2.24: Understand that a Balanced Diet Includes appropriate Proportions of Carbohydrate, Protein, Lipid, Vitamins, Minerals, Water and Dietary Fibre

BALANCED DIET: Diet in which all components needed to maintain health are present in appropriate proportions

• Humans need to eat a balanced diet to ensure the body is provided with components to maintain good health

IMPORTANT DIETS CONSIST OF:

DIET
CARBOHYDRATE	LIPIDS	WATER
PROTEIN	DIETARY FIBRE
VITAMINS	MINERALS

2.26: Understand How Energy Requirements Vary with Activity Levels, Age and Pregnancy

FACTORS THAT AFFECT ENERGY REQUIREMENTS:

FACTOR	EXPLANATION
AGE	Amount of energy required increases towards adulthood for growth and muscle development
ACTIVITY LEVELS	Amount of energy required increases with activity level as more energy is needed to allow muscle contractions to facilitate exercise via respiration
PREGNANCY	Amount of energy required by Females during pregnancy will increase as more energy is needed to support the growth of developing fetus, and the large mass that the Mother will carry around

2.25: 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

DIET	FUNCTION
CARBOHYDRATE	Direct energy source Deficiency: Lack of energy Source: Meat, Starch
PROTEIN	Growth and repair Deficiency: Marasmus - poor growth Source: Meat
VITAMIN A	Healthy eyesight Deficiency: Night Blindness Source: Carrots
VITAMIN C	Heal wounds and rebuilds tissue Deficiency: Scurvy - bleeding gums Source: Lemon
VITAMIN D	Strengthen teeth and bones Deficiency: Rickets - curvature of bones Source: Margarine
LIPID	Insulation and Energy Storage Source: Meat
DIETARY FIBRE	Lowers Cholesterol Deficiency: Constipation Source: Vegetables
CALCIUM	Strengthen Teeth and Bones Deficiency: Rickets - curvature of bones Source: Milk
IRON	Promote Haemoglobin Deficiency: Anaemia - poor Oxygen transport Source: Meat
WATER	Allows chemical reactions to occur Source: Water

2.27: 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

ALIMENTARY CANAL: Digestive tract from Mouth to Anus

STRUCTURE OF ALIMENTARY CANAL:

                                       

Diagram showing Structure of Alimentary Canal

STRUCTURE OF ALIMENTARY CANAL:

STRUCTURE	FUNCTION
MOUTH	Mechanical digestion occurs Large food is turned into a bolus to provide large surface area to volume ratio for salivary Amylase to break down Starch in food into Glucose Saliva lubricates bolus for easy swallow
OESOPHAGUS	Tube connecting Mouth to Stomach Peristalsis (wave-like contractions) occurs to push bolus down the tube towards Stomach
STOMACH	Peristalsis continues mechanical digestion, and enzymes begin chemical digestion Hydrochloric acid maintains Optimum pH to increase rate of enzyme activity and metabolic reactions
SMALL INTESTINE	Lined with Villi to absorb digested soluble molecules into the circulatory system for use
LARGE INTESTINE	Absorbs Water from undigested food to produce faeces (stored in the Rectum and removed through the Anus)
PANCREAS	Synthesises pancreatic enzymes (Amylase, Protease, and Lipase) Secretes pancreatic enzymes into the Stomach and Small intestine for digestion

2.28: Explain How and Why Food is Moved through the Gut by Peristalsis

PERISTALSIS: Wave-like muscle contractions that push food bolus down the Oesophagus from Mouth to Anus - occurs in Stomach and Gut

PERISTALSIS

Diagram showing the Process of Peristalsis

EXPLANATION: Peristalsis occurs as a result of the rhythmic contraction and relaxation of two muscles controlled unconsciously by the nervous system Circular muscle changes the radius of the Oesophagus, while the Longitudinal muscle changes length of Oesophagus Contraction of Circular muscle behind the food bolus constricts the gut to prevent bolus from being pushed back towards the Mouth Contraction of Longitudinal muscle where food bolus is located moves it along the gut As a result, wave-like muscle contractions occur which pushes the food bolus from Mouth to Anus

PURPOSE: As food bolus is pushed only a few centimetres at a time, progression through intestine is slow, allowing time for digestion This allows the churning of semi-digested food as they mix food bolus with enzymes, increasing rate of digestion

2.29: 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

ENZYME	REACTION	MOLECULE
AMYLASE / MALTASE	Starch → Glucose
PROTEASE	Protein → Amino Acids
LIPASE	Lipids → Fatty Acids & Glycerol

2.30: Understand that Bile is Produced by the Liver and Stored in the Gall Bladder

BILE: Alkaline substance produced in the Liver and stored in the Gall Bladder

• Bile emulsifies large Lipid molecules into droplets with larger surface area to volume ratio to increase the rate of digestion

Diagram:

                                   

Diagram showing the Production and Storage of Bile

2.31: Understand the Role of Bile in Neutralising Stomach Acid and Emulsifying Lipids

BILE: Alkaline substance produced in the Liver and stored in the Gall Bladder

FUNCTIONS OF BILE:

FUNCTIONS OF BILE

Diagram showing Production of Bile

FUNCTIONS:     1. NEUTRALISING STOMACH ACID Enzymes in Small intestine function optimally in Alkaline conditions (optimum pH of 8-14) However, churning of food in Stomach by Hydrochloric acid creates Acidic environment Therefore, Bile will neutralise Hydrochloric acid to maintain Alkaline conditions, allowing optimum enzyme activity and increasing the rate of metabolic reactions     2. EMULSIFYING LIPIDS As the breakdown and digestion of Lipid molecules require a long period of time, Bile is used to emulsify large Lipid molecules into small droplets Lipid droplets will have a larger surface area to volume ratio, allowing faster breakdown by Lipase into Fatty acids and Glycerol, hence increasing the rate of lipid digestion

2.33B: Practical: Investigate the Energy Content in a Food Sample

INVESTIGATING ENERGY CONTENT IN FOOD SAMPLE

Diagram showing Investigation of Energy Content in Food Sample via Combustion

METHOD: Measure a fixed volume of Water into a boiling tube Use a thermometer to measure the temperature of Water Use a weighing scale to measure the mass of food sample Burn food sample via complete combustion and hold directly underneath the boiling tube to heat the Water until it burns out Use thermometer to measure the final temperature of Water

EQUATION: Equation to calculate Energy Transferred to Water is (Energy content in Food):

2.32: Understand How the Small Intestine is Adapted for Absorption, Including the Structure of a Villus

VILLUS: Small finger-like projections lining the Intestine wall that absorb digested soluble food molecules

Diagram:

                                      

Diagram showing Structure of Villi

ADAPTATIONS:

ADAPTATION	FUNCTION
THIN CELL WALL	Thin cell wall (one cell thick) to minimise distance of diffusion of digested soluble molecules, therefore increasing the rate of absorption
LARGE SURFACE AREA TO VOLUME RATIO	Folded to increase surface area to volume ratio for diffusion of digested soluble molecules, therefore increasing the rate fo absorption
DENSE CAPILLARY NETWORK	Dense capillary network nearby to provide rich blood supply, creating a strong concentration gradient for the diffusion of digested soluble molecules, therefore increasing the rate of absorption
LACTEAL	Lacteal absorbs and transports Fatty acids and Glycerol from Intestine to Lymphatic system