Cell Theory & Structure
Cell theory has three basic generalizations, according to the University of California at Davis. These generalizations state that all organisms are composed of one or more cells, the cell is the smallest unit that has properties of life, and life continues as a result of division and growth of single cells.
The Facts
Cell theory is often referred to as cell doctrine. The concept that all organisms are made up of similar units called cells was originally formulated by Matthias Jakob Schleiden and Theodor Schwann in 1839. This theory was developed prior to other important theories in biology including Charles Darwin's theory of evolution in 1859.
History
In 1838, Schleiden, a botanist, and Schwann, a zoologist, had a conversation regarding their respective studies of cells. According to Charles Mallery of the Department of Biology, University of Miami, Schwann saw similarities between plant cells that Schleiden discussed and his own observations of animal tissue cells. They proceeded to Schwann's lab and wrote a book about plant and animal cells the following year.
Features
Schwann and Schleiden's conclusions regarding cells stated that cells are a unit of structure, organization and physiology in living things. Furthermore, the cell acts as both a unique entity and as a building block in organism construction, and cells result from free-cell formation that is similar to crystals. Today, biologists know that their first two statements are true, however the third it incorrect. In fact, it was Rudolph Virchow who suggested a more accurate description of cell generation by stating that "all cells only arise from pre-existing cells."
Considerations
While the three generalizations listed in the overview are the core tenets, cell theory has three other statements that add to a more complete picture of cell structure. These tenets state that cells contain hereditary information that passes on from cell to cell during cell division. Furthermore, all cells are considered of the same chemical composition and all energy flow of life (particularly metabolism and biochemical reactions) occur within the cells.
Structure
All cells are considered to have three things in common. Cells have a cell membrane that selects which materials are allowed to pass into and out of the cell. They also have cytoplasm, which is the part of the cell that is enclosed by the cell membrane, and DNA, which is the genetic material of the cell. Furthermore, cells are divided into two types, prokaryotic (simple cells like bacteria) or eukaryotic (more complex cells like plants).
Wednesday, July 7, 2010
Cell Theory
Cell Theory
The discovery of the cell was made possible by the invention of the microscope, which was made possible by improved lens-grinding techniques. Antoni van Leeuwenhoek (1632-1723), a Dutch tradesman, learned to grind lenses and assemble them into simple microscopes. His contemporary Robert Hooke (1635-1703) used such an instrument to observe cork cells, sketches of which appeared in his 1665 publication "Micrographia." Inspired by Hooke's work, Leeuwenhoek began making microscopic examinations of his own. In 1678, he reported to the Royal Society that he had discovered "little animals" -- bacteria and protozoa -- in various samples. The society asked Hooke to confirm Leeuwenhoek's findings, and he did.
protozoaAaron Bell/Visuals Unlimited/Getty ImagesIn 1678, Antoni van Leeuwenhook reported that he had observed "little animals" -- protozoa -- through a microscope.
This paved the way for wide acceptance that a hidden world existed just beyond the limits of human vision and encouraged many scientists to take up the microscope in their investigations. One such scientist was German botanist Matthias Jakob Schleiden (1804-1881), who looked at numerous plant samples. Schleiden was the first to recognize that all plants, and all the different parts of plants, are composed of cells. While having dinner with zoologist Theodor Schwann (1810-1882), Schleiden mentioned his idea. Schwann, who came to similar conclusions while studying animal tissues, quickly saw the implications of their work. In 1839, he published "Microscopic Investigations on the Accordance in the Structure and Growth of Plants and Animals," which included the first statement of the cell theory: All living things are made up of cells.
Then, in 1858, Rudolf Virchow (1821-1902) extended the work of Schleiden and Schwann by proposing that all living cells must rise from pre-existing cells. This was a radical idea at the time because most people, scientists included, believed that nonliving matter could spontaneously generate living tissue. The inexplicable appearance of maggots on a piece of meat was often given as evidence to support the concept of spontaneous generation. But a famous scientist by the name of Louis Pasteur (1822-1895) set out to disprove spontaneous generation with a now-classic experiment that both firmly established the cell theory beyond doubt and solidified the basic steps of the modern scientific method.
The discovery of the cell was made possible by the invention of the microscope, which was made possible by improved lens-grinding techniques. Antoni van Leeuwenhoek (1632-1723), a Dutch tradesman, learned to grind lenses and assemble them into simple microscopes. His contemporary Robert Hooke (1635-1703) used such an instrument to observe cork cells, sketches of which appeared in his 1665 publication "Micrographia." Inspired by Hooke's work, Leeuwenhoek began making microscopic examinations of his own. In 1678, he reported to the Royal Society that he had discovered "little animals" -- bacteria and protozoa -- in various samples. The society asked Hooke to confirm Leeuwenhoek's findings, and he did.
protozoaAaron Bell/Visuals Unlimited/Getty ImagesIn 1678, Antoni van Leeuwenhook reported that he had observed "little animals" -- protozoa -- through a microscope.
This paved the way for wide acceptance that a hidden world existed just beyond the limits of human vision and encouraged many scientists to take up the microscope in their investigations. One such scientist was German botanist Matthias Jakob Schleiden (1804-1881), who looked at numerous plant samples. Schleiden was the first to recognize that all plants, and all the different parts of plants, are composed of cells. While having dinner with zoologist Theodor Schwann (1810-1882), Schleiden mentioned his idea. Schwann, who came to similar conclusions while studying animal tissues, quickly saw the implications of their work. In 1839, he published "Microscopic Investigations on the Accordance in the Structure and Growth of Plants and Animals," which included the first statement of the cell theory: All living things are made up of cells.
Then, in 1858, Rudolf Virchow (1821-1902) extended the work of Schleiden and Schwann by proposing that all living cells must rise from pre-existing cells. This was a radical idea at the time because most people, scientists included, believed that nonliving matter could spontaneously generate living tissue. The inexplicable appearance of maggots on a piece of meat was often given as evidence to support the concept of spontaneous generation. But a famous scientist by the name of Louis Pasteur (1822-1895) set out to disprove spontaneous generation with a now-classic experiment that both firmly established the cell theory beyond doubt and solidified the basic steps of the modern scientific method.
Brain Anatomy
Brain Anatomy
The cerebellum is the portion of the brain that is responsible for the coordination of movement. It is located just above the brainstem, beneath the occipital lobes at the base of the skull. Similar to the cerebrum, the cerebellum contains several folded bulges which add to its surface area and therefore increases the quantity of information that can be processed.
The cerebellum controls movement by processing and coordinating sensory input, then sending the information to the motor nerves. Whenever we perform a physical task, the cerebellum records the information so that we don't forget it. That is why we don't have to re-learn how to walk, run or ride a bike. Think you know all about the cerebellum and the brain? Take the Human Brain Quiz and test your knowledge of human brain anatomy.
The cerebellum is the portion of the brain that is responsible for the coordination of movement. It is located just above the brainstem, beneath the occipital lobes at the base of the skull. Similar to the cerebrum, the cerebellum contains several folded bulges which add to its surface area and therefore increases the quantity of information that can be processed.
The cerebellum controls movement by processing and coordinating sensory input, then sending the information to the motor nerves. Whenever we perform a physical task, the cerebellum records the information so that we don't forget it. That is why we don't have to re-learn how to walk, run or ride a bike. Think you know all about the cerebellum and the brain? Take the Human Brain Quiz and test your knowledge of human brain anatomy.
Bacteriophage
Bacteriophage
A bacteriophage (from 'bacteria' and Greek φᾰγεῖν phagein "to eat") is any one of a number of viruses that infect bacteria. Bacteriophages are among the most common biological entities on Earth. The term is commonly used in its shortened form, phage.
Typically, bacteriophages consist of an outer protein capsid enclosing genetic material. The genetic material can be ssRNA, dsRNA, ssDNA, or dsDNA ('ss-' or 'ds-' prefix denotes single-strand or double-strand) long with either circular or linear arrangement. Bacteriophages are much smaller than the bacteria they destroy.
Phages are estimated to be the most widely distributed and diverse entities in the biosphere. Phages are ubiquitous and can be found in all reservoirs populated by bacterial hosts, such as soil or the intestines of animals. One of the densest natural sources for phages and other viruses is sea water, where up to 9×108 virions per milliliter have been found in microbial mats at the surface, and up to 70% of marine bacteria may be infected by phages. They have been used for over 60 years as an alternative to antibiotics in the former Soviet Union and Eastern Europe. They are seen as a possible therapy against multi drug resistant strains of many bacteria.
A bacteriophage (from 'bacteria' and Greek φᾰγεῖν phagein "to eat") is any one of a number of viruses that infect bacteria. Bacteriophages are among the most common biological entities on Earth. The term is commonly used in its shortened form, phage.
Typically, bacteriophages consist of an outer protein capsid enclosing genetic material. The genetic material can be ssRNA, dsRNA, ssDNA, or dsDNA ('ss-' or 'ds-' prefix denotes single-strand or double-strand) long with either circular or linear arrangement. Bacteriophages are much smaller than the bacteria they destroy.
Phages are estimated to be the most widely distributed and diverse entities in the biosphere. Phages are ubiquitous and can be found in all reservoirs populated by bacterial hosts, such as soil or the intestines of animals. One of the densest natural sources for phages and other viruses is sea water, where up to 9×108 virions per milliliter have been found in microbial mats at the surface, and up to 70% of marine bacteria may be infected by phages. They have been used for over 60 years as an alternative to antibiotics in the former Soviet Union and Eastern Europe. They are seen as a possible therapy against multi drug resistant strains of many bacteria.
Diploid
Diploid
The basic set of chromosomes in an organism is called the monoploid number. This number is indicated by x. In an organism, the ploidy of cells can vary. Humans and almost all mammals, have diploid cells. The gametes or sex cells (egg and sperm) are haploid cells. In this article, we shall understand what is a diploid cell. You can read more on biology.
What is a Diploid Cell?
According to the diploid cell definition, it is an organism or cell that contains double set of chromosome (2n), one inherited from the mother and one inherited from father. Another diploid cell definition also includes an individual that contains a double set of chromosome per cell. The somatic tissues of higher plants and animals contain diploid chromosome content.
Almost all animals have diploid number of cells. All the organisms that produce sexually, have two copies of chromosomes that have different origins, that is, paternal and maternal. This help in mixing of genes that gives rise to better progeny.
There are a few species that have haplodiploid cells. Here, one sex (mostly male) contains haploid cells and the other sex (female) has diploid cells. The male have developed from unfertilized eggs and the females develop from fertilized eggs. Thus, they have a complete set of chromosome. The diploid cell example in such a case, includes insects like ants, bees and wasps, where the queen has diploid number of chromosome. You can read more on human genetics.
Another, diploid cell example is the human race. Humans contain 2 set of chromosomes in their cells. The somatic cells or non-sex cells contains 46 chromosomes each. There are 22 sets of autosomal chromosomes and 1 set of sex chromosome. This brings the total to 23 sets of chromosomes. After fertilization, the somatic cells receive 23 chromosomes from each parent making the number of chromosomes in the cell 46.
The basic set of chromosomes in an organism is called the monoploid number. This number is indicated by x. In an organism, the ploidy of cells can vary. Humans and almost all mammals, have diploid cells. The gametes or sex cells (egg and sperm) are haploid cells. In this article, we shall understand what is a diploid cell. You can read more on biology.
What is a Diploid Cell?
According to the diploid cell definition, it is an organism or cell that contains double set of chromosome (2n), one inherited from the mother and one inherited from father. Another diploid cell definition also includes an individual that contains a double set of chromosome per cell. The somatic tissues of higher plants and animals contain diploid chromosome content.
Almost all animals have diploid number of cells. All the organisms that produce sexually, have two copies of chromosomes that have different origins, that is, paternal and maternal. This help in mixing of genes that gives rise to better progeny.
There are a few species that have haplodiploid cells. Here, one sex (mostly male) contains haploid cells and the other sex (female) has diploid cells. The male have developed from unfertilized eggs and the females develop from fertilized eggs. Thus, they have a complete set of chromosome. The diploid cell example in such a case, includes insects like ants, bees and wasps, where the queen has diploid number of chromosome. You can read more on human genetics.
Another, diploid cell example is the human race. Humans contain 2 set of chromosomes in their cells. The somatic cells or non-sex cells contains 46 chromosomes each. There are 22 sets of autosomal chromosomes and 1 set of sex chromosome. This brings the total to 23 sets of chromosomes. After fertilization, the somatic cells receive 23 chromosomes from each parent making the number of chromosomes in the cell 46.
Lysosome
Lysosome
Structure
The human body comprises of about 50 to 75 trillion cells. The cell is the smallest unit of life and is often called the building block of life. A single cell is made up of many different organelles, that have specific functions, such as the nucleus, Golgi bodies, mitochondria, peroxisomes and lysosomes. In this article, we shall learn about lysosome structure, its function and its importance in the cell.
Lysosomes
Lysosomes are membrane bound organelles that are found in the cytoplasm of both plant and animal cells. The word lysosome was derived from two Greek words, 'lysis' which means destruction or dissolution and 'soma' which means 'body'. Lysosomes were discovered in 1949, by a Belgian cytologist, Christian de Duve.
Lysosome StructureLysosomes are actually membranous sacs filled with enzymes. They are found in all eukaryotic cells and act as 'garbage disposal' or the 'digester' of the cell. Lysosomes are spherical bag like structures that are bound by a single layer membrane, however, the lysosome shape and size may vary to some extent in different organisms. The lysosome size ranges between 0.1 to 1.2μm. The membrane that surrounds the lysosome, protects the rest of the cell from the hydrolytic or digestive enzymes that are contained in the lysosomes.
Lysosomes are manufactured by the Golgi apparatus, by budding, in the cell and the various digestive enzymes, that are present in the lysosomes are produced in the endoplasmic reticulum. These enzymes are then transported to the Golgi apparatus and are distributed to the lysosomes. Some examples of enzymes present in the lysosomes include nucleases, proteases, lipases and carbohydrases. These enzymes are used to dissolve nucleic acids, proteins, lipids and carbohydrates, respectively. All these enzymes are typically hydrolytic and can digest cellular macromolecules. Lysosomes are acidic, with a pH of 4.8. This acidic pH is maintained by pumping protons, from the cytosol that has a pH of 7.2. The protons are pumped across the membrane via proton pumps and chloride ion channels. The membrane thus acts as a protective barrier, that protects the cytosol and the rest of the cell from the hydrolytic enzymes within the lysosome.
Lysosome Function
Lysosomes act as disposal system of the cell. They break down complex proteins, carbohydrates, lipids and other macromolecules into simpler compounds. These simple compounds are returned to the cytoplasm and are used as new cell building materials. They are used for digestion of cellular waste products, dead cells or extracellular material such as foreign invading microbes, that pose a threat to the cell by phagocytosis process. However, phagocytosis is just one process that helps to get rid of unwanted material in the cell. Lysosomes are also involved in other digestive processes including endocytosis and autophagy. Another interesting function of the lysosomes is to repair the damage to the plasma membrane. They serve as membrane patch and help in sealing the wound in the plasma membrane. Lysosomes are also involved in programmed cell death, or autolysis, which is a catabolic process involving degradation of the cell's own components. This is the reason why lysosomes are often called as 'suicide sacs'. Read more on lysosomes function.
Lysosome Defects
Any malfunctioning of the lysosomes or any of the digestive proteins, results in lysosomal storage diseases, such as Tay-Sachs disease and Pompe's disease. These diseases are caused by defective function of the lysosomes or in absence of any of the digestive proteins or lysosomal hydrolytic enzymes.
Structure
The human body comprises of about 50 to 75 trillion cells. The cell is the smallest unit of life and is often called the building block of life. A single cell is made up of many different organelles, that have specific functions, such as the nucleus, Golgi bodies, mitochondria, peroxisomes and lysosomes. In this article, we shall learn about lysosome structure, its function and its importance in the cell.
Lysosomes
Lysosomes are membrane bound organelles that are found in the cytoplasm of both plant and animal cells. The word lysosome was derived from two Greek words, 'lysis' which means destruction or dissolution and 'soma' which means 'body'. Lysosomes were discovered in 1949, by a Belgian cytologist, Christian de Duve.
Lysosome StructureLysosomes are actually membranous sacs filled with enzymes. They are found in all eukaryotic cells and act as 'garbage disposal' or the 'digester' of the cell. Lysosomes are spherical bag like structures that are bound by a single layer membrane, however, the lysosome shape and size may vary to some extent in different organisms. The lysosome size ranges between 0.1 to 1.2μm. The membrane that surrounds the lysosome, protects the rest of the cell from the hydrolytic or digestive enzymes that are contained in the lysosomes.
Lysosomes are manufactured by the Golgi apparatus, by budding, in the cell and the various digestive enzymes, that are present in the lysosomes are produced in the endoplasmic reticulum. These enzymes are then transported to the Golgi apparatus and are distributed to the lysosomes. Some examples of enzymes present in the lysosomes include nucleases, proteases, lipases and carbohydrases. These enzymes are used to dissolve nucleic acids, proteins, lipids and carbohydrates, respectively. All these enzymes are typically hydrolytic and can digest cellular macromolecules. Lysosomes are acidic, with a pH of 4.8. This acidic pH is maintained by pumping protons, from the cytosol that has a pH of 7.2. The protons are pumped across the membrane via proton pumps and chloride ion channels. The membrane thus acts as a protective barrier, that protects the cytosol and the rest of the cell from the hydrolytic enzymes within the lysosome.
Lysosome Function
Lysosomes act as disposal system of the cell. They break down complex proteins, carbohydrates, lipids and other macromolecules into simpler compounds. These simple compounds are returned to the cytoplasm and are used as new cell building materials. They are used for digestion of cellular waste products, dead cells or extracellular material such as foreign invading microbes, that pose a threat to the cell by phagocytosis process. However, phagocytosis is just one process that helps to get rid of unwanted material in the cell. Lysosomes are also involved in other digestive processes including endocytosis and autophagy. Another interesting function of the lysosomes is to repair the damage to the plasma membrane. They serve as membrane patch and help in sealing the wound in the plasma membrane. Lysosomes are also involved in programmed cell death, or autolysis, which is a catabolic process involving degradation of the cell's own components. This is the reason why lysosomes are often called as 'suicide sacs'. Read more on lysosomes function.
Lysosome Defects
Any malfunctioning of the lysosomes or any of the digestive proteins, results in lysosomal storage diseases, such as Tay-Sachs disease and Pompe's disease. These diseases are caused by defective function of the lysosomes or in absence of any of the digestive proteins or lysosomal hydrolytic enzymes.
Animal Cell
Animal Cell
Animal Cell ModelAs the name signifies, an animal cell is an advanced, eukaryotic type of cell isolated from animal species. If you have learned plant and animal cell differences, you might be already aware that the latter type is nearly circular in shape. An animal cell lacks the protective cell wall, hence the shape of the cell is framed by a plasma membrane. Inside the cell, there are various membrane bound organelles, each of which is responsible for specific functions.
Topics concerning plant cell vs animal cell and their similarities are introductory chapters in science subjects. They provide information about the types and functions of cells. However, demonstrating cell models is a better way to understand the lessons precisely and also, in an interactive manner. Thus, in biology experiments, students are often given assignments to prepare an animal cell model or diagram.
How to Make an Animal Cell Model?
Before you get involved in making an animal cell model, try to understand the anatomy and parts of a typical eukaryotic cell. A better alternative is to examine the shapes and structures of the organelles in a labeled animal cell diagram. This will help you in coming up with innovative ideas for your project. With a little creativity and forethought, you can prepare an animal cell model with less effort.
Following is a step by step procedure for building a labeled animal cell model:
Required Materials and Supplies
* Colorful animal cell picture
* Styrofoam balls
* Playdough (or modeling clay)
* Cardboard for base
* Pipe cleaners
* T - Pins
* Duct tape or regular tape
* Glue or adhesive
* Ruler
* Box cutter
* Knife and scissors
Steps for Building an Animal Cell
Step # 1
Gather the required supplies for building an animal cell model. Select a large and detailed animal cell picture with colorful parts. For the cell nucleus part, you can purchase a small ball or Styrofoam block from the garden supplier. You can make remaining cell organelles from this block or playdough.
Step # 2
It is better to make the individual organelles before and stick to the cardboard base with adhesive pr pins. Otherwise, working directly on the model will make the job more tedious and messy. Accordingly, prepare a list of the cell parts, which you are supposed to build. Remember to make appropriate sized organelles with respect to the model size.
Step # 3
Lay the cardboard base and start building an animal cell model. To create plasma membrane, you can use a large rubber band or paint with a brush. Then, stick the nucleus (round plastic ball or Styrofoam ball) in the center with the help of duct tape or glue. For chromatin structures, you can use pipe cleaners in a random manner.
Step # 4
Cut out different shapes of Styrofoam that resemble cell organelles and color each of them with different shades. With reference to the labeled animal cell diagram, attach the colored pieces to the cardboard one by one, making sure that they occupy the correct positions in the animal cell model.
Step # 5
For better understanding, prepare a key on a paper sheet and illustrate the various cell parts. Ensure that the spellings are correct and if possible, explain their main functions in one or two lines. Finally, document the steps of making animal cell model, especially if you are presenting in a science fair project.
So, isn't making animal cell model interesting? After completion of the task, you will be familiar with the functions of the organelles. You can look out for different animal cell model ideas and choose the best for your project. Be accurate with the cell shape, structure and organelles to get good scores. Next time, learn about plant cell structure and parts and portray your understandings by building a plant cell model.
Animal Cell ModelAs the name signifies, an animal cell is an advanced, eukaryotic type of cell isolated from animal species. If you have learned plant and animal cell differences, you might be already aware that the latter type is nearly circular in shape. An animal cell lacks the protective cell wall, hence the shape of the cell is framed by a plasma membrane. Inside the cell, there are various membrane bound organelles, each of which is responsible for specific functions.
Topics concerning plant cell vs animal cell and their similarities are introductory chapters in science subjects. They provide information about the types and functions of cells. However, demonstrating cell models is a better way to understand the lessons precisely and also, in an interactive manner. Thus, in biology experiments, students are often given assignments to prepare an animal cell model or diagram.
How to Make an Animal Cell Model?
Before you get involved in making an animal cell model, try to understand the anatomy and parts of a typical eukaryotic cell. A better alternative is to examine the shapes and structures of the organelles in a labeled animal cell diagram. This will help you in coming up with innovative ideas for your project. With a little creativity and forethought, you can prepare an animal cell model with less effort.
Following is a step by step procedure for building a labeled animal cell model:
Required Materials and Supplies
* Colorful animal cell picture
* Styrofoam balls
* Playdough (or modeling clay)
* Cardboard for base
* Pipe cleaners
* T - Pins
* Duct tape or regular tape
* Glue or adhesive
* Ruler
* Box cutter
* Knife and scissors
Steps for Building an Animal Cell
Step # 1
Gather the required supplies for building an animal cell model. Select a large and detailed animal cell picture with colorful parts. For the cell nucleus part, you can purchase a small ball or Styrofoam block from the garden supplier. You can make remaining cell organelles from this block or playdough.
Step # 2
It is better to make the individual organelles before and stick to the cardboard base with adhesive pr pins. Otherwise, working directly on the model will make the job more tedious and messy. Accordingly, prepare a list of the cell parts, which you are supposed to build. Remember to make appropriate sized organelles with respect to the model size.
Step # 3
Lay the cardboard base and start building an animal cell model. To create plasma membrane, you can use a large rubber band or paint with a brush. Then, stick the nucleus (round plastic ball or Styrofoam ball) in the center with the help of duct tape or glue. For chromatin structures, you can use pipe cleaners in a random manner.
Step # 4
Cut out different shapes of Styrofoam that resemble cell organelles and color each of them with different shades. With reference to the labeled animal cell diagram, attach the colored pieces to the cardboard one by one, making sure that they occupy the correct positions in the animal cell model.
Step # 5
For better understanding, prepare a key on a paper sheet and illustrate the various cell parts. Ensure that the spellings are correct and if possible, explain their main functions in one or two lines. Finally, document the steps of making animal cell model, especially if you are presenting in a science fair project.
So, isn't making animal cell model interesting? After completion of the task, you will be familiar with the functions of the organelles. You can look out for different animal cell model ideas and choose the best for your project. Be accurate with the cell shape, structure and organelles to get good scores. Next time, learn about plant cell structure and parts and portray your understandings by building a plant cell model.
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