Chapter 1
Exercises page 29
1a- albumin
b- stomach
c- churning
d- glucose
e- starch
2a- False, from the digestion of proteins
b- True
c- False, only glycerol and fatty acids pass to the lymph
d- True
e- False, identifies the presence of sugar with heating
f- False, has ridges
3a- They increase the surface area and the network of blood vessels which facilitates
absorption.
b- Bile favors the emulsification (diversion) of lipids which facilitates their digestion.
c- The action of enzymes is specific since each enzyme works only on a specific substrate.
4a- Digestion is the molecular simplification of complex food into simple nutrients.
b- The pepsin enzyme found in the gastric juice secreted by the stomach helps in the
digestion of proteins.
c- All through the digestive tract, chemical digestion is facilitated by mechanical action to
ensure digestion.
51- saliva
2- bile
3- mastication
4- small intestine
5- gastric
6- lymph
7- pepsin
8- amino acid
9- pancreas
6a- Maltose, amino acids are obtained
b- Starch was completely transformed into maltose in the presence of pancreatic amylase.
So, the substrate of pancreatic amylase is starch. Albumin was completely transformed
into amino acids in the presence of trypsin. So, the substrate of trypsin is albumin.
c- Specificity of enzymes (i.e. each enzyme works on a specific substrate) since pancreatic
amylase could only digest starch and not albumin, while trypsin could only digest
albumin and not starch.
7a- 1- mouth
2- salivary glands
3- esophagus
4- liver
5- stomach
6- pancreas
7- small intestine
8- blood vessels
9-large intestine
b- organs where food doesn’t circulate:
salivary glands, liver, pancreas
c- The digestive juices are:
saliva, gastric juice, pancreatic juice, and intestinal juice.
Digestive juices contain the enzymes that are responsible for the breaking down of food
into nutrients (digestion).
8Analysis:
A violet color was seen when performing the biuret test on both rice and milk. A blue color
appeared when performing fehling test with heating on rice whereas a brick-red precipitate
was seen when performing the same test on milk. Finally, a dark blue color appeared when
using iodine solution with rice whereas this solution remained brown-orange with milk.
This indicates that both rice and milk reacted with biuret test whereas only milk reacted to
fehling and only rice reacted to iodine solution.
Conclusion:
Rice contains proteins and starch whereas milk contains proteins and sugar.
9a- figure
b- The control tube is the tube containing boiled potatoes and water, since it is used only
to compare the results of the experiment.
c- Is the setup is appropriate, the tube containing the boiled potatoes and pancreatic juice
will undergo digestion and the boiled potatoes will be broken down into simple
substances (glucose) in the presence of the enzyme (maltose) in the pancreatic juice.
As for the other tube, nothing will occur as no digestion will take place.
10a- Digestion will take place only in tube (4) because all the necessary conditions are
available: specific enzyme (trypsin), specific temperature (37 C) and specific medium
(base).
b- In tube (1), the acidic medium prevented digestion
In tube (2), temperature (0 C)
In tube (3), the enzyme (maltase) not specific for albumin
In tube (5), temperature (70 C)
c- Tube (1): The enzyme works in a specific medium
Tube (2) and (5): The enzyme works in a specific temperature
Tube (3): Specificity of enzymes (work on a specific substrate)
d- Using the biuret test, we can verify that the albumin has been digested when the color
of the biuret solution will change from blue into violet.
11a- The amount of myoglobin would have been 6 g, since no digestion would have taken
place as the enzyme pepsin was heated. (heat destroys enzymes)
b- In tube C, digestion took place and myoglobin was transformed into another substance
(amino acids). This occurred due to the fact that all suitable conditions were present:
specific enzyme (pepsin), specific medium (acidic), specific temperature (37 C), and
enough time.
c- There was no digestion in tube (E) since there is no specific enzyme present in the tube.
d- Tube (A) is a control tube to compare the results at the end of the experiment.
12a- Hypothesis: Fibers are probably not digested in human beings because of the absence of
the enzyme responsible for their digestion.
b- The role of fibers is to keep food moving through the large intestine and they are useful
for the treatment of constipation.
c- Examples of food rich in fibers:
Fruits such as berries, avocado, figs
Vegetables such as artichoke, peas, broccoli
Beans and legumes