1.0 Nutrition: Energy-Giving Nutrients
Nutrition is the process by which an organism obtains and utilizes food for energy, growth, and repair. The two primary sources of fuel for the human body are Carbohydrates and Fats.
1.1 Carbohydrates (Hydrates of Carbon)
Carbohydrates are organic compounds made of Carbon, Hydrogen, and Oxygen, where the ratio of H to O is usually 2:1 (like water).
| Category | Description | Common Examples |
|---|---|---|
| Monosaccharides | Simple sugars; single unit. | Glucose (Grape sugar), Fructose (Fruit sugar). |
| Disaccharides | Double sugars; two units. | Sucrose (Cane sugar), Maltose, Lactose. |
| Polysaccharides | Complex; insoluble; many units. | Starch (Plants), Glycogen (Animal starch), Cellulose. |
1.2 Fats (Lipids)
Fats contain much less oxygen than carbohydrates and provide more than twice the energy per gram (9 kcal/g vs 4 kcal/g).
- Storage: Excess energy is stored as fat in adipose tissue.
- Insulation: Prevents heat loss from the body.
- Protection: Acts as a cushion for delicate internal organs like kidneys.
- Solvent: Necessary for the absorption of Vitamins A, D, E, and K.
In "Give Reasons" questions, you might be asked why humans can't digest Cellulose. The answer: We lack the enzyme cellulase. However, cellulose is still vital as Roughage to help prevent constipation.
C6H12O6
Note: This is the most basic form of carbohydrate used by cells during respiration.
2.0 Proteins: The Body Builders
Proteins are complex organic compounds containing Carbon, Hydrogen, Oxygen, and Nitrogen. Some also contain sulfur and phosphorus. They are essential for growth and the repair of worn-out tissues.
2.1 Amino Acids
Proteins are made up of smaller units called Amino Acids. There are about 20 types of amino acids, which can be linked in various sequences to form different proteins.
- Essential Amino Acids: Cannot be synthesized by the body and must be taken in through diet (e.g., Lysine, Valine).
- Non-Essential Amino Acids: Can be synthesized by the body itself.
- Sources: Lean meat, eggs, pulses (dal), soyabean, and milk.
2.2 Protein-Energy Malnutrition (PEM)
Lack of proteins and calories in the diet leads to severe conditions in children. You must be able to distinguish between the two:
| Feature | Kwashiorkor | Marasmus |
|---|---|---|
| Primary Cause | Severe Protein deficiency. | Deficiency of Proteins AND Calories (Carbs/Fats). |
| Body Appearance | "Pot-belly" due to water retention (Oedema). | Extremely shrivelled, "Old man" face. |
| Skin/Hair | Skin cracks; hair becomes reddish. | Skin becomes thin and folded. |
| Age Group | Usually children above 1 year. | Infants below 1 year. |
In "Identify the disease" questions, look for the keyword Oedema (swelling of the feet and face). Even though the child looks "plump" in the belly, they are actually starving for protein. This is a very common trick question!
All enzymes, many hormones (like insulin), and the hemoglobin in your blood are actually proteins. This is why a deficiency affects every single system in the body.
3.0 Vitamins: Vital for Health
Vitamins are organic compounds that act as catalysts in various biological reactions. They are classified into two groups based on their solubility.
Stored in the liver. These include Vitamins A, D, E, and K.
Not stored in the body; must be supplied daily. These include Vitamin B-complex and Vitamin C.
Vitamin Deficiency Table
| Vitamin | Chemical Name | Deficiency Disease |
|---|---|---|
| Vitamin A | Retinol | Night Blindness / Xerophthalmia |
| Vitamin B1 | Thiamine | Beriberi |
| Vitamin C | Ascorbic Acid | Scurvy (Bleeding gums) |
| Vitamin D | Calciferol | Rickets (children) / Osteomalacia (adults) |
| Vitamin K | Phylloquinone | Haemorrhage (Delayed blood clotting) |
Do not confuse the two! Night Blindness is a nutritional deficiency of Vitamin A and is curable. Color Blindness is a genetic disorder and cannot be cured by diet. This is a common "Differentiate between" question.
Vitamin D is unique because our skin can synthesize it when exposed to ultraviolet (UV) rays from sunlight. This is why it is often called the "Sunshine Vitamin."
4.0 Minerals and Dietary Essentials
4.1 Minerals: The Inorganic Elements
Minerals are required for the formation of body tissues and for various chemical reactions within cells. They are needed in relatively small amounts.
| Mineral | Function | Deficiency Effect |
|---|---|---|
| Iron (Fe) | Constituent of Haemoglobin (O₂ transport). | Anaemia (Weakness, pale skin). |
| Calcium (Ca) | Strengthening bones/teeth; blood clotting. | Brittle bones; Muscle cramps. |
| Iodine (I) | Synthesis of Thyroxine hormone. | Goitre (Swelling in the neck). |
| Phosphorus (P) | Formation of ATP, DNA, and Bones. | Poor bone growth and dental decay. |
4.2 Roughage (Dietary Fibre)
Roughage consists largely of Cellulose from plant cell walls. Although it provides no nutrients, it is indispensable for a healthy digestive system.
- It absorbs water and adds bulk to the faeces.
- It stimulates peristalsis (the wave-like movement of the gut).
- It helps in the regular bowel movement, preventing constipation.
4.3 Water: The Universal Solvent
About 65-70% of our body weight is water. It serves as the medium for all metabolic reactions.
If asked "Why is it important to include roughage in the diet even though it has no nutritional value?", the answer must include the term Peristalsis and the prevention of Constipation.
5.0 Balanced Diet and Experimental Biology
A Balanced Diet is one which contains all the principal constituents of food in proper proportions for growth, repair, and maintenance of the body. The energy value of food is measured in Calories.
5.1 Calorific Value
The energy required depends on age, sex, and the nature of work. For an average adult performing moderate work, the daily requirement is approximately 2500 - 3000 Calories.
- Carbohydrates/Proteins: Provide ~4 kcal/g.
- Fats: Provide ~9 kcal/g.
5.2 Food Tests (Lab Practicals)
In ICSE Biology, identifying nutrients through chemical reactions is a core skill. Here is the definitive guide to the common food tests:
| Nutrient | Reagent Used | Positive Result |
|---|---|---|
| Starch | Iodine Solution | Blue-Black color. |
| Glucose (Sugar) | Benedict's Solution + Heat | Brick-Red precipitate. |
| Proteins | Biuret Reagent (CuSO4 + NaOH) | Violet/Pink color. |
| Fats | Ethanol Emulsion / Paper Test | Cloudy white layer / Translucent spot. |
For the Benedict's test, simply adding the reagent is not enough. You must mention that the mixture is heated in a water bath. Without heat, the chemical reaction will not take place!
- Can you differentiate between simple and complex carbohydrates?
- Do you know the chemical names for Vitamins A, C, and D?
- Can you explain why a growing child needs more protein than an adult?
- Do you know the specific reagent used to test for proteins?