Frank Brothers Solutions for ICSE Class 9 Biology Chapter 16 Digestive System

PAGE NO: 151

Question 1:
Answer:
Nutrition can be defined as the process which involves the utilization of food by an animal to obtain energy for growth and development. There are two types of nutrition - autotrophic and heterotrophic.
Nutrition is the way our bodies get the energy and materials needed to stay alive and healthy. It includes eating food, breaking it down, and using it to build muscles and provide energy for playing.
Teacher's Tip: Think of autotrophs as "Self-Chefs" (plants) and heterotrophs as "Diners" (animals).
Exam Tip: Mention both autotrophic and heterotrophic types for a complete answer.

Question 2:
Answer:
1. Autotrophs: These are the organisms which prepare organic food in their body from simple inorganic materials like carbon dioxide, water, etc. Example - green plants and certain protests.
2. Heterotrophs: The organisms which cannot prepare their own food and depends on ready-made food synthesized by green plants are called heterotrophs. Examples - animals and human beings.
3. Carnivores: The organisms which feed upon other animals and animal products. Examples - tiger, lion, cat, etc.
4. Omnivores: The organisms which feed on all kinds of plant and animal food are called omnivores. Examples - Cockroach and human beings.
5. Herbivores: The organisms that feed on plants only are termed as herbivores. Examples - sheep, cow, goat, etc.
These categories help us understand how different creatures get the fuel they need from their environment. It shows the connection between all living things in a food chain.
Teacher's Tip: Use the first letter: Herbivore = Herbs (plants); Carnivore = Cut (meat).
Exam Tip: Always provide at least two examples for each category as shown in the text.

Question 3:
Answer:
1. Parasites are the organisms that live in or on the body of another organism called host, and obtain nourishment from its body whereas saprophyte is an organism that absorbs soluble organic nutrients from dead and decaying organic matter.
2. Autotroph is an organism which prepares organic food in their body from simple inorganic materials like carbon dioxide, water, etc. whereas heterotroph is an organism which cannot prepare its own food and depends on ready-made food synthesized by green plants.
3. Holozoic nutrition is a nutrition in which animals survive by consuming other organisms whereas saprozoic nutrition is the nutrition in which the animals absorbs soluble organic nutrients from dead and decaying organic matter.
4. Holophytic nutrition is the nutrition in which organisms prepare organic food in their body from simple inorganic materials like carbon dioxide, water, etc. whereas in holozoic nutrition, the animals survive by consuming other organisms.
These comparisons show the incredible variety of ways nature has designed life to get fuel. Some organisms are producers, while others are consumers or decomposers.
Teacher's Tip: "Sapro" usually refers to dead things, like a saprophytic fungus on a rotting log.
Exam Tip: Use `
` to clearly separate the two terms being compared so the examiner can see the difference easily.

Question 4:
Answer:
The steps involved in animal nutrition are:
1. Ingestion - It means taking solid or liquid food inside the body.
2. Digestion - It is the breaking down of complex insoluble food components into simple soluble substances.
3. Absorption - It is the process by which soluble soluble digested food passes from alimentary canal into blood and lymph through intestinal villi.
4. Assimilation - Utilization of absorbed food by different body cells is called assimilation.
5. Egestion - Elimination of undigested food as faeces is called egestion.
This is the total journey food takes from the moment it enters your mouth until it is used by your cells. Each step is critical for turning a meal into energy and growth.
Teacher's Tip: Remember the sequence: I-D-A-A-E (I Drive An Awesome Elephant).
Exam Tip: Define each step in one clear sentence to ensure you cover all the marks.

Question 5:
Answer:
There are four types of teeth:
1. Incisors - These are used for cutting.
2. Canines - These teeth are used for tearing.
3. Premolars - For masticating the food.
4. Molars - For grinding and masticating the food.
Our mouth is like a toolbox with different teeth for different jobs, like cutting fruit or grinding nuts. This variety allows humans to eat many different kinds of food.
Teacher's Tip: Incisors are like scissors (cutting), and Molars are like mortars (grinding).
Exam Tip: State the specific function (cutting, tearing, grinding) for each tooth type clearly.

Question 6:
Answer:
(a) 1. Enamel; 2. Dentine; 3. Blood capillaries; 4. Cement; 5. Blood vessels; 6. Periodontal membrane; 7. crown; 8. root.
(b) Enamel, dentine and cement.
(c) Yes.
(d) The function of the root is to hold the teeth in the jaw and the function of the crown is it completely encircles and protects the teeth.
(e) 32
(f) The dental formula of humans is
I 2/2, C 1/1, P 2/2, M 3/3 (16 \times 2 = 32).
Teeth are the hardest parts of our body, designed to stay strong for many years of eating. The dental formula is a mathematical way of showing how our teeth are arranged in our mouth.
Teacher's Tip: The Enamel is the hardest "shield" in your entire body!
Exam Tip: Write the full dental formula with fractions to score full marks in calculation questions.

Question 7:
Answer:
Human alimentary canal consists of:
(a) Mouth - It is the first organ in the sequence which helps in sucking, chewing, salivation and swallowing. The food is ingested through mouth.
(b) Pharynx - It is situated behind the soft palate and leads into oesophagus. It is divided into three parts - nasopharynx, oropharynx and laryngopharynx.
(c) Oesophagus - It lies upto the middle of the thorax, behind the trachea and the heart. It pushes the food down into the stomach by peristaltic movements.
(d) Stomach - It is the widest organ of the alimentary canal. It is J - shaped and is divided into three parts: cardiac, body and pyloric.
(e) Intestine - It is of two types: small intestine and large intestine. Small intestine is the longest part of the alimentary canal and comprises of three regions - duodenum, jejunum and ileum. It helps in the absorption of food. Large intestine is divisible into three parts - caecum, colon and rectum. It absorbs water from the food.
The alimentary canal is a long, continuous tube where the magic of digestion takes place. Each section has a special shape and job to handle the food as it moves along.
Teacher's Tip: Think of the Oesophagus as a "food slide" that carries food straight to the stomach.
Exam Tip: Label the three regions of the small intestine (duodenum, jejunum, ileum) specifically for extra points.

Question 8:
Answer:
(a) False
(b) False
(c) True
(d) False
These true/false questions check your basic knowledge of the organs in the digestive system. It is important to know that while the stomach is wide, it is not the longest part of the canal.
Teacher's Tip: The small intestine is actually much longer than the stomach, even though it's narrow!
Exam Tip: When answering False, try to remember the correct fact to strengthen your concepts.

Question 9:
Answer:
Digestion - It is the breaking down of complex insoluble food components into simple soluble substances.
Digestion in small intestine:
(a) Digestion of carbohydrates in the small intestine: 40% starch is partially digested by ptyalin while remaining 60% starch is digested by pancreatic amylase.
Starch →Pancreatic Amylase + Cl Maltose + Isomaltose + Limit dextrin.
The enzymes of intestinal juice act as below:
Maltose →Maltase 2 Glucose
Isomaltose →Isomaltase 2 Glucose
Surcrose →Sucrase Glucose + Fructose
Lactose →Lactase Glucose + Galactose
Limit Dextrin →Limit Dextrinase Glucose
The humans cannot digest the cellulose due to the absence of cellulose enzyme.
(b) Digestion of protein the small intestine:
Action of pancreatic juice. It contains proenzymes trypsinogen, chymotry-psinogen and procarboxy peptidase.
Trypsinogen →Enterokinase of interstinal juice Trypsin
Chymotrypsinogen →Trypsin Chymotrypsin
Procarboxypeptidase →Trypsin Carbody - peptidase
Peptones →Trypsin Peptides
Peptones →Chymotrypsin Peptides
Peptides →Carboxypeptidase Smaller peptides + Amino acid
Trypsinogen converts into trypsin in the presence of enterokinase. Trypsin converts chymotrypsinogen into chymotrypsin; procarboxypeptidase into carboxy-peptidase; and peptones into peptides. Chymotrypsin also converts peptones into peptides. Peptides gets converted into smaller peptides and amino acids in the presence of carboxypeptidase.
Enzymes are like tiny chemical scissors that cut up big food molecules into pieces small enough to enter your blood. Without these enzymes, our body could not use the nutrients in the food we eat.
Teacher's Tip: Enzymes often end in "-ase" (like Maltase or Lactase), which makes them easy to spot.
Exam Tip: Use chemical equations with arrows to show how big molecules turn into small ones.

Question 10:
Answer:
Action of intestinal juice. Intestinal juice contains endokinase, aminopeptidase and dipeptidase. Actions of these enzymes are summarized below:
Peptides →Aminopeptidase Smaller peptides + Amino acid
Peptides →Dipeptidase Amino acid
(c) Digestion of Fats:
Digestion of fats occurs in small intestine and reactions occur as below:
Fat →bile Emulsified fat
Emulsified fat →Pancreatic lipase Fatty acid + Glycerol
(d) Digestion of Nucleic Acids:
Nucleic acids are digested in the small intestine as below:
DNA →Dnase Deoxyribonucleotides
RNA →Rnase Ribonucleotides
Nucleotides →Nucleotidase Nucleosides + Phosphate
Nucleosides →Nucleoside Phosphorylase Nitrogenous bases + Pentose phosphate
The enzyme Dnase converts DNA into Deoxyribonucleotides, Rnase converts RNA into ribonucleotides, nucleotidase converts the nucleotides into nucleosides and phosphate and finally nucleoside phosphorylase converts nucleosides into nitrogenous bases and pentose phosphate.
The small intestine is the place where the most thorough chemical work happens to finish digesting your meal. By the end of this process, everything is broken down into its simplest building blocks.
Teacher's Tip: "Emulsification" of fat is like using soap to break up grease on a plate.
Exam Tip: Remember that fats break down into two final products: Fatty acids and Glycerol.

Question 11:
Answer:
Digestion of proteins in humans:
There is no digestion of protein in the oral cavity because protein digestive enzymes are absent in the saliva.
(a) Digestion of protein in the stomach: Gastric juice contains HCl and two proenzyme, pepsinogen and prorennin. HCl maintains a pH of 2 - 3.7 and kills bacteria and other pathogens. Gastric juice mixes with food until it becomes semi-solid mass called Chyme. Proenzymes become activated as below:

Pepsinogen →HCl, 2 - 3.7 pH Pepsin
Prorennin →HCl Rennin
These enzymes act as follows:
Casein (Milk protein) →Rennin Paracasein
Paracasein + Ca → Calcium Paracasinate (Curd)
Calcium paracasinate →Pepsin Peptones
Protein →Pepsin Peptones
(b) Digestion of protein the small intestine:
Action of pancreatic juice. It contains proenzymes trypsinogen, chymotry-psinogen and procarboxy peptidase.
Trypsinogen →Enterokinase of interstinal juice Trypsin
Chymotrypsinogen →Trypsin Chymotrypsin
Procarboxypeptidase →Trypsin Carbody - peptidase
Peptones →Trypsin Peptides
Peptones →Chymotrypsin Peptides
Peptides →Carboxypeptidase Smaller peptides + Amino acid
Action of intestinal juice. Intestinal juice contains endokinase, aminopeptidase and dipeptidase. Actions of these enzymes are summarized below:
Peptides →Aminopeptidase Smaller peptides + Amino acid
Peptides →Dipeptidase Amino acid
Protein digestion is a multi-step process that starts in the stomach and finishes in the small intestine. It turns the proteins from your food into amino acids that your body uses to build muscles.
Teacher's Tip: Pepsin needs an "Acid bath" (HCl) in the stomach to start working properly.
Exam Tip: Clearly state that protein digestion *does not* happen in the mouth.

Question 12:
Answer:
(a) Rennin is produced by the stomach in an inactive form, called prorennin. After milk is consumed, the gastric acids present in stomach activate the inactive prorennin to active rennin which acts upon casein and converts it into paracasein. Paracasein with the help of calcium ions form Calcium Paracasinate or forms coagulated milk. This coagulated milk turns into peptones in the presence of pepsin.
Pepsinogen →HCl, 2 - 3.7 pH Pepsin
Prorennin →HCl Rennin
These enzymes act as follows:
Casein (Milk protein) →Rennin Paracasein
Paracasein + Ca → Calcium Paracasinate (Curd)
Calcium paracasinate →Pepsin Peptones
Protein →Pepsin Peptones
If milk were not coagulated, it would rapidly flow through the stomach and the digestion of proteins will not take place.
(b) Emulsification: Digestion of fats occurs in small intestine and reactions occur as below:
Fat →bile Emulsified fat
Emulsified fat →Pancreatic lipase Fatty acid + Glycerol
(c) Digestion of Fats:
Digestion of fats occurs in small intestine and reactions occur as below:
Digestion of fats occurs in small intestine and reactions occur as below:
Fat →bile Emulsified fat
Emulsified fat →Pancreatic lipase Fatty acid + Glycerol
(d) Digestion of Nucleic Acids:
The enzyme Dnase converts DNA into Deoxyribonucleotides, Rnase converts RNA into ribonucleotides, nucleotidase converts the nucleotides into nucleosides and phosphate and finally nucleoside phosphorylase converts nucleosides into nitrogenous bases and pentose phosphate.
Nucleic acids are digested in the small intestine as below:
DNA →Dnase Deoxyribonucleotides
RNA →Rnase Ribonucleotides
Nucleotides →Nucleotidase Nucleosides + Phosphate
Nucleosides →Nucleoside Phosphorylase Nitrogenous bases + Pentose phosphate
These detailed chemical steps ensure that every complex part of our food is turned into simple parts the body can use. Even DNA and RNA from the plants and animals we eat are broken down for their building blocks.
Teacher's Tip: Rennin is the "milk-curdler" that helps babies digest their milk properly.
Exam Tip: Mention the role of Bile in emulsification as it is the first step in fat digestion.

Question 13:
Answer:
Salivary Glands - Three pairs in man and secrete 1000 to 1500 cc saliva per day.
Saliva is slightly acidic and its pH is 6.8.
There are three types of salivary glands:
1. Parotid glands: It is the largest salivary gland and situated near the ears. It opens into oral cavity by Stenoson's duct.
2. Sublingual glands: It is located beneath the tongue. It opens into the floor of oral cavity by duct of Rivinus.
3. Submadibular or sub-maxillary glands: It is situated at the angles of the lower jaws. It opens inot oral cavity by Whartson's duct.
Each gland secret secretes saliva which is transported to the mouth cavity. At the time secrete saliva.
Saliva is very important because it moistens your food and begins the chemical breakdown of starch right in your mouth. It is produced by three different sets of "faucets" located around your jaw.
Teacher's Tip: Remember "Parotid" as the "Pair-near-the-ear" glands.
Exam Tip: Memorize the pH of saliva (6.8) as it is a frequent objective question.

Question 14:
Answer:
(a) Lipase
(b) Lungs
(c) Rectum
These are specific enzymes and organs that perform vital roles in keeping our bodies running. The rectum is the final holding area for waste before it leaves the body during egestion.
Teacher's Tip: Lipase works on Lipids (fats).
Exam Tip: Identify the organ correctly in one-word answers to ensure you don't lose marks for vague terminology.

Question 15:
Answer:
The pancreatic juice contains proenzymes trypsinogen, chymotry-psinogen, procarboxy peptidase, pancreatic amylase and pancreatic lipase.
(a) Digestion of proteins by pancreatic juice: Trypsinogen converts into trypsin in the presence of enterokinase. Trypsin converts chymotrypsinogen into chymotrypsin; procarboxypeptidase into carboxy-peptidase; and peptones into peptides. Chymotrypsin also converts peptones into peptides. Peptides gets converted into smaller peptides and amino acids in the presence of carboxypeptidase.
Trypsinogen →Enterokinase of interstinal juice Trypsin
Chymotrypsinogen →Trypsin Chymotrypsin
Procarboxypeptidase →Trypsin Carboxy - peptidase
Peptones →Trypsin Peptides
Peptones →Chymotrypsin Peptides
Peptides →Carboxypeptidase Smaller peptides + Amino acid
(b) Digestion of carbohydrates by pancreatic juice: Pancreatic amylase acts upon starch in the presence of chloride ions and converts it into maltose, isomaltose and dextrin.
Starch →Pancreatic Amylase + Cl Maltose + Isomaltose + Limit dextrin.
(c) Digestion of fats: Pancreatic juice contains pancreatic lipase which emusifies the fats into fatty acids and glycerol.
Emulsified fat →Pancreatic lipase Fatty acid + Glycerol
The pancreas is a master factory that sends enzymes to digest all three major food groups: proteins, carbs, and fats. It is located just behind the stomach and is essential for healthy digestion.
Teacher's Tip: The Pancreas is your body's "all-in-one" chemical tool set.
Exam Tip: List all three categories of enzymes when asked about the role of the pancreas.

Question 16:
Answer:
Column A - Column B
1. HCl - Pepsin
2. Rennin - Casein
3. Enteropeptidase - Trypsin
4. Cellulose - Rumen
5. Ptyalin - Starch
6. Vitamin - Pernicious anaemia
7. Intestinal juice - Lactose
8. Bile salt - Micelle
9. Vitamin A - Night-blindness
10. Goitre - Iodine
This exercise connects chemicals, processes, and deficiencies together. For example, it shows that a lack of iodine in our diet can lead to a neck swelling called goitre.
Teacher's Tip: Match Ptyalin with Starch (the first enzyme you meet in your mouth).
Exam Tip: When matching columns, always write the corresponding items together in a table for clarity.

Question 17:
Answer:
Digestion of starch:
(a) Digestion of starch in the oral cavity: Food is mixed with saliva and salivary amylase or ptyalin converts starch into maltose, isomaltose and limit dextrins.
Starch →Salivary Amylase Maltose + Isomaltose + Limit dextrin.
(b) Digestion of starch in stomach: Gastric juice does not contain carbohydrate digestive enzyme, hence no digestion of starch takes place in the stomach.
(c) Digestion of starch in small intestine: 40% starch is partially digested by ptyalin while remaining 60% starch is digested by pancreatic amylase.
Starch →Pancreatic Amylase + Cl Maltose + Isomaltose + Limit dextrin.
The enzymes of intestinal juice act as below:
Maltose →Maltase 2 Glucose
Isomaltose →Isomaltase 2 Glucose
Surcrose →Sucrase Glucose + Fructose
Lactose →Lactase Glucose + Galactose
Limit Dextrin →Limit Dextrinase Glucose
The humans cannot digest the cellulose due to the absence of cellulose enzyme.
Starch digestion begins the moment you chew and finishes in the small intestine where it turns into sugar for your cells. It's interesting to note that the stomach acid actually stops starch digestion for a while!
Teacher's Tip: Chewing bread for a long time makes it taste sweet because starch is turning into sugar.
Exam Tip: State clearly that carbohydrate digestion *does not* happen in the stomach.

Question 18:
Answer:
(a) Carboxypeptidase
(b) Rennin
(c) Caecum
(d) HCl
(e) Pepsin
(f) Digestion
(g) Protein
(h) Bilirubin
These terms identify specific organs, enzymes, and pigments involved in the digestive process. Bilirubin is the pigment that gives waste its color and comes from broken-down blood cells.
Teacher's Tip: HCl is the chemical shorthand for Hydrochloric acid, your stomach's strong acid.
Exam Tip: Be careful with the spelling of technical terms like "Caecum" and "Bilirubin."

Question 19:
Answer:
Digestion of proteins in humans:
There is no digestion of protein in the oral cavity because protein digestive enzymes are absent in the saliva.
(a) Digestion of protein in the stomach: Gastric juice contains HCl and two proenzyme, pepsinogen and prorennin. HCl maintains a pH of 2 - 3.7 and kills bacteria and other pathogens. Gastric juice mixes with food until it becomes semi-solid mass called Chyme. Proenzymes become activated as below:
Pepsinogen →HCl, 2 - 3.7 pH Pepsin
Prorennin →HCl Rennin
These enzymes act as follows:
Casein (Milk protein) →Rennin Paracasein
Paracasein + Ca → Calcium Paracasinate (Curd)
Calcium paracasinate →Pepsin Peptones
Protein →Pepsin Peptones
(b) Digestion of protein the small intestine:
Action of pancreatic juice. It contains proenzymes trypsinogen, chymotry-psinogen and procarboxy peptidase.
Trypsinogen →Enterokinase of interstinal juice Trypsin
Chymotrypsinogen →Trypsin Chymotrypsin
Procarboxypeptidase →Trypsin Carbody - peptidase
Peptones →Trypsin Peptides
Peptones →Chymotrypsin Peptides
Peptides →Carboxypeptidase Smaller peptides + Amino acid
Action of intestinal juice. Intestinal juice contains endokinase, aminopeptidase and dipeptidase. Actions of these enzymes are summarized below:
Peptides →Aminopeptidase Smaller peptides + Amino acid
Peptides →Dipeptidase Amino acid
This is a summary of how your body handles the protein from food like eggs or beans. It takes a lot of different steps and enzymes to break these big molecules down into amino acids.
Teacher's Tip: "Pro"enzymes are "inactive" - they need a "starter" like HCl or Trypsin to begin working.
Exam Tip: Use chemical equations to show the chain reaction of one enzyme activating another.

Question 20:
Answer:
1. Stomach - Pepsin
2. Salivary glands - Salivary amylase/Ptyalin
3. Pancreas - Trypsin, Chymotrypsin, Carboxy peptidase, Pancreatic amylase and Pancreatic lipase.
4. Ileum - Enterokinase, Endokinase, Aminopeptidase and Dipeptidase.
Each organ has its own "enzyme factory" that produces specialized tools for different nutrients. The ileum is the final part of the small intestine where digestion is completed.
Teacher's Tip: The Ileum is the "finish line" for the digestive journey.
Exam Tip: Make sure you can match each enzyme to its correct organ in objective tests.

Question 21:
Answer:
(i) (a) Larynx
(ii) (c) club-shaped villi and Peyer's patches
(iii) (c) 750-1000 ml
(iv) (d) all the above
(v) (b) Gall bladder
(vi) (a) Proteins
(vii) (a) Below ears
(viii) (d) Intestine
(ix) (a) Proteins
(x) (b) Pharynx
(xi) (d) Rat
(xii) (a) Four
(xiii) (b) 2123 / 2123
(xiv) (c) Enamel
(xv) (a) 4
These multiple-choice answers test your detailed knowledge of human and animal biology. For example, it's important to know that humans produce about a liter of saliva every single day!
Teacher's Tip: The dental formula 2123/2123 is for an adult human - count your own teeth if you're curious!
Exam Tip: Read each option carefully in MCQs because some scientific terms look very similar at first glance.