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Allopatric speciation occurs when populations of a species are separated by a physical barrier - this could be a river for animals that cannot swim, for example. Separation of the populations means that t...

DNA (deoxyribonucleic acid) is a double helix composed of units called nucleotides. Each nucleotide is composed of a single deoxyribose sugar, a phosphate group and one of four nitrogen bases. The 4 bases...

Endocrine organs release their products (usually hormones) directly into the blood. The pancreas contains islets of Langerhans which are made up of alpha and beta cells. Beta cells secrete insulin and alp...

. increase in the number of cases of antibiotic resistance . increase in risk of horizontal gene transfer of resistance . resistant bacteria causes harm/ ineffective medical treatments . reduces risk of/ ...

Natural selection describes the selective pressure favouring those species with certain phenotypes (characteristics) which make them better suited to the environment than other species. Those with favoura...