to set prices and assess profitability.

A process of helping rural people improve their farming and living through informal education and communication. It links research institutions with farmers using demonstrations, field days, and advisory services.

A field plot used to show farmers the practical results of improved practices, such as a new variety or fertilizer dose, alongside local practice. It is a common extension teaching tool.

An experimental layout in which treatments are randomly assigned within each block, and each block contains all treatments. Blocking controls field variation and improves the precision of comparisons.

The repetition of a treatment in an experiment so that experimental error can be estimated. More replications generally increase the reliability of conclusions.