The human body is made of over 30 trillion (1 Trillion = 1000 billion) cells, which are divided into around 200 cell-categories e.g. skin cells, stem cells, muscle cells etc.
Imagine the cell to be a tiny rubber-ball-with-spikes?Protein-ball-with-receptors filled with liquid (70% water and 30% protein oil?Enzymes); oil and water don’t mix.
This liquid covers another small ball called nucleus, which is the brain of the cell that has DNA – a set of instructions that tell the cell what to do and how to do it.
When you zoom into the protein oil, you see it to be a chemical laboratory, with equipment for mixing chemicals to do everything from breaking glucose down for energy to building cell walls and allowing the cell to reproduce.
When cells reproduceIt is with dividing/reproducing of cells that we become bigger with age, our nails/hair grow and our bruises and cuts recover., the DNA (instructions) also reproduces suggesting the new cells how to behave.
Viruses are tiny particles (again rubber-balls-with-spikes) incapable of doing anything till they find a host cell, which lends its chemical laboratory.
While incapable of doing anything on their own, viruses are lethal because they have DNA/RNA (instructions), which can mess up existing cell instructions.
Not all viruses can attack all cells; it is like their ‘spikes’ should match the ‘spikes’ of the cell.
E.g. cold & flu viruses attack cells that line the respiratory tracts & HIV attacks the T-cells of the immune system.
Once the ‘spikes’ match, the virus either enters entirely or sends the DNA/RNA into the cell.
The chemical factory has excellent capabilities to reproduce (Point 6 above), so virus multiplies and its copies break out of the cell (by either damaging or killing the cell) and infect other cells.
In case of Coronavirus, an infected person coughs near you, you inhale the virus through mouth/nose/eyes, virus finds the cells with the right spikes and messes up with existing instructions.
Because cell instructions are affected, immune system doesn’t come into action before the virus multiplies, its copies break out of the killed-cell and spread to other cells, bloodstream and lungs.
Dead cells and their liquid clog the lungs making breathing difficult; it is also deadly because in severe cases, the events make the immune system overreact and it starts attacking lung cells, causing uncontrollable damage.
