Why is conversion of heat into work not possible without a sink at lower temperature?

What forbids complete conversion of heat into work?

Why is fertilization not possible without pollination?

Is it possible to heat a body without causing any rise in temperature ?

A sink, that is a system where heat is rejected, is essential for the conversion of heat into work. From which law the above inference follows?

A reversible Carnot engine working between two temperatures converts 1/6 th of the heat supplied into useful work. If the lower temperature is reduced by 65^@C , its efficiency is double. Find the temperatures of source and sink.

A reversible engine converts one - sixth of the heat suplied into work . When the temperature of the sink is reduced by 62^@C , the efficiency of the engine is doubled . The temperatures of the source and sink are