cell theory and unicellular organism

cell theory, WHAT IS A CELL, WHAT IS CELL? UNICELLULAR ORGANISM, IS A CELL A LIVING THING? All living things including plants and animals are made up of cells.

The cell theory is a scientific theory that states that all living things are composed of cells, that cells are the basic unit of life, and that new cells arise from pre-existing cells. The cell theory is one of the most fundamental theories in biology and has been supported by a vast amount of evidence.

The cell theory was first proposed in the mid-19th century by two German scientists, Matthias Schleiden and Theodor Schwann. Schleiden was a botanist and Schwann was a zoologist, and they both studied tissues from plants and animals using microscopes. They observed that all living tissues were made up of small units called cells.

At the time, there was some debate about whether cells were simply building blocks of living things or whether they were actually alive themselves. Schleiden and Schwann argued that cells were the basic unit of life because they were the smallest units of living things that could survive and reproduce independently.

The cell theory has been expanded and refined over time, but the basic tenets of the theory remain the same. We now know that cells are incredibly complex and diverse, but they all share some common features. All cells are surrounded by a plasma membrane, they contain cytoplasm and a nucleus, and they are able to reproduce.

The cell theory is one of the most important theories in biology because it provides a unifying framework for understanding all living things. It helps us to understand how living things are organized, how they function, and how they reproduce.

Here are some of the key features of the cell theory:

  • All living things are made up of cells.
  • Cells are the basic unit of life.
  • New cells arise from pre-existing cells.

The cell theory has revolutionized our understanding of life and has led to many important advances in medicine and other fields. For example, the cell theory has helped us to understand the causes of cancer and other diseases, and it has also helped us to develop new treatments for these diseases.

The cell theory is a foundation of modern biology, and it continues to be an important area of research today.

The cell theory is a foundation of modern biology, and it continues to be an important area of research today.

The cell is regarded as the basis of all living things. Scroll down and see the list of cell parts and their functions

Definition of a cell theory

The cell is defined as the structural and functional unit of a living thing or organism. In other words, the cell is the simplest, smallest and basic unit of life.

what is a cell?

All living things including plants and animals are made up of cells. The cell is regarded as the basis of all living things because it can carry out life activities such as feeding, reproduction, respiration, movement and excretion. All these characteristics exhibited by a cell are the reasons the cell is called a living thing.

CLASSIFICATION OF LIVING ORGANISMS BASED ON THE NUMBER OF CELLS

Living organisms are classified into two major groups based on their number of cells, they are
a. UNICELLULAR OR ACELLULAR ORGANISMS
These organisms consist only of one cell. Examples of unicellular organisms are Amoeba, Chlamydomonas, Euglena and paramecium

WHAT ARE MULTI-CELLULAR ORGANISMS?

as part of the cell theory, These are organisms which consist of two or more cells. This means that this group of organisms is made up of multiple cells. Examples of multi-cellular organisms are Volvox, Spirogyra, man, flowering plants and birds

HISTORY OF THE CELL THEORY

Many scientists contributed to the history of the cell theory. Amongst these brave scientists are

ROBERT HOOKS THEORY OF THE CELL

Robert Hooks is an English scientist who should or can be seen as the father of cells. He was the first human to discover the existence of the honeycomb structure of the cell in 1665.
In his book, Micrographia, he described his observations of a magnified thin slice of a cork of an oak tree. He established that the cork is made up of a thin component or room. He4 then named these components cells.

FELIX DUJARDIN CELL THEORY

This guy is a French Biologist in 1835 who discovered that cells are made up of living substances called protoplasm.

MATTHIAS SCHLEIDEN CELL THEORY

He is a German botanist who in 1838, revealed that the bodies of plants are made up of cells which are described as the units of life
4.

THEODOR SCHWANN DEFINITION OF CELL

This is another German zoologist in 1839 who discovered that the bodies of animals are made up of cells. The discoveries of Schleiden and Theodor led to the postulation of the cell theory in the year 1839

RUDOLF VON VIRCHOW, THEORY OF CELL
This a German biologist in 1855 who wrote that all cells come from previously existing cells

THE CELL THEORY IN PROPER PERSPECTIVE

The cell theory states that
i. The cell is the structural and functional unit of living things
ii. All living organisms are made up of cells
iii. All cells come from previously existing cells
iv. That there are no cells apart from the life of the cells
v. All living things are either unicellular or multi-cellular organisms

THE USE OF  MICROSCOPE TO VIEW CELL

Definition of a microscope
The microscope is an instrument used in the laboratory to observe tiny structures of living organisms which cannot be seen or observed by the naked eye.
Organisms which can only be seen with the aid of a microscope are called MICROSCOPIC organisms
When very tiny living things and small objects are viewed using the microscope, they become magnified and enlarged and the detailed structure can be seen properly and clearly. The study and the use of the microscope will enable us to observe and identify tiny living things and the structure they are made up of.

TYPES OF MICROSCOPE USED FOR VIEWING CELLS

The various types of microscope include the following
i. Compound microscope
ii. Light microscope
iii. Electron microscope
iv. Hand lens
The hand lens is the simplest and the most commonly used magnifier in laboratories for magnifying tiny living things and other objects

PARTS OF A MICROSCOPE

The microscope is made up of many parts which include. The plane mirror: the plane mirror helps to direct light rays to the object for proper lightning so that the object can be seen properly
ii. THE BASE: this part of the microscope represents the metallic base which enables the microscope to rest properly on the table to prevent it from falling

iii. THE STAGE: this part of the microscope represents where the object to be observed is placed
iv. CLIPS: these are tiny structures attached to the microscope itself to help hold the objects for proper viewing
v. HANDLE/ARM: this part is used to carry the microscope itself
vi. CONDENSER: the condenser of the microscope consists of a powerful lens which condenses the light rays coming from the plane mirror and directs them to the objects under observation

vii. THE ROTATORY NASAL PIECE: this part of the microscope is where the objective lenses of varying magnifications are fitted. It can be rotated to allow for a better magnifying
viii. THE EYEPIECE LENSES: this part of the microscope is where the observer places his eyes to view the objects through the microscope

ix. ADJUSTMENT KNOBS: this part of the microscope is made up of two components (a) Coarse adjustment and (b) Fine adjustment
x. THE OBJECTIVE LENS: this lens as part of the microscope, is usually placed slightly above the object, and it is used for magnification

HOW TO USE THE MICROSCOPE
i. Bring out the microscope from where it has been stored or kept with the aid of its handle
ii. Clean the microscope gently with soft cotton or wool. Parts to be cleaned include the following, the eyepiece, objective lenses, condenser, and other parts of the microscope
iii. Adjust the plane mirror in the direction of light to catch and direct the rays of light into the microscope
iv. Where necessary open the lid of the condenser
v. Place the slide of the object which is to be on the stage and use the clip to hold it firmly

vi. Proper adjustment is made on the objective lens to rest on the slide
vii. Adjust the coarse knob to bring out the object into focus
viii. When the object is brought into sharp focus, the fine adjustment knob is then used

to make the object sharper
ix. The object or specimen is then examined carefully and the observations are recorded
x. The objects or specimen is then translated into a diagram using the biology practical workbook

THE BIOLOGY TEACHER IS EXPECTED TO GUIDE AND DEMONSTRATE THE USE OF MICROSCOPE TO STUDENTS IN THE LABORATORY

FORMS IN WHICH LIVING THINGS EXIST

There are four main forms in which living cells exist. They are
i. Single and free-living organisms:
Independent or free-living organisms are organisms which possess only one cell and are capable of living freely on their own. Each organism, even though they have only one cell can carry out all of life’s processes such as feeding, locomotion, excretion, respiration and reproduction, e.g. Amoeba, Euglena, Paramecium and Chlamydomonas

a.

AMOEBA STRUCTURE:

An amoeba is generally shapeless and changes regularly. The protoplasm is made up nucleus and cytoplasm. Embedded in the cytoplasm are food vacuole and contractile vacuole. An amoeba moves with the aid of a pseudopodia
b.

PARAMECIUM STRUCTURE:

 then paramecium is often described as having a slipper shape. The cytoplasm is composed of ectoplasm and endoplasm. The nucleus consists of micro-nucleus and mega-nucleus. The cytoplasm also houses the food vacuole, contractile vacuole and cytostome. Paramecium moves with the aid of a cilia
c.

EUGLENA VIRIDIS CELL STRUCTURE

: Euglena viridis is a protist and a typical example of an organism sharing the characteristics of both plants and animals. The Euglena as an organism possesses flagellum, gullet, contractile vacuole, eye spot, pellicle, myonemes etc. which makes it an animal and also has chloroplast, pyrenoids and paramylum granules. Euglena moves with the aid of a flagellum
d.

CHLAMYDOMONAS CELL STRUCTURE:

Chlamydomonas is a simple microscopic plant. Chlamydomonas is also a unicellular plant. Chlamydomonas moves with the aid of a flagellum. Chlamydomonas has an eye spot, chloroplast, food vacuole and contractile vacuole.
e.
ii.

CELLS EXIST AS A COLONY:

some organisms are made up of many similar cells which are joined or massed together but cannot be differentiated from each other. These cells form a loosely arranged association of two or more cells but the cells cannot be differentiated from each other. This aggregation of independent or protists is called a colony. Examples of organisms that exist as a colony are Volvox, Pandorina and sponges
iii.

CELLS EXIST AS A FILAMENT:

Filamentous cells are cells in which identical cells are joined end to end to form an unbranded filament. Each cell functions as an independent living cell. Such organisms are multi-cellular and therefore exist as filaments. Examples are Spirogyra, Zygnema, Oscilateria and Oedogonium.
iv.

CELLS AS PART OF A LIVING ORGANISM

in any multi-cellular organism, a group of numerous, similar cells arranged together and performing a specific function called a tissue. A group of similar tissues forming a layer in an organism which performs a specific function is called an organ. A group of organs which work together to perform a specific function are called a system. From the explanation above we can clinically say that cells lead to tissues, tissues lead to the organ and organs lead to the system so we can conclusively say that the cell is the unit of living things.

STRUCTURE AND FUNCTIONS OF THE CELL. INCLUDING THEIR COMPONENTS

STRUCTURE OF THE CELL
The structure of plant and animal cells can fully be understood through the aid of a microscope. The cell is composed of two protoplasm which can be divided into two main parts: they are cytoplasm and nucleus. Each cell, either plants or animals is bound by a thin membrane. The cytoplasm is a fluid which consists of cytoplasmic organelles such as lysosomes, Golgi bodies, endoplasmic reticulum, mitochondria, vacuoles etc.
The nucleus is bounded by a nuclear membrane and it consists of chromosomes as chromatin granules and nucleus. The animal cell has centrosomes in addition. The plant cell has starch granules, cellulose cell walls and some plastids e.g. chloroplast.
The structure and functions of the components of the cells or organelles are outlined in the chart or table below.
i.

NUCLEUS:

the nucleus is a spherical body which is covered by a double membrane which contains hereditary materials, chromosomes and genes it is generally located in the centre of the cell, enclosed in the cytoplasm
Function of the nucleus
1. It controls all life activity of the cell
2. It stores hereditary information as it contains DNA inside chromosomes which takes place in cell division

CHROMOSOME:

these are located in the nucleus and contain deoxyribonucleic acid or DNA
Functions of the chromosome
Contains the DNA which stores genetic traits

MITOCHONDRIA:

These are oval or rod-shaped. They are bounded by a double membrane. The inner membrane is folded and the interior is filled with matrix. The matrix contains ribosomes
Functions of MITOCHONDRIA
a. It is often described as the powerhouse of the cell. They are majorly the site of respiration or where energy is released from simple sugar

VACUOLE:

It occupies large central parts of the plant cell. It is lined with a membrane and filled with a cell sap. The cell sap acts as a storehouse for many substances

FUNCTIONS OF A VACUOLE: It contains sap which acts as an Osmo-regulator by helping to remove excess water in the cells

NUCLEOULUS: They are dense structures within the nucleus

FUNCTIONS OF THE NUCLEOLUS
They produce the ribosome for protein synthesis

ENDOPLASMIC RETICULUM:

They are membrane-like structure which forms channels within the cytoplasm

FUNCTIONS OF THE ENDOPLASMIC RETICULUM
They aid the transportation of materials through and within the cytoplasm

GOLGI-BODIES:

These are a series of disc-shaped sacks

FUNCTIONS OF GOLGI BODIES
They function in the synthesis, packaging and distribution of materials

LYSOSOME: These are thin-walled bodies and they contain enzymes

FUNCTIONS OF LYSOSOME They are sites for respiratory enzyme

CHLOROPLAST: These are large green organelles in plant cells. They contain chlorophyll
FUNCTIONS OF THE CHLOROPLAST They contain chlorophyll which aids photosynthesis in plants

RIBOSOMES These are small round bodies attached to the endoplasmic reticulum
FUNCTIONS OF THE RIBOSOMESThey are responsible for protein synthesis

CELL WALL It is a tough, fairly rigid structure that is freely permeable in plant cells
FUNCTIONS OF THE CELL WALL
a. It provides protection, shape and mechanical support for the cell
b. It also allows the free passage of nutrients in and out of the cell

CELL MEMBRANE This is a flexible membrane made up of mainly proteins and lipids. It is selectively permeable.
FUNCTIONS OF THE CELL MEMBRANE
a. It plays a great role in the selective absorption of MATERIALS
b. It also protects the cells

CENTOILES These are two small granules near the nucleus of animal cells from which flagella or cilia
FUNCTIONS OF THE CENTOILES
a. They are very important in cell division
b. They also serve as basal body

STARCH GRANULES These mare oval or round structures are mostly found in plant cells.

FUNCTIONS OF THE STARCH GRANULES
They store starch for the cell

SIMILARITIES BETWEEN PLANTS AND ANIMAL CELLS

Both plants and animal cells have the following lists in common
i. Nucleus
ii. Mitochondria
iii. Chromosomes
iv. Nucleolus
v. Golgi bodies
vi. Cytoplasm
vii. Endoplasmic reticulum
viii. Ribosome
ix. Cell membrane

DIFFERENCES BETWEEN PLANTS AND ANIMAL CELL

i. Plant cell has chloroplast—–Animal cell does not
ii. Plant cell is usually rectangular and definite in shape——Animal cell is spherical or most often no definite shape
iii. Plant cell has rigid cell wall——-Animal cell has flexible cell membrane
iv. Plant cell has large vacuoles——Animal cell has very small vacuoles
v. Plant cell stores lipids as oil——Animal cells stores lipids as fat
vi. Plant cell has the nucleus at the edge of the cytoplasm—–Animal cells have it’s nucleus at the centre of the cytoplasm

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WEED AND THEIR BOTANICAL NAMES
1.

  1. RINDER PESTS
    148. NEWCASTLE DISEASE
    149. BACTERIA DISEASES
    150. ANTHRAX

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