B2

• Cells make up all living things.
• A tissue is a group of specialised cells with a similar structure and function.
• Organs are formed from different tissues, working together to produce a specific function.
• Organs are organised into organ systems, which work together to perform a certain function.
• The digestive system is made up of:

  • Glands (salivary glands + pancreas) - produce digestive juices containing enzymes which break down food
  • Stomach - produces hydrochloric acid to kill bacteria and provide optimum pH for the protease enzyme
  • Small intestine - absorbs soluble molecules into the blood
  • Liver - produces bile stored in the gall bladder, which helps digest lipids
  • Large intestine - absorbs water from undigested food to produce faeces, which are passed out of the body through the rectum and anus
• Enzymes are biological catalysts.
• Enzymes have their own uniquely shaped active site where a substrate binds.
• The Lock and Key Hypothesis explains how enzymes work.
• The lock and key hypothesis:

  1. The shape of the substrate is complementary to the shape of the active site, so when they bond it forms an enzyme-substrate complex
  2. Once bound, the reaction takes place and the products are released from the surface of the enzyme.
• In too high temperatures, an enzyme's active site will change shape and become denatured.
• The optimal temperature for enzymes is 37°C.
• The optimum pH for most enzymes is 7. The exception to this is enzymes produced in acidic conditions such as the stomach.
• If the pH is too high or too low, the forces that hold the amino acid chains that make up the protein will be affected, damaging the active site and denaturing the enzyme.
• Carbohydrases convert carbohydrates into simple sugars.
• Proteases convert proteins into amino acids.
• Lipases convert lipids into fatty acids and glycerol.
• Benedict's test shows a solution to contain sugars if it turns brick red.
• An iodine test shows a solution to contain starch if it turns blue-black.
• A biuret test shows a solution to contain protein if it turns purple.
• An emulsion test shows a solution to contains lipids if there is a cloudy layer (ethanol)
• A Sudan III test shows a solution to contain lipids if a red layer forms on top.
• Bile is produced in the liver and stored in the gallbladder.
• Bile has two roles:

  • It's alkaline to neutralise the hydrochloric acid coming from the stomach
  • It breaks down large drops of fat into smaller ones (emulsifies it)
• The heart is an organ in the circulatory system.
• In the heart:

  • Deoxygenated blood flows into the right atrium, then the right ventricle, which pumps it to the lungs to undergo gaseous exchange
  • Oxygenated blood flows into the left atrium, then the left ventricle which pumps it around the body
• Structure of the heart:

  • Muscular walls - provides a strong heartbeat
  • Muscular wall of the left ventricle is thicker - blood needs to be pumped all around the body rather than just the lungs
  • 4 chambers - separate oxygenated blood from deoxygenated blood
  • Valves - make sure blood doesn't flow backwards
  • Coronary arteries - cover the heart to provide its own oxygenated blood supply
• Process of the heart:

  1. Blood flows into right atrium through the vena cava, and left atrium through the pulmonary vein
  2. Atria contract, forcing blood into the ventricles
  3. Ventricles contract, pushing the blood:

  • in the right ventricle into the pulmonary artery, taking the blood to the lungs
  • in the left ventricle into the aorta, taking the blood around the body

  1. Valves close during this process to stop blood flowing backwards
• A pacemaker is a group of cells found in the right atrium that control the natural resting heart rate.
• Artificial pacemakers are electrical devices that act as pacemakers for those who have an irregular heartbeat.
• Types of blood vessels include:

  1. Arteries - carry blood away from the heart

  • Have layers of muscle in the walls which make them strong
  • Have elastic fibres allowing them to stretch
  • This helps vessels withstand high pressure from pumping of heart

  1. Veins - carry blood towards the heart

  • Lumen is wide to allow low pressure blood to flow through
  • Valves to ensure blood flows in right direction

  1. Capillaries - allow blood to flow very close to cells to enable substances to move between them

  • One cell thick walls create a short diffusion pathway
  • Permeable walls so substances can move across them
• The rate of blood flow is calculated from volume of blood / number of minutes.
• The lumen is the actual tube in which blood flows through.
• The thorax is the top part of the body.
• The lungs are found in the thorax, are protected by the ribcage, and supply oxygen to the blood and remove carbon dioxide.
• The gas exchange system is made up of:

  • Trachea (the windpipe, air moves through)
  • Intercostal muscles (contract and relax to ventilate the lungs)
  • Bronchi (air from trachea move into these, lead to each lung)
  • Bronchioles (bronchi split into these, air moves in)
  • Alveoli (bronchioles lead to them, air sacs where gaseous exchange occurs)
  • Diaphragm (separates lungs from digestive organs, moves down causing inhalation)
• Ventilation:

  1. Ribcage moves up and out, diaphragm moves down - volume of the chest increases
  2. Increased volume = lower pressure
  3. Air drawn into the chest as air moves from high pressure (environment) to low pressure (lungs)
  4. Opposite happens when exhaling
• Gas exchange:

  1. Upon inhalation, alveoli fill with oxygen
  2. Blood in capillaries surrounding alveoli is deoxygenated. It has lots of carbon dioxide - a product of respiration
  3. Oxygen diffuses down conc. gradient from alveoli to capillary bloodstream (with low conc. of oxygen)
  4. Carbon dioxide diffuses down its conc. gradient from blood to alveoli
• Alveoli:

  • Are very small and arranged in clusters - creating large surface area for diffusion
  • Are provided a large blood supply - maintain the conc. gradient
  • Have very thin walls - short diffusion pathway
• Blood is made up of plasma, red blood cells, white blood cells and platelets.
• Plasma carries these components:

  • Red blood cells
  • White blood cells
  • Platelets
  • Glucose
  • Amino acids
  • Carbon dioxide
  • Urea
  • Hormones
  • Proteins
  • Antibodies
  • Antitoxins