Structure, Function, and Information Processing
The cell, the basic unit of life
Name the parts of a cell and what each does, tell a plant cell from an animal cell, and put the levels of organization in order.
In 1665 Robert Hooke put a thin slice of cork under his microscope and saw rows of small empty compartments, packed like a honeycomb. He called each one a cell — the first time the word was used in science, and a good name, because a wall built of bricks is what an onion peel still looks like under a lens today.
The three basic parts
The cell membrane is the outer layer: it separates one cell from the next and, being porous, lets in what the cell needs and lets waste out. Inside it, the cytoplasm fills the space and is where most life processes happen. The nucleus, the rounded body in the middle, regulates what the cell does and how it grows. Plant cells carry a fourth part outside the membrane — a cell wall, which stiffens them.
Have a play
Six parts of a plant cell are marked out here. Take them one at a time, and each will name itself.
Tap any part of the picture.
Worked example
A muscle cell is shaped like a spindle and a nerve cell is long with branches. Why should two cells in the same body look so different?
Ask what each one has to do. A nerve cell carries messages between distant parts of the body.
Starting from the job rather than the picture is what makes the shape look designed instead of arbitrary.
Try it together
An onion peel and a scraping from the inside of a cheek are stained and put under a microscope. Work out what they show.
A word or two for each answer.
1.The onion peel cells look nearly rectangular and sit packed together with no gaps. Which extra part gives them that firm outline?
Have a go
Have a go on your own. A living being whose body is made up of many cells has a one-word name. What is it?
Ready to practice?
Eight questions on what you have just read. Nothing is timed, and you can play as many times as you like.