Animalia
Domain: Eukarya
Description: Organisms of the Kingdom Animalia are multicellular and heterotrophic. They ingest their own food and digest with enzymes in order to obtain organic molecules. Animals lack cell walls, using instead a variety of proteins to provide structure, including the animal-only protein, collagen. Also, animals have specialized cells: muscle and nerve. Both organize into tissues, which allows an animal to move its body and conduct nerve impulses. Finally, animals have several characteristic reproductive features. They mainly reproduce sexually, with their gametes arising from meiotic division. Once the gametes form a zygote, the resulting cleavage produces a multicellular stage called the blastula. This will then develop a particular morphological trait (Body Plan), as they proceed to adulthood. |
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Divergent Event: It is believed that early ancestors of animals diverged from fungi around 1 billion years ago. The common ancestor is similar to the present-day choanoflagellates. The first fossils found date from 565 to 550 million years ago, mainly consisting of sponges. It would not be until the Cambrian Explosion (535-525 million years ago) that animals would undergo massive diversification, giving rise to many phylum we still see today.
Body Plan: Animals are multicellular. Some animals display radial symmetry (Around central axis), but most exhibit bilateral symmetry (One length-wise axis). These organisms with bilateral symmetry have a central nervous system (brain) located at the front end, often called cephalization. The development of germ layers during the embryo stage also creates a specific body plan, resulting in the creation of various tissues and organs. The outer germ layer creates the eventual outer covering while the inner germ layer creates the lining of tracts and organs. Finally, animals have body cavities filled with air or liquid. They have many functions, one of which is to cushion sensitive organs.
Metabolism: Animals are heterotrophic. They require oxygen, which is acquired through respiration. Second, they need organic molecules, which are obtained through ingesting and digesting other organisms. Thus, cellular respiration occurs and the animal is powered to survive.
Body Plan: Animals are multicellular. Some animals display radial symmetry (Around central axis), but most exhibit bilateral symmetry (One length-wise axis). These organisms with bilateral symmetry have a central nervous system (brain) located at the front end, often called cephalization. The development of germ layers during the embryo stage also creates a specific body plan, resulting in the creation of various tissues and organs. The outer germ layer creates the eventual outer covering while the inner germ layer creates the lining of tracts and organs. Finally, animals have body cavities filled with air or liquid. They have many functions, one of which is to cushion sensitive organs.
Metabolism: Animals are heterotrophic. They require oxygen, which is acquired through respiration. Second, they need organic molecules, which are obtained through ingesting and digesting other organisms. Thus, cellular respiration occurs and the animal is powered to survive.
Digestion: Animals digestion is done in a gastrovascular cavity and therefore is extracellular. It is complete, as food can continuously enter through the mouth and exit from the anus. In the digestive tract, enzymes break down food and the nutrients are absorbed by the intestine walls.
Nervous: Due to cephalization, animals with bilateral symmetry usually have their central nervous system concentrated in their anterior (front) ends. Some have localized groups of neural cells called ganglia (invertebrates). More complex animal brains, like human brains, contain several parts. These include the brain stem, cerebellum, hypothalamus, pituitary gland and the cerebral cortex. However, animals with radial symmetry have much simpler nervous systems. The nervous system can be imagined as a net, spread throughout the entire body as micro filaments.
Circulatory: Vertebrates and some invertebrates have a closed system of blood circulation. The animal heart is made of muscle tissue and pumps the blood throughout the body in veins and capillaries. This allows the oxygen, carried by the hemoglobin, to be distributed throughout all parts of the body. The animals with an open system (mainly invertebrates) pump their blood from the hemocoel to body cavities.
Respiratory: Land animals respire through lungs while aquatic animals respire through gills. In both cases, oxygen is brought in and carbon dioxide released so the cycle of cellular respiration can create ATP. Thus, the animals gains energy to survive.
Reproductive: Animals, primarily mammals, carry out sexual reproduction. A male gamete (sperm) fuses with the female gamete (egg) to form a genetically unique zygote. Rounds of mitosis produce an embryo, which will mature into an adult and continue the cycle. Other phylums, mainly arthropoda, can perform asexual reproduction, called parthenogenesis. In this cycle, offspring can develop from an unfertilized egg.
Click on the following link to learn about the phyla within Animalia:
Nervous: Due to cephalization, animals with bilateral symmetry usually have their central nervous system concentrated in their anterior (front) ends. Some have localized groups of neural cells called ganglia (invertebrates). More complex animal brains, like human brains, contain several parts. These include the brain stem, cerebellum, hypothalamus, pituitary gland and the cerebral cortex. However, animals with radial symmetry have much simpler nervous systems. The nervous system can be imagined as a net, spread throughout the entire body as micro filaments.
Circulatory: Vertebrates and some invertebrates have a closed system of blood circulation. The animal heart is made of muscle tissue and pumps the blood throughout the body in veins and capillaries. This allows the oxygen, carried by the hemoglobin, to be distributed throughout all parts of the body. The animals with an open system (mainly invertebrates) pump their blood from the hemocoel to body cavities.
Respiratory: Land animals respire through lungs while aquatic animals respire through gills. In both cases, oxygen is brought in and carbon dioxide released so the cycle of cellular respiration can create ATP. Thus, the animals gains energy to survive.
Reproductive: Animals, primarily mammals, carry out sexual reproduction. A male gamete (sperm) fuses with the female gamete (egg) to form a genetically unique zygote. Rounds of mitosis produce an embryo, which will mature into an adult and continue the cycle. Other phylums, mainly arthropoda, can perform asexual reproduction, called parthenogenesis. In this cycle, offspring can develop from an unfertilized egg.
Click on the following link to learn about the phyla within Animalia: