Cambridge O Level Biology · Syllabus 5090 · Classification
Species
What is Species?
A species is a group of organisms that can reproduce with one another to produce fertile offspring. Members of a species may vary in appearance, so the defining test is not resemblance but whether the offspring produced are themselves able to reproduce.
This definition is part of the Classification chapter in Cambridge O Level Biology.
Species in context
Classification is the placing of living organisms into groups on the basis of the features they share, so that organisms with many features in common sit in the same group. Cambridge O Level Biology (5090) Chapter 2 covers four things: the definition of a species and the binomial naming system, dichotomous keys, the five kingdoms (animal, plant, fungus, prokaryote and protoctist), and the observable features that separate the vertebrate groups, the arthropod groups, ferns from flowering plants and monocotyledons from dicotyledons. Viruses sit apart from all five kingdoms because they have no cellular structure.
A species is a group of organisms that can reproduce with one another to produce fertile offspring. Every species is named using the binomial system: the genus name first, beginning with a capital letter, followed by the species name in lower case, for example Homo sapiens. Both words are italicised when typed and underlined separately when handwritten. Resemblance is not the test — a horse and a donkey produce a mule, which is not fertile, so they are two different species, while two dogs of different breeds belong to one species.
Common mistakes with Species
- 1. Defining a species without the word "fertile" Fix A species is a group of organisms that can reproduce with one another to produce fertile offspring. A horse and a donkey produce a mule, which is not fertile — so they are not one species.
- 2. Capitalising the species part of a binomial Fix Homo sapiens, never Homo Sapiens. Genus capital, species lower case, both italic when typed.
- "Members of a species look identical." Repair They can vary. The defining test is that they can reproduce with one another to produce fertile offspring, not that they resemble each other. Two dogs of different breeds are one species; two identical-looking beetles that cannot produce fertile offspring are two species.
- Writing homo Sapiens. Repair Homo sapiens. The genus takes the capital, the species stays lower case, both are italicised when typed and underlined separately when handwritten.
Questions students ask about Species
What is a species in O Level Biology?
A species is a group of organisms that can reproduce with one another to produce fertile offspring. The word "fertile" is essential: a horse and a donkey can breed, but the mule they produce is not fertile, so they are not one species. Members of a species can vary in appearance — two dogs of different breeds are one species — so "they look alike" is not the test, and neither is "they can breed" on its own.
How do you write a scientific name correctly?
Use the binomial system: the genus name first, beginning with a capital letter, then the species name in lower case, for example Homo sapiens. Both words are italicised when typed and underlined separately when handwritten. Writing Homo Sapiens or homo Sapiens loses the mark, because the capital belongs on the genus only and the species part always stays lower case.