GSEB Class 11 Biology Solutions Chapter 16 Digestion and Absorption

Question 1. Choose the correct answer among the following:
(1) Gastric juice contains
(a) Pepsin, lipase and rennin
(b) Trypsin, lipase and rennin
(c) Trypsin, pepsin and lipase
(d) Trypsin, pepsin and rennin
Answer: (a) Pepsin, lipase and rennin
In simple words: Gastric juice, found in the stomach, has three main enzymes: pepsin, lipase, and rennin. These enzymes help break down proteins and fats in the food we eat.

Exam Tip: Remember the specific enzymes found in gastric juice for stomach digestion. Pepsin is for protein, lipase for fat, and rennin for milk protein.

Question 1. (2) Succus entericus is the name given to
(a) a junction between the ileum and large intestine
(b) intestinal juice
(c) swelling in the gut
(d) None of the options
Answer: (b) intestinal juice
In simple words: Succus entericus is just another name for the juice made in the intestines. This special fluid helps a lot with digestion.

Exam Tip: Know the alternative names for important digestive secretions, such as succus entericus for intestinal juice.

Question 2. Match column I with Column II
Column I
(a) Bilirubin and biliverdin
(b) Hydrolysis of starch
(c) Digestion of fat
(d) Salivary gland
Column II
1. Parotid
2. Bile
3. Lipases
4. Amylases
Answer:
(a) Bilirubin and biliverdin match with 2. Bile
(b) Hydrolysis of starch match with 4. Amylases
(c) Digestion of fat match with 3. Lipases
(d) Salivary gland match with 1. Parotid
In simple words: Bilirubin and biliverdin are found in bile. Starch breaks down with amylases. Lipases help digest fats. The parotid is a salivary gland.

Exam Tip: When matching columns, carefully consider the function or origin of each item to make the correct association. Focus on key terms like 'hydrolysis' and 'digestion'.

Question 3. Answer briefly:
(a) Why are villi present in the intestine and not in the stomach?
Answer: Villi are small, finger-like structures designed to absorb food. Most of the broken-down food is taken in by the intestine, not the stomach. Therefore, villi are found in the intestine, where absorption mainly occurs.
In simple words: Villi help absorb digested food. The intestine absorbs most food, so villi are there, not in the stomach which mainly breaks food down.

Exam Tip: Emphasize the primary function of villi (absorption) and where this process predominantly occurs (small intestine) to explain their location.

Question 3.
(b) How does pepsinogen change into its active form?
Answer: Pepsinogen turns into its active enzyme form, pepsin, when it is exposed to hydrochloric acid. This acid is produced in the stomach, causing this conversion to happen.
In simple words: Pepsinogen becomes active pepsin when stomach acid touches it.

Exam Tip: Highlight hydrochloric acid (HCl) as the crucial factor for activating pepsinogen in the stomach.

Question 3.
(c) What are the basic layers of the wall of the alimentary canal?
Answer: The four fundamental layers making up the wall of the alimentary canal are serosa, muscularis, sub-mucosa, and mucosa.
In simple words: The gut wall has four layers: serosa, muscularis, sub-mucosa, and mucosa.

Exam Tip: List the layers in order, as this shows a clear understanding of the alimentary canal's structure.

Question 3.
(d) How does bile help in the digestion of fats?
Answer: Bile aids in breaking down fats into very tiny droplets called micelles. This process is called emulsification. It also activates lipases, which are enzymes that digest fats; these lipases can only work on emulsified fat.
In simple words: Bile makes fat into tiny drops (emulsification) and helps fat-digesting enzymes (lipases) work better.

Exam Tip: Remember the two key roles of bile in fat digestion: emulsification and activation of lipases.

Question 4. State the role of pancreatic juice in the digestion of proteins.
Answer: Pancreatic juice contains several inactive enzymes vital for protein digestion, including trypsinogen, chymotrypsinogen, and procarboxypeptidases. Trypsinogen becomes active trypsin when exposed to enterokinase, an enzyme from the intestinal lining. This active trypsin then helps activate other enzymes in the pancreatic juice. These activated enzymes break down proteins into smaller peptide units, facilitating their complete digestion.
In simple words: Pancreatic juice has inactive enzymes like trypsinogen. Intestinal enzymes activate trypsinogen into trypsin, which then helps other enzymes in the pancreatic juice break down proteins.

Exam Tip: Focus on the inactive forms of enzymes (zymogens) in pancreatic juice and the role of enterokinase in their activation for protein digestion.

Question 5. Describe the process of digestion of protein in the stomach.
Answer: The stomach's lining contains gastric glands, which have three main types of cells. Peptic or chief cells release proenzyme pepsinogen, and parietal or oxyntic cells produce hydrochloric acid (HCl) and intrinsic factor. When pepsinogen comes into contact with hydrochloric acid, it changes into the active enzyme pepsin, a proteolytic enzyme of the stomach. Pepsin then breaks down proteins into proteases and peptones (peptides). Additionally, rennin, a proteolytic enzyme present in the gastric juice of infants, helps digest milk proteins. HCl also maintains the acidic pH (around 1.8) needed for pepsin to function optimally.
In simple words: In the stomach, glands make inactive pepsinogen and acid. The acid turns pepsinogen into active pepsin. Pepsin then breaks down proteins into smaller parts. For babies, rennin helps digest milk.

Exam Tip: Clearly explain the activation of pepsinogen by HCl and the subsequent action of pepsin on proteins, mentioning rennin's role in infants if relevant.

Question 6. Give the dental formula of human beings.
Answer: Humans, like most mammals, have two sets of teeth during their lifetime: temporary milk or deciduous teeth, which are later replaced by permanent adult teeth. This type of tooth development is known as diphyodont dentition. An adult human typically possesses 32 permanent teeth, classified into four different types, which is called heterodont dentition. These types include incisors (I), canines (C), premolars (PM), and molars (M). The arrangement of these teeth in each half of the upper and lower jaw follows a specific order, I, C, PM, M. The dental formula for humans is 2123/2123, meaning in each half of the jaw, there are 2 incisors, 1 canine, 2 premolars, and 3 molars. The hard, outer chewing surface of the teeth, made of enamel, helps in breaking down food.
In simple words: Humans have two sets of teeth (diphyodont) and 32 permanent teeth of four types (heterodont). The dental formula is 2123/2123 for each half of the jaw, showing incisors, canines, premolars, and molars.

Exam Tip: Define diphyodont and heterodont dentition. Provide the correct dental formula and clearly state the number of each tooth type in an adult human.

Question 7. Bile juice contains no digestive enzymes, yet it is important for digestion. Why?
Answer: Bile juice is crucial for digestion even without enzymes because it helps break down fats into very tiny particles, a process called emulsification. This action increases the surface area for fat-digesting enzymes (lipases) to work effectively. Additionally, bile activates these lipases, which can only function on emulsified fats. Bile also aids in stimulating peristaltic movements, acts as a buffer, and assists in lubricating food for easier passage.
In simple words: Bile juice is important because it breaks fats into small drops (emulsification), which helps enzymes digest them. It also starts gut movements and lubricates food.

Exam Tip: Focus on emulsification and lipase activation as the primary reasons for bile's importance, despite its lack of enzymes.

Question 8. Describe the digestive role of chymotrypsin. Which two other digestive enzymes of the same category are secreted by its source gland?
Answer: Chymotrypsin helps digest proteins by converting proteins, peptones, and proteoses into dipeptides. This action is crucial for breaking down larger protein molecules into smaller, more manageable units. The two other digestive enzymes of the same type secreted by its source gland (the pancreas) are trypsin and carboxypeptidase.
In simple words: Chymotrypsin breaks down proteins into dipeptides. The pancreas also makes trypsin and carboxypeptidase.

Exam Tip: State the function of chymotrypsin clearly and name the other two pancreatic protein-digesting enzymes.

Question 9. How are polysaccharides and disaccharides digested?
Answer: Polysaccharides and disaccharides begin digestion in various parts of the digestive system. In the mouth, salivary amylase, an enzyme in saliva, starts breaking down starch (a polysaccharide) into disaccharides like maltose. Further digestion of carbohydrates occurs in the small intestine. Intestinal juice, or succus entericus, contains different enzymes, including disaccharidases, which break down disaccharides into monosaccharides. The pancreatic juice also supplies pancreatic amylase, which hydrolyses any remaining carbohydrates in the chyme into disaccharides. The mucous lining and bicarbonates from the pancreas protect the intestinal lining from acid and provide an alkaline environment (pH 7.8) necessary for enzymatic activities.
In simple words: Starch digestion starts in the mouth with salivary amylase. In the small intestine, pancreatic amylase breaks down carbs into disaccharides. Then, intestinal juice enzymes break disaccharides into simple sugars for absorption.

Exam Tip: Outline the digestion process chronologically, mentioning the specific enzymes and their locations of action for both polysaccharides and disaccharides.

Question 10. What would happen if HCl is not secreted in the stomach?
Answer: If hydrochloric acid (HCl) were not secreted in the stomach, several key digestive processes would be affected. HCl is essential for converting inactive pepsinogen into active pepsin. Without HCl, this conversion would not happen, meaning pepsin, which plays a vital role in protein digestion, would not be formed. Moreover, HCl creates the acidic environment necessary for pepsin to function optimally. Consequently, gastric digestion of proteins would not take place effectively or at all without HCl.
In simple words: If the stomach didn't make HCl, inactive pepsinogen wouldn't turn into active pepsin. This means proteins wouldn't be digested in the stomach because pepsin needs HCl to work.

Exam Tip: Focus on the dual role of HCl: activating pepsinogen and providing the optimal acidic pH for pepsin's activity. Explain the direct consequence for protein digestion.

Question 11. How does butter in your food get digested and absorbed in the body?
Answer: Digestion of butter (fat) begins in the duodenum (small intestine) with the help of bile juice, which is made by the liver and stored in the gall bladder. Bile emulsifies fats into small micelles. The pancreas then secretes enzymes like lipase into the duodenum, which further breaks down these emulsified fats. For absorption, fatty acids and glycerol are insoluble and cannot directly enter the bloodstream. They are first incorporated into small droplets called micelles, which move into the intestinal lining. Inside the intestinal cells, they are re-formed into tiny protein-coated fat globules called chylomicrons. These chylomicrons are then transported into the lymph vessels (lacteals) within the villi. Eventually, these lymph vessels release the absorbed fats into the bloodstream.
In simple words: Bile and pancreatic lipase break down butter fats in the small intestine. The digested fats form micelles, enter intestinal cells, become chylomicrons, and then travel through lymph vessels to the blood.

Exam Tip: Detail both the digestion (emulsification by bile, breakdown by lipases) and absorption (micelles, chylomicrons, lymphatic system) pathways for fats.

Question 12. Discuss the main steps in the digestion of proteins as the food passes through different parts of the alimentary canal.
Answer: Protein digestion starts in the stomach, where two primary proteolytic enzymes are at work. In the stomach, proenzyme pepsinogen is converted into active pepsin when exposed to hydrochloric acid (HCl). Pepsin then breaks down proteins into proteoses and peptones. Pepsin is most active in the acidic environment of the stomach (pH 1.8). For infants, rennin is also present to help digest milk proteins. Next, in the small intestine, pancreatic juice contains inactive proenzyme trypsinogen. This trypsinogen is activated into active trypsin by enterokinase, an enzyme secreted by the intestinal lining. Active trypsin then activates other pancreatic enzymes like chymotrypsinogen and procarboxypeptidases. Trypsin and chymotrypsin break down proteins, proteoses, and peptones into dipeptides. Carboxypeptidases break down polypeptides from the carboxyl end. Finally, these dipeptides are further broken down into amino acids by dipeptidases, enzymes found in the succus entericus (intestinal juice), allowing for their absorption.
In simple words: Protein digestion begins in the stomach with pepsin breaking them into smaller parts. In the small intestine, trypsin and chymotrypsin further break these down into dipeptides. Lastly, dipeptidases in intestinal juice change dipeptides into amino acids, which the body can absorb.

Exam Tip: Trace the journey of protein digestion through the stomach and small intestine, naming the key enzymes (pepsin, trypsin, chymotrypsin, dipeptidases) and their actions at each stage.

Question 13. Explain the terms thecodont and diphyodont.
Answer:
• Each tooth is embedded within a socket of the jaw bone. This specific type of attachment, where teeth are set firmly in bony sockets, is known as thecodont.
• A set of temporary milk or deciduous teeth that is later replaced by a set of permanent or adult teeth is called diphyodont. This means an organism develops two sets of teeth throughout its life.
In simple words: Thecodont means teeth are fixed in jaw sockets. Diphyodont means having two sets of teeth in a lifetime: baby teeth and then adult teeth.

Exam Tip: Clearly define each term, providing the key characteristic for thecodont (embedded in socket) and diphyodont (two sets of teeth).

Question 14. Name different types of teeth and their number in an adult human.
Answer: An adult human typically has 32 permanent teeth, which are categorized into four different types (heterodont dentition). These types and their numbers in each half of the upper and lower jaw are:
• Incisors (I): 2
• Canine (C): 1
• Premolars (PM): 2
• Molars (M): 3
The dental formula representing this arrangement in humans is 2123/2123. The total number of teeth is calculated as (2 + 1 + 2 + 3) x 4 = 32.
In simple words: An adult human has 32 permanent teeth of four kinds: 2 incisors, 1 canine, 2 premolars, and 3 molars in each half of the jaw.

Exam Tip: List all four types of teeth and specify their correct number in each half of the jaw, then provide the dental formula and the total count.

Question 15. What are the functions of the liver?
Answer: The liver performs many crucial functions, which can be categorized as follows:
(1) Digestive function:
• It produces bile juice, which helps in the emulsification of fats, breaking them into smaller droplets for digestion.
(2) Blood-related functions:
• The liver produces red blood cells (RBCs) during embryonic development.
• It produces prothrombin and fibrinogen, which are essential proteins that help in blood clotting.
• It synthesizes heparin, a substance that prevents blood from clotting inside blood vessels.
• The liver breaks down dead and worn-out RBCs.
• It generates approximately 12% of the body's total heat.
• It stores up to 1.5 liters of blood in its veins.
• The liver stores important nutrients like iron, copper, and vitamins A, D, and B.
• It helps remove toxic and metallic poisons from the blood, detoxifying the body.
(3) Metabolic functions:
• It regulates blood sugar by converting excess glucose into glycogen for storage and releasing glucose when blood sugar levels decrease.
• It breaks down excess amino acids into urea and sugar; urea is then passed out in urine, and sugar is stored.
• It plays a role in the synthesis of fatty acids from carbohydrates.
In simple words: The liver has many jobs. It helps digest fats, makes substances for blood clotting, stores vitamins and minerals, removes toxins, controls blood sugar, and helps break down amino acids.

Exam Tip: Organize your answer by categorizing liver functions (e.g., digestive, blood-related, metabolic) and list specific examples under each category for clarity and completeness.