Variety of living organisms 5.

Classification

The classification of living organisms according to their similarities is called Taxonomy.

There are 5 kingdoms: Animals, Plants, Fungi, Protoctists, Bacteria.

Each kingdom can be further divided according to the following systems until you have reached each individual species. Kingdom-Phylum-Class-Order-Family-Genus-Species.

The Animal Kingdom (Animalia)

These are multicellular organisms.

Their cells do not contain chloroplasts and are not able to carry out photosynthesis.

They do not have cell walls.

They usually have some nervous coordination and are able to move from one place to another.

They often store carbohydrate as glycogen in their muscles and liver.

They are heterotrophic (feeds on other plants or animals)

Animals can be further divided to 2 main categories:

1. Vertebrates: animals with a spine

2. Invertebrates: animals without a spine.

The Plant Kingdom (plantae)

They are multicellular organisms.

Their cells contain chloroplasts and are able to carry out photosynthesis.

They have cell walls made of cellulose.

They store carbohydrates as starch or glucose.

The Fungi Kingdom

These organisms are not able to carry out photosynthesis.

Their body is usually organized in to a mycelium made from thread-like structures called hyphae, which contain many nuclei.

Some of them are unicellular.

They have a cell wall made of chitin.

They use extracellular excretion of digestive enzymes onto food material and absorb the organic product. This is known as saprotrophic/saprophytic nutrition.

They may store carbohydrate as glycogen.

Examples: Mucor (has the typical fungal hyphal structure) ; Yeast (single celled)

The Protoctist Kingdom

These are unicellular organisms

Some have features of an animal cell (e.g. Amoeba, that lives in pond water) and some have features of a plant cell (e.g. chlorella)

Some of them are pathogens (e.g. Plasmodium, which causes malaria)

The Bacteria Kingdom

These are microscopic unicellular organisms

They have a cell wall, cell membrane, and cytoplasm.

They lack a nucleus (known as prokaryotes) but have 2 parts that contain genetic materials: small loops of DNA called Plasmid located in cytoplasm; and a circular chromosome of DNA.

Some of them contain a form of chlorophyll for photosynthesis

Some have a capsule of slime layer

Some species have flagella movement

Examples: Lactobacillus bulgaricus: a rod shaped bacterium used in the production of yoghurt from milk; Pneumococcus: a spherical bacterium that act as the pathogen causing pneumonia.

Virus

These are small particles, much smaller than bacteria.

They are parasitic and can reproduce only inside living cells (their host).

They infect every type of organisms.

They have no cellular structure but have a protein coat (called capsid) and contain one type of nucleic acid, either DNA or RNA

They are not considered as living organisms, as they lack their own metabolism and cellular structure, and cannot independently replicate outside of a host cell

Examples: Tobacco mosaic virus (causes discoloring of the leaves of preventing the formation of chloroplasts), Influenza virus (causes flu and HIV)