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Academia - Collins Scientific Pocket Dictionaries - Biology
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vacuole
vacuum f

gap . A fluid-filled space within a cell's cytoplasm that contains many compounds, such as dissolved sugars. Vacuoles are particularly important in maintaining turgor in plant cells. See cell and contractile vacuole


vagina
vagin m

Vagina. A canal found in most female mammals that receives the penis during copulation. The vagina connects the uterus to the outside, which is the path through which the foetus passes at birth (brith).
See fertilization in humans.


valves
valves fpl

Valves are membranous structures found inside circulatory systems in animals that allow blood to flow in only one direction.

(a) mitral valve (or bicuspid valve)
Two folds between the atrium: the left atrium and the left ventricle in the hearts of birds and mammals.

(b) Tricuspid valve: three folds between the right atrium and the right ventricle in the mammalian heart.

(c) Semilunar valves: crescent-shaped folds in the heart of a mammal between the right ventricle and the pulmonary artery and between the left ventricle and the aorta. Semilunar valves are also found in lymphatics and veins.
See heart heartbeat.


variation
variation f

diversity. Differences in characteristics between members of the same species. There are two main types:
(a) Continuous variations that have degrees of diversity within the population and show a normal distribution around the mean. Such as: height, weight, and pulse rate in humans.

Example: Height data for a sample of adult men.

(b) Discontinuous variations are quite clear, meaning there are no intermediate forms, such as blood types in humans. Discontinuous variations do not show a normal distribution and are used when making genetics crossings.
Variation within a species results from either inherited or environmental factors, or both.

Thus, humans inherit genes that affect their height, for example, but they are also subject to environmental factors such as food. Inherited variations are considered the basis of evolution by natural selection.


vascular bundle
Faisceau m fibro-vascular

Vascular bundle. A strand of longitudinal transmitting tissue within plants consisting mainly of xylem and phloem.
See root, stem, and leaf.

Vascular bundle in the leg


vegetable reproduction (or propagation)
Reproduction in vegetables

Vegetative reproduction or plant reproduction. Asexual reproduction in plants occurs by growing from a mother organism with a multicellular body that may separate and develop independently to become a new plant. See tuber, stolon, rihzome, corm, and bulbs.


vein
vein f

Sweat. vein. 1 - One of the vascular bundles in a plant leaf.
2- A blood vessel transports blood from tissues to the heart. In mammals, veins carry deoxygenated blood (there is an exception to this rule, see pulmonary vessels) formed into smaller vessels called venules, which carry blood from capillaries. The veins are thin-walled, and because the blood pressure in the veins is lower than in the arteries, the veins have valves that prevent the blood from flowing back from the heart.

Valve action in the veins
Vein clip
blood flow
Thin wall
Blood pressure closed valve