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Life Processes in Animals - Digestion in human beings

Grade 7CBSE

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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The human digestive system consists of the alimentary canal and associated glands. The main parts are the buccal cavity, oesophagus, stomach, small intestine, large intestine, rectum, and anus.

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Nutrition in humans is a holozoic process involving five steps: Ingestion, Digestion, Absorption, Assimilation, and Egestion.

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In the Buccal Cavity, teeth perform mechanical digestion. Saliva contains the enzyme salivary amylase which breaks down starch into sugar.

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The stomach secretes mucous, hydrochloric acid (HClHCl), and digestive juices. HClHCl creates an acidic medium (pH<7\text{pH} < 7) to kill bacteria and activate protein-digesting enzymes.

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The small intestine is the site of complete digestion. It receives secretions from the liver (bile juice for fat emulsification) and the pancreas (pancreatic juice for breaking down carbohydrates, proteins, and fats).

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Absorption occurs in the small intestine through finger-like projections called Villi, which increase the surface area for rapid absorption of digested food.

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The large intestine absorbs water and some salts from the undigested food material before the waste is egested through the anus.

📐Formulae

Starch→Salivary AmylaseSugar (Maltose)\text{Starch} \xrightarrow{\text{Salivary Amylase}} \text{Sugar (Maltose)}

Proteins→Pepsin / TrypsinAmino Acids\text{Proteins} \xrightarrow{\text{Pepsin / Trypsin}} \text{Amino Acids}

Fats→Bile JuiceFat Droplets (Emulsification)\text{Fats} \xrightarrow{\text{Bile Juice}} \text{Fat Droplets (Emulsification)}

Fats→LipaseFatty Acids+Glycerol\text{Fats} \xrightarrow{\text{Lipase}} \text{Fatty Acids} + \text{Glycerol}

Carbohydrates→Pancreatic AmylaseGlucose\text{Carbohydrates} \xrightarrow{\text{Pancreatic Amylase}} \text{Glucose}

💡Examples

Problem 1:

Explain why the stomach does not digest itself despite containing strong HClHCl and protein-digesting enzymes.

Solution:

The inner lining of the stomach secretes a thick layer of mucus.

Explanation:

The mucus acts as a protective barrier that prevents the hydrochloric acid (HClHCl) and the enzyme pepsin from coming into direct contact with the stomach wall, thereby preventing self-digestion or ulcers.

Problem 2:

Calculate the total number of teeth in an adult human if each jaw has 44 incisors, 22 canines, 44 premolars, and 66 molars.

Solution:

Total=2×(4+2+4+6)=32Total = 2 \times (4 + 2 + 4 + 6) = 32

Explanation:

In an adult human, there are two jaws (upper and lower). Each jaw contains 1616 teeth (44 incisors + 22 canines + 44 premolars + 66 molars), making a total of 3232 teeth.

Problem 3:

What is the role of the Liver in the digestion of fats?

Solution:

The liver secretes Bile juice, which is stored in the Gallbladder.

Explanation:

Bile juice performs emulsification, which is the process of breaking down large fat globules into smaller droplets. This increases the surface area for the enzyme lipase to act upon, making fat digestion more efficient.