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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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

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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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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

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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

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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

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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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