THE CONCEPT OF CELL.
Plants and animals are made up of units called cells. The cells are microscopic
in such a way that they cannot be seen by our naked
eyes. Some organisms like protozoa, diatoms and bacteria
consist of one cell and are called single-celled or unicellular organisms. Some are made up of many cells and are called
multicellular organisms.
The cell structure of
living things was first seen by Robert Hooke in 1667 when he
examined fine slices of
cork. Robert Hooke believed that the cells were empty and that the cell wall and cell membrane were the most important parts of
the cell but now cell contents are seen to be the most important ones.
Therefore a cell can be defined as the smallest unit of living
things or a cell is a basic unit of life.
THE CHARACTERISTICS OF THE CELL.
Mention the characteristics of the cell
Characteristics of the
cell include the following:
Cells are small microscopic
structures which cannot be seen by our naked eyes.
Cells are capable of
dividing by mitotic process or meiotic process.
Cells contain structures
called organelles.
THE CELL THEORY.
A cell is a basic unit
of structure and function in living organisms.
New cells only come from
pre-existing ones.
Cells contain structures
called organelles.
The cell theories were
proposed jointly by two scientists namely Schleiden, a Belgian botanist, in 1 838 and Schwann, German Zoologist, in 1 839
Difference Between
Various Types of Cells
Differentiate various
types of cells
PROKARYOTIC AND EUKARYOTIC CELLS
Prokaryotic cells are cells with no
membrane-bound nucleus. The DNA lies free in the cytoplasm in a region
known as nucleoid. They have no true nuclei. Examples of prokaryotic organisms are bacteria.
Eukaryotic cells are cells whose nuclei are bounded by nuclear
membrane. They are
surrounded by two
nuclear membranes called nuclear envelope. Examples of eukaryotic organisms are protoctists, fungi, plants and animal cells
Differences between cell wall and cell membrane
Cell wall |
Cell membrane |
It is a non–living |
It is a living
structure |
It is made up of |
It is made up of |
It is freely permeable
|
It is selectively |
Different between prokaryotic and Eukaryotic cells
Eukaryotic cells |
Prokaryotic cell |
They have nuclear
membrane |
Lack nuclear membrane |
Organelles are
surrounded by |
Organelles are not
surrounded by |
Have true nucleus |
Have no true nucleus |
PLANT CELL AND ANIMAL CELLS STRUCTURE
THE ANIMAL CELL STRUCTURE.
PLANT CELL STRUCTURE.
The Functions of Different Parts of Plant and Animal Cells
Explain the functions of
different parts of plant and animal cells
Basically a cell has
three main parts
Cell membrane
Cytoplasm
Nucleus
Cell membrane (plasmalemma)
This is a thin flexible
membrane made of protein and oil. It has the following functions:
The cell membrane
encloses the contents of the cell.
It is freely permeable
to water and gases only and selectively permeable to other
molecules e.g. it allows
food in but keeps unwanted molecules out. Thus cell the
membrane controls the
substances entering and leaving the cell.
Cytoplasm
Cytoplasm is a
transparent jelly-like fluid and may contain particles such chloroplasts or starch grains or oil droplets. It contains up to 80% water and the
remainder is mainly protein. It is a place where chemical reactions
take place
Nucleus
A nucleus is a
ball-shaped or oval body located inside the cytoplasm. It cannot usually be seen unless the cell has been stained with certain dyes. It
consists of nucleoplasm bounded by nuclear membrane.
The nucleus is a cell control centre.
Cell wall
The cell wall is only
found in plant cells. It is made up of cellulose. When the cell is growing the cell wall is fairy plastic and extensible. It becomes
tough and resists
stretching when the cell
has reached full size. The cell wall is non-living. It has the
following functions:
It gives the cell its shape.
It is freely permeable
to all kinds of molecules.
It supports and protects
the cell.
It supports non-woody
plant organs, such as leaves, by turgor pressure.
It osmoregulates by
resisting entry of excess water into cell.
Vacuole
In animal cells, vacuoles are small droplets of fluid in the cytoplasm variable
in size and position. In plant cells, the vacuole is a large,
permanent fluid-filled cavity which occupies a greater part
of the cell. In plants, the fluid is called cell sap. The cell sap may contain salts, sugar and pigments dissolved in water.
The vacuole performs the
following functions:
It is responsible for
food storage and osmoregulation.
The outward pressure of
the vacuole on the cell wall makes the plant cells firm, giving strength and resilience to the tissues.
Mitochondria
Mitochondria are found
in all aerobic eukaryotic cells. A mitochondrion is surrounded by an envelope of two membranes, the inner being folded to form
cristae (singular: crista)
It contains a matrix
with a few ribosomes, a circular DNA molecule and phosphate granules.
Mitochondrion
A mitochondrion is a
power house of a cell. It contains respiratory enzymes involved in respiration. It absorbs oxygen and glucose. The glucose is broken
down to CO2 and H2O.
Energy is released from
glucose bonds to form ATPs (for use in other vital functions e.g. growth, movement, etc.
Chloroplast
Chloroplasts are disc-shaped organelles. They are found in plant cells and
algae cells. A chloroplast contains a green substance called
chlorophyll. It is surrounded by an envelope of two
membranes and contains gel-like stroma through which runs a system of membranes that are stacked in places to form grana.
Chloroplast is an
organelle in which photosynthesis takes place, producing sugars from carbon dioxide and water using light energy trapped by
chlorophyll.
Golgi body
Golgi bodies are stacks
of flattened, membrane-bound sacs
Golgi bodies have the
following functions:
Golgi bodies are
responsible for internal processing and transport system.
Processing of many cell
materials e.g. protein takes place in the cisternae.
Godgi vesicles transport
the materials to the other parts of the cell
Differences between plant cell and animal cells
PLANT CELL |
ANIMAL CELL |
(i) Have definite
shape |
Have no definite shape |
(ii) Have chloroplasts
|
Have no chloroplasts |
(iii)Have large
permanent vacuoles |
Have small temporary |
(iv) Centrioles
usually absent |
Centrioles present |
(v) Have cell wall
made of cellulose |
Have no cell wall |
(vi) The nucleus is
located at the |
The nucleus is
centrally |
Similarities between
animal cell and plant cells
Both have cell membranes
Both contain cytoplasm
Both have nucleus
Both have mitochondria
Both have golgi bodies
Both have ribosomes
Cell Differentiation
When most cells have
finished dividing they become specialized. This means that:
They do one particular
job, They develop a distinct
shape, Special kinds of chemical
change take place in their cytoplasm, The changes in shape and chemical reactions
enable the cell to carry out its special function.
The process by which cells are specialized to perform a particular function is called cell differentiation or ‘division of labour’ within the organism. Similarly, the special functions of mitochondria, ribosomes and other cell organelles may be termed as division of labour within the cell.
DIFFERENCE BETWEEN CELLS, TISSUES ORGANS AND
BODY SYSTEMS.
CELLS
Nerve cells
These are specialized
for conducting impulses of an electrical nature along the fibre. The fibre may be very
long e.g. from the foot to the spinal column. They are the longest cells known Nerve cell
Blood cells
White blood cells:These cells occur in
blood stream and are specialized for engulfing
harmful bacteria. They
are able to change their shapes and move about, even through the walls of blood
vessels into the surrounding tissue.
White blood cell
Red blood cells:These cells are responsible for transportation of oxygen from the
lungs to all parts of the
body.
Red blood cells
Platelet cells: Platelet cells are found
in the blood. They are also called blood platelets. Their function is to
help clot the blood at wounds and so stop bleeding.
Reproductive cells
Sperm cell: it is a male gamete
produced in the testes.
Sperm cell
Egg cell:It is a female gamete
produced in the ovary.
Muscle cells
These are elongated
cells which form the muscle tissues. Muscle cells are highly specialized in that they
are able to shorten a half or even a third of their resting lengths. This characteristic enables the muscles to
contract and expand.
Ciliated cells
These cells form the
lining of the nose and wind pipe.
Root hair cells
These cells form the
outer layer of young roots. The cells are specialized to absorb water and mineral slats
from the soil. The hair-like projections penetrate the soil particles and offer a
large absorbing surface.
Phloem cells
These are food
conducting cells in a plant, joined end to end, and where they meet, perforations occur in
the walls. Through these holes, the cytoplasm of one cell
communicates with the
next.
Xylem cells
The cells conduct water
and mineral salts form the soil to all parts of the plant. They are also responsible for
mechanical support.
Parenchyma cells
Collenchyma cells
Sclerenchyma cells
Epidermal cells
TISSUES
A tissue is a group or
collection of similar cells performing a specific function. Tissues vary in size, shape and
function.
Examples
of tissues
Animal tissues
Animal tissues include
epithelial tissue, muscle tissue, nervous tissue, blood tissue and bony tissue.
Epithelial tissue:
Epithelial tissues cover
the body lining cavities, hollow organs and tubes. They are
responsible for(i) protection of the underlying structure from dehydration, and chemical and mechanical damages;(ii) secretion;
and(iii) absorption.
Columnar epithelium
Squamous epithelium
Cuboidal epithelium
Stratified epithelium
Cliated columnar
Cilliated columnar epithelium with goblet cells
Muscle tissue
Muscle tissue consists
of cells specialized to contract and move the body.
Muscle tissues can be:
skeletal muscle tissue;
smooth muscle tissue; or
cardiac muscle tissue.
Skeletal muscle tissues form those muscles that move the bones
Smooth muscle tissues
They perform the
following functions:
Regulate the diameter of
blood vessels and parts of the respiratory tract.
Propel the contents of
the ureters, ducts of glands and alimentary tract.
Expel contents of the
urinary bladder and uterus.
Cardiac muscle tissue
This kind of muscle
tissue is found only in the heart wall. It helps in contracting and relaxing of heart muscles thus pumping the blood to various body
parts.
Nervous tissues
Nervous tissues have
endings that detect changes in the environment. They transmit and conduct nerve impulses to the brain and spinal cord and to the
effector organs.
Examples of plant
tissues are collenchyma tissue, sclerenchyma tissue, epidermal tissue, conducting tissues e.g. phloem and xylem, palisade tissue
and spongy tissue.
An onion epidermal
tissue
ORGANS
An organ is a collection of tissues working together to perform a certain
function
Examples of animal
organs include skin, testes, ears, noses and the brain.
Examples of plant organs
include leaves, stems, roots, flowers and fruits.
ORGAN SYSTEM
A system refers to
several inter-related organs performing a particular function.
Digestive system
The main organs that
make up the digestive system are alimentary canal, liver and pancreas. The main function of this system is to digest and absorb
food.
Circulatory system
This system consists of
the heart, arteries and veins. The role of the circulatory system is to transport gases, food, hormones and distribute heat.
Lymphatic system
Lymphatic system has
comprises of the lymph vessels and lymph nodes. The main
function of the
lymphatic system is to transport materials and protect against.
Respiratory system
The respiratory system
consists of the trachea and the lungs. The role of the respiratory system is to take in oxygen and expel carbon dioxide gas.
The respiratory system
The urinary system
The main organs of the
urinary system are kidneys, ureter, bladder and urethra.The
urinary system plays a
role in removing metabolic waste products from the body and also it is responsible for osmoregulation.
The nervous system
This system consists of
the brain, spinal cord and nerves.The role of the nervous
system is to detect and
respond to stimuli.
The muscular system
It consists of the
organs muscles and tendons. The role of the muscular system is to
bring about movement.
The reproductive system
It consists of the
ovaries, testes and uterus. Its role is to produce offspring.
Male reproductive system
Female reproductive system
Endocrine system
It consists of endocrine
glands. Its role is to produce hormones.
Skeletal system
It consists of a system
of skeletons. Its function is to support the body, protect internal organs and produce blood cells.
Examples of organ system
in plants
Root system –consists of roots
Function:
Holds the plant firmly
into the soil
Absorption of water and
mineral salts from the soil
Sometimes they act as
storage organs in some plants
Shoot system – consists of the organs flowers, fruits, stem
and leaves
Function
Site of reproduction
Transport of substances
Photosynthesis occurs in
the shoot
Transpiration processes
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