Biology Class 9th Notes Chapter 8 Nutrition Mardan board

Make an informal reading practice for students exercising the KPK board exams in the Biology Class 9th Notes Chapter 8 Nutrition Mardan board Book Note of perfect24u.

Chapter 8 Nutrition Mardan board

Q.1) List all the parts(in order)of the human digestive system through which food passes.

Parts of human digestive system through which food passes:

1- Oral cavity
2- Pharynx
3- Oesophagus
4- Stomach
5- Small intestine (duodenum, jejunum, and ileum)
6- Large intestine (caecum, colon, and rectum)

Q.2) How is food mechanically broken down during digestion?

  The digestion of food is completed by both mechanical digestion and chemical digestion. In mechanical digestion, food is physically broken down into smaller pieces by the acts of chewing (mouth) and churning (stomach).
1) Chewing:
  The break down of food by the grinding action of teeth is called chewing. After chewing, the food enters the stomach from the oesophagus.
2) Churning:
  The walls of the stomach are thick and muscular which physically squeeze and mix the food with strong digestive juices (‘churning’). Once the food enters the stomach, its walls contract to churn (break down) the food into small particles. This churning of food is called “mechanical digestion”. 

Q.3) How does the digestion and absorption of fats differ from the digestion and absorption of carbohydrates and proteins.

i) Digestion and absorption of fats: 

  Fats may be in the form of solid such as animal fats or in liquid form such as cooking oil.

  • Bile is secreted from the liver that acts on fats. It breaks larger fats into smaller droplets. The process is called emulsification.
  • Pancreatic juice contains lipase that digests the fats and converts it into fatty acids and glycerol.
  • The fats are converted into glycerol and fatty acids which are absorbed in the intestine by lacteals and join the bloodstream.

ii) Digestion and absorption of carbohydrates:
  The following different secretions act on carbohydrates:

  • Salivary glands secrete saliva that contains amylase and maltase that digest the starch and glycogen into maltose.
  • Pancreatic amylase acts on starch, which has escaped the action of salivary amylase and converts into simple sugars.
  • Intestinal juice breaks down undigested carbohydrates into simple sugars. absorbed in small intestine.
  • These simple sugars are absorbed into villi present in small intestine.

iii) Digestion and absorption of proteins:

  • Pepsin breaks large proteins into shorter chains of amino acids called peptides.
  • Pancreatic juice contains trypsin that acts on proteins and converts polypeptides into dipeptides and amino acids.
  • Absorption of amino acid occurs in the small intestine by villi.

Q.4) Enlist five environmental hazards related to the use of fertilizers.

Environmental hazards:

  The enivronmental hazards related to the use of fertilizers are:

  • They increase the soil salinity and acidity.
  • Storage and application of some nitrogen fertilizers may cause emissions of the greenhouse gas nitrous oxide.
  • The major risk to groundwater quality from the nutrient application is        NOleaching to groundwater sources. This can harm human and animal health.
  • The major risk to surface water is increased number of algae growing on the surface of the water (eutrophication).

Q.5) What is malnutrition? Why is it considered to be a health hazard?


“Taking a diet in which the required nutrients are not in enough quantity or over the required quantity is called malnutrition”.
 Undernutrition is a consequence of consuming a low amount of essential nutrients while over nutrition means taking too many nutrients. Severe malnutrition may result in death, heart diseases, constipation, and obesity.
 Health hazard:
Protein-energy Malnutrition:
 Two important diseases associated with PEM are marasmus and kwashiorkor.
b) Marasmus:
 They suffer from low body temperature and anaemia due to very low intake of carbohydrates, proteins, and fats. Marasmus can be treated by adding all nutrients to the diet. In severe cases, this disease may lead to death.
c) Kwashiorkor:
Kwashiorkor is a more severe form of PEM. It occurs in children or adults due to inadequate intake of proteins. In severe cases, this disease may also lead to death.
ii) Mineral Deficiency Diseases (MOD):
Mineral deficiencies occur when a person’s mineral intake consistently falls below the recommended requirement. Mineral deficiencies can lead to a variety of diseases e.g. anaemia, goiter, osteoporosis, and rickets.
iii) Over intake of Nutrients (OIN):
The over-consumption of high-calorie diet leads to overweight and obesity. Obese people may suffer from hypertension. liver, renal and heart disorders. 

Q.6) Discuss the role of dietary fiber in a balanced diet.

Role of dietary fiber in balanced diet:

  • Dietary fibres prevent constipation by stimulating the movement of intestinal muscles.
  • Dietary fiber speed up the passage of food through the gut.
  • It reduces the risk of constipation and colon cancer
  • It also absorbs cholesterol and so controls the blood cholesterol level.

Long Questions

Q.1) Overtake of nutrition can lead to serious health disorders. Evaluate the statement by giving examples.

 Over intake of Nutrients (OIN):
   The over-consumption of high-calorie diet leads to overweight and obesity.
Health disorders due to overtake of nutrition:

  • Obese people may suffer from hypertension, liver, renal and heart disorders.
  • Excessive fat consumption can be fatal. Some fats get deposited on the inner walls of the arteries causing arteriosclerosis. It leads to cardiovascular diseases and other complications like hypertension, diabetes etc.
  • Similarly, over intake of vitamin D causes nausea, fatigue, vomiting, renal damage etc. Over-intake of vitamin A leads to dry itchy skin, painful swelling of legs and hands, enlargement of spleen etc.

Q.2) List down major enzymes in the human digestive systems. Elaborate their role in digestion.

Major enzymes in human digestive system:

  The human digestive system has many enzymes which help in digestion. They are:

  • Saliva contains enzymes like amylase and maltase. These enzymes hydrolyze the starch and glycogen into maltose. Maltase reduces maltose into glucose.
  • Gastric juice of stomach contains ‘pepsin’ enzyme which converts proteins into peptides.
  • The pancreatic juice contains the enzymes like trypsin, amylase and lipase. Trypsin acts on peptides and converts them into further small peptides. Pancreatic amylase acts on the starch and converts it into maltose. Lipase acts on emulsified fats and converts them into fatty acids and glycerol.
  • The glands of ileum secrete intestinal juice which breaks down the leftover undigested proteins, carbohydrates, and fats.

Q.3) Explain the importance of water in the human body.

Importance of water:
   Water is the most abundant substance in the human body. We have about 70% water in our body. Water performs many functions. Some are the following:

  • In our bodies, metabolic reactions can only occur when the reactants are dissolved. Water act as the solvent for reactants of metabolism.
  • The water present in blood dissolves oxygen from lungs. In this way, oxygen is transported to cells. Carbon dioxide is transported from cells to lungs in the same way. Similarly, water carries nutrients from the digestive system to all cells of the body.
  • Almost every cell in the body is bathed in interstitial fluid which is almost entirely water.
  • Water acts as reactant in many metabolic reactions e.g. in hydrolysis reaction.
  • Water also acts as a lubricating medium. It is a major part of mucous and other lubricating fluids.
  • Water is the flushing medium for the removal of toxic chemicals e.g. urea through kidneys.
  • Water acts as a stabilizer of body temperature. It absorbs and releases heat very slowly.

Q.4) Explain the role of oral cavity and pharynx in the digestive system.

A) Role of the oral cavity (Buccal Cavity):

  The oral cavity is the first part of the alimentary canal that receives the food. In the oral cavity, there are three important organs:
i) Teeth
ii) Tongue
iii) Salivary glands
i) Teeth:
   The teeth of mammals are specialized to perform particular functions. Among the permanent teeth, the incisor teeth are adapted for cutting orbiting. The canine teeth are adapted for tearing while the premolars and molars are adapted for grinding and mastication of food. This is called the mechanical digestion of food.
ii) Tongue:
  The tongue contains taste buds that can help us to sense the taste of food. It also helps during the grinding of food by keeping it between the teeth. It also helps in the swallowing process.
iii) Salivary glands:
  There are three pairs of salivary glands in the oral cavity. These glands secrete saliva. Saliva is a mixture of water, mucous, salts, and a digestive enzyme. Mucus lubricates the food. The salt sodium bicarbonate present in saliva kills the germs and bacteria and makes the food alkaline. The enzyme called amylase begins the chemical digestion of starch and glycogen. It breaks starch and glycogen into maltose. After the mechanical and partial chemical digestion, the food turns into the form of a ball called a bolus.
B) Role of the pharynx:
   The oral cavity opens into the pharynx. The pharynx is present at the back of the oral cavity. Food in the form of the bolus is pushed back by the action of the tongue.
   The downward movement of the food from the buccal cavity is called swallowing. The beginning of the swallowing is voluntary but once the food reaches the back of the oral cavity, swallowing becomes an automatic or reflex action. The food is forced into and down the esophagus by peristalsis.

Read more: 9th Class Biology Notes Chapter 1 to 5 For Mardan Board

Q.5) Describe the structure of a villus, including the roles of capillaries and lacteals.

Structure of villi:

   The structure of small intestine is in accordance with its absorptive function. The inner lining of the small intestine has large folds. These folds have millions of finger-like projections called villi (Singular: villus). The outer epithelium of villus is made of a single layer of cells. The epithelium of villi also contains microscopic projections called microvilli.
   The microvilli greatly increase the surface area of the villus. Inside villus, there are blood capillaries and a small lymphatic vessel called lacteal.  
Role of capillaries and lacteals in villi:

  • After the complete digestion of food, the end products i.e. amino acids, simple sugars, glycerol, and fatty acids are absorbed from the small intestine into the circulatory system.
  • During absorption, the simple sugars, amino acids, vitamins, minerals, and water enter the blood capillaries in the villi.
  • These capillaries open in the hepatic portal vein, which carries the nutrients to the liver.
  • Fatty acids and glycerol are absorbed Into the lacteals which pour them into the bloodstream.
Describe the structure of a villus, including the roles of capillaries and lacteals

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