Introduction to cell discovery and cell theory - class-XI

• The first man to witness a live cell under a microscope was Anton Von Leeuwenhoek.
• Robert Brown was responsible for discovering the nucleus of a cell.
• Matthias Jakob Schleiden started that all parts of the plant organism are composed of different kinds of cell.
• Theodor Schwann studied that cells had a thin outer layer which is today known as plasma membrane. He also concluded that the plant shows the presence of a cell wall is a unique character of plant cells.
• So, the correct option is " A-(i), B-(iii), C-(iv), D-(ii).

In 1665 Robert Hooke published his book Micrographia which detailed his observations and included drawings. This book was the first important work on microscopy, the study of objects through a microscope. At the end of the book, there are observations of the stars and moon as seen through a telescope.

Leeuwenhoek, a Dutch naturalist was the first to observe and describe various unicellular microorganisms like bacteria, protozoa etc. along with animal cells like RBCs, muscles fibres, through a specialized lens designed by him.

Rudolf Virchow modified the cell theory and gave the concept of 'omnis cellula e cellulae' - means new cells develop by division of the pre-existing cells. This is called theory of cell lineage or common ancestry.

• The  cork cells seen by Robert Hooke were published in his book  'Micrographia'. It was published in January 1665. It was the first book which illustrate the microscopic view of plants and insects. 
  
• Origin of species is a work of scientific literature by Charles Darwin . It was published on 24 November 1859.
• Species Plantarum list every species of plant known at that time. This is a book by Carl Linnaeus , originally published in 1753. 
• Genera Plantarum is a fifth edition of book Species Plantarum .

• Anton Von Leeuwenhoek first saw and described a living cell.
  
• Robert Brown later discovered the nucleus.
• Schleiden observed that all plants are composed of different kinds of cell which form the tissues of the plant . 
  
•  Schwann observed that presence of cell wall is unique character of plant cells.
• So, the correct option is 'Option B'.

Virus are an exception to cell theory. Because of the following reasons

Rudolf Virchow modified the cell theory of gave the concept of 'omnis cellule e cellulae'- means new cells develop by division of the pre-existing cells. This is called theory of cell lineage or common ancestry.

• Cells are called the smallest structural and functional unit of life because all the living organisms are made up of cells and also all the functions taking place inside the body of organisms are performed by cells. 

• The cells are microscopic in size and are not visible to the unaided eye with the size from 0.5 micrometers to 50 micrometers. 
• They need to be enlarged or magnified by a microscope. 
• The electron microscope discovered by Knoll and Ruska was able to magnify the cellular structure.

Mitosis was first observed by Boveri and Flemming (1879) in animal cells. But the term mitosis was given by Flemming (1882).

The organism made up of many cells are known as multicellular.

• Cells are called the smallest structural and functional unit of life because all the living organisms are made up of cells and also all the functions taking place inside the body of organisms are performed by cells. 

• Organisms can consist of one cell to many cells. 
• The cell is the structural unit of life. Unicellular organisms are made up of one cell that performs all the functions.
•  Whereas, a multicellular organism that consists of multiple cells and a different group of cells perform different functions which give complexity to the multicellular organisms.

• The cells are the basic structural, functional and biological unit of all known living organisms. 
• Cells are the smallest unit of life that can replicate independently and are often called the building blocks of life. 
• 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 them.

• The first characteristic of a living thing is that they are made up of cells. A cell is a basic building block of all organisms. 
• It is the smallest unit of organization in a biosphere. A cell performs the life process to maintains the survival of an organism.

Cells can be prokaryotic or eukaryotic. If the cells have dispersed nucleus i.e., nucleoid then these are called as prokaryotic cells. Eukaryotes are organisms, whose cells are organized into complex structures by internal membranes and a cytoskeleton.
So, the correct answer is option C.

• Cells are called the structural and functional unit of life because all the living organisms are made up of cells and also all the functions taking place inside the body of organisms are performed by cells. Cells provide specific conditions, for the occurrence of the metabolic reactions. These have specialized enzymes, which catalyze the biochemical reaction and regulates the functions of the body.

• Tissues are the group of cells, which may be similar or dissimilar in structures, but coordinates to perform specialized functions e.g., xylem.

The first man to witness a live cell under a microscope was Antonie van Leeuwenhoek, who described the algae, Spirogyra, in 1674. He named that cell as animalcules. He is also known as father of microbiology, as he was first to study the microorganism.
So, the correct answer is option D.

• The cell is considered to be the basic unit of life in many pathological processes. 
• In addition, the phenomenon of energy flow occurs in cells in processes that are part of the function known as metabolism. 
• Cells contain hereditary information (DNA), which is passed from cell to cell during cell division and from one generation to next. Thus, the correct answer is option D

Antonie van Leeuwenhoek (1632-1723) described cells in a drop of pond water using a microscope made by him. He was the first person to observe bacteria and protozoa. By observing the movement of bacteria or protozoa he named them animalcules. Therefore, the correct answer is option A.

The size of cells and microorganisms are too small to observe by naked eyes. It was impossible to study them but with the invention of the microscope, cells became visible and many new discoveries were made about them. Therefore, the correct answer is option D.

Cytology is the branch of science which, deals with the study of form, structure, and contents of cells as observed under the microscope. The term was coined by Hertwig in 1893. Cytology has enormous application in genetics, biomedical research etc. It is used for diagnosis and screening of various diseases. It can also be for the study of the genetic composition of a living organism.

Virus are non-living crystallisable entities which replicate in other living cells. They do not have a cellular structure and are an exception to cell theory.

Ribosomes were first seen by Claude in 1941 but first studied by Robinsons and Brown in 1953 in bean root cells. Thus, the correct answer is option D.

Cell biology is a scientific study of the cells. It is concerned with the physiological properties, structure, the organelles it contains, interactions with the environment, life cycle, division and death of the cell. It is associated with the morphological and molecular level of the cell.

Robert
Brown discovered the nucleus. He discovered the presence of nucleus in the
cells of orchid root. Nucleus is a specialized double membrane bound
protoplasmic body which contains all the genetic information for controlling
cellular metabolism. 

Robert
Hooke was mathematician and physicist. He discovered the cell. He took a piece
of spanish oak and prepared thin slice by means of sharp pen knife. A deep
planoconcave lens was used for throwing light on cork piece. The latter was
observed under the microscope. The piece of cork was found to have a honey comb
structure with a number of box like compartments, each having a pore and
separated from others by diaphragms. Robert Hooke named the compartments as
cellulae, now known as cells.
Nucleus
was discovered by Robert Brown. He discovered the presence of nucleus in the
cells of orchid root. Nucleus is a specialized double membrane bound protoplasmic
body which contains all the genetic information for controlling cellular
metabolism and transmission to the posterity.

The majority of cells are small. Normal animal cell size varies from 10 to 30 micrometer, while plant cell stretches from 10 to 100 micron. 

Cells are called the structural and functional unit of life because all the living organisms are made up of cells and also all the functions taking place inside the body of organisms are performed by cells. Cells provide specific conditions, for the occurrence of the metabolic reactions. These have specialized enzymes, which catalyze the biochemical reaction and regulates the functions of the body.

• Virus is an acellular microscopic infection-causing agent. It has only protein cover and a nucleic acid (either DNA or RNA). These are intracellular parasites that depend upon the host for nutrition.

The cell is the basic structural and functional unit of life. Whether it is a complex organism like humans, animals or plants or simple organisms like the bacteria, they are all made of cells. So, the cell forms the most basic level of organization of organisms.

There is a direct correlation between the shape of the cell and the function it performs. For example, the Red Blood Cells (RBCs) have a biconcave disc-shaped structure because they have to squeeze through blood capillaries to deliver oxygen to the various parts of the body. If the RBCs had any other shape, it would be difficult to perform the same function efficiently.

• The cell was discovered by Robert Hook in 1665. But the statement that cell is the structural and functional unit of life generalized as cell theory in 1839 by Schleiden and Schwann. Thus, the correct answer is option C.

(a) 1 Micrometer= 10$^{-6}$m
(b) 1 Nanometer= 10$^{-9}$m
(c) 1 Angstrom= 10$^{-10}$m

"Omnis cellula e- cellula" means new cells are formed from pre-existing living cells. 

A cell possesses several cellular organelles. Each of the organelle such as mitochondria, endoplasmic reticulum etc. have their own specific function in the cell. These organelles are composed of several molecules and ions such as proteins, lipids, calcium and magnesium ions etc. These molecules together help the organelles perform their specific function. However, when present outside the organelle or in a different organelle the same molecules may perform functions that are different. So, the correct option is 'Properties of cellular organelles are present in the molecular constituents of the organelles'.

Cell theory was proposed by a German botanist, Matthias Schleiden and English zoologist, Theodor Schwann in the year 1839. Cell theory was considered as the most acceptable theory which, elucidated the functioning of a cell. The cell theory includes the following points -
1) All living things are made up of cells.
2) The cell is the smallest living thing that can perform all the functions of life.   
Later on, in the year 1855, Rudolf Virchow added a new point in cell theory that all cells must come from pre-existing cells, which was also known as "Omnis cellula e cellula". The modern cell theory is called as 'Cell Principle' or 'Cell Doctrine'.
So, the correct answer is option B.

Leeuwenhoek was the first to see 'free-living cells' under his microscope. In 1809, Lamarck concluded that all living beings are formed of cells. Living substance was first observed by Corti in 1772 and was named sarcode by Dujardin in 1835. Dutrochet believed in the individuality of cells, i.e., living organisms are made up of a number of individual cells. The nucleus was discovered by Robert Brown and Schleiden and Schwann are credited with the formulation of the cell theory. Thus, the correct answer is option A.

In typical biological cells, the ratio of inorganic matter to organic matter is generally accepted as 1:9, reflecting the high concentration of organic compounds like proteins and lipids.

• K.C. Meta -  Investigated the effects of temperature on rust fungi growth.
• P. Maheswari - Discovered the production of haploid by anther culture.
• Cohen and Boyer - Discovered recombinant DNA technology.
• Singer and Nicolson - proposed the fluid mosaic model of the cell membrane.

Cells are called the structural and functional unit of life because all the living organisms are made up of cells and also all the functions taking place inside the body of organisms are performed by cells. Cells provide specific conditions, for the occurrence of the metabolic reactions. These have the specialized enzymes, which catalyze the biochemical reaction and regulates the functions of the body such as respiration (formation of ATP in the cell)
So, the correct answer is option D.

Schleiden and Virchow were recognized the coiled structures in nucleus as chromosomes but the term chromosome was coined by Von Waldeyer-Hartz, 

The center for cellular and molecular Biology or CCMB is located in Hyderabad. The research programs undergoing in CCMB includes the areas of biomedicine & diagnostics, evolution & development, gene regulation in prokaryotes and eukaryotes, host-parasite interactions, membrane biology, protein structure, bioinformatics, functional genomics, theoretical biology, etc.

Arun Kumar Sharma or A. K. Sharma is the father of Indian cytology.

• Dujardin applied the name 'sarcode' to the free plasma without a covering to protect it from the contact with the outer world. So, the living things were named as a sarcode.

Rudolf Virchow famously stated "Omnis cellula e cellula", i.e., "All cells only arise from pre-existing cells."

The nucleus was discovered by Robert Brown while he was working on orchids, under a microscope and he observed an opaque area, which he called the areola or nucleus. It is a site for the genetic material.

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. 

The cell was first discovered by Robert Hooke in 1665, which can be found to be described in his book Micrographia. In this book, he gave 60 'observations' in detail of various objects under a coarse, compound microscope. One observation was from very thin slices of bottle cork. 

Cells are called as the basic unit of life because all the living organisms are made up of cells and also all the functions taking place inside the body of organisms are performed by cells. Cells provide the specific conditions, for the occurrence of the metabolic reactions. These have the specialized enzymes, which catalyze the biochemical reaction and regulates the functions of the body.

• The cell is the basic unit of life. All the living organisms are made up of cells and each cell performs a life-sustaining process. The cell is composed of the cell membrane, cytoplasm, nucleus, cell organelles and cell wall (except animal cells). An organelle is a distinct part of a cell, which has a particular structure and function. 
• Each organelle performs a particular function. For example- mitochondria produce ATPs, lysosomes digest cellular waste and debris, centrioles separates chromosomes during cell division, Ribosome synthesizes proteins, cell wall protects, etc. 
• Due to this, a cell can survive and perform its own functions. Thus, the correct answer is option A.

• Cells are called the structural and functional unit of life because all the living organisms are made up of cells and perform all life process for survival. Unicellular organisms are made up of a single cell and single-cell only performs all the functions of life. Whereas multicellular organisms are made up of multiple cells and perform all the functions of life. Thus, the correct answer is option A.

• The basic living structure of all organisms is a cell. Cell, which was discovered by Robert Hooke in the year 1665, is considered to be the basic structural and functional unit of all the organisms. 
• Many cells combine together to form a tissue. Many tissues together form an organ. Many organs form an organ system and many different organ systems together form a human body.
• So, option cell is the structural and functional unit of all organisms and so option B.

• A group of cells, which are structurally similar and work together to perform a particular function are called tissue. 
• The collection of such tissues, which are joined in a structural unit to perform a certain function, is called an organ. Whereas cytoplasm is the living fluid in the cell. Thus, the correct answer is option A.

• All the living organism is made up of cells which constitute some organic and inorganic molecules and perform all the life process like nutrition (autotrophic or heterotrophic), reproduction (sexual or asexual), excretion. 
• Each cell arises from pre-existing cells, they divide and increase their numbers and has a certain life span, thus they undergo aging and then death. Thus, the correct answer is option D.

• In unicellular (single-celled) organisms, the single cell performs all life processes for survival such as nutrition, transport, excretion, and reproduction. 
• They do not depend on another cell for function and thus exist independently.

• Cells are called an amazing world in itself because all the living organisms are made up of cells and also all the functions taking place inside the body of organisms are performed by cells. 
• These have the specialized enzymes, which catalyze the biochemical reaction and regulates the specialized functions of the body such as the conversion of nutrients into the energy, reproduction in unicellular and division or replication in multicellular.

Robert Hooke was an English scientist who coined the term cell for the Honeycomb structures he saw in a cork slice. Through he didn't see the inside of a cell, he discovered the cell and coined the term. He used a primitive compound microscope . He only saw cell walls as it a dead tissue. He discovered it in $1665$. The first man to witness a live cell under microscope was Antonie Philips van Leeuwenhoek in $1674$.

A micrometre is also known as a micron. It is an SI derived unit of length. Its value is 1×10$^{−6}$ metres or one millionth of a metre. Thus the correct answer is option B.

Living organisations have capacity to reproduce for ex animals give both to young ones of their kind, either directly or through egg.

• Endoplasmic reticulum (ER) is a system of membrane-lined channels found in all eukaryotic cells except mature erythrocytes. 
• Endoplasmic reticulum was discovered by Porter and Thompson (1945). 
• The name endoplasmic reticulum was given by Porter in 1953.
  Hence, option A is correct.

Lysosomes are small vesicles containing hydrolyzing enzymes and surrounded by a single membrane of lipids. They were discovered by Christian de Duve in 1955 but were named and observed under an electron microscope by Novikoff in 1956. 

Pasteur work on fermentation and germ theory of biology. Schleiden and Schwann are the co-founders of cell theory. Robert Brown was a Botanist and he discovered the nucleus. Rudolf Virchow was a German Physician, Biologist, Pathologist as well as a writer. The phrase 'Omnis cellula e cellula' is coined by Virchow which means all cells come from a cell, all cells born from a previous cell. So the answer is 'Virchow'.

Cell principle states that the cell is a fundamental unit of life and has all structural and functional properties of an organism. Also according to this principle cells are made from pre-existing cells and all organisms are made up of cells. Bacteria, algae and fungi obey the cell principle rules whereas viruses are under debate of being living or dead. They have many features of life but according to cell theory, they are not alive. Viruses lack cellular structure (cell wall, cytoplasm, ribosomes etc.) but do have genetic material in the form of RNA and they can only multiply when inside a host cell. Outside a host, they are unable to survive. Since a virus is not a cell, cell principle is not applicable to them. 

• A cell is a unit mass of protoplasm which is surrounded by protective and semi-permeable plasma membrane which separates the cell contents from the environment. 
• It is the basic unit of life and carries out the different functions of life. The body of all organisms is made up of cells so it is the structural unit of life. 
• Also, all the physiological, biochemical and genetic functions of the body are carried out by cells so it is called a functional unit of life. So, the correct answer is option D.

Micrographia is a book written by Robert Hooke when he discovered the cells in 1665. His all observation about the discovery of cells is detailed in this book. Hans and Zacharias designed the first compound microscope and by using this microscope Robert Hooke studied insects, sand, bird feathers, snowflakes and plants. He also observed a piece of cork which made him discover a framework of cells with empty spaces within it. its visual similarity with honeycomb cells made him name those units as the cell. He recorded all such observation through different lenses in the book Micrographia which is the first scientific bestseller.  

The organismal theory posits that the body of an organism is a single continuous unit (a protoplasmic mass) that is incompletely divided into cells, rather than being a collection of independent cells.

In 1838, Matthias Schleiden who was a German Botanist while studying a large number of plants he made an observation that plants also composed of different kinds of cells. These cells were arranged into tissues. Whereas Schwann was studying animal cells and reported the existence of cell membrane that surrounds cytoplasm. Together Schleiden and Schwann proposed cell theory based on their observation plants and animal cells. So Schleiden applied cell theory specifically to plans and Schwann to animals.  

Schleiden and Schwann proposed a cell theory according to which all cells are formed from preexisting cells. After the discovery of protoplasm by Corti, Dujardin observed a living juice inside the cells and named it as sarcode. Purkinje coined the term protoplasm while observing sap of plant cells. Max Schultze established similarity between protoplasm and sarcode that leads him to propose a theory which is called as the protoplasmic theory by Hertwig. This theory states that protoplasm is the physical basis of life. So answer B is correct.

The organismal theory teaches that the organism (even a multicellular organism) is the basic unit of life. It was proposed by Sachs. Thus the correct option is B.

Modern cell theory acknowledges that viruses, which lack cellular organization, are living entities, thereby challenging the original premise that all living beings must be composed of cells.

a) Mutation theory is proposed by Hugo de Vries.  

a) The term cytology was termed by Robert Hooke. Cytology, the study of cells as fundamental units of living things.

Antonie van Leeuwenhoek (1632-1723) described cells in a drop of pond water using his microscope. By using a microscope he observes and describes red blood cells in humans and other animals, as well as sperm cells. Therefore, the correct answer is option B.

Robert Hooke famously described the structure of cork cells in his 1665 book titled Micrographia, which was one of the first major works to document microscopic observations.

a) Theophrastus is known as the father of Botany for his different works in plants. 

The term hypothesis means a proposition or a set of propositions set forth as an explanation for the occurrence of some specific phenomenon. In this case, the phenomenon was smallest constituent entity of living organisms. In 1838, German Botanist Matthias Schleiden found that all plant tissues are made up of cells which have essentially similar structure. German zoologist Theodor Schwann, 1839, working independently observed that animal cells do not have cell wall but are otherwise similar among themselves. Thus, the original idea of both the workers was a hypothesis based on their observation which had to be experimentally verified by other workers.

The concept that cells arise from pre-existing cells (omnis cellula e cellula) was famously popularized by Rudolf Virchow, but Strasburger is often credited with confirming this specifically for the nucleus in plant cells. Other options like Sutton are associated with the chromosomal theory of inheritance.

The most common elements in living things are carbon, hydrogen, oxygen, nitrogen. 
A carbohydrate is a biological molecule consisting of carbon (C), hydrogen (H) and oxygen (O) atoms.
Proteins are made up of amino acids which are organic compounds  (C, H, and O) containing amine (-NH2), along with a side chain (R group) specific to each amino acid.
Each nucleotide consists of a nitrogen-containing aromatic base attached to a pentose sugar (C, H, and O), which is in turn attached to a phosphate group. 

• A micron is a unit of measurement in the metric system that is equal to one-thousandth of a millimeter.
• Therefore, 1 micron is equal to the $10^{-6}$ meter.

• A cell is the smallest form containing genetic material, cell organelles, cytoplasm and it can replicate to give rise to new cells. The cell size is the same in the elephant and in ant. 

The photocell was probably a fermenter living on the preformed organic molecules in the organic soup. The primitive atmosphere was a reducing atmosphere with no free oxygen gas. So, the correct option is "Atmosphere didn't have any oxygen".

The photocell was not considered a cell until it contained the genes. According to the first RNA hypothesis, the first genes and enzymes were RNA molecules. The first protein hypothesis suggested that protein enzymes were needed before nucleic acids could form. So, the correct option is "both (b) and (c)".

Micrographia: or Some Physiological Descriptions of Minute Bodies Made by Magnifying Glasses. With Observations and Inquiries Thereupon. is a historically significant book by Robert Hooke about his observations through various lenses. It is particularly notable for being the first book to illustrate insects, plants etc. as seen through microscopes. Published in January 1665, the first major publication of the Royal Society, it became the first scientific best-seller, inspiring a wide public interest in the new science of microscopy. It is also notable for coining the biological term cell.

• All of the living organisms are made up of cells. Cells can give rise to new cells by cell division. Each cell has a particular life span. Cells possess machinery, enzymes to form living protoplasm from non-living materials. 
• For example, plant cells take up CO$ _2$ and O$ _2$ from the environment and make food in the presence of sunlight. Animal cells break down or oxidize glucose and form ATP. 
• Such ATPs are used as energy currency in cell and various processes of cell formation organelle are carried out. Thus, the correct answer is option D.

Robert Hook discovered cells in 1655 with the help of compound microscope. He was observing insects, sand, bird feathers, fossils and plants. Once he was observing a thin slice of cork under the microscope he found a framework similar to honeycomb-like structure. He named those structures as cells but those were actually non living cell walls. So option A is correct.

Matthias Schleiden (a botanist) and Theodor Schwann (a zoologist) are the two scientists credited with formulating the foundational principles of cell theory in 1838 and 1839.