A saddle is a kind of seat which one uses to sit on an animal, so it must have a seat. It is generally used to sit on a horse, but can be used for any other animal. Stirrups are often attached to saddle but may not be used. A horn is found on western saddles, but not on English saddles.
A nucleus is an essential part of a cell. It is located at the center of a cell. Chlorophyll is not produced by cells, and not all cells are neurons. All living entities, not just animals are made up of cells.
A medal is awarded when one wins, so winning is essential. One may win a swimming or running match, but there are also various other sports to participate and win the match.
14) Mobile phone
A mobile phone's basic function is to make and receive a call which is possible if it has a sim. It may not have a touch screen, keypad or hotspot function.
Without colors, one cannot paint. Books and canvas may not be necessary for painting. Pictures can be taken with a camera.
Essential Part 1
Essential Part 2
Essential Part 4