BGCSE BSSE Biology 1428 flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Prokaryotic cell

A cell without a membrane-bound nucleus or membrane-bound organelles; its DNA is a single circular chromosome in the nucleoid, and it may also contain plasmids.

Osmosis

The diffusion of water across a partially permeable membrane from a dilute solution to a more concentrated solution, down a water potential gradient, without energy input.

Active transport

Movement of substances across a membrane against a concentration gradient using energy from ATP and carrier proteins, allowing cells to accumulate ions or nutrients.

Enzyme active site

The region of an enzyme with a shape complementary to its substrate; binding here lowers activation energy, and the shape is lost on denaturation.

Denaturation

Irreversible loss of an enzyme's active site shape caused by high temperature or extreme pH, so the substrate can no longer bind and the reaction stops.

Benedict's test

A test for reducing sugars in which the blue reagent is heated with the sample and turns brick-red if a reducing sugar such as glucose is present.

Bile function

Bile, made in the liver and stored in the gall bladder, emulsifies fats into small droplets to increase surface area for lipase and neutralises acidic chyme.

Villi

Finger-like projections of the small intestine wall that increase surface area for absorption; they have thin walls and a rich blood supply.

Aerobic respiration

The breakdown of glucose using oxygen to release energy, producing carbon dioxide and water; it releases more energy per glucose molecule than anaerobic respiration.

Alveoli

Tiny air sacs in the lungs with thin, moist walls and a large total surface area, allowing efficient diffusion of oxygen in and carbon dioxide out.

Double circulation

A circulatory system in which blood passes through the heart twice per circuit, once to the lungs and once to the body, maintaining high pressure.

Transpiration

Loss of water vapour from leaves through stomata, driven by evaporation and cohesion-tension in xylem; faster in hot, dry, windy, bright conditions.

Negative feedback

A control mechanism in which a change from the set point triggers a response that reverses the change, restoring stable internal conditions such as temperature or blood glucose.

ADH

Antidiuretic hormone, released by the pituitary gland, increases water reabsorption in the kidney collecting duct, producing more concentrated urine when dehydrated.

Reflex arc

The pathway of a reflex response: receptor, sensory neurone, relay neurone in the spinal cord, motor neurone, and effector, giving a rapid protective reaction.

Synapse

A small gap between two neurones across which a neurotransmitter diffuses to trigger an impulse in the next neurone, ensuring one-way transmission.

Meiosis

A type of cell division that halves the chromosome number, producing four haploid gametes and creating variation through crossing over and independent assortment.

Placenta

An organ in pregnancy that allows oxygen, glucose and antibodies to pass from mother to fetus and carbon dioxide and urea to pass back.

Dominant allele

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

Punnett square

A grid used to predict offspring genotypes by combining the gametes of two parents; a cross of two heterozygotes gives a 3:1 phenotype ratio.

Trophic level

A feeding level in a food chain, such as producer or primary consumer; only about ten per cent of energy passes to the next level.

Eutrophication

Nutrient enrichment of water by fertiliser run-off, causing algal blooms whose decomposition depletes oxygen and kills fish and other organisms.

Natural selection

The process by which organisms with inherited traits suited to their environment survive and reproduce more, so favourable alleles become more common over generations.

Binomial nomenclature

A two-part naming system using genus and species, such as Homo sapiens; the genus is capitalised, the species lower case, and both are italicised.

Vaccination

Introduction of antigens from weakened or killed pathogens to stimulate antibody production and memory cells, giving immunity without causing the disease.

Antibiotic resistance

The ability of bacteria to survive antibiotic treatment, arising when resistant individuals survive and reproduce, passing resistance alleles to offspring.

Mitosis

Cell division producing two genetically identical diploid daughter cells, used for growth, repair and asexual reproduction in organisms.

Cell membrane

A partially permeable phospholipid bilayer with embedded proteins that controls the movement of substances into and out of the cell.

Glycolysis

The first stage of respiration, occurring in the cytoplasm, in which glucose is broken down to release energy and produce pyruvate without requiring oxygen.

Haemoglobin

The red pigment in red blood cells that binds oxygen in the lungs, where oxygen concentration is high, and releases it in respiring tissues.

Insulin

A hormone secreted by the pancreas when blood glucose is high; it promotes glucose uptake by cells and storage as glycogen in the liver.

Phototropism

Growth of a plant shoot towards light caused by auxin accumulating on the shaded side, where cells elongate more, bending the shoot towards the light.