NCERT Solutions Science Biology Notes for Class 11
Biology notes for class 11 : Takshila Learning focuses on online coaching classes by our experienced faculty to the students. We provide Biology notes, Chemistry notes, Physics notes as per the CBSE syllabus, last year question papers for board exams preparation. Our sole objective is to provide quality and result oriented education as well as guidance to the youth of the country in order to achieve their goals. In this article, the following topic ‘Alimentary Canal and Digestion’ from the unit Human Physiology of Biology class 11 syllabus is discussed.
Biology notes for class 11 – Alimentary canal and digestion
Every living organism needs energy for the proper functioning of their body. The ultimate source of energy is the sun. Plants trap the energy from the sun (solar energy) with the help of chlorophyll(a green pigment present in the green leaves of many plants) andsynthesise carbohydrates from carbon di oxide and water. Animals are directly or indirectly are dependent upon plants for their energy needs, the organic compounds synthesized by the plants are the final source of energy in animals.
The food materials consumed by the animals are carbohydrates, proteins, fats, minerals, and vitamins. These food materials cannot be utilized by our body in their original form. They have to be broken down and converted into simple and soluble substances that can be used up by our body.
This process of conversion of complex food substances into simple and soluble forms is called digestion.
During the digestion process:
- Carbohydrates get broken into simple sugars such as glucose.
- Fats into fatty acids and glycerol.
- Proteins into amino acids.
The digestion takes place in the alimentary canal or the digestive tract, also called as the digestive system.
The Alimentary canal
The food passes through a continuous canal called alimentary canal. The canal can be divided into various compartments: (1) Mouth (2) foodpipe or oesophagus, (3) stomach, (4) small intestine, (5) large intestine ending in the rectum and (6) the anus.
The alimentary canal in human beings measures about 8 to 10 meters in length.
The food is taken in through the mouth. The process of taking food into the body is called ingestion. The digestion of food begins in the mouth.The mouth has an oral cavity; it contains gums, teeth, a tongue and muscles. The hard surface of the teeth, made up of enamel (Enamel is the hardest substance in the human body and contains the highest percentage of minerals), helps in the mastication or chewing of food.
Our mouth has the salivary glands which secrete saliva. The saliva breaks down the starch into sugars. The saliva secreted into the oral cavity contains electrolytes (Na+, K+, Cl–) and enzymes,salivary amylase, and lysozyme. Salivary amylase acts upon the starch. About 30 % of starch is hydrolysed here by this enzyme (optimum pH 6.8) into a disaccharide.Mucus in saliva helps in lubricating and adhering the masticated food particles into a bolus. The bolus is then conveyed into the pharynx and then into the oesophagus by swallowing or deglutition.
Lysozyme present in saliva acts as an antibacterial agent that prevents infections. The tongue is a muscular organ that has taste buds. The taste buds help in identifying the taste of the food, like sweet, sour, bitter, or salty.
The oral cavity leads into pharynx which serves as a common passage for food and air. The pharynx connectsoesophagus and the trachea (wind pipe).A cartilaginous flap called epiglottis prevents the entry of food into the wind pipe.
The bolus passes into the food pipe or oesophagus. The oesophagus is a thin, long tube which extends posteriorly passing through the neck, thorax (the part of the body of a mammal between the neck and the abdomen) and diaphragm (separates the thorax from the abdomen in mammals) and leads to a ‘J’ shaped bag like structure called stomach.
The bolus further passes down through the oesophagus by successive waves of muscular contractions called peristalsis. The gastro-oesophageal sphincter controls the passage of food into the stomach.
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The inner lining of the stomach secretes mucous, hydrochloric acid, and digestive juices.
- The mucous protects the lining of the stomach.
- The acid kills many bacteria that enter along with the food and makes the medium in the stomach acidic.
- The digestive juices break down the proteins into simpler substances.
A muscular sphincter (gastro-oesophageal) is a muscular ring which regulates the opening of the oesophagus into the stomach.
The stomach, located in the upper left portion of the abdominal cavity, has three major parts – a cardiac portion into which the oesophagus opens a fundic region and a pyloric portion which opens into the first part of small intestine.
The small intestine is divided into three regions, a ‘C’ shaped duodenum, a long coiled middle portion jejunum and a highly coiled ileum. The opening of the stomach into the duodenum is guarded by the pyloric sphincter. Ileum opens into the large intestine. The small intestine is highly coiled and is about 5 meters long. It receives secretions from the liver and the pancreas. Besides, its wall also secretes juices. The digested food passes into the blood vessels in the wall of the intestine. This process is called absorption. The inner walls of the small intestine have thousands of finger-like outgrowths. These are called villi (singular villus). The villi increase the surface area for absorption of the digested food. Villi are supplied with a network of capillaries and a large lymph (colourless fluid containing white blood cells) vessel called the lacteal.
The absorbed substances are transported via the blood vessels to different organs of the body where they are used to build complex substances such as the proteins required by the body. This is called assimilation. In the cells, glucose breaks down with the help of oxygen into carbon dioxide and water, and energy is released. The food that remains undigested and unabsorbed then enters into the large intestine.
The large intestine is wider and shorter than the small intestine. It is about 1.5 metre in length. Its function is to absorb water and some salts from the undigested food material. The remaining waste passes into the rectum and remains there as semi-solid faeces. The faecal matter is removed through the anus from time-to-time. This is called egestion.
Ingestion → Digestion → Absorption → Assimilation → Egestion
It consists of caecum, colon and rectum. The Caecum is a small blind sac which hosts some symbiotic micro-organisms.