Chapter 40 Basic Principles of Animal Form and Function 1 Chapter 40 Basic Principles of Animal Form and Function Diverse Forms Common Challenges Anatomy the biological form of the animal Natural selection favors those variations in a population that increase relative fitness Because form and function are correlated examining anatomy often provides clues to physiology biological function Concept 40 1 Animal form and function are correlated at all levels of organization An animal s size and shape are fundamental aspects of forms that significantly affect the way the animal interacts with its environment Evolution of Animal Size and Shape The body plan of an animal is the result of a pattern of development programmed by the genome itself the product of millions of years of evolution Exchange with the Environment Such animals share a streamlined body contour a shape that is fusiform meaning tapered on both ends The similar shape is found in these speedy vertebrate is an example of convergent evolution Natural selection often results in similar adaptations when diverse organisms face the same environmental challenge Physical laws also influence animal body plans with regard to maximum size As body dimensions increase thicker skeletons are required to maintain adequate support As bodies increase in size the muscles required for locomotion must represent an ever larger fraction of the total body mass By considering a fraction of the body mass in leg muscles and the effective force such muscles generate scientists can estimate maximum running speed for a wide range of body plans Exchange occurs as substances dissolved in an aqueous solution move across the plasma membrane of each cell Rates of exchange for nutrients waste products and gases are proportional to membrane surface area whereas the amount of material that must be exchanged to sustain life is proportional to cell volume The opportunity for exchange depends on the number of cells in an organism s body Single celled organisms have a sufficient membrane surface area in contact with its environment to carry out all necessary exchange A multicellular organization therefore works only if every cell has access to a suitable aqueous environment either inside or outside the body A common body plan that maximizes exposure to the surrounding medium is a flat shape Many animals with a simple internal organization have body plans that enable direct exchange between almost all their cells and the external environment The bodies of most animals are composed of compact masses of cells with an internal organization much more complex than that of a hydra or a tapeworm In whales and most other animals the evolutionary adaptations that enable sufficient exchange with the environment are specialized surfaces that are extensively branched or folded These exchange surfaces lie within the body an arrangement that protects their delicate tissues from abrasion or dehydration and allows for streamlined body contours In humans the internal exchange surfaces of the digestive respiratory and circulatory systems each have an area more than 25 times that of the skin Internal body fluids link exchange surfaces to body cells The spaces between cells are filled with fluid in many animals called interstitial fluid Exchange between the interstitial fluid and the circulatory fluid enables cells throughout the body to obtain nutrients and get rid of waste Despite the greater challenges of exchange with the environment complex body plans have distinct benefits over simple ones An external skeleton can protect against predators and sensory organs can provide detailed information on the animal s surroundings Internal digestive organs can break down food gradually controlling the release of stored energy Specialized filtration systems can adjust the composition of the internal fluid that bathes the animal s body cells An animal can maintain a relatively stable internal environment while living in a changeable external environment Cells are organized into tissues groups of cells with a similar appearance and a common function Different types of tissues are further organized into functional units called organs Groups of organs that work together provide an additional level of organization and coordination and make up an organ system The skin is an organ of the integumentary system which protects against infection and helps regulate body temperature The pancreas produces enzymes critical to the function of the digestive system and also regulates the level of sugar in the blood as a vital part of the endocrine system One function of the stomach is to initiate the breakdown of proteins Hierarchical Organization of Body Plans Chapter 40 Basic Principles of Animal Form and Function 2 Organ Systems in Mammals This process requires a churning motion of powered by the stomach muscles as well as digestive juices secreted by the stomach lining One cell type secretes a protein digesting enzyme a second secreted concentrated HCl and a third produces mucus which protects the stomach lining Main functions body defense fighting infections and cancer Main function gas exchange uptake of oxygen disposal of carbon dioxide Main function food processing ingestion digestion absorption and elimination Digestive system mouth pharynx esophagus stomach intestines liver pancreas and anus Circulatory system heart blood vessels and blood Main function internal distribution of materials Respiratory system lungs trachea and other breathing tubes Immune and lymphatic system bone marrow lymph nodes thymus spleen lymph vessels and white blood cells Excretory system kidneys ureters urinary bladder and urethra Main functions disposal of metabolic wastes regulation of osmotic balance of blood Endocrine system pituitary thyroid pancreas adrenal and other hormone secreting glands Reproductive system ovaries or testes and associated organs Nervous system brain spinal cord nerves and sensory organs Integumentary system skin and its derivatives such as hair claws and skin glands Skeletal system skeleton bones tendons ligaments and cartilage Muscular system skeletal muscles Main function coordination of body activities detection of stimuli and formation of responses to them Main function protection against mechanical injury infection dehydration and thermoregulation Main function coordination of body activities such as digestion and metabolism Main function body support protection of internal organs and