Biology year 2 D-M

• Diaphragm


  Muscle contraction causes it to flatten and air to be drawn into the lungs
• Diastole, Diastolic


  Stage in the cardiac or heart cycle when the heart muscle relaxes and the heart is filling with blood
• Diastolic pressure


  Blood pressure during the phase of the cardiac cycle when the ventricles are contracting
• Dichotomous key


  Used to identify organisms, there are always two possible answers to each question about the features of the organism
• Dicotyledon, Dicot


  Flowering plants which have two cotyledons in their seeds, including plants such as buttercups, roses and oak trees
• Dietary fibre


  Indigestible polysaccharides, thought to be important in the prevention of 'Western diseases'
• Differentiation, Differentiate


  Process by which cells become specialised for different purposes as an organism grows and develops
• Diffusion, Diffuse


  Movement of molecules from where they are in a high concentration to where they are in a lower concentration
• Diffusion gradient


  Difference in concentration which allows diffusion to take place
• Digestion, Digest


  Process in which large insoluble food molecules are broken down by enzymes to smaller soluble molecules
• Dihybrid inheritance


  Genetic cross involving genes at two different loci, where the inheritance of one pair of alleles does not affect the inheritance of the other pair
• Dipeptide


  Molecule made up of two amino acids joined by a peptide bond
• Diploid


  Cells or organisms with two copies of each chromosome
• Dipole


  Molecule with an unevenly distributed electrical charge, giving a positively charged and a negatively charged end
• Disaccharide


  Carbohydrate made up of two sugar units or monosaccharides
• Discontinuous variation


  Variation in which individuals fall into distinct categories with no intermediates, resulting from the genes inherited
• Disinfectant


  Substance that kills microorganisms when they are outside the body
• Dispersal, Disperse


  Way offspring of an organism are spread and reach new areas, helping to reduce competition
• DNA, Deoxyribonucleic acid


  Molecule that forms the genetic material of all living organisms, consisting of two polynucleotide chains forming a double helix
• DNA polymerase


  Enzyme that catalyses the joining together of individual nucleotides to form a molecule of DNA, essential for DNA replication and used in gene technology
• DNA primer


  Small piece of single-stranded DNA that acts as a signal, binding to and marking the piece of DNA to be copied in PCR
• DNA replication, Replication, Semi-conservative replication

  Process in which a DNA molecule produces two exact copies of itself, with each new molecule consisting of one existing chain and one new chain
• Dominant allele


  Allele whose effect is always shown, such as the allele for tall plants in peas
• Dominant species, Dominant organism


  Species which has an important effect on the other organisms in a community
• Dopamine


  Neurotransmitter secreted by neurones, including many in the midbrain, and involved in Parkinson's disease
• Dormant, Dormancy


  Seed that does not germinate and grow immediately, even in favourable conditions
• Dorsal


  Back or upper surface of an animal or structure associated with it
• Double circulation


  Type of blood system in which blood passes through the heart twice in its passage round the body, as in mammals
• Double-blind test


  Way of conducting a clinical trial where neither the patient nor the researcher knows who is having the drug and who is being treated with a placebo
• Duties


  Things each of us ought to do, such as looking after a child
• Ecosystem


  All the organisms living in a particular area as well as the non-living features of their environment
• Ecstasy, MDMA


  Illegal recreational drug containing MDMA that affects thinking, mood and memory
• Ectotherm


  Animal whose temperature fluctuates with that of its environment, such as a reptile
• Edaphic


  Ecological factor which is part of the abiotic or non-living environment and relates to the soil
• Effectors, Effector cells


  Tissue or organ that responds to a nerve impulse or hormone, bringing about a response or change
• Egg cell, Egg nucleus

  Haploid sex cell or gamete produced by meiosis in female sex organs, which fuses with a male gamete to form a zygote
• Electrocardiogram


  Graphic record of the electrical activity of the heart as it contracts and rests
• Electrochemical gradient


  Imbalance in the distribution of ions across a membrane resulting in an electrical difference
• Electron carrier


  Molecule that passes electrons along an electron transport chain, releasing energy used to produce ATP
• Electron transport chain


  Series of electron carrier molecules along which electrons are passed, releasing energy used to produce ATP