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The below mentioned article provides biology notes on Eukaryotic Cell.
A eukaryote cell is the one which has an organised nucleus and several membrane covered cell organelles. Except monera, the cells of all other kingdoms have eukaryotic organisation. Cell wall is present in cells of plants, fungi and some protists.
It is absent in animal cells and some protists. Wall less cells are generally irregular. Otherwise, internal structure of all cells is somewhat similar. A cell is an organised mass of protoplasm surrounded by a protective and selectively permeable membrane. Protoplasm of a cell is called protoplast.
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It is made up of cytoplasm, nucleus and vacuoles. Initially, cytoplasm was thought to have simple organisation. Electron microscope has shown that cytoplasm has a complex organisation formed of cytoplasmic matrix and cell organelles. There are cytoskeletal structures which not only provide movement to cytoplasm but also other locomotory activities.
Genetic material or DNA is organised into chromosomes and chromatin. Plant cells possess cell wall, plastids and large central vacuole. They are absent in animal cells. Animal cells possess centrioles that are absent in plant cells.
A plant cell consists of cell wall and protoplast. Cell wall is absent in animal cells. Protoplast denotes the whole of protoplasm present in a cell.
It is differentiated into plasma membrane (= plasma lemma or cell membrane), cytoplasm, nucleus and vacuoles. Cytoplasm is distinguishable into cytoplasmic matrix and organelles. Cytoplasmic matrix is also called hyaloplasm. It is a polyphasic colloidal system which exists in two states, sol and gel.
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The gel form usually occurs near the plasma membrane. This region is sometimes called ectoplast in contrast to sol region known as endoplast. Ectoplast is firmer. It is quite conspicuous on the free sides of the cells. In protozoans, ectoplast is prominent on all sides.
Cytoplasmic matrix is generally in perpetual motion. The phenomenon is called cyclosis, cytoplasmic or protoplasmic streaming. Cytoplasmic matrix occupies the volume of the cells. It is the major arena of cellular activities that keep a cell in the living state.
In the cytoplasmic matrix are embedded a large number of cell organelles or organised protoplasmic subunits having specific functions.
They are endoplasmic reticulum, plastids, mitochondria, ribosomes, Golgi bodies, centrioles (central apparatus, centrosome), lysosomes, sphaerosomes, peroxisomes, glyoxysomes, vacuoles, microtubules, microfilaments, etc. Some of them have membrane covering while others are without the same.
Doubling membrane covering occurs around plastids and mitochondria. Single membrane covering is found over endoplasmic reticulum, Golgi apparatus, lysosomes, sphaerosomes, peroxisomes, glyoxysomes and vacuole.
Organelles without a membrane covering are ribosomes, microtubules, microfilaments and centrosomes or centrioles (in animal cells). Ribosomes are found in both prokaryotes and eukaryotes. In eukaryote cells they occur in cytoplasmic matrix, over rough endoplasmic reticulum, inside plastids (found only in plants and some protists and mitochondria).
Cell inclusions include starch grains, glycogen granules, fat droplets, aleurone grains, excretory or secretory products and crystals. Nucleus is also embedded in the cytoplasmic matrix. It is surrounded by a double membrane envelope and contains nucleoplasm, one or more nucleoli and chromatin having DNA. DNA is the genetic material.
