Grade 7 Q&A: Chapter 12: The Muscular System and Digestive System in Human Beings

Concept Questions

Q1: What is the muscular system? How do muscles help in movement?

Answer: The muscular system is a system of muscles in the body that enables various movements. Muscles are bundles of contractile fibers attached to bones by tendons. When muscles contract, they pull on the bones, causing movement. Muscles always work in pairs (one contracts, the other relaxes) because they can only pull, not push.

Q2: Name the three types of muscles found in the human body.

Answer: The three types of muscles are: 1. Skeletal Muscles (Voluntary/Striated Muscles) 2. Smooth Muscles (Involuntary/Non-striated Muscles) 3. Cardiac Muscles (Heart Muscles)

Q3: Differentiate between voluntary and involuntary muscles. Give an example of each.

Answer:

• Voluntary Muscles: Muscles whose movements are under our conscious control, meaning we can move them as per our will. Example: Muscles of our arms and legs (skeletal muscles).
• Involuntary Muscles: Muscles whose movements are not under our conscious control; they work automatically. Example: Muscles in the walls of the stomach or intestines (smooth muscles), or heart muscles (cardiac muscles).

Q4: What are cardiac muscles? Where are they found, and what is their unique characteristic?

Answer: Cardiac muscles are specialized involuntary muscles found exclusively in the wall of the heart. Their unique characteristic is that they are striated (like skeletal muscles) but also branched and interconnected, allowing them to contract continuously and rhythmically without tiring, ensuring continuous blood pumping throughout life.

Q5: List three functions of muscles in the human body.

Answer: 1. Movement: Enable all bodily movements. 2. Posture: Help maintain body posture. 3. Heat Production: Generate heat to maintain body temperature.

Q6: What is digestion? Why is it important?

Answer: Digestion is the process of breaking down complex, insoluble food substances into simpler, soluble forms that can be absorbed by the body. It is important because the body needs these simpler nutrients for energy, growth, and repair.

Q7: Name the main organs of the alimentary canal in sequential order.

Answer: The main organs of the alimentary canal are: Mouth (Buccal Cavity) → Pharynx → Oesophagus (Food Pipe) → Stomach → Small Intestine → Large Intestine → Anus.

Q8: What is the role of saliva in digestion? Which enzyme does it contain?

Answer: Saliva, secreted in the mouth, moistens food for easy swallowing and contains the enzyme salivary amylase (or ptyalin). This enzyme begins the chemical digestion of complex carbohydrates (starch) into simpler sugars.

Q9: Describe the function of hydrochloric acid in the stomach.

Answer: Hydrochloric acid (HCl) in the stomach serves two main functions: 1. It creates an acidic medium necessary for the enzyme pepsin to function. 2. It kills harmful bacteria that may enter the stomach along with food.

Q10: Why is the small intestine considered the main site of digestion and absorption?

Answer: The small intestine is the main site of digestion because it receives digestive juices from the liver (bile) and pancreas, along with its own intestinal juice, which contain enzymes that complete the digestion of carbohydrates, proteins, and fats. It is the main site of absorption due to the presence of millions of villi, which greatly increase the surface area for efficient absorption of digested nutrients into the bloodstream.

Q11: What is bile juice? Where is it produced and stored, and what is its role in digestion?

Answer: Bile juice is a yellowish-green digestive fluid. It is produced by the liver and stored in the gallbladder. Its role in digestion is to emulsify fats, meaning it breaks down large fat globules into smaller ones, making it easier for fat-digesting enzymes (lipase) to act on them. Bile does not contain enzymes.

Q12: What are villi? What is their significance?

Answer: Villi are millions of tiny, finger-like projections found on the inner lining of the small intestine. Their significance is that they vastly increase the surface area of the small intestine, enabling highly efficient absorption of digested nutrients (glucose, amino acids, fatty acids, glycerol) into the bloodstream.

Q13: What is the primary function of the large intestine?

Answer: The primary function of the large intestine is to absorb excess water and some salts from the undigested food material. It also stores the remaining undigested waste (feces) until it is eliminated from the body.

Q14: Explain the process of peristalsis.

Answer: Peristalsis is the rhythmic, wave-like contraction and relaxation of the muscular walls of the oesophagus and other parts of the alimentary canal. This involuntary action pushes food progressively down the digestive tract, ensuring its smooth movement from the mouth to the anus.

Q15: Name the end products of carbohydrate, protein, and fat digestion.

Answer: * Carbohydrates → Glucose * Proteins → Amino Acids * Fats → Fatty Acids and Glycerol

Application-Based Questions

Q16: Imagine you have just eaten a slice of bread. Describe the journey and initial digestion of the bread from your mouth to your stomach.

Answer: When you eat a slice of bread, it enters your mouth. Here, your teeth chew it into smaller pieces (mechanical digestion). Saliva, containing salivary amylase, mixes with the bread, beginning the digestion of starch. The tongue helps in mixing and forms a bolus. This bolus is then swallowed and moves through the pharynx into the oesophagus. In the oesophagus, peristalsis (wave-like muscular contractions) pushes the bread down to the stomach. No digestion occurs in the oesophagus.

Q17: Why do we sometimes get cramps in our muscles after strenuous exercise?

Answer: Muscle cramps after strenuous exercise occur when muscles work too hard and do not get enough oxygen. In such conditions, muscles switch to anaerobic respiration, producing lactic acid instead of just carbon dioxide and water. The accumulation of lactic acid causes pain and muscle fatigue, leading to cramps.

Q18: A person complains of heartburn after eating a heavy meal. Which part of the digestive system is likely causing this, and why?

Answer: Heartburn is typically caused by the backward flow of stomach acid (hydrochloric acid) into the oesophagus. This happens when the muscular valve (sphincter) between the oesophagus and the stomach doesn't close properly after food enters the stomach. The acid irritates the lining of the oesophagus, causing a burning sensation in the chest area, which is commonly referred to as heartburn.

Q19: If a person's liver is not functioning properly, how might this affect their digestion, particularly of fats?

Answer: If a person's liver is not functioning properly, it will impair their digestion significantly, especially the digestion of fats. The liver produces bile juice, which is essential for the emulsification of fats in the small intestine. Without sufficient bile, large fat globules cannot be broken down into smaller ones, making it very difficult for the enzyme lipase to digest them. This can lead to malabsorption of fats and fat-soluble vitamins, causing digestive discomfort and nutritional deficiencies.

Q20: Why is it important to chew food properly before swallowing?

Answer: It is important to chew food properly (mechanical digestion) for several reasons: 1. It breaks down large food particles into smaller ones, increasing the surface area for digestive enzymes to act more efficiently. 2. It mixes food with saliva, initiating carbohydrate digestion and making the food moist and easier to swallow. 3. Proper chewing reduces the burden on the stomach and intestines, promoting smoother digestion and preventing discomfort.

Q21: You notice that your arm muscles become bigger and stronger after regularly lifting weights. Which type of muscles are these, and why does this happen?

Answer: The arm muscles are skeletal muscles (voluntary muscles). They become bigger and stronger due to regular weightlifting because exercise causes microscopic tears in the muscle fibers. In response, the body repairs these tears by adding new muscle proteins, leading to an increase in muscle size (hypertrophy) and strength.

Q22: Why can we hold our breath for a short period, but we cannot stop our heart from beating?

Answer: We can hold our breath for a short period because the muscles involved in breathing (like the diaphragm and intercostal muscles) are primarily skeletal muscles, which are under voluntary control to a certain extent. However, we cannot stop our heart from beating because the heart is made of cardiac muscles, which are entirely involuntary. Their contractions are regulated by the body's autonomous nervous system and are not subject to conscious control.

Q23: A doctor advises a patient to eat a diet rich in fiber. How does fiber help in digestion?

Answer: Fiber (roughage) is an indigestible part of plant food that plays a crucial role in digestion, even though it's not broken down. It adds bulk to the stool, making it softer and easier to pass through the digestive tract. This helps prevent constipation and maintains regular bowel movements. It also aids in cleansing the digestive tract.

Q24: Explain how two muscles work together to bend and straighten your arm at the elbow.

Answer: To bend and straighten your arm, two muscles, the biceps and triceps, work in opposition (antagonistically). * To bend (flex) the arm: The biceps muscle (on the front of the upper arm) contracts and shortens, pulling the forearm bone (radius/ulna) upwards. Simultaneously, the triceps muscle (on the back of the upper arm) relaxes. * To straighten (extend) the arm: The triceps muscle contracts and shortens, pulling the forearm bone downwards. Simultaneously, the biceps muscle relaxes. This paired action, where one muscle contracts and the other relaxes, allows for smooth and controlled movement.

Q25: If the villi in the small intestine were damaged, what would be the impact on the human body?

Answer: If the villi in the small intestine were damaged, the body would suffer from severe malabsorption. Villi greatly increase the surface area for nutrient absorption. Without functional villi, the body would be unable to absorb essential digested nutrients (glucose, amino acids, fatty acids, vitamins, minerals) efficiently into the bloodstream. This would lead to severe nutritional deficiencies, weight loss, lack of energy, and various health problems despite consuming adequate food.

Textbook Exercise Solutions

A. Fill in the blanks:

1. The muscular system allows us to perform various movements.
2. Muscles are firmly attached to the bones by means of tendons.
3. Muscles work in pairs.
4. Muscles found in the stomach and intestines are smooth muscles.
5. The process of breaking down food into simpler forms is called digestion.
6. Saliva contains an enzyme called salivary amylase that digests starch.
7. The stomach secretes hydrochloric acid and pepsin.
8. The largest gland in the human body is the liver.
9. The final digestion of food takes place in the small intestine.
10. Undigested food material is expelled through the anus.

B. State true or false:

1. Skeletal muscles are involuntary muscles. False
2. Cardiac muscles are found only in the heart. True
3. Digestion of food begins in the oesophagus. False
4. Bile juice contains digestive enzymes. False
5. Villi increase the surface area for absorption in the small intestine. True
6. The large intestine absorbs digested nutrients. False

C. Match the following:

Column A

1. Skeletal muscles
2. Smooth muscles
3. Cardiac muscles
4. Salivary amylase
5. Pepsin
6. Bile juice
7. Villi

Column B

1. Heart
2. Starch digestion
3. Emulsification of fats
4. Voluntary movement
5. Absorption
6. Protein digestion
7. Involuntary movement of internal organs

Answers:

1. Skeletal muscles - Voluntary movement
2. Smooth muscles - Involuntary movement of internal organs
3. Cardiac muscles - Heart
4. Salivary amylase - Starch digestion
5. Pepsin - Protein digestion
6. Bile juice - Emulsification of fats
7. Villi - Absorption

D. Answer the following questions briefly:

Q1: What are muscles?

Answer: Muscles are bundles of contractile fibres in the body that enable movement and maintain posture.

Q2: Name the different types of muscles.

Answer: Skeletal muscles, smooth muscles, and cardiac muscles.

Q3: What is peristalsis?

Answer: Peristalsis is the rhythmic, wave-like contractions of the muscular walls of the oesophagus and other digestive organs that push food along the alimentary canal.

Q4: Name the two digestive juices secreted in the small intestine.

Answer: Pancreatic juice (from the pancreas) and intestinal juice (from the small intestine wall).

Q5: What is the function of the large intestine?

Answer: The large intestine's function is to absorb water and some salts from the undigested food and store feces until elimination.

E. Answer the following questions in detail:

Q1: Describe the different types of muscles with their functions.

Answer: The three types of muscles are:

1. Skeletal Muscles (Voluntary/Striated):
   • Location: Attached to bones.
   • Control: Voluntary (under conscious control).
   • Appearance: Striated (striped).
   • Function: Responsible for all movements of limbs, trunk, head, and facial expressions (e.g., walking, lifting).
2. Smooth Muscles (Involuntary/Non-striated):
   • Location: Walls of internal organs like stomach, intestines, blood vessels.
   • Control: Involuntary (not under conscious control).
   • Appearance: Smooth (non-striated).
   • Function: Control internal bodily functions like food movement in digestion (peristalsis), blood vessel constriction, etc.
3. Cardiac Muscles (Heart Muscles):
   • Location: Only in the heart wall.
   • Control: Involuntary.
   • Appearance: Striated, branched, and interconnected.
   • Function: Responsible for the continuous, rhythmic pumping of blood throughout the body.

Q2: Explain the process of digestion in human beings with the help of a well-labelled diagram. (Note: Diagram cannot be generated, but detailed description is provided.)

Answer: Digestion is the process of breaking down complex food into simpler, absorbable forms. It occurs in the alimentary canal, a long tube, with the help of digestive juices.

1. Mouth: Mechanical digestion (chewing) breaks food. Saliva (containing salivary amylase) starts carbohydrate digestion.
2. Oesophagus: Food moves down by peristalsis. No digestion.
3. Stomach: Muscular walls churn food. Gastric juice (HCl and pepsin) kills bacteria and starts protein digestion. Food becomes chyme.
4. Small Intestine: Main site of digestion and absorption. Receives bile (from liver/gallbladder) for fat emulsification and pancreatic juice (from pancreas) for carbohydrate, protein, and fat digestion. Intestinal juice completes digestion. Villi absorb nutrients into blood.
5. Large Intestine: Absorbs water and some salts from undigested food. Forms feces.
6. Anus: Undigested waste (feces) is eliminated.

Associated Glands: Salivary glands, liver, pancreas, gastric glands, intestinal glands secrete digestive juices.

Q3: Give reasons for the following:

a) We should chew our food properly.

Answer: We should chew our food properly because chewing (mechanical digestion) breaks down large food particles into smaller ones. This increases the surface area for digestive enzymes to act more efficiently in the stomach and small intestine, leading to better and quicker digestion. It also makes swallowing easier.

b) We should drink plenty of water.

Answer: We should drink plenty of water because water is essential for the proper functioning of the digestive system and overall body health. It helps in the smooth passage of food through the alimentary canal, aids in the absorption of nutrients, and helps soften stool to prevent constipation. Water also acts as a medium for various chemical reactions in the body.

c) Muscle cramps occur due to insufficient oxygen supply.

Answer: Muscle cramps occur due to insufficient oxygen supply during strenuous exercise. When muscles work intensely without enough oxygen, they switch to anaerobic respiration. This process produces lactic acid as a byproduct. The accumulation of lactic acid in muscle cells causes pain, fatigue, and involuntary contractions, leading to muscle cramps.

References

1. Maharashtra State Board 7th Standard Science Textbook (Based on current curriculum for Chapter 12)
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