Life's Amazing Mini Machines What do a tree and an elephant have in common A trunk Jokes aside they are both made of cells So is every other living thing from the tiniest microbes to plants to humans to the marvelously giant whale Cells are like tiny machines carrying out all the work needed to keep us alive They are the smallest units of life capable of reproducing themselves Is It Alive How can you tell if something is alive For something to be considered an organism a living thing it has to display every single trait on this checklist It is made up of one or more cells It uses energy It maintains a steady stable internal environment It grows It reproduces It is capable of detecting and responding to changes in its environment What about viruses Are they alive The answer is no While they carry all the information needed to make more of themselves they can’t reproduce on their own Instead they have to infect a cell and force its machinery to do the job 4
Some organisms are unicellular meaning they are made up of a single cell Bacteria yeast and amoeba are all unicellular Other organisms are multicellular with bodies made up of more than one cell and sometimes trillions of cells Cells by the Numbers How many cells does an organism have Lactobaccillus a bacteria used to make yogurt 1 cell Simple roundworm 1,000 cells Adult human 37,000,000,000,000 37 trillion cells Yogurt Lactobaccillus 5
The diversity of cells is mind-blowing They come in a huge array of sizes and shapes These characteristics are influenced by where a cell lives and what work it needs to do to survive The human body has an estimated 37 2 trillion cells A fruit fly has 50,000 cells Scientists recently discovered Cells of All Shapes and Sizes bacterial cells so tiny that 150,000 could fit into the tip of a human hair Cells can also be huge An ostrich egg yes it’s a single cell is about the size of a melon and weighs over three pounds 1 kilogram while a giraffe nerve cell can be several meters long 6
A cell’s size and shape can tell us a lot about what it does Unicellular organisms tend to be small Their size allows them to take up nutrients and reproduce quickly sometimes within minutes These things help them to adapt to new environments organism there can be hundreds of cell types Their many shapes and sizes help them carry out different life-supporting functions within that organism In a single multicellular Cell Power Nerve cells send signals from one part of the body to another They have a long thin shape with branches that reach out in different directions This allows them to communicate with other cells quickly and efficiently Skin cells can be wide and flat allowing fewer cells to cover a greater area They are also packed tightly together This allows them to form a smooth strong and stretchy barrier that protects the body from the outside environment 7
