Cell The Unit of Life Class 11 Biology Exam Questions

Please refer to Cell The Unit of Life Class 11 Biology Exam Questions provided below. These questions and answers for Class 11 Biology have been designed based on the past trend of questions and important topics in your class 11 Biology books. You should go through all Class 11 Biology Important Questions provided by our teachers which will help you to get more marks in upcoming exams.

Class 11 Biology Exam Questions Cell The Unit of Life

Class 11 Biology students should read and understand the important questions and answers provided below for Cell The Unit of Life which will help them to understand all important and difficult topics.

Objective Type Questions

Question. There is an extensive compartmentalization of cytoplasm through membrane bound organelles in all except
(a) Prokaryotes
(b) Diatoms
(c) Plants and fungi
(d) Animals

Question. Cell membrane is absent in living
(a) Prokaryotic cells
(b) RBC
(c) Mesophyll
(d) None

Question. The best material for the study of the structure of cell membrane is
(a) RBC of human
(b) RBC of frog
(c) Kidney cell
(d) Muscle cell

Question. In cell membrane, lipid are arranged in a
(a) Bilayer
(b) Monolayer
(c) Multilayer
(d) Unilayer at some places and bilayers at other places

Question. Lipids are arranged with in the membrane with
(a) Polar heads towards inner side and hydrophobic tail towards outer side
(b) Both heads and tails towards innerside
(c) Heads towards outer side and tail towards inside
(d) Both heads and tails towards innerside

Question. Why tail of lipids in membrane are towards inner part?
(a) The tail is non polar hydrocarbon and so protected within an aqueous environment
(b) The tail is polar hydrocarbon and so is protected within aqueous environment
(c) The non polar or hydrophobic hydrocarbon tails of lipid, being on inner side ensures their protection from aqueous environment
(d) The tail is Hydrophilic so it tends to be located in the aqueous inner side of membrane

Question. The molecules in a membrane that limit its permeability are the
(a) Carbohydrates
(b) Phospholipids
(c) Proteins
(d) Water

Question. Who proposed the fluid mosaic model of plasma membrane in 1972?
(a) Singer nicolson
(b) Robertson
(c) Robert brown
(d) Camillo golgi

Question. According to fluid mosaic model of the cell membrane the proteins are located
(a) In a continuous layer over the outer surface of the membrane only
(b) In a continuous layer over the inner surface only
(c) In a discontinuous arrangement, both on surface and in interior of the membrane
(d) In the middle of the membrane between the lipid layers only

Question. The fluid mosaic model explains
(a) Only structural aspects of cell membrane
(b) Only functional aspects of cell membrane
(c) Both structural and functional aspects of cell membrane
(d) Only fluidity of membrane

Question. Select the incorrect statement
(a) A membrane is a mosaic or composite of diverse lipid and proteins
(b) In 2003, the chemistry noble Prize was awarded for work on aquaporins
(c) A membrane is held together primarily by hydrophobic attraction
(d) Proteins, not lipids are responsible for fluid behavior

Question. Plasma membrane is
(a) Semipermeable
(b) Permeable
(c) Selectively permeable
(d) Impermeable

Question. Which of the following is false about osmosis?
(a) It is specific form of diffusion
(b) It refers to the movement of water along its concentration gradient
(c) It is a passive movement of water
(d) It occurs through a carrier protein and needs ATP

Question. The polar molecules
(a) Can pass through bilayers of lipid of plasma membrane
(b) Cannot pass through bilayers of lipid of plasma membrane
(c) Need carrier proteins of the membrane to facilitate their transport accross the membrane
(d) (b) and (c)

Question. Unicellular organisms are
(a) Not capable of independent existence because they cannot perform all the essential functions of life
(b) Not capable of independent existence but they can perform all the essential vital functions
(c) Are capable of independent existence and perform all the essential vital functions
(d) Are capable to lead independent existence but they perform some vital functions

Question. Cell is the fundamental structural and functional unit of all living organisms is evidenced by the fact like
(a) Anything less than a complete structure of a cell doesn’t ensure independent living
(b) Subcellular components can regenerate whole cell
(c) A cell arises by fusion of two cells
(d) Cell are totipotent

Question. Which of the following statements was not explained in the cell theory given jointly by Schleiden and Schwann?
(a) All living organisms are composed of cells and product of cells
(b) Cell is the structural and functional unit of living organisms
(c) Explanation of formation of new cells
(d) None

Question. A. The shape of cells may vary with the function they perform
B. Human RBC is about 7.0 mm in diameter
C. Cytoplasm is the main arena of cellular activities
D. Various chemical reactions occur in cytoplasm to keep the cell in living state
Options :
(a) All are correct
(b) Only A and B are correct
(c) Only D is correct
(d) All are wrong

Question. All statements are correct except
(a) The organisation of the cells is fundamentally similar
(b) Prokaryotes show a wide variety of shapes and functions
(c) Few prokaryotes have cell walls
(d) There is no well-defined nucleus

Question. Which of the following are exceptions to the cell theory?
(a) Viruses
(b) Viroid
(c) Prions
(d) All

Question. Amyloplasts – Store starch, e.g. potato
Elaioplasts – Stores oil and fat
Aleuroplast – Store proteins
The above types of plastids are included under
(a) Leucoplasts (colourless plastid)
(b) Chromoplast
(c) Chloroplast
(d) None

Question. Which of the following statements concerning prokaryotes is/are true?
(a) Because prokaryotes do not contain organelles, they cannot photosynthesize or carry out cellular respiration
(b) Prokaryotes have no chromosomes and therefore lack DNA
(c) Prokaryotic flagella are similar in structure to eukaryotic flagella
(d) None of the above

Question. Which one is correct about mesosome?
(a) A Characteristic of bacteria
(b) Infolding of cell membranes
(c) Maybe in the form of vesicles tubules lamellae
(d) All

Question. Most prokaryotic cells, particularly the bacterial cells, have
(a) A chemically simple nerve envelope
(b) A chemically complex cell envelope
(c) No cell envelope
(d) Cell envelope only in the form a cell membrane

Question. Which one is the correct about bacterial cell envelope?
(a) The outer most cell wall followed by glycocalyx and then plasma membrane
(b) The outer most glycocalyx followed by plasma membrane and then cell wall
(c) The outer most glycocalyx followed by cell wall and plasma membrane
(d) Cell envelope is chemically very simple and consists of only plasma membrane

Question. Which is mismatched pair?
(a) Capsule- thick and tough glycocalyx
(b) Slime layer- loose glycocalyx
(c) Pili- motility organ
(d) Bacterial cells- motile or non-motile

Question. In chloroplast, chlorophyll is present in
(a) Thylakoid
(b) Stroma
(c) Outer membrane
(d) Inner membrane of envelope

Question. Bacterial flagellum consists of all of the following parts except
(a) Filament
(b) Microtubule
(c) Hook
(d) Basal body

Question. Select the incorrect statement about prokaryotic ribosomes
(a) 50s and 30s subunits unite to form 70s ribosomes
(b) Polysome/polyribsome consists of many ribosomes only
(c) Ribosome is the site of protein synthesis
(d) Polysome indicate the synthesis of identical polypeptide in multiple copies

Question. The eukaryotes include
(a) Fungi
(b) Protists
(c) Plants and animals
(d) All

Very Short Answer Type Questions:

Question. Mention a single membrane bound organelle which is rich in hydrolytic enzymes.
Ans. Lysosomes are the membrane bound vesicular structures formed by Golgi apparatus.
These vesicles on isolation have been found to be rich in all types of hydrolytic enzymes i.e., hydrolase, lipases, proteases and carbohydrases which digest carbohydrates proteins,
lipids and nucleic acid at acidic pH.

Question. What is the function of a polysome? (Gk. Poly = many, Soma = body).
Ans. A polysome consist of a cluster of ribosomes that are held, simultaneously by a strand of messenger RNA (mRNA) in rosette or helical group.They contain a portion of the genetic code that each ribosome is translating and are used in formation of multiple copies of same polypeptide. They are found in the cytoplasm during the process of active protein
synthesis.

Question. What is referred to as satellite chromosome?
Ans. The chromosomes may have additional constriction or secondary constriction at their ends as distal part of the arm formed by chromatin thread are known satellite chromosome.
These constriction gives appearance of an out growth or small fragment.
These are also known as (sat) chromosomes or marker chromosome number.
Chromosome 13, 14, 15, 16, 21 and 22 are satellite chromosomes.

Question. What is the feature of a metacentric chromosome?
Ans. In metacentric chromosome centromere is median, i.e., centromere lie in the middle portion. Thus, forming two equal arms of chromosome.

Question. What is the significance of vacuole in a plant cell?
Ans. The vacuole is a membrane bound space found in the cytoplasm. It contain water, sap, excretory product and other materials that are not seful for the cell. In plants osmosis vacuoles occupy 90% of the volume of the cell. They help in maintaining cell fluid balance, and shape of the cell by maintaining turger pressure against the cell well.

Question. What are gas vacuoles? State their functions.
Ans. Gas vacuoles are also known as pseudovacuoles or air vacuoles. Gas vacuoles are the characteristic feature of prokaryotes reported only in prokaryotes. Each gas vesicles are made of sub-microscopic hexagonal vesicles and are surrounded by a thin protein membrane. Gas vacuoles store metabolic gases and take part in buoyancy regulation.

Question. What does ‘S’ refer in a 70S and 80S ribosome?
Ans. ‘S’ refers to Svedbergs unit for sedimentation coefficient. Sedimentation coefficient depicts that how fast a cell organelle sediments during the ultracentrifugation.
In cells heavier the structure, higher is the sedimentation coefficient.
The value of S is equal to 10⁻¹³ seconds (1 s = 1 x 1 seconds) × =⁻¹³.

Short Answer Type Questions:

Question. Comment on the cartwheel structure of centriole.

Ans. (d) Centrosome is an organelle usually containing two cylindrical structures called centrioles. They are surrounded by amorphous pericentriolar materials both the centriole in centrosome lie perpendicular to each other in which each has an organisation like that of an ‘cartwheel’.
A centriole possess a whorl of 9 peripheral fibrils. There fibrils are absent in the centre, hence the arrangement is called 9 + 0. Each fibrils is made of 3 sub-fibres. Therefore, called triplet fibril.
The centrioles form the basal body of cilia and flagella. It also forms spindle fibres that gives rise to spindle apparatus during cell division in animals.

Question. What are histones? What are their functions?
Ans. Histones are the basic group of globular proteins that have a high content of basic amino acis, i.e., arginine and lysine. Histones forms the part of the chromosomal material in eukaryotic cells.
There are five types of histone proteins H₁, H₂ A , H₂ B, H₃ and H₄. Four of them (H₂A ,H₂B ,H₃ and H₄) occur in pairs to produce histone octamer called Nubody or core of nucleosome.
Functions Histones bear positively charged ends, that attaract negetively charged strands of DNA.
Histones provides a medium around which DNA winds, and they play a vital role in gene regulation, as they act as gene repressor. They form the chromatin material and provide stability as are not coagulated by heat.

Question. Briefly describe the cell theory.
Ans. Schleiden and Schwann in 1838-39, formulated the cell theory, which originally contained following two statements
(i) All living beings are made up of cells and products formed by the cells.
(ii) Cells are the structural and functional units of life.
The cell theory stated by Schleiden and Schwann failed to explain the question of origin of cells. A major expansion of the cell theory was expressed by Virchow in 1855, in his statement ‘Omnis cellula e cellula’ (all cells arise from pre-existing cells).This concept, was the actual idea of Nagelli (1846), which later on was elaborated by Virchow, along with considerable evidences in its support. The work of Nagelli and Virchow established cell division as the central phenomenon in the continuity of life.
Thus, the modern cell theory is based on two facts
(i) all living organisms are composed of cells and products of cell.
(ii) cells are the bosic structural and functional unites of life.
(iii) all cells arise from pre-existing cells.
Viruses are exception to cell theory as they are not composed of cell. They consist of a nucleic acid (DNA or RNA) surrounded by a protein sheath and are incapable of independent existence, self regulation and self reproduction.

Question. Differentiate between Rough Endoplasmic Reticulum (RER) and Smooth Endoplasmic Reticulum (SER).
Ans. Difference between Rough Endoplasmic Reticulum (RER) and Smooth Endoplasmic Reticulum (SER) are as below

RER (Rough Endoplasmic Reticulum)	SER (Smooth Endoplasmic Reticulum)
1. RER possesses ribosomes attached to its surface.	SER does not bear ribosomes attach to their surface.
2. Mainly formed of cisternae and few tubules.	Mainly formed of vesicles and the tubules.
3. RER takes part in the synthesis of proteins and enzymes.	SER takes part in the synthesis of glycogen, lipids and steroids.
4. RER is internal and connected with nuclear envelope.	SER is peripheral. It may be connected with plasmalemma.
5. It may develop from the nuclear envelope.	It may develop from RER.
6. Enzymes for detoxification are absent in RER	It has the enzymes for detoxification.
7. It forms lysosomes through the agency of Golgi apparatus.	SER gives rise to sphaerosomes.

Question. Discuss briefly the role of nucleolus in the cells actively involved in protein synthesis.
Ans. Nucleolus is the round, naked and a slightly irregular structure, which is attached to the chromatin at a specific region called as Nucleolar Organizer Region (NOR)
Nucleolus was first discovered by Fontana (1781).

(i) Nucleolus is the chief site for the ribosomal RNA synthesis.
(ii) It is the centre for the formation of ribosome components.
(iii) It is the colloidal complex that fills the nucleus.
(iv) It combines rRNA with proteins to produce ribosomal sub-units. After their formation, the ribosomes sub-units pass out and get established in the cytoplasm.
(v) It also receive and store ribosomal proteins formed in the cytoplasm.
(vi) These ribosomal proteins formed are the sites for protein synthesis in the cell.
(vii) Nucleolus is essential for spindle formation during nuclear division.

Question. Give the biochemical composition of plasma membrane. How are lipid molecules arranged in the membrane?
Ans. Chemical composition of plasma membrane

Lipids are the major components of the cell membrane as they form the continuous structural frame of the cell membrane. Lipids such as phospholipids, glycolipids, and steroids are found in membranes.

The lipid molecule possess both polar hydrophilic (water loving) and non-polar hydrophobic (water repelling) ends. The hydrophilic region is in the form of a head, while the hydrophobic
part contains two tails of fatty acid.
Hydrophobic tail is present towards the centre of the membrane. This structures results is the formation of lipid bilayer known as unit membrane/biological membrane/cell membrane.

Question. What are plasmids? Describe their role in bacteria.
Ans. A plasmid is usually a circular (sometime linear), double strandad DNA, that can replicate itself autonomously. These are found in the cytoplasm of the bacterial cell, plasmids normally remain separated from the chromosome, but sometimes may integrate into it temporarily and replicate with it incidentally.
Role of Plasmids in Bacteria
Plasmids are the extrachromosomal circular, independently replicating unit besides nucleoid in the bacterial cell.
Plasmids are used to transfer the information from one cell to another, i.e., transfer of important genes (e.g., they may confer resistance of particular, antibiotics to their bacterial cells), enabl to metabolise a nutrient, which normally a bacteria is unable to. It also helps in conjugation of bacteria. These days, plasmids are used in a variety of recombination experiments, as cloning vectors. A such example of plasmid vector is given below in figure.

Question. Explain the association of carbohydrate to the plasma membrane and its significance.
Ans. Sugar residues or carbohydrates attaches either with proteins or lipids usually making up less than 10% of the membrane weight, they can give rise to a wide variety of structures in relatively short chains. They give individual cell types a distinguishing features. Therefore, they may be involved in.
Cell Recognition e.g., surface of RBC have carbohydrates arranged in branched chains:
differences in the arrangement give rise to different blood group antigens (i.e., AB and O).
Cell surface differences are also responsible for the specificity of action of cells with hormones, drugs, viruses or bacteria. The cause of cell surface differences is related to characteristic surface due to carbohydrate component.

Long Answer Type Questions:

Question. Write the functions of the following
(a) Centromere (b) Cell wall
(c) Smooth ER (d) Golgi apparatus
(e) Centrioles
Ans. (a) Centromere It is required for proper chromosome segregation. The centromere consists of two sister chromatids. It is also necessary at the point chromosome attaches to the spindle apparatus during mitosis and meiosis.
(b) Cell wall It gives a definite shape to the cell and protects the cell from mechanical injury and infections. It also helps in cell to cell interaction and act as a barrier for undesirable
macromolecules.

(c) Smooth ER It helps in synthesis of lipids, metabolism of carbohydrates, regulation of calcium concentration, drug detoxification and attachment of receptor on cell membrane proteins.
The smooth ER also contain enzymes-glucose 6 phosphatase, which converts glucose 6 phosphate to glycogen, essential in glucose metabolism.

(d) Golgi apparatus It is the important site for the formation of glycoprotein and glycolipids.
It is also involved in the synthesis of cell wall materials and also play an important role in formation of cell plate during cell division.

(e) Centrioles They form the base body of cilia and flagella and spindle fibres that gives rise to spindle apparatus during cell division in animal cells. They help in formation of microtubules and sperm tail. They also help in cell division by forming asters, which acts as spindle pole.

Question. Structure and function are correlatable in living organisms. Can you justify this by taking plasma membrane as an example?
Ans. In animals and plants, plasma membrane structure and function are correlated. A cell membrane consists of protein, lipid and carbohydrates.
The protein component present in membrane acts as a solute channels allowing the flow of minerals, hormones and cellular information from one organelle to another or from one cell to another.
In case of plants where minerals are absorbed actively from the soil. The plasma membrane possess proteinaceous carrier.
The oligosaccharides attached to membrane serve as recognition centres and help in recognising foreign entities before allowing them entry into the cell.
The lipid content of plasma membrane in plant and animal cells are arranged with their hydrophilic polar head directed outwards and non-polar hydrophobic tails directed inwards providing fluidity to the membrane. Glycocalyx present in cell membrane also helps in cellular attachment.

Question. What structural and functional attributes must a cell have to be called a living cell?
Ans. All organisms are made up of cells, which further organises themselves into tissues, organs and organ systems. Thus, forming the building blocks of organisms cells also the property of totipotency, capable of developing into a new organism.
Besides, forming the structural unit they perform different specialised functions in the same way as each organ or system carries out in an organism. Thus, exhibiting division of labour i.e., cell organelles are specific in their functions.

Question. Is there a species specific or region specific type of plastids? How does one distinguish one from the other?
Ans. Plastids are species specific and are found in all plant cells and in euglenoids. They bear some specific pigments thus, imparting specific colours to the part of the plant which
possess them. Based on the type of pigments plastids are classified into three main types, i.e., leucoplasts, chromoplasts and chloroplasts.
Leucoplasts They are colourless plastids which store food material based on there storage products, they are of three types
(a) Amyloplasts Stores starch, e.g., tuber of potato, grain of rice, grain of wheat.
(b) Elaioplasts These store fats, e.g., rose
(c) Aleuroplasts They are protein storing plastids, e.g., castor endosperm 
Chromoplast These are non photosynthetic coloured plastids which synthesise and store carotenoid pigments. They appear orange, red or yellow. These mostly occur in ripe fruits (tomato and chilles) carrot roots, etc.
Chloroplasts These are green colour plastids which help in synthesising food material by photosynthesis. They contain chorophyll and carotenoid pigments which trap light energy.
Each chloroplast is oval or spherical, double membrane bound cell organelle.
The space present inside inner membrane is called stroma. A number of organised flattened membranous sacs called thylakoids are present in the stroma. Thylakoids are arranged in
stacks are called grana.
The thylakoids of different grana are connected by membranous tubules called the stroma lamellae. The stroma of the lamellae contain the enzymes that are required for the synthesis
of carbohydrates and proteins.

Question. Eukaryotic cells have organelles which may
(a) not be bound by a membrane
(b) bound by a single membrane
(c) bound by a double membrane
Group the various sub-cellular organelles into these three categories.
Ans. (a) Cell organelles with no membrane In eukaryotic cell, ribosomes occur freely in the cytoplasmic matrix and are attached to the outer cytoplasmic surface of the rough endoplasmic reticulum and nuclear envelope. The ribosomes are also found in the matrix of mitochondria and stroma of plastids called as mitoribosomes and plastidoribosomes, respectively.
(b) Cell organelles with single membrane A lysosome is a tiny sac bounded by a single unit membrane of lipoprotein. The lysosomes occurs in all animal cells and protozoans.
Prokaryotic cell lack lysosomes.
Number of lysosomes varies with the cell type. Lysosome contain a dense, finely granular fluid consisting of glycoproteinaceous hydrolytic (digestive) enzymes called acid hydrolases. Cell organelles like sphaerosomes and microbodies also possess single membranes.
(c) Cell organelles with double membrane Mitochondria are double membrane bound structures with the outer membrane and inner membrane dividing its lumen distinctly into two aqueous compartments.
The inner compartment is called the matrix whereas the outer membrane forms the continuous limiting boundary of the organelle. Chloroplast and nucleus are also double membrane bound organelles.

Question. The genomic content of the nucleus is constant for a given species where as the extrachromosomal DNA is found to be variable among the members of a population. Explain.
Ans. In bacteria, additional to the genomic DNA, small circular DNA molecules are present in cytoplasm. These small molecules are called plasmids. They confer unique phenotypic character to bacteria, i.e., resistance to antibiotics. It is also used to monitor bacterial transformation with foreign DNA.
In eukaryotes, the extra DNA molecules are present in chloroplast (stroma) and mitochondria (matrix). Because of the presence of this DNA molecule, they are treated as self autonomous organelles. In case of highly active organism, the DNA extrachromosomal is found to be more as compared to the less active ones.

Question. Briefly give the contributions of the following scientists in formulating the cell theory
(a) Rudolf Virchow
(b) Schleiden and Schwann
Ans. (a) Rudolf Virchow (1855) first explained that the cells divide and new cells are formed from the pre-existing cells (omnis cellula e cellula).
Virchow was the first to demonstrate that the cell theory applies to diseased tissue as well as to healthy tissue. He also engaged his research in the fields of archeology and anthropology.
(b) Schleiden and Schwann observed the cells and cell membranes for the first time. They proposed the cell theroy which explains that the animal and plant cells are composed of cells and product of cells.
Theodore Schwann (1839) studied different types of animal cells and reported that cells had a thin outer layer which is called as plasma membrane. Schleiden also concluded on plant studies, i.e., the presence of cell wall is a unique character of plant cells. Thus, they proposed that plants and animals are composed of cells and their products.

Question.Justify the statement, ‘Mitochondria are power houses of the cell’.
Ans. Mitochondria is a sausage shaped or cylindrical structure having a diameter of 0.2 to 1.0 μm and length 1.0 – 4.1 μm. Each mitochondrion is a double membrane bound structure
with outer membrane and inner membrane dividing its lumen distinctly into two aqueous compartments.
The inner compartment is called matrix and outer one forming infoldings is called cristae towards the matrix. These cristae are associated with an increase in surface area.
The mitochondria are the actual sites of aerobic respiration. They produce cellular energy in the form of ATP, hence are called as power house of the cell.

This ATP generated is used in performing vital functions by the organism. The matrix of mitochondria also possess a single circular DNA molecule of itself and a few RNA molecules, ribosomes (70S) and the compartments required for the protein synthesis.

Question. Are the different types of plastids interchangeable? If yes, give examples where they are getting converted from one type to another.
Ans. Yes, plastids are interchangeable in their form. Generally, three types of plastids are present in plant cells, i.e., leucoplasts (storage), chromoplast (coloured) and chloroplasts (synthesis of food green pigment).
Depending upon the circumstances, one type of plasmid may be converted into another type. e.g.,
(i) In Capsicum, the cells of ovary consist of leucoplasts. When ovary changes into fruit, leucoplasts are transformed into chloroplasts. When the fruit ripens chloroplast are converted into chromoplast.
(ii) The leucoplast in stem tubers of potato, on exposure to sunlight transform to chloroplasts.
In some cases the chloroplasts gets converted during ripening of fruits, e.g., tomato chilli when they change colour from green to red. In occurs because of chlorophyll and degeneration of lamella.

Question. Is extragenomic DNA present in prokaryotes and eukaryotes? If yes, indicate their location in both the types of organisms.
Ans. Yes, extragenomic DNA is present in both prokaryotes and eukaryotes. In case of eukaryotes, extragenomic DNA is present in two organelles, e.g., plastids and mitochondria.
Extrachromosomal DNA in Prokaryotes In case of prokaryotic cells, the extragenomic DNA is present in the form of plasmids. The plasmid are circular DNA molecules, which confer certain unique phenotypic characters to the bacteria.
One such character is antibiotic resistance to bacteria. The plasmid DNA is also used to monitor bacterial transformation with foreign DNA. Bacteria transformation is the method of sexual reproduction in bacteria.
Extrachromosomal DNA in Eukaryotes
Mitochondrial DNA (mtDNA) is usually circular. Mitochondrial DNA spans about 16,500 DNA building blocks (base pairs) representing a small fraction of the total DNA in cells.
mtDNA contains 37 genes, all of which are essential for normal mitochondrial functions.
Thirteen of these genes provides instruction for making enzymes involved in oxidative phosporylation.
Mitochondrial genes are among the estimated 20000-25000 total genes in the human genome.
Plastids These are small bodies found free in most plant cells and are of three types leucoplast, chromoplast and chloroplast. These are double membrane bound structures for trapping radiation and storage purpose.
It contains small, double stranded circular DNA molecules and ribosomes essential in synthesising certain proteins. As they both can synthesise proteins and replicate on their own they are known as semi-autonomous organelles.