Use the Nelson text, "Biology 11", pp. 208-210 to complete the blanks.


Unlike plants (which are _________________), heterotrophs must consume _________________ (containing carbon) compounds to survive. These organic compounds, called ________________, are digested in the ____________________ tract, absorbed, and transported by the ____________________ system to the cells of the body. Once inside the cells, the _________________ supply the body with _________________ or the raw materials for ____________________ of essential chemical compounds.

The digestive system is responsible for the breakdown of ______________, ______________ organic materials into _______________ components that are utilized by the tissues. The four components of digestion are:

1. Ingestion 
2. Digestion 
3. Absorption 
4. Egestion 

Digestive Enzymes

The rate at which an enzyme functions best to break down complex molecules is affected by two factors: ________________ and _________. (sketch Fig. 1 and 2 on pg. 208)

In general, as the ___________________ increases, more _______________ is added, and the greater the enzyme ________________ (higher rxn rate). However, efficiency peaks at about __________ and then drops. This is because enzymes are _____________ that when subjected to high temperatures change _____________ (called "denaturation") after which the enzyme is no longer active.

Enzymes function best (have highest rxn rate) within certain ________ ranges. The enzyme _____________ (blue curve in Fig. 2), works best at a ________ pH (ie. a pH of ____). It is found in the _______________ environment of the _____________. The enzyme amylase (grey curve in Fig. 2) works best in ________________ pH environments (ie. a pH of _______), such as the mouth. The enzyme ____________ (green curve in Fig. 2) works best in ____________ environments (ie. pH of ______), such as the small _________________.

Digestion in Simpler Organisms

The simplest form of digestion occurs in organisms such as _________________, which digest their meals inside food ______________ within cells. An _______________ engulfs its food by ________________ and a vacuole is formed which then fuses with ______________________ in the cell. The lysosomes contain _____________________ enzymes which use molecules of ______________ to break food down (see Fig. 3, pg. 209).

Many simple organisms, such as ___________, have a digestive sac with a single opening. This pouch is called a _____________________ cavity. Digestive ________________ are released into the cavity breaking down the larger food molecules. Then the ________________ food molecules are engulfed by cells that _____________ the digestive cavity and digestion continues with the ___________________ of the cells. Wastes are expelled from the same ________________ which ingested the food (see Fig. 4, pg. 209).

Digestion in More Complex Organisms

More complex animals digest food along digestive ______________, called _______________________ canals. These long tubes have a separate opening for a _______________ and an __________. The canal is specialized along its length for breakdown and ________________ of food in a stepwise process.

Food ingested through the ________________ travels through the muscular ______________ and into the ________________. Depending on the species, it is held in the __________________ or ____________. Animals that don't have _______________ have a muscular __________________ that physically breaks down food particles. Pulverized food then moves into the _______________ where hydrolytic _________________ complete the stage of ________________ digestion. Then _______________ are absorbed across the lining of the _____________________ into the ________________. The ____________________ system carries the digested nutrients to the cells of the body. Undigested wastes are removed through the _____________. (Sketch or trace the diagrams of the worm and bird and label and make brief notes on steps a-f)