Kingdoms of Life: Protists, Fungi, Plants and Animals

Protists

Protists are unicellular or multicellular, eukaryotic organisms that are either autotrophs or heterotrophs.

Protozoa

Protozoa are heterotrophs and, like most organisms, reproduce asexually through division. They are divided into several groups:

• Sarcodina: they move and capture food using pseudopods. Amoebas and foraminifera belong to this group.
• Flagellates: they possess a flagellar system for locomotion.
• Ciliates: their structure is more complex, and they have various cilia formations with specialized functions. They also exchange genetic material through conjugation.
• Sporozoans: they are parasitic and reproduce through multiple fission. Their locomotion is based on flexion or gliding movements.

Algae

Algae are photosynthetic and aquatic organisms, either unicellular or multicellular, and their reproduction is varied.

• Diatoms: unicellular and surrounded by a silica shell.
• Green algae: contain chlorophyll and live in fresh water and shallow surface zones.
• Brown algae: marine, containing fucoxanthin and chlorophyll, with a brown pigment that allows them to absorb light.
• Red algae: live in marine environments at greater depths. They contain phycoerythrin, a red pigment that allows them to absorb the bluish light that penetrates the water.

Slime molds reproduce through spores and are heterotrophs.

Fungi

Fungi are heterotrophs, either unicellular (yeasts) or multicellular. Their mycelium is made up of a set of hyphae, which may be septate or aseptate.

• Zygomycota: their hyphae lack septa, and this group includes molds that decompose food.
• Deuteromycota: their hyphae are septate. Some species are used for the production of antibiotics.
• Ascomycota: they have a septate mycelium and produce characteristic structures called asci, which originate from fertilization and meiosis.
• Basidiomycota: they have septate hyphae and are characterized by the presence of basidia, the reproductive structures that bear the spores.

Plants

Plants (metaphytes) are multicellular, photosynthetic, eukaryotic organisms and diplobionts. They are divided into two main groups:

Bryophytes

Bryophytes are among the first plants to have evolved and need moist environments to live. They have a thallus organization, without true roots, stems or leaves. Mosses and liverworts belong to this group.

Tracheophytes (Vascular Plants)

Tracheophytes are more evolved plants, distinguished by their vascular tissues. They include:

• Pteridophytes: plants with spores, such as ferns.
• Spermatophytes: plants with seeds. This group includes gymnosperms, whose naked seeds are not protected by a fruit (for example, pines), and angiosperms, whose seeds are enclosed in fruit and which have reproductive organs called flowers.

Angiosperms are divided into monocotyledons (grasses) and dicotyledons (flowering plants).

Animals

Animals (metazoans) are multicellular, heterotrophic, eukaryotic organisms and diploblasts. The most representative phyla are:

• Porifera (sponges): primitive animals whose body is like a bag with holes.
• Cnidarians: have a sac-shaped body open to the exterior, with two layers of cells and a gelatinous layer between them (for example, corals).
• Platyhelminthes: their body can be divided into two halves (for example, tapeworms).
• Nematodes: cylindrical worms with an unsegmented body and a body cavity that allows the presence of internal organs (for example, roundworms).
• Annelids: cylindrical body divided into segments called metameres, each of which repeats the organs (for example, earthworms).
• Molluscs: their body can be divided into parts and many have a shell (for example, snails).
• Arthropods: have a large number of jointed appendages such as legs and antennae, undergo a molting process, and have complex nervous systems and sensory organs. This group includes myriapods, arachnids, insects and crustaceans.
• Echinoderms: have five-part radial symmetry and a seabed lifestyle; their skeleton is made of calcareous plates.
• Chordates: present in the dorsal region at some stage a rigid structure, the notochord, which has a supporting function. This group includes cyclostomes, fish, amphibians, reptiles, birds and mammals.