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CELL STRUCTURE AND ORGANIZATION.
 THE CELL
The cell is a structural and functional basic unit of life. 

Cells are small microscopic units that make up the bodies of all living organisms.
The cell is fundamental to Biology as the atom is to Chemistry. The cell is the simplest collection of matter that can live. 

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.

Therefore a cell can be defined as the smallest unit of living things or a cell is a basic unit of life.

History of the cell.
In 1665, Robert Hooke discovered the structural and functional unit of all living organisms called the cell.
In 1839, Schleiden J.M. and Theodore Schwann, put forward the cell theory, which states that, “Cells are of universal occurrence and the fundamental units of an organism”.


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.
The Characteristics  

Characteristics of the cell include the following:
  1. Cells are small microscopic structures which cannot be seen by our naked eyes.
  1. Cells are capable of dividing by mitotic process or meiotic process.
  1. Cells contain structures called organelles.
The cell theory 

The cell theory state that
  • All living things are composed of cells.
  • Cells are the basic unit of structure and function in all living things
  • All cells are produced from other cells
  • cells contain inherited information which controls their activities
  • All cells are basically the same in chemical composition
  • all life processes take place in the cell

Unicellular and multicelular.

Unicellular are organism that are made up of only one cell, eg. Bacteria, amoeba, and paramecium.

Multicellular are organisms that are composed of many cells, eg. Human being, lion, trees, and housefly

TYPES OF THE CELL

There are two types. namely


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.

Characteristics of a cell.

· Is microscopic

· Is membrane bound

· It has structures that are sites of chemical reactions called organelles

· Have the ability to replicate since it contains the genetic material, i.e. DNA and RNA.


Different between prokaryotic and Eukaryotic cells

Eukaryotic cells                                              Prokaryotic cell
They have nuclear membraneLack nuclear membrane
Organelles are surrounded by envelopes

Have true nucleus		Organelles are not surrounded by envelopes

Have no true nucleus

The Functions of Different Parts of Plant and Animal Cells

Basically a cell has three main parts
  1. Cell membrane
  1. Cytoplasm
  1. Nucleus

Cell membrane (plasmalemma)

This is a thin flexible membrane made of protein and oil. It has the following functions:
  1. The cell membrane encloses the contents of the cell.
  1. 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
Cell wall                                 
Cell membrane
It is a non–living structure
It is a living structure
It is made up of cellulose
It is made up of lipoprotein
It is freely permeable
It is selectively permeable

2..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


3.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.

 The functions of the nucleus:
  1. It controls the formation and development of a cell.
  2. The nucleus also controls chemicals which the cell manufactures.
  3. The nucleus contain chromosomes which carry genetic material i.e. DNA which is responsible for controlling genetic information.

4.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.

  functions:

 1.It gives the cell its shape.
 2. It is freely permeable to all kinds of molecules.
3.It supports and protects the cell.
4.It supports non-woody plant organs, such as leaves, by turgor pressure.
5.It osmoregulates by resisting entry of excess water into cell.


5.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

functions:
  1. It is responsible for food storage and osmoregulation.
  1. The outward pressure of the vacuole on the cell wall makes the plant cells firm, giving strength and resilience to the tissues.

6.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.

Functions of mitochondria.
-Are the sites or respiratory reaction, which yield energy for the cell

7.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.

Functions of chloroplast.
They are the sites of photosynthesis, ie. The process by which green plants manufacture carbohydrates.
 -The reaction of light stage of photosynthesis take place in the grana.
 -The reaction of the dark stage of photosynthesis take place in the stroma of the chloroplast

Golgi body

Golgi bodies are stacks of flattened, membrane-bound sacs
The  functions:
  1. Golgi bodies are responsible for internal processing and transport system.
  2. Processing of many cell materials e.g. protein takes place in the cisternae.
  3. Godgi vesicles transport the materials to the other parts of the cell
PLANTS AND ANIMAL CELLS


Animal cell




Plant cell



Differences between plant cell and animal cells

Animal cell
Plant cell
Have no cell wall
Have cell wall made of cellulose
Have small temporary vacuole
Have large permanent vacuole
Ho no chloroplasts
Have chloroplasts
Hove no definite shape
Have definite shape
Have centrioles and normally exist in pairs
They usually lack centrioles.
They store fats and glycogen.
They store oils, proteins and starch.
The cytoplasm occupies most of the cell with the nucleus centrally located in the cytoplasm.
The cytoplasm and the nucleus are located towards the periphery.
They are usually smaller.
They are normally larger.


Similarities between animal cell and plant cells

  1. Both have cell membranes
  2. Both contain cytoplasm
  3. Both have nucleus
  4. Both have mitochondria
  5. Both have golgi bodies
  6. Both have ribosomes
CELL DIFFERENTIATION CELL
An organism made up of one cell is called unicellular organism. Example. are a Amoeba. paramecia and bacteria and 
An organism made up of more than one cell are called Multicelllrar organism.A multicellular organism consists millions of cells 

CELL DIFFERENTIATION 
 is the way cells adapted so that they can carry out function efficiently.
or
The process by which cells are specialized to perform a particular function
These involves the changes in shape and chemical reactions enable the cell to carry out its special 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.

TISSUE. 
is formed when a group of cells that perform the same function.. Examples.animal tissue. are bone, muscle, and skin. 
Plant tissue. Xylem and Phloem.Animal organ includes Hearts,Liver, and brain
 and  Plant organs includes the stem, flowers, and roots.

 A SYSTEM.
is made up of organs that work together to perform a certain functions..Examples
 are respiratory system, digestive system . reproductive system, Hormonal system skeletal system and blood circulatory system.

AN ORGANISM
Is made up of different system working together. 

Therefore there is special organization from the  
Cell----tissue-----organ-----system------organism

 THE IMPORTANCE OF CELL DIFFERENTIATION.

Leads to division of labour. Means each cell does a specific function.

This help the body to carry out all life processes at the same time and more efficently, organs and body systems
 .
SPECIALIZES ANIMAL CELLS.


ANIMAL CELL

1. 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

2.BLOOD CELL

  • 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.
Egg cell

4.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.

Muscle cell


5 Ciliated cells

These cells form the lining of the nose and wind pipe.


PLANT CELL


1.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.
2.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 TISSUE
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:
  1. skeletal muscle tissue;
  1. smooth muscle tissue; or
  1. cardiac muscle tissue.
1Skeletal muscle tissues form those muscles that move the bones

Skeletal muscle fibres

2.Smooth muscle tissues

These are found in the walls of hollow organs. 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.

Smooth muscle fibres

3.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.

Cardiac muscle fibres


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.

PLANT TISSUE

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

Animal organs

Other examples of animal organs include skin, testes, ears, noses and the brain.

Plant organs

Examples of plant organs include leaves, stems, roots, flowers and fruits.
Plant organs

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.

The digestive system


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.

The circulatory system


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.

Lymphatic system


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 urinary system


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.

Muscular system


The muscular system
It consists of the organs muscles and tendons. The role of the muscular system is to bring about movement.

The skeletal muscles


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.

Endocrine system


Skeletal system
It consists of a system of skeletons. Its function is to support the body, protect internal organs and produce blood cells.

Skeletal system
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.