Digestive System

Multiple Choice Type

Question 1

Pylorous is an opening from

1. oesophagus into stomach
2. mouth cavity into oesophagus
3. stomach into intestine ✓
4. intestine into rectum

Question 2

Gastric juice contains

1. HCl and pepsin ✓
2. pepsin and trypsin
3. trypsin and HCl
4. amylopsin and pepsin

Question 3

The water from the digested food is mainly absorbed by

1. stomach
2. duodenum
3. colon ✓
4. rectum

Question 4

Which one of the following pairs of types of teeth perform one common function as stated against it?

1. Incisors, canines — Holding
2. Canines, premolars — Tearing
3. Premolars, molars — Grinding ✓
4. Molars, incisors — Tearing

Very Short Answer Type

Question 1

What is the dental formula of a normal human adult?

Answer

Human adult: $\dfrac{2, 1, 2, 3}{2, 1, 2, 3} = 32$ (permanent teeth with 4 wisdom teeth added)

Question 2

Mention two reflexes which occur when a person chews and swallows food.

Answer

The two reflexes which occur when a person chews and swallows food are-

1. Reflex when a person chews — Secretion of saliva.
2. Reflex when a person swallows — The tongue presses upward and back against the roof (palate) of the mouth and this forces the bolus (the ball of chewed food ) into the throat or the pharynx.

Question 3

Consider the following two statements A & B and select the statements from (i) – (iv) that hold true.

A. Small intestine is shorter than large intestine.

B. Small intestine is wider than large intestine.

Options:

(i) Both the statements are correct.

(ii) Both the statements are wrong.

(iii) Statement A is correct, B is wrong.

(iv) Statement B is correct, A is wrong.

Answer

The statement that holds true is:

(ii) Both the statements are wrong.

Reason — Small intestine is longer than the large intestine. It is about 7 meters longer while large intestine is about 1.5 meters long. Large intestine is wider than the small intestine.

Short Answer Type

Question 1

What is digestion? Why do only animals require a digestive system?

Answer

Digestion is any change which makes the food soluble and of such chemical nature that it can be absorbed readily through living membranes.

Animals require a digestive system for the following reasons:

1. Need for complex and larger molecules such as carbohydrates, lipids, proteins to be broken down into simpler particles which are later absorbed and used by the body.
2. This process of disintegrating larger molecules to finer particles is possible only due to the process of digestion.
3. The breakdown of different larger macro molecules takes place in different parts of the digestive system.

Question 2

What are the end-products of the digestion of: starch, proteins and fats respectively?

Answer

The end products are as follows:

Starch — Maltose
Proteins — Small peptides and amino acids
Fats — Glycerol and fatty acids

Question 3

Why is there no enzyme to digest vitamins?

Answer

Vitamins themselves are small enough that they do not need to be digested with enzymes in order to be absorbed into the bloodstream. They are absorbed directly from the digestive tract and transported by the blood to the cells, the cells absorb them and utilize them when required.

Question 4

How is thorough chewing of food helpful in digestion?

Answer

It is very important to chew our food thoroughly as chewing of food helps to break down complex food materials into simpler substances. Chewing causes the saliva to be secreted by the salivary glands. Saliva moistens food and forms bolus which can be easily swallowed. Saliva contains special enzymes which causes the disintegration of carbohydrates.

Question 5

What is the function of rectum?

Answer

The rectum is the last part, about 15cm long which opens at the anus. Rectum serves as a temporary storage site for undigested food. It possesses smooth muscles that are voluntary in nature and eliminates faeces from the body through the anus.

Question 6

What is roughage? Give two examples.

Answer

Roughage is the undigestible portion of the diet. It is a dietary fibre that majorly contains cellulose. Examples – Green leafy vegetables, fruits, beans, nuts.

Question 7

Mention two ways in which the ileum of a mammal is adapted for the absorption of digested food.

Answer

The two ways in which the ileum of mammals is adapted for the absorption of digested food are:

1. Very long to provide much more surface area for absorption.
2. Ileum has numerous villi which further causes the surface area to increase thereby increasing the quantity of absorption of digested food.

Question 8

The stomach secretes gastric juice, which contains hydrochloric acid. What is its function?

Answer

Hydrochloric acid performs the following functions in the stomach-

1. It kills any germs which may have entered along with the food.
2. It activates pepsin to act on proteins. Pepsin digests proteins into peptides.

Long Answer Type

Question 1

Prepare a possible vegetarian menu for your dinner which would provide all the necessary nutrients.

Answer

Vegetatrian menu for dinner -

Question 2

What are the main characteristics of an enzyme?

Answer

Main characterstics of enzymes are-

1. It is a protein and is, therefore, destroyed by heating.
2. It acts only on one kind of substance called the substrate i.e. it is specific.
3. It always forms the same end-product(s) from the substrate.
4. It only affects the rate of a chemical reaction and always speeds up the reaction.
5. Like a catalyst, it can be used again and again.
6. It acts best only at a particular pH,i.e. at a particular degree of acidity or alkalinity.
7. It acts best within a narrow temperature range, usually between 35°and 40°C which is also called the optimum temperature.

Question 3

Why is the small intestine the most important organ of the digestive system?

Answer

The small intestine serves two important functions of digestion and absorption. In the duodenum, it receives two digestive juices:

1. The bile
2. The pancreatic juice

Both the juices virtually complete the process of digestion of proteins, starch, carbohydrates etc. Once the food is broken down, the small intestine is responsible to absorb simple particles such as amino acids, glucose etc.

Question 4

How is the liver an important organ in our body?

Answer

The liver is the largest gland of the body and it performs the following functions:

1. Controls amino acid levels
2. Produces foetal red blood cells
3. Produces heparin and fibrinogen
4. Checks blood volume
5. Destructs dead red blood cells
6. Detoxifies
7. Produces bile
8. Generates heat
9. Controls blood sugar levels
10. Storage of minerals and vitamins
11. Excretes metallic and toxic substances

Question 5

Define the following terms:

1. Peristalsis
2. Omnivore
3. Pylorus
4. Kilocalorie
5. Assimilation

Answer

1. Peristalsis — It is defined as the rhythmic contraction and relaxation of the muscles of the alimentary canal which pushes the food along the gut.
2. Omnivore — These are the organisms that consume both plants and animals.
3. Pylorus — It is the passage at the lower end of the stomach which opens into the duodenum.
4. Kilocalorie — A kilocalorie is defined as the unit of energy required to raise the temperature of 1 kg water by 1 degree Celsius.
5. Assimilation — It is the conversion of the absorbed digested food into body material.

Question 6

List the enzymes and their action on food in the stomach and intestine.

Answer

The table below shows the different regions, enzymes and the action of the enzymes on the food -

Question 7

Give any four reasons why water is necessary in our body.

Answer

Importance of water in our body :

1. Water is the major component of blood which carries nutrients and oxygen, to and from all the cells.
2. Water is the fundamental necessity for digesting food as well as absorbing food.
3. It forms the chief constituent of another major liquid in the body – saliva and mucous which bring about lubrication of the membranes which line the digestive system starting with the mouth.
4. It is crucial in maintaining the body temperature.

Question 8

You have been supplied with a sample of food. How will you perform tests for the presence of starch and proteins in it?

Answer

The following tests can be carried out:

Test for starch:

Aim — To detect the presence of starch in the sample

Procedure and Inference —

1. Add some starch powder to a test tube containing water, shake well. Boil well to make a solution.
2. Add some drops of iodine solutions when the solution cools down.
3. Iodine solution can be prepared by dissolving 1g iodine with 1g potassium iodide in 100ml of distilled water, dilute this solution before using.
4. The solution in the test tube would turn blur-black indicating the presence of starch.

Test for proteins:

Aim — To detect the presence of proteins in the given sample

Procedure and Inference—

1. In a test tube add a few pieces of the sample (hard-boiled egg)
2. Add a few drops of dilute nitric acid so as to seal the food
3. Gently heat the test tube, rinsing off the acid with water, to this add ammonium hydroxide
4. Observe the changes – from the initial white, color changes to yellow
5. After adding ammonium hydroxide – the color changes from yellow to orange.

Structured / Application / Skill Type

Question 1

Draw a labelled diagram to show the internal structure of a mammalian tooth with two roots.

Answer

Question 2

Try to swallow the saliva in your mouth, and feel your neck with your hand. What happens in the neck?

Answer

When saliva is swallowed, there is a shift in the movement of larynx, it is pulled upwards so as to get it closer to the back of the tongue when the epiglottis (a flap) closes its opening. It then goes towards the Oesophagus.

Question 3

Complete the following table by filling in the blanks 1 to 8.

Answer

1 – Stomach
2 – Proteins
3 – Polypeptides
4 – Amylase
5 – Starch
6 – Ileum
7 – Maltase
8 – Glucose

Question 4

Study the diagram given below and then answer the questions that follow:

(a) Name the parts labeled 1, 2, 3, 4, 5 and 6.
(b) Identify the tooth and give a reason to support your answer.
(c) Describe the structure of the part labeled '3'.
(d) Give the total number of the type of tooth mentioned in '1' above, in the mouth of an adult and state its function.

Answer

(a) The parts are-

• 1 → Enamel
• 2 → Dentine
• 3 → Pulp
• 4 → Gum
• 5 → Crown
• 6 → Cement

(b) The type of teeth shown in the given figure has only one root. Hence it is a canine or incisor that is used to bite or pierce.

(c) The part labelled '3'(Pulp) is a soft connective tissue present in the pulp cavity of the tooth. It consists of blood capillaries, lymph vessels and nerve fibres. From the crown of the tooth, the pulp opens through the pulp cavity at the base of the root.

(d) The type of teeth mentioned in the figure and its function are as follows:

Question 5

Study the following dental formula and then answer the questions that follow:

$i\dfrac{3}{4} \enspace c\dfrac{0}{0} \enspace pm\dfrac{0}{1} \enspace m\dfrac{1}{1}$

(a) What is the total number of teeth in the (i) upper jaw and (ii) lower jaw?

(b) State the total number of teeth present in the dentition.

(c) Give the dental formula of an adult human being.

Answer

(a) The total number of teeth in the upper jaw are 8 and lower jaw are 12.

(b) The total number of teeth present in the given dentition are 20 teeth.

(c) The dental formula of an adult is as follows:

Human adult: $\dfrac{2, 1, 2, 3}{2, 1, 2, 3} = 32$ (permanent teeth with 4 wisdom teeth added)