Welcome to Your Biology Notes: Understanding Nutrition!

Hello future Biologists! Get ready to explore one of the most fundamental processes of life: Nutrition. This chapter explains how living organisms—from tiny plants to huge humans—obtain and use the energy and materials they need to survive, grow, and function.

Think of nutrition as the fuel system for any living engine. Understanding it is key to understanding the structure and function of every organism! Don't worry if some terms look intimidating; we'll break everything down step-by-step. Let's dive in!


Section 1: The Basics of Nutrition

1.1 What is Nutrition?

Nutrition is the intake of food, required by all living organisms, and the processes that convert this food into energy and materials for growth, repair, and metabolism.

Two Main Types of Nutrition

Living things get their food in one of two fundamental ways:

  • 1. Autotrophic Nutrition ("Self-Feeding"): Organisms that make their own food, usually using light energy.
    • Example: Plants, algae.
  • 2. Heterotrophic Nutrition ("Feeding on Others"): Organisms that cannot make their own food and must consume other organisms (or organic matter) to obtain nutrients.
    • Example: Animals, fungi, some bacteria.
Quick Review: Plants are Auto, People are Hetero.

Section 2: Autotrophic Nutrition – Photosynthesis

The ultimate source of energy for almost all life on Earth comes from the process used by plants: Photosynthesis.

2.1 The Process of Photosynthesis

Photosynthesis is the chemical process where plants use energy from sunlight to convert carbon dioxide (CO₂) and water (H₂O) into glucose (sugar) and oxygen (O₂).

The Photosynthesis Equation

This is a core concept—you must know this equation!

Word Equation:
Carbon Dioxide + Water \(\xrightarrow{\text{Light Energy/Chlorophyll}}\) Glucose + Oxygen

Chemical Equation:
$$6\text{CO}_2 + 6\text{H}_2\text{O} \xrightarrow{\text{Light Energy/Chlorophyll}} \text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2$$


(Note: Glucose is the food the plant makes. Oxygen is a waste product, which is lucky for us!)

2.2 Requirements for Photosynthesis

For photosynthesis to happen, four things are essential:

  1. Carbon Dioxide (CO₂): Absorbed from the air through tiny pores in the leaves called stomata.
  2. Water (H₂O): Absorbed from the soil through the roots and transported up the stem via xylem vessels.
  3. Light Energy: Usually sunlight, but artificial light works too! This provides the energy to drive the reaction.
  4. Chlorophyll: The green pigment found in structures called chloroplasts. Chlorophyll's job is to capture light energy.

Did you know? Chlorophyll absorbs red and blue light most efficiently, but reflects green light, which is why most leaves appear green!

2.3 Leaf Adaptations for Photosynthesis

The leaf is specially structured to maximise the efficiency of photosynthesis:

  • Large Surface Area: Maximises the absorption of sunlight.
  • Thin Structure: Ensures a short diffusion distance for CO₂ to reach the cells inside.
  • Veins (Vascular Bundles): Contain xylem (for water transport) and phloem (for transporting the produced glucose away, often stored as starch).
  • Stomata: Pores, usually on the underside of the leaf, which open to allow CO₂ in and O₂/Water vapour out.
  • Chloroplasts (in Mesophyll cells): Packed with chlorophyll to capture light. The palisade mesophyll layer is located near the top of the leaf to get maximum sunlight.

KEY TAKEAWAY: Photosynthesis converts light energy into chemical energy (glucose), and the leaf is perfectly designed to make this happen.


Section 3: Heterotrophic Nutrition – A Balanced Diet

Since we cannot make our own food, humans and animals must consume a variety of substances to fulfil our nutritional needs.

3.1 Why Do We Need Food?

Food serves three main purposes in heterotrophs:

  1. Energy: For all life processes (movement, growth, maintaining body temperature).
  2. Growth and Repair: Building new cells and tissues, and fixing damage.
  3. Raw Materials: Providing essential chemical compounds that the body cannot synthesise itself.

3.2 Components of a Balanced Diet

A balanced diet is a diet that provides all seven essential food components in the correct proportions necessary to maintain health.

Mnemonic Alert! To remember the seven components, try this phrase: "Carla Found Protein Very Much In Fresh Water."

Component Main Role/Function Good Sources
1. Carbohydrates Primary source of energy. Bread, rice, pasta, potatoes.
2. Fats (Lipids) Energy storage, insulation, protective layer, essential for cell membranes. Oils, butter, nuts, fatty meat.
3. Proteins Essential for growth and repair; making enzymes, antibodies, and hormones. Meat, fish, eggs, beans.
4. Vitamins Needed in small amounts for specific body functions (e.g., healthy immune system, vision). Fruits and vegetables.
5. Minerals Inorganic substances needed for structure (bones) and essential processes (nerve signals). Salt, milk, leafy greens.
6. Fibre (Roughage) Provides bulk to food, aids peristalsis (movement of food through the gut), prevents constipation. Whole grains, vegetables, fruit skins.
7. Water Solvent for chemical reactions, transport medium (blood), temperature control (sweating). Drinking water, drinks, fruits.

3.3 Special Roles of Specific Components

Important Vitamins and Minerals to Know:
  • Vitamin C: Essential for maintaining healthy connective tissue and immune function. Found in citrus fruits.
  • Vitamin D: Needed for the absorption of calcium and phosphate in the gut. Synthesised by the skin in sunlight; found in oily fish.
  • Calcium: Mineral essential for building strong bones and teeth, and for blood clotting. Found in dairy.
  • Iron: Mineral essential for making haemoglobin, the pigment in red blood cells that transports oxygen. Found in red meat, spinach.

Remember this! Iron is needed to carry oxygen. Calcium is needed to make bones hard.

KEY TAKEAWAY: A balanced diet requires seven components in the right ratio. Carbohydrates and fats are for energy; proteins are for growth and repair.


Section 4: Malnutrition and Deficiency Diseases

Malnutrition occurs when a diet lacks the correct balance of nutrients—either too much, or more commonly, too little, of one or more components.

4.1 Common Deficiency Diseases

A lack of specific vitamins or minerals leads to serious health conditions:

  • Cause: Lack of Vitamin C
    Disease: Scurvy
    Symptoms: Bleeding gums, slow wound healing, weakness. (Historically common among sailors on long voyages).
  • Cause: Lack of Vitamin D and/or Calcium
    Disease: Rickets (in children) / Osteomalacia (in adults)
    Symptoms: Soft, weak bones leading to bowed legs. Vitamin D is needed for Calcium absorption!
  • Cause: Lack of Iron
    Disease: Anaemia
    Symptoms: Fatigue, paleness, breathlessness. This is because there isn't enough haemoglobin to transport oxygen efficiently.
  • Cause: Lack of Protein (especially in combination with low energy intake)
    Disease: Kwashiorkor and Marasmus
    Symptoms: Kwashiorkor causes growth failure and swelling/bloated abdomen (oedema). Marasmus is severe wasting due to general energy/protein lack.

Common Mistake to Avoid! Don't confuse the mineral (Calcium) with the vitamin (Vitamin D). You need Vitamin D to absorb Calcium!

4.2 Factors Affecting Dietary Needs

The amount of food and the type of nutrients an individual needs vary based on several factors:

  • Age: Growing children and teenagers need proportionally more protein and energy.
  • Sex: Men often require slightly more energy than women, and menstruating women need more iron.
  • Activity Level: Highly active people (e.g., athletes) need much more energy (carbohydrates/fats) than sedentary people.
  • Pregnancy/Lactation: Pregnant or breastfeeding women need extra calcium, iron, protein, and energy to support the baby.

You made it! You now have a strong grasp of the fundamental principles of nutrition, from how a leaf captures sunlight to what your body needs to stay healthy. Keep practising those equations and remember the roles of the seven key nutrients!