Vitamins are essential organic micronutrients required in tiny (minute) amounts in the human diet for normal metabolism, growth, and the maintenance of good health.

Key Characteristics of Vitamins:

• Organic compounds: Unlike mineral ions (such as iron or calcium), vitamins contain carbon-hydrogen bonds synthesized by living organisms.
• Micronutrients: They provide no direct energy (unlike carbohydrates, proteins, or fats), but are needed in very small quantities to regulate cellular processes.
• Dietary requirement: The human body cannot synthesize most vitamins in sufficient amounts (or at all), meaning they must be obtained through a balanced diet.
• Metabolic role: They frequently function as coenzymes or precursors to enzymes that catalyze biochemical reactions.

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Vitamins

Core Vitamins

• Vitamin C (Ascorbic Acid)
• Role in the body: Essential for the synthesis of collagen (a key structural protein), which maintains healthy skin, blood vessels, gums, cartilage, and connective tissues. It also promotes wound healing and aids the absorption of iron.
• Main dietary sources: Citrus fruits (oranges, lemons, limes), strawberries, bell peppers, tomatoes, and fresh green vegetables.
• Deficiency disease: Scurvy (symptoms: bleeding gums, loose teeth, poor wound healing, small red or purple spots on the skin due to broken capillaries).

• Vitamin D (Cholecalciferol)
• Role in the body: Promotes the absorption of calcium and phosphate from the small intestine, which is required for building and maintaining strong, healthy bones and teeth.
• Main dietary sources: Oily fish (salmon, tuna, mackerel), egg yolks, fortified dairy products/cereals, and synthesis in the skin upon exposure to sunlight (UV rays).
• Deficiency disease: Rickets in children (soft, weak bones leading to bowed legs and skeletal deformities) and osteomalacia in adults.

• Vitamin A (Retinol)
• Role in the body: Needed for the formation of rhodopsin (a light-sensitive pigment in the retina) for night and low-light vision; maintains healthy epithelial tissues and immune response.
• Main dietary sources: Liver, dairy products, eggs, and beta-carotene from orange/dark-green vegetables (carrots, sweet potatoes, spinach).
• Deficiency condition: Night blindness (difficulty seeing in dim light) and dry, damaged epithelial layers.

Food Containing Rich Nutrients

Foods containing�high proteins

Foods containing�high lipids

DV stands for Daily Value.

It is a reference amount of nutrients to consume each day

• There is no single food in this world that contains all nutrients required by our body in one. However, milk are the most complete foods you can find.
• Think about it. A baby cow can only drink milk. This means milk must have all the nutrients that the baby cow needs to grow.

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Complete Food

Milk contains almost all the major nutrients your body needs: proteins, fats, carbohydrates, vitamins, and minerals

For the same reason, eggs are also considered a complete food.

Let’s watch a short video clip

Core Biochemical Food Tests

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We can use basic chemical tests to detect the presence of starch, glucose, protein, or lipids in food.

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• Starch detection 🡪 Iodine Test
• Glucose detection🡪 Benedict’s Test
• Protein detection 🡪 Biuret Test
• Lipid detection 🡪 Ethanol Emulsion Test

Iodine Test

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• When you add iodine solution to the starch, iodine’s brown color changes into dark blue (blue-black) or purple color.

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• Method
• Step 1: Place a small amount of your food sample onto a clean spotting tile (or inside a test tube). This can be a solid piece like potato or a liquid suspension.
• Step 2: Use a dropper pipette to add a few drops of yellow-brown iodine solution directly onto the sample.
• Step 3: Observe any color change immediately.

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Benedict’s Test

• Mono-saccharides like glucose (reducing sugars). They can reduce an alkaline solution of copper(II) sulfate to copper(I) oxide. When this happens, the blue color of the copper sulfate solution gradually turns into a brick-red color.
• Method
• Step 1: Add a small spatula measure of your food sample into a clean test tube.
• Step 2: Add about 2 cm depth of water and shake gently to dissolve the sample.
• Step 3: Add several drops of blue Benedict's solution until the mixture turns bright blue.
• Step 4: Set up a water bath by placing a beaker half-filled with water on a tripod and gauze over a Bunsen burner.
• Step 5: Place the test tube into the beaker and heat the water to a boil for about 2 to 3 minutes.

Biuret Test

• Peptide bonds in proteins react with copper ions in an Biuret solution. This reaction produces a distinct color change.�Pale blue 🡪 Purple
• Method
• Step 1: Add a small amount of your food sample (such as powdered egg white) into a clean test tube.
• Step 2: Add about 2 cm depth of water and shake the tube well to mix or dissolve the sample.
• Step 3: Add few drop of Biuret solution.
• Step 4: Gently shake the test tube and observe the mixture at room temperature—no heating is required.

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Ethanol Emulsion Test

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• When you add water to the ethanol-lipid mixture, it forces the dissolved lipid to separate out into tiny droplets, which creates the cloudy emulsion.

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• Method
• Step 1: Add a drop of your sample (e.g., olive oil) into a clean test tube using a pipette.
• Step 2: Pour in about 2 cm depth of ethanol.
• Step 3: Shake the tube thoroughly so the lipid dissolves in the ethanol.
• Step 4: In a second test tube, fill it about three-quarters full with cold water.
• Step 5: Pour the ethanol mixture into the tube containing the cold water.

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Energy from Food

• Food is the animal body’s primary source of energy.
• Some foods contain more energy than others. It depends on the proportions of carbohydrate, lipid and protein that they contain. Their energy content is measured in kilojoules (kJ).
• If a gram of carbohydrate is fully oxidized, it produces about 17 kJ, whereas a gram of lipid yields over twice as much as this (39 kJ). Protein can produce about 18 kJ per gram.

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• Measuring the Energy Content of a Food
• Do you remember that respiration and combustion involve the same chemical reaction?
• Cellular respiration was described as the slow burning of food (glucose) at low temperatures.
• Therefore, if you want to find out how much chemical energy a food contains, you can simply burn that sample.

Step 1 (Weigh the food): Measure and record the mass of the food sample using a balance.

Step 2 (Prepare the water): Pour a fixed volume of water (20 cm³) into a boiling tube clamped to a retort stand.

Step 3 (Record initial temperature): Measure and note the starting temperature of the water using a thermometer.

Step 4 (Ignite the sample): Mount the food on the tip of a needle and hold it in a Bunsen burner flame until it catches fire.

Step 5 (Heat the water): Immediately place the burning food directly beneath the boiling tube to heat the water. Relight the sample if it goes out, repeating until it cannot burn any longer.

Step 6 (Record final temperature): Stir the water gently with the thermometer to distribute heat evenly, then record the highest temperature reached.

1 cm^3�= 1 cc�= 1ml

If you had a piece of pasta weighing 1 g. The starting temperature of the 20 g of water was 21 °C. After using the burning pasta to heat up the water, the temperature of the water was 43°C.

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What was the energy content of the pasta?

1 cm^3�= 1 cc�= 1 ml

= 1 g

• The energy needed to raise the temperature of�one gram of water by 1 °C is 4.2 joules.
• A volume of 1 cm³ of water has a mass of 1 g.

More Practice

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If you had a piece of fat weighing 0.24 g. The starting temperature of the 20 g of water was 22 °C. After using the burning pasta to heat up the water, the temperature of the water was 45°C.

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What was the energy content of the fat?

• The energy needed to raise the temperature of�one gram of water by 1 °C is 4.2 joules.
• A volume of 1 cm³ of water has a mass of 1 g.

The Digestive System

• Role of the Digestive System
1. Digestion (Breakdown of food) : It breaks down large, insoluble food molecules into small, soluble molecules.
2. Absorption (Uptake of nutrients) : The soluble food molecules will be taken into the blood stream.

Digestion

Blood vessel

Only animals have�the Digestive System

Absorption

More related terms

• Ingestion:The process of taking food into the body through the mouth
• Egestion: The removal of undigested and unabsorbed food material (faeces) from the body via the rectum and anus

Human Digestive Organs

• Mouth: Where food enters the digestive system
• Oesophagus (Gullet): A muscular tube that transports food from the mouth to the stomach via peristalsis.
• Stomach: A muscular bag that churns food and begins protein digestion.
• Small Intestine: The primary site for chemical digestion and absorption of nutrients.
• Large Intestine: Involved in water absorption and faeces formation.
• Rectum: Stores faeces before egestion.
• Anus: The opening at the end of the alimentary canal through which faeces are expelled.

Alimentary canal:

the continuous tube through which food passes.

• Mouth🡪 Oesophagus 🡪 Stomach �🡪 Intestines 🡪 Rectum 🡪 Anus

Human Digestive Organs

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The Mouth

The mouth is an organ that performs both mechanical and chemical digestion.

• First, the mouth does:
• Cutting, tearing, grinding by using teeth … these are mechanical digestion
• Second, in the mouth:
• Saliva is mixed with food.
• Saliva contains digestive enzyme “Amylase”
• Amylase breaks down starch into maltose.

The Oesophagus

It is a muscular tube connecting mouth to stomach. The oesophagus preforms no digestion. It only transfers food from mouth to stomach through “peristalsis”.

• Peristalsis
• This is a series of automatic, wave-like muscle contraction movement.

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The muscles behind the food squeeze tightly

These two steps make the food to slide down smoothly

As these two steps repeat one after another

That's why food moves down to your stomach all on its own

This movement defies gravity! Even if you are hanging upside down, the food moves toward the stomach.

The Stomach

The stomach is a thick muscular sack that churns and mixes food with gastric juice. This organ performs both mechanical and chemical digestion. And, it performs also absorption.

• Gastric Juice
• A highly acidic fluid secreted by glands in the stomach.
• Key components:
• Hydrochloric acid (HCl) … pH 1.5~2 (very strong acid), kills bacteria.
• Pepsin … this is a digestive enzyme that breaks down protein into peptides.
• Absorption in Stomach
• The stomach is not the organ that�major absorption of nutrients occurs.
• Small amount of water and alcohol�are absorbed through the stomach.

10 cm

• Jejunum
• Digestion began in Duodenum continues.
• Ileum
• The ileum is the major site for the absorption of digested nutrients and water into the blood and lymph.
• Let’s think about this:

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223.6 cm

111.80 * 2 *10 = 2,236 mm = 223.6 cm

??

10 cm

10cm�width

2236cm²

This is 2D folding.

What about 3D folding?

• So, the very inner layer of Ileum has this:

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This we call villi.

(The singular of villi is 'villus’ )

Each villus is only about 1-2 mm long, but there are millions of them, so that the total area of this lining is thought to be about 300 m².

Area of tennis court is around 200 m²

The surface of a villus is made of a single layer of cells called an epithelium.

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This single cell layer allows fast and easy absorption.

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The epithelium cells contain many mitochondria, which supply the energy needed for active transport of nutrient molecules.

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Each cell consisting of epithelium has hundreds of minute projects called microvilli. This increase the surface area for absorption even more!

The lacteal is a tube that transports a liquid called lymph.

The cross-section of a villus

Each villus contains a network of blood capillaries.

Most of the digested food enters the blood vessels, but the products of fat digestion, enter the lacteal.

The Large Intestine

The large intestine is the organ egestion occurs. Even after nutrients are absorbed in the small intestine, undigested waste still remains and passes into the large intestine. This waste still contains a lot of water, and the large intestine absorbs this water.