Animals must balance their food consumption, storage, and usage in order to survive and reproduce. Sea otters, for example, maintain a high metabolic rate by consuming up to 25% of their body weight each day.

Eating too little, too much, or the improper combination of meals can be harmful to an animal's health. In this chapter, we'll look at animal nutritional needs, different evolutionary adaptations for acquiring and processing food, and the control of energy intake and expenditure.

The food of an animal must provide chemical energy, organic building components, and vital nutrients. An appropriate diet must provide three nutritional demands in total: chemical energy for cellular activities, organic building blocks for macromolecules, and vital nutrients.

The activity of cells, tissues, organs, and complete animals are all dependent on chemical energy sources in food. This energy is utilized to generate ATP, which is used to power activities ranging from DNA replication and cell division to vision and flight.

To satisfy their ATP requirements, animals consume and digest nutrients such as carbs, proteins, and lipids, which are then used in cellular respiration and energy storage.

The Functions of Essential Nutrients This biosynthetic process demonstrates some of the typical activities of important nutrients.

All four groups of necessary nutrients are involved in the conversion of linoleic acid to g-linoleic acid by the enzyme fatty acid desaturase, as labeled in blue. As demonstrated in the partial sequence for fatty acid desaturase, nearly all enzymes and other proteins in mammals contain certain necessary amino acids.

To produce a complete set of proteins, all organisms require a standard set of 20 amino acids (as shown in the attached ). Plants and microbes are typically capable of producing all 20. As long as their food contains sulfur and organic nitrogen, most animals have the enzymes to synthesis around half of these amino acids.

The remaining amino acids must be acquired in premade form from the animal's diet and are hence referred to as necessary amino acids.

Many animals, including adults, need the consumption of eight amino acids: isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. (Human babies require a ninth nutrient, histidine.)

Proteins found in animal products such as meat, eggs, and cheese are “complete,” which means they include all of the essential amino acids in the correct amounts.

Most plant proteins, on the other hand, are “incomplete,” meaning they lack one or more necessary amino acids. For example, corn (maize) is low in tryptophan and lysine, whereas beans are low in methionine. Vegetarians, on the other hand, may readily acquire all of the required amino acids by consuming a diverse diet of plant proteins.

Circulatory systems connect exchange surfaces to cells all over the body.

The molecular exchange that an animal engages in with its surroundings—gaining O2 and nutrients while releasing CO2 and other waste products—must eventually encompass every cell in the body.

Small molecules in and around cells, such as O2 and CO2, move randomly due to diffusion, which is caused by random thermal motion (as shown in the attached image).

• The term Diffusion refers to occuring in net movements when there is a concentration difference, such as between a cell and its immediate surroundings. However, such movement is extremely sluggish at distances more than a few millimeters. This is due to the fact that the time it takes for a material to disperse from one location to another is proportional to its size.

The attached image shows the internal transport in gastrovascular activities.

Aurelia, a cnidarian moon jelly. The underside of the jelly is shown here (oral surface). The mouth leads to a complex gastrovascular cavity comprised of radial canals going to and from a circular canal.

Fluid circulates throughout the cavity thanks to the ciliated cells that line the canals.

A circulatory system consists of three fundamental components: a circulatory fluid, a network of interconnected vessels, and the heart, a muscle pump.

The heart drives circulation by utilizing metabolic energy to increase the hydrostatic pressure of the circulatory fluid, which is the pressure the fluid exerts on surrounding arteries. The fluid then circulates through the arteries and returns to the heart.

The circulatory system connects the watery environment of the body cells to the organs that exchange gases, absorb nutrients, and dispose of wastes by moving fluid throughout the body. O2 from breathed air, for example, diffuses across only two layers of cells in the lungs before reaching the blood in mammals.

Circulatory systems connect exchange surfaces to cells all over the body.

A gastrovascular cavity promotes exchange between the environment and cells that may be accessed via diffusion in animals with basic body designs. Because diffusion is sluggish over long distances, most sophisticated creatures have a circulatory system that can glide passively for extended periods of time with little muscular effort.

During a dive, their heart rate and oxygen consumption rate fall, and the majority of their blood is sent to critical structures like the brain, spinal cord, eyes, adrenal glands, and, in pregnant seals, the placenta. The blood flow to the muscles is limited or, during long drives, completely cut off. A Wedd was present during these dives.

In animals, double circulation is driven by coordinated cycles of cardiac contraction.

The right ventricle is responsible for pumping blood to the lungs, where it loads O2 and unloads CO2. The left atrium receives oxygen-rich blood from the lungs, which is then pushed to the bodily tissues via the left ventricle. The right atrium is where blood returns to the heart.

The cardiac cycle, which is the full sequence of the heart's pumping and filling, consists of a time of contraction, known as systole, and a period of relaxation, known as diastole. The pulse (the number of times the heart beats per minute) and cardiac output (the volume of blood pumped by each ventricle per minute) can be used to measure heart function.

The heartbeat is initiated by impulses from the right atrium's sinoatrial (SA) node (pacemaker). They cause atrial contraction, which is subsequently delayed at the atrioventricular (AV) node before being carried through the bundle branches and Purkinje fibers, causing ventricular contraction.

The neurological system, hormones, and body temperature all have an impact on the pacemaker.

Blood pressure and flow patterns reflect the shape and arrangement of blood arteries.

The architecture of blood arteries are well suited to function. Capillaries have small dimensions and thin walls that allow for interchange.

Because of their huge overall cross-sectional area, capillary beds have the slowest blood flow velocity. Arteries have strong elastic walls that keep blood pressure stable. Veins have one-way valves that aid in the return of blood to the heart. Blood pressure is affected by variations in cardiac output as well as changing arteriole constriction.

Blood components perform exchange, transport, and defensive functions.

Whole blood is made up of cells and cell fragments (platelets) floating in plasma, a liquid matrix. Plasma proteins have an effect on blood pH, osmotic pressure, and viscosity, as well as lipid transport, immunity (antibodies), and blood clotting (fibrinogen).

Red blood cells, also known as erythrocytes, carry oxygen. White blood cells, or leukocytes, are made up of five different kinds that fight bacteria and foreign substances in the blood.

Platelets play a role in blood clotting by initiating a chain reaction that transforms plasma fibrinogen to fibrin.

A multitude of illnesses impedes the circulatory system's function.

Gas exchange happens with the use of specific respiratory surfaces.

A gas undergoes net diffusion from where its partial pressure is greater to where it is lower at all gas exchange locations. Because air has a greater O2 concentration, lower density, and lower viscosity than water, it is more favorable to gas exchange.

The form and arrangement of respiratory surfaces differ amongst animals. Gills are body surface out folding that are specialized for gas exchange in water.

Ventilation and countercurrent exchange between blood and water improves the efficiency of gas exchange in some gills, notably those of fish. In insects, gas exchange is carried out by a tracheal system, which is a branching network.

Breathing mechanics differ greatly amongst animals.

Positive pressure breathing, which drives air down the trachea, is used by amphibians to ventilate their lungs. Birds utilize a system of air sacs as bellows to maintain air moving through their lungs in just one direction, preventing incoming and outgoing air from mingling. Negative pressure breathing, which draws air into the lungs as the rib muscles and diaphragm flex, is used by mammals to ventilate their lungs. Incoming and exiting air mix, reducing ventilation efficiency.

Sensors monitor the pH of cerebrospinal fluid (which reflects the quantity of CO2 in the blood), and a control center in the brain regulates breathing rate and depth to meet metabolism.

Pigments that bind and transport gases are examples of gas exchange adaptations.

Gradients in partial pressure in the lungs encourage net diffusion of O2 into the blood and CO2 out of the circulation. In the remainder of the body, the situation is the inverse. Respiratory pigments like hemocyanin and hemoglobin bind O2, boosting the quantity of O2 carried by the circulatory system significantly.

Some animals have evolved characteristics that allow them to meet extreme O2 needs. Deep-diving animals accumulate O2 in their blood and other tissues and gradually deplete it.