A Eukaryote is any organism whose cells contain a nucleus and other organelles enclosed within membranes.
Eukaryotes belong to the taxon Eukarya or Eukaryota. The defining feature that sets eukaryotic cells apart from prokaryotic cells (Bacteria and Archaea) is that they have membrane-bound organelles, especially the nucleus, which contains the genetic material and is enclosed by the nuclear envelope. The presence of a nucleus gives eukaryotes their name, which comes from the Greek eu, "well" or "true" and karyon, "nut" or "kernel". Eukaryotic cells also contain other membrane-bound organelles such as mitochondria and the Golgi apparatus. In addition, plants and algae contain chloroplasts. Eukaryotic organisms may be unicellular or multicellular. Only eukaryotes form multicellular organisms consisting of many kinds of tissue made up of different cell types.
1.1.1. Characteristics of Eukaryotic Cells
· Eukaryotic cells are larger than prokaryotic cells.
· They have a "true" nucleus i.e. the nucleus with true membrane.
· They have membrane-bound organelles such as mitochondria and chloroplasts
· The nucleus of the eukaryotic cells are covered by the protein coat called histones
· They have a large size of ribosomes i.e. 80’s ribosomes
· The cilia and flagella are arranged in the pattern of 9+2
Test your understanding
01. Summarize the structural differences between the prokaryotic cell and the Eukaryotic cell
02. Briefly describe the following cellular parts basing on the prokaryotic cell
a. DNA
b. Flagella and cilia
c. Ribosomes
03. By means of a clear diagram or otherwise draw the structure of the typical prokaryotic cell and compare it with that of eukaryotic cell.
1.1.2. Types of Eukaryotic Cells
Eukaryotic cells can be categorised into;-
i. Animal cell
ii. Plant cell
1.1.3. Animal Cell
Animal cells are typical of the eukaryotic cell, enclosed by a plasma membrane and containing a membrane-bound nucleus and organelles. Unlike the eukaryotic cells of plants and fungi, animal cells do not have a cell wall instead they do possess the cell membrane/plasma membrane in which in some cell they develop some extensions called pynocytic extensions or micro villi (villus). The cytoplasm containing living bodies of various shapes and size, these are called cytoplasmic organelles. They include mitochondria, Golgi bodies, ribosomes and endoplasmic reticulum. The cytoplasm also contains non-living materials called cytoplasm inclusions like food granules. The vacuole if present is small and temporary. The nucleus is found at the centre of the cell. Examples of anima cells are liver cells, muscle cells red blood cells and nerve cells.
1.1.3.1. Structure of Animal Cells under the Light Microscope
When an animal cell is viewed in the light microscope few organelles are observed and are not much clear.
1.1.3.2. Structure of Animal Cell under the Electronic Microscope
When an animal cell is observed under electronic microscope many organelles are observed and the features are very clear.
1.1.4. Characteristics of Animal Cell
A typical animal cell is characterised by the following features
· It is irregular shape
· It possess centrioles which are involved in the process of spindle formation
· It lack cell wall
· The nucleus is at the centre
· Vacuole if present is small and temporary
· They store food in form of glycogen
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