9: Module 7- The Digestive System - Biology

9: Module 7- The Digestive System - Biology

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9: Module 7- The Digestive System

9: Module 7- The Digestive System - Biology

School Biology Notes: Introduction to cell organisation

CELL ORGANISATION - an introduction

organisation of cells => tissues => organs => organ systems

Doc Brown's school biology revision notes: GCSE biology, IGCSE biology, O level biology,

US grades 8, 9 and 10 school science courses or equivalent for

14-16 year old students of biology

Introduction and reminders

Many organisms consist of a huge number of cells. ( cell structure )

But, how are they organised to form e.g. a fully functioning animal?

Cells are the building blocks of multicellular organisms.

In the process called differentiation, cells become specialised to carry out a particular function.

Differentiation happens during the growth and development of a multicellular organism.

Specialised cells form tissues, which can connect to form organs and these connect together to form organ systems.

Large multicellular organisms like animals have different organ systems for exchanging and transporting substances.

A tissue is a group of similar specialised cells that work together to carry out a particular function.

Obviously the cells must be connected in someway AND there may be different types of cell cooperating with each other.

Examples of tissues

(a) Epithelial tissue

Layers of epithelial cells make up epithelial tissue which covers a lot of the body, including the inside of the gut, including the stomach.

muscle tissue

Muscular tissue must have the ability to contract (and relax) to move whatever the tissue is attached to e.g. bones.

(c) Glandular tissue

Glandular tissues are production sites for enzymes and hormones - important secretions for the efficient functioning of organs.

An organ is a group of different specialised tissues that work together to perform specific functions.

Examples of organs

(a-c) The stomach

The stomach is an organ that uses all of the three tissues mentioned above.

The inside and outside lining of the stomach is made from epithelial tissue - it holds the stomach together and contains food starting to be digested.

The wall of the stomach has attached muscle tissue to enable it to churn up food prior to digestion.

Glandular tissue makes digestive juices to breakdown the food at the start of the digestion process.

(Other examples of glandular tissue structures include the pituitary gland, the adrenal gland and the thyroid gland.)

Organ systems

An organ system is a group of organs that work together to perform overall a more complex function - each organ performs its own function as part of the overall process

Examples of organ systems

The digestive system of mammals is an excellent example of an organ system - this organ system breaks down food and absorbs the molecules and ions.

It consists of a whole series of organs and glands working together.

(1) The pancreas and salivary glands produce digestive juices containing enzymes to break down food.

(2) The stomach and small intestine digest the food - nutrients pass from the small intestine to the blood stream - absorption of soluble food molecules.

(3) The liver produces bile that helps digestion in the small intestine.

(4) The large intestine absorbs water from undigested food to leave the waste as faeces.

See Enzymes - structure, function, optimum conditions, investigation experiments for more on digestive enzymes

Other organ systems in the human body

The human body contains 11 important organ systems, including the circulatory, respiratory, digestive (described above), excretory, nervous and endocrine systems. They also include the immune, skeletal, muscle and reproductive systems.

All these systems work closely together to maintain a fully functioning healthy human body.

The failure of any of the organ systems can lead to a serious, and potential fatal, medical condition.

e.g. typical animal example:

epithelial cell ==> epithelial tissue ==> stomach lining ==> upper part of digestive system

Some learning objectives for this page

Know that the cells of multicellular organisms may differentiate and become adapted for specific functions - specialised cells.

Know that tissues are aggregations of similar cells and organs are aggregations of tissues performing specific physiological functions eg heart and liver.

Know that organs are organised into organ systems, which work together to form organisms.

Know that large multicellular organisms develop systems for exchanging materials.

Know that during the development of a multicellular organism, cells differentiate so that they can perform different functions.

The specialised cells form tissues, one or more types of tissue are structured to form organs and two or more organs can work together in an organ system.

Bigger multicellular systems e.g. animals like mammals have several different organ systems for absorbing (e.g. gut), transporting (e.g. blood system) and exchanging materials (e.g. lungs).

You should develop an understanding of size and scale in relation to cells, tissues, organs and organ systems.

Know that a tissue is a group of specialised cells with similar structure and carry out a particular function.

Know that examples of tissues include:

muscular tissue, which can contract to bring about movement eg contraction and relaxation to move limbs

glandular tissue, which can produce and secrete substances such as enzymes to enable chemical reactions and hormones to control certain functional features of an organism,

epithelial tissue, which covers some parts of the body including the inside of the gut and the skin.

General HUMAN BIOLOGY revision notes

Keywords for gcse biology revision notes on tissue types organ systems: GCSE 9-1 biology biological science IGCSE revision notes tissue types organ systems KS4 biology Science notes on tissue types organ systems GCSE biology guide notes on tissue types organ systems for schools colleges academies science course tutors images pictures diagrams for tissue types organ systems science revision notes on tissue types organ systems for revising biology modules biology topics notes to help on understanding of tissue types organ systems university courses in biological science careers in science biology jobs in the pharmaceutical industry biological laboratory assistant apprenticeships technical internships in biology USA US grade 8 grade 9 grade10 AQA GCSE 9-1 biology science notes on tissue types organ systems GCSE notes on tissue types organ systems Edexcel GCSE 9-1 biology science notes on tissue types organ systems for OCR GCSE 9-1 21st century biology science notes on tissue types organ systems OCR GCSE 9-1 Gateway biology science notes on tissue types organ systems WJEC gcse science CCEA/CEA gcse science gcse biology revision notes on tissue types organ systems

Selina Concise Biology Class 9 ICSE Solutions Digestive System provides step by step solutions for Selina Concise ICSE Solutions for Class 9 Biology Chapter 9 Chapter 11 Digestive System. You can download the Selina Concise Biology ICSE Solutions for Class 9 with Free PDF download option. Selina Publishers Concise Biology for Class 9 ICSE Solutions all questions are solved and explained by expert teachers as per ICSE board guidelines.

Selina ICSE Solutions for Class 9 Biology Chapter 11 Digestive System

  1. (iii) stomach into intestine
  2. (i) HCl and pepsin
  3. (iii) colon
  4. (iii) Premolars, molars – Grinding

Solution B.1.

Solution B.2.

The two reflexes which occur when a person chews and swallows food are:

  1. Reflex when a person chews – Secretion of saliva
  2. Reflex when a person swallows – Tongue presses upward and back against the roof (palate)

Solution B.3.

(ii) Both the statements are wrong. Small intestine is longer (7 metres) than large intestine (1.5 metres). Also, large intestine is so called because of its width which is larger than that of small intestine.

Solution C.1.

Digestion is the process of breaking down complex food materials into simpler substances by the action of enzymes.

Need for a digestive system:

  1. Large complex molecules like carbohydrates, proteins and lipids need to be broken down to simpler molecules. These simpler molecules can then be absorbed and utilized by the body.
  2. The breaking down of complex food molecules into their simpler form is possible only through the process of digestion.
  3. During digestion, large complex macromolecules present in food are converted into small simpler molecules, which can be simplified in different compartments of digestive system only.

Solution C.2.

Starch Maltose
Proteins Small peptides and amino acids
Fats Fatty acids and glycerol

Solution C.3.

Vitamins are used in their original form by the cells. They do not require digestion. They are either water soluble or fat soluble, hence no enzyme is required to digest vitamins. They are absorbed directly from the digestive tract, transported by blood to the cells, and the cells absorb and use them whenever they need. Besides, vitamins themselves act as catalysts or enzymes in essential chemical reactions that take place in the body.

Solution C.4.

It is very important to chew our food thoroughly as chewing of food helps to break down complex food materials into simpler substances. The act of chewing stimulates the salivary glands to release saliva. The saliva helps to moisten the food and form bolus, which can be swallowed easily. Saliva also contains special enzymes that help to break down carbohydrates.

Solution C.5.

Rectum acts as a temporary storage site for undigested food. It has voluntary smooth muscles that remove the faeces out of the body through the anus.

Solution C.6.

Roughage is a dietary fibre that largely consists of cellulose. It cannot be digested by our body as our body does not contain cellulose-digesting enzymes.

Examples of roughage:

Solution C.7.

Adaptations of ileum for the absorption of digested food:

  1. Very long to provide more surface area for absorption
  2. Presence of large number of villi to further increase the surface area

Solution C.8.

Functions of hydrochloric acid:

  1. It gets mixed with food and kills the bacteria present in food.
  2. It activates pepsin to act on proteins.

Solution D.1.

Vegetarian menu for dinner:

Foodstuffs Weight (gm/ml)
Cereals 320
Pulses 70
Green leafy vegetables 100
Root vegetables 75
Fruits 75
Milk 600
Fat and oil 30
Brown sugar and jaggery 30

Solution D.2.

Main characteristics of an enzyme:

  1. It is a protein and therefore, gets destroyed by heating.
  2. It acts only on one kind of substance called the substrate. So, it is very specific.
  3. It acts as a catalyst, so it can be used again and again.
  4. It only affects the rate of a chemical reaction and always speeds up the reaction.
  5. It always forms the same end products from the fixed substrate.
  6. It acts best only at a particular pH.
  7. It acts best within a narrow temperature range, usually between 35°C-40°C.

Solution D.3.

The small intestine is the most important organ of the digestive system as it serves both, for digestion and absorption. It receives two digestive juices the bile and the pancreatic juice in the duodenum. These two juices virtually complete the digestion of starch, proteins, carbohydrates, etc. After the breakdown of food, the small intestine absorbs simple substances such as glucose, amino acids, etc.

Solution D.4.

Liver is an important organ in our body as it serves the following functions:

  • Production of bile
  • Control of blood sugar levels
  • Control of amino acid levels
  • Synthesis of foetal red blood cells
  • Produce fibrinogen and heparin
  • Regulate blood volume
  • Destroy dead red blood cells
  • Store vitamin and minerals
  • Excrete toxic and metallic poisons
  • Produce heat
  • Detoxification

Solution D.5.

(i) Peristalsis: Peristalsis is the rhythmic contraction and relaxation of the muscles of the alimentary canal that pushes the food along the gut.
(ii) Omnivore: Omnivores are organisms that consume both plants and animals.
(iii) Pylorus: Pylorus is the passage at the lower end of the stomach that opens into the duodenum.
(iv) Kilocalorie: A kilocalorie is a unit of energy. It is the energy required to raise the temperature of 1 kg of water by 1 Celsius.
(v) Basal metabolic rate: Basal metabolic rate refers to the minimum amount of energy in the form of calories that our body requires to complete its normal functions.

Solution D.6.

Stomach Pepsin Acts on proteins and converts it into polypeptides
Small intestine
Duodenum Amylopectin Acts on starch and converts it into maltose
Trypsin Acts on remaining proteins, proteoses and peptones to produce peptides and amino acids
Ileum Erepsin Acts on proteins and polypeptides and converts them into small peptides and amino acids
Sucrase Acts on sucrose and converts it into glucose and fructose
Lactase Acts on lactose and converts it into glucose and galactose

Solution D.7.

Importance of water in our body:

  1. Water is the major component of blood, which carries nutrients and oxygen, to and from all the cells.
  2. It is the major component of saliva and mucous, which lubricate the membranes that line our digestive system beginning with the mouth.
  3. It helps in regulating the temperature of the body.
  4. Water is very essential for digestion as well as absorption of food.

Solution D.8.

Test for starch:

  1. Takethe food item to be tested. Put it into a test-tube containing water and boil to make a solution.
  2. Cool the solution and add 2-3 drops of dilute iodine solution to it.
  3. Blue-black colour of the solution indicates the presence of starch in the food item.

Test for proteins:

  1. Take the food item to be tested in a test tube.
  2. Add few drops of dilute nitric acid to it.
  3. Heat the test-tube gently.
  4. Rinse off the acid with water and add few drops of ammonium hydroxide to it.
  5. Colour changefrom colourless to yellow and then from yellow to orange redindicates the presence of protein in the food item.

Solution E.1.

Solution E.2.

While swallowing saliva in the mouth, the larynx is pulled upwards to bring it close to the back of the tongue, when a flap called epiglottis closes its opening. Then, it goes towards the oesophagus.

Solution E.3.

Organ Enzyme Food acted upon Find product
Stomach Pepsin Proteins Polypeptide
Mouth Amylase Starch Disaccharide
Ileum Maltase Maltose Glucose

Solution E.4.

1 → Enamel
2 → Dentine
3 → Pulp
4 → Gum
5 → Crown
6 → Cement

(b) The tooth shown in the diagram has only one root, so it is an incisor or canine which is used for biting and piercing.

(c) The part labelled 𔃳’ (pulp) is a soft connective tissue present in the pulp cavity of the tooth. It consists of blood capillaries, lymph vessels and nerve fibres. These extend from the crown of the tooth and open through the pulp cavity at the base of the root.

(d) Type of teeth in the mouth of an adult:

  1. Incisors (8) → Used for biting and cutting
  2. Canines (4) → Used for holding and tearing of food
  3. Premolars (8) → Used for grinding and crushing of food
  4. Molars (12)→ Used for grinding and crushing of food

Solution E.5.

a) A total of 20 teeth are present in the given dentition.

(b) The given dentition is that of a herbivore because there are no canines present in the dentition. Canines are required by carnivores as they help in holding and tearing of food. The teeth of herbivores are used for cutting, gnawing, and biting, while the teeth of carnivores are sharper and more suited for catching, killing and tearing the prey.

(c) The given dentition is likely to be present in any herbivore such as deer.


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What are the organs of the digestive system?

How does food move through the digestive system?

The Digestive system is also called alimentary canal and it is supported by organs like teeth, tongue, liver, and others. The digestive system helps to convert food into energy and nutrients to nourish the body. The food we take in is thoroughly digested and absorbed by our body and the wastes are eliminated through the excretory system. The alimentary canal is a lengthy tube through which the food goes down to our system. It starts at the mouth or the oral cavity going through the pharynx, esophagus or food pipe, stomach, small intestines, large intestines, rectum andanus. The food particles get digested in every stage of the alimentary canal as they move.

Oral /Mouth and the Buccal Cavity

The mouth has many accessory organs such as the tongue, teeth, and salivary glands, which help in the digestion of food. Food starts the first step of digestion in the mouth, also known as the buccal cavity or the oral cavity. Food is grinded by the teeth. Salivary amylase is the digestive juices given off by the salivary glands. This moistens the food, and break the food down into usable and absorbable components and then the food is pushed down into the pharynx.


The pharynx acts as a passage for the chewed food from the mouth to the esophagus. It has a flap of tissue known as the epiglottis preventing the food from getting into the wind pipe and helps us from getting choked while we eat.

Esophagus or Food Pipe

The esophagus is a tube joining the pharynx to the stomach. It is made of flexible muscle to help pushing of food easily. It carries swallowed food down its long tube and pushes it to the stomach.


The stomach is a thick-wall made of muscle in the form of a bag that is located on the left side of the abdominal cavity. It is the largest part of our digestive system. Stomach acts as a storage place for food. And slowly digests food. It gets food from the food pipe and sends it to the small intestine. The stomach has digestive acids which help reduce food into further absorbable substances. Mucous protects the inner walls of the stomach. This can otherwise get damaged while digesting food. Because the acid reacts with the bacteria and kills it that enters our body with food. The digestive enzymes break down proteins into simpler substances.

Small Intestine

The small intestine is just named small. But it is the longest part our digestive system. It is made in such a way that it is highly coiled it’s quite thin tubular form but still about 7.5 meters long. (The length of the small intestine depends on the diet of the organism.) A major proportion of digestion takes place in the small intestines. Nutrients get digested here. The walls of the small intestine also secrete juices for digesting food. The enzymes in the intestine convert the carbohydrates into glucose, proteins to amino acids and fats into fatty acids and glycerol.


The liver releases bile. This neutralizes the acidity level of the food. The pancreatic juice digests the proteins and lipids. Once the food is broken down into the simple particles, it is ready to be absorbed by the body. The absorbed food is then carried to different parts of the body through the blood vessels for cell activities.

Large Intestine

The large intestine is a thicker tube than the small intestine. The large intestine absorbs water and left over nutrients from the remaining food with the help of many bacteria in it. The remaining food waste passes into the rectum, where it is ready to get out as semi-solid wastes. Feces then are excreted by the body through the anus.

Chapter 15: Study Guide

Original Document: Chapter 15 Study Guide

1. What is peristalsis? __ muscular movements that push food through the alimentary canal __
2. What are papillae and where are they located? _______ taste buds, tongue ________________________
3. What is the roof of the oral cavity called (2 parts): _ soft and hard palate
Where is the uvula? back of the mouth, throat area
4. What are the three salivary glands and where are they located? parotid (ear), submandibular (below jaw), sublingual (below tongue)
5. What are the two types of movements within the alimentary canal? ___ mixing and propulsion ___
6. What are the three main functions of the digestive system?
1) mechanical and chemical break down of food
2) ____ absorption ____________ of nutrients
3) _____ elimination _____________ of wastes

7. What is the name of the opening where the esophagus pass through the diaphragm? _____ esophageal hiatus __________
8. What layer of the alimentary canal carries out absorption? mucosa
What layer contains glands, blood vessels, and nerves? submucosa
What layer contains the muscles? muscular
What layer covers the structures? serosa

9. What valve opens from the esophagus to the stomach? cardiac sphincter
What valve opens from the stomach to the small intestine? pyloric sphincter

10. What structure connects the tongue to the floor of the mouth? frenulum
11. What digestive enzyme is produced by the salivary glands? amylase
12. The part of the stomach that sits slightly above the esophagus is called the fundus
13. What is the hardest substance found in the body? tooth enamel
14. The central cavity of the tooth is made of dentin
The top of the tooth is called the crown
The part of the tooth that extends below the gums is called the root

15. The front teeth are called __ incisors ______. The back teeth are called ___ molars
The pointed teeth after the incisors are the ____ canines or cuspids __

16. What is food called after it has been broken down into a paste? chyme
What are the folds inside the stomach called? rugae

17. What causes jaundice in newborns? liver is not functioning
18. Trace the path of food once it enters the colon (follow through the parts)
ascending colon to transverse colon to descending colon
19. What is the function of the pancreas? digest foods
20. What does the bile duct connect? _ gall bladder _ to the duodenum
21. Where is the hepatic portal vein located? the liver
22. Trace the path of food from the stomach and through all of the parts of the small intestine:
stomach : duodenum >> jejunum >> ileum
* Which section is the longest? ileum
23. What is the function of the gall bladder? store bile
What is the function of bile? digest fats
24. What membrane holds the coils of the small intestine together? __ mesentery _
What membrane covers the organs of the digestive system like a curtain ? _____ greater omentum _______
25. What is the function of the intestinal villi? increase surface area for absorption

26. What part of the colon is located right before the rectum? __ sigmoid colon _________
27. Where is the cecum located? at the junction between the small intestine and the large intestine
What “useless” structure is attached to it? appendix
28. What part of the system stores waste prior to its elimination? rectum
29. What is a mass movement? defecation, elimination of solid waste

30. The “flora” of the large intestine is what? bacteria
31. What is the function of the large intestine? reabsorption of water
if this function does not work, what sickness can result? dysentery or diarrhea
32. If part of the small intestine pokes through the abdominal muscles, a person has a hernia
33. Hepatitis (A,B, or C) affects which organ of the digestive system? liver
34. The majority of a human’s diet should consist of what? grains, vegetables
35. What substance is mainly responsible for breaking down fats? bile
What substance is created in the stomach and breaks down food? pepsin

36. What is lactose intolerance? inability to break down milk (lactose)
37. What is another name for gastroesophageal reflux disease? acid reflux
38. The biliary system refers to the liver, pancreas and gall bladder.
What are the three ducts found in that system? hepatic, cystic, common bile

39. If a person has dysentery , they have a dangerous form of diarrhea

40. Be able to label structures of the digestive system on an image. (This includes a close-up view of the stomach and biliary system)

1. Esophagus
2. Cardiac Sphincter
3. Stomach
4. Pyloric Sphincter
5. Duodenum
6. Transverse Colon
7. Ascending Colon
8. Jejunum
9. Descending Colon
10. Sigmoid Colon
11. Ileum
12. Rectum
13. Appendix

GCSE Biology (9-1) - Digestive System - Worksheet & Video

This worksheet and video cover the role of the digestive system, and the functions of each of the organs involved. We also cover the villi and bile.


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9: Module 7- The Digestive System - Biology

Anatomy is the examination of the structures of the body. Physiology is the functions of the body.
Digestive system- Organs associated with the digestion of food form the digestive system. Learn about parts of digestive system, glands associated, enzymes involved in digestion and the process of digestion as a whole.
Learn about the human dentition(arrangement of teeth in bucal cavity).

View Lessons & Exercises for Human Digestive System &rarr View Lessons & Exercises for Digestion of Food &rarr View Lessons & Exercises for Digestion of Food in Small Intestine &rarr

Interactive resources for schools

Hydrochloric acid

Mineral acid, made in the stomach

Digestive system

The organ system in the body which breaks down large insoluble food molecules into small soluble molecules which can be used by the body

Balanced diet

A diet which contains the correct amounts of carbohydrates, proteins, lipids, vitamins, minerals and fibre to provide your cells with the resources they need.


Breaking down the large insoluble food molecules into small soluble molecules


A list of often difficult or specialised words with their definitions.


Reusable protein molecules which act as biological catalysts, changing the rate of chemical reactions in the body without being affected themselves

The basic unit from which all living organisms are built up, consisting of a cell membrane surrounding cytoplasm and a nucleus.

Yellowy-green alkaline liquid made in the liver. It is stored in the gall bladder and released along the bile duct to the small intestine where it neutralises stomach acid and emulsifies fats.

What does your body do with the food you eat?

Human beings need to eat a balanced diet to stay healthy. The food we eat has to be broken down before it can be used by the cells of the body. This is the job of the digestive system.

The digestive system is made up of many different organs working together. It takes in food, breaks it down both physically and chemically, moves the digested food into the blood stream and removes the undigested waste.


People must eat everything their cells are going to need. It is important to take in a range of different types of food molecules, and to take in enough food to supply the needs of the body.

The food we eat is made up of chunks of material containing large, insoluble molecules. Digestion is the process by which we break down these large insoluble molecules into small soluble ones that can be absorbed into the bloodstream and used in our bodies. The organs of the digestive system make chemicals such as enzymes, hydrochloric acid and bile which help us digest the food quickly and efficiently.

The stomach is an important part of the digestive system. Firstly it secretes HCL which kills bacteria and other harmful organisms preventing food poisoning and it also provides the optimum conditions for the enzyme pepsin to work in (pH 1.5 - 2). In addition, the stomach secretes pepsin which starts the digestion of proteins into polypeptides and amino acids. Theses can then be absorbed by the villi in the small intestine.

The small intestine is where the final stages of digestion occur. The intestinal wall secretes enzymes and it also receives enzymes from the pancreas. However the main function of the small intestine is the absorption of the small food particles resulting from digestion. It contains many villi which increase the surface area for absorption.

The large intestine moves the material that has not been digested from the small intestine and absorbs water. This produces solid faeces which are then egested through the anus.

  1. Secretes HCL which kills bacteria.
  2. HCL provides optimum pH for pepsin.
  3. Secretes pepsin for protein digestion.
  1. Intestinal wall secretes enzymes
  2. Receives enzymes from the pancreas.
  3. Has villi for absorption of food particles.
  1. Moves material that has not been digested along.
  2. Absorbes water.
  3. Produces faeces.

Watch the video: Digestive System. The Dr. Binocs Show. Learn Videos For Kids (January 2023).