Chapter 2: Nutrition

Chapter 2: Nutrition Part II

2.2 Balanced Diet Balanced Diet A balances diet is a diet which consists of all classes of food in a correct proportions.

A balances diet is important to: Supply the required energy maintain a healthy body, prevent various deficiency disease, such as scurvy and rickets.Factors that determine a persons balances diet: Age Body sizes Gender/ sex Job/ Physical activity Climate State of health FactorWho ?Why ?AgeBabies, children and teenagers need more protein More active and their life process are faster (growing) Body sizes A big sized person normally needs more food than a small sizes personBig sized person need more energy for their life processGender/ sexMen generally need more food than women of the same age and body size Men are more active FactorWho ?Why ?Job/ Physical activity A person doing heavy work needs to eat more than a person doing light workHeavy work require more energy to performClimatePeople living in cold countries need more energy to keep them warm More energy is required to maintain the body temperature in a cold place State of health People with health problems should be careful with their diets Imbalanced diet can direct affect a persons health

Read the food label

Calorific value of food The calorific value of food is the total energy produced when one gram of food is completely burnt.The quantity of energy in a food is measured in calorie (cal) or joule (j) 1 calorie (cal) = 4.3 joule (j) 1 kilocalorie (kcal) = 4.2 kilojoules (kJ)

2.3 Human Digestive System

Digestive System Digestion is the breaking down of complex food into simpler form so that they can be absorbed into the bloodstream.

Digestion take place in two stages: Physical digestion big pieces of food are broken down into smaller pieces by teeth Chemical digestion Enzymes break up complex food molecules into smaller molecules Digestive System Enzymes Enzymes are proteins that speed up the process of digestion.Enzymes break up complex food molecules to smaller and simpler molecules. Characteristic of enzymes:Enzymes are small quantities onlyEnzymes are not destroyed at the end of digestion Specific enzymes act only in specific acidic or alkaline conditionsSpecific enzymes act only on specific foods Enzymes function best at normal body temperature (37 C). Enzymes are destroyed at high temperature .Digestive System The digestive system consists of all the organ in the body that help in the digestion of food.The alimentary canal is made up of the mouth, oesophagus, stomach, small intestine, large intestine and anus (starts from the mouth and ends at the anus). Food is pushed along the alimentary canal by the muscular walls that contract and expand alternately through the process of peristalsis.

In the mouth Food is chewed and broken up into small pieces In the mouth, the salivary gland secrets salivaSaliva is alkaline and contains salivary amylase enzymes. Salivary amylase digests starch into maltose (sugar) Salivary gland Tongue Amylase

Oesophagus Food is pushed through the oesophagus into stomach by the alternating contraction and relaxation of the oesophagus.This process of alternating muscular contraction and relaxation is known as peristalsis.Stomach The stomach secretes gastric juice which contain hydrochloric acid and enzymes (rennin and pepsin).

Function of hydrochloric acid: Providing an acidic medium for enzymic action Killing bacteria found in food Neutralising the alkaline property of saliva

StomachIn the stomach, Pepsin digest protein to peptones / polypeptides

Rennin coagulates milk in the stomach to help in the enzymic enzymes

Pepsin Rennin

Small intestine Duodenum is the first part of the small intestine. - It receives bile and pancreatic juice.

Bile - emulsification of fat - preparation of an alkaline medium for enzymic action.

Pancreatic juice contains three types of enzymes: a) Maltese b) Protease c) Lipase

Duodenum- Pancreatic juice Pancreatic juice contains maltase, protease, and lipase. The maltase break down maltose into glucose

The protease break down peptones into amino acids

The lipase digests fat into fatty acids and glycerol

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Small intestine Digestion is completed in small intestine.

The digest food is then ready to be absorbed through the thin walls of the small intestine into the bloodstream.

The end products of digestion are: a) Carbohydrate glucose b) Protein amino acids c) Fats fatty acids + glycerol

Large intestine Water is reabsorbed in the large intestine.Undigested food is expelled from the body through the anus as faeces.

2.4 Absorption of Digested Food Absorption of digested food takes place in the small intestine The end products of digestion, vitamins and minerals are absorbed by the villi into the bloodstream.

Absorption of digested food The small intestine has several characteristics that enable the effective absorption of end products of digestion.It has a lot of villi of its surface. This increases the surface area for absorption.Each villus has a thin epithelial wall to enable the diffusion of digested food. There is a rich network of blood capillaries in each, villus.

Villus

LabAt the beginning of experiment, the water in the beaker is tested with iodine solution and Benedicts solution. Both the glucose and starch are not present in the water.After 30 minutes, the two tests above are repeated.It is found that the water in the beaker be contains glucose.

Conclusion: This shows that glucose has diffused through the wall of the Visking tube.The starch molecules are too big and hence cannot diffuse through the wall of Visking tube. To show the absorption of glucose through a Visking tube.

2.5 Reabsorption of Water and Defecation The undigested food, minerals and excess water pass into the large intestine.The large intestine does not secrete any enzyme and hence, no digestion occurs in the large intestine.The process of reabsorption takes place in the large intestine. Water and minerals are reabsorbed. Reabsorption of Water and DefecationAfter the water is reabsorbed, the undigested food turns into faeces.The feaces is stored in the rectum.Defecation is the process in which feaces is expelled from the body through the anus.Insufficient fibre and water in our diet will cause constipation.

Reabsorption of Water and DefecationReabsorption of water + minerals + vitamins

2.6 Practice the Habits of Healthy eatingUnhealthy eating habits can cause diet-related diseases such as diabetes, obesity, high blood pressure and cancer. Choose nutritious food, Avoid junk food!