3 The plasma membrane is semipermeable because -
A phospholipids let through both polar and nonpolar substances.
B proteins in the membrane act like gates to control entrance and exit of molecules.
C cholesterol makes the membrane too rigid to let small molecules through.
D moving materials through the membrane always requires the use of ATP.

B) proteins in the membrane act like gates to control entrance and exit of molecules.

Explanation: Plasma membrane is composed of phospholipids bilayer in which the hydrophobic regions of the phospholipids face each other to form the core of the bilayer. Proteins are embedded in the bilayer through an interaction between the amino acid side chains and the nonpolar acyl chains of the phospholipids. The embedded membrane proteins form channels for passage of ions and other molecules. Each membrane protein is selected for one or more ions or molecules that passes through it. The membrane is said to be semipermeable because it allows the passage of some molecules and excludes the passage of others.

answer: - few nutrients

high pressure

low temperatures

explanation: 1. few nutrients:   open-ocean zone is located way far from the land, which is the main source of the essential nutrients.2. high pressure: pressure increases by 1 atmosphere for every 10 meters increase in depth.3. ample sunlight: a large fraction of the sunlight is reflected back to the atmosphere from the sea surface. 4. varying salinity: below the thermocline, the water is isolated from the atmosphere so the salinity remains stable over the year.5. low temperatures:   the temperature of open-ocean zone ranges from a low of -2°c to an average of 17°c

sheep is a herbivore animal whereas grasshopper belongs to the class chordates but both of them feed on greens.  

if grasshopper and sheep feeding on a pasture land, i do not think both of them will have any impact on each other. however, the number of the species can make difference. since sheep feed on greens, there is a possibility there left no pasture land for the grasshoppers or they may get extinct.