Classification systems change over time. All living thing used to be lumped together into two kingdoms: plants and animals. There are now 5 kingdoms. Living organisms are classified according to shared characteristics. The five kingdoms are:
- Kingdom: Protista/protoctista-Features: Single celled, have a nucleus, some have some chloroplasts, no cell wall, organelles present- Feeding Method: Photosynthesis or ingestion of other organisms or both- Movement: Move using cilia or flagella.
- Kingdom: Monera (prokaryotes)-Features: Single celled, no nucleus, no chloroplasts, have a cell wall- Feeding Method: Absorb nutrients through cell wall, or produce their own.- Movement: May or may not move.
- Kingdom: Fungi-Features: Multicellular, have a nucleus, no chloroplasts, have a cell wall-Feeding Method: acquire nutrients from decaying material.- Movement:no mechanism for movement.
- Kingdom: Plants- Features: Multicellular, have a nucleus, chloroplasts and cell walls- Feeding Method: require sunlight to make food through photosynthesis -Movement: Most dont move.
- Kingdom: Animals- Features: Multicellular, have a nucleus, no chloroplasts, no cell walls- Feeding Method: acquire nutrients by ingestion -Movement: move using cilia, flagella or muscles.
This classification system may need to be updated/changed in te future as more species are found and new discoveries, especially in genetics, are made. Accepted systems of classification have historically changed.
Problems classifying Organisms
Some organisms from different species can mate and reproduce to give birth to a hybrid. Hybrids aren't fertile so they can't be called a new species.
Classifying some organisms, e.g. those in a micro-environment, can be difficult. The variety of life is a continuous spectrum which makes it difficult to place some organisms into distinct groups. Organisms that only reproduce asexually can be hard to classify.Organisms are constantly changing to suit their environment.