Cameroon GCE O-Level Human Biology flashcards

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

Cell membrane

A thin partially permeable layer surrounding the cell that controls which substances enter and leave, allowing diffusion, osmosis and active transport to occur.

Mitochondrion

An organelle with folded inner membranes where aerobic respiration takes place, releasing energy from glucose for the cell's activities.

Mitosis

A type of cell division producing two daughter cells with the same diploid chromosome number as the parent, used for growth, repair and asexual reproduction.

Meiosis

A reduction division producing four haploid gametes with half the chromosome number, increasing genetic variation through crossing over and independent assortment.

Osmosis

The net movement of water molecules across a partially permeable membrane from a region of higher water concentration to a region of lower water concentration, without energy input.

Enzyme denaturation

Loss of enzyme function when high temperature or extreme pH alters the shape of the active site so the substrate no longer fits, and the change is usually irreversible.

Bile

A green fluid made by the liver and stored in the gall bladder that emulsifies fats into small droplets and neutralises acidic food entering the small intestine.

Villi

Finger-like projections of the small intestine lining that increase surface area for absorption, each with a thin wall, capillaries and a lacteal.

Peristalsis

Wave-like contractions of muscles in the wall of the gut that push food along the alimentary canal during digestion.

Haemoglobin

The red iron-containing pigment in red blood cells that combines with oxygen in the lungs and releases it in respiring tissues.

Double circulation

A circulatory arrangement in which blood passes through the heart twice per complete circuit, once to the lungs and once to the body.

Pacemaker

A group of cells in the right atrium that generates electrical impulses setting the rhythm of the heartbeat.

Alveolus

A tiny air sac in the lungs with a moist, one-cell-thick wall and a dense capillary network, adapted for gas exchange by diffusion.

Anaerobic respiration

Release of energy from glucose without oxygen, producing lactic acid in human muscle and ethanol plus carbon dioxide in yeast.

Ventilation

The mechanical movement of air into and out of the lungs caused by pressure changes produced by the diaphragm and intercostal muscles.

Homeostasis

The maintenance of a stable internal environment, such as constant body temperature, blood glucose and water content, using negative feedback.

Nephron

The functional unit of the kidney that filters blood at the glomerulus and reabsorbs useful substances before urine is formed.

ADH

Antidiuretic hormone released by the pituitary gland that increases water reabsorption in the kidney tubules, producing smaller amounts of more concentrated urine.

Vasodilation

Widening of blood vessels near the skin surface, increasing blood flow and heat loss by radiation to cool the body when it is too warm.

Reflex action

A rapid, automatic response to a stimulus that travels through a reflex arc without conscious control, protecting the body from harm.

Synapse

The junction between two neurones or a neurone and an effector, across which an impulse is carried by a chemical transmitter.

Insulin

A hormone secreted by the pancreas that lowers blood glucose by promoting its uptake by cells and its conversion to glycogen in the liver.

Antagonistic muscles

A pair of muscles that work in opposition at a joint, one contracting while the other relaxes, because muscles can only pull, not push.

Synovial joint

A freely movable joint where cartilage covers bone ends, synovial fluid lubricates them, and ligaments hold the bones together.

Ovulation

The release of a mature egg from an ovary, usually around the middle of the menstrual cycle, after which it travels along the fallopian tube.

Placenta

An organ formed in the uterus that allows nutrients, oxygen and waste to pass between mother and fetus and secretes hormones maintaining pregnancy.

Antibody

A protein produced by lymphocytes that binds specifically to a pathogen's antigen and helps destroy it, giving immunity after infection or vaccination.

Vaccination

Introduction of weakened or inactive antigens into the body so that antibodies and memory cells form without the person suffering the disease.

Allele

One of the alternative forms of a gene, such as the dominant or recessive form, that determines a particular characteristic.

Genotype

The combination of alleles an organism carries for a characteristic, described as homozygous or heterozygous and written with letters.

Food chain

A sequence showing the transfer of energy from a producer through consumers, with arrows pointing in the direction of energy flow.

Eutrophication

Enrichment of water with nitrates and phosphates from fertiliser runoff, causing algal blooms, decay and oxygen depletion that kills aquatic animals.