Prokaryotic Cells and Viruses
Viruses (aren't in a kingdom) are generally thought of as disease-causing organisms. They can cause disease in animals and plants and they're extremely small. They are only visible with an electron microscope.
They're called non-cells due to the fact that they have no cytoplasm, nor organelles and no chromosomes. Outside of a living cell a virus exists as an inert (non-reaction unreactive reactions) 'virion' and for this reason they're not classed as living - they don't perform all 7 of the life processes, for example, no excretion, they don't grow, etc.
When a virus invades a cell they're able to take over the cell's metabolism and multiply within the host cell. They're able to do this as they can insert their genetic material into the genetic material of the host cell. Each virus is made up of a core of nucleic acid surrounded by a protein coat called the capsid. Viruses found in animal cells and bacteria tend to have DNA. Some animal viruses and plant viruses however carry RNA. The well studied virus T2 phage, a bacteriophage, infests the bacterium E.coli.
Because viruses can insert their genetic material into that of another cell, they've been used as vectors, carrying genes from one organism to another suchc as in genetic engineering.
Comparison of animal and plant cells
Plasmodesmata are microscopic channels which tranverse the cell walls of plant cells and some algal cells, enabling transport and communication between them.
Levels of organisation
Multicellular organisns contain a variety of specialised cells. Cells specialise in a process called differentiation. Undifferentiated cells are called stem calls, and these cells can potentially different into all cell types.
If a stem cell is totipotent it can become all cell types, as seen in embryonic stem cells. Pluripotent stem cells can become a few different cell types such as adult somatic stem cells found in bone marrow - these…