Animal Structure Hierarchy PDF

The Hierarchy of Structure in Animals 3.1 Multicellular organisms, such as animals, are made up of many different specialized types of cells. Each cell is specialized to perform a particular function....

The Hierarchy of Structure in Animals 3.1 Multicellular organisms, such as animals, are made up of many different specialized types of cells. Each cell is specialized to perform a particular function. The stinging cells of jellyfish help it capture its prey, whereas the light-emitting cells of female fireflies can be used to attract a mate. Less unusual cells, but still highly specialized, include muscle and bone cells, blood cells, and sensory cells responsible for detecting sights, sounds, and odours. Single-celled organisms, such as bacteria and blue-green algae, function independently. They do not directly depend on any other cells. In contrast, specialized animal cells cannot survive on their own. A single bone cell, hair cell, or stomach cell would quickly die if separated from its surrounding cells. These cells live and work as part of a much larger group of cells that collectively make up the body of the animal. In fact, the body of a large animal may be made up of trillions of individual cells. It is this entire collection of cells working together as a whole organism that is capable of survival and reproduction. The complexity of animal bodies varies considerably. Some animals, such as sponges, have a simple body structure. Slugs and snails are more complex. Vertebrates (animals with backbones), such as birds, have highly complex bodies (Figure 1). (a) (b) (c) Figure 1 A sponge (a), a sea slug (b), and a cardinal (c) show increasing levels of complexity. To understand how specialized cells work together in complex organisms, consider the many major tasks that must be performed by entire organisms, such as feeding, breathing, moving, and reproducing. In this section, you will examine how the animal body is organized for carrying out these functions. The Animal Body—Levels of Organization The bodies of animals look very different. A snail does not resemble a penguin. Yet all animals are made up of cells that are organized in a way that allows them to perform all of life’s functions. There are levels of organization within each animal. These levels of organization form a hierarchy, with the “most complex” at the top and the “least complex” at hierarchy an organizational structure, the bottom. with more complex or important things at the top and simpler or less important You are already familiar with some of these levels of organization. In things below it earlier grades, you learned about some human organs and the digestive and circulatory systems, and you may even have used the word “tissue.” These terms all refer to the hierarchy of structure within the animal body. How many levels are there? How are they arranged in terms of complexity? NEL 3.1 The Hierarchy of Structure in Animals 73  Consider the hierarchy of organization within a specific animal: a white- tailed deer. Let’s start with the simplest level of organization. Figure 2(a) shows a single muscle cell in the deer’s heart. Each heart muscle cell is branched, allowing it to connect to other heart muscle cells. Together, these tissue a collection of similar cells that muscle cells make up the muscle tissue (Figure 2(b)). Figure 2(c) shows the perform a particular, but limited, function heart itself, at the organ level of the hierarchy. An organ is made up of two organ a structure composed of different or more types of tissues that work together to perform a complex function. tissues working together to perform a In addition to muscle tissue, the heart includes two other types of tissue: complex body function nerve tissue and connective tissue. An organ system consists of one or organ system a system of one or more more organs and other structures that work together to perform a vital body organs and structures that work together function. The heart, blood vessels, and blood are all parts of the circulatory to perform a major vital body function system (Figure 2(d)). The organism—in this case, the deer in Figure 2(e)— such as digestion or reproduction is made up of many different organ systems working together. (a) Cellular level (b) Tissue level (c) Organ level (d) Organ system level (e) Organism level heart muscle cell heart muscle tissue heart circulatory system deer Figure 2 Levels of structural organization in an animal (a white-tailed deer) The functioning of the whole organism depends on the hierarchy of organization within the animal. The deer needs a circulatory system to deliver nutrients and oxygen to its entire body. This system requires an organ, such as the heart, to pump the blood. It also needs a network of arteries and veins to distribute the blood throughout the body. In turn, the heart is itself made up of muscle tissue, which contracts, and nerve tissue, which keeps the heart beating regularly. The tissues are groups of specialized cells. Living things are very complex. You might be wondering how many different organs and organ systems there are. Does each organ system have its own set of organs and associated tissues? How do these systems work together? Organ Systems All animals accomplish the same basic functions regardless of their appearance, behaviour, or where they live. They all obtain oxygen and nutrients and eliminate wastes. They all sense and respond to their environment, grow and repair damage, and reproduce. The task of organ systems is to perform these basic functions. Some well-known human organ systems are illustrated in Figure 3. You will learn about some of these in more detail as you work through this chapter. 74 Chapter 3 Animal Systems NEL  Figure 3 The human body has many organ systems, some of which are (a) (b) (c) shown here. The musculoskeletal The respiratory system The nervous system system supports the body takes oxygen from the sends messages around and makes movement air and removes carbon the body. possible. dioxide from the body. The digestive system WRITIng Tip The reproductive system The circulatory system breaks down the food you produces eggs (in females) transports substances eat and makes it available Spell Check and sperm (in males). In around the body. to the body. Carefully check your spelling of some animals, the female The urinary system scientific terms such as the names of reproductive system also excretes waste and keeps tissues or organs. Since many of these supports the growing fetus the correct amount of terms are not used often in everyday until it is born. water in the body. speech or print, it is helpful to keep your own list of unfamiliar terms such as “musculoskeletal,” “epithelial,” and “cytokinesis” so you can easily check Organs their meaning and correct spelling. Each organ system is made up of highly specialized organs and other structures that work together to perform the overall function of the system. For example, the digestive system is made up of many organs, including the stomach, small and large intestines, liver, and pancreas. Most organs work within a single organ system. For example, the stomach is part of the digestive system and of no other system. Some organs, however, play a role epithelial tissue (or epithelium) a thin sheet of tightly packed cells that covers in more than one system. For example, the pancreas is part of the digestive body surfaces and lines internal organs system and the endocrine system. and body cavities Tissues connective tissue a specialized tissue that provides support and protection for Animals have four major types of tissue: epithelial tissue, connective tissue, various parts of the body muscle tissue, and nerve tissue. Each of these types of tissue contains many muscle tissue a group of specialized types of specialized cells, and each is found in most organ systems. Table 1, tissues containing proteins that can on the next page, summarizes these four types of tissue. Where do these contract and enable the body to move tissues come from? How does an animal produce these different cell and nerve tissue specialized tissue that tissue types, which are then organized into organs and organ systems? You conducts electrical signals from one part will begin to answer these questions in the next section. of the body to another NEL 3.1 The Hierarchy of Structure in Animals 75  Table 1 Animal Tissue Types Type Example Description Function epithelial tissue skin thin sheets of tightly packed protection from cells covering surfaces and dehydration lining of the digestive system lining internal organs low-friction surfaces connective tissue bone various types of cells and support fibres held together by a tendons insulation liquid, a solid, or a gel, known blood as a matrix muscle tissue muscles that make bones bundles of long cells called movement move muscle fibres that contain specialized proteins capable muscles surrounding the of shortening or contracting digestive tract heart nerve tissue brain long, thin cells with fine sensory branches at the ends nerves in sensory organs communication within the capable of conducting body electrical impulses coordination of body functions B In SUMMARY The bodies of animals are organized in a Tissues are groups of similar cell types that structural hierarchy. perform a common function. The levels of organization are organ systems, There are four main tissue types: epithelial, SB organs, tissues, and cells. connective, muscle, and nerve. CHECK YOUR LEARnIng 1. Create a concept map to illustrate the hierarchy of 4. Make a list of the main functions that must be performed organization within an animal. Include examples in your by all living things. For each main function, name an organ concept map. K/U C system that is involved in performing that function. K/U 2. Give an example of an organ that is found in 5. Most animals have the same kinds of organ systems. Why B do you think there are not dozens or even hundreds of (a) only one organ system completely different kinds of organ systems? T/I (b) more than one organ system K/U 6. Why is there no hierarchy of organization within 3. In what way are organ systems more complex than highly single-celled organisms? K/U specialized cells? K/U SB 76 Chapter 3 Animal Systems NEL