definitions - set 5 Flashcards
mitosis
nuclear division giving rise to genetically identical cells in which the chromosome number is maintained by the exact duplication of chromosomes
monoculture
a large area of the same crop plant
monosaccharide
a simple sugar; a carbohydrate whose molecules are made of one sugar unit
morphology
the overall shape and form of an organism’s body
movement
an action by an organism or part of an organism causing a change of position or place
mutagen
a substance that causes mutations
mutation
a change in a gene or a chromosome
myelin
a fatty substance surrounding the axons of many neurones, enabling the nerve impulse to travel faster
natural selection
the greater chance of passing on of genes by the best-adapted organisms
nectary
a gland producing a sugary fluid, found in many insect- or bird- pollinated flowers
negative feedback
a mechanism used in homeostasis, in which a change in a parameter brings about actions that push it back towards normal
nephron
one of the thousands of tiny tubules in a kidney, in which urine is produced
nerve
a bundle of axons or dendrons belonging to many different neurones
nerve impulse
an electrical signal that sweeps along a neurone
neurone
a nerve cell; a cell specialised for the rapid transfer of electrical impulses
nicotine
an addictive drug found in tobacco smoke
nitrifying bacteria
bacteria that obtain their energy by converting ammonia or nitrite ions to nitrate ions
nitrogen fixation
changing unreactive nitrogen gas into a more reactive nitrogen compound such as nitrate or ammonia
nitrogenous waste
excretory products containing nitrogen - for example, ammonia, urea, uric acid
non-biodegradable
not able to be broken down by microorganisms
normal distribution
a curve in which the largest number occurs near the midpoint, with approximately equal quantities on either side of this point and a gradual decrease towards the extremes
nucleus
a large organelle in which chromosomes are found
nutrition
taking in materials that are required for energy, growth and development
oesophagus
the part of the alimentary canal along which food travels from the mouth to the stomach
oestrogen
a hormone secreted by the ovaries that helps to control the menstrual cycle
optimum temperature
the temperature at which something happens most rapidly
organ
a structure made up of a group of tissues, working together to perform specific functions
organ system
a group of organs with related functions, working together to perform body functions
organelle
a structure within a cell
organic
a term used to describe substances that have been made by living organisms, or whose molecules contain carbon, hydrogen and oxygen
organism
a living thing
osmosis
the diffusion of water molecules from a region of high water potential to a region of lower water potential, through a partially permeable membrane
ovary
an organ in which female gametes are made
oviduct
the tube leading from an ovary to the uterus
ovulation
the release of an egg from an ovary
ovule
a structure in the ovary of a flower which contains a female gamete
oxygen debt
the extra oxygen that must be taken in by the body following strenuous exercise, when anaerobic respiration took place; the oxygen is needed to break down the lactic acid that accumulated as a result of anaerobic respiration
oxygenated blood
blood containing a lot of oxygen; in humans, blood becomes oxygenated in the lungs
palisade layer
the upper mesophyll layer in a leaf, made up of rectangular cells containing many chloroplasts
pancreas
an organ lying close to the stomach, which is both an endocrine gland (producing insulin and glucagon) and an exocrine gland (producing pancreatic juice)
pancreatic juice
the liquid secreted into the pancreatic duct by the pancreas; it flows into the duodenum where its enzymes help with digestion of fats, proteins and carbohydrates
partially permeable
allowing some molecules to pass through, but not others
passive immunity
having antibodies provided from another organism, that temporarily protect against a pathogen
pathogen
a disease-causing organism
pelvis
(in kidney) the part from which the ureter emerges
penicillin
an antibiotic which destroys bacteria by damaging their cell walls
pepsin
a protease enzyme found in the stomach
peripheral nervous system
all the nerves and receptors in the body, not including the brain or spinal cord
peristalsis
rhythmic contractions of muscles that ripple along a tube - for example, peristalsis pushes food through the alimentary canal
petiole
a leaf stalk
