WHAT IS CELL? IS CELL A LIVING THING?
Definition of a cell
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.
All living things including plants and animals are made up of cells. The cell is regarded as the basic of all living thing because they or it can carry out life activity 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.
CHARACTERISTICS OF LIVING ORGANISMS BASED ON THE NUMBER OF CELLS
Living organisms are classified into two major group based on their number cells, they are
a. UNICELLULAR OR ACELLULAR ORGANISMS
These organisms which consists only of one cell. Examples of unicellular organisms are Amoeba, Chlamydomonas, Euglena and paramecium
b. MULTI-CELLULAR ORGANISMS
These are organisms which consists of two or more cells. Which means th4ese group of organisms is made up of multiple cells. Examples are Volvox, Spirogyra, man, flowering plants and birds
HISTORY OF THE CELL
Many scientists contributed to history of the cell theory. Amongst thee brave scientists are
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 honey comb 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 rooms. He4 then named these components cells.
This guy is a French Biologist in 1835 who discovered the cells are made up of living substances called protoplasm.
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
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,/h3>
This a German biologist in 1855 who wrote that all cells comes from previously existing cells
THE CELL THEORY
The cell theory states that
i. The cell is the structural and functional unit of living things
ii. All living organism are made up of cells
iii. All cells comes from previous existing cells
iv. That there is no cells apart from the life of the cells
v. All living things are either unicellular or multi-cellular organisms
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 eyes.
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
The various types of microscope includes 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 the laboratories for magnifying tiny living things and other objects
PARTS OF A MICROSCOPE
The microscope is made up of many parts which includes
i. 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 represent the metallic base which enables the microscope to rest properly on the table so as to prevent it from falling
iii. THE STAGE: this part of the microscope represent 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 EYE PIECE LENSES: this part of the microscope is where the observer places his eyes for viewing the objects through the microscope
ix. ADJUSTMENT KNOBS: this part of the microscope is made up of two components are (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 been stored or kept with the aid of its handle
ii. Clean the microscope gently with soft cotton or wool. Parts to be cleaned includes the following ,the eye piece, objective lenses, condenser, and other parts of the microscope
iii. Adjust the plane mirror in the direction of light in order 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 so as 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 diagram using the biology practical work book
THE BIOLOGY TEACHER IS EXPECTED TO GUIDE AND DEMONSTRATE THE USE OF MICROSCOPE TO STUDENTS IN THE LABORATORY
FORMS IN WHICH LIVING THINGS EXISTS
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
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
PARAMECIUM STRUCTURE:,/h3> then paramecium is often described as having a slippers 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 cyto-stome. Paramecium moves with the aid of a cilia
EUGLINA VIRIDIS 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 have chloroplast, pyrenoids and paramylum granules. Euglena moves with the aid of a flagellum
Chlamydomonas is a simple microscopic plant. Chlamydomonas is also a unicellular plant. Chlamydomonas moves with the aid of a flagellum. Chlamydomonas has eye spot, chloroplast, food vacuole and contractile vacuole.
CELLS EXISTS AS A COLONY:
some organism 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 protist is called a colony. Examples of organisms that exist as a colony are Volvox, Pandorina and sponges
CELLS EXISTN AS A FILAMENT:
Filamentous cells are cells in which identical cells are joined end to end to form unbranded filament. Each cell function as an independent living cell. Such organism are multi-cellular and therefore exist as filament. Examples are Spirogyra, Zygnema, Oscilateria and Oedogonium.
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 works together to perform a specific function are called a system. From the explanation above we can clinically say that cells leads to tissues, tissues leads to organ while organs leads to system and 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 cell 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 bound4ed by a thin membrane. The cytoplasm is a fluid which consists of cytoplasmic organelles such as lysosome, 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 wall and some plastids e.g. chloroplast.
The structure and functions of the components of the cells or organelles are outline in the chart or table below.
the nucleus a spherical body which is covered by a double membrane which contains hereditary materials, chromosomes and genes which 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
these are located in the nucleus and contains deoxyribonucleic acid or DNA
Functions of the chromosome
Contains the DNA which stores genetic traits
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 often described as the power house of the cell. They are majorly the site of respiration or where energy is released from simple sugar
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 store house for many substances
FUNCTIONS OF A VACUOLE:
It contain sap which acts as a Osmo-regulator by helping to remove excess water in the cells
They are dense structures within the nucleus
FUNCTIONS OF THE NUCLEOLUS
They produce the ribosome for protein synthesis
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
These are series of disc shapes sacks
FUNCTIONS OF GOLGI BODIES
They function in synthesis, packaging and distribution of materials
These are thin walled bodies and they contain enzymes
FUNCTIONS OF LYSOSOME
They are sites for respiratory enzyme
These are large green organelles in plant cell. They contain chlorophyll
FUNCTIONS OF THE CHLOROPLST
They contain chlorophyll which aid photosynthesis in plants
These are small round bodies attached to the endoplasmic reticulum
FUNCTIONS OF THE RIBISOMES
They are responsible for protein synthesis
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
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 selective absorption of MATERIALS
b. It also protects the cells
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 the cell division
b. They also serves as basal body
These mare oval or round structures mostly found in plant cells.
FUNCTIONS OF THE STARCH GRANULES
They store starch for the cell
SIMILIARITIES BETWEEN PLANTS AND ANIMAL CELLS
Both plants animal cells have the following lists in common
v. Golgi bodies
vii. Endoplasmic reticulum
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 in shape 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 cell s stores lipids as fat
vi. Plant cell has the nucleus at the edge of the cytoplasm—–Animal cells has it’s nucleus at the centre of the cytoplasm
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