● An `color{violet}"onion peel"` and/or `color{violet}"human cheek cells"` can be observed under the `color{violet}"microscope"`.

● The onion cell which is a `color{violet}"typical plant cell"`, has a distinct `color{brown}"cell wall"` as its outer boundary and just within it is the `color{brown}"cell membrane"`.

● The cells of the `color{violet}"human cheek"` have an outer membrane as the `color{violet}"delimiting structure"` of the cell.

● Inside each cell is a dense `color{violet}"membrane bound structure"` called `color{brown}"nucleus"`.

● This `color{violet}"nucleus"` contains the `color{brown}"chromosomes"` which in turn contain the genetic material, `color{brown}"DNA"`.

● Cells that have `color{violet}"membrane bound nuclei"` are called `color{brown}"eukaryotic"` whereas cells that `color{violet}"lack a membrane"` `color{violet}"bound nucleus"` are `color{brown}"prokaryotic"`.

● In both prokaryotic and eukaryotic cells, a `color{violet}"semi-fluid matrix"` called `color{brown}"cytoplasm"` occupies the volume of the cell.

● The cytoplasm is the `color{violet}"main arena of cellular activities"` in both the plant and animal cells.

● Various `color{violet}"chemical reactions"` occur in it to keep the cell in the `color{violet}"living state"`

● Besides the nucleus, the eukaryotic cells have other `color{violet}"membrane bound distinct structures"` called `color{brown}"organelles"` like the endoplasmic reticulum (ER), the golgi complex, lysosomes, mitochondria, microbodies and vacuoles.

● The prokaryotic cells lack such `color{violet}"membrane bound organelles"`.

● `color{brown}"Ribosomes"` are `color{violet}"non-membrane bound organelles"` found in all cells – both eukaryotic as well as prokaryotic.

● Within the cell, ribosomes are found not only in the cytoplasm but also within the `color{violet}"two organelles"` – `color{brown}"chloroplasts"` (in plants) and `color{brown}"mitochondria"` and on `color{brown}"rough ER"`.

● Animal cells contain another `color{violet}"non-membrane bound organelle"` called `color{brown}"centriole"` which helps in cell division.

● Cells differ greatly in size, shape and activities.

● For example, `color{brown}"Mycoplasmas"`, the smallest cells, are only `color{violet}"0.3 µm"` in length while bacteria could be `color{violet}"3 to 5 µm"`.

● The `color{violet}"largest"` isolated single cell is the `color{brown}"egg of an ostrich"`.

● Among `color{violet}"multicellular organisms"`, human `color{brown}"red blood cells"` are about `color{violet}"7.0 m"` in diameter.

● `color{brown}"Nerve cells"` are some of the `color{violet}"longest cells"`.

● Cells also `color{violet}"vary greatly"` in their shape.

● They may be `color{violet}"disc-like, polygonal"`, `color{violet}"columnar, cuboid"`, `color{violet}"thread like"`, or even `color{violet}"irregular"`.

● The `color{violet}"shape of the cell"` may vary with the `color{violet}"function they perform"`.

● The prokaryotic cells are represented by `color{violet}"bacteria"`, `color{violet}"blue-green algae"`,`color{violet}" mycoplasma"` and `color{violet}"PPLO"` (Pleuro Pneumonia Like Organisms).

● They are `color{violet}"generally smaller"` and `color{violet}"multiply more rapidly"` than the eukaryotic cells.

● They may `color{violet}"vary greatly"` in shape and size.

● The `color{violet}"four basic shapes"` of bacteria are `color{violet}"bacillus"` (rod like), `color{violet}"coccus"` (spherical), `color{violet}"vibrio"` (comma shaped) and `color{violet}"spirillum"` (spiral).

● The `color{violet}"organisation"` of the prokaryotic cell is `color{violet}"fundamentally similar"` even though prokaryotes exhibit a wide variety of shapes and functions.

● `color{violet}"All prokaryotes"` have a `color{brown}"cell wall"` surrounding the `color{brown}"cell membrane"`.

● The `color{violet}"fluid matrix"` filling the cell is the `color{brown}"cytoplasm"`.

● There is `color{violet}"no"` `color{brown}"well-defined nucleus"`.

● The `color{violet}"genetic material"` is `color{violet}"basically naked"`, not enveloped by a nuclear membrane.

● In addition to the `color{brown}"genomic DNA"` (the single chromosome/circular DNA), many bacteria have `color{violet}"small circular DNA"` outside the genomic DNA.

● These `color{violet}"smaller DNA"` are called `color{brown}"plasmids"`.

● The plasmid DNA confers certain `color{violet}"unique phenotypic characters"` to such bacteria.

● One such character is `color{violet}"resistance to antibiotics"`.

● This plasmid DNA is used to `color{violet}"monitor bacterial transformation"` with foreign DNA.

● `color{brown}"Nuclear membrane"` is found in `color{violet}"eukaryotes"`.

● `color{violet}"No organelles"`, like the ones in eukaryotes, are found in prokaryotic cells except for `color{violet}"ribosomes"`.

● Prokaryotes have `color{violet}"something unique"` in the form of `color{brown}"inclusions"`.

● A `color{violet}"specialised differentiated form"` of cell membrane called `color{brown}"mesosome"` is the characteristic of prokaryotes.

● They are essentially `color{violet}"infoldings of cell membrane"`.