1. Cells and the Definition of Life
Images by 柑橘類

2. But how do we know something is living?
Bio- means life
-logy means study
So biology means
the study of life!
But how do we know something is living?

3. All living things are made of one or more cells.

4. Cells are the building blocks of life, and they are the smallest structures that can be classified as living. And only living things are made of cells!

5. Robert Hooke’s microscope and his drawing of plant cells.
The word cell means small room in Latin. It was first used by Robert Hooke in 1665 when he compared the plant cells he was looking at through his microscope to small rooms.
Robert Hooke’s microscope and his drawing of plant cells.

6. It was the invention of the microscope that allowed scientists to discover tiny living things like bacteria that are made of only one cell.
Protist
Bacteria
Image by 柑橘類

7. An organism is a single, complete living thing.
Important Vocabulary
An organism is a single, complete living thing.
Image by 柑橘類
This paramecium
is an organism.
This mushroom is an organism.
Photo by Joachim Huber
This zebra
is an organism.

8. Uni- means one Unicellular organisms are made of one cell.
Image by 柑橘類
These can also be called
single-celled organisms.
Image by 柑橘類

9. Multicellular organisms are made of many cells.
Multi- means many
Multicellular organisms are made of many cells.
Organisms that can be clearly seen without a microscope are multicellular.

10. All living things are made of cells, but there are a few other things that all living things have in common.
Photo by Andy Murray
Bacteria
Human
Insect

11. Living things can reproduce themselves.

12. They can perform chemical reactions like getting energy out of food.

13. All living things contain a set of instructions in the form of DNA.
Segment of DNA
All living things contain a set of instructions in the form of DNA.
Chromosome
DNA
DNA is stored in the form of chromosomes.