Chapter 41 (2)

Food processing can be divided into four distincti stages?

The first stage, __, is the act of eating. Food can be ingested in many liquid and solid forms.

In __, the second stage of food processing, food is broken down into molecuels small enough for the body to absorb. This stage is necessry because animals cannot directyl use proteins, carbs, nucleic acids, fats and phospholipids in food. These molecuels are too large to pass through membranes and enter the cells of the animal. In addition, the large molecuels in food are not all identical to those the animal needs for its particular tissue and fucntions. When large molecuels in food are broken down into their components, the animal can use these smaller molecules to assemble the large molecules it needs.

A cell makes a macromolecuel or fat by linking together smaller components; it does so by removing a moleucle of water for each new covalent bond formed. Chemical digestion by enymes reverses this process by breaking bonds with the addition of __. This splitting process is called __.

A variety of enzymes catalyze the digestion of large molecuels in food. __ are __ are split into simple sugars; proteins are broken down into __; nucleic acids are cleaved into __. __ also releases __ and other components from fats and phospholipids. Such chemical digestin is typically preceded by __- by chewing for instance. __ breaks food into smaller peices, increasing the surface area available for chemical processes.

The last two stages of food processing occur after the food is digestied. In the third stage, __, the animal's cell take up (absorb) small molecules suchas amino acids and simple sugars.
- __ completes the process as undigested material passes out of the digestive system.

Digestive enzymes hydrolyze the same biological amaterials that make up the bodies of the animal sthemselves. How, then, are animals able to digest food without digesting their own cells and tissues.
o The evolutionary adaptation found across a wide range of animal species is what?
----- Such compartments can be __, in teh form or food vacuoles, or __, as in digestive organs adn systems.

__- cellular organelles in which hydrolytic enzymes break down food-a re the simplest digestive compartments. THe hydrolysis of food inside vacuoles, called __, begins after a cell engulfs solid food by __ or liquid food by __. Newly formed food vacuoles fuse with __, organelles containing hydrolytic enzymes. This fusion of organelles brings food together with the enzymes, allowing digestion to occur safely within a compartment enclosed by a protective membrane. A few animals, like sponges, digest their food entirely by this intracellular mechanisms.

In most animals, at least some hydrolysis by __, the breakdown of food in compartments that are continuous with the outside of the animal body. Having one or more extracellular compartments for digestion enables an animal to devour much larger sources of food than cn be ingested by __.

Many animals with relatively simple body plans have a digestive compartment with a single opening. This pounch, called a __, functions in digestion as well as in the distribution of nutrients throughout the body. The carnivorous cnidarians called __ provide a good example of how a __ works. It uses its tentacles to stuff captured prey thorugh it smouth into its ___. Specialized gland cells of its __, teh tissue layer that lines the cavity, then secrete digtestive enzymes that break the soft tissues of the prey into tiny pieces. Other cells of the __ engulf these food particles, and mos t of the actual hydrolysis of macromolecules occurs intracellularly, as in sponges.

After a hydra has digested its meal, undigested materials that remain in the __, like exoskeletons of small animals, are eliminated through the same opening by which food entered. Manyh flatworms also have a __ with a single opeining.

Most animals have a digestive tube extending between two openings, a __ and an __. Such a tube is called a __, or more commonly an __. Because foood moves along the __ in a single direction, the tube can be organized into specialized compartments that carry out digestion and nutrient absorption in a stepwise fashion. An animal with an __ can ingest food while earler meals are still being digested, a feat that is likely to be difficult or inefficient for animals with __.