Organisation

• A tissue is a group of cells with a similar structure and function.
• An organ is a group of tissues working together for a specific function.
• The stomach contains muscle tissue and also glandular tissue which releases enzymes.
• Organs are grouped into organ systems which work together to form organisms.
• Food contains three main nutrients: carbohydrates such as starch, protein, and lipids, also known as fats.
• Large food molecules are broken down into small molecules by enzymes during digestion.
• The human digestive system consists of the mouth, esophagus, stomach, small intestine, and large intestine.
• In the mouth, food is chewed and enzymes in the saliva begin to digest a starch into smaller sugar molecules.
• The food then passes down the esophagus into the stomach where enzymes begin the digestion of proteins and the stomach also contains hydrochloric acid which helps the enzymes to digest proteins.
• The food spends several hours in the stomach, and the churning action of the stomach muscles turns the food into a fluid increasing the surface area for enzymes to digest the fluid.
• The fluid passes into the small intestine where chemicals are released into the small intestine from the liver and pancreas.
• The pancreas releases enzymes which continue the digestion of starch and protein and start the digestion of lipids.
• The liver releases bile which helps to speed up the digestion of lipids and also neutralizes the acid released from the stomach.
• The fluid makes its way through the large intestine where water is absorbed into the bloodstream and finally the feces is released from the body.
• In the digestive system, large food molecules are digested into smaller molecules and then the products of digestion are absorbed into the bloodstream.
• The products of digestion are then used by the body to build new carbohydrates, lipids, and proteins.
• Some of the glucose produced is used in respiration.
• Enzymes catalyze chemical reactions, speeding them up.
• Enzymes are large protein molecules with a groove on their surface called the active site.
• The substrate is the molecule that the enzyme breaks down.
• Proteins are broken down by enzymes called proteases and these are found in the stomach, pancreatic fluid, and small intestine.
• When proteins are digested, the protease enzymes convert the protein back to the individual amino acids which are then absorbed into the bloodstream.
• When amino acids are absorbed by the body cells, they join together in a different order to make human proteins.
• Starch consists of a chain of glucose molecules and is broken down by enzymes called carbohydrates.
• Specific enzymes called amylase are found in the saliva and pancreatic fluid and they digest carbohydrates like starch.
• Lipids are digested by the enzyme lipase, which produces glycerol and fatty acids.
• Lipase is found in the pancreatic fluid and small intestine.
• Bile is not an enzyme but it speeds up the digestion of lipids by converting large lipid droplets into smaller droplets.
• Bile also emulsifies the lipid, massively increasing the surface area of the lipid droplets, which increases the rate of lipid breakdown by lipase.
• Bile is alkaline and it neutralizes stomach acids, creating alkaline conditions in the small intestine, which increases the rate of lipid digestion by lipase.
• Enzymes speed up chemical reactions and have a groove on their surface called the active site where the substrate molecule fits perfectly.
• Enzymes are specific because the substrate must fit perfectly into the active site, a concept known as the lock and key theory.
• The rate of an enzyme catalyzed reaction increases as the temperature increases, up to a certain point known as the optimum temperature, after which the activity of the enzyme decreases to zero due to denaturation.
• The optimum temperature for most human enzymes is 37 degrees Celsius, which is human body temperature.
• As the temperature increases past the optimum temperature, the activity of the enzyme decreases to zero due to denaturation.
• The effective pH on enzyme activity is altered by changing the pH of an enzyme catalyzed reaction, with the enzyme having an optimum pH where the activity is maximum.
• If the pH is made more acidic or more alkaline, the activity of the enzyme drops to zero as the active site denatures.
• Each enzyme has a specific optimum pH, for example, a protease enzyme in the stomach works best at an acidic pH, while an enzyme released from the pancreas into the small intestine, such as lipase, works best at an alkaline pH.
• The chemical tests for carbohydrates, proteins, and lipids are required practicals that contain a lot of detail.
• The key things to learn for these tests are the chemicals used to test for each food group and the positive results.