9th class biology Chapter 5 Important Long Questions Prepare Online

Question: 1

Define reproduction. Describe its importance in life.

Answer: 1

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The most basic characteristic of life is reproduction. Definition It is a biological process in living things by which they produce their young ones which are similar to parents. Levels of Reproduction Reproduction occurs at different levels of organization. (i) Parts of the cell such as the chromosomes produce new chromosomes. (ii) Cells then produce new cells (iii) Individuals produce off springs like themselves. Reproduction for continuation of life Rudolf Virchow proposed an important biological principle that all cells come from pre¬existing cells. This principle tells us that the continuation of life, including all aspects of reproduction, is based on the reproduction of cells. We commonly refer cellular reproduction as cell division and it is a part of whole life of a cell i.e. cell cycle.

Question: 2

Define inter-phase. Explain the stages of inter-phase.

Answer: 2

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Inter-phase is the time when a cell's metabolic activity is very high, as it performs its various functions. Stages of interphase It is divided into three phases. G1 (first gap) S (synthesis) G2 (second gap) G1 Phase After its production, a cell starts its cell cycle in G1 phase. During this phase, (i) The cell increases its supply of proteins, (ii) Cell increases the number of its organelles (such as mitochondria, ribosomes) (iii)Cell grows in size. (iv)This phase is also marked by the synthesis of various enzymes that are required in the next phase i.e. S phase, for the duplication of chromosomes. S Phase In this phase, DNA replication takes place, as a result the cell duplicates its chromosomes. As a result, each chromosome consists of two sister chromatids. G2 Phase In the G2 phase, the cell prepares proteins that are essential for mitosis, mainly for the production of spindle fibers. After the G2 phase of inter-phase, the cell enters in the division phase i.e. M phase. It is characterized by mitosis, in which the cell divides into the two daughter cells.

Question: 3

What is mitosis? Describe its Discovery and phases.

Answer: 3

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Inter-phase is the time when a cell's metabolic activity is very high, as it performs its various functions. Stages of interphase It is divided into three phases. G1 (first gap) S (synthesis) G2 (second gap) G1 Phase After its production, a cell starts its cell cycle in G1 phase. During this phase, (i) The cell increases its supply of proteins, (ii) Cell increases the number of its organelles (such as mitochondria, ribosomes) (iii)Cell grows in size. (iv)This phase is also marked by the synthesis of various enzymes that are required in the next phase i.e. S phase, for the duplication of chromosomes. S Phase In this phase, DNA replication takes place, as a result the cell duplicates its chromosomes. As a result, each chromosome consists of two sister chromatids. G2 Phase In the G2 phase, the cell prepares proteins that are essential for mitosis, mainly for the production of spindle fibers. After the G2 phase of inter-phase, the cell enters in the division phase i.e. M phase. It is characterized by mitosis, in which the cell divides into the two daughter cells.

Question: 4

Define meiosis and explain its phases in detail.

Answer: 4

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Question: 5

Describe significance of meiosis?

Answer: 5

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. Introduction The significance of meiosis for reproduction and inheritance was described in 1980 by German biologist August Weizmann. (i) Maintenance of chromosome number August Weizmann noted that meiosis was necessary not only to maintain the number of chromosomes in the next generation but also to produce variations in next generation. (ii) Meiosis for sexual reproduction of Eukaryotas Meiosis is essential for sexual reproduction and therefore occurs in all eukaryotes including single celled organisms that reproduce sexually. Meiosis does not occur in prokaryotes, which reproduce asexually by binary fission. (iii) Meiosis in humans In human diploid gametes, mother cells or germ line cells undergo meiosis to produce haploid gametes. Male and female gametes unite to form diploid zygote which undergoes repeated mitosis and develops into the new diploid human. (iv) Gamete formation in fungi and protozoa Many haploid fungi and protozoa produce haploid gametes through mitosis. (v) Meiosis in plants Plants' life cycle shows alternation of generation. The cells of the diploid sporophyte generation undergo meiosis to produce haploid spores, which grow into haploid gametophyte generation. The haploid gametophyte generation produces haploid gametes through mitosis. The gametes combine to produce the diploid zygote. The zygote undergoes mitosis to become the diploid saprophyte. (vi) Meiosis as a source of genetic variations The chromosome pairs of each parent undergo crossing over during meiosis. So daughter cells i.e. gametes have genetic variations. When gametes fuse and form zygote; its genetic make-up is different from both parents. Thus meiosis allows a species to bring variations which help organisms to adapt to the changes in environment.

Question: 6

Write a note on necrosis.

Answer: 6

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Question: 7

What is apoptosis? What happens in it? Describe its importance.

Answer: 7

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"Between 50 billion to 70 billion cells die each day due to apoptosis in an adult human". Apoptosis is one of the main types of programmed cell death. Events of apoptosis Following is the series of events in apoptosis: (i) Cell shrinks and becomes rounded due to the breakdown of the cytoskeleton by enzymes. (ii) Chromatin undergoes condensation and the nuclear envelope breaks. (iii)In this way, nucleus spreads in the form of several discrete chromatin bodies. (iv)The cell membrane makes irregular buds known as blabs. (v) The blebs break off from the cell and are now called apoptotic bodies, which are then phagocytosed by other cells. Causes of apoptosis Apoptosis can occur when a cell is damaged, or undergoes stress conditions. Significance of apoptosis(i) Removal of damaged cell Apoptosis removes the damaged cell, preventing it from getting further nutrients or to prevent the spread of infection. (ii) Differentiation of fingers and toes in embryo Apoptosis generally gives advantages during development. For example, during the formation of fingers, the cells between them undergo apoptosis and the digits separate.

Question: 8

Q no: 5 (A) What is apoptosis? Describe Series of events in Apoptosis.

Answer: 8

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Apoptosis is one of the main types of programmed cell death. During apaptosis cell shrinks and become rounded due to the breakdown of cytoskeleton by enzymes. It chromation undergoes condensation and nuclear encelaps breaks . In this way nuclesus spread in the from of several discrete chormatin bosies . cell memberne makes irregular buds known as blebs . Blebs breake from the cell and one know called apoplotic bodies . Which are than phagocylosed by their cells.

Apoptosis con occur when a cell is demaged or endergoes stress condition apoptosis removes the demaged cell. preventing oit from getting further nutrients or to prevent this spread of infection Apaptosis also gives advantages during development. For Example

during the formation of fingers. The cell between them under go apaptosisand the digit separate

Question: 9

Q no: (B) What is cell cycle and describe all the phases of <gwmw class="ginger-module-highlighter-mistake-type-1" id="gwmw-15859120920584447283643">interphase</gwmw> in detail.

Answer: 9

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Cell cycle:

Cell cycle is series of event from the time a cell is produced until. It completes mitosis and produce new cell. Cell cycle consist of two major phase interphaseand mitotic phase.

Mitotic Phase:

is a relatively short peviod of cell cycle . It alternates with the much longer interphasewhere cell prepare itself for division.

Interphase:

Interphase is the time when a cell metabalicactivity is very high as its perform itsvarious function it is divided into three phase.

G1 phase:

After is reproduction a cell starts is cellcycle in G1 phase During this phase cell increase its supply of proteins increase the number of its organells or grow in size. This phase is also marked by the synthesis of various enzymes that are required in next phase

S phase:

In this phase cell duplicates its choromosomes . As a result each chromosomes. As a result each chromosome consist of two writerchronatids.

G2 phase:

In The G2phase cell prepares proteins that are essential for mitosis mainly for the production of spindle fibres.

Go Phase:

In multicellular eukaryotic cell enter Go phase from G1 and stop dividing some oneremain in Go for indefinite perioudof neurons.

Question: 10

Q no<gwmw class="ginger-module-highlighter-mistake-type-6" id="gwmw-15859150051247305654841">:</gwmw>6 (A) Explain the changes which take place during prophase of mitosis.

Answer: 10

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Prophase of mitosis:

Normally the genetic materials in nucleus is in a loose thread-like form called chromatin At the onset of prophasechromatin condenses into highly ordered structures called chromosome. Sine the genetic materials has already been duplicatiedeither in S phase each chromatids. bound together at the same centromereEach chromosomes also has kinetochore at centomere. There are two centrioles. Eachcentriols duplicae and thus two daughter centrosomesare formed Both centrosomesmigrate to the opposite poles of cell . The microtubulesthus formed are called spindle fibres. complete set of rpindlefibresis known as mitotic spindle. By this time nucleaslusand nuclear envelops have degraded and pindlefibreshave invaded the central phase.

Question: 11

Q no: (B) Write short note Necrosis.

Answer: 11

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Necrosis is the accidental death of cell and living tissues.Necrosis is less sequential than apoptosis there are many cause of necrosis including injury inflection concerect. Necrosis may occur when a cell is given hypoxiaenviroments

During necrasisthere is a release of special enzymes from lysosomes uysosomesenzymes break cellulancomponents and may also may be released outsides cell to break surrounding cell. Cells that necrosis may also release harmful chemicals that damage other cells.

Question: 12

Q no: 7 (A) Describe the Significance of Meiosos Meiosis:<div></div>

Answer: 12

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The significance of meisos for reproduction and inheritance was described in 1890 by german biologsis August weismann.

Maintenance of the chromosomes number in next generation:

Meiosis is essential for sexual reprodution in humans diplaidgemetemathercells otgerm line cell undergo meisosis to produce haploid gemeter male and female gemetesunite to form diploid zygoat. Which undergoerrepeated mitosis and develops into a new dipliodsHumans.

Production of variation in next generation:

The chromomespaios of each parent undergo crossing over during meiosis. So daughter cell gametes have genetic vaiation. when gemeterfuse and form zygote

ERRORS In MEIOSIS:

During anaphasechromoseomesseparated and go to opposite poles with during anaphaseanaphase2 sister chromosomes seprated. It is called

Disjunction:

Some time the seperation is not normal and it is called NoN Disjunction.

It result abnormalchromosomes number in next generation for example 47 or 45 chromosomes in humans

Question: 13

Describe <gwmw class="ginger-module-highlighter-mistake-type-1" id="gwmw-15859202853488600818329">prophase</gwmw>of Meiosis:

Answer: 13

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Prophase is the longest phase in meiosis during this stage chromatin condenses into chromosomes. The nomologuechromosomes line up with each other. form pairs by a process is called synapsisEach pair of homologuechromosomes is called bivalent Each bivalent has far chromosomes so it may also be called terrad The two non sister chromotidsof homologous chromosomes join each other at certain points along their length . This point of attachment are called chiasmataIn the next stage the non sister chromotidsof homologuechromosomes exchange their segments are the phenonmenonis known as Crossing over. Two kinetochoresof chromoseswhile the spindle fibresattach with a pair of chromosomes in mitosis we have seen that two kinetochorspindle fibresattach with one chromosomes

Question: 14

Define cell cycle . Explain its phases

Answer: 14

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Cell cycle : It is the series of events from the time a cell is produced until it completes mitosis and produces new cell

Phases of cell cycle :

It consists of two major parts

1: Interphase : The phase of cell cycle in which n a cell's metabolic activity is very high , as it performs its various functions but it is non-dividing phase of cell cycle

2: Mitotic phase : Mitotic phase is relatively short period of cell cycle . It alternates with much longer interphase where cell prepares itself for division

Interphase last for at least 90% of the total time required for the cell cycle

-Division of interphase : It is divided into three phases G1 (first gap) S(synthesis) and G2(Second gap)

-G1 phase : During this phase , a cell increases its supply of proteins and increase the number of its organelles (such as Ribosomes , Mitochondria ) and grows in size and synthesize various enzyme that are required in next phase i-e S phase for the duplication of chromosomes

Question: 15

Define mitosis . Explain its phases

Answer: 15

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Mitosis : The type of cell division in which a cell divides into two daughter cells . Each with a same number of chromosomes as were present in parent cell

Discovery of Mitosis: In 1880's German biologist , Walther Flemming discovered mitosis

Occurrence of mitosis : Mitosis occurs only in eukaryotic cell . In multicellular organisms the somatic cells undergo mitosis

Binary fission : In prokaryotic cell , it is a process in which one organism divide into two organisms

Phases of mitosis : Mitosis is complex it has two major phases

1: Karyokinesis : The division of nucleus is called Karyokinesis

2: Cytokinesis : The division of cytoplasm is called cytokinesis

KaryokinesisIt is further divided into four phases

1: Prophase

2: Metaphase

3: Anaphase

4: Telophase

1: Prophase :

Chromatin : Normally the genetic material in nucleus is in loose thread like form called chromatin

Chromosomes : (Chromo=color , Soma= body )

During cell division chromatin condenses into highly ordered structure called chromosomes

Kinetochore : It is a complex protein structure that is the point where spindle fibers attach

Centrosomes : The two centrioles are collectively called centrosomes

Spindle fiber : Mitochondria join together and form spindle fibers

Mitotic fibers : Complete set of spindle fibers is called mitotic fibers

Question: 16

What is the singnificance of mitosis ?

Answer: 16

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Importance of mitosis is maintenance of chromosomal set following are the occasions in lives organisms where mitosis happen

Development and growth :

The number of cell within an organism increase by mitosis . This is the basic of development of multicellular body from single cell i-e zygote and also the basis of the growth of multicellular body

Question: 17

What happens if errors in mitosis occurs ?

Answer: 17

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Errors in mitosis : Errors in the control of mitosis may cause cancer . All cells have genes that controls the timing and number of mitosis

Tumor: Sometimes mutation occur in such genes and cells contain to divide its result in growth of abnormal cells called tumors

Benign Tumors : A ling as the tumors remain in their original location they are called Benign Tumors

Malignant Tumors/ Cancerous Tumors

If the Benign Tumors invade other tissues they are called Malignant

Question: 18

Define meiosis . Explain its phase

Answer: 18

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Crossing over : After the formation of chiasmata the non-sister chromatids of homologous chromosomes exchange their segments and the phenomenon is known as crossing over

Process :

1: Chromosomes condense further the nuclei envelope disappear and nuclear envelope disintegrates

2: Centrioles which were duplicated during interphase migrate to the two poles and form spindle fibers

3: The kinetochore spindle fibers attach with kinetochore of chromosomes

4: Two kinetochore spindle fibers attach with a pair of chromosomes

Metaphase 1 : The pairs of homologous chromosomes align along equatorial plane forming the metaphase plate

3: Anaphase 1: kinetochore spindle fibers shorten . It results in pulling apart the chromosomes of each pair .Since one chromosomes is pulled towards one pole , two haploid sets are formed . Each chromosomes still contains a pair of sister chromatids

4: Telophase 1: Chromosomes arrive at the poles . Each pole now has the number of chromosomes each chromosomes still consists of two chromatids . Spindle network disappears , and nucleus envelope is formed around each haploid set . Chromosomes uncoil back into chromatin

a) Cytokinesis : The pinching of cell membrane in animal cells or the formation of cell wall in plant cells is called cytokinesis . It occurs and creation of two haploid daughter cells is completed

Question: 19

What is the significance of meiosis ?

Answer: 19

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The significance of meiosis for reproduction and inheritance was described 1890 by German biologists August Weismann . He pointed out that meiosis was necessary not only to maintain the number of chromosomes in the next generation but also to produce variations in next generation

1: Maintenance of chromosomes number in next generation :

Meiosis is essential for sexual reproduction

In humans : Meiosis is essential for sexual reproduction . In human diploid gamete-mother cells or germ line cells undergo repeated mitosis and develops into a new diploid human

In fungi and protozoans : Many haploid fungi and protozoans produce haploid gametes through mitosis

Question: 20

What happens if errors in meiosis occur?

Answer: 20

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During anaphase 1 , homologous chromosomes separate and go to the opposite poles while during anaphase 2 sister chromosomes separate it is called disjunction

Example:

In normal separation 46 chromosomes are present

Non disjunction :

Sometimes separation is not normal and it is called non disjunction

Increasing in number of chromosomes cause abnormality because meiosis results in the production of gametes which have either more or less than the normal number of chromosomes in the next generation

Question: 21

Write note on<div>1: Apoptosis 2: Necrosis</div>

Answer: 21

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Apoptosis and Necrosis are two phenomenon of cell death

1:Apoptosis:

Apoptosis is one of the main types of programmed cell death , and involves a series of biochemical events . This process is controlled by extracellular signals (e.g hormones ) or intracellular signals (e.g good deprivation , viral infection

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9th Class Chapter 5 Biology Long Questions

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