Mendelian/Classical Genetics

MEIOSIS I

Meiosis is the process by which replicated chromosomes undergo two nuclear divisions to produce four haploid cells, also called meiocytes (sperms and eggs). Diploid (2n) organisms rely on meiosis to produce meiocytes, which have half the ploidy of the parents, for sexual reproduction. Halving the ploidy in meiocytes is essential for restoring the genetic content of the zygote to that of the parents. Meiosis uses similar mechanisms as those employed during mitosis to accomplish the separation and redistribution of chromosomes. However, several features, namely, the pairing and genetic recombination between homologous chromosomes, are unique to meiosis.

The steps leading up to meiosis are similar to those of mitosis – the centrioles and chromosomes are replicated. The amount of DNA in the cell has doubled, and the ploidy of the cell remains the same as before, at 2n. In meiosis I, the phases are analogous to mitosis: prophase I, metaphase I, anaphase I, and telophase I (below figure). Meiosis I proceeds directly to meiosis II without going through interphase.

Meiosis I is unique in that genetic diversity is generated through crossing over and random positioning of homologous chromosomes (bivalent chromosomes). In addition, in meiosis I, the chromosomal number is reduced from diploid (2n) to haploid (n) during this process. (See figure below, where meiosis I begins with a diploid (2n = 4) cell and ends with two haploid (n = 2) cells.) In humans (2n = 46), who have 23 pairs of chromosomes, the number of chromosomes is reduced by half at the end of meiosis I (n = 23).

 

 

 

 

 

 

 

 

 

 

 

 

Prophase I

During prophase I, chromosomal condensation allows chromosomes to be viewed under the microscope. In late prophase I, homologous chromosomes (also called bivalent chromosomes, or bivalents) pair laterally, or side-by-side. At this time they are said to be in synapsis. During synapsis, crossovers – cross-connections that form from breakage and rejoining between sister chromatids – can occur between the paired bivalents, leading to genetic recombination (exchange of genetic material) between the strands involved. The point where a crossover occurs is called a chiasma (plural chiasmata) (see below figure). In figure below, following crossing over, the blue and red chromosomes, which originally carried AA and aa alleles, respectively, now carry Aa alleles in both chromosomes at the end of prophase I. Note that these bivalents have two chromosomes and four chromatids, with one chromosome originating from each parent.

Metaphase I

In metaphase I, each pair of bivalents (two chromosomes, four chromatids total) align on the metaphase plate. This is different from metaphase in mitosis, where all chromosomes align single file on the metaphase plate. The position of each chromosome in the bivalents is random – either parental homolog can appear on each side. This means that there is a 50-50 chance for the daughter cells to get either the mother’s or father’s homolog for each chromosome (see figure below). As shown in the below figure, during metaphase I, bivalents from either parent can align on either side of the cell. In an organism with two sets of chromosomes, there are four ways in which the chromosomes can be arranged, resulting in differences in chromosomal distribution in daughter cells after meiosis I. (A diploid organism with 2n chromosomes will have 2ⁿ possible combinations or ways of arranging its chromosomes during metaphase I.)

In a diploid cell with 2 pairs of chromosomes, there are 4 ways to arrange the chromosomes during metaphase I.

Anaphase I

In anaphase I, homologous chromosomes separate. Homologous chromosomes, each containing two chromatids, move to separate poles. Unlike in mitosis, the centromeres do not split and sister chromatids remain paired in anaphase I.

Telophase I and Cytokinesis

In telophase I, the homologs of each bivalent arrive at opposite poles of the cell, and a new nuclear membrane forms around each set of chromosomes. Cytokinesis then divides the cell into two daughter cells. Each of the two daughter cells is now haploid (n), with half the number of chromosomes per nucleus as in meiosis I. In some species, the nuclear membrane briefly forms around the chromosomes, while in others it does not. The cell now proceeds into meiosis II, with the chromosomes remaining condensed.

MEIOSIS II

Chromosomal replication does not occur between meiosis I and meiosis II; meiosis I proceeds directly to meiosis II without going through interphase. The second part of the meiosis, meiosis II, resembles mitosis more than meiosis I. Chromosomal numbers, which have already been reduced to haploid (n) by the end of meiosis I, remain unchanged after this division. In meiosis II, the phases are, again, analogous to mitosis: prophase II, metaphase II, anaphase II, and telophase II (see figure below). As shown in the figure below, meiosis II begins with two haploid (n = 2) cells and ends with four haploid (n = 2) cells. Notice that these four meiocytes are genetically different from one another. In humans (2n = 46), who have 23 pairs of chromosomes, the number of chromosomes remains unchanged from the beginning till the end of meiosis II (n = 23).

Prophase II

Spindle fibers reform and attach to centromeres in prophase II.

Metaphase II

The chromosomes align on the metaphase plate during metaphase II in preparation for centromeres to divide in the next phase.

Anaphase II

In anaphase II, chromosomes divide at the centromeres (like in mitosis) and the resulting chromosomes, each with one chromatid, move toward opposite poles of the cell.

Telophase II and Cytokinesis

Four haploid nuclei (containing chromosomes with single chromatids) are formed in telophase II. Division of the cytoplasm during cytokinesis results in four haploid cells. Note that these four cells are not identical, as random arrangements of bivalents and crossing over in meiosis I leads to different genetic composition of these cells.

In humans, meiosis produces genetically different haploid daughter cells, each with 23 chromosomes that consist of one chromatid. These haploid cells become unfertilized eggs in females and sperm in males. The genetic differences ensure siblings of the same parents are never entirely genetically identical.

DNA

Deoxyribonucleic acid or DNA is a molecule that contains the instructions an organism needs to develop, live and reproduce. These instructions are found inside every cell, and are passed down from parents to their children.

DNA structure

DNA is made up of molecules called nucleotides. Each nucleotide contains a phosphate group, a sugar group and a nitrogen base. The four types of nitrogen bases are adenine (A), thymine (T), guanine (G) and cytosine (C). The order of these bases is what determines DNA’s instructions, or genetic code. Human DNA has around 3 billion bases, and more than 99 percent of those bases are the same in all people, according to the U.S. National Library of Medicine (NLM).

 

Similar to the way the order of letters in the alphabet can be used to form a word, the order of nitrogen bases in a DNA sequence forms genes, which in the language of the cell, tells cells how to make proteins. Another type of nucleic acid, ribonucleic acid, or RNA, translates genetic information from DNA into proteins.

Nucleotides are attached together to form two long strands that spiral to create a structure called a double helix. If you think of the double helix structure as a ladder, the phosphate and sugar molecules would be the sides, while the bases would be the rungs. The bases on one strand pair with the bases on another strand: adenine pairs with thymine, and guanine pairs with cytosine.

DNA molecules are long — so long, in fact, that they can’t fit into cells without the right packaging. To fit inside cells, DNA is coiled tightly to form structures we call chromosomes. Each chromosome contains a single DNA molecule. Humans have 23 pairs of chromosomes, which are found inside the cell’s nucleus. 

 

DNA discovery

DNA was first observed by a German biochemist named Frederich Miescher in 1869. But for many years, researchers did not realize the importance of this molecule. It was not until 1953 that James Watson, Francis Crick, Maurice Wilkins and Rosalind Franklin figured out the structure of DNA — a double helix — which they realized could carry biological information. 

Watson, Crick and Wilkins were awarded the Nobel Prize in Medicine in 1962 “for their discoveries concerning the molecular structure of nucleic acids and its significance for information transfer in living material.” Franklin was not included in the award, although her work was integral to the research. [Related: Unraveling the Human Genome: 6 Molecular Milestones]

DNA sequencing

DNA sequencing is technology that allows researchers to determine the order of bases in a DNA sequence. The technology can be used to determine the order of bases in genes, chromosomes, or an entire genome. In 2000, researchers completed the first full sequence of the human genome, according to a report by the National Human Genome Research Institute. 

Ribonucleic acid (RNA) is a polymeric molecule essential in various biological roles in coding, decoding, regulation, and expression of genes. RNA and DNA are nucleic acids, and, along with lipids, proteins and carbohydrates, constitute the four major macromolecules essential for all known forms of life. Like DNA, RNA is assembled as a chain of nucleotides, but unlike DNA it is more often found in nature as a single-strand folded onto itself, rather than a paired double-strand. Cellular organisms use messenger RNA (mRNA) to convey genetic information (using the nitrogenous bases guanine, uracil, adenine, and cytosine, denoted by the letters G, U, A, and C) that directs synthesis of specific proteins. Many viruses encode their genetic information using an RNA genome.

 

There are 4 types of RNA, each encoded by its own type of gene.

The genomic DNA contains all the information for the structure and function of an organism.

In any cell, only some of the genes are expressed, that is, transcribed into RNA.

There are 4 types of RNA, each encoded by its own type of gene:

• mRNA – Messenger RNA: Encodes amino acid sequence of a polypeptide.
• tRNA – Transfer RNA: Brings amino acids to ribosomes during translation.
• rRNA – Ribosomal RNA: With ribosomal proteins, makes up the ribosomes, the organelles that translate the mRNA.
• snRNA – Small nuclear RNA: With proteins, forms complexes that are used in RNA processing in eukaryotes. (Not found in prokaryotes.)

GENETICS

CHROMOSOMES

Placement of chromosomes in the cell:

Forms of a complex various protein that partners help package into a tiny space. This DNA-protein complex is called chromatin, wherein the mass of protein and the nucleic acid is nearly equal. Within cells, chromatin usually folds into characteristic formations called chromosomes. Each chromosome contains a single double-stranded piece of DNA along with the aforementioned packaging proteins

Eukaryotic chromosomes consist of repeated units of chromatin called nucleosomes.

Nucleosomes are made up of double-stranded DNA that has complexed with small proteins called histones.

The chromatids are made of a substance called chromatin. This is a single, very long strand of DNA. … The chromatin is copied, so you now have 92 strands, that are each spiraled up to form the chromatids. The 2 copies of each chromatid are joined together by a centromere to form a chromosome.

MITOSIS

During interphase (1), chromatin is in its least condensed state and appears loosely distributed throughout the nucleus. Chromatin condensation begins during prophase (2) and chromosomes become visible. Chromosomes remain condensed throughout the various stages of mitosis (2-5).

The chemical division process called mitosis is split into the following 6 steps, such that: interphase, prophase, metaphase, anaphase, telophase, cytokinesis. The first step of mitosis is characterized by the presence of one cell, but at the end of the process there exist two identical cells.

 

LAW OF SEGREGATION

When sperm and egg unite at fertilization, each contributes its allele, restoring the paired condition in the offspring. This is called the Law of Segregation. Mendel also found that each pair of alleles segregates independently of the other pairs of alleles during gamete formation.

 

LAW OF INDEPENDENT ASSORTMENT

The Principle of Independent Assortment describes how different genes independently separate from one another when reproductive cells develop. Independent assortment of genes and their corresponding traits was first observed by Gregor Mendel in 1865 during his studies of genetics in pea plants.

A dihybrid cross is a cross between individuals heterozygous at two different loci. Mendel’s second law is also known as the law of independent assortment. The law of independent assortment states that the alleles of one gene sort into gametes independently of the alleles of another gene.

 

MICROORGANISM

 

 

 

 

Microorganisms or microbes,  which may exist in its single celled form, or in colony of cells.

The existence of microscopic organisms was

discovered during the period 1665-83 by two

Fellows of The Royal Society, Robert Hooke and

Antoni van Leeuwenhoek. In Micrographia

(1665), Hooke presented the first published

depiction of a microoganism, the

microfungusMucor. Later, Leeuwenhoek was

1st to observed micro organism under pound of

water and described microscopic protozoa and

bacteria.

5 Types of Microbes

                                                                      Bacteria a unicellular organisms. The cells

                                                                      are described as prokaryotic because they

                                                                      lack a nucleus. According to the way their

                                                                      cell wall structure stains, bacteria can be

                                                                      classified as either Gram-positive or Gram-

                                                                      negative when using the Gram staining.

                                                                      According to the way they obtain energy,

                                                                      bacteria are classified as heterotrophs or

                                                                      autotrophs. Autotrophs make their own food by using the energy of sunlight or chemical reactions. Heterotrophs obtain their energy by consuming other organisms. Bacteria that use decaying life forms as a source of energy are called saprophytes.

 

Archaea or Archaebacteria differ from true bacteria in their cell wall structure and lack peptidoglycans. They are prokaryotic cells with avidity to extreme environmental conditions

Fungi (mushroom, molds, and yeasts) are eukaryotic cells (with a true nucleus). Most fungi are multicellular and their cell wall is composed of chitin. They obtain nutrients by absorbing organic material from their environment (decomposers), through symbiotic relationships with plants (symbionts), or harmful relationships with a host (parasites). Fungi reproduce by releasing spores.

Protozoa are unicellular aerobic eukaryotes. They have a nucleus, complex organelles, and obtain nourishment by absorption or ingestion through specialized structures. They make up the largest group of organisms in the world in terms of numbers, biomass, and diversity. Their cell walls are made up of cellulose.

Algae, also called cyanobacteria or blue-green algae, are unicellular or multicellular eukaryotes that obtain nourishment by photosynthesis. They live in water, damp soil, and rocks and produce oxygen and carbohydrates used by other organisms. It is believed that cyanobacteria are the origins of green land plants.

Viruses are noncellular entities that consist of a nucleic acid core (DNA or RNA) surrounded by a protein coat. Although viruses are classified as microorganisms, they are not considered living organisms. Viruses cannot reproduce outside a host cell and cannot metabolize on their own. Viruses often infest prokaryotic and eukaryotic cells causing diseases.

 

Types of Bacterial Shapes

 

Due to the presence of a rigid cell wall, bacteria maintain a definite shape, though they vary as shape, size and structure. The three basic bacterial shapes are coccus (spherical), bacillus (rod-shaped), and spiral (twisted), however pleomorphic bacteria can assume several shapes.

 

Cocci (or coccus for a single cell) are round cells,

sometimes slightly  flattened when they are

adjacent to one another.

Bacilli (or bacillus for a single cell) are rod-shaped

bacteria.

                                                        Spirilla (or spirillum for a single cell) are curved

bacteria which can range  from a gently curved shape to a corkscrew-like spiral.  Many spirilla are  rigid and capable of movement.  A special group of spirilla known as  spirochetes are long, slender, and flexible.

 

Arrangement of Cocci

Cocci bacteria can exist singly, in pairs (as diplococci ), in groups of four (as tetrads ), in chains (as streptococci ), in clusters (as stapylococci ), or in cubes consisting of eight cells (as sarcinae). Cocci may be oval, elongated, or flattened on one side. Cocci may remain attached after cell division. These group characteristics are often used to help identify certain cocci.

1. Diplococci

The cocci are arranged in pairs.

Examples: Streptococcus pneumoniae, Moraxella catarrhalis, Neisseria gonorrhoeae, etc

2. Streptococci

The cocci are arranged in chains, as the cells divide in one plane.

Examples: Streptococcus pyogenes, Streptococcus agalactiae

3. Tetrads

The cocci are arranged in packets of four cells, as the cells divide in two plains.

Examples: Aerococcus, Pediococcus and Tetragenococcus

4. Sarcinae

The cocci are arranged in a cuboidal manner, as the cells are formed by regular cell divisions in three planes. Cocci that divide in three planes and remain in groups cube like groups of eight.

Examples: Sarcinaventriculi, Sarcinaureae, etc.

5. Staphylococci

The cocci are arranged in grape-like clusters formed by irregular cell divisions in three plains.

Examples: Staphylococcus aureus

Arrangement of Bacilli

The cylindrical or rod-shaped bacteria are called ‘bacillus’ (plural: bacilli).

1. Diplobacilli

Most bacilli appear as single rods. Diplobacilli appear in pairs after division.

Example of Single Rod: Bacillus cereus

 

Examples of Diplobacilli: Coxiellaburnetii, Moraxella bovis, Klebsiellarhinoscleromatis, etc.

2. Streptobacilli

The bacilli are arranged in chains, as the cells divide in one plane.

Examples: Streptobacillusmoniliformis

3. Coccobacilli These are so short and stumpy that they appear ovoid. They look like coccus and bacillus.Examples: Haemophilusinfluenzae, Gardnerellavaginalis, and Chlamydia trachomatis
   4. Palisades

   The bacilli bend at the points of division following the cell divisions, resulting in a palisade arrangement resembling a picket fence and angular patterns that look like Chinese letters.

   Example: Corynebacteriumdiphtheriae

   Arrangement of Spiral Bacteria

4. Spirilla (or spirillum for a single cell) are curved bacteria which can range from a gently curved shape to a corkscrew-like spiral.  Many spirilla are rigid and capable of movement.  A special group of spirilla known as spirochetes are long, slender, and flexible.
   1. Vibrio

   They are comma-shaped bacteria with less than one complete turn or twist in the cell.

   Example: Vibrio cholerae

   2. Spirilla

   They have rigid spiral structure. Spirillum with many turns can superficially resemble spirochetes. They do not have outer sheath and endoflagella, but have typical bacterial flagella.

   Example: Campylobacter jejuni, Helicobacter pylori, Spirillum winogradskyi, etc.

   3. Spirochetes

   Spirochetes have a helical shape and flexible bodies. Spirochetes move by means of axial filaments, which look like flagella contained beneath a flexible external sheath but lack typical bacterial flagella.

   Examples: Leptospira species (Leptospirainterrogans), Treponema pallidum, Borreliarecurrentis, etc.

   Bacteria can help or harm. They can make us sick or neutralize viruses that are attacking our bodies. Friendly bacteria produce antibodies and are found on our skin and in our digestive tracts. Bacteria have been cultivated for many beneficial uses, from medicine to biotechnology.

   Benefits of Bacteria on the Environment

   Uses in Medicine

   Bacteria are used to produce vaccines, antibiotics and other drugs that fight infections. Antibiotics kill or inhibit the growth of bacteria. Although antibiotics are not effective against viral infections, such as the common cold, some bacteria have been discovered that can help resist viruses. Vaccines are designed to help the body’s immune system fight diseases.

   Beneficial Bacteria in Food

   We come into contact with a lot of bacteria through the food we eat. Bacteria are used to make products like bread, beer and cheese. It is possible these bacteria not only make food taste good, but also are good for us. Probiotics is a process in which friendly bacteria are added to foods like yogurt and chocolate.

   Benefits to the Body

   The human body contains 10 times more bacteria than cells. Bacteria help the body with functions like digestion, immunity and keeping potentially harmfulbacteria like E. coli from making us sick. Bacteria helps synthesize vitamins like biotin, vitamin K and folic acid.

   Biotechnology

   Biotechnology is a branch of science that uses bacteria and other microorganisms. This field has recreated helpful substances found in the body, like growth hormones and human insulin. Biotechnology also is used in agriculture. Specially mutated forms of bacteria have been introduced to soil as a way to make it more fertile.

    

   Examples of Microbial Infections and Its Causative Agents

    

   AIDS (Acquired immunodeficiency syndrome) is a spectrum of conditions caused by infection with the human immunodeficiency virus (HIV).

   

    

   Chickenpox, also known as varicella, is a highly contagious disease caused by the initial infection with varicella zoster virus

    

    

   Dengue fever is a mosquito-borne tropical disease caused by the dengue virus.                          

   Bacteria are everywhere. They are responsible for the basic functions of the             environment. They break down dead plants and animals, and make nutrients for other living things. Some plants store bacteria in their roots to break down nutrients in the soil.

   If there are good microbes there are also bad that can cause microbial infection

 

CELL(videos)

HIV/AIDS

 

 

 

 

CELL

WHO DISCOVERED CELL?

First Cells Seen in Cork

While the invention of the telescope made the Cosmos accessible to human observation, the microsope opened up smaller worlds, showing what living forms were composed of. The cell was first discovered and named by Robert Hooke in 1665. He remarked that it looked strangely similar to cellula or small rooms which monks inhabited, thus deriving the name. However what Hooke actually saw was the dead cell walls of plant cells (cork) as it appeared under the microscope. Hooke’s description of these cells was published in Micrographia. The cell walls observed by Hooke gave no indication of the nucleus and other organelles found in most living cells. The first man to witness a live cell under a microscope was Anton van Leeuwenhoek, who in 1674 described the algae Spirogyra. Van Leeuwenhoek probably also saw bacteria.

WHAT ARE THE TWO TYPES OF CELL?

Two Basic Types of Cells

Prokaryotic cells are evolutionarily ancient. They were here first and for billions of years were the only form of life. Today most life is prokaryotic, and these cells are supremely successful. All bacteria and bacteria-like Archaea are prokaryotic organisms. Eukaryotes can be single celled or multi-cellular organisms. Eukaryotic cells are more complex, having evolved from a prokaryote-like predecessor. Most of the living things that we are typically familiar with are composed of eukaryotic cells; animals, plants, fungi and protists.

 

Binary Fission

Features of Prokaryotes

Pro = “before”, karyon = “nucleus”

Prokaryotes are primarily distinguished by the fact that they lack the eukaryotic feature of a membrane-bound nucleus. In fact, the only membrane in prokaryotic cells is the plasma membrane–the outer boundary of the cell itself. Their genetic material is naked within the cytoplasm, ribosomes are their only type of organelle.

Features of Eukaryotes

Eu = “true”, 

karyon = “nucleus”

 

Eukaryotic cells are larger, more complex and more evolutionarily recent than prokaryotes. Whereas prokaryotes are bacteria and Archaea, eukaryotes are literally everything else … amoebae, earthworms, mushrooms, grass,

bugs, you.

 

Eukaryotes also have specialized energy producing organelles called mitochondria and plants also have chloroplasts. Both mitochondria and chloroplasts are believed to have evolved from prokaryotes that began living symbiotically within eukaryotic cells long ago. 

These vital organelles are involved in metabolism and energy conversion within the cell.

Eukaryotic cells also have an endomembrane system composed of different membrane-bound organelles that transport materials around the cell. The endomembrane system includes the nuclear membrane, rough and smooth endoplasmic reticulum, Golgi apparatus and different types of transport vesicles. 

DIFFERENTIATE BETWEEN THE ANIMAL CELL AND PLANT CELL?

Differences Between Animal Cells and Plant Cells

1. Size: Animal cells are generally smaller than plant cells. Animal cells range from 10 to 30 micrometers in length, while plant cells range from 10 and 100 micrometers in length.
2. Shape: Animal cells come in various sizes and tend to have round or irregular shapes. Plant cells are more similar in size and are typically rectangular or cube shaped.
3. Energy Storage: Animals cells store energy in the form of the complex carbohydrate glycogen. Plant cells store energy as starch.
4. Proteins: Of the 20 amino acids needed to produce proteins, only 10 can be produced naturally in animal cells. The other so-called essential amino acids must be acquired through diet. Plants are capable of synthesizing all 20 amino acids.
5. Differentiation: In animal cells, only stem cells are capable of converting to other cell types. Most plant cell types are capable of differentiation.
6. Growth: Animal cells increase in size by increasing in cell numbers. Plant cells mainly increase cell size by becoming larger. They grow by absorbing more water into the central vacuole.
7. Cell Wall: Animal cells do not have a cell wall but have a cell membrane. Plant cells have a cell wall composed of cellulose as well as a cell membrane.
8. Centrioles: Animal cells contain these cylindrical structures that organize the assembly of microtubules during cell division. Plant cells do not typically contain centrioles.
9. Cilia: Cilia are found in animal cells but not usually in plant cells. Cilia are microtubules that aid in cellular locomotion.
10. Cytokinesis: Cytokinesis, the division of the cytoplasm during cell division, occurs in animal cells when a cleavage furrow forms that pinches the cell membrane in half. In plant cell cytokinesis, a cell plate is constructed that divides the cell.
11. Glyoxysomes: These structures are not found in animal cells, but are present in plant cells. Glyoxysomes help to degrade lipids, particularly in germinating seeds, for the production of sugar.
12. Lysosomes: Animal cells possess lysosomes which contain enzymes that digest cellular macromolecules. Plant cells rarely contain lysosomes as the plant vacuole handles molecule degradation.
13. Plastids: Animal cells do not have plastids. Plant cells contain plastids such as chloroplasts, which are needed for photosynthesis.
14. Plasmodesmata: Animal cells do not have plasmodesmata. Plant cells have plasmodesmata, which are pores between plant cell walls that allow molecules and communication signals to pass between individual plant cells.
15. Vacuole: Animal cells may have many small vacuoles. Plant cells have a large central vacuole that can occupy up to 90% of the cell’s volume.

WHAT ARE THE SIGNIFICANCE OF THE CELL?

  Cell swelling stimulates formation of glycogen and proteins and cellular release of organic osmolytes.

Cells are the basic building blocks of all living things. The human body is composed of trillions of cells. They provide structure for the body, take in nutrients from food, convert those nutrients into energy, and carry out specialized functions. Cells also contain the body’s hereditary material and can make copies of themselves.

Cells have many parts, each with a different function. Some of these parts, called organelles, are specialized structures that perform certain tasks within the cell.

WHAT IS THE REFLECTION OF CELL FEATURES IN THE SOCIETY TODAY?

Cell is the basic unit of life, it reflects that cell is like a family which all the parts have functions even the smallest part in the family have function.

Vacuole is the storage of nutrients, it reflects that vacuole is like a factory in which all the product process in that factory.

Cell wall is the protection of the plant cell, it reflects that cell wall is to protect to the enemies around them

Mitochondria it is the power energy of the cell, it like a transformer which it store the energy.

 

Discovery of Microorganisms

The existence of microscopic organisms was discovered during the period 1665-83 by two Fellows of The Royal Society, Robert Hooke and Antoni van Leeuwenhoek. In Micrographia (1665), Hooke presented the first published depiction of a microganism, the microfungus Mucor. Later, Leeuwenhoek observed and described microscopic protozoa and bacteria. These important revelations were made possible by the ingenuity of Hooke and Leeuwenhoek in fabricating and using simple microscopes that magnified objects from about 25-fold to 250-fold. After a lapse of more than 150 years, microscopy became the backbone of our understanding of the roles of microbes in the causation of infectious diseases and the recycling of chemical elements in the biosphere.

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