Need For Food Food is needed for: Energy - provide heat and allow movement Building Materials - For growth and tissue repair Protection - prevent illness and disease

Chemicals in food Foods are separated into 3 groups: Fats, Carbohydrates, and Proteins All 3 types contain Carbon (C), Hydrogen (H), and Oxygen (O) Proteins also contain Nitrogen (N)

Carbohydrates Energy-rich foods In plants Excess glucose is converted into starch and cellulose - both large insoluble substances Cellulose is indigestable - forms roughage in the diet (bulks up faeces) In animals Excess glucose is stored as glycogen in the liver

Fats Releases about twice as much energy as carbohydrates Composed of fatty acids and glycerol Excess fat is stored under the skin and around the kidneys Provides insulation and padding

Fats Releases about twice as much energy as carbohydrates Is composed of fatty acids and glycerol Copy figure 12.5 in the textbook - pg. 112 Excess fat is stored under the skin and around the kidneys - provides and insulation and padding.

Protein Protein is made up of many building blocks - called amino acids Excess protein cannot be stored in the human body. Minimum daily intake is 80g - required for growth and tissue repair. Excess protein is used for energy. Structural proteins make up tissues - only used as an energy source in an emergency (eg starvation)

Anorexia “I eat too much to die, and not enough to stay alive. I’m sitting in a riddle, waiting..” “I want to be so skinny that I rot from view. I want to walk in the snow and not leave a footprint” Rachel James Taken from Manic Street Preachers, The Holy Bible - Track 7: 4st 7lb

Need For Digestion Every cell needs a supply of food. Food is carried to the cells by the bloodstream. Food must be digested first. Digestion : breakdown of large insoluble food particles into small soluble particles for absorption into the bloodstream.

Teeth Teeth break food down mechanically into small pieces Omnivore Eats both plant and animal material Have 4 sets of teeth all of roughly equal size Incisor - for biting Canine - for tearing Molar and Pre-Molar - for crushing & grinding

Teeth (2) Carnivore Normally only eats animal material Long curved canine teeth - for piercing and holding Premolars & Molars - sharp cutting edges Carnassial teeth - at the back of the mouth, effective at shearing bone and slicing tendons

Teeth (3) Herbivore Only eats plant material Incisors & Canines - on lower jaw only. Bite against a horny pad on lower jaw to crop grass. Large space between front teeth and back teeth Jaws move side to side so enamel ridges on teeth slide over each other - can grind down tough plant material.

Digestive System on food Food passes along the alimentary canal Associated organs connected to canal by ducts ( salivary glands, pancreas, liver) These produce digestive juices Food passed along the alimentary canal by peristalsis Gut muscle contracts (squeezes) behind food, and relaxes in front of it In the stomach, muscle contractions churn the food Sphincter muscles open and close to let food in and out

Digestive Enzymes Promote the digestion of foodstuffs Amylase: Found in saliva & pancreas Digests starch into sugar (maltose) Pepsin: a protease enzyme found in the stomach Digests protein into amino acids Works best at a low pH (acidic) Lipase: Made in pancreas, works in small intestine Digests fat into fatty acids Fat digestion helped by bile (from gall bladder) Food digestion involves several digestive enzymes