Animal Structure & Function Part II: Nutrition
Why do we eat?
An animal’s diet must satisfy three needs: 1) _____________________ to make ATP, 2) __________________ for biosynthesis,
3) ______________ nutrients – molecules the body cannot __________________.
Chemical Energy Animals must have a constant supply of energy (mainly _________________)
to live. Most of the energy taken in is used to produce ATP to power resting ________________
and ____________________ regulation. ATP can also be used for _____________________.
Carbohydrate concentrations in the blood are kept at a constant level (__________________) by
feedback loops. After a meal, when blood glucose is _______ (1), _____________ from the
pancreas (2) stimulates liver and muscle cells to store glucose as ______________, lowering the
blood glucose level (3). After the liver is saturated with glycogen, insulin stimulates
_________________ to convert glucose into _________________ for storage. Adipose tissue
produces __________ in response to filling with lipids. Leptin cues the brain to _____________
_______________, increase _________________ activity, and ________________ production.
Between meals when blood glucose drops (4), _________________ from the pancreas (5)
stimulates liver and muscle cells to release glucose from glycogen, raising the blood glucose
level (6). Only after the liver is _______________ of glycogen will adipocytes be stimulated to
break down ____________________ to release fatty acids for energy production.
Raw Materials Food must supply _________________________ molecules to use as building blocks for growth. Essential
nutrients – ____________________, ____________________, and ________________ that cannot be made by the body – must
be supplied in the diet.
How do we eat?
Animals are classified as herbivores, carnivores, or omnivores based on the main part of their diet. Most animals are
____________________ feeders in that they eat foods outside of their main dietary category on occasion. There are four main
feeding methods: 1) ______________-feeders: animals that _______ food particles from water. 2) ______________-feeders:
animals that ____________ their food source, eating their way through food. 3) __________-feeders: animals the survive by
______________ nutrient-rich fluids from a living host. 4) _______-feeders: animals that eat relatively ____________ of food.
The four main stages of food processing are ingestion, digestion, absorption, and elimination. 1) _______________: the act of
eating. 2) ________________: the process of breaking food down into molecules, by _______________________, that are small
enough for the body to absorb. 3) _________________: the animal’s cells take up small molecules such as amino acids, fatty
acids, and simple sugars. 4) _________________: undigested material passes out of the digestive compartment.
Evolution of Digestion
Digestion occurs in specialized compartments to reduce the risk of ____________________. The most primitive digestion is
___________________ digestion, using ____________________ with hydrolytic enzymes to break down food without digesting
the cell’s cytoplasm. ____________________ digestion breaks down of food outside cells. Diploblastic animals have
____________________________, which function in both the digestion and distribution of nutrients throughout the body.
Triploblastic animals evolve complete digestive tracts, or _______________________, with both a _______ and an _____. The
advantage is that animals can ingest ____________________ before earlier meals are completely digested. Nematodes introduce
the first ______________ – an organ for both ______________ and _____________ nutrients. Nematodes also have a muscular
___________ for sucking food into the digestive system. Annelids add more specialization: the esophagus, crop, and gizzard.
The _______________ pushes food down into the crop. The _______ stores swallowed food until it can be digested. The
___________ crushes food, helping with _________________ digestion. Mollusks combine the crop and gizzard into a single
organ – the ______________ – for both storage and digestion of food.
Digestion in mammals begins in the mouth: Chewing – _________________ digestion;
____________ (in saliva) – incompletely hydrolyzes ____________ (plant starch) into
disaccharides – ______________ digestion. After swallowing (using the esophagus), the
stomach continues preliminary digestion: The stomach secretes ___________________ and
mixes them with food by a churning motion – _______________ digestion. Gastric juices
contain _____________________ and _________, an enzyme; both begin the hydrolysis of
____________ – chemical digestion. The stomach protects itself from digestion in two ways: 1)
______________ cells produce a thick layer of mucus that coats the stomach wall. 2) Pepsin is
made as an inactive ______________ called __________________, which is only activated after
it reaches the acidic lumen of the stomach.
Absorption in the Intestines
After leaving the stomach, food (now in a liquid form called ________) enters the small intestine.
The acidic pH of chyme is quickly neutralized by digestive juices from the _____________ and
_________ from the liver. The small intestine is divided into three sections – the
_____________________ (first 25 cm), _______________ (2.5 m long), and ___________ (4 m).
________________ digestion of food continues in the duodenum and is completed in the
_________________. Two ________________________ – hormones made by the duodenum –
regulate digestion: 1) ______________ stimulates pancreas to release pancreatic juice,
2) ___________________________ (CCK) stimulates the ___________________ to contract and
Digestion of carbohydrates The pancreas produces more ______________, which continues the
digestion of amylose (starch) into _____________________. The small intestine produces a
variety of enzymes (____________, ____________, ______________) to digest disaccharides into
____________________________. These enzymes are all attached to
the intestinal _______________, so that when monosaccharides are
released, they can be immediately absorbed.
Digestion of proteins The pancreas produces the enzymes
______________________ and ____________, which continue to break
proteins into smaller ____________________. Similarly to pepsin,
chymotrypsin and trypsin are produced as inactive _________________
(chymotrypsinogen, trypsinogen). Both proenzymes are activated by the
enzyme _____________________ in the small intestine. The small
intestine produces two peptidases, _______________________ and
______________________, that can hydrolyze the last amino acid from
any ____________. These two enzymes complete the digestion of the
peptide fragments produced by ___________, trypsin, and chymotrypsin.
Digestion of lipids
Hydrolysis of lipids is a special problem because ____________________ lipid
molecules are ________________ in water. Bile (produced in the liver) is a
solution of ___________________________ that act as detergents - they
_______________ (break up into small micelles) lipids so that they can float in
water. By emulsifying lipids, bile also increases the _____________________
over which _____________ (produced by the pancreas) can hydrolyze
________________________ into fatty acids and monoglycerides.
Absorption of Nutrients
Nutrients are absorbed in all three parts of the _______________________. To increase the rate of absorption, the lining of the
small intestine is folded into ________, which increase the ___________________________ of the small intestine. The
___________ surface of the columnar epithelium lining each villus is covered in extensions called __________________, which
further increase the surface area. Each villus contains a net of _______________ and a small vessel of the lymphatic system
called the ____________. __________________________ and _________________ are absorbed across the epithelium and
enter the blood via the ___________________. Lipids are also absorbed into the __________________, where they are packaged
with cholesterol and carrier proteins into packets called ___________________. These enter the lymph via the _____________.
Left Side Assignment: Complete the "Enzymatic Digestion in Humans" table.
Enzymatic Digestion in Humans
Fill in the enzymes and products of digestion at each step.
Carbohydrate Digestion Protein Digestion Lipid Digestion
Mouth Polysaccharide (starch)
Lumen of Polysaccharide (starch) Protein Fat globules
Answer the following:
1) Explain how pepsin, trypsin, and chymotrypsin are prevented from digesting the epithelia of the stomach and small intestine.
2) If aminopeptidase and carboxypeptidase can completely digest any protein, explain why humans have pepsin, trypsin, and
chymotrypsin – how do these enzymes help? Include in your answer some reference to the primary structure of proteins.
3) List the first phylum to evolve each of the following organs, along with the purpose of the organ:
Organ Appears in phylum: Purpose