Cell specialisation & Gas exchange


Specialised cells

  • Erythrocytes have a large SA:V, with their biconcave shape, they also lack a nucleus, so more haemoglobin can bestored
  • Neutrophils have a multilobed nucleus allowing them to move and engulf materials more easily
  • Sperms have tails to enable them to move. There is a high density of miutochondria to provide ATP to the tail. Sperm cells have a streamline shape and a specialised lysosome head that contains digestive enzymes to enter the cell
  • Squamous epithelial cells are thin and flat to shorten the diffusion distance for gas exchange
  • Ciliated epithelial cells in the trachea have cilia to move mucus along the trachea
  • Palisade cells contain lots of chloroplasts, are long and cylindrical allowing close packing. The chloroplast can be moved by the cytoskeleton to maximise light absorption
  • Guard cells control the opening and closing of the stomata. ATP is used to pump k+ ions into the cell, making water move in by osmosis in order to open the stomata for gas exchange
  • Root hair cells have protrusion to increase their surface area for water abroption. They also have protein pumps and lots of mitochondria to transport minerals into the cell in order to lowerthe cells water potential.
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Gas exchange

  • Single celled organisms can exhange oxygen and carbon dioxide directly through their plasma membrane via diffusion
  • Insects exchange gas in their tracheal system. Air enter via spiracles, travel through trachea and tracheoles, delivering oxygen directly to every tissue.Tracheal fluid limits diffusion to cells.
    • Larger insects can also ventilate by movement of the abdomen, flight muscles chaning the volume of the thorax and the presence of air sacs
  • Gas exchange in fish occur via gills
    • They ventilate their gills by a buccal-opercular pump
    • The oreintation of the gill filaments and lamellae ensures that water flowing over them moves in the opposite direction to the direction of blood flow to create a counter current flow. This helps to maintain the concentration gradient

                                                      Image result for fish counter current system

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Human Gas Exchange System

  • In humans gas exchange occurs via the lung
  • The alveolar epithelium is adapted by gas exchange by having large surafce area, good blood supply, thin walls & elastic fibres which help recoil
  • Ventilation is the process of breathing in (inspiration) and out (expiration)
  • Inspiration
    • External intercostal muscles contract, rib cages moves up and out, diaphragm contracts, volume of the thorax is increased
      • The atmospheric pressure is greater than pulmonary pressure and air is forced into the lungs
  • Expiration
    • Internal intercostal muscles contract, ribs move down and inwards, diaphragm relaxes, volume of the throax decreases
      • The pulmonary pressure is greater than atmospheric pressure ad air is forced out
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Human Gas Exchange System Continued...

  • Spirometers measure the volume and function of the lungs. Inhalation and exhalation moves the lid of the spirometer which is recorded by the datalogger. Carbon Dioxide is aborbed by soda lime in the chamber
  • Vital capacity = Maximum amount of air that can be moved by the lungs in one breath
  • Residual volume = Volume of air left in the lungs after a forced expiration
  • Tidal volume = volume of air moved in and out of the lungs with a normal breath

            Image result for spirometer charrt

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Surface Area to Volume Ratio

  • The bigger the organism the smaller the ratio
  • Larger organisms therefore need specialised exchange surfaces and transport mechanisms to meet their metabolic requirements
  • Specialised exchange surface have: large surface area, thin barriers and associated transport systems to maintain a steep diffusion gradient
  • Also, organisms with higher metabolic rate require more nutrients and produce more waste, therefore require a specialised exchange surface

                                                 Image result for sa;V

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Stem cells

  • Stem cells are undifferentiated cells that are able to express all of their genes and divide by mitosis
  • During development, stem cells undergo cell differentiation. This is the process by which cells become specialised for their function
  • Fully developed cells are unable to divide by mitosis

                      Image result for types of stem cells

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Stem Cells continued...

  • Totipotent stem cells are only present in mammals in the first few cell divisions of an embryo. During development, totipotent cells become specialised by expressing different genes and producing different proteins
  • Induced pluripotent stem cells are unipotent stem cells that have been preprogrammed to become pluripotent by using protein transcription factors to express genes associated with pluripotency
  • Pluripotent cells can be used to replace cells and treat human disorders like leukaemia and diabetes
  • Bone marrow stem cells can differentiate into any type of blood cell
  • Meristem cells in plants are involved in the production of new xylem and phloem tissue.
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