The more economical types of plywood are the C & D grades. You'll see more repaired knots and voids on a sheet, and some defects will be left as is. This type of plywood grade is a good choice for projects where you will ultimately cover the plywood panel with some other type of cover material-like a smoother MDF sheet.ll large knots are replaced with football-shaped patches, which can be sanded and finished with the rest of the panel. Also, any gaps or voids along the edges of the panel are usually filled and smoothed off with wood putty. With the A & B grades, the number of repaired patches and voids on any given sheet will be low.
Cell Wall. Plant cells have a rigid cell wall that surrounds the cell membrane. Animal cells do not have a cell wall. When looking under a microscope, the cell wall is an easy way to distinguish plant cells.
The cell wall in plants and the cell membrane in animals and bacteria.