definitions - set 8 Flashcards
umbilical cord
an organ linking an embryo to the placenta, containing blood vessels
unicellular
made of one cell
urea
the main nitrogenous excretory product of mammals, produced in the liver from excess amino acids
ureter
a tube that leads from a kidney to the bladder
urethra
a tube that leads from the bladder to the outside
urine
a solution of urea and other excretory products in water, produced by the kidneys
uterus
the organ in a mammal in which the embryo develops
vaccination
the introduction to the body of dead or weakened pathogens, to make a person immune to an infectious disease
variation
differences between individuals of the same species
vascular bundle
a vein in a plant, containing xylem vessels and phloem tubes
vasoconstriction
narrowing of blood vessels
vasodilation
widening of blood vessels
vein
a blood vessel that carries blood towards the heart
vesicle
a very small vacuole (space inside a cell)
villus (plural: villi)
a tiny, finger-like process on the inner wall of the small intestine; villi increase the surface area for digestion and absorption
vitamins
organic substances required in small quantities in the diet
voluntary action
an action taken as the result of a conscious decision
water potential
a measure of the tendency for water to move out of a solution; the more water in the solution, the greater its water potential
xerophyte
a plant adapted to live in dry conditions
xylem vessels
long hollow tubes made up of dead, empty cells with lignified walls, which transport water in plants and help to support them
zygote
the diploid cell produced when two gametes fuse
