Summary AQA GCSE Biology Combined Science - Organisation Notes

ORGANISATION
PRINCIPLES OF ORGANISATION
 Cells make up all living things
 Tissue: a group of specialised cells with a similar structure and function
 Organ: a number of different tissues, working together to produce a specific function
 Organ system: a group of organs which work together to perform a certain function




THE HUMAN DIGESTIVE SYSTEM
 The function of the digestive system is to break down large, insoluble food molecules so it
can be absorbed by cells
 The digestive system is made up of:
o Glands: produce digestive juices containing enzymes which break down food
o Stomach: produces hydrochloric acid to kill bacteria and provide the optimum pH for
protease, churns food
o Small intestine: food molecules are absorbed into the blood
o Liver: produces bile which helps with the digestion of lipids
o Large intestine: absorbs water from undigested food




FOOD TESTS
 Benedict’s test: for sugars, turns brick red
 Iodine test: for starch, turns blue-black
 Biuret test: for protein, turns purple
 Ethanol test: for lipids, ethanol turns cloudy




ENZYMES
 Enzymes are biological catalysts
o A biological catalyst is a substance that increases the rate of reaction without being
used up
 Each enzyme has its own uniquely shaped active site where the substrate binds
 THE LOCK AND KEY HYPOTHESIS
o The shape of the substrate is complementary to the shape of the active site
o They form an enzyme-substrate complex
o Reaction takes place and the products are released
 ENZYMES REQUIRE AN OPTIMUM pH AND TEMPERATURE AS THEY ARE PROTEINS
o Optimum temperature is 37 degrees

,  Rate of reaction increases with the temperature up to the optimum, above
this it rapidly decreases and the reaction eventually stops
 The bonds in the structure break
 This changes the shape of the active site so the substrate no longer fits
 The enzyme is denatured
o Optimum pH is 7
 If the pH is too high or low, the forces that hold the amino acid chains that
make up the protein will be affected
 The shape of the active site changes and the enzyme is denatured
 DIGESTIVE ENZYMES
o AMYLASE
 Converts starch into maltose
 Produced in the salivary glands, pancreas and small intestine
 Found in the mouth
o PROTEASE
 Converts protein into amino acids
 Produced in the stomach, pancreas and small intestine
 Found in the stomach and small intestine
o LIPASE
 Converts lipids into fatty acids and glycerol
 Produced in the pancreas and small intestine
 Found in the pancreas and small intestine




THE HEART
 The circulatory system carries oxygen and nutrients to every cell in the body and removes
waste products
 The heart pumps blood around the body in a double circulatory system. This means there
are two circuits:
o Deoxygenated blood: flows into the right atrium and then into the right ventricle
which pumps it to the lungs to undergo gas exchange
o Oxygenated blood: flows into the left atrium and then into the left ventricle which
pumps oxygenated blood around the body
 STRUCTURE OF THE HEART
o Muscular walls to provide a strong heartbeat
o The muscular wall of the left ventricle is thicker because blood needs to be pumped
all around the body rather than just to the lung like the right ventricle
o 4 chambers that separate the oxygenated blood from the deoxygenated blood
o Valves to make sure blood does not flow backwards
o Coronary arteries cover the heart to provide its own oxygenated blood supply
 PROCESS
o Blood flows into the right atrium through the vena cava and left atrium through the
pulmonary vein
o The atria contract forcing the blood into the ventricles