IB DP Biology: SL复习笔记1.2.5 Exocrine Pancreatic & Palisade Mesophyll Cells

Exocrine Pancreatic & Palisade Mesophyll Cells

Exocrine gland cells of the pancreas

  • The pancreas contains two types of gland cells: endocrine and exocrine cells
  • The function of the exocrine gland cells (acinar cells) is to secrete digestive enzymes into the pancreatic ducts. These enzymes then travel to the duodenum where digestion occurs
  • To perform this function the exocrine gland cells have organelles that enable the enzymes (proteins) to be synthesised, processed for secretion, transported to the plasma membrane and released
  • Thus the plasma membrane and the following organelles can be seen in electron micrographs of the exocrine gland cells:
    • Nucleus - where DNA is transcribed into mRNA (that contains the instructions for building the enzymes)
    • Rough endoplasmic reticulum - has ribosomes attached where the enzymes are synthesised
    • Mitochondria - provide the ATP required for all the metabolic processes
    • Golgi apparatus - where the enzymes (proteins) are processed and packaged ready for secretion
    • Vesicles - 'pinch off' the Golgi apparatus and contain the pancreatic digestive enzymes (e.g. pancreatic amylase) that will be released into the ducts (may appear dark in electron micrographs or at least with many dark specks within)
    • Lysosomes - contain hydrolytic enzymes that will digest the unwanted substances in the cell

Palisade mesophyll cell

  • The palisade mesophyll cells are located in the leaves of plants and are structured to maximise the efficiency of the leaf's function - photosynthesis
  • The palisade mesophyll cells are situated towards the top of the leaf and are column-like in shape increasing surface area to absorb light, carbon dioxide and water
  • Along with the key organelles mentioned for the exocrine gland cell, the palisade mesophyll cell contains the following organelles:
    • Chloroplasts - the location of light absorption, it provides the energy for producing glucose and oxygen
    • Permanent vacuole - it is large and central pushing the chloroplast to the edge of the cell maximising absorption of light. It also helps maintain water balance
  • The palisade mesophyll cell also contains the extra-cellular structure:
    • Cell wall - it is mainly made of cellulose, is freely permeable (allowing carbon dioxide and water to move through easily) and its strength gives support to the cell (prevents the cell from bursting)