Chapter 40: Basic Principles of Animal Form and Function

Animals inhabit almost every part of the biosphere Despite their amazing diversity all animals face a similar set of problems, including how to nourish themselves

The comparative study of animals reveals that form and function are closely correlated

Natural selection can fit structure, anatomy, to function, physiology by selecting, over many generations, what works best among the available variations in a population

Concept 40.1: Physical laws and the environment constrain animal size and shape Physical laws and the need to exchange materials with the environment place certain limits on the range of animal forms

Physical Laws and Animal Form The ability to perform certain actions depends on an animal’s shape and size

Evolutionary convergence r eflects different species’ independent adaptation to a similar environmental challenge Tuna Shark Penguin Dolphin Seal

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 Exchange with the environment occurs as substances dissolved in the aqueous medium diffuse and are transported across the cells’ plasma membranes

A single-celled protist living in water has a sufficient surface area of plasma membrane to service its entire volume of cytoplasm Diffusion (a) Single cell

Multicellular organisms with a sac body plan h ave body walls that are only two cells thick, facilitating diffusion of materials Mouth Gastrovascular cavity Diffusion (b) Two cell layers

Organisms with more complex body plans h ave highly folded internal surfaces specialized for exchanging materials Respiratory system Digestive system Excretory system Circulatory system

Concept 40.2: Animal form and function are correlated at all levels of organization Animals are composed of cells Groups of cells with a common structure and function make up tissues Different tissues make up organs which together make up organ systems

Tissue 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, muscle, and nervous

Epithelial Tissue Epithelial tissue – Covers the outside of the body and lines organs and cavities within the body – Contains cells that are closely joined

Connective Tissue – Functions mainly to bind and support other tissues – Contains sparsely packed cells scattered throughout an extracellular matrix

Muscle Tissue Muscle tissue – Is composed of long cells called muscle fibers capable of contracting in response to nerve signals – Is divided in the vertebrate body into three types: skeletal, cardiac, and smooth

Organs and Organ Systems In all but the simplest animals different tissues are organized into organs

Lumen of stomach Mucosa. The mucosa is an epithelial layer that lines the lumen. Submucosa. The submucosa is a matrix of connective tissue that contains blood vessels and nerves. Muscularis. The muscularis consists mainly of smooth muscle tissue. 0.2 mm Serosa. External to the muscularis is the serosa, a thin layer of connective and epithelial tissue. In some organs t he tissues are arranged in layers

Organ systems represent a level of organization higher than organs – Organ systems carry out the major body functions of most animals

Organ systems in mammals:

Concept 40.3: Animals use the chemical energy in food to sustain form and function All organisms require chemical energy for growth, repair, physiological processes, regulation, and reproduction

Bioenergetics --The flow of energy through an animal – Ultimately limits the animal’s behavior, growth, and reproduction – Determines how much food it needs Studying an animal’s bioenergetics – Tells us a great deal about the animal’s adaptations

Energy Sources and Allocation Animals harvest chemical energy from the food they eat Once food has been digested, the energy- containing molecules are usually used to make ATP, which powers cellular work

After the energetic needs of staying alive are met by remaining molecules from food can be used in biosynthesis Organic molecules in food Digestion and absorption Nutrient molecules in body cells Cellular respiration Biosynthesis: growth, storage, and reproduction Cellular work Heat Energy lost in feces Energy lost in urine Heat External environment Animal body Heat Carbon skeletons ATP

Quantifying Energy Use An animal’s metabolic rate is the amount of energy an animal uses in a unit of time – Can be measured in a variety of ways

One way to measure metabolic rate is to determine the amount of oxygen consumed or carbon dioxide produced by an organism This photograph shows a ghost crab in a respirometer. Temperature is held constant in the chamber, with air of known O 2 concentration flow- ing through. The crab’s metabolic rate is calculated from the difference between the amount of O 2 entering and the amount of O 2 leaving the respirometer. This crab is on a treadmill, running at a constant speed as measurements are made. (a) (b) Similarly, the metabolic rate of a man fitted with a breathing apparatus is being monitored while he works out on a stationary bike.

Bioenergetic Strategies An animal’s metabolic rate is closely related to its bioenergetic strategy

Birds and mammals are mainly endothermic, meaning that their bodies are warmed mostly by heat generated by metabolism – They typically have higher metabolic rates

Amphibians and reptiles other than birds are ectothermic, meaning that: – They gain their heat mostly from external sources – They have lower metabolic rates

Influences on Metabolic Rate The metabolic rates of animals are affected by many factors

Size and Metabolic Rate Metabolic rate per gram is inversely related to body size among similar animals

Activity and Metabolic Rate The basal metabolic rate (BMR) – Is the metabolic rate of an endotherm at rest The standard metabolic rate (SMR) – Is the metabolic rate of an ectotherm at rest For both endotherms and ectotherms – Activity has a large effect on metabolic rate

In general, an animal’s maximum possible metabolic rate i s inversely related to the duration of the activity Maximum metabolic rate (kcal/min; log scale) AH A H A A A H H H A = 60-kg alligator H = 60-kg human 1 second 1 minute 1 hour Time interval 1 day 1 week Key Existing intracellular ATP ATP from glycolysis ATP from aerobic respiration

Energy Budgets Different species of animals use the energy and materials in food in different ways, depending on their environment

An animal’s use of energy is partitioned to BMR (or SMR), activity, homeostasis, growth, and reproduction Endotherms Ectotherm Annual energy expenditure (kcal/yr) 800,000 Basal metabolic rate Reproduction Temperature regulation costs Growth Activity costs 60-kg female human from temperate climate Total annual energy expenditures (a) 340,000 4-kg male Adélie penguin from Antarctica (brooding) 4, kg female deer mouse from temperate North America 8,000 4-kg female python from Australia Energy expenditure per unit mass (kcal/kgday) 438 Deer mouse 233 Adélie penguin 36.5 Human 5.5 Python Energy expenditures per unit mass (kcal/kgday) (b)

Concept 40.4: Animals regulate their internal environment within relatively narrow limits The internal environment of vertebrates is called the interstitial fluid, and is very different from the external environment Homeostasis is a balance between external changes and the animal’s internal control mechanisms that oppose the changes

Regulating and Conforming Regulating and conforming are two extremes in how animals cope with environmental fluctuations

An animal is said to be a regulator if it uses internal control mechanisms to moderate internal change in the face of external, environmental fluctuation (endotherms) An animal is said to be a conformer if it allows its internal condition to vary with certain external changes (ectotherms)

Mechanisms of Homeostasis Mechanisms of homeostasis moderate changes in the internal environment

A homeostatic control system has three functional components – A receptor, a control center, and an effector Response No heat produced Room temperature decreases Heater turned off Set point Too hot Set point Control center: thermostat Room temperature increases Heater turned on Too cold Response Heat produced Set point

Most homeostatic control systems function by negative feedback where buildup of the end product of the system shuts the system off

A second type of homeostatic control system is positive feedback, which involves a change in some variable that triggers mechanisms that amplify the change Positive Feedback and Global Warming

Concept 40.5: Thermoregulation contributes to homeostasis and involves anatomy, physiology, and behavior Thermoregulation – Is the process by which animals maintain an internal temperature within a tolerable range

Ectotherms and Endotherms Ectotherms – Include most invertebrates, fishes, amphibians, and non-bird reptiles Endotherms – Include birds and mammals

In general, ectotherms t olerate greater variation in internal temperature than endotherms River otter (endotherm) Largemouth bass (ectotherm) Ambient (environmental) temperature (°C) Body temperature (°C)

Endothermy is more energetically expensive than ectothermy – But buffers animals’ internal temperatures against external fluctuations – And enables the animals to maintain a high level of aerobic metabolism

Modes of Heat Exchange Organisms exchange heat by four physical processes Radiation is the emission of electromagnetic waves by all objects warmer than absolute zero. Radiation can transfer heat between objects that are not in direct contact, as when a lizard absorbs heat radiating from the sun. Evaporation is the removal of heat from the surface of a liquid that is losing some of its molecules as gas. Evaporation of water from a lizard’s moist surfaces that are exposed to the environment has a strong cooling effect. Convection is the transfer of heat by the movement of air or liquid past a surface, as when a breeze contributes to heat loss from a lizard’s dry skin, or blood moves heat from the body core to the extremities. Conduction is the direct transfer of thermal motion (heat) between molecules of objects in direct contact with each other, as when a lizard sits on a hot rock. Figure 40.13

Balancing Heat Loss and Gain Thermoregulation involves physiological and behavioral adjustments that balance heat gain and loss

Insulation Insulation, which is a major thermoregulatory adaptation in mammals and birds – Reduces the flow of heat between an animal and its environment – May include feathers, fur, or blubber

In mammals, the integumentary system acts as insulating material Hair Sweat pore Muscle Nerve Sweat gland Oil gland Hair follicle Blood vessels Adipose tissue Hypodermis Dermis Epidermis

Circulatory Adaptations Many endotherms and some ectotherms can alter the amount of blood flowing between the body core and the skin

In vasodilation – Blood flow in the skin increases, facilitating heat loss In vasoconstriction – Blood flow in the skin decreases, lowering heat loss

Many marine mammals and birds h ave arrangements of blood vessels called countercurrent heat exchangers that are important for reducing heat loss In the flippers of a dolphin, each artery is surrounded by several veins in a countercurrent arrangement, allowing efficient heat exchange between arterial and venous blood. Canada goose Artery Vein 35°C Blood flow Vein Artery 30º 20º 10º 33° 27º 18º 9º Pacific bottlenose dolphin Arteries carrying warm blood down the legs of a goose or the flippers of a dolphin are in close contact with veins conveying cool blood in the opposite direction, back toward the trunk of the body. This arrangement facilitates heat transfer from arteries to veins (black arrows) along the entire length of the blood vessels. 1 Near the end of the leg or flipper, where arterial blood has been cooled to far below the animal’s core temperature, the artery can still transfer heat to the even colder blood of an adjacent vein. The venous blood continues to absorb heat as it passes warmer and warmer arterial blood traveling in the opposite direction. 2 As the venous blood approaches the center of the body, it is almost as warm as the body core, minimizing the heat lost as a result of supplying blood to body parts immersed in cold water

Some specialized bony fishes and sharks also possess countercurrent heat exchangers 21º 25º 23º 27º 29º 31º Body cavity Skin Artery Vein Capillary network within muscle Dorsal aorta Artery and vein under the skin Heart Blood vessels in gills

Many endothermic insects have countercurrent heat exchangers that help maintain a high temperature in the thorax

Cooling by Evaporative Heat Loss Many types of animals: – Lose heat through the evaporation of water in sweat – Use panting to cool their bodies

Bathing moistens the skin, which helps to cool an animal down

Behavioral Responses Both endotherms and ectotherms use a variety of behavioral responses to control body temperature

Some terrestrial invertebrates have certain postures that enable them to minimize or maximize their absorption of heat from the sun

Adjusting Metabolic Heat Production Some animals can regulate body temperature by adjusting their rate of metabolic heat production

Many species of flying insects use shivering to warm up before taking flight PREFLIGHT WARMUP FLIGHT Thorax Abdomen Temperature (°C) Time from onset of warmup (min)

Feedback Mechanisms in Thermoregulation Mammals regulate their body temperature by a complex negative feedback system that involves several organ systems

In humans, a specific part of the brain, the hypothalamus, contains a group of nerve cells that function as a thermostat Thermostat in hypothalamus activates cooling mechanisms. Sweat glands secrete sweat that evaporates, cooling the body. Blood vessels in skin dilate: capillaries fill with warm blood; heat radiates from skin surface. Body temperature decreases; thermostat shuts off cooling mechanisms. Increased body temperature (such as when exercising or in hot surroundings) Homeostasis: Internal body temperature of approximately 36–38  C Body temperature increases; thermostat shuts off warming mechanisms. Decreased body temperature (such as when in cold surroundings) Blood vessels in skin constrict, diverting blood from skin to deeper tissues and reducing heat loss from skin surface. Skeletal muscles rapidly contract, causing shivering, which generates heat. Thermostat in hypothalamus activates warming mechanisms.

Adjustment to Changing Temperatures In a process known as acclimatization, many animals can adjust to a new range of environmental temperatures over a period of days or weeks

Acclimatization may involve cellular adjustments – Or in the case of birds and mammals, adjustments of insulation and metabolic heat production

Torpor and Energy Conservation Torpor is an adaptation that enables animals to save energy while avoiding difficult and dangerous conditions – Is a physiological state in which activity is low and metabolism decreases

Hibernation is long-term torpor t hat is an adaptation to winter cold and food scarcity during which the animal’s body temperature declines Additional metabolism that would be necessary to stay active in winter Actual metabolism Body temperature Arousals Outside temperature Burrow temperature JuneAugustOctoberDecemberFebruaryApril Temperature (°C) Metabolic rate (kcal per day)

Estivation, or summer torpor – Enables animals to survive long periods of high temperatures and scarce water supplies Daily torpor – Is exhibited by many small mammals and birds and seems to be adapted to their feeding patterns