Made of Cells — Characteristics of Life

What Makes Something Alive?

The first thing we'll discuss is the fact that all living things are made of cells.

That weird mushroom growing in the yard? It's made of cells.

Your grandma? She's made of cells.

The microorganisms living in your stomach? Cells.

A cell is the smallest unit of life. It is a collection of tiny, functional things enclosed in a membrane. Surprisingly enough, they are very complex and organized despite their tiny size.

Living things can be divided into two categories: unicellular and multicellular. Unicellular organisms are exactly what they sound like. They're made of a single cell. Bacteria and yeast are two types of unicellular organisms.

Similarly, multicellular organisms are exactly what they sound like. Multicellular organisms are made of many cells, most of which have specific "jobs". You, yes, you, are a multicellular organism with around 85 different types of cells.

$$\color{#8925AE}{\text{Vocabulary Review:}}$$

$\color{#8925AE}{\text{Cell}}$ : Smallest unit of life

$\color{#8925AE}{\text{Reproduction}}$ : Making offspring. Sexual reproduction is when two organisms combine their genetic information to create a unique offspring. Asexual reproduction is when one organism creates a copy of itself

$\color{#8925AE}{\text{Heredity}}$ : The genetic information inherited from the organism's parents

$\color{#8925AE}{\text{Development}}$ : How organisms grow and mature

$\color{#8925AE}{\text{Homeostasis}}$ : A regulatory mechanism that maintains a state of equilibrium

$\color{#8925AE}{\text{Metabolism}}$ : Using chemical reactions to harvest energy for biological functions

What Are Cells?

In order to be considered living, an organism must be made of one or more cells.

There are three main ideas when it comes to cells. Let's take a look:

Key Vocabulary:

1. Cell
2. Unicellular
3. Multicellular
4. Organism

What Is Cell Theory?

Cells are the basic building block of life. While things like viruses, which are not cells, are still up for debate when it comes to being "alive", cells are pretty much the gold standard for life.

Some living organisms are only one cell, or unicellular. Things like bacteria and amoebas are single cell organisms. Other organisms, like mushrooms, dogs, and humans, are multicellular. Because cells are able to differentiate and perform different tasks, multicellular organisms can become very complex. For example, red blood cells can carry oxygen throughout the body. A group of cells can also work together to perform a certain task.

Cells also have the special ability to make more cells. Every living cell is the product of a parent cell.

For something to be considered alive, it must be composed of one or more cells.

How Do We Classify Cells?

Because cells are the most fundamental unit of life, there are many ways we can organize them. Here are some common distinctions scientists make.

• Prokaryotic cells vs. eukaryotic cells

Does the cell have a nucleus or not?

• Animal cells vs. plant cells

What type of organism is the cell found in? Plant and animal cells have some different internal structures.

Types of Cell Structures

While there are some differences, all cells share a few key structures. One of the most important ones is a barrier that surrounds the cell called the cell membrane. You will also find some form of DNA, either in a nucleus or floating around freely. If it's a eukaryotic cell, you'll be able to see many organelles inside. These are sites of specialized activity within the cell.

Plant and fungal cells also have a tough outer cell wall to give them more shape and support.

(Video) The Wacky History of Cell Theory - Lauren Royal-Woods

by TED-Ed

Watch this video to learn more about cell theory. In this video, you will learn about previous hypotheses, how cells came to be discovered, and what tools were used to see them. These discoveries all led to the idea of cell theory.