Biology [Chapter # 04]

 

CHAPTER# 04

CELLS AND TISSUES

Q. What is light microscope?

LIGHT MICROSCOPE

In a light microscope, visible light passes through the specimen. A photograph of an image taken through a microscope is called micrograph. The magnification of a light microscope is formed by using a mixture of the powers of the eye piece and the objective lens.

Q. What is Electron microscope?

ELECTRON MICROSCOPE:

Electron microscopes produce an image of a specimen by using a beam of electrons rather than a beam of light. Electrons have a much shorter wavelength than visible light, and this allows electron microscopes to produce higher-resolution images. Electron microscopes can be used to examine not just whole cells, but also the subcellular structures and compartments within them.

Electron microscope has a resolution as small as 0.2 nanometer (nm) and magnification up-to 250,000 times. There are two major types of electron microscopes.

1.      Scanning electron microscopy (SEM)

2.      Transmission electron microscopy (TEM)

 

SCANNING ELECTRON MICROSCOPE

In scanning electron microscopy, a beam of electrons moves back and forth across the surface of a cell or tissue, creating a detailed image of the 3D surface.

TRANSMISSION ELECTRON MICRSCOPE

In transmission electron microscopy, the sample is cut into extremely thin slices before imaging, and the electron beam passes through the slice rather than skimming over its surface. TEM is often used to obtain detailed images of the internal structures of cells.

Q. Write some important event takes place from 1665 to 1862 in the field of development of Biology?

HISTORY AND DEVELOPMENT OF CELL

YEAR	HISTORY
1665	Cell was first observed by Robert Hooke, an English scientist, discovered a honeycomb-like structure in a cork slice using a primitive compound microscope and named it as ‘cell’.
1670	First living cells were seen by Anton van Leeuwenhoek, a Dutch biologist, from pond water with a microscope.
1683	Anton van Leeuwenhoek discovered the first protozoa and bacteria.
1833	Robert Brown discovered the nucleus
1839	Schwann proposed that not only plants but animals tissues also composed of cell
1839	He also pulled together and organized previous statement on cells into one theory, which states: ·        Cells are organisms and all organisms consist of one or more cells. ·        The cell is the basic structure unit for all organisms
1840	Albrecht von Roelliker discovered that sperm and eggs are also cells
1845	Carl Heinrich Braun reworked the cell theory, calling cells the basic unit of life
1855	3rd part to the cell theory added by Rudolf Virchow, a German physiologist/physician/pathologist added that cell is not Denovo structure. This translates mean that all cells develop only from existing cells.
1862	Louis Pasteur was a French biologist; microbiologist and chemist provided the experimental proof of this idea.

 

Q. What is cell theory? Who proposed the cell theory?

CELL THEORY

Cell theory was the result of combine efforts of Schleiden, Schwann ad Rudolf Virchow. The Main postulates of cell theory are as under

1.      All living organisms are composed of one or more cell.

2.      Cell is the basic structural and functional unit of life.

3.      New cells arise by the division of pre-existing cells.

4.      The cell contains the hereditary material which is passed from generation to generation.

 

Q. Describe types of cell on the basis of Nucleus?

TYPES OF CELL ON THE BASIS OF NUCLEUS

On the basis of cell, there are two types of cells:

·        Prokaryotic cell

·        Eukaryotic cell

 

 

S#	Prokaryotic cell	S#	Eukaryotic cell
01	It has not distinct nucleus	01	It has distinct nucleus
02	Cell organelles are absent	02	Cell organelles are present
03	Nucleosome is absent	03	Nucleosome is present
04	One but not true chromosomes are found.	04	More than one true chromosomes are found.
05	True membrane organelles are absent.	05	True membrane organelles are present.
06	Lysosomes are peroxisomes are absent.	06	Lysosomes are peroxisomes are present.
07	ER, Golgi apparatus, vacuoles and mitochondria are absent.	07	ER, Golgi apparatus, vacuoles and mitochondria are present.
08	Ribosomes are 70s	08	Ribosomes are 80s
09	Instance include bacteria and Cyanobacteria	09	Instance include Plant, animal cell

 

Q. Distinguish between plant cell and animal cell.

S#	Plant cell	S#	Animal cell
01	Almost all plants cells contain plastids such chloroplasts, chromoplasts and leucoplasts.	01	Do not contain plastids.
02	Have a rigid cellulose cell wall in addition to the cell membrane.	02	No cell wall.
03	Contain plasmodesmata and pits.	03	Animals do not have plasmodesmata or pits.
04	Large central vacuole filled with cell sap in mature cells.	04	Few vacuoles (if any).
05	Nucleus is found near the edge or periphery of the mature cell.	05	Nucleus is generally found at the center of the cytoplasm.
06	Plant cells rarely contain lysosomes as the plant vacuole handles molecule degradation.	06	Animal cells possess lysosomes which contain enzymes that digest cellular macromolecules.
07	Plant cells do not typically contain centrioles.	07	Animal cells contain these cylindrical structures that organize the assembly of microtubules during cell division.

 

Q. What is cell? Name the parts of cell.

CELL

Cell is the basic structural and functional unit of life, which maintains the shape of the body and also perform all the necessary functions (digestion, respiration, assimilation) etc.

PARTS OF CELL

Following are the most important parts of cell:

·        Cell wall [Plant and bacterial cell]

·        Cell membrane/ plasma membrane

·        Nucleus

·        Cytoplasm

 

TYPES OF ORGANSISMS ON THE BASIS OF CELL

On the basis of cell, the organisms can be categorized into three types

·        Acellular organisms

·        Unicellular organisms

·        Multicellular organisms

 

ACELLULAR ORGANISMS

Those organisms which body contains no cell are called acellular organisms. Such organisms either have DNA or RNA as their functional unit

For instance: Virus

UNICELLULAR ORGANISMS

Those organisms which consists of single cell are called unicellular organisms

For instance: Bacteria

MULTICELLULAR ORGANISMS

Those organisms which consists of more than one cell are called multi cellular organisms.

For instance: Cat, Tiger, Frog, Brassica flower etc.

Q. Write a note on Cell wall.

CELL WALL

Cell wall; the only non-living part of the cell is present in plant, bacterial, algae and fungal cell and absent in animal cell structure. It is found at the border of the cell behind the cell membrane.

COMPOSITION

·        Bacterial cell wall is made up of sugar and amino acids called peptidoglycan.

·        Fungal cell walls are made up of chitin, glucans, and proteins.

·        It is usually made up of strong fibers of cellulose.

 

In plant Cell wall is consists of three layers:

·        Primary wall: It lies on the inside of the middle lamella and is mainly composed of cellulose.

·        Secondary wall: It lies along-side the cell membrane. It is made up of a thick and tough material of cellulose which is held together by a hard, water proof substance called lignin. It is only found in cells which provide mechanical support in plants, i.e. Some cells of xylem like tracheid and vessels

·        Middle lamella: It separates one cell from another. It is a thin membranous layer on the outer side of the cell and is made of a sticky substance called pectin and cellulose.

 

FUNCTIONS

1.      It helps to maintain the structure of cell

2.      It helps in rigidity

3.      It acts as transport layer

4.      It protects the cellular components

5.      It provides mechanical support to the plant

 

Q. What is plasmodesmata?

The openings in the cell wall are called plasmodesmata which contain strands of cytoplasm that connect adjacent cells. This allows cells to interact with one another, allowing molecules to travel between plant cells.

 

Q. Write note on Cell membrane.

CELL MEMBRANE/ PLASMA MEMBRANE

It occurs just beyond the cell wall in plants but in animal cell it founds at the border of the cell. It is also named as ‘Selective/ partial permeable membrane’ as it allows fats soluble substances to move inside while the fats insoluble substances are not allowed by the membrane.

 

FLUID MOSAIC MODEL

In 1972, S.J. Singer and G.L. Nicolson proposed the Fluid Mosaic Model of the cell membrane.

This model describes the structure of the cell membrane as a fluid structure with various protein and carbohydrate components floating freely in the membrane. All the exchanges between the cell and its environment have to pass through the cell membrane. The cell membrane is selectively permeable to ions (e.g. hydrogen, sodium), small molecules (oxygen, carbon dioxide) and larger molecules (glucose and amino acids) and controls the movement of substances in and out of the cells.

COMPOSITION

It composed of about 60 % Protein and 40% phospholipids.

PROTEINS

Protein itself consists of

i.        Integral protein

ii.      Peripheral protein

Phospho lipid also consists of

i.        Hydrophilic part

ii.      Hydrophobic part

 

FUNCTIONS

·        The function of cell membrane is to act as selective barrier, helps in transportation.

·        It also acts as ion exchange etc.

·        It maintains the structure of cell

·        It acts as supportive layer in animal cell

 

Q. Write note on Transport.

TRANSPORT

The movement of molecule from one region to other; carrying certain a substance is called transport.

In animal and plant cell, the transport may be of two types

·        Active transport

·        Passive transport

 

ACTIVE TRANSPORT

The type of transport which requires energy to occur is called active transport.

PASSIVE TRANSPORT

The type of transport which doesn’t require transporting substances from one region to other.

Passive transport is of three types:

·        Diffusion

·        Osmosis

·        Facilitated diffusion

 

DIFFUSION

The movement of molecule from the region of higher concentration to the region of lower concentration without any semi permeable membrane is called diffusion. It does not require energy.

 

OSMOSIS

The movement of molecule from the region of higher concentration to the lower concentration through semi permeable membrane is called osmosis

FACILITATED DIFFUSION

Facilitated diffusion is a special form of diffusion which allows rapid exchange of specific substances. Particles are taken up by carrier proteins which change their shape as a result. The change in shape causes the particles to be released on the other side of the membrane.

Q. Write note on Cytoplasm.

Cytoplasm: The cytoplasm is the jelly-like substance that fills the cell. It consists of up to 90% water. It also contains dissolved nutrients and waste products. Its main function is to hold together the organelles which make up the cytoplasm. It also nourishes the cell by supplying it with salts and sugars and provides a medium for metabolic reactions to occur.

Q. Write note on Nucleus.

NUCLEUS

Nucleus was discovered by Robert Brown.

Nucleus is covered by two phospholipids membranes known as nuclear envelope that separates the nucleus and its contents from the cytoplasm. Nuclear pores are found in the nuclear envelope and help to regulate the exchange of materials (such as RNA and proteins) between the nucleus and the cytoplasm. Inside nuclear envelope, a granular fluid is present called nucleoplasm. In nucleus an aggregation of RNA is also present called nucleolus.

Within nucleus, each chromosome, a single unit of DNA associates with several proteins contains thousands unit of hereditary material called GENES. Genes control the most aspect of the cellular structure and function.

OCCURRENCE

It occurs in the center of animal cell but in plant cell, it is present at periphery.

SHAPE

Shape may be spherical, oval or circle.

FUNCTION

It controls all the activity of cell.

Q. Write note on Mitochondria.

MITOCHONDRIA [CHONDRIOSOMES]

It is refers as “Power House” of the cell, because it generates ATP (source of energy). A cell may have few as hundred or as many as several thousand mitochondria, depending on its activity. It is the self-replicating organelle.

STRUCTURE

It consists of an outer mitochondrial membrane and an inner mitochondrial membrane with a small fluid dilled space between them. Inner mitochondrial membrane contains cristae while fluid filled cavity is matrix.

Mitochondria in ear lobes cells are nearly 50, in heart muscle they are nearly 350.

FUNCTION

·        It helps in production of energy in the form of ATP

·        It also plays an important role in Apoptosis.

 

Q. Write note on Endoplasmic Reticulum.

ENDOPLASMIC RETICULUM

The endoplasmic reticulum (ER) is an organelle found in eukaryotic cells only. The ER has a double membrane consisting of a network of hollow tubes, flattened sheets, and round sacs. These flattened, hollow folds and sacs are called cisternae. The ER is located in the cytoplasm and is connected to the nuclear envelope.

STRUCTURE

Cell contains two distinct forms of Endoplasmic reticulum (ER).

·        Rough endoplasmic reticulum [RER] OR Granulated Endoplasmic Reticulum

·        Smooth endoplasmic reticulum [SER] OR Agranulated Endoplasmic reticulum

 

Smooth Endoplasmic Reticulum: does not have any ribosomes attached. It is involved in the synthesis of lipids, including oils, phospholipids and steroids. It is also responsible for metabolism of carbohydrates, regulation of calcium concentration and detoxification.

Rough Endoplasmic Reticulum: is covered with ribosomes giving the endoplasmic reticulum its rough appearance. It is responsible for protein synthesis and plays a role in membrane production.

Q. Write note on Ribosomes.

RIBOSOMES

It is also called protein factory. These are the granules and they contain high content of RNA (Ribo nucleic acid).

STRUCTURE

Ribosome usually consists of two sub units’ i.e. 30s and 50s. They found freely in the cell but at the time of requirement, they come close to each other and join themselves forming 70s.

FUNCTION

They help in protein synthesis. Ribosomes are composed of RNA and protein. They occur in the cytoplasm and are the sites where p r o t e in synthesis occurs. Ribosomes may occur singly in the cytoplasm or in groups or may be attached to the endoplasmic reticulum thus forming the rough endoplasmic reticulum

Q. Write note on Golgi Body.

GOLGI BODIES/ GOLGI APPARATUS/ DICTYOSOME

Golgi bodies was first discovered by Camilo Golgi thus named as Golgi bodies. It is a small, flattened sac with bulging edges, single membrane structure.

STRUCTURE

It consists of 3-20 cisternae which are often curved giving Golgi bodies a cup like shape. The cisternae contains enzymes which modify the package products of the Golgi body.

FUNCTIONS

It modifies, packages, and transport proteins received from Rough Endoplasmic Reticulum. For this reason, Golgi body is also called ‘Post office’ of the cell.

 

Q. Write note on Vesicles.

VESICLES

Vesicles are small, membrane-bound spherical sacs which facilitate the metabolism, transport and storage of molecules. Vesicles can be classified according to their contents and function. For instance transport vesicles transport molecules within the cell.

Q. Write note on Lysosome.

LYSOSOMES

Lysosomes are formed by the Golgi body and contain powerful digestive enzymes that can potentially digest the cell. These powerful enzymes can digest cell structures and food molecules such as carbohydrates and proteins. Lysosomes are abundant in animal cells that ingest food through food vacuoles.

 

Q. Write note on Vacuole.

VACUOLE

Certain fluid filled cavities are present in the cell which are termed as vacuoles.

STRUCTURE

They are small or completely absent in animals but in plant cell they are few in numbers with large sizes. Tonoplast is a selective permeable membrane which surrounds the vacuole. Vacuole contains cell sap that is a fluid consists of water, minerals, salts, sugars and amino acids.

FUNCTION

Vacuole plays an important role in hydrolysis, excretion of cellular waste, storage of water, organic and inorganic substances

Q. Write note on Centriole.

CENTRIOLE

The centriole is a cylindrical tube-like structure that is composed of 27 microtubules arranged in a very particular pattern of triplets in rows. The site where two centrioles arranged perpendicular to each other are referred to as a centrosome. The centrosome plays a very important role in cell division. The centrioles are responsible for organizing the microtubules that position the chromosomes in the correct location during cell division.

 

Q. Write note on Plastids.

PLASTIDS

Plastids are the double membrane organelles also called color producer, found in algae and higher plants. Plastids are of three different types.

·        Chloroplast

·        Chromoplast

·        Leucoplast

 

CHLOROPLAST

It is a green color plastid. It contains chlorophyll which is responsible to provide green color to the leaves, stem etc.

CHROMOPLAST

It is the color pigment rather than green and it provides all the color colors with exception of green to Fruits, Flowers etc.

LEUCOPLAST

These are the colorless plastids and found under the soil. They are storage granules of the roots.

Q. What do you know about Chloroplast?

CHLOROPLAST

The chloroplast is a double membraned organelle. Within the double membrane is a gel-like substance called stroma. Within the stroma, grana; stack like structures are suspended. Each granum is a stack of thylakoid discs. The chlorophyll molecules are found on the surface of the thylakoid discs. Chlorophyll absorbs energy from the sun for photosynthesis.

Q. Define Tissue. Explain Animal tissues.

TISSUES

The group of similar structural and functional cell is called Tissue.

OR A group of similar cells that work together to perform a common function is known as a tissue.

ANIMAL TISSUES

In man and other higher animals, tissues are of four different types, which are:

·        Epithelial tissue

·        Muscular tissue

·        Connective tissue

·        Nervous tissue

 

EPITHELIAL TISSUE

This type of tissues covers the body surfaces and line hollow organs, body cavities and ducts. They also form glands. This tissue allows the body to interact with internal and external environment.

On the basis of cell layers, epithelial tissues are of two types:

·        Simple epithelial tissue: A type of tissue in which cells are arranged in a single layer

·        Stratified epithelial tissue: A type of tissue in which cells are arranged in a two or more layers

 

TYPE	SIMPLE EPITHELIAL TISSUE	STRATIFIED EPITHELIAL TISSUE
Squamous	Found in lungs	Skin
Cuboidal	Lumen of collecting ducts in kidneys, thyroid glands	Glands [adrenal, pituitary, parathyroid etc.]
Columnar	Female reproductive system, digestive tract	Reproductive system

 

CONNECTIVE TISSUE

Connective tissues are one of the most abundant and widely distributed tissues in the body. They bind together, support and strengthen the tissues. They may be soft, liquid or hard tissues.

Soft tissues: Cartilage, adipose

Fluid tissue/ liquid tissue: Blood

Hard tissues: Bones

 

CARTILAGE	BONE	ADIPOSE	BLOOD
Soft connective tissue	Hard connective tissue	Soft connective tissue	Liquid connective tissue
Dense tissues	Dense or spongy	Dense	Fluid
Ear, nose	Humerus, radius, ulna	Involves in storage of fats (energy)	Involves in transportation

 

MUSCULAR TISSUE

These are formed by the muscular fibers. They consist of elongated cells. Muscle tissues are responsible for contraction and relaxation of muscles.

Based on their structure, location and function, muscular tissues may be:

·        Skeletal muscles

·        Smooth muscles

·        Cardiac muscles

 

SKELETAL MUSCLES	SMOOTH MUSCLES	CARDIAC MUSCLES
Striated	Unstriated	Striated
Voluntary	Involuntary	Involuntary
Legs, arms	Blood vessels, urinary bladder, uterus etc.	Only in the walls of heart

 

NERVOUS TISSUES

Nervous tissue is composed of neurons, which transmit information to other cells.

Nervous tissue is found in the brain, spinal cord, and nerves.

It is responsible for coordinating and controlling many body activities. It stimulates muscle contraction, and plays a major role in emotions, memory, and reasoning.

Q. Explain types of plant tissues.

PLANT TISSUES

Plant cells are grouped into tissues with characteristic functions such as photosynthesis, transport etc. Plants generally consist of two major type of tissues which are describing below:

·        Meristematic tissue

·        Permanent tissue

 

MERISTEMATIC TISSUES:

These tissues are composed of cells, which have the ability to divide. The cells are thin walled, have large nucleus and number of small vacuoles. Usually they do not have inter-cellular spaces, so the cells are arranged compactly.

There are two main types of meristematic tissues:

·        Apical meristems are present at the apex of roots and stems. Stem and root increase in length by the division of cells of these tissues. This type of growth is called primary growth

·        Lateral meristems are located on the lateral sides of roots and shoot. By dividing, they are responsible for increase in growth of plant parts. This growth is called secondary growth.

 

PERMANENT TISSUES

Permanent tissues originate from meristematic tissue. The cells of these tissues do not have the ability to divide and may have intercellular spaces in between cells.

There are two types of permanent tissues:

1.                  Simple permanent tissue

2.                  Compound or complex tissue

 

1.                 SIMPLE PERMANENT TISSUE

Simple permanent tissues are made up of only one type of cell.

Epidermal Tissues

Epidermal tissues are composed of a single layer of cells and they cover plant body.

§  In roots, they are also responsible for the absorption of water and minerals.

§  On stem and leaves they secrete cutin which prevents evaporation.

 

Ground Tissues

Ground tissues are simple tissues made up of parenchyma cells. Overall they are spherical but flat at point of contact. They have thin primary cell walls and have large vacuoles for storage of food.

·        In leaves, they are called mesophyll and are the sites of photosynthesis.

·        In other parts, they are the sites of respiration and protein synthesis.

 

Supporting Tissues

These tissues provide strength and flexibility to plants. They are further of two types.

·        Collenchyma

·        Sclerenchyma

 

Collenchyma Tissues

They are found in cortex (beneath epidermis) of young stems and in the midribs of leaves and in petals of flowers. They are made of elongated cells. They are flexible and function to support the organs in which they are found.

Sclerenchyma Tissues

They are composed of cells with rigid secondary cell walls. Their cell walls are hardened with lignin.

2.                 COMPOUND (COMPLEX) TISSUES

A plant tissue composed of more than one type of cell is called a compound or complex tissue. Xylem and phloem tissues, found only in vascular plants, are examples of compound tissues.

Xylem Tissues

Xylem tissue is responsible for the transport of water and dissolved substances from roots to the aerial parts. Xylem tissue also provides support to plant body.

Two main types of cell are found in xylem tissue i.e. vessel and tracheids.

Phloem Tissues

Phloem tissue is responsible for the conduction of dissolved organic matter (food) between different parts of plant body. Phloem tissue mainly contains sieve tube cells and companion cells.