Prokaryotic cells are mitochondria, plastids, endoplasmic reticulum, Golgi apparatus, lysosomes and endosomes. Due to the presence of a larger cytoplasmic structure, eukaryotic cells are larger than prokaryotic cells. What is common between prokaryotic cells and eukaryotic cells is the presence of genes that store genetic information. Ribosomes (cytoplasmic structures that function as sites for protein synthesis) are also present in both types of cells. Examples of prokaryotes are bacteria and archaea.
2. Eukaryotes
Eukaryotic cells are the site of DNA replication (the process by which DNA segments are duplicated) and transcription (the process by which mRNA transcripts are produced). Instead, this process occurs in the cytoplasm of the prokaryotic cell. The presence of a nucleus organizes the genetic material and these processes. The nuclear envelope prevents the easy entry of molecules and thus regulates the passage of molecules in and out of the nucleus. Examples of eukaryotes include protists, fungi, plants and animals.
3. Unicellular organisms
Unicellular organisms are organisms that consist of only one cell. Examples of unicellular prokaryotes are bacteria and archaea and unicellular eukaryotes are certain protists and fungi. Multicellular organisms include plants and animals.
4. Multicellular organisms
Multicellular organisms consist of many cells that act as a unit carrying out a specific function. In multicellular organisms, a group of cells forms a network. The cells in a tissue have a similar structure and function. The following is an example of the network:
Animal tissue is nervous tissue, muscle tissue, vascular tissue, and connective tissue. Plant tissue is meristematic tissue, permanent tissue, and reproductive tissue. A group of tissues organized into an anatomical unit is called a biological organ. Examples of animal organs are as follows: heart, lungs, brain, stomach, skin, pancreas, liver, intestines, kidneys, and sex organs. In plants the organs are roots, stems, leaves, flowers, fruits, and seeds.
5. Taxonomic classification
Living things are classified into three main domains as proposed by Carl Woese. These domains are Archaea, Eubacteria (true bacteria), and Eucarya. Below the domain are the other major taxonomic levels: kingdom, phylum, class, order, family, genus, and species.
Archaea domain and eubacteria domain
Archaea and Eubacteria are both prokaryotes while Eucarya includes eukaryotes. Thus, Archaea and Eubacteria do not have membrane-bound organelles. However, there are subtle differences between the two which lead to their separation into different domains. Archaea have certain genes and metabolic pathways that are more closely related to eukaryotes than to eubacteria.
Domain eucarya
Living organisms included in the Domain Eucarya are as follows:
Protists are living things characterized by having a relatively simple organization. Some of them are single-celled and others are multi-celled. Fungi are eukaryotes known for their heterotrophic mode of nutrition because they lack chlorophyll (an important pigment in photosynthesis). Plants are multicellular photosynthetic life forms. One of the main characteristics of plants is the presence of chloroplasts which contain a chlorophyll system that collects light energy from light sources to be converted into chemical energy through photosynthesis. Animals are multicellular eukaryotes. Cells in tissues join via cell junctions (e.g. tight junctions, gap junctions, and desmosomes). Their lack of chloroplasts (and the green pigment, chlorophyll) renders them incapable of photosynthesis. Thus, they depend on other organisms for survival.
6. Viruses and Viroids
Viruses are organisms or not is a matter of debate. Similar to living things, viruses have genetic material. However, they seem to live only when inside a host. Whereas viroids are another example of acellular entities. They appear to be alive because they are pathogenic.
2023-08-03 06:05:06
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