Flowering Seed Plants—Angiosperms

    Flowering plants, called angiosperms (“covered seeds”), are vascular seed plants with specialized reproductive structures, which include both flowers and fruit. Instead of depending on currents of wind or water for the dispersal of their gametes and seeds, plants with flowers and fruit provide protection and attract animals that then serve as the means of fertilization.

 

    Flowering plants are divided into two classes, monocots and dicots. Monocot seeds have a single cotyledon, while dicots have two cotyledons in each seed. Monocots and dicots are covered in more detail in the section on the Structure and Function of Plants.

 

    Kingdom Animalia

    Animals are eukaryotic, multicellular, and heterotrophic. Animals also have specialized tissues to perform various functions. Most animals are motile, at least during part of their life cycle, reproduce sexually, and have nervous systems that allow them to respond rapidly to changes in their environment.

 

    Taxonomists use several observable features to classify animals into groups according to their evolutionary relationships. One of the most important of these features is body symmetry. In bilateral symmetry, the left half of the organism is the mirror image of the right half, but the top does not resemble the bottom, and the front is dissimilar to the back. In radial symmetry, the organism has a circular body plan, with similar structures arranged like spokes on a wheel, such as a starfish. Most animals have three layers of cells: the ectoderm, mesoderm, and endoderm. Almost all animals have a hollow tube inside, which acts as a digestive tract; the opening where food enters is called the mouth, and the opening where digested material exists is called the anus.

 

    Animals are the most diverse of the kingdoms. Any of their various phyla may come up on the SAT II Biology, though the vertebrates come up most often.

 

    Phylum Porifera (Sponges)

    Sponges are sessile (nonmoving), complex colonies of flagellated unicellular protozoalike organisms. They do not exhibit any clear symmetry, and they are the only animal phylum that does not possess at least two distinct embryonic tissue layers. Their unique lack of tissue organization has prompted taxonomists to classify sponges as parazoa (“next to animals”). Nonetheless, some sponge cells are specialized for reproductive or nutritional purposes, and this slight organizational complexity gives them a toehold on the edge of the animal kingdom. Although sponges do have a hollow space inside, they do not have a digestive gut like other animals. Water flows into the central space through the many pores in the sponge’s outer surface and flows out through the large opening at the top of the sponge. The flow of water brings food and oxygen and carries away waste and carbon dioxide. All sponges secrete a skeleton that maintains their shape (you might use these skeletal remains as “natural sponges” in bathing).