The Fundamental Unit Of Life - Class 9 Biology - Extra Questions

Name the cell part which is
composed of cellulose

The cell wall is composed of cellulose.


If a cell has a membrane bound nucleus it is known as ___cell.

A cell is defined as eukaryotic if it has a membrane-bound nucleus. In a prokaryotic cell, there is no well-defined nucleus and it is called an incipient nucleus. 
So, the correct answer is "eukaryotic".
Eukaryotic Cell - The Definitive Guide | Biology Dictionary


________ are bigger when compared with prokaryotic cells.

Eukaryotic cells are bigger than prokaryotic cells as they are more advanced and developed containing a well-defined nucleus and other cell organelles.


Describe the structure of nucleus.

The nucleus is a sphere-shaped organelle found in eukaryotic cells. It contains the genetic material of the cell in the form of nucleic acids. It is responsible for controlling all activities of the cell. and contains a nuclear membrane, chromosomes, nucleolus and nucleoplasm.
660028_568396_ans_f5476f2d0fd44871aeb31dae7aaf6578.PNG


Given below are groups of terms. In each group, the first pair indicates the relationship between the two terms. Rewrite and complete the second pair on a similar basis.
Example : Oxygen : Inspiration : : Carbon dioxide : Expiration
Cytoplasm : Cytokinesis : : Nucleus : _________

The physical process of cell division in which the cytoplasm of a parental cell is divided into two daughter cells is called cytokinesis. 
The process of division of the nucleus of a cell during the phase of cell division (mitosis or meiosis) is called karyokinesis.
So, the correct answer is - Cytoplasm : Cytokinesis :: Nucleus : Karyokinesis


Short / Long answer type questions.
What are the two principal roles of the nucleus? What biomolecule is responsible for these roles?

The nucleus contains the genetic material of an organism and controls and regulates all the functions of the rest of the cell organelles. The nucleic acids present in the nucleus confer it its properties, functions, and roles.


Fill in the blanks with appropriate words.
The two types of nuclei in Paramecium are the ..........,which controls normal cellular metabolism, and the .........., which is involved in reproduction.

The two types of nuclei in Paramecium are macronucleus which controls normal cellular metabolism and the micronucleus that is involved in reproduction. 


Introduce a prokaryote and a eukaryote, giving an example of each.

The prokaryotic cell lacks membrane bound organelles and the genetic material, DNA, is not organised into distinct chromosomes. Whereas the eukaryotic cell contains membrane bound organelles and the DNA is located in chromosomes. The cells of bacteria and cyanobacteria are examples of prokaryotic cells, whereas the cells of all organisms other than bacteria and cyanobacteria are eukaryotic like plant and animal.


Very short answer type.
Name a cell that has many nuclei.

Rhizopus is a genus of saprophytic fungi on plants. They are also parasitic to man. They usually have more than two nuclei in their cells and those nuclei are not separated by walls between them.


Fill in the blanks with appropriate words.
S.J. Singer and G.L. Nicholson (1972) introduced the .......... to explain the structure of cell membrane

Fluid Mosaic Model


Differentiate between the following pairs of terms:
Nucleolus and nucleus.

 Nucleolus Nucleus
 1. It is a sub organelle of nucleus present inside it. 1. The large spherical body inside a cell is called nucleus.
 2. It is not bounded by a nuclear membrane. 2. It is bounded by a double layered nuclear membrane.
 3. It doesn't contain any Chromosomes but is rich in RNA. 3. It is rich in DNA and chromosomes.
 4. It controls the arrangement of ribosomes and involved in RNA metabolism.
 4. It controls cellular functions and inheritance.

2141204_833177_ans_fd3efa938d314d1aafa3dd7994d3cbd7.png


Draw the detailed structure of the Nucleus.

The nucleus is the major part of a eukaryotic cell, that contains the genetic material. The genetic material is found inside the nucleus in the form of chromatin fibres or chromosomes. Each nucleus remains enclosed in a nuclear membrane or nuclear envelope. It is a double membrane surrounding the nucleus. It has some minute pores called the nuclear pore. It contains another structure called the nucleolus, which is a small dense spherical structure. 

1097922_1006728_ans_0bc93c9ef83a4377b9b421bb725c6a7b.jpeg


Draw a nucleus and label its parts. What is the function of nucleus in a cell ?

The main function of the nucleus is to control gene expression as it contains genetic material. It controls the hereditary characteristics of an organism. It also regulates cell metabolism and growth.  
996728_1091491_ans_17c5486060394b889bfd32fbb5b43bfa.png


Name the positively charged & negatively charged components of the nucleosome.

 A nucleosome is composed of histone protein and DNA. DNA carries the negative charge due to the phosphodiester linkage and histone is basic in nature and carries a positive charge because histones are made up of basic amino acids. DNA wrapped around the histone octamer (H2A-H2B, H3, H4 two copies of each) through the H- bonding. So, the negatively charged component of the nucleosome is DNA and the positively charged components of nucleosomes are histone octamer.


Draw a well labelled diagram of nucleus.

  • The nucleus is considered as the director or controller of the cell. 
  • The nucleus is a double membrane-bound organelle. The nuclear envelope consists of two membranes, an outer membrane, and an inner membrane.
  • The nuclear membrane is perforated by apertures known as nuclear pores.
  • Nuclear membranes surround the cytoplasm of nucleus known as nucleoplasm. DNA is present in nucleoplasm in the form of chromatin. When the cell prepares to divide, the chromatin condenses and thickens into chromosomes.
  • Within the nucleus is present a spherical body known as nucleolus which is closely associated with nucleolar organizer region of two or more chromosomes of the set.

1009201_1084054_ans_f524a9b8a9584f2799c356c2eaf0bf7e.png


What is the characteristic of nuclear envelope?

The nuclear envelope is also called nuclear membrane, is a double membrane layer that separates the contents of the nucleus from the rest of the cell. It is a barrier that physically protects the cells DNA from the chemical reactions that are occurring elsewhere in the cell. The envelope also contains a network of proteins that keep the genetic material in place inside the nucleus.


Name the different types of endoplasmic reticulum.

There are two types of endoplasmic reticulum – rough endoplasmic reticulum (RER) and smooth endoplasmic reticulum (SER). RER looks rough under a microscope because it has particles called ribosomes attached to its surface. The ribosomes, that are present in all active cells, are the sites of protein manufacture. The manufactured proteins are then sent to various places in the cell depending on the need. The SER helps in the manufacture of fat molecules, or lipids, important for cell function.


Describe the structure of the controlling centre of the cell.

Nucleus is considered as the director or controller of the cell. The various structural components of nucleus are:
  • Nuclear membrane: Nucleus is a double membrane-bound organelle. The nuclear envelope consists of two membranes; an outer membrane and an inner membrane that are separated by perinuclear space. The nuclear membrane is perforated by apertures which are called nuclear pores.
  • Nucleoplasm: It is interior fluid just like the cytoplasm, which is enclosed by the nuclear membrane.
  • Nucleolus: The spherical body within the nucleus is placed centrally or peripherally in close association with the nucleolar organizer region of chromosomes. It is the site of RNA synthesis. 
  • Chromatin: The organization of DNA and proteins inside the nucleus. When the cell prepares to divide, the chromatin condenses and becomes thick to form specialized structures called chromosomes. 

1018505_1091311_ans_a216318420c84434b093224c63800d7b.png


Write short note on nucleus.

Definition:
  • In cell biology, nucleus is a membrane-bound organelle found in all eukaryotic cells except mammalian red blood cells, which have no nuclei. 
  • Nucleus is composed of the nuclear envelope and a nuclear matrix.

    Functions:
  • Nucleus helps in maintaining the security of the genes
  • It controls the functions of the cell by regulating gene expression
  • It controls the hereditary traits of the organism
  • Furthermore, it stores DNA strands and proteins
  • The nucleus is the site of RNA transcription
  • It governs gene expression and also facilitates DNA replication.
  • It also controls the synthesis of enzymes.

2150195_1061376_ans_9df48637fb13457c8eb10018894060c2.png


Write short note on : Cytoplasm and Nucleus.

  • The jelly-like fluid that fills a cell is called cytoplasm. It is made up of mostly water and salt.
  • Cytoplasm is present within the cell membrane of all cell types and contains all organelles and cell parts. Most of the important activities of the cell occur in the cytoplasm.
  • Cytoplasm contains molecules such as enzymes that are responsible for breaking down waste and also aid in metabolic activity. 
  • Cytoplasm is responsible for giving a cell its shape. It helps to fill out the cell and keeps organelles in their place. Without cytoplasm, the cell would be deflated and materials would not be able to pass easily from one organelle to another. 
  • Cytosol is the part of the cytoplasm that does not contain organelles. 

  • The nucleus is a membrane-bound structure that contains the cell's hereditary information and controls the cell's growth and reproduction. It is commonly the most prominent organelle in the cell.
  • The nucleus is surrounded by a structure called the nuclear envelope. This membrane separates the contents of the nucleus from the cytoplasm. 
  • The outer membrane usually remains continuous with the endoplasmic reticulum and also bears ribosomes on it. At a number of places, the nuclear envelope is interrupted by minute pores, which are formed by the fusion of its two membranes. 
  • These nuclear pores are the passages through which the movement of RNA and protein molecules takes place in both directions between the nucleus and the cytoplasm. 
  • The cell's chromosomes are also housed within the nucleus. Chromosomes contain DNA which provides the genetic information necessary for the production of other cell components and for the reproduction of life.


Give the functions of Nucleus.

Functions of the Nucleus include-
  • They serve as the control centre of the cell.
  • They encapsulate and protect the hereditary material which is DNA.
  • They are sites for the synthesis of ribonucleoproteins.
  • The nucleus is also the site for ribosome assembly.


In a cell, genes are located in ______.

In cells, genes are located in the chromosomes within "nucleus".


What is the significance of pores present on the nuclear membrane? 

The pores present on the nuclear membrane allow transport of water-soluble molecules across the nuclear envelope. RNA and ribosomes move out of the nucleus, whereas carbohydrates, lipids, and proteins move into the nucleus.


Difference between Prokaryotic cell and Eukaryotic cell.

 Prokaryotic cell Eukaryotic cell
They lack a well-defined nucleus, have a nucleoid instead.Have a well-defined nucleus enclosed in the nuclear membrane.
Usually have double-stranded, circular DNA.Have a linear double-stranded nucleus.
Do not have mitochondria. Mitochondria are present.
Have 70S ribosomes.Have 80S ribosomes.
Golgi apparatus and endoplasmic reticulum also absent.They do have Golgi apparatus and endoplasmic reticulum.


Name the organelle which shows the analogy as written below:
Control room of the cell.

Control room of the cell is the nucleus. It guides the cells to carry out various metabolic processes.


Why is it said that, "a cell without a nucleus is without any future"

The genetic material or DNA is present inside the nucleus in the form of chromosomes. Only when this DNA replicates, does the cell divide to form new cells. The functional units of this DNA, also known as genes , are responsible for the synthesis of proteins. Thus, the nucleus is very important for cellular reproduction and all the other developmental processes of a cell, without which the cell cannot have a stable future. Due to this it is said that, " a cell without a nucleus is without any future".


The undefined nuclear region of prokaryotes are also known as:
A. Nucleus
B. Nucleolus
C. Nucleic acid
D. Nucleoid

In a prokaryotic cell, The genetic material is accumulated indefinitely in a region called nucleoid and is not surrounded by a nuclear membrane. Prokaryotes are the most primitive organisms and hence they do not have well-developed nucleus and other membrane-bound organelles.
So, the correct option is 'Nucleoid'.



Read the following statements and write the appropriate term against each statement.
A. I control the functions of a cell. Who am I? ________
B. I am like a policeman. I do not allow anything and everything to get in and out of the cell. Who am I? _______ 
C. I transfer characters from parents to offsprings. Who am I?

A. I control the function of a cell.
I am the nucleus
B. I am like a policeman. I do not allow anything and everything to get in and out of the cell.
I am the cell membrane
C. I transfer characters from parents to offsprings.
I am genes .


Name the parts labelled 1 and 3.
1540791_5c9da593cb564be3b9c91eb71bcfb0e8.JPG

  • The given diagram of the anaphase stage of mitosis division labeled 1, 2 and 3.
  • Labeling 1 represents chromosomal fibres or kinetochore fibres. These fibres provide a site for attachment of spindle fibers to pull apart the sister chromatids.
  • Labeling 1 represents centriole. The centriole is a tube-like structure and is made of tubulin protein which is mainly found in the animal cell.
  • Labeling 1 represents a chromosome. The chromosome is a long DNA molecule with has the genetic material of an organism. 


Explain cell division? 

 The German biologist Walter Flemming was the first who observed the process of cell division. and gave it the term mitosis. A cell division is a process by which a single cell multiplies in number. A growing cell undergoes interphase (a period of non-apparent division) and the period of division. In interphase, cell doubles in size and chromosomes duplicate. Therefore, cell division can be considered a process of ensuring exact duplication of cellular information and its  distribution to the daughter cells. Thus, the two type of cell divisions observed, are mitosis and meiosis. 


Give functions.

Nucleus

Functions of the nucleus: 
• It is the control centre of a cell as it controls all the activities of the cell. 
• It also contains gene-containing chromosomes which are the units of inheritance in an organism. 


In plants during cell division, cytoplasm is divided in which phase? 

The division of cytoplasm occurs after karyokinesis in the cytokinesis phase of mitosis. 


How is a prokaryotic cell different from a eukaryotic cell? 

 Prokaryotic cell Eukaryotic cell
 1. They are generally small in size (1-10 micrometer). 1. Eukaryotic cells are comparatively larger in size.
 2. 70S type ribosome is present. 2. 80S type ribosome is present.
 3. It lacks any membrane bound organelles, i.e., ER, Golgi body, mitochondria etc, are absent. 3. It is characterized by presence of membrane bound organelles. 
 4. Nuclear matter is undefined without any nuclear membrane and is called as nucleoid.

Example- Bacterial cell		 4. A true nucleus with nuclear membrane is present. 

Example- Plant cell and Animal cell


Describe the structure and function of the nucleus?

Robert Brown in 1831 discovered the nucleus in the cell.
Structure: The nucleus is of large size, more dense, spherical or oval and prominent organelle of the cell.
The structure of the nucleus can be divided into three parts:
1. Nuclear membrane: Nucleus is enclosed by a double-layered nuclear membrane. In bacteria and blue-green algae, the nuclear membrane is not found. 
2. Nucleoplasm: In nucleus is present a thick jelly-like semi-fluid nucleoplasm. In nucleus a network of fine thread-like structures called chromatin network is present. At the time of cell division, the chromatin forms  structures called chromosomes. The number of chromosomes is fixed for every species of animals and plants. The man has 23 pairs of chromosomes. Wheat has 21 pairs of chromosomes. The two partners of chromosomes pair are called homologous chromosomes.
$$\to$$ Chromosomes: Chromosomes are composed of specific proteins and a nucleic acid called Deoxyribose Nucleic Acid (DNA) Genes are segments of DNA. Genes control and carry the hereditary characters.
3. Nucleolus: Nucleolus contains RNA, commonly there is a single nucleolus, but two or more may be present. The nucleolus is the seat for the synthesis of cytoplasmic Ribosomes. During cell, division nucleolus disappears in early stages and reappears on the same location in the daughter nuclei.

The functions of the nucleus are as follows: 
1) The nucleus controls the activities of the cell, through its DNA molecule.
2) The main function of the nuclear reticulum is participation in cell-division.
3) Genes are located in a linear fashion in chromosomes. The genes are composed of DNA. Genes control and carry the hereditary characters from one generation to another generation.
4) Nucleolus assists in protein synthesis. Formation of ribosomes takes place in the nucleolus.  
2035469_1838285_ans_c86784d89e7142f1ac5bdb8e439f6cd4.png


Discuss briefly the role of nucleus in the cells actively involved in protein synthesis.

The nucleus contains the genetic material which gets translated into different proteins. The site for active ribosomal RNA (rRNA) synthesis is the nucleolus present in the nucleus. Ribosomal RNA is processed further to make subunits of ribosomes. Eventually. the ribosomes take part in protein synthesis. Thus. nucleolus plays an important role in protein synthesis. 


Between a prokaryote and a eukaryote, which cell has a shorter cell division time? 

A Prokaryotic cell has a shorter cell division time. Example, E. coli has a division time of 20 mins.


What is the role of mitosis and meiosis in the development of an organism?

Mitosis is the process by which one cell divides to form two cells leading to the growth of an organism. Meiosis results in the conversion of a diploid number of chromosomes to a haploid number so that daughter cells receive an equal amount of the genetic material from the parent. 


Name the cell part which is formed of an irregular network of tubular membranes.

The Endoplasmic reticulum is formed of an irregular network of membranous tubules


Which cell organelle is the key to the life of a cell?

The nucleus is the key to the life of a cell. It regulates the functions of the cell. It contains genes, which control heredity characters and governs critical life processes such as reproduction and growth of the cell. It functions as a control centre.


Name the part of the cell in which:
A network of chromatin fibers occurs.

The site in the cell where a network of chromatin fibers occur is the nucleus.


Name the part of the cell in which:
Cellulose forms the main component.

Cellulose forms the main component of the cell wall in a plant cell.


Identify $$A,B,C,D$$ and $$E$$ in the given figure.
2018189_1e28b6631069498c9be21224aa085e90.png

Answer:
A - Centriole: Two centrioles are found in every mammalian cell. During cell division, they aid the cell.
B - Smooth endoplasmic reticulum: Smooth ER is also in charge of steroid hormone synthesis and secretion.
C - Golgi apparatus: The packaging and secretion of proteins is its primary function. Endoplasmic Reticulum provides it with proteins.
D - Ribosomes: Ribosomes are macromolecular machinery that perform biological protein synthesis and are found in all living cells.
E -Rough endoplasmic reticulum: It synthesizes and secretes proteins in the liver, hormones and other substances in the glands.



Describe the structure of the following with the help of labelled diagrams.
(i) Nucleus
(ii) Centrosome

(i) Nucleus
The nucleus is a double wall membrane structure. It regulates the cellular activities . It constitutes the following parts-
Nuclear membrane : It is a double membrane separating the contents of the nucleus from the cytoplasm. The narrow space between the two membranes is called the perinuclear space. Nuclear membrane has tiny holes called nuclear pores. These holes allow specific substances to be transferred into a nucleus and out from it.
Nucleoplasm/Nuclear matrix : It is a homogenous granular fluid present inside the nucleus. It contains the nucleolus and chromatin. The nucleolus is a spherical structure that is not bound by any membrane. It is rich in protein and RNA molecules and is the site of ribosome formation. Chromatin is an entangled mass of thread-like structures. It contains DNA and some basic proteins called as histones.
(ii) Centrosome
Centrosome has two cylindrical structures called centrioles. Each has a cartwheel-like organisation. A centriole is made up of microtubule triplets in a ring. The adjacent triplets are linked together. There is a proteinaceous hub in the central part of a centriole. The hub is connected to the triplets via radial spokes. These centrioles help in organising the spindle fibres and astral rays during cell division. They form the basal body of cilia and flagella as well.

388005_424429_ans.png


Does nucleoplasm possess cyclosis?

Cyclosis is streaming of cytoplasm within a living cell without deformation of the external cell membrane. A cell  structure has two main parts, nucleoplasm, and cytoplasm
Nucleoplasm is a type of protoplasm that is made up mostly of water, various molecules, and dissolved ions. It is a gel-like sticky material covered by nuclear envelope and supports the chromosomes and nucleoli. It does not have cyclosis or streaming.Cytoplasm has an outer plasma membrane, number of organelles and the fluid part containing minerals, sugars, and proteins. It forms a bulk of cell and is in constant motion or cyclosis to carry out different metabolic activities of cell function.


Which organelle is known as the powerhouse of the cell? Why. 

Mitochondria is known as powerhouse of the cell because Mitochondria are tiny organelles inside the cells that are involved in in releasing energy from food. This process is know as cellular respiration.The energy released is in the form of adenosine triphosphate (ATP).



Give the differences between cytoplasm and nucleoplasm.

Cytoplasm
1.    It is present inside the cell
2.    Enclose by the cell membrane.
3.    It is found in all cells
4.    It is a fluid mass of the cell which is composed of cell organelles.
5.    It is the site of ribosome functioning.
6.    It is divided into two cells during cytokinesis.    

Nucleoplasm
1.    It is present inside the nucleus
2.    Enclosed by the nuclear membrane.
3.    It is found only in eukaryotic cells.
4.    It is the sap of the nucleus which contains the nucleolus.
5.    It is the site of ribosome formation.
6.    It is released during nuclear division and refilled after the formation of the nuclear membrane.


Write a start note on : Cytoplasm & Nucleus

  • Cytoplasm: The jelly-like fluid that fills a cell is called cytoplasm. It is made up of mostly water and salt. Cytoplasm is present within the cell membrane of all cell types and contains all organelles and cell parts.
  • Nucleus: It stores the cell's hereditary material or DNA, and it coordinates the cell's activities, which include intermediary metabolism, growth, protein synthesis, and reproduction (cell division). 


Class 9 Biology Extra Questions