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

A cell is the smallest unit of a living thing. A living thing, like you, is called an organism. Thus, cells are the basic building blocks of all organisms.

In multicellular organisms, several cells of one particular kind interconnect with each other and perform shared functions to form tissues (for example, muscle tissue, connective tissue, and nervous tissue), several tissues combine to form an organ (for example, stomach, heart, or brain), and several organs make up an organ system (such as the digestive system, circulatory system, or nervous system). Several systems functioning together form an organism (such as an elephant, for example).

There are many types of cells, and all are grouped into one of two broad categories: prokaryotic and eukaryotic. Animal cells, plant cells, fungal cells, and protist cells are classified as eukaryotic, whereas bacteria and archaea cells are classified as prokaryotic. Before discussing the criteria for determining whether a cell is prokaryotic or eukaryotic, let us first examine how biologists study cells.

Microscopy

Cells vary in size. With few exceptions, individual cells are too small to be seen with the naked eye, so scientists use microscopes to study them. A microscope    is an instrument that magnifies an object. Most images of cells are taken with a microscope and are called micrographs.

Light microscopes

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

The optics of the lenses of a light microscope changes the orientation of the image. 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. Due to the manner in which light travels through the lenses, this system of lenses produces an inverted image (binoculars and a dissecting microscope work in a similar manner, but include an additional magnification system that makes the final image appear to be upright).

Most student microscopes are classified as light microscopes ( [link] a ). Visible light both passes through and is bent by 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

now that we have an estimate for the diameter of the cell.what estimate can we make about the volume of the cell?
faxhood Reply
why too much insulin result in low blood sugar
Leri Reply
difference between DNA and RNA
Eyitayo Reply
DNA is deoxyribonuclaic acid. Deoxy refers to a lack of oxygen. The Ribose moity is missing an OH group. I think it is missing from the second C of the ring. RNA is ribonucleic acid. DNA has our genetic code in on it. RNA is translated from DNA and carries the blue print for protein synthesis.
Eric
The OH group on RNA prevents it from being reactive. But it is very unstable though. Would you want such a power tool floating around in your body, no. And you have three types of RNA: mRNA, tRNA and rRNA. Please let me know it this helped?😄
Eric
o
Browse
what determines the aeration level in the soil
Shola Reply
what is homeostasis?
Sarita Reply
What is biology
Don Reply
Biology z the study of life
GOLDEN
what's biology
buran
biology is the study of living nd none living organism
Chinaza
Biology is the study of life
Quadri
yes Sir
Said
what's cell biology
Prince
biology is the study of life
Raheal
what is asexual reproduction,?
Awoi Reply
A type of reproduction which does not involve the fusion of gametes or a change in the number of chromosomes
Serena
Reproduction without sex... In which form a single organism or cell makes a copy of itself.
Serena
Please explain the concept of mitosis and meiosis
Serena
I guess you could use it for study buddies and brushing up on what you need to
Serena
what is mitosis
Klp
Asexual reproduction?
Serena
why pepsin and trypsin released in active form?
Yacqub
mitosis is the type cell division in which two daughter cells have same no. of chormosomes
syed
Hi
Don
chromosome number remains the same in mitosis
mc
Ello
Henry
Hii
Nikky
Yrr help me.
Nikky
Physical chemistry..... Koi h jo mujhe physical chem ki notes send kr ske
Nikky
what is asexual reproduction
Targbe
what makes golgi body in plants
Abdulkareem Reply
name the membrane of the plants
Abdulkareem
how can turners syndrome be corrected before birth
Balinda
which animal survive from being preyed just because of being humble, slow, and not aggressive
Balinda
Plants have golgi body's also. Plants are eukaryotic cells. And membrane bound organelles are a characteristic of eukaryotic cells. Moreover golgi body's are creatted from the ER. Also do not forget plants have plastids and animal cells do not.
Eric
During organs transplantation, the organs cannot be taken from just anybody since the graft would be rejected sooner or later due to
Liter Reply
Non-MHC compatibility on the organ and an attack from the patient's immune system.
Eric
what makes golgi body in plants
Abdulkareem
why trypsin and pepsin released in active form
Yacqub
Let us remember MHC'S on our cells. This is how our cells determine self from n o n s e l f. Transplanted tissue has to have a certain amount markers. These have to match to the recipiant's markers. Even with this, immunosuppresant medacine is prescribed to the recipient.
Eric
Even with these measures the body may still reject the transport. This can occur even after the recipient excepting the transport for some time.
Eric
what is integument system
Joy Reply
This system is our skin. This includes the skin lining our alimentary system which includes the tissue from our mouth to our anus. Our skin is our largest organ system. It is mostly made up of epithelial tissue.
Eric
Cellular respiration
Lucy Reply
This is how our cells make energy. They use glucose + oxygen. There are other facors involves also. But these are the main two reactant used, for aerobic respiration. The main product is ATP. ATP is a high energy molecule which is paramount for life.
Eric
what are the characteristics of living things
Ruth Reply
Movement Respiration Nutrition/Feeding Irritability/Sensitivity Growth Excretion Reproduction Deat/Life span
Hashim
What makes children from the same father and mother sometimes don't look alike?
Hashim
One of the main one's is the abilit reproduce. That is why viruses are not considered living. Because they do not have the ability to replicate on they own.
Eric
identification of problems
Nana Reply
what happens in the process of raising the human arms
Nana
what is biology
Brandi Reply
first step in scientific method
Brandi
The study of living things.
Eric
In an investigation the pancreatic duct of a mammal was blocked.It was found that the blood sugar regulation remained normal while food digestion was impaired.Explain
Mac Reply
To begin with, obstruction of pancreatic duct will alter the blood sugar level as the juices responsible for glucose regulation will be rendered inconsequential. This will in turn affect the rate of digestion and absorbtion of digested food substances by the Villus .
Muktar

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Source:  OpenStax, Concepts of biology. OpenStax CNX. Feb 29, 2016 Download for free at http://cnx.org/content/col11487/1.9
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