Digestive System

Pharynx → Oesophagus → Stomach → Small intestine → Large intestine

1. Molars
2. Canine
3. Incisors
4. Premolar

1. Crown
2. Enamel
3. Pulp
4. Cementum
5. Neck

1. True
2. False
   Corrected Statement — Saliva contains Ptyalin (Salivary amylase) which digests starch, not proteins.
3. True
4. True
5. True
6. False
   Corrected Statement — Gastric juice is acidic.
7. True

1. Parotid glands
2. Sub-mandibular glands
3. Sublingual glands

1. True
2. False
   Corrected Statement — Intestine is narrow for slow movement of food.
3. True
4. True
5. True
6. True

1. Duodenum, Jejunum, Ileum
2. Caecum, Colon, Rectum

1. Salivary amylase or Ptyalin
2. Intestinal lipase
3. Trypsin
4. Sucrase/invertase

1. Amino acid
2. Fatty acid and Glycerol
3. Maltose
4. Glucose and Fructose

1. Liver stores glucose as glycogen .
2. Liver produces RBC only in embryo.
3. Urea is produced in liver by the deamination of extra amino acid .
4. For testing the action of saliva on starch, the material has to be kept at a temperature of about 38°C.

1. Protein
2. Starch
3. Glucose
4. Minerals

stomach into intestine

Reason — The opening of the stomach into intestine is called pylorus. It has a ring of muscles (sphincter).
Oesophagus into stomach is called the cardiac sphincter. It allows food to pass from the oesophagus into the stomach and prevents acid from flowing back up.
In mouth cavity into oesophagus food passes from the mouth to pharynx then to oesophagus during swallowing, coordinated by muscles.
intestine into rectum occurs at the junction of the large intestine (colon) and rectum.

HCl and pepsin

Reason — Gastric juice is acidic and contains HCl and pepsin.
Pepsin is present in the stomach and trypsin is a pancreatic enzyme that works in the small intestine.
Trypsin is from the pancreas and acts in the intestine and HCl is in the stomach.
Amylopsin digests carbohydrates in the small intestine, not in the stomach and pepsin is in the stomach.

colon

Reason — Colon absorbs most of the water and left-over nutrients.
Stomach mainly digests food (especially proteins) using gastric juice. It absorbs very little water. Duodenum is mainly involved in digestion with enzymes and bile. Colon is responsible for absorbing most of the remaining water from undigested food, helping to form solid feces. Rectum mainly stores feces before elimination.

Premolars, molars — Grinding

Reason — Premolars and molars carry out grinding of food.
Incisors are used for biting, Canines are used for tearing. Premolars are used to crush and grind food. Molars grind food thoroughly.

Enamel

Reason — Enamel, which forms outer most covering of teeth is hardest substance of the human body.
Bones are strong and rigid, but they are not the hardest substance in the body. Cement covers the root of the tooth and helps anchor it, but it is much softer than enamel. Dentine lies beneath enamel. It is hard but not as hard as enamel.

Premolars

Reason — Premolar has two hill-like projections or cusps on its surface.
Molars have multiple cusps (usually 4–5) and are used for grinding, not called bicuspids. Incisors are flat, chisel-shaped teeth used for cutting; they do not have cusps. Canines have a single pointed cusp and are used for tearing, so they are not bicuspids.

35° to 40°C

Reason — 35° to 40°C is the optimum temperature range when enzymes act best.
Enzymes can work in 20° to 30°C range, but activity is not at its peak for human enzymes. At 40° to 45°C enzymes begin to denature, reducing activity. 35° to 50°C range is too broad, and temperatures above ~45°C can damage enzymes.

Humans

Reason — Mammals have teeth of different shapes (Heterodont dentition). Snakes have homodont dentition—their teeth are mostly similar in shape and function. Frogs also have homodont teeth, which are small and similar, mainly used to hold prey. Most lizards have homodont dentition as well.

Sucrase

Reason — Sucrase is present in intestinal juice.
Trypsinogen is an inactive enzyme secreted by the pancreas. Amylopsin digests starch into simpler sugars. It is a component of pancreatic juice. Steapsin breaks down fats into fatty acids and glycerol. It is also present in pancreatic juice.

Glycogenesis

Reason — The excess glucose present in our body is converted into glycogen by liver.
Glycolysis is the process where glucose is broken down into pyruvate to release energy (ATP). Glycogenolysis is the breakdown of glycogen into glucose when the body needs energy. Defaecation is the process of removal of undigested food as feces from the body. It is unrelated to glucose metabolism.

P — Parotid, Q — Sublingual, R — Submandibular

Reason — The saliva is secreted by three pairs of salivary glands :

• parotid glands are located just in front of and beneath each ear,
• submandibular glands are located close to the inner side of the lower jaw on each side,
• sublingual glands are below the tongue.

Nishtha and Prakriti

Reason

Therefore, only Nishtha and Prakriti supplied two enzymes that each act on some form of carbohydrate.

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

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.

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.

1. Alimentary canal and digestive glands.
2. Salivary gland, liver and pancreas.
3. Parotid glands, sub-mandibular glands and sublingual glands.
4. Duodenum, Jejunum, Ileum.
5. Caecum, Colon, Rectum.

1. Steapsin is odd one out. Remaining terms (Pepsin, Trypsin and Erepsin) are protein digesting enzymes.
2. Peptidase is odd one out. Lactase, Invertase and Maltase are sugar digesting enzymes.
3. Starch is odd one out. Glucose, Fructose and Galactose are simple sugar.
4. Colon is odd one out. Ileum, Duodenum and Jejunum are parts of small intestine.
5. Palate is odd one out. Crown, Root and Neck are parts of teeth.

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

(b) Enzymes — An enzyme is a protein that acts on a specific substance to form a specific end product. It best acts at a particular temperature and pH.

(c) Peristalsis — It is defined as the rhythmic contraction and relaxation of the muscles of the alimentary canal which pushes the food along the gut.

(d) Dentition — The arrangement of teeth in a particular species is called dentition.

(e) Defaecation — The expulsion of undigested remains of food from the alimentary canal is called defaecation.

(f) Assimilation — It is the conversion of the absorbed digested food into body material.

The end products are as follows:

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

(a) located in upper right side of abdomen just below the diaphragm.

(b) close to the inner side of the lower jaw on each side.

(c) between stomach and small intestine.

(d) located behind the stomach.

(e) at junction of large and small intestine.

(a) Rectum temporarily stores undigested food and wastes, to be defaecated through the anus.

(b) Gastric juice plays two key roles (i) it kills any germs which may have entered along with the food (ii) it activates pepsinogen to act on proteins.

(c) Epiglottis closes the opening of wind pipe.

(d) Most of the digestion and absorption of nutrition occur in small intestine.

(e) Tongue helps in mixing of food in buccal cavity and pushes it through pharynx.

(a) Animals are heterotrophs. They obtain their nutrients by consuming organic matter, such as other organisms or plant material. Hence, they need a digestive system to break down complex molecules, such as proteins, carbohydrates, and lipids, into smaller, absorbable forms. In contrast, plants are autotrophs, capable of synthesizing their own food through photosynthesis. Hence, they don't require a digestive system.

(b) Vitamins do not need digestion. They are absorbed directly through the intestine wall.

(c) Chewing of food breaks the food into small particles which helps in easy digestion.

(d) Bile contains a lot of sodium bicarbonate which neutralises the acid content of the food received from the stomach and makes it alkaline so that pancreatic and intestinal enzymes can act on it.

(e) The villi enormously increase the inner surface area of the intestines which facilitates the absorption of digested food.

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

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.

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.

Main characteristics 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.

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.

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

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

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.

Below labelled diagram shows the internal structure of a mammalian tooth with two roots :

1 – Stomach

2 – Proteins

3 – Polypeptides

4 – Amylase

5 – Starch

6 – Ileum

7 – Maltase

8 – Glucose

(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:

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

(a)

• A → Incisor
• B → Canine
• C → Premolar
• D → Molar

(b)

• A → Broad and sharp
• B → Conical and sharply pointed
• C → Two hill-like projections(bicuspid)
• D → Large grinding surface

(c)

• A → Four, centre of each jaw
• B → Two, one on each side of incisor
• C → Four, two on side of each canine
• D → Six, three on each side

(d) Calcium and phosphorous.

(e) Last molar on each side of jaw is called wisdom teeth.

Below is the labelled diagram of the "Microscopic Structure of an intestinal villus":

(a) A large number of villi enormously increase the inner surface area of the small intestine which facilitates the absorption of digested food.

(b) The fatty acids and glycerol are absorbed into the lacteals to enter the lymphatic system which forms a network all over the body to ultimately empty its contents into the blood stream.

(c) Intestinal juice

(d)

1. Salivary gland - Saliva (amylase)
2. Stomach - Gastric juice
3. Liver - Bile
4. Pancreas - Pancreatic juice

(a) Gall bladder

(b) Liver

(c) Trypsin – Acts on proteins, Amylopsin (Pancreatic amylase) – Acts on carbohydrates (starch), Steapsin (Pancreatic lipase) – Acts on emulsified fats

A is false and R is True.

Reason — A is false as the wisdom tooth is not related to intelligence or mental ability. It is simply the last tooth to erupt in the dental arch.
R is True as the wisdom teeth usually erupt between the ages of 17 and 25, a period sometimes referred to as the "age of wisdom."

Therefore, A is false and R is True is the correct option.

A is True and R is False.

Reason — A is True as dentine is the main structural component of a tooth. It lies beneath the enamel and forms the bulk (major portion) of both the crown and the root of the tooth.
While dentine is a bone-like tissue, it does not fix the root of the tooth. The structure that covers and anchors the root in position is called cementum, not dentine. Hence, R is False.

Therefore, A is True and R is False is the correct option.

Both A and R are true and R is the correct explanation of A.

Reason — A is true as ptyalin is secreted by salivary glands. Amylopsin is secreted by the pancreas into the small intestine. Despite being secreted from different glands, both enzymes perform the same function: they break down starch into maltose.
R is true as both enzymes catalyze the hydrolysis of starch (a polysaccharide) into maltose (a disaccharide).

Therefore, Both A and R are true and R is the correct explanation of A is the correct option.

A is false but R is true.

Reason — A is false because the pylorus is located at the lower end of the stomach. It controls the passage of food from the stomach to the small intestine (duodenum).
R is true that the pylorus has a ring of muscles that acts like a valve but it is located at the back end of the stomach.

Therefore, A is false but R is true is the correct option.

Both A and R are true and R is the correct explanation of A.

Reason — A is true because bile juice is produced in the liver. It is stored in the gallbladder.
R is true as bile is released into the duodenum via the common bile duct. It neutralizes the acidic chyme from the stomach, making it alkaline. This alkaline environment is necessary for the action of pancreatic enzymes like trypsin and lipase.

Therefore, Both A and R are true and R is the correct explanation of A is the correct option.

A is false and R is True.

Reason — A is false as the small intestine is actually much longer than the large intestine.
R is True as the small intestine is highly coiled to fit within the limited space of the abdomen. This coiling increases the surface area for absorption.

Therefore, A is false and R is True is the correct option.

(a) The fluid secreted in the mouth is saliva, and it is secreted by the salivary glands.

(b) The three pairs of salivary glands are:

1. Parotid glands
2. Submandibular glands
3. Sublingual glands

(c) The three constituents of saliva are:

1. Water
2. Salivary amylase
3. Mucus

(d) Yes, this fluid help in digestion.

Enzymatic reaction:

Starch $\xrightarrow[\text{(Saliva)}]{\text{Ptyalin (Salivary amylase)}}$ Maltose

(e) Two other functions of saliva are:

1. Lubricates food to help in swallowing and forming a bolus.
2. Keeps the mouth moist and helps in speech.