Chapter 40: Basic Principles of Animal Form and FunctionOverview: Diverse Forms, Common Challenges- Animals inhabit almost every part of the biosphere. Despite their great diversity, all animals must solve a common set of problems. All animals must obtain oxygen, nourish themselves, excrete wastes, and move.• Anatomy is the study of the structure of an organism.• Physiology is the study of the functions an organism performs. Natural selection can fit structure to function by selecting, over many generations, the best of the available variations in a population.- Searching for food, generating body heat and regulating internal temperature, sensing and responding to environmental stimuli, and all other animal activities require fuel in the form of chemical energy.- The concept of bioenergetics—how organisms obtain, process, and use energy resources—is a connecting theme in the comparative study of animals.Concept 40.1 Physical laws and the environment constrain animal size and shape- An animal’s size and shape, features often called “body plans” or “designs,” are fundamental aspects of form and function that significantly affect the way an animal interacts with its environment. The body plan or design of an animal results from a pattern of development programmed by the genome, itself the product of millions of years of evolution due to natural selection.Physical Laws and Animal Form- Physical requirements constrain what natural selection can “invent.”- This shape minimizes drag in water, which is about a thousand times denser than air.- The similar forms of speedy fishes, birds, and marine mammals are a consequence of convergent evolution in the face of the universal laws of hydrodynamics. Convergence occurs because natural selection shapes similar adaptations when diverse organisms face the same environmental challenge, such as the resistance of water to fast travel.Exchange with the Environment- An animal’s size and shape have a direct effect on how the animal exchanges energy and materials with its surroundings.- An animal’s body plan must allow all of its living cells to be bathed in an aqueous medium, a requirement for maintaining the fluid integrity of the plasma membrane of its cells- Exchange with the environment occurs as dissolved substances diffuse and are transported across the cells’ plasma membranes For example, a single-celled protist living in water has a sufficient surface area of plasma membrane to service its entire volume of cytoplasm. Surface-to-volume ratio is one of the physical constraints on the size of single-celled protists.- In contrast, an animal is composed of numerous cells, each with its own plasma membrane that acts as a loading and unloading platform for a modest volume of cytoplasm. This only works if all the cells of the animal have access to a suitable aqueous environment. For example, a hydra, built as a sac, has a body wall only two cell layers thick. Because its gastrovascular cavity opens to the exterior, both outer and inner layers of cells are bathed in water.- A flat body shape is another design that maximizes exposure to the surrounding medium- While two-layered sacs and flat shapes are designs that put a large surface area in contact with the environment, these solutions do not permit much complexity in internal organization.- Most animals are more complex and are made up of compact masses of cells; their outer surfaces are relatively small compared to the animal’s volume. Most organisms have extensively folded or branched internal surfaces specialized for exchange with the environ.- Despite the greater challenges of exchange with the environment, complex forms have distinct benefits. A specialized outer covering can protect against predators; large muscles can enable rapid movement; and internal digestive organs can break down food gradually, controlling the release of stored energy. Because the cells’ immediate environment is the internal body fluid, the animal’s organ systems can control the composition of the solution bathing its cells, allowing the animal to maintain a relatively stable internal environmentwhile living in a variable external environment. A complex body form is especially well suited to life on land, where the external environment may be highly variable.Concept 40.2 Animal form and function are correlated at all levels of organization1Tissue Structure and Function- Tissues are groups of cells with a common structure and function. Different types of tissues have different structures that are suited to their functions.- Tissues are classified into four main categories: epithelial, connective, nervous, and muscleEpithelial Tissue- Occurring in sheets of tightly packed cells, epithelial tissue covers the outside of the body and lines organs and cavities within the body. The cells of an epithelium are closely joined and in many epithelia, the cells are riveted together by tight junctions. The epithelium functions as a barrier protecting against mechanical injury, invasive microorganisms, and fluid loss.- Some epithelia, called glandular epithelia, absorb or secrete chemical solutions. The glandular epithelia that line the lumen of the digestive and respiratory tracts form a mucous membrane thatsecretes a mucus that lubricates the surface and keeps it moist.- Epithelia are classified by the number of cell layers and the shape of the cells on the free surface. A simple epithelium has a single layer of cells, and a stratified epithelium has multiple tiers of cells. A “pseudostratified” epithelium is single-layered but appears stratified because the cells vary in length.- The shapes of cells on the exposed surface may be cuboidal, columnar, or squamous.Connective Tissue- Connective tissue functions mainly to bind and support other tissues. Connective tissues have a sparse population of cells scattered through an extracellular matrix. The matrix gen. consists of a web of fibers embedding in a uniform foundation that may be liquid, jellylike, or solid. In most cases, the connecti ve tissue cells secrete the matrix.- There are three kinds of connective tissue fibers, which are all proteins: collagenous, elastic, and reticular fibers.- Collagenous fibers are made of collagen, the most abundant protein in the animal kingdom. Collagenous fibers are nonelastic and do not tear easily when pulled lengthwise.- Elastic fibers