Well, it depends on what type of cell you are talking about. If it's an animal cell, the outer covering would be the cell membrane. In a plant cell, the outermost one is the cell wall, then the cell membrane.
The cell membrane
In plant cells, it is the cell wall.
the cell wall is a rigid outer layer unique to plant cells. it shapes and protects the cell, unlike animal cells, whose outer most layer is the plasma membrane (a layer that lies beneath the cell wall in plant cells)
cuticle it on the leaf for the bugs to eat to keep out posion
Striatrd are the muscles are attached to bones by tendons. Tendons are thick bands that pull on the bone as the muscle contracts and these muscles are voluntary.
Plant cells have CELL WALLs, thick protective coverings on the outside of the cell that surrounds the cell membrane.
The strong membrane that surrounds the surface of the bone is called the periosteum. There is no periosteum at the joints of the long bones, like the femur.
Protoplasm
cuticle is the thick layer outside the leaf to prevent loss of water.
A seals outer covering is thick skin.
The thick outer covering you are refering to is called the cell wall found in plant cells. I dont know why they have it I guess its just there.
Schlera
cell membrane is the thick outer layer that dicides what enters and exites the cell.
on the outer layer of the cell ----------------------------------------- The membrane is found around the edge of a cell - it encases the cell and controls what goes in and out of it. In plants, the membrane is protected by a thick cell wall.
The cell wall
because it has a thick outer membrane called the pellicle
The muscular structer that grinds soil is the gizzard.
the cell wall is a rigid outer layer unique to plant cells. it shapes and protects the cell, unlike animal cells, whose outer most layer is the plasma membrane (a layer that lies beneath the cell wall in plant cells)
Cacti have thick stems and skins because they need to store water over long periods of time, and the liquid would evaporate quickly in deasert conditions.