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By the end of this section, you will be able to:
  • Describe the role of cells in organisms
  • Compare and contrast light microscopy and electron microscopy
  • Summarize cell theory

A cell is the smallest unit of a living thing. A living thing, whether made of one cell (like bacteria) or many cells (like a human), is called an organism. Thus, cells are the basic building blocks of all organisms.

Several cells of one kind that interconnect with each other and perform a shared function form tissues, several tissues combine to form an organ (your stomach, heart, or brain), and several organs make up an organ system (such as the digestive system, circulatory system, or nervous system). Several systems that function together form an organism (like a human being). Here, we will examine the structure and function of cells.

There are many types of cells, all grouped into one of two broad categories: prokaryotic and eukaryotic. For example, both animal and plant cells are classified as eukaryotic cells, whereas bacterial cells are classified as prokaryotic. Before discussing the criteria for determining whether a cell is prokaryotic or eukaryotic, let’s first examine how biologists study cells.

Microscopy

Cells vary in size. With few exceptions, individual cells cannot be seen with the naked eye, so scientists use microscopes (micro- = “small”; -scope = “to look at”) to study them. A microscope    is an instrument that magnifies an object. Most photographs of cells are taken with a microscope, and these images can also be called micrographs.

The optics of a microscope’s lenses change the orientation of the image that the user sees. A specimen that is right-side up and facing right on the microscope slide will appear upside-down and facing left when viewed through a microscope, and vice versa. Similarly, if the slide is moved left while looking through the microscope, it will appear to move right, and if moved down, it will seem to move up. This occurs because microscopes use two sets of lenses to magnify the image. Because of the manner by which light travels through the lenses, this system of two lenses produces an inverted image (binocular, or dissecting microscopes, work in a similar manner, but include an additional magnification system that makes the final image appear to be upright).

Light microscopes

To give you a sense of cell size, a typical human red blood cell is about eight millionths of a meter or eight micrometers (abbreviated as eight μm) in diameter; the head of a pin of is about two thousandths of a meter (two mm) in diameter. That means about 250 red blood cells could fit on the head of a pin.

Most student microscopes are classified as light microscopes ( [link] a ). Visible light passes and is bent through the lens system to enable the user to see the specimen. Light microscopes are advantageous for viewing living organisms, but since individual cells are generally transparent, their components are not distinguishable unless they are colored with special stains. Staining, however, usually kills the cells.

Questions & Answers

What's the function of epiglottis
Ugo Reply
What Is The Other Name For Intestinal Juice?
Justin Reply
what is the largestest planet of the universe
rick Reply
what are the types of cell
Bernard Reply
prokaryotic and eukaryotic
Yazi
prokaryotic cell and eukaryotic cell
Grace
what is the protein found in the blood?
Tobias Reply
globin
Joelia
Globin
globulins
EZRA
globulins
SASMITA
globulins
Grace
what is parasitic movement
Emmanuel Reply
Parasitic movement is a problem for all of us. So is its companion, parasitic tension. Parasitic movement is the excess contraction of muscles that you don't actually need to complete an action.
freya
HW a u
Nyandera
cool
Bigenis
am OK how a u
Ocen
absorption may simply mean utilization of food in the body
Bigenis
what are eukaryotic cells
Thiza Reply
eukaryotic cells which posses a true nucleus that is the DNA is enclosed and covered by a nuclear membrane
Grace
what is the mean of pair of chromosomes
Kazula Reply
hi
Lagos
23 haploid and 23diploid
Patson
how are you studying in this quarantine? .. how are you keeping yourselves motivated?
sivajijadhav @815.com
good morning guyz
Joelia
morning
Kazula
hi
Justin
Good
Angela
tell me if you know what can be used...than reading pls hint me pls 🙏🙏🙏
Angela
what is the important of sex
Aremu Reply
why did human being need sex?
Aremu
because he/she have feelings
Chripine
reproduction...to make more
Yazi
due to active harmon
Manish
One important of sex is to reproduce
Emma
to ensure the countinuty of life
Yusuf
all of you are right
Edith
for sexual satisfaction and birth
Grace
what is momentum
Asiya Reply
The strength or force that allows something to continue or grow stronger or faster as time pass
Emma
What is Centripetal Force?
Justin
centrepital force is the inward force required to keep a body moving with constant speed in a circular path
Yusuf
what is the test for protein
Takii Reply
List four condition necessary for seed germination
Tedeka Reply
water,air(oxygen),light,temperature
Hassan
water, light, oxygen and temperature
lilchris
water, oxygen, light temperature
Mike
water oxygen light and temperature
John
importance of biology
Alabina Reply
importance of boilogy
Alabina
what is soil
Amina Reply
soil is the upper part of the earth
Alabina
what is importance of studying biology
Alabina
soil is the uppermost layer of the earth on which plant grows
Yusuf
soil is defined as the thin surface of the upper most layer of the earth crust on which plants grow
Thanni
soil is the upper part of the earth which plants grow on
Emma
soil is the uppermost layer of the earth in which most of the necessary nutrient are found and serve as habitats for some organisms
Grace
soil is the uppermost layer of the earth in which most of the necessary nutrients are found and serve as habitats for some organisms
Grace
soil is the uppermost layer of the earth in which most of the necessary nutrient are found and serve as habitats for some organisms
Grace
soil is the uppermost layer of the earth in which most of the necessary nutrients are found and serve as habitats for some organisms
Grace
soil is the accumulation of lose weathered materials which covers much of the land surface of the earth
rick

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Source:  OpenStax, Biology. OpenStax CNX. Feb 29, 2016 Download for free at http://cnx.org/content/col11448/1.10
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