Organisation

• A tissue is a group of cells with a similar structure and function
• An organ is a group of tissues that work together to perform a specific function
• The stomach contains muscle tissues and glandular tissue (which release enzymes)
• Organs are grouped into organ systems which work together to form organisms
• Food contains three main nutrients: carbohydrates(starch), proteins and lipids (fats). These are large molecules. They are too large to be absorbed into the bloodstream. So they have to be digested
• During digestion, large food molecules are broken down into small molecules by enzymes so that can be absorbed into the bloodstream
• Digestive system - mouth, oesophagus, stomach, liver, pancreas, intestines, rectum, anus
• Food digestion


  1. Chewed in mouth

  2. Enzymes in saliva digest starch into smaller sugar molecules

  3. Food passed down to oesophagus

  4. Food enters stomach

  5. Enzymes digest proteins

  6. Stomach contains hydrochloric acid to help digest proteins

  7. Stomach muscles churn food into fluid

  8. Fluid passes into small intestine

  9. Chemicals released from liver and pancreas

  10. Pancreas releases enzymes to digest starch, proteins and lipids

  11. Liver releases bile to speed up lipid digestion

  12. Small intestine walls release enzymes to continue protein and lipid digestion

  13. Small food molecules absorbed into bloodstream

  14. Fluid goes to large intestine

  15. Water absorbed into bloodstream

  16. Faeces released from body
• Enzymes catalyse (speed up) chemical reactions
• Enzymes are large proteins that help speed up metabolism, or the chemical reactions in our bodies
• Enzymes have an active site where the substrate fits and the enzyme catalyses the reaction
• The substrate must fit perfectly into the active site (the lock and key theory)
• Proteins are broken down by enzymes called proteases
• Proteins are long chains of chemicals called amino acids
• Starch is a chain of glucose molecules. Carbohydrates are broken down by enzymes called carbohydrases. The starch is called amylase. Amylase is found in the saliva and pancreatic fluid
• A lipid molecule is a molecule made up of a glycerol molecule and three fatty acids. Lipid molecules are digested by the enzyme lipase and this produces glycerol and fatty acids. Lipase is found in the pancreatic fluid and the small intestine
• Bile is in the liver and it helps speed the digestion of lipids but bile is not an enzyme. Bile is also an alkaline substance that neutralises stomach acid
• The products of digestion are absorbed into the bloodstream in the small intestine
• The small intestine has large surface area for the absorption of the products of digestion
• There's many villi's in the small intestine and they increase the surface area for the absorption of molecules
• Antibodies and hormones are transported to the blood
• Blood is pumped around the body by the heart. The heart has four chambers - two atria and two ventricles
• The artria is the upper chambers of the heart which receive blood from veins 
• The ventricles are the lower chamber of the heart that receives blood from the atrium and pumps it into arteries
• The blood pumps through two circuits: the pulmonary circuit and the systemic circuit.
• Pulmonary circulation - the part of the circulatory system that involves the right side of the heart, the lungs, and the blood vessels that connect them together
• Systemic circulation - The part of the circulatory system that includes the left side of the heart, the rest of the body apart from the lungs, and the blood vessels that connect them together
• At the lungs the oxygen diffuses into the blood from the alveoli - the blood become oxygenated