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Two types of neurons are present in the body.

This happens in alveoli. The pressure difference between air in alveoli and gases in capillaries facilitates removal of carbon dioxide from blood and addition of oxygen to blood.

Gall bladder.

Functions of nose: 

• Provides passage to air. 
• Traps dust particles from air. 
• Moistens the air entering the respiratory system. 
• Gives sense of smell.

Correct answer is (c) Medulla

Bile enzyme is produced by the liver.

Human beings get two sets of teeth in their lifetime. This phenomenon is called diphyodont.

The cartilaginous flap at the entry of windpipe and foodpipe is called epiglottis.

The small intestine can be divided into three portions, viz. duodenum, jejunum and ileum. 

Duodenum: This is the anterior- most portion of small intestine and is connected to pylorus. All the digestive juices come into duodenum and digestion of food takes place here. 

Jejunum: This is the middle portion of small intestine. Absorption of most of the digested food takes place in jejunum. Absorption is carried by specialized cells which are called enterocytes. 

Ileum: This is the last portion of small intestine and is connected to large intestine. Some of the substances which are not absorbed by jejunum are absorbed in this portion, e.g. bile salts and vitamins.

This is a vestigial organ at the junction of small intestine and large intestine.

Duodenum, Jejunum and Ileum.

Stomach can be divided into three parts which are as follows: 

Cardia: This part is at the left and is connected to the oesophagus. 

Fundus: This part lies between cardia and pylorus. 

Pylorus: This part opens into small intestine.

Rennin is an enzyme to digest milk protein.

A ductless gland is called endocrine gland.

The tail-like structure in a neuron is called axon.

The functional unit of nervous system is called neuron. It is unicellular structure.

Cerebellum, pond and medulla.

(c) Midbrain

Pepsin enzyme is produced in stomach and digests protein.

Hydrochloric acid.

Large intestine is divided into Four parts.

Pylorus part of stomach is connected to small intestine.

(a) Duodenum

Following changes take place in adolescent boys: 

• Shoulders become broad. 
• Body becomes muscular. 
• There is a sudden increase in height. 
• Voice becomes deeper. 
• Facial hairs appear. 
• Hairs grow under armpit and in pubic area

Salivary gland.

Correct answer is (c) Rennin

Progesterone and estrogen.

Liver is the largest gland in the human body. It is situated below the diaphragm and its major portion is towards right side. Liver is composed of about 100,000 hexagonal functional units which are called liver lobules. Liver produces bile which goes to the gall bladder through hepatic duct system. From gall bladder, bile goes to the small intestine through hepatopancreatic duct.

This is a J-shaped structure which lies between oesophagus and duodenum. The stomach lies towards left in the abdominal cavity and just behind the diaphragm. This is a flexible organ which can accommodate up to three litres of food. Stomach can be divided into three parts, viz. cardia, fundus and pylorus. 

Functions of stomach are as follows: 

• Churning the food into fine paste. 
• Killing any germs in food. 
• Partial digestion of food.

Following are the three types of salivary gland: 

Parotid gland 

Sub-mandibular gland 

Sublingual gland

Salivary gland is situated in the buccal cavity. There are three types of salivary glands, viz. parotid, submandibular and sublingual. Parotid glands are situated near cheeks. Submandibular glands are situated near jaws. Sublingual gland is situated below tongue. Salivary gland is composed of glandular epithelium and is exocrine in function.

Structure of nephrons: It consists of a Bowman’s capsule in which glomerulus is present (cluster of capillaries). The afferent artery brings the impure blood to nephron. The cup shaped structure (Bowman’s capsule) form a tubular part of nephron which leads to collecting duct. 

Working of Nephron:

1. Filtration: The renal artery or afferent artery is wider and slowly it becomes a narrow tube in the glomerulus. Due to difference in the width, pressure difference is caused and water with dissolved impurities are squeezed out from the tube. It is collected in the Bowman’s capsule which is cup-like structure and passes into the tube. 

2. Reabsorption: The above filtrate passes through the tubule where the major amount of water, glucose, amino acids are selectively reabsorbed by the capillaries which are surrounding the tubule. 

3. Urine formation: The water and impurities which is not reabsorbed is sent to a collecting duct. This filtrate contains more of dissolved nitrogenous wastes i.e. urea and hence it is termed as urine. From here the urine enters the ureter and is collected in urinary bladder.