Species, populations

An organism is one individual living thing. Example: one dog, one sunflower, or one bacterium.

No. A herd is many organisms. One elephant is one organism.

A species is a group of organisms that can breed together and produce fertile offspring.

Fertile offspring means the babies can grow up and have babies of their own.

Yes. They can breed and produce fertile puppies, so they are the same species.

No. They do not normally produce fertile offspring, so they are different species.

Classification helps scientists identify organisms and organise the huge variety of life.

If you know the group an organism belongs to, you can predict features. Example: if it is a mammal, it likely has hair and feeds milk to young.

A binomial name is a two-part scientific name: Genus then species. Example: Homo sapiens.

Write Genus with a capital letter and species in lower case, and put both in italics (or underline). Example: Homo sapiens.

A genus is a group of closely related species. Example: Canis includes dogs, wolves, and coyotes.

Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species.

Some organisms have mixed features. Example: a platypus has fur like a mammal but lays eggs.

New evidence, especially DNA evidence, can show organisms are more or less related than we thought.

Can they breed and produce fertile offspring? If yes, they are the same species.

Homo sapiens.

It makes biodiversity and population data accurate, so scientists can make correct conclusions and conservation decisions.

Examples include leaf shape, flower colour, number of petals, or presence of thorns.

Examples include number of legs, wings, antennae, or body segments.

A dichotomous key is an identification tool that uses a series of paired choices to identify an organism.

It means “two choices”. At each step you must choose between two contrasting options.

1 Read both choices. 2 Pick the choice that matches your organism. 3 Follow to the next step until you reach a name.

It is quick and low cost, and it can be used in fieldwork without lab equipment.

If the organism is damaged, very young, or looks similar to other species, you may choose the wrong path and get the wrong identification.

A caterpillar is an immature stage and may not have the adult features the key expects, so it can be misidentified.

Always read both choices carefully before deciding.

A population is a group of the same species living in the same area at the same time. Example: wolves in one national park.

A species is all organisms of that type worldwide. A population is one local group of that species in one place.

Births and immigration increase population size. Deaths and emigration decrease population size.

An abiotic factor is a non-living condition. Examples: temperature, light, water, pH, or salinity.

A biotic factor is a living influence. Examples: predation, competition, disease, or availability of food.

Low water can limit plant populations because photosynthesis and growth slow down.

An increase in predators can reduce prey population size by increasing deaths.

A limiting factor is something that restricts the size, growth, or distribution of a population.

A tolerance curve shows how well a species survives as one abiotic factor changes, such as temperature.

The optimum is the best condition where the species does best (highest survival or growth).

The zone of stress is near the limits: the species may survive but grows or reproduces poorly.

A fish may grow best at about 22°C. It may survive from about 10°C to 35°C. Outside that range it may die.

Abiotic factors are non-living conditions. Biotic factors are living interactions.