Kingdoms of Life — Reading Comprehension Lesson

Reading Passage

Kingdoms of Life

Scientists classify all living things into groups based on their shared characteristics — a system called taxonomy. The broadest grouping is the kingdom. Most biologists today recognize six kingdoms of life: Animalia (animals), Plantae (plants), Fungi, Protista, Eubacteria, and Archaebacteria. Every organism on Earth belongs to one of these six kingdoms. Classification helps scientists communicate about organisms, understand evolutionary relationships, and study the diversity of life. Within each kingdom, organisms are further divided into progressively smaller groups: phylum, class, order, family, genus, and species.

Kingdom Animalia includes all multicellular organisms that cannot make their own food and must eat other organisms to obtain energy. Animals have cells without cell walls, most can move, and they reproduce sexually. The animal kingdom is extraordinarily diverse, from sponges and jellyfish to insects, fish, birds, and mammals. Kingdom Plantae includes multicellular organisms that make their own food through photosynthesis. Plant cells have rigid cell walls made of cellulose and contain chloroplasts. Plants are the primary producers in most terrestrial ecosystems, forming the base of food chains.

Kingdom Fungi includes organisms such as mushrooms, molds, and yeasts that obtain nutrients by secreting digestive enzymes onto their food and absorbing the broken-down molecules — a process called external digestion. Fungi play a crucial role in ecosystems as decomposers, breaking down dead organic matter and recycling nutrients. Kingdom Protista is a diverse catch-all group of mostly unicellular eukaryotes that do not fit neatly into the other kingdoms. It includes algae (which photosynthesize), amoebas (which engulf food), and paramecia (which use hair-like cilia to move and feed). Some protists cause significant human diseases, including malaria.

The two bacterial kingdoms — Eubacteria and Archaebacteria — consist of prokaryotic organisms: simple, single-celled life forms without a membrane-bound nucleus. Eubacteria are the familiar bacteria found everywhere — in soil, water, air, and living organisms. They include helpful bacteria that aid digestion and fix nitrogen in soil, as well as pathogens that cause disease. Archaebacteria are ancient microorganisms that live in extreme environments, such as hot springs, highly salty lakes, and deep-sea hydrothermal vents. They represent some of the earliest forms of life on Earth and are so different from other bacteria that many scientists now group all life into three domains: Bacteria, Archaea, and Eukarya.

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