The People's Share

GED Life Science, room one

Alive or Not?

What life science studies, two films, and the seven signs of life.

Life science

Life science is the study of living things: what they are made of, how they work, how they grow, and how they pass life on. It covers everything from a bacterium too small to see to a whale, and it covers you.

Every living thing is made of cells. Some living things are a single cell. Your body is about thirty trillion cells, and every one of them is busy right now.

Start with two short films. The first is an animation made for Harvard University by a studio of medical artists. Everything in it happens inside one white blood cell, in one blood vessel, and every shape was drawn from what scientists have measured. Watch it once for the pleasure of it, the way you would watch the first pictures sent back from another planet. Then watch the second version, where a biology teacher stops the film and names what you are seeing.

The Inner Life of the Cell (with music, about 3 minutes)

Video not starting? Watch it at video.byui.edu.

The same film, with a teacher's narration (about 11 minutes)

Video not starting? Watch it on YouTube.

One correction to the narration. When the film shows a protein walking along a thread inside the cell, pulling a round bag behind it, the narrator calls it dynein. That walker is kinesin. Both are motor proteins, and both walk along the same kind of thread, called a microtubule. They walk in opposite directions: kinesin carries its load outward, toward the edge of the cell, and dynein carries its load inward, toward the center.

These videos need the page to be on a website. Opened as a file on your computer, the players will not start. Use the links above.

Watch for these. You will meet each one by name in room three.

Near the end, the teacher says something worth keeping. The rods and threads in the film build themselves and take themselves apart, but nobody calls them alive. They are proteins. Their movements are what keep the cell alive, and the cell is what keeps you alive. So where does "alive" begin? That is the question of this room.

What makes something alive?

Anyone can tell a dog from a rock. Biologists need a test that also works on the hard cases: a seed, a flame, a virus. The test is a list of seven signs. Something is alive if it shows all seven. Each sign has a plain name and a scientific name; the GED uses the scientific ones, so both are here.

1. It is made of cells

cellular organization

Every living thing is built of cells, the smallest units that are alive on their own. A bacterium is one cell. You are about thirty trillion, and in a body like yours the cells specialize: muscle cells, nerve cells, skin cells. Cells of one kind working together make a tissue; tissues working together make an organ, like the heart; organs working together make you.

2. It uses energy

metabolism

Living things take in energy and spend it to keep themselves running. Inside every cell, chemical reactions break food down and build new parts. All of those reactions together are called metabolism. Breaking things down to release energy is catabolism; building things up is anabolism. When metabolism stops, life stops.

3. It keeps a steady inside

homeostasis

Living things keep their insides steady while the outside changes. On a cold day and a hot one, your body holds its temperature close to 98.6 degrees. It keeps the water and salt in your blood in balance, and it keeps the acid level of your blood inside a narrow range. All that balancing is homeostasis. A rock is the temperature of the air around it; you are not.

4. It responds to its surroundings

response to stimuli

Living things notice changes around them and react. A plant bends toward light. A bacterium swims toward sugar. You pull your hand back from a hot pan before you have had time to think. Scientists call the change a stimulus and the reaction a response.

5. It grows and develops

growth and development

Living things grow, by making their cells bigger or by making more of them. They also develop: they change form in a set order, following instructions carried in their DNA, the set of instructions every living thing carries inside its cells. A tadpole becomes a frog. A seed becomes a tree. A child becomes an adult. A crystal gets bigger too, but it follows no instructions, and it never becomes anything else.

6. It reproduces

reproduction

Living things make more of their own kind and pass their instructions, their DNA, to the young. Some split in two, so the young are copies of one parent: asexual reproduction. Some mix the instructions of two parents: sexual reproduction. One living thing may never reproduce, but its kind can.

7. Its kind changes over the generations

evolutionary adaptation

Over many generations, kinds of living things change. The ones best suited to their surroundings survive and leave more young, so their traits become common. This is evolutionary adaptation. It happens to a population over generations, never to one animal in its own lifetime.

Two of the signs cause most of the arguments. The signs describe a kind of living thing, not one individual: a mule cannot have young, and a person may never have children, but both are alive. And a thing must show all seven: a flame uses energy and spreads, a crystal grows, a robot responds, and none of them is alive.

Alive or not? Sort, then check

Tap a case, then tap the bin it belongs in. Put anything you cannot decide in Not sure. When all eight are sorted, tap Check.

Alive

Not alive

Not sure