D Flashcards
Deamination
The process, which takes place in the liver, where the nitrogen-containing part of amino acids is removed to form ammonia. ammonia is then converted into urea.
Decay
The breakdown of dead organisms and waste material by decomposers.
Decomposers
Microorganisms, mainly bacteria and fungi that gain their energy by breaking down dead organisms and waste material.
Deficiency disease
A condition when an important nutrient, such as a vitamin or mineral, is missing and results on a disease.
Deforestation
The removal of trees by humans in order to exploit the land.
Denitrification
Conversion of nitrate ions into nitrogen gas by bacteria.
Denitrifying bacteria
Bacteria which live in anaerobic conditions, such as water-logged soil, and convert nitrate ions into nitrogen gas.
Development
An increase in complexity as an embryo grows and gains new tissues, organs and organ systems.
Diabetes
A medical condition in which the blood glucose concentration is not controlled. one cause of diabetes is the failure of the pancreas to secrete insulin.
Dialysis
The use of a partially permeable membrane to separate substances.
Diaphragm
A sheet of muscular and fibrous tissue that separates the thorax from the abdomen. its movements cause air to flow in and out of the lungs
Diarrhoea
A condition where the faeces released are loose and watery. a symptom of diseases, such as cholera.
Dicotyledon
A type of flowering plant with an embryo that has two cotyledons and a net-like arrangement of veins in its leaves. (Also known as eudicotyledon.)
Diffusion
The net movement of molecules or ions, from a place with a higher concentration to a place with a lower concentration down a concentration gradient as a result of random movement.
Digestion
The breakdown of large, insoluble food molecules into small, water-soluble molecules using mechanical and chemical processes.
Digestive system
The organ system that breaks down food and absorbs it into the blood.
Diploid nucleus
A nucleus containing two sets of chromosomes (e.g. in body cells).
Discontinuous variation
Limited number of phenotypes for a feature with no intermediates, e.g human blood groups.
DNA
The molecule that forms the genetic material. the sequence of bases in DNA codes for the sequence of amino acids in proteins.
Dominant
An allele that is expressed if it is present (e.g. T or G).
Drug
Any substance taken into the body that modifies or affects chemical reactions in the body.
Duodenum
The first part of the small intestine.
