Page 24 - Innovator's Science-8

Like animal and plant cells, the cells of Nucleoid
Science microorganisms are surrounded by a cell
Bytes
membrane. Fungi cells also have a cell wall but
Testimony
An electron microscope lack chloroplasts, so they cannot make their own
was first built in 1931 by food through photosynthesis. Bacteria are
German scien sts Ernst different because they do not have a well-
Ruska and Max Knoll. It
uses a beam of electrons defined nucleus or nuclear membrane; instead, A bacterial cell showing
instead of light to they have a nucleoid region where their DNA is the nucleoid region
magnify objects. Modern
electron microscopes can found. This difference separates bacteria from yeast, protozoa, algae,
magnify spellmens more fungi, plants, and animals, which have a nucleus. Cells have many other
than one million mes, parts that can only be seen with very powerful microscopes called electron
allowing scien sts to see
fine details inside cells. microscopes, which magnify cells a million times or more. All living beings,
including microorganisms, are made of one or more cells, but their cells
differ in size, shape, and structure. Understanding these differences helps
us learn how different organisms work. While many microorganisms are

helpful, some can cause diseases in plants, animals, and humans, which will
be studied later.

Thus, whether in microorganisms or in complex multicellular beings, the
cell remains the fundamental unit of structure and function.

Know Your Scientist
Robert Hooke (1635-1703) was an English scientist who first discovered and described the structure of a cell.
In 1665, he used a simple microscope to observe thin slices of cork. He noticed that the cork looked like a
honeycomb made up of tiny compartments, which he called “cells”. Although Hooks was actually seeing the
cell walls of dead plant tissue, his discovery opened the door to a completely new filed of biology–cell theory.
Hooke's invention of the compound microscope and his famous book Micrographia helped people see the
microscopic world for the first time. His work laid the foundation for later discoveries about living organisms
and how all life is made up of cells.

Grasp-Up

Cell: The basic unit of life that makes up all living organisms. It carries out all the essen al func ons. needed for
survival.
Cell Wall: A rigid outer layer found in plant, fungal, and bacterial cells that provides support and protec on to
the cell.
Cell Membrane: A thin, flexible layer that surrounds the cell and controls the movement of substances in and
out of the cell.
Nucleus: The central part of a cell that contains gene c material (DNA) and controls the cell's ac vi es. (Note:
Bacteria do not have a well-defined nucleus.)
Tissue: A group of similar cells that work together to perform a specific func on in the body.
Unicellular Organisms: Organisms made up of only one cell. Example: bacteria, protozoa.
Mul cellular Organisms: Organisms made up of many cells. Example: plants, animals.

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Science-8