Membrane phospholipids
a. have hydrophobic heads that face the center of the membrane and are shielded from water.
b. have hydrophilic tails that face outward and are exposed to water.
c. are able to drift about in the plasma membrane.
d. remain fluid because they are tightly packed against one another.

Option-C

Explanation:

The phospholipids are the major constituents of the cell membrane of a cell. The phospholipids contains the glycerol attached to the phosphate group and forms the hydrophilic heads whereas the fatty acid tails from the hydrophobic portion of the membrane.

The hydrophobic head face outwards whereas the tails face inwards.  The structure of the membrane as arranged in bi lipid layer form and in such a way that the membrane molecules can move.  The other molecules present in the membrane like the proteins can drift in the membrane.

Thus, Option-C is correct.

explanation:

b,bacteria convert nitrates

into nitrogen gas.

d,plants and animals take in

and use nitrogen compounds.

e,bacteria break down waste    

products and return nitrogen  

to the soil.

a,bacteria convert atmospheric

nitrogen to ammonia.

c,bacteria convert ammonia

to nitrites and nitrates.

1. loamy sand is about 80% sand with 10% clay and defined mostly by sand particles with some clay to provide structure and fertility. the sand particles are easily visible and the soil holds structure but breaks apart easily.

2. scott sand can improve his soil quality by incorporating more silt and organic matter into the soil. peat moss and organic matter can also be incorporated.