Chapter 19. Rain Forest Riches. Eukaryotic diversity. A eukaryote is any organism of the domain Eukarya ; eukaryotic cells are characterized by the presence of a membrane-enclosed nucleus and organelles. Eukaryotic diversity.
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Land plants first evolved from water-dwelling algae about 450 million years ago, when life on earth was confined primarily to the seas. As plants radiated and diversified on land, they evolved a number of adaptations that made them increasingly independent of water.
The earliest plants to make the transition from water to land were small, seedless plants called bryophytes. Bryophytes lack roots and tissue for transporting water and nutrients throughout their bodies, and therefore can grow only in damp environments, where they can easily absorb water.
The first true vascular plants were ferns. Like bryophytes, ferns do not produce seeds. Ferns can stand upright and grow tall because vascular tissue keeps stems rigid and transports water and nutrients from one end of the plant to the other.
Seed plants first emerged about 360 million years ago, during the late Devonian period. A seed, which envelopes a plant’s embryo, is an ideal package for withstanding harsh conditions and traveling to a location where it can grow into a new plant.
Many features can be used to group and sort animals. Historically, anatomical and embryological evidence were relied upon most, but in recent years it has become more common to use DNA. It is clear that all animals descended from the same common ancestor and diversified into the different forms we see today.
Early in their history, animals branched into three main lineages, the legacy of which can be seen in three distinct animal body plans in existence today: no symmetry, radial symmetry, and bilateral symmetry.
The simplest living animals, such as sponges, lack defined tissues or organs and have an amorphous shape. These asymmetrical organisms are likely similar to the earliest animals to have populated the oceans.
An arthropod’s exoskeleton– a hard external skeleton that covers the body – serves multiple functions: it protects the organism from predators, keeps it from drying out, and affords structure and support for movement, just as our internal endoskeleton does.
Fungus (plural: fungi) is a unicellular or multicellular eukaryotic organism that obtains nutrients by secreting digestive enzymes onto organic matter and absorbing the digested product. By breaking down organic matter into smaller particles, fungi help release trapped nutrients.
Multicellular fungi have a body composed of threadlike structures known as hyphae. Each individual hypha is a chain of many cells, capable of absorbing nutrients. Fungal hyphae interweave to form a spreading mass known as a mycelium.
A protistis a eukaryote that cannot be classified as a plant, animal, or fungus. Protists are usually unicellular. Some protists are similar to animals in that they are heterotrophic, but because they are unicellular they are not technically animals.
An alga (plural: algae) is a uni- or multicellular photosynthetic protist. Multicellular algae share with plants the ability to photosynthesize, but they differ from plants in lacking specialized adaptations for living on land, such as roots, stems, and leaves.