A one-page recap of where we’ve been and our science studies through week seven. All the capitalized terms are vocabulary that might be new to you but are very important for understanding biology. – Scott Forbes – 10.06.2020 -
The basic unit of life is the CELL, meaning that if a CELL isn’t present, life isn’t present. So far as we know, CELLS are needed for life.
Viruses are an interesting way to study life because a virus, by itself, is not considered to be living. We’ll return to viruses after we talk a bit about cells.
We talked, a bit, about the basic building blocks of matter – which are ATOMS. There are about 100 different kinds of atoms in nature. You probably already know the names of many of them. Iron, Oxygen, Carbon, Gold, Copper, and others.
In chemistry we dive a little deeper into the structure of an atom. For now, we should know that an atom has a NUCLEUS (a center that has a positive charge.) The positive charge in the NUCLEUS comes from the PROTONS that are found in the NUCLEUS. There is another type of particle in the NUCLEUS that has no charge. It’s called a NEUTRON. Surrounding the center of an ATOM are these very fast moving, negatively charged particles called ELECTRONS.
Our universe is about 14 billion years old and the first kinds of atoms in it were just Hydrogen and Helium. These two elements were around after the BIG BANG, the beginning of our universe.
We know that there, probably, was a BIG BANG – a moment where all space and matter were created, because we’ve graphed the distances and velocity of distant galaxies and we can tell that everything in the universe used to be together in one place.
The first life arose here on Earth about 4 billion years ago because Earth had the right mix of ELEMENTS for life. Especially Carbon, Hydrogen, Oxygen, and Nitrogen. The first life was probably a “simple” CELL, that looked like a BACTERIA. Bacteria are cells with no NUCLEUS.
The first cells gave DNA (a very long MOLECULE) a “safe” place to make copies of itself. We’re not sure if EUBACTERIA or ARCHAEBACTERIA came first. We used to consider all bacteria as one, big, kingdom of living things. It turns out ARCHAEBACTERIA live in very “extreme” environments. There is even speculation that they might exist in the acidic clouds of the planet VENUS.
As life became more complex, cells developed a NUCLEUS. (Not to be confused with the NUCLEUS of an ATOM, they, simply, share the same name.) CELLS combine to form TISSUE, and TISSUE can combine to form organs.
We are the result of four billion years of evolution. We are complex organisms that have CELLS that have a NUCLEUS and all of our ORGANS (like heart, lungs, liver, etc.) are made of tissues, which are made of cells, which are – in turn – made of molecules. Finally, ATOMS combine to form MOLECULES.
VIRUSES are very small “packets” of DNA that can invade cells and force the cell to make copies of the VIRUS. (Some VIRUSES are packets of RNA, which is very similar to DNA.)