Plant and Animal Kingdoms: Characteristics and Classification
Plants: Characteristics and Classification
Plants appeared millions of years ago, approximately 500 million years ago. It is believed that they evolved from some group of green algae that were able to adapt to the terrestrial environment. This hypothesis is supported because plants and algae share several characteristics:
- Both own photosynthetic pigments.
- Both store starch reserves.
- They have cellulose cell walls.
- They make their cell division after mitosis through a cellulose partition, the phragmoplast.
General Characteristics
Plants are eukaryotes, multicellular, photoautotrophs with a haplodiplont life cycle and adapted to the terrestrial environment. With the exception of a primitive group (bryophytes), all have true tissues, that is, their organization is of the corm type. Generally, they live fixed to their substrate, they get water and mineral salts from the soil, and they obtain carbon dioxide and oxygen from the air. In their adaptation to the terrestrial environment, they have been solving various services:
A) Water loss: To avoid this loss, they have been covered with waterproof tissue, such as the epidermis and the suber. In turn, they control the output of water through stomata.
B) Support: Living in the water, they do not need a support system. On the mainland, they do. For that, they have developed tissues that form a large part of the trunks, roots, and branches that hold them upright and expose the leaves to the sun.
C) Transport systems: Algae bathed in water do not need a transport system because water carries nutrients to all their cells. Plants do need to carry nutrients through their body, made of leaves that absorb mineral salts from the root.
Classification
Plants are classified into two major groups:
A) Non-vascular plants: They do not have conducting tissues. Their structure is of the thallus type. The main edge that includes them are the bryophytes. They are very primitive plants adapted to the terrestrial environment incompletely because they still need water to reproduce. For that reason, they grow in very humid environments: mosses.
B) Vascular plants: They have a chromium-type organization, true tissues. This group is divided into two groups:
- Pteridophytes: Vascular plants that do not have the embryo protected by a seed. They lack flowers. It consists of three edges, of which the most representative are ferns.
- Seed plants: They are the most evolved plants. They have very specialized tissues. Their embryo is protected within the seed and, in turn, it is located inside the fruit, the stems of the flower. There are two types:
- Gymnosperms: They have unisexual flowers grouped in inconspicuous cones. The seed originates unprotected by a fruit. These are conifers, cycads, and Ginkgo.
- Angiosperms: They have showy, hermaphroditic, or unisexual specialized flowers. They produce seeds and fruit, enclosing the seeds. There are two edges: dicotyledons (the seed is formed by two cotyledons) and monocotyledons (the seed has only one cotyledon).
Animals: Characteristics and Classification
Animals appeared 750 million years ago. They evolved from a group of protozoa that became multicellular.
General Characteristics
Higher animals, called metazoans, are eukaryotic, heterotrophic, multicellular, whose cells do not have a cell wall. There are two major groups of animals:
A) Parazoa: They are primitive. They do not have differentiated tissues. They do not have symmetry. Example: sponges: Porifera phylum.
B) Metazoa: They are the rest of the true animals. They have tissues and symmetry.
Metazoans
They are preferentially classified by the type of symmetry, the number of embryonic layers that form in the zygote’s development, and whether or not they have an internal cavity called a coelom.
A) Embryonic Layers: The embryo is formed from the division of the zygote into millions of cells. These cells are organized into sheets or embryonic layers. These layers are:
- Ectoderm: Layer of cells surrounding the embryo. It is the outermost layer.
- Endoderm: Innermost layer of the embryo cells.
- Mesoderm: Layer that is located between the ectoderm and the endoderm.
The groups of animals whose embryo has only the ectoderm and the endoderm are called Diploblastic. If they have the three embryonic leaves, they are called Triploblastic.
B) Presence of Coelom: The coelom, or coelomic cavity, is a gap that opens in the mesoderm and is filled with a liquid that cushions the organs, providing support. According to whether they have this cavity, animals can be:
- Acoelomates: They do not have a coelom. The mesoderm has no holes.
- Pseudocoelomates: They have a cavity, but it is not derived from the mesoderm, but it is formed between the mesoderm and the ectoderm.
- Coelomates: They have an authentic coelom, formed in the mesoderm.