organisation

• cells make up all living things
• a tissue is a group of specialised cells with similar structure and function
• organs are formed from different tissues which work together to perform a specific function
• organs are organised into organ systems which work together to preform a specific function
• digestive system:

  • salivary gland and pancreas, digestive juices with enzymes break food down
  • stomach, produces hydrochloric acid to kill bacteria and provide optimum pH for protease enzyme to work
  • small intestine, where soluble molecules are absorbed into blood
  • liver, produces bile stored in gall bladder which helps digestion of lipids
  • large intestine, absorbs water from undigested food to make faeces which is excreted via rectum and anus
• enzymes are biological catalysts that increase rate of reaction without being used up
• enzymes are protein molecules
• each enzyme has its own uniquely shaped active site and substrate
• lock and key theory:

  • shape of substrate is complementary to the active site so when they bond they form an enzyme-substrate complex
  • once bound, the reaction takes place and products are released from the enzyme surface
• enzymes require an optimum pH and temperature because they are proteins
• optimum temperature of the body is 37 degrees celcius
• what happens to enzymes when temperature is too high:

  • rate of reaction increases with temperature but above optimum it rapidly decreases and reaction stops
  • when temperature becomes too hot, bonds in the structure break
  • this changes shape of the active site so substrate does not fit
  • enzyme is therefore denatured and cannot work
• optimum pH for most enzymes is 7 but in the stomach the pH is acidic
• what happens when pH isn't right for enzymes:

  • if pH is too high or low, forces holding amino acid chains making up the protein will be affected
  • this changes the shape of the active site so substrate cannot fit
  • enzyme is denatured and no longer works
• carbohydrase (enzyme)

  • converts carbohydrates into simple sugars
  • e.g amylase breaks down starch into maltose
  • produced by salivary glands, pancreas, small intestine
• protease (enzyme)

  • converts proteins into amino acids
  • e.g pepsin in the stomach
  • found in pancreas and small intestine too
• lipase (enzyme)

  • covert lipids into fatty acids and glycerol
  • produced in pancreas and small intestine
• Benedict's is the test used for sugars, if present it turns brick red
• Iodine test is the test used for starch, if present it turns blue-black
• Biuret Reagent is the test used for protein, if present it turns purple
• Emulsion test is the test for lipids, if present there is a cloudy layer
• bile is produced in the liver and stored in the gall bladder, where it is then released into the small intestine
• roles of bile

  • alkaline to neutralise hydrochloric acid in stomach, enzymes in small intestine have higher optimum pH than in the stomach
  • emulsifies fat, the larger the surface area allows lipase to chemically break down lipids into fatty acids and glycerol faster
• test for enzymatic reactions (breakdown starch to maltose by amylase)

  • place drop of iodine on spotting tile
  • use water bath to warm amylase solution, starch and a buffer solution (IV)
  • at regular points, place drops of the solution in wells
  • starch is no longer present and completely broken down when the iodine solution remains brown
  • rate = change$\div$time
  • repeat for different pH values
• the heart is an organ in the circulatory system
• 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

  • deoxygenated blood flows into the right atrium and goes to the right ventricle which pumps it into the lungs to undergo gas exchange
  • oxygenated blood flows into the left atrium and then into the left ventricle which pumps oxygenated blood through the body
• structure of the heart

  • muscular walls provide a strong heartbeat
  • muscle wall on left ventricle is thicker as blood needs to be pumped across the entire body
  • 4 chambers separating the oxygenated and deoxygenated blood
  • valves to prevent blood flowing backwards
  • coronary arteries cover heart to provide its own blood supply
• process of the heart

  • blood flows into right atrium via vena cava, and left atrium through the pulmonary vein
  • atria contracts forcing blood into the ventricles
  • ventricles contract pushing blood into the pulmonary artery to take to the lungs, and blood in left ventricle to be taken to the aorta to be taken around the body
  • valves close to make sure blood does not flow backwards
• a natural resting heart rate is 70 beats per minute controlled by a group of cells in the right atrium that act as a pacemaker
• the pacemaker in the heart provides stimulation through electrical impulses which pass as a wave across the muscle causing it to contract
• an artificial pacemaker can be used if an individual has an irregular heartbeat
• arteries

  • carry blood away from heart
  • layers of muscle in the walls to make them strong
  • elastic fibres allow them to stretch
  • help vessels withstand high pressure created by the pumping of the heart
• veins

  • carry blood towards the heart
  • lumen is wide to allow low pressure blood to flow through
  • valves to ensure blood flows in the right direction
• capillaries

  • allow blood to flow close to cells to enable substances to move between them
  • one cell thick so short diffusion pathway
  • permeable walls so substances can move across them
• rate of blood flow = volume of blood $\div$ number of minutes
• lungs are found in your thorax and are protected by the ribcage, they supply oxygen to the blood and remove carbon dioxide
• parts of the gas exchange system:

  • trachea
  • intercostal muscles
  • bronchi
  • bronchioles
  • alveoli
  • diaphragm
• ventilation

  • ribcage moves up and out, and diaphragm moves down causing the volume of the chest to increase
  • increased volume results in lower pressure
  • air is drawn into the chest as air moves from areas of high to low pressure
  • opposite happens when exhaling
• gas exchange:

  • upon inhalation, the alveoli fill with oxygen
  • blood in capillaries surrounding alveoli is deoxygenated and has lots of carbon dioxide as it is a product of respiration
  • oxygen diffuses down a concentration gradient into capillary bloodstream
  • carbon dioxide diffuses down a concentration gradient from the blood to the alveoli