Classification of Organisms and Photosynthesis

Classification of Organisms

Taxonomy: the branch of science that deals with classifying organisms

Carl Linneaeus developed a hierarchy of levels for classifying organisms. As you travel down the levels, they become more and more specific.

Organisms are classified into three domains.

  • Archaea: single-celled organisms that live in extreme environments

  • Bacteria: single-celled bacteria in everyday life

  • Eukarya: the only domain that has cells with a nucleus

The kingdoms of the domain Eukarya:

  • Protists: single-celled, microscopic organisms

  • Fungi: reproduce by spores, include mushrooms

  • Plants: multicellular organisms that produce their own food

  • Animals: include humans, mammals, etc.

Some important animal phyla:

  • Cnidarians: aquatic invertebrates (ex. jellyfish)

  • Mollusks: invertebrates (ex. octopuses, clams, and oysters)

  • Annelids: segmented worms (ex. earthworms and leeches)

  • Arthropods: invertebrates with exoskeletons (ex. insects)

  • Echinoderms: marine animals with radial symmetry (ex. starfish)

  • Chordates: animals with backbones (ex. humans and dogs)

Some important plant phyla:

  • Mosses: plants without true leaves, roots, or stems

  • Ferns: reproduce with spores

  • Conifers: reproduce with seeds found in cones (ex. pine trees)

  • Flowering plants: reproduce with seeds found in flowers (ex. roses)

Binomial nomenclature: the system of naming organisms where both genus and species names are used (for example, Homo sapiens; Homo is the genus and sapiens is the species)

Scientific definition of a species: a group of similar-looking organisms that can interbreed under natural conditions and produce offspring that are capable of reproduction

Factors that help scientists classify organisms:

  • Presence or absence of cellular structures, such as the nucleus, mitochondria, or a cell wall

  • Whether the organism is single-celled or multicellular

  • How the organism gets their food


Photosynthesis: a necessary life process for plants that transforms light energy (sunlight) into chemical energy (sugar)

Chloroplast: the organelle in a plant where photosynthesis takes place

Chlorophyll: a chemical in chloroplasts that can absorb light energy

Photosynthesis involves a series of chemical reactions in which light energy is used to change carbon dioxide and water into sugar (glucose) and oxygen. The sugar is a form of stored energy that the plant can use later.

Plants convert the sugars they produce into other materials that are used by themselves and animals that eat these plants for growth, repair, and energy needs.

Photosynthesizing organisms are often called producers and form the foundation of all food webs.


Sources Used and Helpful Links