Biological molecules

Definitions:

Balanced diet:

• A balanced diet contains the correct amounts of protein, carbohydrates, fats, vitamins, and minerals to meet the body's needs.

• The amount of food required depends on:

  • Energy expenditure during the day, influenced by factors like:

    • Body mass

    • Age

    • Body size

    • Activity levels

• Examples:

  • A manual worker requires more energy than a secretary.

  • A pregnant or lactating woman requires more protein than an average adult.

Why?

• Protein is essential for the growth of new cells.

• A pregnant woman needs to provide protein to her baby.

• Protein is also crucial for quality breast milk.

Energy Requirements

• Energy from food is measured in kilojoules (kJ).

• The energy provided by the diet must be enough to:

• Maintain internal body temperature.

• Support internal processes like respiration.

What is food needed for?

Growth of cells and repair of tissues

For energy released from respiration in the mitochondria

For a healthy immune system

The 7 components of a balanced diet:

1. Water

2. Simple and complex carbohydrates

3. Vitamins

4. Minerals

5. Lipids(fats)

6. Fibre

7. Protein

Apparatus:

• Boiling tube

• Stand, boss, and clamp

• Tongs

• Bunsen burner and mat

• Three types of biscuits

• Thermometer

• 10 cm³ measuring cylinder

• Access to an electronic balance

Method:

1. Measure 10 cm³ of tap water and pour it into the boiling tube.

2. Assemble the apparatus as shown by the teacher.

3. Record the initial temperature of the water.

4. Measure the mass of the biscuit piece.

5. Using tongs, light the biscuit and hold it under the boiling tube of water, ensuring to:

   • Hold the biscuit at an angle with the unburnt part higher.

   • Keep turning the biscuit to burn all parts.

6. Once the biscuit burns out, record the final temperature of the water.

Diagram:

• Shows a boiling tube held by a stand with water and a thermometer inside.

• The burning biscuit below is heating the water in the boiling tube.

Variables:

              • Independent Variable (Changed): Type of biscuit used.

              • Dependent Variable (Measured): Change in temperature of water.

              • Control Variables (Kept the same):

                           ○ Volume of water.

                           ○ Height of the biscuit from the flame.

Results:

Food     Mass of Food (g)             Initial Temp (°C) Final Temp (°C)           Temp Difference (°C)      Energy Content (J/g)

Ryvita    4.5        20         42         22         205

Cream Crackers 3.2        20         37         17         223

Digestive            4.7        20         41         21         188

Energy Calculation Formula:

Energy content (J/g)=Difference in temperature (°C)×Mass of water (g)×4.2(J/°C)Mass of food (g)\text{Energy content (J/g)} = \frac{\text{Difference in temperature (°C)} \times \text{Mass of water (g)} \times 4.2 (J/°C)}{\text{Mass of food (g)}}Energy content (J/g)=Mass of food (g)Difference in temperature (°C)×Mass of water (g)×4.2(J/°C)​

              • Note: 1 cm³ of water = 1 g.

Evaluation (Limitations):

              • Heat loss to surroundings (flame not always the same distance from water).

              • Inaccurate reading of the meniscus of the water.

              • Difficulty in burning the entire biscuit (breakage or incomplete combustion).

What is a calorimeter:

This is a calorimeter, a more accurate way of calculating the energy content of food. It works by using an electrically powered ignition coil to ignite the food in an atmosphere of pure oxygen.

How does this improve this experiment?

It has an insulated outer container resulting in little to no heat or energy escaping. The measurement of the temperature is also much more accurate and in a much more controlled environment. Furthermore, the oxygen supplied is much more pure whereas just from the surroundings. Having an electric heater also allows the sample to be heated up quicker and also prevents lost energy on the way from the Bunsen burner to the water bath. Due to stirrer, the heat is much more evenly distributed and since the Themometer is not near the source of ignition, it is not affected by the ambient temp.

Carbohydrates                                  

These contain carbon, hydrogen and oxygen.

They are mainly used as a source of energy that is released by respiration.

There are two types; simple and complex.

Complex carbohydrates are polymers built up from simple sugars. monomers and dimers   

Fibre

• Fibre consists of the bran of cereals and the cell walls of plant cells.

• It is indigestible by humans and passes unchanged through the digestive system.

• High-fibre foods add bulk, aiding peristalsis, which helps move food through the gut.

• Lack of fibre is linked to constipation and bowel cancer.

• Sources: cereals, brown bread, fruits, and vegetables.

Proteins

• Proteins are made of carbon, hydrogen, oxygen, and nitrogen, with some amino acids also containing sulfur.

• Proteins are polymers of amino acids, with 20 different amino acids.

• The body can produce some amino acids, but essential amino acids must come from the diet.

• Sources: meat, legumes (beans, lentils, chickpeas), and leguminous plants.

• Functions:

• Cell growth and tissue repair.

• Formation of hormones, antibodies, and enzymes.

• Excess proteins are broken down and used as energy since they cannot be stored.

Lipids (Fats and Oils)

• Lipids are made of carbon, hydrogen, and oxygen, but contain less oxygen than carbohydrates.

• Each lipid molecule consists of:

• A glycerol molecule.

• Three fatty acids.

Types of Lipids:

1. Saturated Fats:

   • Contain saturated fatty acids.

   • Solid at room temperature.

   • High intake can lead to coronary heart disease.

   • Sources: mostly animal fats (meat, dairy).

2. Unsaturated Fats:

   • Contain unsaturated fatty acids.

   • Liquid (oils) at room temperature.

   • Considered healthier.

   • Sources: mostly plant lipids (vegetable oils, margarine).

Functions of Lipids:

1. Store vitamins (especially Vitamin A).

2. Provide energy through respiration.

3. Form cell membranes.

4. Protect delicate organs by fat deposition.

5. Provide insulation.

Water

• Essential for survival: a person can live without food for weeks but only days without water.

• Found in liquids and many fruits and vegetables.

Functions of Water:

1. Integral to the cytoplasm for cell chemical reactions.

2. Makes up 55% of blood, allowing transport of food and waste.

3. Acts as a lubricant in joints, reducing friction and preventing damage.

4. Regulates body temperature through sweating.

5. Dissolves waste products, enabling their removal (e.g., urea in urine).

Vitamins

• These are complex chemicals which are only needed in very small quantities in the diet. 

• They are used to maintain the health and normal functioning of the body

1. Fat Soluble – found in the fat of fatty foods, stored in the body (usually in the liver) e.g. vitamins D and A.

2. Water Soluble – found in the water in foods and cannot be stored by the body e.g. vitamin C.

Minerals

These are inorganic elements which are needed in very small amounts in the diet.  They all have specific functions in the body.

Food Tests Summary

1. Test for Starch (Dimple Tile):

   • Reagent: Iodine solution (orange).

   • Colour Change: Turns blue-black if starch is present.

2. Test for Glucose (Heat):

   • Reagent: Benedict’s solution (blue).

   • Colour Change: Red-orange precipitate if glucose is present; green indicates less glucose, darker red indicates more.

   • Safety Concern: Heat in a water bath.

3. Test for Lipids:

   • Reagent: Ethanol and water.

   • Colour Change: Cloudy white emulsion if fat is present.

4. Test for Protein (Purple Protein):

   • Reagent: Biuret solution (pale blue).

   • Colour Change: Turns purple if protein is present

Important equations:

Glucose + Galactose = Lactose + water

Glucose + Glucose = Maltose and water

Glucose + fructose = sucrose + water