The eukaryotes include all the protists, plants, animals and fungi.
- In eukaryotic cells, there is extensive compartmentalization of cytoplasm through the presence of membrane-bound organelles.
- Eukaryotic cells possess an organized nucleus with a nuclear envelope.
- In addition, eukaryotic cells have a variety of complex locomotory and cytoskeletal structures.
- Their genetic material is organized into chromosomes.
- All eukaryotic cells are not identical.
- Plant and animal cells are different as the former possess cell walls, plastids and a large central vacuole which are absent in animal cells.
- On the other hand, animal cells have centrioles which are absent in almost all plant cells.
Differences between Plant Cell and Animal Cell
An Overview of Eucaryotic Cell
- A plant cell consists of a cell wall and protoplast.
- The cell wall is absent in animal cells.
- Protoplast denotes the whole protoplasm present in a cell.
- It is differentiated into plasma membrane (= plasmalemma or cell membrane), cytoplasm, nucleus and vacuoles.
- The cytoplasm is distinguishable into cytoplasmic matrix and organelles.
- Cytoplasmic matrix is also called hyaloplasm.
- It is a polyphasic colloidal system that exists in two states, sol and gel.
- The gel form usually occurs near the plasma membrane.
- This region is sometimes called ectoplast in contrast to the 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 its living state.
- In the cytoplasmic matrix are embedded a large number of cell organelles or organized 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.
- The single membrane covering is found over the endoplasmic reticulum, Golgi apparatus, lysosomes, sphaerosomes, peroxisomes, glyoxysomes and vacuole.
- Organelles without a membrane covering are ribosomes, microtubules, microfilaments and centrosomes in both prokaryotes and eukaryotes.
- In centrioles (in animal cells), Ribosomes are found over mitochondria.
- Cell inclusions include starch, glycogen granules, fat droplets, aleurone grains, excretory or secretory products and crystals.
- The 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.
Functions of Cell Parts
1. Cell Wall - Shape, rigidity and protection to the cell.
2. Plasma membrane - Regulation of substances leaving or entering a cell.
3. Cytoplasm -
(a) Endoplasmic Reticulum Cytoskeleton, channelization, synthesis of fats, steroids, proteins, formation of vacuoles and vesicles.
(b) Ribosomes- Protein synthesis.
(c) Mitochondria Krebs cycle, amino acid synthesis, fatty ac synthesis.
(d) Chloroplasts- Photosynthesis.
(e) Amyloplasts- Storage of starch.
(f) Golgi Apparatus- Storage, secretion, excretion, wall synthesis, some chemical transformations, membrane transformation, lysosome formation.
(g) Centrioles- Formation of astral poles, flagella.
(h) Lysosomes- Separation and storage of hydrolytic (digestive) enzymes, digestion, autophagy.
(i) Sphaerosomes- Metabolism, storage and synthesis of fats.
(j) Glyoxysomes- Glyoxylate cycle, conversion of fat to carbohydrates.
(k) Peroxisomes- Photorespiration, peroxide metabolism.
(l) Microtubules- Cytoskeleton, formation of spindle and flagella.
(m) Microfilaments-Holding of membrane proteins, controlling cleavage and cyclosis.
(n) Vacuole- Osmotic pressure, storage.
4. Nucleus - Carrier of hereditary information, control of cell metabolism, synthesis of DNA and RNA, formation of ribosomes, control of reproduction.