⚡ Quick Revision : Classes of Food
1. What is Nutrition?
Nutrition is the process by which all living organisms obtain and utilize food for growth, repair, and maintenance of the body. Food substances are divided into six main classes:
2. Energy-Giving Foods
Carbohydrates: These are compounds of Carbon, Hydrogen, and Oxygen ($C, H, O$). They are the principal source of energy.
- • Sugar: Soluble in water (Glucose, Fructose, Sucrose).
- • Starch: Insoluble storage form in plants (Potatoes, Rice).
- • Cellulose: Found in plant cell walls; provides Roughage to the human diet.
Fats (Lipids): Composed of $C, H, O$ but contain much less oxygen than carbohydrates. They provide **twice the energy** per gram compared to carbs.
3. Quick Comparison
| Nutrient | Function | Sources |
|---|---|---|
| Carbohydrates | Immediate Energy source | Rice, Wheat, Maize, Sugar |
| Fats | Storage of energy; Insulation | Butter, Ghee, Oil, Nuts |
Question: Why is cellulose important in our diet if we cannot digest it?
Answer: Cellulose acts as Roughage. It absorbs water and adds bulk to the undigested food, stimulating peristalsis and preventing constipation.
Glucose is the "ready energy" used by cells. Glycogen is the form in which excess glucose is stored in our liver and muscles for future use.
⚡ Quick Revision : Body-Building Foods & Minerals
1. Proteins (Body-Building Foods)
Proteins are large, complex molecules made of Carbon, Hydrogen, Oxygen, and Nitrogen. Some also contain sulfur and phosphorus.
- ✔ Basic Unit: Proteins are made of chains of Amino Acids.
- ✔ Primary Function: Growth of new tissues, repair of damaged cells, and making enzymes/hormones.
- ✔ Deficiency Diseases: Kwashiorkor (protein deficiency) and Marasmus (protein and calorie deficiency).
2. Essential Minerals
Minerals are required in small quantities for various metabolic functions and structural roles.
| Mineral | Function | Deficiency Result |
|---|---|---|
| Iron (Fe) | Synthesis of Hemoglobin in RBCs. | Anaemia |
| Calcium (Ca) | Bone and tooth formation; blood clotting. | Rickets (in kids); weak bones. |
| Iodine (I) | Production of Thyroxine hormone. | Goitre |
| Sodium (Na) | Nerve impulse conduction; water balance. | Muscle cramps |
Question: Why do growing children and pregnant women require more protein?
Answer: Growing children need proteins for the rapid formation of new cells and tissues. Pregnant women need it for the development of the fetus's body.
Kwashiorkor is recognized by a "pot-belly" and swollen legs (oedema) due to water retention. Marasmus results in an extremely thin, wasted body with visible ribs.
⚡ Quick Revision : Protective Foods (Vitamins)
1. Understanding Vitamins
Vitamins are complex organic compounds required in very minute quantities for healthy growth and protection against diseases. They do not provide energy but regulate chemical reactions in the body.
Vitamins are classified into two groups:
- Fat-Soluble: Vitamins A, D, E, and K (Stored in the liver).
- Water-Soluble: Vitamins B-complex and C (Not stored; must be taken daily).
2. Major Vitamins & Deficiency Symptoms
| Vitamin | Scientific Name | Deficiency Disease | Symptoms |
|---|---|---|---|
| A | Retinol | Night Blindness | Poor vision in dim light. |
| B1 | Thiamine | Beri-beri | Nervousness, weak muscles. |
| C | Ascorbic Acid | Scurvy | Bleeding gums, loose teeth. |
| D | Calciferol | Rickets | Soft bones, bow legs. |
| K | Phylloquinone | Hemorrhage | Delayed blood clotting. |
Question: Why is it recommended to include citrus fruits in our daily diet?
Answer: Citrus fruits are rich in Vitamin C, which is water-soluble. Since the body cannot store it and excretes it daily through urine, a fresh supply is needed every day to maintain immunity and healthy gums.
Vitamin D can be synthesized by the skin in the presence of sunlight, while all other vitamins must be obtained through food sources.
⚡ Quick Revision : Balanced Diet & Food Tests
1. The Balanced Diet
A Balanced Diet is one which contains all the principal constituents of food (Carbs, Fats, Proteins, Vitamins, Minerals, Water, and Roughage) in the correct proportion for a particular person.
The composition of a balanced diet depends on:
- Age: Growing children need more protein.
- Occupation: A laborer needs more carbohydrates than an office worker.
- Gender: Men generally require more calories; women may require more iron.
2. Chemical Tests for Food Components
In ICSE practicals and theory, you must know the reagents and the specific color changes for each nutrient.
| Test For | Reagent Used | Positive Result |
|---|---|---|
| Starch | Iodine Solution | Blue-Black Color |
| Glucose | Benedict's Solution + Heat | Brick-Red Precipitate |
| Proteins | Million's Reagent | White ppt turns Red on heating |
| Fats | Paper Spot Test | Translucent Spot |
3. Caloric Value
The energy value of food is measured in Calories (or Joules). 1 Calorie is the amount of heat required to raise the temperature of 1 gram of water by 1°C.
- • 1g Carbohydrate = 4.1 kcal
- • 1g Protein = 4.1 kcal
- • 1g Fat = 9.45 kcal
Question: Why do we use Benedict's test instead of Iodine for honey?
Answer: Honey primarily contains simple sugars like glucose and fructose, not starch. Iodine only reacts with starch, while Benedict's solution reacts with reducing sugars to show a color change.
The Biuret Test is another common test for proteins where a Violet/Purple color indicates the presence of peptide bonds.