organisation

• human digestive system:

  • glands (salivary and pancreas)
  • stomach
  • liver
  • gall bladder
  • small intestine
  • large intestine
  • rectum and anus
• an enzyme is a biological catalyst.
• enzymes optimum temperature is 37C: the rate of reaction will increase up to this point but above this temperature, it will rapidly decrease and stop.

  this is because the bonds in the structure break so the active site changes shape and becomes denatured.
• enzymes optimum Ph is 7: but those developed in acidic conditions (such as the stomach) have a low optimum Ph.

  if Ph levels are too low or high, the forces that hold the amino acid chains together are affected, which will change the shape of active site so it becomes denatured.
• carbohydrase converts carbohydrates in simple sugars (amylase breaks starch down into maltose).
• proteases convert protein into amino acids (pepsin in the stomach)
• lipases convert lipids into fatty acids and glycerol
• lipase is produced in the pancreas and small intestine
• protease is produced in the stomach, pancreas and small intestine
• carbohydraese is produced in the salivary glands, pancreas and small intestine.
• What happens to the products of digestion (enzymes)?

  Soluble glucose, amino acids, fatty acids and glycerol pass into the bloodstream to be carried to cells around the body. They are used to produce new enzymes, protein and glucose is used in respiration.
• Iodine test for starch:

  1. Put some of the food sample into a test tube
  2. Add a few drops of iodine solution to the food sample using a pipette
  3. If starch is present, the solution will turn from brown to blue-black.
• Benedicts test for reducing sugars:

  1. Add at least equal volume of benedicts to the food sample in a test tube
  2. Place in a hot water bath for 5 minutes
  3. If reducing sugar is present, a brick red precipitate forms. If reducing sugar is absent, solution stays blue
• Test for protein

  1. Add a few drops of biurets reagent to the food sample in a test tube
  2. Shake the solution to mix well and wait a few minutes
  3. If protein is present, mixture will turn from blue to purple
• Test for lipids:

  1. Add 3cm cubed of ethanol to the food sample
  2. Pour this mixture into a test tube with equal volume of distilled water
  3. If lipids are present, a white emulsion is formed on the surface of the mixture
  4. This is called the emulsion test
• bile is produced in the liver and stored in the gallbladder and then released into the small intestine.
• bile is alkaline to neutralise the HCL from the stomach as the enzymes in the small intestine have a higher optimum Ph than those in stomach
• bile emulsifies large drops of fat into smaller ones- the larger surface area allows lipase to chemically break down the lipid into glycerol and fatty acid faster
• the heart pumps the blood around the body in a double circulatory system:

  1. deoxygenated blood flows into the right atrium and then right ventricle which pumps it to the lungs
  2. oxygenated blood flows into the left atrium and then left ventricle which pumps oxygenated blood around the body.
• structure of the heart:

  • muscular walls provide strong heartbeat
  • muscular wall of left ventricle is thicker as blood needs to pumped around the whole body rather than just the lung
  • 4 chambers that separate deoxygenated and oxygenated blood
  • valves to make sure blood does not flow backwards
  • coronary arteries cover heart to provide own oxygenated blood supply.
• process of heart beat:

  1. blood flows into right atrium through the vena cava and left atrium through the pulmonary vein
  2. the atria contract forcing blood into ventricles
  3. the ventricles contract pushing blood in right ventricle into pulmonary artery, and blood in left ventricle to the aorta to be taken around the body
  4. as this happens, valves close to stop blood flowing backwards.
• what direction do arteries carry blood?

  away from the heart
• elastic fibers allow arteries to stretch
• layer of muscles in the walls make arteries strong
• the layers of muscles and elastic fibers in the artery walls help it to withstand high pressure created by the pumping of the heart.
• what is wide enough to allow the low blood pressure to flow through the vein?

  the lumem
• veins have valves to ensure blood flows in the right direction
• capilleries allow the blood to flow very close to cells to enable diffusion of substances, this is enabled by:

  • one cell thick walls
  • permeable walls
• the lungs are found in the thorax
• the gas exchange system:

  1. trachea
  2. intercostal muscles (contract and relax to ventilate the lungs)
  3. bronchi
  4. bronchioles
  5. alveoli
  6. diaphragm (seperate lungs from digestive system)
• how does ventilation work?

  1. the ribcage moves up and out and the diaphragm moves down causing chest volume to increase
  2. results in lower pressure
  3. air is drawn into chest as it moves from areas of high pressure (environment) to low pressure (lungs)
  4. opposite when exhaling
• how does gas exchange occur?

  1. during inhalation, the alveoli fill with oxygen
  2. the blood in the capillaries surrounding the alveoli is deoxygenated (come from pulmonary vein)
  3. oxygen diffuses down conc gradient into capillary bloodstream, which has low oxygen conc
  4. carbon dioxide diffuses down conc gradients from blood to alveoli
• how are alveoli adapted?

  1. small and arranged in clusters, creating large surface area for diffusion to take place
  2. surrounding capillaries provide large blood supply, maintaining conc gradients
  3. walls are very thin, so short diffusion pathway
• what is the role of plasma?

  carries components in the blood, rbc, wbc, platelets, glucose, urea, hormones, proteins etc.
• explain the lock and key theory?

  1. shape of the substrate is complementary to the shape of the active site so they create an enzyme-substrate complex when they bond
  2. a reaction takes place and the substrate is broken down into products
  3. the products are released from the enzyme surface
• what is the function of xylem tissue?

  transports water and dissolved mineral ions from the roots to the leaves
• transpiration is the loss of water vapour from the leaves and stems of the plant due to gaseous exchange as the stomata open
• the stages of the transpiration stream:

  1. evaporation of water from cells inside the leaf
  2. water vapour diffuses through air spaces in spongy mesophyll and out of the leaf through the stomata
  3. water passes from the xylem into the leaf to replace the water that has been lost
  4. finally water is drawn into the root hair cells and up the xylem vessels into the leaf
• what does the transpiration stream transport?

  dissolved mineral ions and water
• what does the evaporation if water from the leaf do?

  cools it down