Unit 3

• how do insects reduce water loss

  spiracles - open and close to prevent water evaporation

  rigid exoskeleton - covered with waterproof chitin

  small SA:V
• how do insects have an efficient gas exchange system

  tracheoles - increases surface area + shorter diffusion pathway

  abdominal pumping - reduces pressure + helps to maintain concentration gradient by creating mass movement of air in and out of tracheoles
• describe the importance of the counter current flow system in fish

  blood and water flow in opposite directions

  maintains a diffusion gradient of oxygen

  gradient is maintained along the whole length of the lamellae
• describe inspiration (inhalation)

  external intercostal muscles contract

  internal intercostal muscles relax

  ribs are pulled upwards

  volume of the thorax increases

  diaphragm contracts - flattens

  atmospheric pressure is higher than pulmonary pressure so air moves inwards down a pressure gradient
• describe expiration (exhalation)

  external intercostal muscles relax

  ribs are pulled downwards

  volume of the thorax decreases

  diaphragm relaxes

  atmospheric pressure is lower than pulmonary pressure so air moves outwards down a pressure gradient

  elastic tissue in the alveolar walls recoils to increase pressure and force air out of the lungs
• state the equation for pulmonary ventilation rate

  PVR = bpm x tidal volume
• describe the digestion of proteins

  endopeptidases hydrolyse peptide bonds in the middle of a polypeptide

  exopeptidases hydrolyse peptide bonds at the end of a polypeptide

  dipeptidases hydrolyse peptide bonds between two amino acids in a dipeptide
• what is the function of lipases

  hydrolyse the ester bonds in lipids and split lipids into monoglycerides and fatty acids
• where are bile salts produced

  liver
• where are bile salts stored

  gall bladder
• what is the function of bile salts

  emulsify lipids

  increases surface area

  increases the rate of lipid hydrolysis
• what are micelles made from and how are they absorbed

  monoglycerides and two fatty acids ( phospholipids ) and bile salts

  simple diffusion through the phospholipid bilayer as they are lipid soluble
• arteries:

  carry blood away from the heart

  thick muscle layer - contracts and relaxes to control blood pressure

  thick elastic layer - stretches during systole and springs back during diastole (this is called elastic recoil ) + helps to maintain high pressure and smooths out pressure surges

  smooth folded endothelium - reduces friction

  narrow lumen - maintains high pressure

  no valves as blood is under constant high pressure so it cant floe backwards
• state the correlation between size and surface area to volume ratio

  As size increases surface area to volume ratio decreases
• Why are smaller units such as micrometers used when calculating values such as oxygen uptake

  Small uptake
• How does oxygen in the air reach capillaries surrounding alveoli

  Oxygen moves down trachea then to bronchi to bronchioles

  Down a pressure gradient

  down a diffusion gradient

  across alveoli epithelium

  Diffuses across capillary endothelium
• Explain the digestion and absorption of chylomicrons

  Move out of epithelial cells by exocytosis

  enter lymphatic capillaries called lacteals at the centre of each villus

  pass via lymphatic vessels into blood stream

  triglycerides are hydrolysed by lipases in the endothelial cells of capillaries

  diffuse into cells
• Describe translocation

  At the source cell sucrose is actively transported into the phloem

  by companion cells

  the water potential in the phloem decreases

  water moves in by osmosis

  produces high hydrostatic pressure

  mass flow of sucrose towards sink cells

  at the sink sugars are removed / used in respiration
• what is the equation for pulmonary ventilation rate

  tidal volume x breathing rate
• define tidal volume

  the volume of air breathed in with each normal breath
• Which blood vessel supplies the heart with deoxygenated blood?

  Vena Cava
• What is Fick's Law?

  the rate of diffusion is proportional to surface area x difference in concentration divided by length of diffusion pathway
• What are the adaptations of the alveolar epithelium

  alveoli are one cell thick - short diffusion pathway

  surrounded by network of capillaries - maintained concentration gradient

  many alveoli - large surface area

  folded - large surface area

  moist - gases can dissolve for diffusion
• Where is there High partial pressure of CO2? and what is the effect

  In respiring tissues

  the curve will shift to the right

  Hb has a lower affinity

  unloading more oxygen
• Where is there low partial pressure of CO2?

  In the alveoli.

  This causes the curve to shift left

  which increases the affinity of oxygen

  loading more oxygen.
• where are lipases produced and what do they do

  Produced in the pancreas

  hydrolyse the ester bonds in the triglycerides to form monoglycerides and fatty acids.
• Where does the digestion of proteins occur?

  stomach

  then duodenum

  fully digested in ileum
• Where is amylase present?

  Salivary glands

  pancreas.
• what are the adaptations of the phloem

  sieve plates - has sieve pores which allow for the continuous flow of organic compounds

  cellulose cell wall - provides strength to withstand high turgor and hydrostatic pressure that moves assimilates

  no organelles - maximise space for translocation of assimilates

  thin cytoplasm - reduced friction to facilitate movement of assimilates
• Where is there High partial pressure of CO2

  respiring tissues

  curve shifts to the right

  haemoglobin has lower affinity for oxygen

  more oxygen unloaded
• Where is there low partial pressure of CO2?

  alveoli

  curve shifts to the left

  haemoglobin has a higher affinity for oxygen

  more oxygen loaded
• Why do insects leave their spiracles closed a majority of the time

  prevent water loss
• describe the absorption of lipids

  micelles diffuse into the epithelial cells lining the villi

  monoglycerides and fatty acids are released

  monoglycerides and fatty acids are transported to the smooth endoplasmic reticulum where they recombine to form triglycerides

  triglycerides are transported to the Golgi body where they associate with cholesterol and lipoproteins to form chylomicrons

  chylomicrons leave epithelial cells by exocytosis and enter lacteals
• adaptations of phloem

  sieve plates with sieve pores - allow for continuous movement of organic compounds

  cellulose cell wall - provides strength to withstand hydrostatic pressure that moves the assimilates

  no organelles - maximise space for translocation

  thin cytoplasm - less friction to facilitate movement of assimilates
• adaptations of xylem

  lignin in walls - gives strength to prevent collapse due to hydrostatic pressure

  lignin kills cells because it is waterproof = no organelles in cells = continuous column = unimpeded flow of water

  pits in wall - lateral movement of water + continuous flow if air bubbles form

  no end plates forming a long continuous tube - assists cohesion of water molecules as adhesive forces of hydrogen bonding is not impeded
• describe alveoli

  minute air sacs at the end of bronchioles

  collagen and elastic fibres between alveoli

  lined with epithelium

  elastic fibres - allow them to stretch as they fill with air when breathing in and spring back during exhalation to expel carbon dioxide rich air
• what cells produce mucus

  goblet
• Describe the cohesion-tension theory of water transport in the xylem 

  water transpires from leaves - evaporates from mesophyll cells into air spaces and diffuses through open stomata

  reduces water potential in mesophyll cells

  water is drawn out of xylem down a water potential gradient

  created tension in xylem

  cohesive forces between water molecules due to hydrogen bonding

  water is pulled up as a continuous unbroken column

  water adheres to xylem walls

  water enters root by osmosis
• why is diffusion of gases between the alveoli and the blood rapid

  red blood cells slowed as they pass through capillaries so there is more time for diffusion

  red blood cells are flattened as they pass through capillary walls so short diffusion pathways

  alveoli epithelium and capillary endothelium are one cell thick so short diffusion pathway

  many capillaries and alveoli so large surface area

  breathing allows for steep concentration gradient

  blood flow through capillaries maintains concentration gradient
• why is oxygen uptake a measure of metabolic rate

  oxygen is used in respiration which provides ATP