Download Week 12 Text Solutions – The Digestive System

Year 11 ATAR Human Biology
Unit 3 – The Digestive System
Week 12 – Text Solutions
Chapter 9 – The Digestive System
Review Questions:
1.
Basic activities of the Digestive System
 Ingestion of food and water
 Mechanical digestion of food
 Chemical digestion of food
 Movement of food along the alimentary canal
 Absorption of digested food and water into the blood and lymph
 Elimination of material that is not absorbed
2.
Table on the Digestive System
Organ
Function in Digestion
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Mechanical digestion by teeth as
they break food into small pieces;
chemical digestion by saliva;
forms bolus of food

Carries food from mouth to stomach

Mouth
Oesophagus
How Structure is Suited to Function


Stomach



Small
intestine


Large
intestine
Mechanical digestion by churning
food into liquid; chemical digestion of
proteins bypepsin;
stores food as it is eaten; absorbs
some substances such as alcohol

Mechanical digestion continues with
churning of food, and bile salts
added to emulsify fats;
chemical digestion and absorption of
all nutrientsby enzymes from
pancreas and intestinal glands;
absorbs water

Water and mineral nutrients absorbed;
faeces formed
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Moist and has three salivary glands;
Teeth shaped for biting, tearing,
crushing and grinding;
tongue is a strong muscle that moves
food
Muscular tube that can push food
toward stomach;
has moist lining (slippery) circular and
longitudinal muscle to push food
along by peristalsis
Muscular sac containing gastric
glands that secrete digestive juices;
secretes mucus to protect surface;
glands secrete HCl to produce low
pH; circular, longitudinal and oblique
muscle layers allow churning motions
to mix food with stomach juices
Very long (6 m) muscular tube with
folded inner lining or mucosa that has
a vast surface area for maximum
absorption due to villi and microvilli;
vascular/networks of blood vessels to
absorb nutrients and water;
lymph capillary in each villus to
absorb lipids
Long tube; contains bacteria that
produce vitamins;
larger diameter than small intestine to
store faeces
3.
4.
Explain the digestive function of each of the following.
(a) Gastric Juice
Gastric juice contains hydrochloric acid, mucus and digestive enzymes. Chemical
digestion is brought about by the digestive enzymes contained in the gastric juice.
Most of the chemical activity in the stomach is concerned with the start of protein
Digestion — pepsin breaks down proteins to polypeptides.
(b)
Bile
Bile does not contain any digestive enzymes, but bile salts are very important in
the digestion of fats. They act like a detergent and emulsify the fat, breaking it into
tiny droplets. This is a form of mechanical digestion, increasing the surface area on
which the lipases can act to bring about the chemical breakdown of fat.
(c)
Pancreatic Juice
Pancreatic juice enters the duodenum and helps to neutralise the acid that has
come with the material from the stomach. Many of the enzymes involved in the
digestion of food are contained in pancreatic juice. These include:
 pancreatic amylase which breaks down starch
 trypsin (or pancreatic protease) which splits proteins into much smaller units
 ribonuclease and deoxyribonuclease which are enzymes that digest RNA and
DNA
 pancreatic lipases which are enzymes that break down fats into fatty acids and
glycerol.
(d)
Intestinal Juice
Intestinal juice contains many enzymes that complete the digestion of carbohydrates,
fats and proteins.
(a)
How does the absorption of fatty acids and glycerol differ from the absorption of
amino acids and simple sugars?
From the walls of the villi, simple sugars and amino acids are absorbed into the
blood capillaries. Fatty acids and glycerol recombine in the cells of the villi to form
fats and, along with the fat-soluble vitamins, enter the lacteals.
(b)
How does the absorption of water differ from the absorption of simple sugars?
Both substances are absorbed into the blood capillaries within the villi, water by
osmosis and sugars by diffusion. Sometimes sugars may be actively transported
across the membrane depending on the concentration gradient.
5.
Difference between excretion and elimination
Excretion is the removal of metabolic (made) wastes where elimination is the removal of
undigested wastes.
6.
Effect of speed of food in the following …
(a)
Consuming a large meal
Slow due to the quantity of food in the canal
(b)
High fat meal
As fat is difficult to break down the food slows down when in the canal.
(c)
Consuming alcohol
A meal ‘lines’ the mucosa and mixes with the alcohol, thus taking longer to be
absorbed. Secretion of gastric juice to digest the meal dilutes the alcohol—lower
concentration of alcohol produces slower rate of diffusion through the stomach
mucosa.
7.
What are the advantages of consuming a diet that is high in both soluble and
insoluble fibre? List the foods that would be high in soluble and insoluble fibre.
Both soluble and insoluble fibre are found only in foods derived from plants. Soluble fibre
includes pectins, gums and mucilage. Soluble fibre intake has been linked to lower
cholesterol levels in the blood, decreased risk of heart disease and cancer, and beneficial
effects on blood glucose levels.
Fats in the intestines are trapped by soluble fibre, thereby helping to prevent their
absorption by the body. This is thought to be the reason that soluble fibre helps to lower
blood cholesterol
levels.
Good sources of soluble fibres are fruits, vegetables, oat bran, barley and soy products.
Insoluble fibre stimulates peristalsis and helps to prevent constipation and may protect
against bowel cancer and diverticulitis.
8.
Why are people who suffer from coeliac disease likely to become malnourished?
People with coeliac disease are unable to tolerate a protein called gluten which is found in
wheat, rye and barley. If such people eat food containing gluten, their immune systems
respond by damaging or destroying the villi in the small intestine.
Without healthy villi, nutrients cannot be absorbed and the patient becomes malnourished
no matter how much food is eaten.
Apply Your Knowledge:
1.
Exchange surfaces and how a large surface area is achieved.
Small intestine—achieved through being very long and folding of internal lining which
decreases volume, but increases surface area in the gut; also villi and microvilli.
2.
For the alimentary canal explain how the concentration difference is maintained.
Alimentary canal—highly vascular with blood flow constantly removing nutrients and
delivering them to cells, such that nutrient concentration in the canal blood is low ⇒
movement from high concentration in the canal to low concentration in the blood is
maintained. Peristalsis and segmentation constantly changes the contents that are in
contact with the mucosa so helping to maintain the concentration difference.
3.
Explain how the digestive system is involved in maintaining substances in the body
at a constant level.
The digestive system delivers nutrients, especially glucose, to cells every time food is
ingested. The body then stores nutrients so that there is constant availability even when
food is not taken in.
4.
Explain why the small intestine has a much larger surface area than the large
intestine.
The small intestine has to absorb all nutrients and some water from the lumen of
the gut; the large intestine only absorbs water so doesn’t need to be as effi cient.
5.
The faeces contain the remains of cells. Suggest why cell remains should be in the
faeces.
Cells throughout the alimentary canal have a very short life span due to their function and
constant wear and tear. These cells, once shed from the tissues, are waste and cannot be
absorbed by the intestines, hence they are expelled in the faeces.
6.
Alcohol Absorption
(a)
Why alcohol is much slower to affect a person’s mood when consumed with a
meal.
A meal ‘lines’ the mucosa and mixes with the alcohol, thus taking longer to be
absorbed. Secretion of gastric juice to digest the meal dilutes the alcohol—lower
concentration of alcohol produces slower rate of diffusion through the stomach
mucosa.
(b)
7.
Would the nature of the meal, for example, a meal high in carbohydrate
compared with a meal high in fat, have any influence on alcohol absorption?
Yes, a high fat meal takes much longer to digest and stays in the digestive system
longer, thus alcohol will be absorbed more slowly.
Effect of bowel Cancer on normal functioning
Less vitamins and water would be absorbed due to the shorter bowel. Other effects could
include:
 A change in bowel habits.
 Blood (either bright red or very dark) in the stool.
 Diarrhea, constipation, or feeling that the bowel does not empty all the way.
 Stools that are narrower than usual.
 Frequent gas pains, bloating, fullness, or cramps.
 Weight loss for no known reason.
 Feeling very tired.
 Vomiting.