Answer:
- the answer for the exercise 6 is water
- the answer for the exercise 7 is population
- the answer for the exercise 8 is ecosystem
The function of the semi permeable membrane is to allow substances to diffuse (transport) across it, because its only semi permeable the substance are able to cross. If it was a non permeable membrane it wouldn't allow the transport of substances.
Most important and abundant one are the phospholipids - amphiphatic molecules with an hydrophilic head and a hydrophobic hydrocarbon tails. They compose the membrane bilayer. Also important are the membrane proteins, which can be periheric and internal and can serve as channels, receptors, pumps etc.
Depending on the cell type the membrane can also contain cholesterol (in animal cells, enhances the membrane stability) or hopanes(in prokaryotes, same function as cholesterol) or ether-phospholipids with branched hydroharbon tails(in archaea, make the membranes more stable and resistant to severe conditions, as archaeas are extremophiles)
The agent of erosion is the pressure
