Physical laws can have an impact on animal body designs, to the largest size possible thickness increases as body dimensions grow.

Skeletons are needed to provide appropriate support. These Internal skeletons, such as those of vertebrates, are affected, as are exterior skeletons, such as those of insects as well as other arthropods. Furthermore, when our bodies grow in size, the muscles necessary for movement must account for an increasing proportion of total body mass.

Mobility comes to an end at some time as it gets constrained by taking into account the percentage of body mass in leg muscles and the effective force generated by such muscles. Scientists can calculate the maximum running speed for a variety of animals with a variety of body plans.

At all levels of the organization, animal form and function are linked.

The size and shape of an animal are basic characteristics of form that have a substantial impact on how the animal interacts with its surroundings.

Size and form may be referred to as parts of a "body plan" or "design," but this does not indicate an intentional creation process. The body plan of an animal is the outcome of a development pattern encoded by the genome, which is the result of millions of years of evolution.

Many diverse body designs have evolved throughout time, yet these variants all fit within basic parameters. The spectrum of animal forms is limited by physical constraints that control strength, diffusion, mobility, and heat exchange.

Consider how certain characteristics of water limit the available forms for creatures that are fast swimmers as an illustration of how physical rules control evolution. Water is approximately 1,000 times denser than air and considerably more viscous. As a result, each bump on an animal's body surface that generates drag hinders a swimmer more than a runner or flyer.

Tuna and other fast-moving ray-finned fish may reach speeds of up to 80 km/h (50 miles/hour). Sharks, penguins, dolphins, and seals are all good swimmers. As seen in the image attached, these creatures all have a fusiform shape, which means they are tapered on both ends.

The streamlined form shared by these fast animals is an example of convergent evolution (as shown in the image attached above). When various creatures encounter the same environmental difficulty, such as resisting drag when swimming, natural selection frequently results in identical adaptations.

Animals must interchange nutrients, waste materials, and gases with their surroundings, which places extra constraints on body designs. Substances dissolved in an aqueous solution exchange as they travel through the plasma membrane of each cell. A single-celled creature, such as the amoeba in Figure 40.3a, has enough membrane surface area in touch with its surroundings to carry out the required exchange.

A mammal, on the other hand, is made up of numerous cells, each with its own plasma membrane across which exchange must take place. The rate of exchange is proportional to the membrane surface area engaged in the exchange, whereas the quantity of material that must be traded is proportional to the amount of material that must be exchanged.

Many animals rely on feedback control to maintain their internal habitat.

If an animal controls an internal variable, it is a regulator; if it permits an internal variable to vary in response to external changes, it is a conformer. Homeostasis is the ability to maintain a constant condition despite internal and external changes.

The majority of homeostatic processes are based on negative feedback, in which the reaction lowers the stimulus. Positive feedback, on the other hand, entails the response's amplification of a stimulus and frequently results in a change in status, such as the transition from pregnancy to delivery.

Change in the internal environment must be regulated for normal operation. Circadian rhythms are daily variations in metabolism and behavior that are synchronized with light and dark cycles in the environment.

Other environmental changes may cause acclimatization, which is a transient alteration in the steady-state.

Thermoregulation homeostatic processes involve shape, function, and behavior. Thermoregulation is the process through which an animal keeps its internal temperature within an acceptable range.

Endothermic creatures are primarily warmed by heat produced by metabolism. Ectothermic creatures acquire the majority of their heat from outside sources. Endothermy necessitates a higher energy expenditure. The temperature of the body can change depending on the environment.

Body temperature can change in response to external temperature, as in poikilotherms, or it can be relatively stable, as in homeotherms.

Physiological and behavioral adaptations balance heat input and loss caused by radiation, evaporation, convection, and conduction. Insulation and countercurrent exchange decrease heat loss, but panting, sweating, and bathing promotes evaporation and therefore chill the body. Many ectotherms and endotherms alter their rate of heat exchange with their environment by vasodilation or vasoconstriction, as well as through behavioral reactions.

Many animals and birds alter their body insulation in response to temperature variations in the environment.

The amount of energy required by an animal is determined by its size, activity, and surroundings.

Animals get chemical energy from their diet and store it as ATP for short-term usage. An animal's metabolic rate is defined as the total quantity of energy used in a unit of time.

Endotherms' basal metabolic rate is significantly greater than ectotherms' standard metabolic rate under identical conditions and for animals of the same size. Among comparable species, the minimum metabolic rate per gram is inversely related to body size. Animals use energy to maintain their basal (or standard) metabolism, activity, homeostasis, growth, and reproduction.

Torpor, a reduced state of activity and metabolism, conserves energy during environmental changes.

At all levels of the organization, animal form and function are linked.

The evolution of an animal's size and shape is governed by physical principles. These limitations help to drive the convergent development of animal body shapes.

Every animal cell requires access to an aquatic environment.

Flatforms and simple two-layered sacs enhance exposure to the surrounding media. More sophisticated body designs contain highly folded interior surfaces that are specialized for material exchange.

Animal bodies are made up of a series of cells, tissues, organs, and organ systems that are organized in a hierarchy. On the exterior and interior surfaces, epithelial tissue creates active interfaces; connective tissue binds and supports other tissues; and muscle tissue contracts.

The endocrine and neurological systems are the two systems that communicate between various parts of the body.

The endocrine system sends signaling molecules called hormones throughout the body via the circulation, but only particular cells respond to each hormone. To convey information to particular places, the nervous system employs dedicated cellular circuits incorporating electrical and chemical impulses.