(This page is here for young readers, non-native speakers of English and maybe any reader who wants an easy text to begin learning the basics of biology for being able to then read more pages on this site.)
(Best to first read Easy Science if you don’t know about matter, atoms and molecules!)
Click on the dark blue words to see what they mean.
Biology is the science of life. It is the study of all living things. Biology is about people (humans), animals (like cats, dogs, and birds), and plants. It is also about insects (bugs are insects) and other tiny living things.
Some living things are so small that you cannot see them with your eyes. For example, cells are the tiny building blocks of life. You need a microscope to see a cell. But you can see bigger things, like your skin or a tree, that are made of cells.
All living things are made of cells. You have many cells in your body. Your skin has cells, your heart has cells, and every part of you—from your head to your toes—is made of cells. Cells can be very different from each other, but they all help living things survive.
Humans are living things. We are alive, just like animals and plants. Humans are also mammals. Dogs, cats, monkeys, and bears are mammals too.
Mammals have four legs—or two legs and two arms, like humans and monkeys. Mammals are a type of animal, but not all animals are mammals. One special thing about mammals is that they are warm inside. Most other animals are cold inside. Mammals also have hair or fur, which helps keep them warm.
An animal cell can have many shapes. But all animal cells have a cell membrane, which is the surface that surrounds the cell.
Inside the cell, it is wet. Cells contain a lot of water, but this water also has many molecules and structures in it. The cell membrane holds the water and all the parts of the cell together. It is like the rubber of a balloon that keeps air inside. But instead of air, a cell has water and many important things inside it.
The cell membrane separates the inside of the cell from the outside. However, it also allows certain things to pass through, letting in what the cell needs and keeping out what it doesn’t.
Cells have a nucleus. The nucleus is like a small cell inside the cell. It holds very long molecules of DNA.
All living things have DNA. DNA is found in every cell of every living thing. It contains all the information a cell needs to build itself and to work properly.
The information in DNA is written like letters in a code. It is made of four different kinds of molecules, arranged in a special order like a chain. This is similar to computer code or computer data, but for life.
Cells are living things. This means they can multiply. But instead of having children, a cell splits into two. One cell becomes two new cells.
When a cell splits, it breaks apart, and each part becomes a new cell. Inside the cell, the nucleus also splits. The parts of the old nucleus become the nuclei of the new cells.
Before a cell splits, its DNA makes a copy of itself. This way, each new cell gets all the DNA it needs. The DNA tells the new cells how to build, repair, and keep working properly.
DNA contains information. This information is copied into another long molecule called RNA. The RNA leaves the nucleus and helps make new parts of the cell.
RNA carries instructions to make proteins. Proteins are molecules made of many atoms. The information in DNA is used to create protein molecules, which have different jobs in the cell.
Some proteins are structural proteins. These proteins help build the cell, just like bricks build a house. For example, RNA can create proteins that become part of the cell membrane.
Other proteins are called enzymes. Enzymes act like tools. They help move proteins, put them together, and make important chemical reactions happen inside the cell.
Humans have many different kinds of cells. Different parts of the body have different types of cells.
Humans have blood, and even blood is made of blood cells. Blood flows through the body inside blood vessels, pushed by the heart.
Humans also have lungs, which fill with air when we breathe in. The air we breathe is important for our body.
All mammals have a heart, blood, blood vessels, and lungs! This means humans, dogs, cats, monkeys, and bears all have these same important parts inside their bodies.
The blood does many important things for the body. One of the most important things it does is carry oxygen from the air in the lungs. Oxygen is a part of the air we breathe in. It is a molecule made of two atoms, and it is very necessary for all the cells in the body. Cells would die without oxygen.
Blood vessels are found all over the body. As blood flows through the body, it travels through smaller and smaller vessels called capillaries. In the lungs, the capillaries take oxygen from the air we breathe.
The red blood cells carry oxygen molecules (O₂) to all the cells in the body. From the capillaries, the oxygen-rich blood moves into bigger vessels, then even bigger vessels, until it reaches the heart.
The heart then pushes the blood through smaller and smaller vessels to the cells all over the body. After the cells use the oxygen, the blood returns through larger and larger vessels back to the heart. From there, the heart pumps the blood back to the lungs through small vessels to get more oxygen.
The large blood vessels are like highways, and the small blood vessels are like narrow roads that lead to and from the cells.
Oxygen is needed to create energy. With oxygen, the cells in the body can get energy from the food we eat. This is why we need oxygen to stay alive. Without it, we would have no energy and we would die.
After the cells use oxygen to get energy from food, they produce carbon dioxide as a waste product. We need oxygen, but not carbon dioxide. So, the carbon dioxide travels through the blood back to the lungs, where the body breathes it out. This way, the body gets rid of the carbon dioxide and keeps oxygen in the blood to make energy.
A virus is much smaller than a living cell. It attacks cells and can make people sick. Some viruses also make other mammals, animals, and even plants sick. For example, COVID-19 can make people and some other mammals sick.
A virus does not contain any cells, so it is not really alive. But it is also not really dead! A virus can multiply or (replicate), but it cannot do this on its own. It needs to find a cell to replicate inside.
To replicate, a virus needs to find the right kind of cell. Once inside, it makes new viruses that go to new cells and create more and more viruses. As the virus replicates, it spreads through the body.
COVID-19 is a virus that can replicate in humans and some other mammals, which is why it can make them sick. Unfortunately, COVID-19 can make some people very, very sick.
Viruses contain either DNA or RNA. This is because they need the information that a cell uses to create more viruses, allowing the virus to replicate.
Now you can read the Easy page on COVID-19 to learn more about how the virus that causes COVID-19 replicates inside humans and sometimes makes us very sick.
©2020 Dr. Michael Herrera