Enzymes and the digestive system

Enzymes and the digestive system 2.1 Enzymes and digestion

Settler Activity: Can you find today's 16 key words?

Learning Objectives All students should be able to: • Define digestion. • Give the structure and function of the major parts of the digestive system. • Understand how the digestive system breaks down food both physically and chemically. • Understand the role of villi and microvilli. • Outline the role of enzymes in digestion. Specification reference: 3.1.2

Success Criteria • I can rearrange fragments of a sentence to give the correct definition of digestion. • I can label the digestive system. • I can name the structures of the digestive system when given theirfunction and vice versa. • I can draw a labelled diagram of the lining of the small intestine and answer questions related to its key features. • I can answer exam questions on digestion and digestive enzymes.

Starter Activity: Can you rearrange these fragments of a sentence to give the correct definition of digestion? hydrolysed by Digestion Digestion is the process in which large molecules are hydrolysed by enzymes into small molecules which can be absorbed and assimilated. and assimilated. molecules which molecules are enzymes which large absorbed can be is the process in into small

Activity 1: The human digestive system • The human digestive system is made up of a long muscular tube and its associated glands. • The glands produce enzymes that break down large molecules into small ones ready for absorption. • The digestive system therefore provides an interface with the environment because food substances enter the body through it. Missing words: small interface glands enter enzymes muscular large absorption

Activity 2: Can you label the human digestive system? X A W B V C U D E T S F G R H K I P Q J O N M L

Activity 4: Question 1 • Which parts of the digestive system does the food pass through? • Mouth, oesophagus, stomach, small intestine (duodenum, jejunum, ileum), large intestine (caecum, colon, rectum), anus.

!!! • The contents of the intestines are NOT inside the body! Molecules and ions only truly enter the body when they cross the cells and cell-surface membranes of the epithelial lining of the intestines.

Activity 5: How well do you know the major parts of the digestive system? ??? ???

This part is the final section of the intestines. The faeces are stored here before periodically being removed via the anus in a process called egestion. RECTUM

These are situated near the mouth. They pass their secretions via a duct into the mouth. These secretions contain the enzyme amylase, which breaks down starch into maltose. SALIVARY GLANDS

This part is a muscular sac with an inner layer that produces enzymes. Its role is to store and digest food, especially proteins. It has glands that produce enzymes which digest protein. Other glands in its wall produce mucus. The mucus prevents this organ being digested by its own enzymes. STOMACH

This is a large gland situated below the stomach. It produces a secretion. This secretion contains proteases to digest proteins, lipase to digest lipids and amylase to digest starch. PANCREAS

This part absorbs water. Most of the water that is reabsorbed comes from the secretions of the many digestive glands. The food within this part therefore becomes drier and thicker in consistency and forms faeces. LARGE INTESTINE

This is a long muscular tube. Food is further digested here by enzymes that are produced in its walls and by glands that pour their secretions into it. The inner walls of this organ are folded into villi, which gives them a large surface area. The surface area of these villi is further increased by millions of tiny projections, called microvilli, on the epithelial cells of each villus. This adapts this organ for its purpose of absorbing the products of digestion into the bloodstream. SMALL INTESTINE

The lining of the small intestine

This part carries food from the mouth to the stomach. It is therefore adapted for transport rather than for digestion or absorption. It is made up of a thick muscular wall. OESOPHAGUS

Activity 6: Question 1 • Can you distinguish between the terms ‘absorption’ and ‘assimilation’? • Taking soluble molecules into the body. • Incorporating absorbed molecules into body tissues. (Absorption) (Assimilation)

!!! • All organisms are made up of the same biological molecules and therefore our food consists almost entirely of other organisms or parts of them. We must first break them down into molecules that are small enough to pass across cell surface membranes.

Activity 6: Question 2 • Unscramble the anagrams to reveal the two stages of human digestion. (Physical breakdown) • Hysipalcrobewkand • Halcmicetindogies (Chemical digestion)

Activity 7: Physical Digestion • If the food is large, it is broken down into smaller pieces by means of structures such as the teeth. This not only makes it possible to ingest the food but also provides a large surface area for chemical digestion. Food is churned up by the muscles in the stomach wall and this also physically breaks it up. Missing words: surface area physically stomach teeth chemical ingest large muscles

Activity 8: Chemical Digestion • This breaks down large, insoluble molecules into smaller, soluble ones. It is carried out by enzymes. • All digestive enzymes function by hydrolysis (the splitting up of molecules by adding water to the chemical bonds that hold them together). The general term for such enzymes is hydrolases. • Enzymes are specific and so it follows that more than one enzyme is needed to break down a large molecule. Usually one enzyme splits a large molecule into sections and these sections are then hydrolysed into smaller molecules by one or more additional enzymes. Missing words: specific enzymes hydrolysed hydrolysis smaller large additional insoluble soluble hydrolases splits

Activity 9: Question 1 • Can you name the three different types of digestive enzyme? These breakdown carbohydrates, ultimately to monosaccharides. These breakdown lipids (fats and oils) into glycerol and fatty acids. These breakdown proteins, ultimately to amino acids. Carbohydrases Lipases Proteases

Chemical digestion continued... • Once the large food molecules have been hydrolysed into monosaccharides, glycerol, fatty acids and amino acids, they are absorbed by various means from the small intestine into the blood. • They are carried to different parts of the body and are often built up again into very large molecules, although these are not necessarily of the same type as the molecules from which they were derived. • These molecules are incorporated into body tissues and/or used in processes within the body. This is called assimilation. Missing words: fatty acids, tissues, large, monosaccharides, glycerol, amino acids, assimilation, derived, blood,

Plenary Activity: Answer these 4 questions under test conditions! • State one way in which the stomach is adapted: • To churn food • To prevent the enzymes it produces from digesting the surface of the stomach. 2. What is hydrolysis? 3. Which two structures produce amylase? 4. Suggest a reason why the stomach does not have villi or microvilli.

Answers 1. a. By having a muscular wall. b. By secreting mucus. 2. Hydrolysis is the breakdown of molecules by the addition of water to the bonds that hold these molecules together. 3. Salivary glands, pancreas 4. Villi and microvilli increase surface area to speed up the absorption of soluble molecules. As the food in the stomach has not yet been broken down into soluble molecules they cannot be absorbed and so villi and microvilli are unnecessary.

Learning Objectives All students should be able to: • Define digestion. • Give the structure and function of the major parts of the digestive system. • Understand how the digestive system breaks down food both physically and chemically. • Understand the role of villi and microvilli. • Outline the role of enzymes in digestion. Specification reference: 3.1.2

Enzymes and the digestive system