4. Give reasons.

(1) Food becomes acidic in the stomach.

Ans: Hydrochloric acid is a powerful acid that is present in the stomach. Once the food reaches our stomach, the acid is released and mixes with the food to help it get broken down into tiny bits and easily digested.

Hence, the food becomes acidic in the stomach.

(2) Cardiac muscles are said to be involuntary muscles.

Ans: Cardiac muscles are said to be involuntary because they are not controlled by our will. These muscles are found in the heart and are the only ones that work throughout life as involuntary, smooth muscles, without getting tired or fatigued.

(3) Intoxicating substances should not be consumed.

Ans: Consuming intoxicating, addictive substances can cause harm to our health. Tobacco, smoking cigarettes, and consuming alcohol are bad addictive habits that can cause cancer in various organs. Also, the functioning of the systems of the body is disturbed due to such habits. Therefore, we should not consume intoxicating substances.

(4) Your muscles should be strong and efficient.

Ans: We use muscles for various movements like talking, laughing, walking, jumping, throwing, and various other vital functions in our body. Hence, our muscles should be strong and efficient to do our day-to-day activities well and facilitate the smooth functioning of life processes.

5. Answer the following.

(a) How many types of muscles are there ? Which are those types ?

Ans: There are three types of muscles. They are;

1. Skeletal or voluntary muscles.

2. Smooth or involuntary muscles.

3. Heart or cardiac muscles.

(b) What causes the problem of acidity ? What is its effect on the body?

Ans: Hydrochloric acid is a powerful acid that is present in the stomach. If the level of this HCl exceeds its normal levels, it results in acidity, acid reflux, burning sensations in the throat and heart, headache, vomiting, rashes on the skin, etc. Exposure to higher levels of HCl for longer durations can also result in the development of peptic ulcers or ulcers in the stomach.

(c) Name the different types of teeth. What is the function of each type ?

Ans: There are four types of teeth, namely, incisors, canines, premolars and molars. 

The function of the incisors is mostly to bite into food. The function of canines is to tear food apart. The function of the premolar is to tear and crush the food, and the molar helps to grind, tear, and crush the food so that it can be swallowed without difficulty.

6. Sketch and label a diagram of the digestive system and describe it in your own words.

Ans: Digestion is the process by which food is converted into small molecules. The digestive system consists of digestive organs, the alimentary canal, digestive enzymes, and juices.

The digestive organs in humans are as follows:

1. Mouth

2. Salivary Glands 

3. Pharynx

4. Oesophagus

5. Pancreas

6. Stomach

7. Large Intestine

8. Small Intestine

9. Anus

(i) The food is taken into the mouth, where the salivary amylase enzyme helps in the primary breakdown of starch.

(ii) The food then passes to the stomach through the oesophagus, or food pipe. The gastric juices present in the stomach help in the partial breakdown of proteins into peptides.

(iii) The chyme formed in the stomach then enters the small intestine, where pancreatic juice, bile juice, and intestinal juice completely digest lipids into fatty acids and glycerol, proteins into amino acids, and carbohydrates into monosaccharides.

(iv) The small intestine helps in the absorption of food into the blood.

(v) The undigested food and other waste materials are transported to the large intestine, where they are excreted in the form of urine.