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Biology 12
DIGESTIVE SYSTEM ASSIGNMENT KEY
Learning Objectives: see LO’s I.
Reference: Chapter 12
Part I.
Vocabulary and Question Assignment
1.
Why is digestion of food in a human called an extracellular process? It’s
digested outside of the body’s cells and then the nutrients are absorbed into
the cells of the body.
2.
What are the functions of the digestive system? It’s needed to first ingest food,
then break down nutrients mechanically and chemically from polymers to
monomers. Finally it is needed to absorb the nutrients to be distributed to
other parts of the body via the circulatory and lymphatic systems and
eliminate the un-digestible products.
Mouth.
3.
Distinguish between chemical and mechanical digestion. How is food
mechanically digested in the mouth?
Mechanical digestion breaks food into smaller pieces of the same substance
thereby increasing the surface area to speed up chemical digestion. Chemical
digestion, with the aid of enzymes, breaks food into the monomers it is made
of i.e. a chemical change occurs so that the original substance is no longer
there. In the mouth it is chewed by teeth and squished by the tongue to make
the smaller pieces.
4.
Why is salivary amylase classed as a hydrolytic enzyme? It brings H2O in
contact with starch to start its break down.
5.
Once again, what is the role of water in the digestion of starch or any nutrient
polymer? It is the H2O that disrupts the bonds between the monomers of starch
and therefore causes its digestion and the dissociated ions reform the monomers.
Pharynx
6.
Identify the need for an epiglottis. It is needed to prevent food from entering
the glottis and eventually the trachea. Every time we swallow it moves down
to cover the opening of the voice box.
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Esophagus
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7. Define the term peristalsis. It is a wave-like contraction of the smooth muscles of
the digestive tract starting with the esophagus and ending with the colon.
8. Where else does peristalsis occur in the digestive system? Why would peristalsis
be a rather slow-acting set of muscle contractions in other parts of the digestive
system? It occurs along the entire length of the digestive track. Once beyond
the esophagus, it allows the food that is being digested to remain in the same
region of the tract for a longer time the food is more properly digested and
absorbed.
9.
Describe the structure and operation of a sphincter. Name the sphincter
separating the esophagus and stomach. It is a circular muscle that when
constricted closes off the tube it is a part of. The sphincter that separates the
esophagus from the stomach is the cardiac sphincter. It is well developed so
stomach acid can’t leak past it into the esophagus to cause heartburn.
Stomach
10.
How is food mechanically digested in the stomach (2 ways)? It is churned and
mashed-up by the stomach muscles and the protein connective tissue is
broken apart by the HCl.
11.
List 3 roles of HCl in the stomach. Increases acidity of the stomach so enzymes
can function at optimum levels; causes the physical break up of protein’s
connective tissue; kills bacteria.
12.
What is meant by the term acid chyme? It is the very watery but acidic solution
of mechanically digested food (will also contain partially chemically-digested
protein and starch) that squirts from the stomach to enter the small intestine.
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Name the sphincter that separates the stomach and small intestine. It’s called the
pyloric sphincter.
14.
What enzyme is present in the stomach? What is its inactive form called?
Pepsin. Pepsinogen.
Small Intestine
15.
Would the emulsification of fat by bile salts be an example of chemical or
physical (mechanical) digestion? Explain. It’s physical since the fat is broken
into small fat droplets not into the monomers that make up the fat
(dispersed).
16.
What are two benefits of sodium bicarbonate (NaHCO3), being secreted by the
pancreas into the small intestine? It is needed to neutralize the pH of the
chyme so that the enzymes that will be working on it are working in the
optimum environment. It also protects the delicate tissue of the small
intestine from being burnt by the acidity of the chyme.
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17.
What is the role of pancreatic juice? Be specific and use your notes as a
reference. The enzymes released in the pancreatic juice are responsible for
continuing the digestion of starch and protein into smaller polymers and
completely digesting fat into monomers.
18.
Insulin is made by the pancreas and secreted into the blood, not the intestine.
Explain its importance to the body. Insulin is necessary so that every cell in the
body can take up glucose. Glucose levels must be maintained at specific
levels if the brain is to function, too much can cause a coma and death as can
too little.
19.
What is the general role of enzymes secreted from the duodenum and jejunum?
The walls of the small intestine secrete enzymes that do the final break down
of nutrients so that they can be absorbed. (Disaccharides broken down into
monosaccharides, and dipeptides to amino acids).
20.
Why are ALL digestive enzymes described as hydrolytic? Each one uses H2O to
break the bonds between the monomers (one monomer bonds to an H+ the
other to OH- ).
21.
List seven major roles of the liver.
1. detoxifies the blood
2. produces urea
3. stores glycogen/ releases glucose
4. makes bile
5. breaks down hemoglobin
6. makes blood proteins
7. stores iron and fat soluble vitamins
Large Intestine
22.
What are the functions of the colon (= large intestine)? It absorbs water, and
salts & minerals. It is the home of bacteria that can continue the digestion of
non-digestible materials (cellulose) and produce some vitamins useful to us.
Finally, it is a storage site for undigested food until it can be expelled.
23.
Fiber can reduce cholesterol in the blood and help prevent cancer. Explain how it
accomplishes both of these beneficial effects. It reduces cholesterol in the
blood because it binds to it and prevents its absorption by the intestine. It
can prevent cancer in 2 ways. First, it dilutes the concentration of bile by
reabsorbing water. Bile can be altered by bacteria into a carcinogen and so
if it is diluted it has a smaller affect on the cells of the intestine. Second, fiber
speeds the movement of substances through the intestine, therefore
carcinogens have less time to do damage to cells.
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What is the value of bacteria found in the large intestine?
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E. coli and obligate anaerobes break down non-digestible material for us plus
they make some vitamins (Vit. K) and other chemicals that we need.
25.
Briefly describe why a human diet must contain carbohydrates, proteins, fats,
vitamins, minerals and water, that is, describe the contribution of each to our
metabolism. Give some specific examples.
Carbohydrates are important as a source of energy (immediate source =
glucose, short term = starch, glycogen), some also form a structural function
(glycoproteins). Fiber also helps by binding with cholesterol so it isn’t
absorbed.
Proteins are important so we can build our own structural and functional
proteins (muscles, enzymes, hormones, hemoglobin, and blood proteins). ( In
special instances amino acids can also be broken down to form glucose for an
energy source.)
Fats are important as a long-term source of energy. They make up certain
structures (plasma membrane). They also form certain hormones (estrogen,
testosterone). Cholesterol can be a problem, if levels rise, in the formation of
cardiovascular diseases. A certain fatty acid, linoleic acid, must be
consumed. It is essential in the formation of phospholipids & therefore of the
plasma membranes of cells.
Vitamins are important for the normal metabolic activities of the cell. Vit. B
is necessary because the different forms are part of coenzymes that help
promote certain reactions. Vit A is a precursor for visual purple, a pigment
necessary to avoid night blindness.
Minerals are important because they can form structural components of
tissue (calcium = bones, teeth). Some are part of molecules that have specific
functions (iron = hemoglobin, iodine = formation of hormone thyroxin). Still
other ions are very important in the normal functioning of the body e.g. Ca +2
needed for nerve impulse conduction.
Part II
Absorption of Products of Digestion
Structure of a Villus
1.
Draw an enlarged diagram of a villus (Fig. 12.6) See notes
2.
Colour the blood vessel capillary bed and lymph vessel. See notes
3.
Label all significant parts. See notes
4.
Distinguish between villi and microvilli.
The microvilli are the epithelial cells of the villus. They appear fuzzy because they
have a heavily folded membrane (brush border). The villus is a fold in the intestinal
wall.
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Methods of Absorption (Ref. Ch. 4)
5.
Make brief notes for each of the following processes. Include a diagram where
requested.
a) Diffusion Movement of small molecules from areas of high concentration to
low until equally distributed. No ATP required (passive).
b) Osmosis Movement of H2O across a semi-permeable membrane from an area of
high concentration to low until equilibrium is met. No ATP required (passive).
c) Facilitated transport (diagram) Movement of small molecules across a semipermeable membrane while being bonded to a carrier protein (each molecule
needs its own carrier protein). It is always along a concentration gradient
therefore requires no ATP.
d)
Active Transport (diagram) Movement of ions or molecules against a
concentration gradient by actively binding to a carrier protein. When a
phosphate group is attached or detached to the carrier protein it changes
shape allowing the ion/molecule to combine with it. The phosphate group of
course comes from ATP, therefore energy is needed.
e)
Endocytosis (diagram )
i.
pinocytosis Cell drinking the forming of a vesicle around a
macromolecule (e.g. protein) by the plasma membrane.
phagocytosis Cell eating the forming of a vesicle around a large substances
(dead cell, bacteria) by the plasma membrane. Digestion occurs when
a lysosome fuses with it.
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6.
The following nutrients are absorbed by the SI. List which process(es) listed above
ensure their absorption.
a)
glucose: initially by facilitative transport (diffusion) but active
transport by carrier proteins will ensure all glucose is absorbed from
the lumen of the duodenum.
b)
amino acids: same as above
c)
glycerol: diffusion
d)
fatty acids: diffusion
7.
Once absorbed the nutrients either enter a capillary or a lacteal. Indicate for each of the
nutrients which vessel it enters and the process by which it is absorbed.
a)
glucose: enters capillaries by diffusion
b)
amino acids: enters capillaries by diffusion
c)
lipids (reformed where?): reformed in the epithelial cells of the villi
(lipoproteins) and diffuse from there into a lacteal
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Part III
Digestive System Chart: Role of Enzymes in Digestion
Organ/Region
PH
Substrate
Enzyme
Origin of Enzyme
Product or Products
Mouth
7.0
Starch
Salivary amylase
Salivary glands
maltose
Stomach
2
(HCl)
(Protein)Polypeptides
Pepsin
Small Intestine
Duodenum (lumen)
8.2
Lipid
(bile)
Lipase
Gastric glands
(goblet
cells
stomach)
pancreas
Lumen
(sodium bicarbonate)
8.2
polypeptides
Trypsin
pancreas
fatty acids and.....
glycerol
Absorbed by villus
Peptides
Lumen
8.2
Starch
Amylase
pancreas
Maltose
Microvilli
8.2
Polypeptides
Dipeptides
Peptidase
Intestinal glands of the Amino acids
brush border
Absorbed by villus
Microvilli
8.2
Sucrose
Sucrase
Intestinal glands of the Glucose + fructose
brush border
Absorbed by villus
Microvilli
8.2
Maltose
Maltase
Intestinal glands of the glucose and glucose
brush border
Absorbed by villus
Microvilli
8.2
Lactose
Lactase
Intestinal glands of the Glucose + galactose
brush border
Absorbed by villus
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Peptides
of