Introduction

Welcome! In this chapter, we are going to look at three very practical areas of Human Biology: how we use and look after our teeth, how we measure if our body weight is in a healthy range (BMI), and how we keep our food safe to eat. These topics are all part of the Nutrition and Digestion section because they focus on the "entry point" of our nutrients and how those nutrients affect our long-term health.

Note: For details on what makes a balanced diet or how enzymes break down food, please see the other chapters in this section!

1. All About Teeth

Teeth are essential for mechanical digestion. Before enzymes can work on your food, your teeth have to break it down into smaller pieces to increase the surface area.

Types of Teeth and Their Functions

Humans have four main types of teeth, each with a specific job:

  • Incisors: These are the sharp, chisel-shaped teeth at the front. Their job is biting and cutting pieces of food.
  • Canines: These are the more pointed teeth next to the incisors. They are used for tearing food.
  • Premolars and Molars: These are the large, flat teeth at the back of the mouth. They are used for crushing and grinding food into a paste before you swallow.

The Structure of a Tooth

If you were to look at a cross-section of a tooth, you would see several distinct layers:

  1. Enamel: The extremely hard outer layer. It protects the tooth but can be dissolved by acids.
  2. Dentine: A bone-like layer under the enamel. It is hard but not as tough as enamel.
  3. Pulp Cavity: The hollow center of the tooth containing blood vessels (to provide nutrients) and nerves (which allow you to feel heat, cold, or pain).
  4. Cement: This layer helps anchor the tooth into the jawbone.
  5. Gums: The soft tissue that covers the bone and surrounds the base of the teeth.

Care of Teeth and Gums

Bacteria in your mouth mix with saliva and food particles to form a sticky film called plaque. If you eat too much sugar, these bacteria turn the sugar into acid, which dissolves the enamel and causes tooth decay (cavities). To prevent this, you should:

  • Brush regularly to remove plaque.
  • Use fluoride toothpaste (fluoride strengthens enamel).
  • Avoid sugary snacks between meals.

Did you know? Gum disease is often caused by plaque building up around the base of the tooth, which can make gums bleed and eventually cause teeth to fall out!

Quick Review: Teeth

Key Takeaway: Incisors cut, canines tear, and molars grind. Keeping them healthy requires low sugar intake and regular cleaning to prevent acid damage.

2. BMI and Health Risks

How do we know if a person is a healthy weight for their height? One common tool is the Body Mass Index (BMI).

Calculating BMI

In your exam, you may be asked to calculate BMI. You must memorize this formula:

\( \text{BMI} = \frac{\text{mass in kg}}{(\text{height in m})^2} \)

Example: If a person weighs \( 70 \text{ kg} \) and is \( 1.75 \text{ m} \) tall:
1. Square the height: \( 1.75 \times 1.75 = 3.0625 \)
2. Divide the mass by that number: \( 70 \div 3.0625 = 22.86 \)
3. Their BMI is approximately \( 22.9 \).

Obesity and Disease

A very high BMI usually indicates obesity. This isn't just about weight; it has serious health consequences:

  • Early-onset Diabetes: Obesity is a major risk factor for developing Type 2 diabetes, where the body’s cells stop responding properly to insulin.
  • High Cholesterol and Atherosclerosis: If a diet is too high in certain fats, cholesterol levels in the blood can rise. This leads to atherosclerosis, which is the hardening and narrowing of the arteries. This can eventually lead to heart disease.

Common Mistake: When calculating BMI, students often forget to square the height. Always remember: \( \text{mass} \div (\text{height} \times \text{height}) \)!

Quick Review: BMI

Key Takeaway: BMI is a ratio of weight to height. High BMI (obesity) increases the risk of diabetes and heart problems like atherosclerosis.

3. Food Hygiene

Food hygiene is all about preventing pathogenic microorganisms (like bacteria) from entering our bodies through the food we eat.

Hygienic Preparation and Cooking

  • Preparation: Always wash hands before touching food. Use different chopping boards for raw meat and vegetables to avoid cross-contamination.
  • Cooking: High temperatures kill most bacteria. It is important to ensure food (especially meat) is cooked all the way through to the center.

Storage and Preservation

Bacteria need warmth, moisture, and nutrients to grow. We can stop them by changing their environment:

  • Refrigeration (Storage): Keeping food at low temperatures (around \( 5^\circ\text{C} \)) slows down the growth of bacteria.
  • Freezing: Stops bacterial growth completely, though it doesn't always kill the bacteria—they just become inactive.
  • Preservation Techniques:
    • Canning: Food is heated to kill bacteria and then sealed in an airtight tin to keep others out.
    • Pickling: Using vinegar (acid) to create an environment where bacteria cannot survive.
    • Drying/Salting: Removing water so bacteria cannot grow.

Don't worry if this seems like a lot to remember! Just think about what bacteria need to live (warmth and water). If you take those away, the food stays safe!

Quick Review: Hygiene

Key Takeaway: Hygiene involves killing bacteria (cooking), slowing their growth (cooling), or preventing their entry (sealing/canning).

Summary Checklist

Can you:
1. Name the four types of teeth and their functions?
2. Identify enamel, dentine, and the pulp cavity on a diagram?
3. Use the BMI formula correctly in a calculation?
4. Explain how obesity leads to diabetes and atherosclerosis?
5. List three ways to preserve food and explain how they work?