CBSE Class 7 Science Human Digestive System Worksheet

1. PROJECT WORK: Make a project on any one topic. The project should be innovative. Collect information from internet, books, newspaper etc. It should be handwritten. Paste relevant pictures.

(i) Environmental degradation due to improper disposal of garbage.

(ii) Conservation of water & waste water management

2. MODEL MAKING (STATIC/WORKING)

(i) Nutrition in amoeba

(ii) Human digestive system

3. Do the given questions----

(i) How leguminous plants help in nitrogen fixation?

(ii) What are villi? What is their function & location?

(iii) Name the carbohydrate that can be digested by ruminants but not by humans. Give reason also.

(iv) Explain the general conditions required for photosynthesis.

(v) Why do we get instant energy from glucose?

(vi) Can we survive on grass. Why?

(vii) Why shearing of wool is done in summer only?

(viii) Why caterpillar shed their skin when they enter the pupa stage?

(ix) Differentiate b/w nutrition in amoeba & human beings.

(x) Name the four types of teeth & write their function.

Note : - The complete Holidays Homework must be submitted on 20th June, 2014 between 09:00am – 11:00am.

1. Food → Carbohydrates, Proteins and Fats. (Have Calorific value)
• Vitamins and Minerals (Non calorific value but important)
• Food source of energy → for growth and repair of tissues.
• The water → plays an important role in metabolism

2. Biomacromolecules →
• Not utilized by body as such so → Digestion needed

3. Digestion →
• Macromolecules broken down and converted into simple substances
• conversion of complex food substances to simple absorbable forms
• carried out by our digestive system by mechanical and biochemical methods.

4. The human digestive system consists of →
• The alimentary canal and
• The associated glands.

5. Alimentary Canal
• The alimentary canal begins with an anterior opening – the mouth, and it opens out posteriorly through the anus.

6. The mouth leads to the buccal cavity or oral cavity.

7. The oral cavity has
• a number of teeth and
• a muscular tongue.

8. Each tooth is embedded in a socket of jaw bone → Thecodont teeth

9. In human being forms two sets of teeth during their life → Diphyodont teeth
• a set of temporary milk or deciduous teeth
• a set of permanent or adult teeth.

10. An adult human has
• 32 permanent teeth
• Four different types → Heterodont dentition
✓ incisors (I), canine (C), premolars (PM) and molars (M).
• Dental formula → Arrangement of teeth in each half of the upper and lower jaw ( I, C, PM, M)
✓ In human → 2123 / 2123
• Enamel → The hard chewing surface of the teeth
✓ Helps in the mastication of food @ (Mechanical Process)

11. Tongue:
• Freely movable muscular organ
• Attached to the floor of the oral cavity by the frenulum.

1. Food → Carbohydrates, Proteins and Fats. (Have Calorific value)
• Vitamins and Minerals (Non calorific value but important)
• Food source of energy → for growth and repair of tissues.
• The water → plays an important role in metabolism

2. Biomacromolecules →
• Not utilized by body as such so → Digestion needed

3. Digestion →
• Macromolecules broken down and converted into simple substances
• conversion of complex food substances to simple absorbable forms
• carried out by our digestive system by mechanical and biochemical methods.

4. The human digestive system consists of →
• The alimentary canal and
• The associated glands.

5. Alimentary Canal
• The alimentary canal begins with an anterior opening – the mouth, and it opens out posteriorly through the anus.

6. The mouth leads to the buccal cavity or oral cavity.

7. The oral cavity has
• a number of teeth and
• a muscular tongue.

8. Each tooth is embedded in a socket of jaw bone → Thecodont teeth

9. In human being forms two sets of teeth during their life → Diphyodont teeth
• a set of temporary milk or deciduous teeth
• a set of permanent or adult teeth.

10. An adult human has
• 32 permanent teeth
• Four different types → Heterodont dentition
✓ incisors (I), canine (C), premolars (PM) and molars (M).
• Dental formula → Arrangement of teeth in each half of the upper and lower jaw ( I, C, PM, M)
✓ In human → 2123 / 2123
• Enamel → The hard chewing surface of the teeth
✓ Helps in the mastication of food @ (Mechanical Process)

11. Tongue:
• Freely movable muscular organ
• Attached to the floor of the oral cavity by the frenulum.
✓ an ascending,
✓ a transverse and
✓ a descending part.
• The descending part opens into the rectum which opens out through the anus.

17. THE WALL OF ALIMENTARY CANAL
• All most similar from oesophagus to rectum
• Possesses four layers namely
✓ Serosa,
✓ Muscularis,
✓ Sub-mucosa and
✓ Mucosa.

• Serosa →
✓ the outermost layer
✓ made up of a thin mesothelium (epithelium of visceral organs) with some connective tissues.

• Muscularis →
✓ formed by smooth muscles
✓ usually arranged into
1. an inner circular and
2. an outer longitudinal layer.
✓ An oblique muscle layer may be present in some regions.

• Submucosal layer →
✓ formed of loose connective tissues containing nerves, blood and lymph vessels.
✓ In duodenum, glands are also present in sub-mucosa.

• Mucosa →
✓ The innermost layer
✓ Lining the lumen of the alimentary canal
✓ This layer forms
1. irregular folds (rugae) in the stomach
2. small finger-like foldings called villi in the small intestine
✓ The cells lining the villi produce numerous microscopic projections → MICROVILLI
1. Giving a brush border appearance.
2. Increase the surface area enormously.
✓ Villi are supplied with a network of capillaries and a large lymph vessel called the LACTEAL.
✓ Mucosal epithelium has GOBLET CELLS
1. Goblet cells secrete mucus → help in lubrication
✓ Mucosa also forms glands in the stomach (gastric glands) and crypts in between the bases of villi in the intestine (crypts of Lieberkuhn).
✓ All the four layers show modifications in different parts of the alimentary canal.

18. Digestive Glands
• Associated with the alimentary canal
• These are →
✓ The salivary glands,
✓ The liver and
✓ The pancreas.

19. Salivary Glands →
• Three pairs of salivary glands,
✓ the parotids (cheek),
✓ the sub-maxillary/sub-mandibular (lower jaw) and
✓ the sublinguals (below the tongue).
• These glands situated just outside the buccal cavity secrete salivary juice into the buccal cavity. (Saliva is mainly produced)

20. Liver →
• Largest gland of the body
• Weighing about 1.2 to 1.5 kg in an adult human.
• It is situated
✓ in the abdominal cavity,
✓ just below the diaphragm
• Liver has two lobes.

• THE HEPATIC LOBULES →
✓ The structural and functional units of liver
✓ Containing hepatic cells arranged in the form of cords.
✓ Each lobule is covered by a thin connective tissue sheath called the GLISSON’S CAPSULE.
• The bile secreted by the hepatic cells passes through the hepatic ducts and is stored and concentrated in a thin muscular sac called the GALL BLADDER.
• The duct of gall bladder (CYSTIC DUCT) along with the hepatic duct from the liver forms the common bile duct.
• The bile duct and the pancreatic duct open together into the duodenum as the common hepato-pancreatic duct which is guarded by a sphincter called the SPHINCTER OF ODDI. 

21. Pancreas
• A compound elongated organ
• situated between the limbs of the ‘C’ shaped duodenum.
• Have both exocrine and endocrine portions
• The exocrine portion →
✓ secretes an alkaline pancreatic juice containing enzymes
• The endocrine portion →
✓ secretes hormones, insulin and glucagon.

22. DIGESTION OF FOOD
• Involves mechanical and chemical processes.
• The buccal cavity performs two major functions,
✓ Mastication of food and
✓ Facilitation of swallowing.
• The teeth and the tongue
✓ with the help of saliva
✓ masticate and mix up the food thoroughly.

• Role of 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.
• 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.
• The saliva secreted into the oral cavity contains electrolytes and enzymes, salivary amylase and lysozyme.
• The chemical process of digestion is initiated in the oral cavity by the hydrolytic action of the carbohydrate splitting enzyme, the salivary amylase.
• About 30 per cent of starch is hydrolysed here by this enzyme (optimum pH 6.8) into a disaccharide – maltose.
• LYSOZYME present in saliva acts as an antibacterial agent that prevents infections.
• The mucosa of stomach has gastric glands.
• Gastric glands have three major types of cells namely –
✓ Mucus neck cells which secrete mucus;
✓ Peptic or chief cells which secrete the proenzyme pepsinogen
✓ Parietal or oxyntic cells which secrete HCl and intrinsic factor

1. Intrinsic factor essential for absorption of vitamin B12
• The stomach stores the food for 4-5 hours.
• The food mixes thoroughly with the acidic gastric juice of the stomach by the churning movements of its muscular wall and is called the CHYME.
• The proenzyme pepsinogen, on exposure to HCl gets converted into the active enzyme pepsin, the proteolytic enzyme of the stomach.
• Pepsin converts proteins into proteoses and peptones (peptides).
• The mucus and bicarbonates present in the gastric juice play an important role in lubrication and protection of the mucosal epithelium from excoriation by the highly concentrated hydrochloric acid.
• HCl provides the acidic pH (pH 1.8) optimal for pepsins.

• RENNIN
✓ a proteolytic enzyme
✓ found in gastric juice of infants
✓ helps in the digestion of milk proteins.
• Small amounts of lipases are also secreted by gastric glands.
• Small intestine movements are generated by the muscularis layer
✓ These movements help in a thorough mixing up of the food with various secretions in the intestine → facilitate digestion.
• The bile, pancreatic juice and the intestinal juice are the secretions released into the small intestine.
• Pancreatic juice and bile are released through the hepato-pancreatic duct.
• The pancreatic juice contains inactive enzymes –
✓ trypsinogen,
✓ chymotrypsinogen,
✓ procarboxypeptidases,
✓ amylases, lipases and
✓ nucleases.
• Trypsinogen is activated by an enzyme, enterokinase, secreted by the intestinal mucosa into active trypsin, which in turn activates the other enzymes in the pancreatic juice.
• The bile released into the duodenum

• The bile contains →
✓ bile pigments (bilirubin and bili-verdin),
✓ bile salts,
✓ cholesterol and
✓ phospholipids

• THE BILE → ENZYMES ABSENT.
• Bile helps in emulsification of fats,
✓ i.e., breaking down of the fats into very small micelles.
• Bile → activates lipases.
• The intestinal mucosal epithelium has goblet cells which secrete mucus.

• INTESTINAL JUICE OR SUCCUS ENTERICUS →
✓ The secretions of the brush border cells of the mucosa along with the secretions of the goblet cells
✓ This juice contains a variety of enzymes like disaccharidases (e.g., maltase), dipeptidases, lipases, nucleosidases, etc.
• The mucus along with the bicarbonates from the pancreas protects the intestinal mucosa from acid as well as provide an alkaline medium (pH 7.8) for enzymatic activities. Sub-mucosal glands (Brunner’s glands) also help in this.
• Proteins, proteoses and peptones (partially hydrolysed proteins) in the chyme reaching the intestine are acted upon by the proteolytic enzymes of pancreatic juice
• Fats are broken down by lipases with the help of bile into di-and monoglycerides.
• Nucleases in the pancreatic juice acts on nucleic acids to form nucleotides and nucleosides
• The enzymes in the succus entericus act on the end products of the above reactions to form the respective simple absorbable forms.
• These final steps in digestion occur very close to the mucosal epithelial cells of the intestine.
• The simple substances thus formed are absorbed in the jejunum and ileum regions of the small intestine.
• The undigested and unabsorbed substances are passed on to the large intestine.

• NO SIGNIFICANT DIGESTIVE ACTIVITY OCCURS IN THE LARGE

INTESTINE.
• The functions of large intestine are:
✓ Absorption of some water, minerals and certain drugs;
✓ Secretion of mucus which helps in adhering the waste (undigested) particles together and lubricating it for an easy passage.
• The undigested, unabsorbed substances called faeces
• Faeces enters into the caecum of the large intestine through ileocaecal valve, which prevents the back flow of the faecal matter.
• Faeces temporarily stored in the rectum till defaecation.

23. Control Of Digestive System:
• Under neural and hormonal control
• The sight, smell and/or the presence of food in the oral cavity can stimulate the secretion of saliva.
• Gastric and intestinal secretions are also, similarly, stimulated by neural signals.
• The muscular activities of different parts of the alimentary canal can also be moderated by neural mechanisms, both local and through CNS.
• Hormonal control of the secretion of digestive juices is carried out by local hormones produced by the gastric and intestinal mucosa.

24. ABSORPTION OF DIGESTED PRODUCTS
• Absorption→ end products of digestion pass through the intestinal mucosa into the blood or lymph.
• It is carried out by passive, active or facilitated transport mechanisms.
• Simple diffusion → Small amounts of monosaccharides like glucose, amino acids and some electrolytes like chloride ions
• Facilitated transport → Some substances like glucose and amino acids are absorbed with the help of carrier proteins.
• Transport of water depends upon the osmotic gradient.
• Active transport → occurs against the concentration gradient and hence requires energy. e.g. amino acids, monosaccharides like glucose, electrolytes like Na+ are absorbed into the blood by this mechanism.
• Fatty acids and glycerol being insoluble, cannot be absorbed into the blood. They are first incorporated into small droplets called MICELLES which move into the intestinal mucosa.
• They are re-formed into very small protein coated fat globules called the CHYLOMICRONS which are transported into the lymph vessels (lacteals) in the villi.
• These lymph vessels ultimately release the absorbed substances into the blood stream.
• Absorption of substances takes place in different parts of the alimentary canal, like mouth, stomach, small intestine and large intestine.

• HOWEVER, MAXIMUM ABSORPTION OCCURS IN THE SMALL INTESTINE.

25. The absorbed substances finally reach the tissues which utilise them for their activities. This process is called ASSIMILATION.

26. DEFAECATION →
• The egestion of faeces to the outside through the anal opening
• Faeces in the rectum initiate a neural reflex
• a voluntary process and
• is carried out by a mass peristaltic movement.

27. DISORDERS OF DIGESTIVE SYSTEM
• The inflammation of the intestinal tract is the most common ailment due to bacterial or viral infections.
• The infections are also caused by the parasites of the intestine like tapeworm, roundworm, threadworm, hookworm, pin worm, etc.

• JAUNDICE:
✓ The liver is affected,
✓ skin and eyes turn yellow due to the deposit of bile pigments.

• VOMITING:
✓ ejection of stomach contents through the mouth.
✓ This reflex action is controlled by the vomit centre in the medulla.

• DIARRHOEA:
✓ The abnormal frequency of bowel movement
✓ increased liquidity of the faecal discharge
✓ It reduces the absorption of food.

• CONSTIPATION:
✓ the faeces are retained within the rectum
✓ the bowel movements occur irregularly.

• INDIGESTION:
✓ the food is not properly digested
✓ leading to a feeling of fullness.
✓ The causes of indigestion are inadequate enzyme secretion, anxiety, food poisoning, over eating, and spicy food.