B2

• A tissue is a group of specialised cells that have a similar structure and function. They can be made up of more than one type of cell. Examples: muscular tissue, epithelial tissue, nervous tissue.
• Organs are formed from a number of different tissues, working together to produce a specific function. Example: the stomach, which has muscular tissue and epithelial tissue.
• Organs are organised into organ systems, which work together to preform a certain function. The stomach is part of the digestive system, along with organs such as the liver and small intestine.
• The digestive system is an organ system which does a specific function: food is large and insoluble and needs to be broken down in order for it to be in a form that can be absorbed by cells.
• The digestive system is made up off:

  • Glands (salivary glands and the pancreas) produce digestive
  • juices containing enzymes which break down food.
  • The stomach produces hydrochloric acid to kill bacteria and provide the optimum pH for the protease enzymes to work.
  • The small intestine is were soluble molecules are absorbed into the blood.
  • The liver produces bile which is stored in the gall bladder, which helps with the digestion of lipids.
  • The large intestine absorbs water from the undigested food to produce faeces.
• Enzymes: biological catalysts (a substance that increases the rate of a reaction without being used up)

  • Enzymes are present in reactions so that they can be controlled.
  • They can both break up large molecules and join small ones.
  • They are protein molecules and the shape of the enzyme is vital to its function.
  • This is because each enzyme has its own uniquely shapes active site where the substrate binds.
• The lock and key theory:

  • The shape of the substrate is complementary to the shape of the active site, so when they bond it forms an enzyme-substrate complex.
  • Once bound, the reaction takes place and the products are released from the surface of the enzyme.
• Enzymes require an optimum pH and temperature, because they are proteins.
• The optimum temperature for enzymes is around 37 degrees celsius (body temp.)

  • The rate of reaction increases with an increase in temperature up to the optimum.
  • Above the optimum temperature the enzyme's rate of reaction will rapidly decrease and eventually stop.
  • When the temperature becomes too hot then the bonds in the structure will break.
  • This changes the shape of the active site therefore the substrate will no longer fit. This is called: denatured.
• Carbohydrases convert carbohydrates into simple sugars.

  • Example: amylase breaks down starch into maltose.
  • - It is produced in your salivary glands, pancreas and small intestine.
• Protease convert proteins into amino acids.

  • Example: pepsin which is produced in the stomach, other forms can be found in the pancreas and small intestine.
• Lipases convert lipids into fatty acids and glycerol.

  • Produced in the pancreas and small intestine.
• Soluble, glucose, amino acids, fatty acids and glycerol pass to the bloodstream to be carried to all the cells around the body. They are used to build new carbohydrates, lipids and proteins with some glucose being used in respiration.
• There are different tests that can be carried out to determine whether a solution is made of carbohydrate, protein or lipid.

  • Benedict's test for sugars (turns bright red)
  • Iodine test for starch (turns blue-black)
  • Biuret test for protein (turns purple)
  • Emulsion test for lipids (add ethanol which results in a cloudy layer if a lipid is present)
  • Sudan ||| test (red layer forms on top)
• Bile is produced in the liver and stored in the gallbladder. It is then released into the small intestine.
• Bile has two rolls:

  • It is alkaline to neutralise the hydrochloric acid which comes from the stomach.
  • it breaks large drops of fat down into smaller ones. (Emulsifies it)
• The heart is an organ in the circulatory system.
• The circulatory system carries oxygen and nutrients to every cell in the body and removes the waste product.
• The heart pumps blood around the body in a double circulatory system. This means there are two circuits.

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

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

  1. Blood flows into the right atrium through the vena cava, and left atrium through the pulmonary vein.
  2. The atria contract forcing the blood into ventricles.
  3. The ventricles, then contract, pushing the blood in the right ventricle into the pulmonary artery to be taken to the lungs, and blood in the left ventricle to the aorta be taken around the body.
  4. As this happens, valves closed to make sure the blood does not flow backward.
• The natural resting heart rate (around 70 beats per minut) is controlled by a group of cells, found in the right atrium that act as a pacemaker- they provide stimulation through small electrical impulses which pass as a wave across the heart muscle, causing it to contract.
• An artificial pacemaker can be used if the individual has an irregular heart beat. It is an electrical device that produces a signal causing the heart to beat a normal speed.
• Arteries carry blood AWAY from the heart.

  • Layers of muscle in the walls make them strong.
  • Elastic fibres allow them to stretch.
  • This helps the vessels with stand the high-pressure created by the pumping of the heart.
• Veins carry blood TOWARDS the heart:

  • The lumen (the actual tube in which blood flows through) is wide to allow the low pressure blood to flow through.
  • They have valves to ensure the blood flows in the right direction.
• Capillary allow the blood to flow very close to cells to enable substances to move between them:

  • One cell thick walls create is short diffusion pathway.
  • Permeable walls so substances can move across them.
• The rate of blood flow = volume of blood flow / time taken for blood to flow
• The lungs are found in the thorax (top part of your body) and protected by your ribcage. They supply oxygen to your blood and remove carbon dioxide.
• The gas exchange system is made up of the:

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

  1. The rib cage moves up and out, and the diaphragm moves down, causing the volume of the chest to increase.
  2. Increased volume results in lower pressure.
  3. Air is drawn into the chest as air moves from areas high-pressure (the environment) to low pressure (the lungs).
  4. The opposite happens when exhaling.
• Gas exchange:

  1. Upon inhalation, the alveoli fill with oxygen.
  2. The blood in the capillaries surrounding the alveoli is deoxygenated (ithas come from the pulmonary vein). It has lots of carbon dioxide as this is a product of respiration.
  3. Oxygen diffuses down its concentration gradient into the capillary bloodstream, which has a low concentration of oxygen.
  4. Carbon dioxide diffuses down its concentration gradient from the blood to the alveoli.
• Alveoli are adapted for gas exchange to take place in a number of ways:

  • They are very small and arranged in clusters, creating a large surface area for diffusion to take place over.
  • The capillaries provide a large blood supply, maintaining the concentration gradient.
  • The walls of the alveoli are very thin, meaning there's a short diffusion pathway.
• Breathing rate = number of breaths/ number of minute.
• Blood is made of plasma, red blood cells, white blood cells and platelets.
• Plasma is liquid that carries the components in the blood.
• Red blood cells:

  • They carry oxygen molecules from the lungs to all the cells in the body.
  • The bioconcave disc shape provides a large surface area.
  • They have no nucleus, allowing more room to carry oxygen.
  • They contain the red pigment haemoglobin which binds to oxygen and forms oxyhaemoglobin.
• White blood cells:

  • They are part of the immune system.
  • They have a nucleus.
  • There are a number of types:
  • -Those that produce antibodies against microorganisms.
  • -Those that engulf and digest pathogens.
  • -Those that produce anti-toxins to neutralise toxins produced by microorganisms.
• Platelets: Small fragments of cells that help blood clot and form scabs.

  • No nucleus
  • Without them, cuts would result in excessive bleeding and bruising.