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11.7Problems

 

 

If two types of cell expressing different types of cadherin are dissociated and then reassembled and cultured, what arrangement might they take?

 

 

Explain the functions of tight junctions in normal tissues.

 

 

Which of the following substances can pass through both gap junctions and plasmodesmata? Amino acids, ATP, Ca2+, phospholipids in the plasma membrane, endoplasmic reticula

 

 

If a tobacco leaf is treated with enzymes, hemicellulase and cellulase, to degrade its cell walls, protoplasts are produced. How will these protoplasts be shaped in a solution with appropriate osmotic pressure? Also, explain why endogenous cellulase is necessary for plants to grow.

 

 

If two types of cell expressing different types of cadherin are dissociated and then reassembled and cultured, what arrangement might they take?

Cadherins are known to adhere to molecules of the same type. Cadherins of different types mixed together may either be separated or undergo cell sorting. Whether the cells are separated or sorted depends not only on the cadherin type but also on the amount of cadherin in the plasma membrane.

 

 

Explain the functions of tight junctions in normal tissues.

Tight junctions support the role of epithelial tissues in strictly separating two environments (the body’s external and internal areas). Tight junctions tightly connect epithelial cells. Since this type of junction connects cells so tightly that it is impermeable even to ions, sheet epithelial tissues serve as impermeable walls. If tight junctions do not function properly, organisms cannot maintain their body’s internal environment.

 

 

Which of the following substances can pass through both gap junctions and plasmodesmata? Amino acids, ATP, Ca2+, phospholipids in the plasma membrane, endoplasmic reticula

Small molecules in the cytoplasm, such as amino acids, ATP and Ca2+, can easily pass through gap junctions and plasmodesmata. Phospholipids in the plasma membrane diffuse by moving on the membrane surface of plasmodesmata, since the plasma membranes of adjacent cells are connected in a plasmodesma. Such movement does not occur in gap junctions in which the adjacent plasma membranes are not connected. Organelles such as endoplasmic reticula are too large to move.

 

 

If a tobacco leaf is treated with enzymes, hemicellulase and cellulase, to degrade its cell walls, protoplasts are produced. How will these protoplasts be shaped in a solution with appropriate osmotic pressure? Also, explain why endogenous cellulase is necessary for plants to grow.

The protoplasts will be round in shape. When plants grow, cell elongation and cell division occur. For cells to elongate, it is necessary to cut existing cellulose fibers and synthesize/add new ones. This is why endogenous cellulase is necessary.

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