The document discusses the cell theory, which states that all living things are made of cells, cells are the basic unit of structure and function, and new cells are produced from existing cells. It describes some key aspects of cell theory such as cells having a nucleus, cytoplasm, and organelles. The discovery of cells is attributed to Robert Hooke and early formulations of cell theory came from Schleiden, Schwann, and Virchow. The shape and size of cells vary depending on their function.
In the realm of biology, understanding the cell is akin to unlocking the secrets of life itself. The Class 11 Biology curriculum introduces students to the fascinating world of cells, encapsulating the intricate processes that sustain living organisms. The chapter aptly titled "Cell: The Unit of Life" serves as a foundational cornerstone, laying the groundwork for a comprehensive understanding of biology and the complexity of life.
la celula su origen y diferencias ademas esta en inglesEstefaniaBeltrn
This unit discusses cell biology and the reductionist approach. It introduces the cell theory which emphasizes that all living things are made of cells that arise from pre-existing cells. It describes how cells can be studied using physico-chemical methods to understand biological processes at the molecular level. Chapter 8 will provide an overview of cell structure, including the differences between prokaryotic and eukaryotic cells. Chapter 9 will briefly describe biomolecules that make up cells.
- A cell is the basic unit of structure and function in living organisms.
- Eukaryotic cells have a membrane-bound nucleus and organelles, while prokaryotic cells like bacteria do not have a nucleus.
- Key organelles in eukaryotic cells include the nucleus, which contains DNA; the cell membrane, which encloses the cell; mitochondria, which generate energy; and ribosomes, which produce proteins. Plant cells also have a cell wall, chloroplasts, and a vacuole.
The document discusses the history and key discoveries related to cells. It begins with Robert Hooke observing cork cells under a microscope in 1665. Later scientists like Anton van Leeuwenhoek discovered protozoa and red blood cells. The cell theory was developed based on the combined work of Schleiden, Schwann, and Virchow, stating that all living things are composed of cells, cells are the basic unit of life, and cells only come from preexisting cells. The document also describes cell diversity in size, shape, and internal structures between prokaryotic and eukaryotic cells, and provides examples of organelles like the nucleus, mitochondria, chloroplasts and their functions.
Lecture 1 Introduction to Cell Structure and Composition.pdfotienowhitney445
This document provides an introduction and overview of the Cell Biology course SBL 203. It outlines the course goals, learning outcomes, delivery mode, assessment, references and reading materials, course outline, and contact information for the lecturer. The course aims to provide an introduction to basic cell biology principles including the structure and function of cellular components in prokaryotic and eukaryotic cells, cellular division processes, and the synthesis of biomolecules like DNA, RNA, and proteins. Students will learn through lectures, group work, assignments, essays and practical experiments. Their performance will be evaluated through exams, tests, and practical assessments.
This document provides an overview of cellular biology and the history of cell discovery. It discusses how:
1) Robert Hooke first observed cells in 1663 when examining cork under a microscope.
2) In the 1830s, botanist Schleiden and zoologist Schwann independently developed cell theory, establishing that organisms are composed of distinct cellular units.
3) Advances in microscopy, including electron microscopy in the 1950s, have driven discoveries like DNA structure and greatly increased understanding of cellular structures and functions.
The document compares and contrasts eukaryotic and prokaryotic cells, noting that eukaryotic cells have a nucleus surrounded by a nuclear membrane which contains the DNA, while prokaryotic cells do not have a nucleus and have their DNA spread in the cytoplasm. It also explains some of the key differences in structures between the two types of cells like the presence of organelles like the endoplasmic reticulum in eukaryotic cells which helps produce and transport proteins and lipids. The nucleus plays an important role in eukaryotic cells by controlling cell division and functions through its instructions based on the DNA contained within it.
In the realm of biology, understanding the cell is akin to unlocking the secrets of life itself. The Class 11 Biology curriculum introduces students to the fascinating world of cells, encapsulating the intricate processes that sustain living organisms. The chapter aptly titled "Cell: The Unit of Life" serves as a foundational cornerstone, laying the groundwork for a comprehensive understanding of biology and the complexity of life.
la celula su origen y diferencias ademas esta en inglesEstefaniaBeltrn
This unit discusses cell biology and the reductionist approach. It introduces the cell theory which emphasizes that all living things are made of cells that arise from pre-existing cells. It describes how cells can be studied using physico-chemical methods to understand biological processes at the molecular level. Chapter 8 will provide an overview of cell structure, including the differences between prokaryotic and eukaryotic cells. Chapter 9 will briefly describe biomolecules that make up cells.
- A cell is the basic unit of structure and function in living organisms.
- Eukaryotic cells have a membrane-bound nucleus and organelles, while prokaryotic cells like bacteria do not have a nucleus.
- Key organelles in eukaryotic cells include the nucleus, which contains DNA; the cell membrane, which encloses the cell; mitochondria, which generate energy; and ribosomes, which produce proteins. Plant cells also have a cell wall, chloroplasts, and a vacuole.
The document discusses the history and key discoveries related to cells. It begins with Robert Hooke observing cork cells under a microscope in 1665. Later scientists like Anton van Leeuwenhoek discovered protozoa and red blood cells. The cell theory was developed based on the combined work of Schleiden, Schwann, and Virchow, stating that all living things are composed of cells, cells are the basic unit of life, and cells only come from preexisting cells. The document also describes cell diversity in size, shape, and internal structures between prokaryotic and eukaryotic cells, and provides examples of organelles like the nucleus, mitochondria, chloroplasts and their functions.
Lecture 1 Introduction to Cell Structure and Composition.pdfotienowhitney445
This document provides an introduction and overview of the Cell Biology course SBL 203. It outlines the course goals, learning outcomes, delivery mode, assessment, references and reading materials, course outline, and contact information for the lecturer. The course aims to provide an introduction to basic cell biology principles including the structure and function of cellular components in prokaryotic and eukaryotic cells, cellular division processes, and the synthesis of biomolecules like DNA, RNA, and proteins. Students will learn through lectures, group work, assignments, essays and practical experiments. Their performance will be evaluated through exams, tests, and practical assessments.
This document provides an overview of cellular biology and the history of cell discovery. It discusses how:
1) Robert Hooke first observed cells in 1663 when examining cork under a microscope.
2) In the 1830s, botanist Schleiden and zoologist Schwann independently developed cell theory, establishing that organisms are composed of distinct cellular units.
3) Advances in microscopy, including electron microscopy in the 1950s, have driven discoveries like DNA structure and greatly increased understanding of cellular structures and functions.
The document compares and contrasts eukaryotic and prokaryotic cells, noting that eukaryotic cells have a nucleus surrounded by a nuclear membrane which contains the DNA, while prokaryotic cells do not have a nucleus and have their DNA spread in the cytoplasm. It also explains some of the key differences in structures between the two types of cells like the presence of organelles like the endoplasmic reticulum in eukaryotic cells which helps produce and transport proteins and lipids. The nucleus plays an important role in eukaryotic cells by controlling cell division and functions through its instructions based on the DNA contained within it.
The Differences Between Eukaryotic And Prokaryotic CellsRochelle Schear
The essay discusses the theory of endosymbiosis, where eukaryotic cells were formed when a prokaryotic cell ingested aerobic bacteria. Over time, the bacteria evolved into organelles in the host cell through endosymbiosis. This includes how mitochondria likely evolved from ingested aerobic bacteria and chloroplasts from ingested photosynthetic bacteria. Endosymbiosis played a key role in the development of complex eukaryotic cells from simpler prokaryotic cells.
Cell as basic unit of life ppt 88 slidesICHHA PURAK
This Power point presentation describes Cell as basic unit of life. The slides provide information about Discovery of cell,cell theory,number,size,shape and cell types .Differentiates prokaryotic and eukaryotic cell types and point out major differences in plant and animal cell and also about structure and function of cell organelles
All living organism can be categorized as prokaryotes or eukaryotes according to their cell type. This article deals with detailed about prokaryotes and eukaryotes with examples and figures and their similarities and dissimilarities.
The document discusses the history and discovery of cells, beginning with Hooke observing cork cells under a microscope in 1665. It then outlines the cell theory developed by Schleiden, Schwann, and Virchow stating that all living things are composed of cells, cells are the basic unit of life, and all cells come from preexisting cells. The document also examines cell diversity in terms of size, shape, internal structures between prokaryotic and eukaryotic cells, and the functions of key cellular organelles.
This document provides an introduction to cell biology. It discusses key topics like what is a cell, the cell theory, differences between prokaryotic and eukaryotic cells, cell size and structure, and early discoveries of cells by scientists like Hooke, Leeuwenhoek, Schleiden, and Schwann. It also outlines course policies and provides an overview of topics to be covered, including cell organelles, cell types, microscopy, and cell evolution.
The basic unit of life is the cell. All living things are composed of cells, which are the basic units of structure and function. Cells come in two main types - prokaryotic cells, which lack a nucleus and membrane-bound organelles, and eukaryotic cells, which have a nucleus enclosed within membranes and other membrane-bound structures. Cells vary greatly in their size, shape, and internal structures, depending on their function in different living things.
The document discusses the structure and function of cells. It begins by stating that cells are the basic structural and functional units of all organisms, though their sizes and structures may vary depending on their functions. It then describes the cell theory proposed by Schleiden and Schwann in 1838, which states that all organisms are composed of cells, the cell is the basic unit of life, and new cells are formed from existing cells. The document goes on to describe the key components of cells, including the plasma membrane, cytoplasm, and nucleus. It distinguishes between prokaryotic and eukaryotic cells, and between plant and animal cells.
This document provides an overview of cell structure and types of organisms. It discusses the history of cell discovery and defines unicellular and multicellular organisms. The key components of the cell are then described in detail, including the plasma membrane, nucleus, cytoplasm, organelles like the endoplasmic reticulum, Golgi complex, lysosomes, mitochondria, plastids, and vacuoles. Each component's structure and functions are outlined. The document concludes by stating that vacuoles serve as storage sacs within the cell.
It presents the history of the Earth through geologic time. It discusses the earth's structure, composition, and processes. Issues, concerns, and problems pertaining to natural hazards are also included. It also deals with the basic principles and processes in the study of biology.
The document provides an overview of cell biology, describing cell theory which states that all living things are composed of cells, cells provide structure and carry out functions to sustain life, and organisms can be single-celled or multi-cellular. It defines key aspects of cells like the nucleus, cytoplasm, organelles, and cell membranes, and provides examples of cellular structures and their functions. The document includes interactive questions to test understanding of cell theory.
Learning Module in Teaching Science in the Elementary Grades.pdfDagameBohol1
The document provides an overview of a learning module for teaching science in elementary grades. It includes definitions and descriptions of biology and chemistry. It discusses cells as the basic unit of life, describing the different types of cells (prokaryotic and eukaryotic), their parts, and functions. It also compares and contrasts prokaryotic and eukaryotic cells. The module aims to help students understand these key concepts in biology and chemistry.
Together with his family, comedian Dagul Pastrana won the P200,000 jackpot prize prize in Monday's episode of GMA's game show "Family Feud!"Together with his family, comedian Dagul Pastrana won the P200,000 jackpot prize prize in Monday's episode of GMA's game show "Family Feud!"
The document discusses cells, which are the basic units of life. It covers the milestones in the discovery of cells, defines what a cell is, explains the cell theory, and discusses the number, size, shape, and types of cells. The key points are:
- Cells were first observed by Robert Hooke in 1665 and are the smallest units of living matter that compose all living things.
- The cell theory established that all organisms are made of cells, cells are the basic units of life, and new cells are produced from existing cells.
- There are three main types of cells: prokaryotic, eukaryotic, and mesokaryotic, which differ in their nuclear and
The document provides details about a three day lesson plan for middle school EL students on cells. Day one involves introducing cell vocabulary through a PowerPoint presentation and having students label a graphic organizer and cell model. Day two has students making edible cell models using candy to represent organelles. Day three involves students describing the structures and functions of organelles to peers and explaining similarities and differences between plant and animal cells. The lesson aims to help students understand cell parts and their functions.
Prokaryotic cells lack a nucleus and organelles, while eukaryotic cells have a nucleus enclosed in a nuclear envelope and various membrane-bound organelles. Prokaryotic cells are typically smaller than eukaryotic cells. While both contain DNA and ribosomes, prokaryotic DNA is found in the nucleoid region and eukaryotic DNA is organized into linear chromosomes within the nucleus. Eukaryotic cells also have a more complex internal structure due to the presence of organelles.
There are two major types of cells - eukaryotic and prokaryotic. Eukaryotic cells contain organelles like the nucleus, mitochondria and chloroplasts which are surrounded by membranes. They have a more complex structure than prokaryotic cells. Prokaryotic cells like bacteria do not have a nucleus or organelles, and their DNA is not enclosed in a nucleus. While they differ in their complexity, both eukaryotic and prokaryotic cells share some basic components like the cell membrane, cytoplasm and ribosomes.
The cell is the basic unit of life. Animal cells lack cell walls and contain organelles like the nucleus, mitochondria, endoplasmic reticulum, Golgi bodies, lysosomes, and ribosomes surrounded by a plasma membrane. The nucleus contains DNA and controls cell activities. Mitochondria generate energy through cellular respiration. The endoplasmic reticulum and Golgi bodies process and transport proteins. Ribosomes synthesize proteins using mRNA. Together, these organelles allow animal cells to carry out specialized functions and maintain homeostasis.
This document provides an overview of a biology module on cells. It includes:
- An introduction to cells as the basic building blocks of life, composed of organelles that perform specialized functions.
- Learning objectives that cover cell structures and functions, transport mechanisms, cellular division and energy production.
- Outlines of lessons that will examine the cell theory, structures and modifications of plant and animal cells, and methods of substance transport.
- Resources including a textbook, online materials and formative assessments to support learning over the 5-week module.
This document provides an overview of cells including their characteristics, types, and parts. It begins with defining the cell as the basic structural and functional unit of living organisms. It then discusses the characteristics of cells, including that all living things are made up of cells, cells are the smallest units of life, and all cells come from preexisting cells. The document introduces the types of cells including prokaryotic and eukaryotic cells as well as unicellular and multicellular organisms. It provides information about the parts and functions of plant and animal cells and compares the differences between them. Videos and activities are included to reinforce the concepts covered.
The Differences Between Eukaryotic And Prokaryotic CellsRochelle Schear
The essay discusses the theory of endosymbiosis, where eukaryotic cells were formed when a prokaryotic cell ingested aerobic bacteria. Over time, the bacteria evolved into organelles in the host cell through endosymbiosis. This includes how mitochondria likely evolved from ingested aerobic bacteria and chloroplasts from ingested photosynthetic bacteria. Endosymbiosis played a key role in the development of complex eukaryotic cells from simpler prokaryotic cells.
Cell as basic unit of life ppt 88 slidesICHHA PURAK
This Power point presentation describes Cell as basic unit of life. The slides provide information about Discovery of cell,cell theory,number,size,shape and cell types .Differentiates prokaryotic and eukaryotic cell types and point out major differences in plant and animal cell and also about structure and function of cell organelles
All living organism can be categorized as prokaryotes or eukaryotes according to their cell type. This article deals with detailed about prokaryotes and eukaryotes with examples and figures and their similarities and dissimilarities.
The document discusses the history and discovery of cells, beginning with Hooke observing cork cells under a microscope in 1665. It then outlines the cell theory developed by Schleiden, Schwann, and Virchow stating that all living things are composed of cells, cells are the basic unit of life, and all cells come from preexisting cells. The document also examines cell diversity in terms of size, shape, internal structures between prokaryotic and eukaryotic cells, and the functions of key cellular organelles.
This document provides an introduction to cell biology. It discusses key topics like what is a cell, the cell theory, differences between prokaryotic and eukaryotic cells, cell size and structure, and early discoveries of cells by scientists like Hooke, Leeuwenhoek, Schleiden, and Schwann. It also outlines course policies and provides an overview of topics to be covered, including cell organelles, cell types, microscopy, and cell evolution.
The basic unit of life is the cell. All living things are composed of cells, which are the basic units of structure and function. Cells come in two main types - prokaryotic cells, which lack a nucleus and membrane-bound organelles, and eukaryotic cells, which have a nucleus enclosed within membranes and other membrane-bound structures. Cells vary greatly in their size, shape, and internal structures, depending on their function in different living things.
The document discusses the structure and function of cells. It begins by stating that cells are the basic structural and functional units of all organisms, though their sizes and structures may vary depending on their functions. It then describes the cell theory proposed by Schleiden and Schwann in 1838, which states that all organisms are composed of cells, the cell is the basic unit of life, and new cells are formed from existing cells. The document goes on to describe the key components of cells, including the plasma membrane, cytoplasm, and nucleus. It distinguishes between prokaryotic and eukaryotic cells, and between plant and animal cells.
This document provides an overview of cell structure and types of organisms. It discusses the history of cell discovery and defines unicellular and multicellular organisms. The key components of the cell are then described in detail, including the plasma membrane, nucleus, cytoplasm, organelles like the endoplasmic reticulum, Golgi complex, lysosomes, mitochondria, plastids, and vacuoles. Each component's structure and functions are outlined. The document concludes by stating that vacuoles serve as storage sacs within the cell.
It presents the history of the Earth through geologic time. It discusses the earth's structure, composition, and processes. Issues, concerns, and problems pertaining to natural hazards are also included. It also deals with the basic principles and processes in the study of biology.
The document provides an overview of cell biology, describing cell theory which states that all living things are composed of cells, cells provide structure and carry out functions to sustain life, and organisms can be single-celled or multi-cellular. It defines key aspects of cells like the nucleus, cytoplasm, organelles, and cell membranes, and provides examples of cellular structures and their functions. The document includes interactive questions to test understanding of cell theory.
Learning Module in Teaching Science in the Elementary Grades.pdfDagameBohol1
The document provides an overview of a learning module for teaching science in elementary grades. It includes definitions and descriptions of biology and chemistry. It discusses cells as the basic unit of life, describing the different types of cells (prokaryotic and eukaryotic), their parts, and functions. It also compares and contrasts prokaryotic and eukaryotic cells. The module aims to help students understand these key concepts in biology and chemistry.
Together with his family, comedian Dagul Pastrana won the P200,000 jackpot prize prize in Monday's episode of GMA's game show "Family Feud!"Together with his family, comedian Dagul Pastrana won the P200,000 jackpot prize prize in Monday's episode of GMA's game show "Family Feud!"
The document discusses cells, which are the basic units of life. It covers the milestones in the discovery of cells, defines what a cell is, explains the cell theory, and discusses the number, size, shape, and types of cells. The key points are:
- Cells were first observed by Robert Hooke in 1665 and are the smallest units of living matter that compose all living things.
- The cell theory established that all organisms are made of cells, cells are the basic units of life, and new cells are produced from existing cells.
- There are three main types of cells: prokaryotic, eukaryotic, and mesokaryotic, which differ in their nuclear and
The document provides details about a three day lesson plan for middle school EL students on cells. Day one involves introducing cell vocabulary through a PowerPoint presentation and having students label a graphic organizer and cell model. Day two has students making edible cell models using candy to represent organelles. Day three involves students describing the structures and functions of organelles to peers and explaining similarities and differences between plant and animal cells. The lesson aims to help students understand cell parts and their functions.
Prokaryotic cells lack a nucleus and organelles, while eukaryotic cells have a nucleus enclosed in a nuclear envelope and various membrane-bound organelles. Prokaryotic cells are typically smaller than eukaryotic cells. While both contain DNA and ribosomes, prokaryotic DNA is found in the nucleoid region and eukaryotic DNA is organized into linear chromosomes within the nucleus. Eukaryotic cells also have a more complex internal structure due to the presence of organelles.
There are two major types of cells - eukaryotic and prokaryotic. Eukaryotic cells contain organelles like the nucleus, mitochondria and chloroplasts which are surrounded by membranes. They have a more complex structure than prokaryotic cells. Prokaryotic cells like bacteria do not have a nucleus or organelles, and their DNA is not enclosed in a nucleus. While they differ in their complexity, both eukaryotic and prokaryotic cells share some basic components like the cell membrane, cytoplasm and ribosomes.
The cell is the basic unit of life. Animal cells lack cell walls and contain organelles like the nucleus, mitochondria, endoplasmic reticulum, Golgi bodies, lysosomes, and ribosomes surrounded by a plasma membrane. The nucleus contains DNA and controls cell activities. Mitochondria generate energy through cellular respiration. The endoplasmic reticulum and Golgi bodies process and transport proteins. Ribosomes synthesize proteins using mRNA. Together, these organelles allow animal cells to carry out specialized functions and maintain homeostasis.
This document provides an overview of a biology module on cells. It includes:
- An introduction to cells as the basic building blocks of life, composed of organelles that perform specialized functions.
- Learning objectives that cover cell structures and functions, transport mechanisms, cellular division and energy production.
- Outlines of lessons that will examine the cell theory, structures and modifications of plant and animal cells, and methods of substance transport.
- Resources including a textbook, online materials and formative assessments to support learning over the 5-week module.
This document provides an overview of cells including their characteristics, types, and parts. It begins with defining the cell as the basic structural and functional unit of living organisms. It then discusses the characteristics of cells, including that all living things are made up of cells, cells are the smallest units of life, and all cells come from preexisting cells. The document introduces the types of cells including prokaryotic and eukaryotic cells as well as unicellular and multicellular organisms. It provides information about the parts and functions of plant and animal cells and compares the differences between them. Videos and activities are included to reinforce the concepts covered.
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Introduction to Cell & Cell Theory _ Biology Class 11 - NEET.pdf
1. 8/10/23, 8:59 PM Introduction to Cell & Cell Theory | Biology Class 11 - NEET
https://edurev.in/studytube/Microbodies/9d425343-d7ee-43cc-8cc8-6120c31631c7_t#Shapes_of_Cells 1/9
Introduction to Cell & Cell Theory
What is a Cell?
Cell
2. 8/10/23, 8:59 PM Introduction to Cell & Cell Theory | Biology Class 11 - NEET
https://edurev.in/studytube/Microbodies/9d425343-d7ee-43cc-8cc8-6120c31631c7_t#Shapes_of_Cells 2/9
The cell is a basic unit of life as no living organism can have life without being cellular because the cell is a unit of both its
structure and function.
All life begins as a single cell. A number of organisms are made of single cells.
They are called unicellular or acellular, e.g. Amoeba, Chlamydomonas, Acetabularia, bacteria, yeast.
A single cell is:
(i) capable of independent existence and
(ii) able to perform all the essential functions of life.
Anything less than a complete cell can neither lead an independent existence nor perform all the functions of life.
A multicellular organism is made of many cells.
A higher animal or plant contains billions of cells. For example, a newly born human infant has 2 x 1012 cells.
The number increases to 100 trillion (100 x 1012 or 1014) cells in the body of a 60 kg human being. About 25% (25 x 1012) of
them are found in the blood.
A drop of blood contains several million cells. Large-sized organisms do not have large-sized cells. Instead, they possess a higher
number of cells.
In multicellular organisms, cells are building blocks of the body or basic units of body structure. Of course, they become
specialized for performing different functions.
The human body has some 200 types of cells, e.g., erythrocytes, leucocyte types, epithelial cell types, muscle cells, nerve cells, fat
cells, cartilage cells, bone cells, connective tissue cells, gland cells, germinal cells, pigment cells, etc.
Cells are grouped into tissues, tissues into organs and organs into organ systems, Occurrence of different types of tissues,
organs and organ systems results in the division of labour or performance of different functions of the body by specialized
structures.
3. 8/10/23, 8:59 PM Introduction to Cell & Cell Theory | Biology Class 11 - NEET
https://edurev.in/studytube/Microbodies/9d425343-d7ee-43cc-8cc8-6120c31631c7_t#Shapes_of_Cells 3/9
An Overview of Cell
The cells of the human cheek have an outer membrane as the delimiting structure of the cell.
Inside each cell is a dense membrane-bound structure called the nucleus.
This nucleus contains the chromosomes which in turn contain the genetic material, DNA.
Cells that have membrane-bound nuclei are called eukaryotic whereas cells that lack a membrane-bound nucleus are prokaryotic.
In both prokaryotic and eukaryotic cells, a semi-fluid matrix called cytoplasm occupies the volume of the cell.
The cytoplasm is the main arena of cellular activities in both plant and animal cells.
Various chemical reactions occur in it to keep the cell in the ‘living state’.
Besides the nucleus, the eukaryotic cells have other membrane-bound distinct structures called organelles like the endoplasmic
reticulum (ER), the Golgi complex, lysosomes, mitochondria, microbodies and vacuoles.
The prokaryotic cells lack such membrane-bound organelles. Ribosomes are non-membrane-bound organelles found in all cells –
both eukaryotic as well as prokaryotic.
Within the cell, ribosomes are found not only in the cytoplasm but also within the two organelles – chloroplasts (in plants) and
mitochondria and on rough ER.
Animal cells contain another non-membrane-bound organelle called centriole which helps in cell division.
For example, Mycoplasmas, the smallest cells, are only 0.3 μm in length while bacteria could be 3 to 5 μm.
The largest isolated single cell is the egg of an ostrich. Among multicellular organisms, human red blood cells are about 7.0 μm in
diameter.
Nerve cells are some of the longest cells. Cells also vary greatly in their shape.
They may be disc-like, polygonal, columnar, cuboid, thread-like, or even irregular.
The shape of the cell may vary with the function they perform.
4. 8/10/23, 8:59 PM Introduction to Cell & Cell Theory | Biology Class 11 - NEET
https://edurev.in/studytube/Microbodies/9d425343-d7ee-43cc-8cc8-6120c31631c7_t#Shapes_of_Cells 4/9
The Discovery of Cell
The first microscope was built by Zacharias Janssen in 1590. It was first modified by Galileo (1610) and then by Robert Hooke.
Robert Hooke (1635-1703) was a mathematician and physicist. He developed a new microscope with which he studied the
internal structure of a number of plants. His work is famous for the study of cork cells.
In 1665, Robert Hooke wrote a book "Micrographia: or Some Physiological Descriptions of Minutae made by magnifying glasses
with observations and enquiries thereupon."
The chapter which gave birth to cell biology is "Observe XVIII of the schematism or texture of cork and of the cells and pores of
some other such frothy bodies".
He took a piece of cork of Spanish oak and prepared a thin slice by means of a sharp penknife.
A deep planoconcave lens was used for throwing light on the cork piece. The latter was observed under the microscope.
The piece of cork was found to have a honeycomb 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 (singular-cellula) now known as cells
(Latin cella hollow spaces or compartments).
He did not know the significance of these structures and regarded them as passages for conducting fluids.
Actually, the 'cells' of Hooke were cell walls enclosing spaces left by dead protoplasts. Robert Hooke found that the cells or boxes
were not very deep.
A cubic inch contained 1259,712,000 cells, a square inch 1,66,400 and one inch strip 1080 cells.
The term "cell" is actually a misnomer as a living cell is neither hollow nor always covered by a wall.
5. 8/10/23, 8:59 PM Introduction to Cell & Cell Theory | Biology Class 11 - NEET
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Cell Theory
In 1838, Malthias Schleiden, a German botanist, examined a large number of plants and observed that all plants are composed of
different kinds of cells which form the tissues of the plant.
At about the same time, Theodore Schwann (1839), a British Zoologist, studied different types of animal cells and reported that
cells had a thin outer layer which is today known as the ‘plasma membrane’.
He also concluded, based on his studies on plant tissues, that the presence of cell walls is a unique character of the plant cells.
On the basis of this, Schwann proposed the hypothesis that the bodies of animals and plants are composed of cells and products
of cells.
Schleiden and Schwann together formulated the cell theory. This theory, however, did not explain how new cells were formed.
The microscope used by Robert Hooke
6. 8/10/23, 8:59 PM Introduction to Cell & Cell Theory | Biology Class 11 - NEET
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Rudolf Virchow (1855) first explained that cells are divided and new cells are formed from pre-existing cells (Omnis cellula-e
cellula).
He modified the hypothesis of Schleiden and Schwann to give the cell theory a final shape.
Fundamental Features of Cell Theory
Five fundamental observations of the cell theory are:
1. All living organisms are composed of cells and their products.
2. Each cell is made of a small mass of protoplasm containing a nucleus in its inside
and a plasma membrane with or without a cell wall on its outside.
3. All cells are basically alike in their chemistry and physiology.
4. Activities of an organism are the sum total of activities and interactions of its
constituent cells.
Modern Cell Theory
It is also known as cell doctrine or cell principle. Modern cell theory states that The bodies of all living beings are made up of cells
and their products
Cells are units of a structure in the body of living organisms. Every cell is made up of a mass of protoplasm, having a nucleus,
organelles and a covering membrane.
Cells are units of function in living organisms, that is, the activities of an organism are the sum total of the activities of its cells.
While a cell can survive independently, its organelles cannot do so.
The cells belonging to diverse organisms and different regions of the same organism have a fundamental similarity in their
structure, chemical composition and metabolism.
Life exists only in cells because all the activities of life are performed by cells.
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Depending upon the specific requirements, the cells get modified, e.g., elongated in muscle and nerve cells, loss of nucleus in
RBCs or cytoplasm in outer skin cells.
The growth of an organism involves the growth and multiplication of its cells.
Genetic information is stored and expressed inside cells.
Life passes from one generation to the next in the form of a living cell.
New cells arise from pre-existing cells through division. All new cells contain the same amount and degree of genetic information
as contained in the parent cell.
All the present-day cells/organisms have a common ancestry because they are derived from the first cell that evolved on the
planet through a continuous line of cell generations.
Basically, the cells are totipotent (i.e., a single cell can give rise to the whole organism) unless and until they have become
extremely specialized.
No organism, organ or tissue can have an activity that is absent in its cells.
Significance of Cell Theory
(i) There is a structural similarity in cells belonging to diverse groups of organisms.
(ii) All the cells perform similar metabolic activities.
(iii) Life exists only in the form of cells.
(iv) Life passes from one generation to the next as cells.
(v) All living beings are descendants of a primitive cell that developed on earth as the first eucaryote and prior to that as the first procaryote.
Shapes of Cells
The cells vary in their shapes.
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They may be disc-like, polygonal, columnar, cuboid, amoeboid, thread-like or irregular.
The shape of the cell is related to its position (flat in surface cells, polygonal in the cortex) and function (e.g., RBCs are biconcave
to pass through capillaries and carry WBCs are irregular to do phagocytosis, nerve cells are long to conduct impulses, sperms
have a tail for motility etc.
On the basis of the organization of DNA, the cells are of two types-procaryotic and eucaryotic.
The organisms having procaryotic cells are called prokaryotes.
They are nowadays placed in a superkingdom called Procaryota.
Other organisms (having eukaryotic cells) are included in superkingdom Eukaryota.
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Procaryotic cells occur in bacteria, blue-green algae, chlamydiae, Archaebacteria and Mycoplasma or PPLO.
Different shapes of cells found in the
human body