Biology IGCSE Food and Digestion

Enzymes

Enzyme action – Lock and Key Theory

Enzymes and temperature AMore kinetic energy More collisions Rate increases BOptimum CDenaturation Active site destroyed Rate reduced Temperature Rate 40 A B C

Enzymes and pH Enzymes have optimal pH Pepsin is a protease It is found in the stomach Its optimal pH is pH 2 pH Rate 2 7

Food Energy Fibre Energy Insulation Protection Enzymes Haemoglobin Muscle Antibodies Energy Carbohydrates Fats Proteins

Carbohydrates “Fuel” 5% of body mass Made of C, H and O. Monosaccharides and disaccharides = sugars eg. glucose, fructose. Polysaccharides = polymers of sugar eg. starch, glycogen, cellulose.

Lipids 10% of body mass Made of C, H and O, but less O. Fats and oils Made of glycerol + 3 fatty acids Saturated and unsaturated fatty acids

Proteins 18% of body mass Made of C, H, O, N and sometimes other elements in small quantities eg S Polymers of amino acids About 20 different amino acids

Proteins Genes determine the order of the amino acids. The order of the amino acids determine the shape of the protein. The shape of the protein determines its function.

Food Vitamins and minerals - needed in small amounts to stay healthy and prevent disease Eg vitamin D for bones (rickets) Iron for haemoglobin (anaemia)

Visking tubing experiment Semi-permeable membrane Filled with starch and amylase Wait 5 minutes Test both solutions with iodine with Benedict’s solution

Visking tubing experiment Inside membrane Iodine goes black Benedict’s goes red Both starch and sugar present

Visking tubing experiment Outside membrane Iodine stays brown Benedict’s goes red Starch is too large to cross the membrane

Digestion Why do we digest food? To turn large molecules into smaller molecules so we can absorb them into our body. How do we digest food? Using enzymes – biological catalysts. Molecules which speed up reactions without being altered themselves.

Digestive Organs Mouth Teeth Mechanical digestion

Digestive Organs Mouth Saliva Chemical digestion

Starch A carbohydrate store in plants A polysaccharide Made of many glucose molecules Too big to pass through cell membranes

Digestion of starch Amylase Salivary amylase Pancreatic amylase

Digestion of starch Maltose (a disaccharide)

Digestive Organs Oesophagus Pushes bolus of food to stomach by peristasis

Peristalsis Circular muscles contract behind the bolus

Peristalsis Circular muscles relax in front of the bolus

Peristalsis Longitudinal muscles contract This pulls the gut back over the advancing food

Peristalsis Eventually the bolus is squeezed into the stomach

Digestive Organs Stomach Digests food chemical - enzymes mechanical - churning Sterilises food

Digestive Organs Pancreas Releases digestive enzymes Releases hormones (e.g. insulin)

Digestive Organs Small intestine Digests food Food absorbed into blood

Digestive Organs Liver Stores vitamins Stores glycogen Breaks down proteins to form urea Produces bile Gall bladder Stores bile releases bile into the small intestine

Small intestine Villi Large surface area Muscle Peristalsis

Protein Found in meat / pulses Long chain of amino acids Many types of amino acids Too big to pass through cell membranes

Digestion of proteins Proteases Stomach (from stomach lining) Small intestine (from pacreas)

Digestion of proteins Amino acids

Lipids Fats / Oils Glycerol joined to 3 fatty acids saturated (animal fats) unsaturated (plant oils) Too big to pass through cell membranes

Digestion of lipids Lipases Small intestine (from pancreas)

Digestion of lipids Glycerol Fatty acids

Digestion of lipids

Add Bile salts

Villi and Microvilli

Small intestine Each epithelial cell has microvilli

Digestive Organs Large intestine Absorbs water

Digestive Organs Rectum Compacts faeces Stores faeces Anal sphincter Ring of muscle Releases faeces