The Five Kingdoms and Classifying Organisms Study Guide

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Updated on Apr 25, 2014


Life began as very simple molecules that were bound by membranes. Eventually, these membrane-bound molecules were assembled into more complex structures we call cells. These cells evolved into many forms and even became multicelled collections, leading to organisms such as ourselves. All these organisms adapted to their environment and have characteristics that distinguish them from each other. Scientists have developed systems to organize and classify all of Earth's organisms.


Life first appeared on Earth as very simple, very tiny microorganisms. These creatures were mostly groups of organic molecules surrounded by a membrane. However, they could feed themselves in some fashion and were able to grow and reproduce. Gradually, over time and through the process of evolution, organisms assumed new forms. Eventually, life on Earth developed into many diverse forms and formed complex relationships. We have been able to organize life into five large groupings called Kingdoms. Each Kingdom contains organisms that share significant characteristics that distinguish them from organisms in the other Kingdoms. The five Kingdoms are Animals, Plants, Fungi, Protists, and Bacteria.

The Animal Kingdom

The organisms classified into this Kingdom are multicellular and, because they do not have chlorophyll, are unable to photosynthesize. We call them heterotrophs, meaning "eater of others," because they must eat preexisting organic matter (either plants or other animals) to sustain themselves. Animals have tissues that are more complexly constructed than plants and one-celled organisms. Animals also possess nervous tissue, which has reached high stages of development into nervous systems and brains. Animals are able to move from place to place (locomote) using their muscular systems. We usually divide the Animal Kingdom into two large groups, the vertebrates (animals with backbones) and the invertebrates (animals without backbones).

The Plant Kingdom

Plants are multicellular organisms that use chlorophyll in specialized cellular structures called chloroplasts to capture sunlight energy and convert it into organic matter. We refer to plants as autotrophs (self-feeders). Also included in the Plant Kingdom are algae that are not multicellular, but are cells with a nucleus (unlike bacteria).

Besides the algae, most plants are divided into one of two groups, the nonvascular plants (such as mosses) and the vascular plants (such as most crops, trees, and flowering plants). Vascular plants have specialized tissue that allows them to transport water and nutrients from their roots to their leaves and back again, even when the plant is several hundred feet tall. Nonvascular plants cannot do this and remain very small in size. Vascular plants are able to inhabit moist as well as dry environments, whereas nonvascular plants are mostly found in moist, marshy areas because they have no vascular tissue to transport water.

The Fungi Kingdom

Organisms in this Kingdom share some similarities with plants yet maintain other characteristics that make them more animal-like. They lack chlorophyll and cannot perform photosynthesis, so they don't produce their own food and are called heterotrophs. However, they reproduce by spores like plants do. They also resemble plants in appearance. The most common representative organisms in this Kingdom are mushrooms, yeasts, and molds. Fungi are very common and are a major benefit to other organisms, including humans. The bodies of fungi are made of filaments called hyphae. In large fungi, the hyphae interconnect to form tissue called mycelium. The largest organism in the world is believed to be a soil fungus whose mycelium tissue extends for many acres.

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