The Animal Kingdom Part 1

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Introduction to Animals:

Animal Body Systems Introduction to Animals


Objectives Summarize the functions of the digestive, respiratory, circulatory, nervous, skeletal, and excretory systems. Compare a gastrovascular cavity with a one-way digestive system. Differentiate open from closed circulatory systems. Distinguish asexual from sexual reproduction.

Tissues and Organs:

Tissues and Organs Specialization within the tissues creates more opportunities for the animal to exploit their environment. Digestion: All animals except for single-cell organisms and sponges digest their food outside the cells. For sponges and single-cell animals, this means that what they eat can not be larger than the cell it is digested in. All other digestion occurs in some sort of digestive cavity within the body. Enzymes are released and mixed with the food to break it down to a chemical and physical composition small and simple enough that individual cells can use it. This allows animals to prey on organisms larger than their own body cells.


Digestion Simple animals like the hydra and flatworms have a gastrovascular cavity (A digestive tract with only one opening). This does not allow for specialization because all the cells are exposed to all phases of the digestive process. Other animals have a digestive tract (gut system) with two opening: a mouth and an anus. Food enters the mouth and moves in only one direction. There may be several sections used from breaking down different types of nutrients physically and chemically. The useful nutrients are absorbed and the unusable parts leave the body through the anus.


Respiration Respiration: The uptake of Oxygen and the release of Carbon dioxide. In simple animals gas exchange occurs directly with the environment by diffusion. This can happen only across a moist surface. In larger more complex animals, simple diffusion can not provide the volume of oxygen necessary and so a system for bringing air actively into the body is required. Some organisms have gills (structures that allow gas exchange to occur underwater) while others have respiratory organs such as lungs to draw air into the body.


Circulation In simple animals, all body cells are exposed to either the gastrovascular cavity or the external environment. This puts all the cells in contact with the source of oxygen and food. More complex animals, with tissue layers several cells in thickness, must have a system in place to carry oxygen and nutrients to interior cells and carry away their waste products.

Open Circulatory System:

Open Circulatory System Open Circulatory System: The heart pumps fluid containing oxygen and nutrients through a series of vessels out into the body cavity. There the fluid washes over the body’s interior cells supplying them with food and oxygen. The fluid collects into open spaces in the body and returns to the heart to be cleansed and replenished.

Closed Circulatory System:

Closed Circulatory System Closed Circulatory System: The heart pumps blood through a system of blood vessels that infiltrate every part of the body becoming increasingly smaller until they form capillaries that are small enough for molecular gas exchange and nutrients to pass through the vessel walls. The pressure of the system pushes the blood on through the capillaries into other vessels that return the blood to the heart. At no time does it leave the blood vessels or come into direct contact with the body’s surfaces.

Nervous System:

Nervous System Simple organisms like the hydra have a nerve net or network or nerve fibers that run over the interior of their entire bodies. They have no specialized features to process or interpret the messages these nerves carry.

Nervous System:

Nervous System More complex animals have clusters of nerves called ganglia that act as amplifiers and decision makers for the body. These are usually located along a central line of the body and branch out from a common main nerve. In large developed animals, the ganglia further specialize until a brain is formed to act as the decision maker for the entire body. This is a cluster of specialized nerve cells capable of receiving and interpreting the signals from the body’s nervous system.

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