definitions - set 4 Flashcards
heterozygous
having two different alleles of a gene (e.g. Tt or Gg), not pure-breeding
hilum
the scar where a seed was attached to a fruit
homeostasis
the maintenance of a constant internal environment
homologous chromosomes
the two chromosomes of a pair in a diploid cell; they have genes for the same features at the same positions
homozygous
having two identical alleles of a particular gene (e.g. TT or gg). Two identical homozygous individuals that breed together will be pure-breeding
hormone
a chemical substance produced by a gland, carried by the blood, which alters the activity of one or more specific target organs and is then destroyed by the liver
hydrophyte
a plant adapted to live in wet conditions
hyperglycaemia
having too much glucose in the blood
hypertension
high blood pressure
hypoglycaemia
having too little glucose in the blood
hypothalamus
a part of the brain that helps to regulate body temperature
immune
able to fight off a particular type of pathogen before it causes any symptoms in the body
implantation
the movement of a young embryo into the lining of the uterus, and its attachment there
ingestion
taking substances (e.g. food, drink) into the body through the mouth
inheritance
the transmission of genetic information from generation to generation
inorganic
substances that are not made by living organisms
insulin
a hormone secreted by the pancreas, which reduces blood glucose level
intercostal muscles
muscles between the ribs, which help to produce breathing movements
involuntary action
an action taken automatically, without conscious thought
iris
the coloured part of the eye, which controls the amount of light allowed through to the lens and the retina
islets of Langerhans
groups of cells in the pancreas which secrete insulin and glucagon
key
a series of questions whose answers lead you to the identification of an organism
kingdom
one of the five large groups into which all living organisms are classified
kwashiorkor
a deficiency disease caused by lack of protein in the diet
lactation
production of milk by mammary glands
lag phase
the early stage of population growth, when numbers scarcely change
lamina
the main part of a leaf
LH
luteinising hormone; a hormone secreted by the pituitary gland which causes an egg to be released from an ovary
light microscope
a microscope that uses light to produce images
lignin
a tough, waterproof material that makes up the walls of xylem vessels; wood is mostly lignin
limiting factor
something present in the environment in such short supply that it restricts life processes
lipase
an enzyme that digests fats (lipids) to fatty acids and glycerol
lipids
fats, oils and waxes
log phase (exponential phase)
the stage in population growth when numbers increase exponentially
lymph
the fluid found inside lymph vessels, formed from tissue fluid
lymph nodes
organs in which large numbers of white blood cells (which can destroy bacteria or toxins) collect
maltase
an enzyme that breaks down maltose to glucose
marasumus
a disease resulting from a severe lack of energy in the diet
maltose
a disaccharide produced by the digestion of starch
mechanical digestion
the breakdown of large pieces of food to smaller ones, incresasing their surface area; it is done by teeth in the mouth and by the contraction of muscles in the stomach wall
medulla (in kidney)
the central area in a kidney
meiosis
reduction division in which the chromosome number is halved from diploid to haploid
memory cells
cells produced by activated lymphocytes, that remain in the body and are able to respond quickly to a pathogen
menstruation
the loss of the uterus lining through the vagina
mesophyll
the tissues in the centre of a leaf, where photosynthesis takes place
metabolic reactions
the chemical reactions that take place inside a living organism
micrometre
1 x 10 -6 metres
micropyle
a tiny hole in the testa of a seed
mineral
an inorganic ion required in small quantities by living organisms
mitochondria
organelles in which aerobic respiration takes place, releasing energy for use by the cell
