Chapter 40 Basic Principles of Animal Form and Function Overview Diverse Forms Common Challenges Despite their great diversity all animals must solve a common set of problems All animals must obtain oxygen nourish themselves excrete wastes and move Animals inhabit almost every part of the biosphere 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 comparative study of animals The concept of bioenergetics how organisms obtain process and use energy resources is a connecting theme in 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 membranes For example a single celled protist living in water has a sufficient surface area of plasma membrane to service Exchange with the environment occurs as dissolved substances diffuse and are transported across the cells plasma 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 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 and unloading platform for a modest volume of cytoplasm 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 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 Most organisms have extensively folded or branched internal surfaces specialized for exchange with the environ 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 environment while 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 organization 1 Tissue 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 muscle Epithelial 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 that secretes 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 There are three kinds of connective tissue fibers which are all proteins collagenous elastic and reticular fibers 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 Connective tissue functions mainly to bind and support other tissues 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 Reticular fibers are very thin and branched Elastin fibers provide a rubbery quality that complements the nonelastic strength of collagenous fibers Composed of collagen and continuous with collagenous fibers they form a tightly woven fabric that joins