Resources gathered by animals• Food for energy and macromolecules• Water • Shelter from enemies (Enemy Free Space) • Space • Thermal energy• Chemicals used for signalingAnimals are Heterotrophs Plants are Autotrophs• Heterotrophs are incapable of producing their own energy as plants do via photosynthesis• Heterotrophs must consume food that contains energy, and both organic and inorganic chemical nutrientsSome Animals obtain their food symbiotically• Corals, and some sponges and jellyfish contain symbiotic algae that photosynthesize and transfer energy to their coral hosts in exchange for certain nutrients• Thermal vent worms (Annelida: Vestimentifera) obtain most of their nutrients from symbiotic bacteria in exchange for H2S and CO2that they absorb from the water • Some beetles (ambrosia) transport, farm, and consume fungi to obtain most of their nutrients and energy • No animals can obtain all their energy without transfer from or consumption of other organisms Annelida: Vestimentifera –Thermal vent tube worms• For any animal, a nutritionally adequate diet is essential for homeostasis, a steady-state balance in body functions.– A balanced diet provides fuel for cellular work and the materials needed to construct organic molecules.•A nutritionally adequate diet satisfies three needs:–fuel (chemical energy) for all the cellular work of the body; –the organic raw materials animals use in biosynthesis (carbon skeletons to make many of their own molecules);–essential nutrients, substances that the animals cannot make foritself from any raw material and therefore must obtain in food in prefabricated form.• The flow of food energy into and out of an animal can be viewed as a “budget,” with the production of ATP accounting for the largest fraction by far of the energy budget of most animals.– ATP powers basal or resting metabolism, as well as activity, and, in endothermic animals, temperature regulation. However, most invertebrates are ectothermic – their body temperatures conform to the ambient temperature of their environment Homeostatic mechanisms manage an animal’s fuel• Nearly all ATP is derived from oxidation of organic fuel molecules - carbohydrates, proteins, and fats - in cellular respiration.– The monomers of any of these substances can be used as fuel, though priority is usually given to carbohydrates and fats.– Fats are especially rich in energy, containing twice the energy of an equal amount of carbohydrate or protein.•When an animal takes in more calories than it needs to produce ATP, the excess can be used for biosynthesis.–This biosynthesis can be used to grow in size or for reproduction, or can be stored in energy depots.• In addition to fuel for ATP production, an animal’s diet must supply all the raw materials for biosynthesis.– This requires organic precursors (carbon skeletons) from its food.– Given a source of organic carbon (such as sugar) and a source of organic nitrogen (usually in amino acids from the digestion of proteins), animals can fabricate a great variety of organic molecules - carbohydrates, proteins, and lipids. An animal’s diet must supply essential nutrients and carbon skeletons for biosynthesis• Besides fuel and carbon skeletons, an animal’s diet must also supply essential nutrients.– These are materials that must be obtained in preassembled form because the animal’s cells cannot make them from any raw material.– Some materials are essential for all animals, but others are needed only by certain species.• For example, ascorbic acid (vitamin C) is an essential nutrient for humans and other primates, guinea pigs, and some birds and snakes, but not for most other animals.• Animals require 20 amino acids to make proteins.• Most animals can synthesize half of these if their diet includes organic nitrogen.• Essential amino acids must be obtained from food in prefabricated form.– Eight amino acids are essential in the adult human with a ninth, histidine, essential for infants.– The same amino acids are essential for most animals.• While animals can synthesize most of the fatty acids they need, they cannot synthesize essential fatty acids.– These are certain unsaturated fatty acids, including linoleic acids required by humans.– Most diets furnish ample quantities of essential fatty acids, and thus deficiencies are rare. • Minerals are simple inorganic nutrients, usually required in small amounts.– Mineral requirements vary with animal species.– Humans and other vertebrates require relatively large quantities of calcium and phosphorus for the construction and maintenance of bone among other uses.– Iron is a component of the cytochromes that function in cellular respiration and of hemoglobin, the oxygen binding protein of red blood cells.• Ingestion, the act of eating, is only the first stage of food processing.– Food is “packaged” in bulk form and contains very complex arrays of molecules, including large polymers and various substances that may be difficult to process or may even be toxic. The four main stages of food processing are ingestion, digestion, absorption, and elimination• Animals cannot use macromolecules like proteins, fats, and carbohydrates in the form of starch or other polysaccharides.– First, polymers are too large to pass through membranes and enter the cells of the animal.– Second, the macromolecules that make up an animal are not identical to those of its food.• In building their macromolecules, however, all organisms use common monomers.• For example, soybeans, fruit flies, and humans all assemble their proteins from the same 20 amino acids.• Digestion, the second stage of food processing, is the process of breaking food down into molecules small enough for the body to absorb.– Digestion cleaves macromolecules into their component monomers, which the animal then uses to make its own molecules or as fuel for ATP production.• Polysaccharides and disaccharides are split into simple sugars.• Fats are digested to glycerol and fatty acids.• Proteins are broken down into amino acids.• Nucleic acids are cleaved into nucleotides. • Chemical digestion is usually preceded by mechanical fragmentation of the food - by chewing, for instance.– Breaking food into smaller pieces increases the surface area exposed to digestive juices containing hydrolytic enzymes.•After the food is digested, the animal’s