Selina Concise Solutions for ICSE Class 6 Biology Chapter 4 Digestive System

Synopsis:

- The food we consume fall into seven different catagories.

1. carbohydrates
2. fats
3. proteins
4. minerals
5. vitamins
6. water
7. roughage

- The process of nutrition is conducted in five steps

1. ingestion
2. digestion
3. absorption
4. assimilation
5. egestion

- When some part of food is chewed, the tongue makes it a spherical mass called Bolus.

- Peristalsis is a wave of constriction in the circular muscles in the wall of the gut to push the food further into the food canal.

- The food canal is also called alimentary canal which starts from the mouth and ends at the anus.

- The digestive glands include

1. Salivary glands
2. Liver
3. Pancreas

- The teeth which are similar in size and shape are called homodont teeth.

- They are usually found in fishes, frogs, reptiles etc.

- The last molar on each side in each jaw is called wisdom tooth which appears at the age of 17-20 years.

- The human teeth develop in two sets; the first set is called milk teeth or temporary teeth while the second set which replaces the milk teeth are called permament teeth.

- The milk teeth are twenty in number while the permament are thirty two in number.

- The part of the teeth which can be seen is called crown while the part which is fixed in the jaw is called root.

- The tooth is made up of:

1. enamel
2. dentin
3. pulp

- The hardest substance of the body is called Enamel.

- The yellow, stick substance found on the teeth due to poor oral hygeine is called plaque. It consists of sugar and bacteria.

- Mineralised or hard plaque is called tartar.

- The functions of tongue are:

1. manipulates food while chewing
2. helps in tasting the food
3. mixes food with saliva
4. cleans the teeth.
5. helps in speaking.

- The enzyme contained in saliva is called amylase which digests starch into glucose.

- The food pipe is the oesophagus. No digestion takes here

- The organ which serves for both digestion and absorption of the food is small intestine.

- The small intestine is 7 metres long while the large intestine is 1.5 metres long.

- No enzyme is secreted by the large intestine.

- Glucose, amino acids, vitamins and minerals are transported to the liver.

- Amino acids are used in the production of proteins for growth and repair of tissues.

- The human digestive system is a complex network that transforms food into energy and nutrients. It involves both mechanical breakdown by teeth and chemical breakdown by enzymes secreted by various glands.

Teacher's Tip: Remember the phrase "I Drink A lot of Apple Energy" to recall the five steps of nutrition: Ingestion, Digestion, Absorption, Assimilation, Egestion.
Exam Tip: Always specify the length of the small intestine as 7 metres and the large intestine as 1.5 metres to show precision in your answers.

Review Questions

Multiple Choice Questions :

Put a tick (✓) against the most appropriate alternative in the following statements.

Question (i): The teeth which help in tearing the food are the:
(a) Incisors
(b) Canines
(c) Premolars
(d) Molars

Answer: (b) Canines
Canines are the sharp, pointed teeth situated on either side of the incisors. They are specially designed for gripping and tearing tough food materials like meat.
Teacher's Tip: Think of a dog (canine) having long sharp teeth to tear meat; that is exactly what your canines are for!
Exam Tip: Draw a small pointed tooth next to this answer to help visualize the function of tearing.

Question (ii): Last molar tooth in human beings is called:
(a) Adult tooth
(b) Wisdom tooth
(c) Child tooth
(d) Elders tooth

Answer: (b) Wisdom tooth
The last molar is called the wisdom tooth because it typically erupts much later than other teeth. Most people develop these teeth between the ages of 17 and 21, which is considered a more "mature" age.
Teacher's Tip: You don't actually get smarter when this tooth grows, but it marks the transition into adulthood!
Exam Tip: Mention the age group 17-20 years if the question asks for more detail about wisdom teeth.

Question (iii): The hardest substance in your body?
(a) Dentine
(b) Bone
(c) Cement
(d) Enamel

Answer: (d) Enamel
Enamel is the highly mineralized outer layer of the tooth crown. It is even tougher than bone, allowing our teeth to withstand the high pressure of chewing and grinding food throughout our lives.
Teacher's Tip: Enamel is like a "shield" for your teeth; once it is gone, it cannot be naturally replaced, so take care of it!
Exam Tip: Always name Enamel specifically as the hardest substance, not just "the tooth."

Question (iv): Saliva converts starch into:
(a) Glucose
(b) Sucrose
(c) Maltose
(d) Lactose

Answer: (c) Maltose
Saliva contains the enzyme amylase, which begins the chemical digestion of carbohydrates. It breaks down complex starch molecules into a simpler sugar called maltose while the food is still in the mouth.
Teacher's Tip: If you chew a piece of plain bread for a long time, it starts to taste sweet because of this conversion!
Exam Tip: Remember the enzyme responsible for this is Salivary Amylase or Ptyalin.

Question (v): Proteins of the milk are converted into curd by the enzyme:
(a) Trypsin
(b) Rennin
(c) Pepsin
(d) Steapsin

Answer: (b) Rennin
Rennin is a digestive enzyme produced in the stomach that specifically acts on milk proteins. It curdles the milk, turning it into a semi-solid state so that other enzymes can digest it more effectively.
Teacher's Tip: Rennin is mostly active in infants who rely entirely on milk for their nutrition.
Exam Tip: Don't confuse Rennin (digestive enzyme) with Renin (a hormone found in the kidneys).

Question (vi): Bile juice is produced by :
(a) Stomach
(b) Liver
(e) Pancreas
(d) Gall bladder

Answer: (b) Liver
The liver is the largest gland in the body and produces bile juice continuously. Although the gallbladder stores and concentrates the bile, the liver is the actual organ where it is manufactured.
Teacher's Tip: The liver is the "factory" that makes the bile, and the gallbladder is the "warehouse" that stores it.
Exam Tip: If the question asks where bile is $stored$, the answer is Gallbladder; if it asks where it is $produced$, it is Liver.

Write True or False in the following statements.
 

1. Molars help in cutting and tearing food.
Answer: False
Correct - Molars help in finer crushing and grinding.

2. Carbohydrates are digested into glucose.
Answer: True

3. Proteins are digested into fatty acids.
Answer: False
Correct - Proteins is digested into amino acids.

Molars have a broad, flat surface designed for mashing food into a paste. Proteins are complex chains that must be broken down into their building blocks, known as amino acids, to be absorbed by the body.
Teacher's Tip: Think of fatty acids as the end product of fats, and amino acids as the end product of proteins.
Exam Tip: When correcting a false statement, always provide the full corrected sentence to ensure full marks.

Fill in the blanks.

1. The teeth called are a total of four in number on the sides of incisors.
2. The teeth called canines are a total of four in number on the sides of incisors.
3. Pharynx is a common opening of food pipe and wind pipe.
4. Molars are meant for crushing the food.
5. Incisors are used for biting and cutting the food.
6. The canines are used for tearing the food.
7. The premolars and molars are used for crushing and grinding the food.
8. In an adult human, there are a total of 32 teeth.
9. The human teeth appear in two sets, the first set is called primary which consists of only twenty teeth.

Answer: (As filled in the bold text above)
Adult humans have 32 permanent teeth, while children have 20 primary (milk) teeth. Each type of tooth is specialized: incisors for cutting, canines for tearing, and premolars/molars for grinding.
Teacher's Tip: Remember the dental formula for adults: 2-1-2-3 (Incisors-Canines-Premolars-Molars) for each half of the jaw.
Exam Tip: Use the term "primary teeth" or "milk teeth" interchangeably, but check which one your specific textbook prefers.

Name the following :

1. End product of starch after digestion - glucose.
2. The organ where protein digestion-begins - stomach.
3. The organ into which the pancreatic juice and the bile juice are poured - small intestine.
4. The enzyme which digests fat - lipases.
5. The simplest form of carbohydrates - glucose.
6. The part of alimentary canal where water from undigested food is absorbed - large intestine.
7. The end-product of proteins after digestion - amino acids.

Answer: (As named in the bold text above)
Digestion is the process of breaking down complex nutrients into their simplest forms: starch to glucose, and proteins to amino acids. Most chemical digestion and absorption happen in the small intestine, while the large intestine focuses on water recovery.
Teacher's Tip: Most names of fat-digesting enzymes end in "-ase," like Lipase.
Exam Tip: For the "organ where protein digestion begins," always write Stomach, even though it finishes in the small intestine.

Identify and name the four type of teeth shown below and give their functions.

A - incisor
Function -Its major function is biting and cutting of food.
B - canine
Function - Its major function is tearing of the food.
C - pre-molar
Function - Used for crushing and grinding of food.
D - molar
Function - Used for crushing and grinding of food.

Answer: (As identified above)
The shape of each tooth reflects its job: incisors are flat like scissors, canines are sharp like daggers, and molars are broad like millstones. Together, they perform the mechanical digestion needed before chemical enzymes take over.
Teacher's Tip: You can remember the order from front to back as I-C-P-M (Incisors, Canines, Premolars, Molars).
Exam Tip: When drawing these, ensure the incisor has a straight edge and the molar has multiple roots.

State whether the following statements are True or False.

(i) Wisdom tooth appears at the age of 5-6 years when the child starts going to school.
(ii) The temporary set of teeth includes incisors, canines and premolars only.
(iii) The ducts from the salivary glands open into the duodenum.
(iv) Saliva changes starch into maltose.

Answer:
(i) False
(ii) False
(iii) False
(iv) True
Saliva specifically converts starch into maltose in the mouth. Wisdom teeth are actually the very last to appear, usually not until late adolescence or early adulthood.
Teacher's Tip: Salivary glands open into the mouth (buccal cavity), not the duodenum which is in the small intestine!
Exam Tip: Always double-check "True/False" statements that involve specific ages or locations.

Fill in the blanks in the table (1-5) by selecting the suitable names of substances from the list given below:
(steapsin, peptones, fatty acids, proteoses, protein).
Digestive enzymes: (i) Pepsin, (ii) Lipases(1)
acts on: (2) proteins, fats
to convert into: (3) peptones and (4) proteoses, (5) fatty acids

Answer:
(i) Pepsin acts on (2) proteins to convert into (3) peptones and (4) proteoses.
(ii) Lipases(1) acts on fats to convert into (5) fatty acids.

The stomach enzyme pepsin breaks down proteins into intermediate stages like peptones. Lipase is the specialized enzyme that breaks down fats into glycerol and fatty acids for easier absorption.
Teacher's Tip: Think of proteins as a long train; pepsin breaks the train into smaller cars (peptones) before they are finally broken into individual seats (amino acids).
Exam Tip: In tables, match the enzyme to the specific substrate (what it acts on) and the resulting product.

(i) Name the juice secreted by the liver.
Ans. Bile

(ii) Name the organ where this juice is temporarily stored.
Ans. Gallbladder

(iii) What is the main function of this juice ?
Ans. The main function of bile is digestion of fats.

Answer: (As provided above)
Bile is a greenish-yellow fluid that does not contain enzymes but is essential for fat digestion. It acts like a detergent, breaking large fat globules into tiny droplets so enzymes can work better.
Teacher's Tip: The process of breaking down fats into tiny droplets is called "emulsification."
Exam Tip: If asked for the $storage$ of bile, always write Gallbladder.

Question : Name the three enzymes found in pancreatic juice. (i)..... (ii)..... (iii) ......
Answer:
(i) Starch digesting - amylase
(ii) Protein digesting - trypsin
(iii) Fat - digesting - lipases

The pancreas is a vital gland that secretes a "cocktail" of enzymes to finish the digestion of all major food groups. These enzymes enter the small intestine and break down any remaining starch, protein, and fat.
Teacher's Tip: You can remember these as the "Pancreatic Trio" - Amylase, Trypsin, and Lipase.
Exam Tip: Specify which enzyme acts on which food group (e.g., Trypsin for proteins) to get full marks.

Question : Name the three regions of the large intestine.
Answer:
1. Caecum
2. Colon
3. Rectum

The large intestine starts with the caecum (where the appendix is attached), continues as the long colon, and ends at the rectum. Its primary job is to absorb water and salts from the waste material before it leaves the body.
Teacher's Tip: The colon is the longest part of the large intestine and is shaped like an upside-down 'U'.
Exam Tip: List the regions in the correct order: Caecum → Colon → Rectum.

Question : Given alongside is the diagram of the human alimentary canal.
(i) Name the parts 1-11 indicated by guidelines.
1. Stomach, 2. Bile duct, 3. Pancreas, 4. Large intestine, 5. Small intestine, 6. Rectum, 7. Appendix, 8. Pancreatic duct, 9. Gall Bladder, 10. Liver, 11. Anus
(ii) State the function of the juice secreted by the part 1.
The gastric juice being acidic kills the germs and activates pepsin.
(iii) State the function of the three enzymes found in the juice secreted by part 3.
1. amylase - digests starch
2. trypsin - digests protein
3. lipase - digests fat

Answer: (As identified and described above)
The alimentary canal is a continuous muscular tube where different organs have specialized roles. The stomach provides an acidic environment for initial protein breakdown, while the pancreas provides enzymes to complete digestion in the small intestine.
Teacher's Tip: Notice that the stomach is a 'J'-shaped sac on the left side of your body.
Exam Tip: When labeling diagrams, use straight guidelines and write the names in neat block letters.

Long Answer Questions

Question 1: Define the term nutrition.
Answer:
The process by which living beings receive the food and utilise it to grow and become healthy is called nutrition.
On the basis of nutrition, living beings can be classified into the following types:
1. Holozoites
2. Parasites
3. Saprophytes
4. Symbionts
Holozoits can be further classified into
1. herbivores
2. carnivores
3. ommivores

Nutrition is more than just eating; it is the entire process of getting energy and nutrients from the environment. Humans are holozoic, meaning we ingest solid or liquid organic matter and digest it internally.
Teacher's Tip: Holozoic literally means "animal-like" nutrition.
Exam Tip: Include the classification of living beings based on nutrition to show a comprehensive understanding of the topic.

Question 2: What is the role of the liver and the pancreas respectively in the digestion of food ?
Answer:
1. Liver: It produces a green yellow fluid called the bile which emulsify fats making it easy to be digested. The bile also contains sodium bicarbonate which neutralises the acid of food coming from the stomach and makes it alkaline.
2. Pancreas: It produces the digestive juice called the pancreatic juice which acts on carbohydrates, proteins and fats and convert them into simpler units called glucose, amino acids and fatty acdis respectively.

The liver and pancreas are accessory organs, meaning food doesn't pass $through$ them, but they are essential for chemical breakdown. They work together to turn the acidic mix from the stomach into a neutral or alkaline environment where intestinal enzymes can function.
Teacher's Tip: The liver is like a heavy-duty chemical factory that cleans and produces, while the pancreas is a precise enzyme dispenser.
Exam Tip: Mention that bile creates an "alkaline medium" as this is a specific requirement for pancreatic enzymes to work.

Question 3: Name the digestive juice secreted by the stomach and give its function.
Answer:
The digestive juice secreted by the stomach is the gastric juice. The gastric juice contains
1. water
2. hydrochloric acid
3. enzyme
Which have the following roles :
1. Hydrochloric acid serves to kill the germs and activates pepsin. Pepsin converts proteins into peptones and proteoses.
2. Enzyme rennin converts the milk caesin into curd.

Gastric juice is highly specialized for starting the breakdown of protein-rich foods. The hydrochloric acid is so strong it can dissolve metal, but it mainly serves to create the perfect environment for pepsin to work and to destroy harmful bacteria.
Teacher's Tip: Hydrochloric acid is the "key" that unlocks the "door" (activates) for the pepsin enzyme to start working.
Exam Tip: List the three main components of gastric juice (water, HCl, enzymes) separately for clarity.

Question 4 (i) Name the types of teeth seen in humans.
Answer:
Human teeth are of four kinds:
1. Incisors are the four front teeth at the middle of each jaw. They are chisel-shaped for biting and cutting.
2. Canines are one on either side of the incisors in each jaw. They are pointed for tearing the food.
3. Premolars are two on each side of canines in each jaw. They help in crushing and grinding the food.
4. Molars are the last three teeth on each side in each jaw. They have broad uneven surface for finer crushing and grinding of ingested food.

Our mouth is equipped with a complete set of "tools" to handle any kind of diet. Incisors act like scissors, canines like forks, and molars like a mortar and pestle to prepare food for swallowing.
Teacher's Tip: Note that only adults have the full 32 teeth; children lack the third set of molars (wisdom teeth).
Exam Tip: Use the specific terms "chisel-shaped" and "pointed" to describe tooth shapes.

(ii) How is the small intestine best suited for the digestion and absorption of food ?
Answer:
The small intestine's inner lining contain a large number of tiny finger-like projections called villi. The villi greatly increases the inner surface area for the absorption of digested food.

The small intestine is not just long, but its surface is folded into millions of tiny villi to maximize nutrient pickup. This structure ensures that almost all the useful nutrients from your food enter your bloodstream before reaching the large intestine.
Teacher's Tip: Imagine a flat rug versus a shag carpet; the shag carpet (villi) has much more thread surface area in the same amount of space!
Exam Tip: Always mention "villi" and "increased surface area" when explaining absorption.

(iii) What do you mean by absorption of food ?
Answer:
The absorption of food means to pass the digested food products into the blood system and lymph vessels to be used further by body for various life functions.

Absorption is the vital bridge between the digestive system and the rest of the body. Once nutrients are absorbed into the blood, they can be delivered to every single cell to provide energy and building materials.
Teacher's Tip: Absorption is when the food finally "enters" your body's internal systems.
Exam Tip: Include "blood system and lymph vessels" to show you know exactly where the food goes.

Question 5: Define the following terms: Egestion, digestion, assimilation.
Answer:
Egestion - The process of removal of the undigested food from the body is defined as egestion.
Digestion - The process of breaking the food into smaller and simpler substances so that they can be easily used by the body is called digestion.
Assimilation - The process of using the digested food by the body is called assimilation.

Digestion prepares the food, absorption brings it in, and assimilation is when the body actually "builds" itself using those nutrients. Egestion is the final cleanup step to remove what the body couldn't use.
Teacher's Tip: Assimilation is like using bricks from a delivery truck to actually build the walls of your house.
Exam Tip: Be careful not to confuse Egestion (removing undigested food) with Excretion (removing metabolic waste like urine).

Question 6: Rewrite the following parts of the human alimentary canal in their correct sequence: Stomach, Oesophagus, Large instestine, Small intestine, Pharynx.
Answer:
Pharynx → Oesophagus → Stomach → Small intestine → Large intestine.

Food follows a specific "one-way" path through the body to ensure each organ can do its job in the right order. This journey starts at the throat (pharynx) and moves through the food pipe into the main digestion and absorption centers.
Teacher's Tip: Remember the order: P-O-S-S-L (Pharynx, Oesophagus, Stomach, Small, Large).
Exam Tip: Use arrows (→) to show the direction of flow for a clearer answer.

Question 7: What is the fate of excess glucose in our body ?
Answer:
The excess glucose is converted by the liver into insoluble glycogen and stores it, whenever required. Liver can reconvert the glycogen into glucose.

The liver acts like a rechargeable battery for the body's energy. It saves up extra sugar from a big meal as glycogen and releases it back into the blood whenever your energy levels drop, like between meals.
Teacher's Tip: Glycogen is like the body's "energy savings account" in the Liver bank.
Exam Tip: State clearly that the liver performs this conversion both ways (glucose to glycogen and vice versa).

Question 8: Define the term 'digestion'.
Answer:
The process of converting the complex food substances into simpler and smaller units so that they can be easily utilised by the body is defined as digestion. e.g. proteins are converted to amino acids.

Most of the food we eat consists of very large molecules that cannot pass into our blood. Digestion uses mechanical chewing and chemical enzymes to "chop" these big molecules into tiny pieces that our cells can use.
Teacher's Tip: Digestion is a two-part process: mechanical (teeth) and chemical (enzymes).
Exam Tip: Always include an example, like starch to glucose or proteins to amino acids, to strengthen your definition.

Question 9: State the four ways in which saliva is useful to us.
Answer:
The four ways in which saliva is useful to us are:
1. Moistens and lubricates the oral cavity and the tongue to make speaking and swallowing easy.
2. Acts as a solvent, dissolving some part of food to stimulate taste
3. Cleans the mouth and destroys germs
4. Initiates digestion by converting starch into simpler form, maltose.

Saliva is much more than just water; it is a protective and digestive fluid. It contains lubricants for the throat, chemicals to kill bacteria, and the very first enzymes that start breaking down your lunch.
Teacher's Tip: Saliva helps you taste food because your taste buds can only "detect" chemicals that are dissolved in liquid.
Exam Tip: Remember "Lubrication" and "Initial Digestion" as the two primary roles if you are in a hurry.

Question 10: Food are classified into three groups on the basis of the function they perform in our body. Name the three categories, and briefly give their functions. Also give their two sources each.
Answer:
Function
1. energy giving food (carbohydrates and fats) - Sources: cereals, fats, sugar
2. bodybuilding food (proteins) - Sources: pulses, milk, meat chicken
3. regulatory and protective foods (vitamins and minerals) - Sources: fruits and vegetables

A balanced diet needs all three types: energy foods for fuel, bodybuilding foods for growth, and protective foods to keep us from getting sick. Each food group provides specific nutrients that our organs need to function correctly every day.
Teacher's Tip: Think of it as: Fuel for the engine, Bricks for the walls, and a Repairman for the house.
Exam Tip: When listing sources, always group them by the nutrient they provide (e.g., pulses for proteins).

ADDITIONAL QUESTIONS

A. Fill in the blanks.

1. Grinding of food is brought about by premolars and molars.
2. Steapsin is also called lipase.
3. Saliva contains salivaiy amylase which changes starch to maltose.
4. Peristalsis is caused by wave-like motion of muscles in food pipe.
5. Pepsin acts on proteins to change them into proteoses and peptones.
6. Liver and Pancreas help in digestion but food does not pass through them.
7. Removal of undigested food is called egestion.

Answer: (As filled in the bold text above)
Peristalsis is the automatic muscle movement that keeps food moving down the oesophagus, even if you are standing on your head! Enzymes like pepsin and lipase are the chemical tools that do the heavy lifting of breaking down food.
Teacher's Tip: Remember that "steapsin" is just another name for pancreatic lipase.
Exam Tip: Mention the "wave-like motion" when describing peristalsis for a better score.

B. Write true or false for each statement. Rewrite the false statements correctly.

1. The process of taking in food is called assimilation.
Answer: False. The process of taking in food is called ingestion.

2. The pancreas secretes bile juice.
Answer: False. The liver secretes bile juice.

3. Pancreatic juice does not contain any enzyme.
Answer: False. Bile juice does not contain any enzyme.

4. Saliva contains lipase which digests carbohydrates.
Answer: False. Saliva contains salivary amylase which digests carbohydrates.

5. The wave-like motion of stomach muscles to push the food is called peristalsis.
Answer: False. The wave-like motion of oesophagus muscles to push the food is called peristalsis.

6. Digestion of food in intestine takes place in the presence of dilute hydrochloric acid.
Answer: False. Digestion of food in stomach takes place in the presence of dilute hydrochloric acid.

7. Absorption of food takes place in small intestine.
Answer: True

8. Water is absorbed in large intestine.
Answer: True

9. The removal of faeces through anus is called excretion.
Answer: False. The removal of faeces through anus is called egestion.

10.All the absorbed nutrients are immediately required by the body.
Answer: False. All the absorbed nutrients are not immediately required by the body.

Many people confuse egestion and excretion; remember that egestion is specifically for $undigested$ food waste. Similarly, the acidity of the stomach is a unique feature to kill bacteria and help protein digestion, whereas the rest of the tract is neutral or alkaline.
Teacher's Tip: Bile is the *only* major digestive juice that has no enzymes in it!
Exam Tip: When correcting false statements, ensure you swap the incorrect term with the correct biological one.

C. Put the following processes in their correct sequence of occurrence during digestion.

peristalsis ; tongue pushes the food ; grinding and mixing saliva ; cutting and tearing of food
Answer:
The correct sequence of the processes occurring during digestion are.
Cutting and tearing of food → grinding and mixing saliva → tongue pushes the food → peristalsis.

Digestion starts the moment food enters the mouth, with mechanical cutting followed by chemical mixing. Once the tongue forms a bolus and pushes it back, automatic muscle waves (peristalsis) take over to move it to the stomach.
Teacher's Tip: Think about your lunch: you bite first (cut/tear), then chew (grind/mix), then swallow (tongue/peristalsis).
Exam Tip: Sequence questions are common; practice this flow from mouth to esophagus.

D. Find the odd one out. Give reasons for your choice.

1. Oesophagus, gizzard, small intestine, liver.
Answer: Oesophagus: No digestion of food occurs in oesophagus all other helps in digestion of food.

2. canines, incisors, saliva, premolars.
Answer: Saliva: As all are the types of teeth and saliva is a fluid secreted by salivary glands.

3. Salivary amylase, pepsin, trypsin, erepsin.
Answer: Salivary amylase: As it acts on starch and all others act on proteins.

4. Lactase, maltase, lipase, sucrase
Answer: Lipase: It is a fat digesting enzyme all other acts on carbohydrates.

Grouping enzymes and organs by their function helps identify their unique roles. For instance, amylase is specialized for starches, while pepsin, trypsin, and erepsin form a "protein-breaking" team.
Teacher's Tip: Most sugar-digesting enzymes end in "-ose" or "-ase," like Lactase for lactose.
Exam Tip: Always provide a clear reason describing why the "odd" one doesn't fit the category of the others.

E. Give reasons for the following:

Question 1: Meat eating animals have strong canines.
Answer:
Meat eating animals have strong canines as they have to tear the flesh. Meat eating animals like dog, wolves and lions eat raw meat by tearing it so they have sharp canines.

In the animal kingdom, teeth are adapted to the diet of the creature. Carnivores rely on their canines as tools for hunting and for ripping through tough hide and muscle.
Teacher's Tip: Look at a picture of a lion's mouth; those huge "fangs" are just really large canines!
Exam Tip: Mention the word "tear" or "flesh" to explain the specific need for sharp canines.

Question 2: All teeth in the mouth are not alike.
Answer:
The dentition in animals is based on the type of food they eat. So we have different kinds of teeth. All teeth in the mouth are not alike as we eat both meat and plants. Due to different type of food eating habits teeth are of different types.

Humans are omnivores, meaning we eat a mix of plants and animals. Having different shapes of teeth (Heterodont dentition) allows us to efficiently handle various textures, from soft fruits to tough meats.
Teacher's Tip: Diversity in teeth reflects a diverse diet!
Exam Tip: Use the term "Heterodont" if you want to use the scientific word for having different kinds of teeth.

F. Differentiate between.

Question 1: Digestion and Absorption.
Answer:
Digestion:
1. It is the process of converting complex food into a simple absorbable form.
2. It is a series of mechanical and chemical reactions.
3. Many enzymes are associated with digestion
Absorption:
1. It is the process of passing digested food through thin walls of blood capillaries and enters the blood stream.
2. No mechanical or chemical reaction occurs in absorption.
3. No enzyme is associated with absorption.

Digestion is about "breaking down," while absorption is about "moving in." You can think of digestion as preparing a package and absorption as the package being delivered into the body's internal mail system (blood).
Teacher's Tip: Digestion happens *inside* the canal, but absorption happens *across* the canal wall.
Exam Tip: Contrast the "mechanical/chemical" nature of digestion with the purely physical movement of absorption.

Question 2: Mechanical digestion and Chemical digestion.
Answer:
Mechanical digestion:
1. In mechanical digestion the ingested food is broken down in the mouth by chewing it.
2. Teeth help in mechanical digestion
3. Food is not completely digested in it.
Chemical digestion:
1. In chemical digestion the food is digested by the action of enzymes.
2. Enzymes are involved in chemical digestion.
3. Proper digestion of food occurs in it.

Mechanical digestion increases the surface area of food by crushing it into smaller bits. Chemical digestion then uses enzymes to break the actual molecular bonds, turning the food into a liquid form that the body can finally absorb.
Teacher's Tip: Mechanical digestion is like a hammer; chemical digestion is like acid.
Exam Tip: Mention that mechanical digestion "prepares" the food for chemical digestion.

Question 3: Small intestine and Large intestine.
Answer:
Small intestine:
1. It is 7 metres long and 2.5 cm wide.
2. It has finger like projections called villi.
3. Food is completely digested here.
Large intestine:
1. It is 1.5 - 1.8 m long and 6.5 m wide.
2. Villi are absent in large intestine.
3. Excess of water is absorbed here

Despite their names, the "small" intestine is actually much longer than the "large" one! It is called "small" because it is narrower, whereas the large intestine is shorter but much wider in diameter.
Teacher's Tip: Almost all "work" (digestion/absorption) is finished in the small intestine; the large intestine is for waste management.
Exam Tip: Compare their lengths (7m vs 1.5m) and widths clearly for a full-mark answer.

G. Write short answers.

Question 1: What is ingestion ?
Answer:
The process of taking in food through the mouth is called ingestion.

This is the very first step of the entire nutritional process. It simply means putting food into your mouth and starting the journey through the alimentary canal.
Teacher's Tip: "In-" means going inside!
Exam Tip: Define it as the "act of taking food into the buccal cavity."

Question 2: What is dental plaque ?
Answer:
When a mixture of saliva, food and bacteria begins to form over the teeth within half an hour of eating, is called a dental plaque.

Plaque is a sticky film that constantly forms on our teeth. If it isn't brushed away, the bacteria in it produce acids that eat away at our tooth enamel, causing cavities.
Teacher's Tip: This is why you must brush your teeth twice a day - to stop the plaque from hardening!
Exam Tip: Mention that it consists of "food particles, saliva, and bacteria."

Question 3: Define homodont dentition.
Answer:
An homodont dentition all the teeth in the jaws are similar in shape and structures, e.g. in frogs and fish.

Homodont means "same teeth." Animals like lizards and fish don't chew their food the way humans do; their teeth are all the same shape and are mostly used for catching or holding prey.
Teacher's Tip: "Homo-" means the same, just like in "homogeneous."
Exam Tip: Use "frogs and fish" as standard examples for this definition.

Question 4: What is peristalsis ?
Answer:
The process by which the food passes from the pharynx to the stomach through the oesophagus by a series of contractions is known as peristalses.

Peristalsis is an involuntary, rhythmic wave of muscle contraction and relaxation. It acts like a tube of toothpaste being squeezed from the bottom to push the food toward the stomach.
Teacher's Tip: Because of peristalsis, you can actually swallow food even if you are hanging upside down!
Exam Tip: Use the phrase "wave-like muscle contractions" for a scientific definition.

Question 5: What do you means by emulsification of fat?
Answer:
Digestion of fats in to tiny droplets to provide larger surface area for the enzymes to act is called emulsification of fats.

Fat doesn't dissolve in water, so it forms large clumps in the stomach. Bile acts as an emulsifier to break these big clumps into tiny droplets, allowing lipase enzymes to reach and digest them efficiently.
Teacher's Tip: Emulsification is like using dish soap to break up a greasy puddle on a plate.
Exam Tip: Mention that "bile" is the substance responsible for emulsification.

Question 6: Write the names of three enzymes which are found in pancreatic juice.
Answer:
Three enzymes found in pancreatic enzymes are :
1. Trypsin - act on proteins, proteoses and peptones and changes them in to polypeptides.
2. Lipase - acts on fats and changes them to fatty acids and glycerol.
3. Erepsin - acts on peptones and peptides and changes them to amino acids.

The pancreatic juice is a chemical powerhouse that breaks down all major types of nutrients. Trypsin and erepsin work together to reduce complex proteins into simple, absorbable amino acids.
Teacher's Tip: Note that "Erepsin" is actually produced by the small intestine, though often discussed alongside pancreatic enzymes in basic biology.
Exam Tip: For each enzyme, list what it $acts$ on and what it $produces$.

H. Complete the following enzymatic reactions.

1. Proteins $\xrightarrow{pepsin}$ proteoses + peptones
2. Fats $\xrightarrow{lipase}$ fatty acids + glycerol
3. Maltose $\xrightarrow{maltase}$ glucose
4. Sucrose $\xrightarrow{sucrase}$ glucose + fructose

Answer: (As completed in the bold text above)
Enzymatic reactions are the "chemical math" of biology. They show how large molecules are broken down step-by-step into the tiny units that our body can finally use for energy and growth.
Teacher's Tip: Notice how the enzyme name usually sounds like the food it digests (Sucrase for Sucrose)!
Exam Tip: Use arrows to show the direction of the reaction and write the enzyme name above the arrow.

I. Answer in detail.

Question 1: What is meant by digestion ? How does it differ from nutrition ?
Answer:
The process of changing complex food into simple, absorbable form by the action of certain enzymes is called digestion. Many organs are associated with digestion. Digestion is of two types mechanical and chemical digestion. In mechanical digestion, food is broken down in the mouth when we chew it with our teeth. In chemical digestion, the food is digested by the actions of certain enzymes. Digestion is necessary because the food which is obtained is in complex form and our body is not able to absorb nutrients from it. So it is converted in to simple absorbable form.
Nutrition is the process of obtaining and using food by the organisms. It is different in different organisms. Ingestion, digestion, absorption, Assimilation and egestion are the various steps involved nutrition.

Digestion is just one "chapter" in the larger story of nutrition. While digestion focuses on the physical and chemical breakdown, nutrition encompasses everything from finding the food to using its energy for your heartbeat.
Teacher's Tip: Digestion is a process *within* nutrition.
Exam Tip: To get full marks, list the five steps of nutrition when explaining how it differs from digestion.

Question 2: Name the four types of teeth and their functions
Answer:
The four types of teeth are :
Incisors: These are situated at the front and are flat and straight with sharp edges. Which are used for biting and cutting the food.
Canines: These are situated one on either side of the incisors in each jaw. There are two canines in each jaw. These are sharp and pointed and are used for holding and tearing the food.
Premolars: There are 4 premolars in each jaw, situated next to the canines. Each premolar has one or two roots and two cusps. These are used for crushing and grinding the food.
Molars: These are 6 molars in each jaw. The molars have more than one root. These are used for crushing and grinding the food. The last molar of each side in each jaw is also called wisdom tooth because it appears last generally at the age of 17-20 years.
The ingested food is first broken down in mouth when we chew it with our teeth. This process is called mastication or mechanical digestion. It prepares the food for chemical digestion that is, the digestion by the action of enzymes.

Teeth are the specialized tools our body uses to begin the process of mechanical digestion. By breaking food into smaller bits, they increase the total surface area that digestive enzymes can reach, making chemical digestion much faster.
Teacher's Tip: "Mastication" is just the scientific word for chewing!
Exam Tip: Mention the specific number of each type of tooth in one jaw (e.g., 4 incisors) for a very detailed answer.

Question 3: Liver does not secrete any enzymes yet it helps in digestion. How ?
Answer:
Liver does not secrete any enzyme yet it helps in digestion it secretes bile which helps in digestion of fats by breaking down fats in to tiny droplets to provide larger surfaces area for the enzymes to act. This process is called emulsification of fats. Bile secreted by liver is stored in gall bladder. Bile provides an alkaline medium in the duodenum for the action of enzymes of the pancreatic juice.

The liver is essential because fats are difficult to digest in a watery environment. By emulsifying them and neutralizing stomach acid, bile creates the perfect conditions for the lipase enzyme to finish the job.
Teacher's Tip: Think of the liver as the "fat-prep" station of the body.
Exam Tip: Focus your answer on two points: "Emulsification of fats" and "Creating an alkaline medium."

Question 4: What changes occur in food in the mouth ?
Answer:
The mouth is the first part of digestive system. It receive food and start mechanical digestion. The ingested food is first broken down in the mouth when it is chewed.
Simultaneously it get mixed with the saliva. This process is called mastication or mechanical digestion. It prepares the food for chemical digestion, that is, the digestion by action of enzyme. The teeth help in chewing down the food. There are 4 kinds of teeth. These are incisors, canines, premolars and molars, incisors are the cutting teeth. These help in biting and cutting the food. Canines are the tearing teeth that helps to tear and hold the food. Premolars and molars are the crushing and grinding teeth which helps in grinding the food.
When we chew the food it is mixed with saliva, secreted by salivary glands softens the food. Saliva contains an enzyme called salivary amylase also called ptyalin, acts on starch to convert it in to maltose.
starch $\xrightarrow{Salivary/amylase}$ maltose.

Inside the mouth, food undergoes both a physical change (crushing) and the very beginning of a chemical change (starch breakdown). Saliva plays a double role by killing germs and providing the moisture needed to swallow safely.
Teacher's Tip: The tongue also helps by moving the food around so the teeth can reach every bit.
Exam Tip: Be sure to name the specific enzyme (amylase/ptyalin) and the food group it acts on (starch).

Question 5: What happens to the nutrients absorbed in the blood stream from the small intestine ?
Answer:
The villi of the small intestine increase the inner surface area for absorption of digested food. Villi contain blood capillaries, The digested food passes through these blood capillaries and enters the blood stream. This process is called absorption. All the absorbed nutrients are not required immediately by the body. So they are changed in to various forms that can be stored until they are needed. This process is called assimilation.
1. Glucose is converted in to glycogen and is stored in the liver. When it is required by the liver glycogen is converted in to glucose. Excess of glucose is also converted in to fat and stored in the adipose tissue. Fatty acids either provide energy or are used for synthesis of fats which is stored under the skin.
2. Amino acids are used for synthesis of protein. Excess amount of amino acids are converted in to urea which is removed by the kidneys.
glucose $\xrightarrow{liver}$ glycogen
Amino acids → Proteins
Amino acids → urea

Once absorbed, nutrients don't just float around; they are put to work building muscles or stored for future use. The liver is the main "manager" that decides which nutrients go to the cells and which ones get tucked away as fat or glycogen.
Teacher's Tip: This "storage and usage" phase is what we call Assimilation.
Exam Tip: Mention "Glycogen" and "Urea" to show you know the specific storage and waste forms of glucose and amino acids.

Question 6: You had eaten bread in the morning. Starting from the mouth, explain how it is digested ?
Answer:
Bread contains starch. The digestion of starch starts in the mouth. When we chew the bread, saliva gets mixed with it. It softens the food. Saliva is secreted by salivary glands. Saliva contains the enzyme salivary amylase (ptyalin) which acts on starch to convert it in to maltose
starch $\xrightarrow{Salivary/amylase}$ maltose.
After chewing, the food is swallowed in to the pharynx. No further digestion takes place in pharynx. From here the food moves in to the oesophagus, by peristaltic movements it is pushed in to the alimentary canal. In the small intestine (duodenum) rest of the starch is broken down in to smaller units by pancreatic amylase. Further Maltose is changed in to glucose by maltose in small intestine (ileum).

The journey of a piece of bread is mostly a "carbohydrate story" because bread is rich in starch. By the time it reaches the end of the small intestine, that complex starch has been completely turned into simple glucose sugar, ready to power your body.
Teacher's Tip: Remember that no digestion happens in the pharynx or oesophagus; they are just "transport tubes."
Exam Tip: Trace the path step-by-step: Mouth → Pharynx → Oesophagus → Small Intestine.