Eukaryotic Cells

  • A typical eukaryotic cell is bounded by a plasma membrane.
  • Cell wall is present in the case of plant cells,
  • The protoplasm is divisible into nucleus and cytoplasm.
  • The cytoplasm is in constant motion called cytoplasmic streaming. The streaming movement of cytoplasm around the vacuole is called cyclosis. It contains membrane bounded bodies called organelles, such as mitochondria, plastids, endoplasmic reticulum, ribosomes, Golgi bodies, etc.
  • The nucleus is bounded by a porous nuclear membrane allows the exchange of materials between the nucleoplasm and the cytoplasm.

cell_diagram_yourgenome.png

Cell wall

  • Cell wall is a rigid and protective protective covering, outer to plasma membrane in plants, bacteria, fungi and some protists.
  • It is absent in animal cells.
  • It is made up of cellulose in plants, of chitin in fungi and of proteins and noncellulosic carbohydrates in bacteria.
  • Other substances present in the cell wall are pectin, hemicellulose, lignin, suberin, cutin, chitin, fatty acids, minerals such as Ca, Mg etc.

The cell wall is a complex structure composed of the following layers

Primary cell wall:

  • It is the first formed cell wall in the immature meristematic and parenchymatous cells.
  • It is comparatively thin and permeable.

Secondary cell wall:

  • The primary cell wall is followed by thick permeable secondary cell wall.
  • It is composed of three concentric layers which occur one after another.

Tertiary cell wall

  • In certain plant cells, a thin layer occurs beneath the secondary cell wall is called tertiary cell wall.
  • It differs from the primary and secondary cell walls in its morphology, chemistry and staining property.
  • It is present in the xylem of gymnosperms.

Middle lamella:

The adjacent cells are cemented together by an intercellular matrix made up of pectin, lignin, calcium pectate and some proteins known as middle lamella.