2.6 Nutrition (in Human)

REVISION NOTES

IGCSE Edexcel Biology

2.6 Nutrition (in Human)

2.6.1 Understand that a balanced diet should include appropriate proportions of carbohydrate, protein, lipid, vitamins, minerals, water and dietary fibre

Balanced diet

The necessary food groups are:
- Carbohydrates
- Proteins
- Lipids
- Vitamins
- Minerals
- Dietary fibre
- Water

2.6.2 Identify the sources and describe the functions of carbohydrate, protein, lipid (fats and oils), vitamins A, C and D, the mineral ions calcium and iron, water and dietary fibre as components of the diet

2.6.3 Understand how energy requirements vary with activity levels, age and pregnancy

2.6.4 Describe the structure and function of the human alimentary canal, including the mouth, oesophagus, stomach, small intestine (duodenum and ileum), large intestine (colon and rectum) and pancreas

2.6.5 Understand how food is moved through the gut by peristalsis

Peristalsis

- Helps move food along the alimentary canal (gut)
- Muscles in the oesophagus walls create waves of contractions
  - Forces the bolus along
  - Bolus is churned into chyme in the stomach
  - And it continues on to the small intestine
- Controlled by circular and longitudinal muscles
  - Circular muscles contract
  - Reduce the diameter of the lumen
  - Longitudinal muscles contract
  - Reduce the length of that section

Mucus lubricates the food mass and reduces friction

Dietary fibre provides the roughage

Required for the muscles to push against during peristalsis

2.6.6 Understand the role of digestive enzymes, including the digestion of starch to glucose by amylase and maltase, the digestion of proteins to amino acids by proteases and the digestion of lipids to fatty acids and glycerol by lipases

Carbohydrases:

Breakdown carbohydrate to simple sugars
Amylase
- Made in salivary glands, pancreas and small intestine
- Break down starch into maltose
Maltase
- Made in small intestine
- Break down maltose into glucose

Proteases:

Breakdown protein into amino acids
Pepsin & Trypsin
- Made in stomach and pancreas
- Breakdown proteins into small polypeptide chains
Other proteases such as peptidases
- Made in small intestine
- Breakdown peptides into amino acids

Lipases:

Made in pancreas
Breakdown lipids into glycerol and fatty acids

2.6.7 Understand that bile is produced by the liver and stored in the gall bladder

- Alkaline substance
- Produced in the liver
- Stored in gallbladder

Released into the small intestine

2.6.8 Understand the role of bile in neutralising stomach acid and emulsifying lipids

Role of bile

Neutralise hydrochloric acid (stomach acid)
- Bile is alkaline
- Reacts with and neutralise acids
- Neutralisation is necessary:
  - Enzymes in the small intestine have a higher optimum pH
Emulsifying lipids
- Breaks large drops of fat into smaller drops
- Increase the surface area of fats
- Increases rate of digestion
- Chemical break down

2.6.9 Understand how the small intestine is adapted for absorption, including the structure of a villus

Absorption:

Movement of small digested food molecules
From digestive system to blood and lymph

Adaptations of small intestines:

- Very long

Highly folded surface with millions of villi

Increased surface area

Structure of villi:

Large surface area

- Microvilli increase the surface area
Short diffusion distance
- Wall of a villus is one cell thick
Steep concentration gradient
- Network of blood capillaries take glucose and amino acids away from small intestine
- A lacteal transports fatty acids and glycerol away from the small intestine i
- Concentration gradient is maintained
- Small molecules transported at a rapid rate

2.6.10B Practical: investigate the energy content in a food sample

Method:

Add 25cm3 of water into a boiling tube
Record the starting temperature of the water
Weigh the initial mass of the food sample
Set fire to the sample of food using the bunsen burner
Hold the sample 1cm from the boiling tube until it has completely burned
Record the final temperature of the water
(Once cooled) weigh the mass of any remaining food sample and record
Repeat the process with different food samples
- e.g. popcorn, nuts, crisps

Results

A larger increase in water temperature indicates a larger amount of energy contained by the sample
We can calculate the energy in each food sample using the following equation:

Energy transferred (J) =

(mass of water (g) x 4.2 x temperature increase (°C)) ÷ (mass of food (g))