Botany Solved Past Paper 2nd year 2015 Karachi Board


Choose the correct answer for each from the given options:

i) They study of Earth’s surface texture is termed:
* Topographic factor
* Edaphic factor
* Climatic factor
* Biotic factor

ii). Double fertilization is the characteristics of:
* Bryophytes
* Gymnosperms
* Pteridophytes
* Angiosperms

iii) The formation of mRNA from DNA in the nucleus is called:
* Transformation
* Transcription
* Transduction
* Conjugation

iv) The diameter of stem and root increases due to:
* intercalary meristem
* lateral mcristem
* Apical meristem
* Superficial meristem

v) Plants growing in shade are termed:
* Halophytes
* Heliophytes
* Sciophytes
* Hydrophytes

vi) The running water of rivers, springs and streams is called:
* Lentic
* Estuary
* Niche
* lotic
vii) The particular array of chromosomes present in an individual is called:
* Autosome
* Genotype
* Karyotype
* Phenotype

viii) Bivalents are formed at this stage:
* Zygotene
* Pachytene
* Diplotene
* Diakinesis

ix) Organisms responsible for recycling of minerals within an ecosystem are called:
* Producers
* Primary consumers
* Secondary consumers
* Decomposers

x) A cell having 16 chromosomes divides by meiosis. At telophase-l, the number of chromosomes in each nucleus will be:
* 08
* 16
* 24
* 32

xi) A type of programmed cell death is:
* Apoptosis
* Synapsis
* Necrosis
* Diakinesis

xii) During cell division, when homologous chromosomes fail to separate properly, the phenomenon is called:
* Polyploidy
* Euploidy
* Pleiotropy
* Non-disjunction

xiii) Chromosomes normally occur as homologous pair in alan:
* spenn cell
* egg cell
* zygote
* gamete

xiv) This hormone acts as growth inhibitor causing stomata to close:
* Cytokinin
* Ethene
* Abscisic acid
* Gibberellin

xv) The plant cells that have their cell walls removed are called:
* Protoplasm
* Cytoplasm
* Protoplasts
* Tonoplasts

xvi) Cells found at the stem and root apices are termed:
* Cambium
* Lateral meristem
* Intercalary meristem
* Apical meristem


i) What is the role of Auxins in plants?
Auxins are indole acetic acid (1M) or their variants chemically.
Role of Auxins:
1. In stem, promote cell enlargement in region behind apex. Promote cell division in cambium.
2. In root, promote growth at very low concentrations, inhibits growth at higher concentrations eg: Geotropism, promote growth of roots from cutting and calluses.
3. Promote bud initiation in shoots but sometimes antogonistic to cytokihins and inhibitory.
4. Sometime promote bud initiation in intact plant if apical dominance broken. .
5. Promote apical dominance and fruit growth.
6. It can sometimes induce parthenocarpy.
7. Causes delay in leaf senescenece in few species.
8. It inhibits Abscission.
9. It acts as weed killer.
10. It also control dormany in seeds.
11. Overcome sterility.
12. Shortening of internodes occurs due to auxins.

ii) Write a note on natural methods of Asexual reproduction in
Asexual Reproduction: It is a kind of reproduction that requires only one parent which give rise to off springs resulting an adult organism with diploid number of chromosomes. The resulting offspring of this kind are genetically identical to their parents.
Natural Methods of Asexual Reproduction: Naturally, plants reproduce asexually by following methods.
1- Sporulation
2- Apomixis
3- Parthenocarpy
4- Vegetative propagation. (cutting, grafting, perennating organs.)
Artificial Method of Asexual Reproduction: ‘Plants may asexually reproduce by different techniques. One of them is tissue culturing.
a) Test Tube Cloning
b) Protoplast Fusion

iii) Explain Chromosomal aberration.
It is a type of mutation in which a visible change occurs in segments of chromosome. It is of following types.
a) Deletion: It is a type of chromosomal mutation in which a small segment of choromosome is missing.

Question Answer

Question Answer



v) Describe Test cross or Incomplete dominance.
Test cross: The cross between phenotypically dominant individual with a homozygous recessive individual is called Test Cross.
Condition-1 (Homozygosity): When homozygous dominant parent is crossed with recessive all the offspring will be phenotypicaliy dominant.
Condition-2 (Heterozygosity): When heterozygous dominant parent cross with recersive then half of the offspring will be phenotypically dominant and half will be recessive type.
Example: (Homozygosity): When homozygous dominant parent is crossed with recessive all the offspring will be phenotypically dominant

tall dominant type plants

tall dominant type plants

Incomplete dominance: The phenomenon in which neither of the contrasting character is dominant over each other resulting the mixture or a blend of two characters. This is also known as Blending Inheritance or Partial Dominance.

vi) Describe the types of RNA.
There are actually several types of ribonucleic acid or RNA, but most RNA falls into one of three categories:
mRNA or Messenger RNA: mRNA transcribes the genetic code from DNA into a form that can be read and used to make proteins. mRNA carries genetic information from the nucleus to the cytoplasm of a cell.
rRNA or Ribosomal RNA: rRNA is located in the cytoplasm of a cell, where ribosomes are found. rRNA directs the translation of mRNA into proteins.
tRNA or Transfer RNA: Like rR A, tRNA is located in the cellular cytoplasm and is involved in protein synthesis. Transfer RNA brir\gs or transfers amino acids to the ribosome that correspond to each threenucleotide  codon of rRNA. The amino acids then can be joined together and processed to make polypeptides and proteins.

vii) Why did Mendel choose pea plant as an experimental material?
Mendel Father of Genetics and his laws were known as Mendelism. Choise of material and methadology are the two main objectives of Mendel’s study.
Mendel selected experimental plant. i.e., Pisum sativum (Garden Pea) because of following useful characters.
1. These plants are cultivated easily, as their generation time is very short.
2. These are self-polinating plant’s but cross polination can only take place artificially.
3. Artifical breeding is easy as flowers are comparatively large with numerous varities are available with sharply define contrasting characters. That may include.
a. Height oTplant (tall or dwarf)
b. Shape of the seed (round or wrinkled)
c. Colour of seed (Green or Yellow)
d. Shape of the pod (Smooth or consticted)
e. Colour of pod (Yellow or Green)
f. Colour of flower (Red or White) etc.
4. These plants produce fertile hybrid.
5. This plant do not show complexities that had troubled earfier worker.

viii) What adaptations do plants make to cope with the effects of hot and cold temperatures?
Plants adapt two mechanisms to regulate temperature.
Low Temperature: Low temperature affects the fluid nature of plasma membrance of plant cell. To prevent solute ‘transport plant cell increases the proportion of unsaturated fatty acids. It also prevent crystal formation,
At freezing temperature, plants develp mechanism that inhibit crystal formation by developing crystals in cell walls rather than cytoplasm. So, the cytosol is super cooled, below freezing point.
High Temperature: High temperature is more hannful as all the enzymes denature. To cool down the temperature, plant transpire rapidly.
At 40°C or above, plants synthesized special type of proteins that prevent enzymes from denaturation tenned as heat-shock proteins.
Plants may also develop other modifications to prevent high temperature, such as shiny waxy cuticle, reduce leaf surface area, wilting etc.

ix) Write a note on Excretion in plants.
It is defined as “a process through which metabolic wastes, excess substances {e.g. salts, water and drugs etc} remove or excreted”. Excretion in plants is not complex such as animals. There are no specific organs for excretion like in animals. Mosj of the end products of plant metabolism are carbohydrate based and end products C02 and water are comparatively less harmful as nitrogenous end products of animals. There are two ways through which plants excrete excess water and salts.
It is a process through which excess water is removed from aerial parts of the plant in the fonn of vapours. It is of three types, stomatal, lenticular and cuticular.

x) Describe Desert ecosystem with reference to Pakistan.
Deserts in Pakistan consist of sandy hills and plains. Wind is also play important role along with rain fall. Different kinds of vegetation found in two different hills.
Sandy hills consist of vegetation like Euphorbia, Acacia, Capparis, Calotropis etc.
Plains consist of vegetation like, Prosopis, Capparis, Lycium etc. Due to dry season these area are unavailable for farming.
But can be used dry farming of Sorghum and Bajra.
Deserts show wide variety of temperatures difference like days are very hot and nights have low temperature.
Example: Thur desert of sindh.
Producers: Plants are mostly xerophytic.
Such as Accacia, Prosopis, Salvadora, Capparis, ground vegetation include Panisetum, Tribulus etc. Consumers: Most common are Tenebrionid beetles, mantis, graSShopper, centiped and spider, frog and toad, reptiles include lizards, uromastic, calotes, snake (Vipers, cobras). Birds include quail bustard, partridge. Mammals include ant-eaters, hedgehogs, porcupines, bats etc.
Decomposers: Due to poor vegetation and scanty of water, organic
matter is low, so the decomposers are very few. Mostly they are thermophilic bacteria and fungi.

xi) What is Syndrome? Describe the effects of XXV Trisomic condition in humans.
A group of symptoms that collectively indicate or characterize a disease, psychological disorder, or other abnormal condition.
Effects of XXY Trisomic condition: Klinefelter’s Syndrome is a condition of trisomy with one extra sex chromosome in males 47 (i.e. 2n+1) or 44 autosome-XXY. It occurs one out of thousand males birth (1/1000).
Abnormalities of Klinefelter’s Syndrome: The abnormalities of this syndrome includes .
Tendency to tallness .
Obesity frequently enlarged breasts .
Small testes with no sperms .
At puberty, these men show mixed secondary sexual characters .
They are always fuctional sterile.

xii) Write a.note on Light as a climatic factoz
Light is the form or radiant energy and is essential for all green plants, photosynthetic bacteria and all living organism. Only 3% of total sunlight utilized by the plants. The light effect in three ways. light Intensity: It depends on angle of incidence and seasons, latitudes and time of the day. Cholorophyll synthesis depends on it, and high intensity of light may destroy the chlorophyll molecule. Plants may also classify in two groups.
(i) Heliophytes: Those plants which require light.
(ii) Sciophytes: Those plants which required shade.
Other examples that effect by light intensity are pigment development, opening and closing of stomata; permeability of cell membrane etc.
Light Duration: The duration of light or photoperiod directly effect the flowering in plants, growth, leaf fall and dormancy etc. In animals biological rhythm regulated by photoperiod.
Example: Nesting behaviour in spring. migration of birds in autumn,
shelter in dark etc.
Light Quality: The visible light of electromagnetic spectrum is ranges from 400 to 780 ml and consist of seven different colour. The cholorophyll absorbs red and blue colour of light for photosynthesis. Ultraviolet rays of sun absorbed or reflected back by ozone layer. It is harmful and may cause skin cancer and sun bum in human beings.

xiii) Define Interphase. Name and explain its sub-stages.
Interphase is the stage between two successive of cell divisions.
However, some time it is refered as “Resting stage”, But most of the
biochemical activities occurs during this phase, Hence it is also known as “Preparatory Stage” of cell cycle.
It consist of 3 sub phases, which are as-under
G-Phase (Gap-1-Phase): It is metabolically active phase. During this phase, certain enzymes and DNA-nucleitodes are gathered for DNA synthesis.
S-Phase (Synthesis Phase): DNA synthesis occurs in this stage as
a result number of chromosome double.
GrPhase (Gap-2-Phase): It is refered as premitotic phase. In this phase all the requirements necessary for cell division become ready like, stored energy, proteins, RNA, Microtubules etc.

xiv) Define Meristem. Give the types of Meristems and state their functions.
Plants retain a group of immature cells which are capable of division and form the actively growing tissues. These tissues called meristem. There are three types of meristem found in plants which are responsible for the growth.
1. Apical meristem.
2. Lateral meristem
3. Intercalary meristem.
Apical Meristem: These are found at the tips of roots and shoots and are responsible for primary growth of the plant.
These tissues are responsible for increase in the number of cells at apices. so.jhey increase the length of the plant through tips.
Intercalary Meristem: These are found below the nodes in monocotyledonous plants. Also found at the base of internode and at the base of leaves in many plants.
These meristem get separated form the apical meristem by permanent tissues and left behind the apical meristem.
They help in increase the length of the plant other than apices. They
are also responsible in production of leaves and flowers.
Lateral Meristem: These are found in a cylinder towards the outside of stem and roots. They are present in dicot and Gymnosperms.
They play an important role in increase in girth of stem and root and
in formation of secondary tissues (also called secondary growth).
There are two types of lateral meristem.
a) Vascular cambium b) Cork cambium

xv) Write a note on anyone of the following:
(a) Growth correlation
The development of plants is correlated with the growth of plant organs and their relation. Therefore, the growth of one organ of a plant is related with the growth of other organ, this reciprocal re!ationsihp is known as “correlation”.
Appical dominance is the most important correlation found in plant. In many plants, only apical bud grows, while the growth of axillary bud is suppressed and plants grow vertically. When apical bud is remove the growth of axillary bud initiated. So, the active shoot apex controls the development of lateral buds.
The auxin synthesize in the meristematic cells of apex and diffused to lower cells from the bud. So, causing apical dominance and inhibited the growth of lateral branches. This effect of auxin is called “Inhibitory effect”, while the removal of apex (diff~se auxin from apex to lower cells) release the lateral buds from apical. dominance is called “compensatory effects“.
Cytokinins also play important role in apical dominance. Many experiments showed that if cytokinin is directly applied on the inhibited lateral buds, it allows lateral buds to release from apical dominance.
Apical dominance plays an important role in tap root development and the inhibition of sprouting of lateral buds (eyes) in potato tuber by applying synthetic auxin. In the later causes the sprouting of eyes is prevented and storing period is increased from one to three years .’

(b) Seed dormancy
Dormant means sleeping or resting. Biologist use the term dormancy for the stage of life cycle of plants which is characterized by low metabolic rates of growth and development known as seed stage. Seed dormancy increases the chances that germination will occur at a time and place most advantageous to the seedling. Breaking dormancy generally requires certain environmental conditions. Seeds of desert plants, for instance, germinate only after a substantial rainfall. If they were to germinate after modest drizzle the soil might soon be too-9 dry to support the seedlings. Where natural fires are common, many seeds requires intense heat to break dormancy. seedlings are therefore most abundant after fire has cleared away competing vegetation. Where winters are harsh, seeds may require extended exposure to cold; seeds’ sown during summer or fall do not germinate until the following spring.
This assures a long growth season before the next winter. Very small seeds, such as those of some lettuce varieties, require light for germination and will break dormancy only if they are buried shallow enough for the seedlings to poke through the soil surface. Some seeds have coats that must be weakened by chemical attack as they pass through an animal’s digestive tract and thus are likely to be carried some distance before germinating.
The length of time a dormant seed remains viable and capable of germinating varies from a few days to decades or even longer, depending on the species and environmental conditions. Most seed are durable enough to last a year or two until conditions are favourable for  germinating. Thus the soil has a pool of ungerminated seeds that may have accumulated for several years. This is one reason vegetation can come back so rapidly after a fine, drought, flood or some other environmental disruption


(i) Describe Watson and Cricks Model of DNA. How does DNA replicates semi-conservatively.
Watson and Crick model of DNA: In 1953, Watson and Crick reported their molecular model for DNA: the double helix .. They suggested ladder type organizatton of DNA. Each molecule of DNA is made up of two polynucleotide chains, Which are twisted around each other and form a double helix. The uprights of the iadder are made up of sugar and phosphate part of nuCleotide and the rungs are made up of paired nitrogenous bases. The pairs are always as follows:

Adenine always pairs with thymine and cytosine with guanine. There is no other alternative possible. Two polynucleotides chains, which are complimentary to each other, are held together by hydrogen bonds. There are two hydrogen bonds between A=T, and three between C=G. Both nucleotide strands remain separated by 20AO distance. Along the length of a polynucleotide strand, 10 mononucleotide OCGur per complete turn

The Watson-Crick model explained Chargaffs rutes. Wherever one strand of a DNA molecule has an A, the partner strand has a T and G in one strand is always paired with a C in the complimentary strand. Therefore, in the DNA of any organism, the amount of adenine equals the amount of thymine, and the amount of guanine equals the amount pf cytosine. Although the base-pairing rules dictate the combinations of nitrogenous bases that form the rungs of the double helix, they d~ not restrict the sequence of nucleotide along each DNA strand. Thus, the linear sequence of the four bases can vary in countless ways, and each gene has a unique order, or base sequence



Replication of DNA: The Watson-Crick model immediately suggested that to copy the DNA molecule, one need only unzip the duplex and construct a new complimentary chain along each naked strand.

The form of DNA replication suggested by the VV.:t on-Cnck model is called semi conservative because, after one round 01 replicauon. the original duplex is not conserved; instead, each strai of the duplex becomes part of another duplex. If ore were to ‘Jnz;p i 1,)moteci.le. one would need only to assemble the appropriate comp.imen .ary n.icleotide on the exposed single strands to form two dauqnter dtplexes of the same sequence. This prediction of the Watson Cr.c-, mcoel was tested in 1958 by Mathew Meselson and Frank Stahl. Tnese ~wo scientists grew bacteria for several generations in a medium ccntairioc the heavy isotope of nitrogen N15, then transferred Ire glowng ~,lJs to a new medium containing the lighter isotope N14 and ha-vested the ON.l\, at various intervals.

At first the DNA that the bacteria manu’acturec W’c!5 811 neavy. But as the new DNA that was being formed incorporatea the dghter nitrogen isotope, DNA density fell. These results indicated that after one round of  replication, each daughter DNA duplex possessea one c: the labelied heavy strands o~ the parent molecule. When this f1ybrid duplex replicated, it contributed one heavy strand to form another hyorid duplex and one light strand to form a light duplex. Meselson and Stahl’s experiment thus clearly confirmed the prediction of the Watson-Crick model that DNA’replicates in a semi conservative manner.

(ii) What is Movement in plants? Describe various types of Paratonic movements in plants.
There are two main types of movement found In plants in response to stimuli.
1- Autonomic or spontaneous movement.
2- Induced or paratonic movement.
Paratonic Movement: The movement due to external stimuli called induced movement. There are two types of paratonic rncve-nents discussed below.
i- Tropic movement.
ii- Nastic movement.



Tropic movement: The word tropic is derived from Greek word “Tropes” meaning “turn” In this condition the whole part or organ show growth or curvature movement.
Tropic movements are in response of unidirectional stimuli. I is clearly seen in symmetrical parts of the plants, such as root and shoot.On the basis of nature, it is further divided into following types.

Phototropism: This type of tropic movement causes due to unidirectional effect of light. It is also known as Heliotropism.
1- Positive Phototropism: The movement of plant parts toward the light is called positive phototropic movement (shoot).
2- Negative Phototropism: The movement of plant’s parts away from the source of light stimuli is called negative phototropic movement (root).
B-Geotropism: It is the movement of growth curvature causes in response to gravitational stimulus.
i- Positive Geotropism: The movement of plant’s parts tOY”3 rd the gravitational force called positive geotrapic movement.
Example: Primary roots of many plants

ii- Negative Geotropism: The movement of plant’s parts away from the gravititional force called Negative Geotropic movement.
Example: Shoot of the plants .
ii-Negative Chemotropism: Some of the parts grow negatively cnernotropic.
D-Hydrotropis.1: The movement of plant parts in response of water
stimulus is called hydrotropism.
Example: Roots are positivety hydrotropics.
E-Thigmotropism: The movement of plant parts in response to touch stimulus.
Example: Q Twinners and climbers
When the plant parts touch the solid object the growth on the opposite side of contact increases and the tendrils coiled around the support.
ii- Nastic Movement: Nastic movements are the type of movement which occurs due to non-directional external stimuli. This type of movement mostly observed in leaves, flowers, petals etc.
According to types of stimuli, there are different kinds of Nastic movement.
2. Thermonasty
4. llaptonasty

1. Photonasty: The non directional movements caused by light stimulus is called photonastic movement. It occurs due to change in light intensity.
Flowers of Oxalis and Portulaca open in day and closed at night.
Flowers of Nicotia close in day and open at night.

2. Thermonasty: The nastic movement due to temperature stimulus is called thermonastic movement.
Example: The flowers of tulip close at night because ‘of rapid growth in the lower side by upward and inward bending of the petals.
3. Seismonasty: The nastic movement that result due to shock is called seismonasty.
Example: Mimosa pudica (touch-me-not) shows shock movement due to touch.

Scismonastlc Movement

Scismonastlc Movement

Haptonasty: These are the nastic movements occurs due to stimuli of touch. This movement is observed in many insectivores plants.
Example: Dionea (venus fly trap), Drosera (sun dew).
Nyctinasty: These are the nastic movement in response to external
stimuli leading to differential growth. These are also called diurnal sleep movement.
Example: Photonastic and therrnonastic movement of the flowers also termed as, Nyctinastic movement.

OR Describe various components of Pond Ecosystem.
“A pond is a body of standing or stagnant water which posses abundent vegitation and having large number of microorganisms, large plants and animals”.
A pond can be taken as a good example of fresh water ecosystem. It is self regulating interdependent and complete ecosystem by all means.
COMPONENTS OF POND ECOSYSTEM: It of two main components.
1-Abiotic components.,
2-Biotic Components

1) Abiotic Components: They are non living components of an ecosystem.
1. They include organic and inorganic components.
2. Abiotic cor-ionent includes micronutreint like iron, manganese, copper. ZII1C ana macronutreint includes potassium magensium and sulphur.
3. These nutre’nts are present in dissolved form in water and are radially available.
4. Solar radiaticn is the energy received from sunlight and traped by
the producers.

2-Biotic Compnents: Living components of an ecosystem are called motte co-rponer-ts. They may be classified into Autotroph and Heterotroph
Autotrophic Components: The organisms which prepare their own
food, these ircludes green plants which are capable of preparLng their own food oy simple inorganic material that is C02 and H20 in presence of sunlight and chlorophyll. These producers are of two types.
Microphytes (Lower Plants): Includes phytoplanktoris consist of free floatirg alqae like Chlanydomonas, spirogyrcf, Nostoc Diatoms.
Macrophytes (Higher Plants): These are rooted or large floating plants that grow in snaliow water. These consist of both types of hydrophytes means total submerqed such as potamageton, Hydrilla, Vallisnaria, Trapa etc, and partially submerged plants like water lily, Nelumbium (lotus). Eichorrua (water hyacinth) etc.
Heterotrophic Components: These are the individual that are unable to prepare their own food due to lack of chlorophyll and hence are depenoen: on other organisms to fullfill their nutritional requirements. On the bases of mode of nutrition biotic compnents are classified into.
1- Consumers
2- Decomposers

CONSUMERS. These includes heterotrophic members of an ecosystem that can not synthesize their OWj:1 food so feed upon the food prepared by other members of an ecosystem.
The consumers are classified into:
i) Primary consumers. .
ii) Secondary consumers.
iii) Teritiary consumers.

i) Primary Consumers: These are herbivorous members of an ecosystem. They feed upon producers to fullfill their nutritional requirement. Primary consumers of pond ecosystem include protozoans, crustaceans, molluscs, herbivore fishes and some yong insects.
ii) Secondary Consumers: These includes carnivorous and omnivorous animals . In pond ecosystem carnivorous includes frog, snail, snake, fishes and Diving beetles
Omnivorous includes sparrow.
iii) Tertiary Consumers: These are predatory members of an ecosystem. They feed upon secondary consumers but are themselves not eaten by other members. They got their physical death.
>In pond ecosystem tertiary consumers are turtles and large fishes.
DECOMPOSERS: They are also called microconsumers and are saprotroph. They decomposes complex compounds of living and nonliving protoplasm and use some of the nutrition from dead organic mater and they are very important to keep the balance of various materials in environment. Fungi and bacteria are the decomposers of pond ecosystem.

Pond Ecosysttm

Pond Ecosysttm

(iii) Describe various stages of Mitotic Cell division.
Mitosis: It is a type of cell division in which chromosome number in daughter cells remain constant as in mother cell. It is also known as somatic cell division or somatogenesis. The process of mitosis is similar in both animal and plant cell that taking place during embryonic development and growth.
Although mitosis is a continuous process, but for better understanding it may be divided into two phases.
i- Karyokinesis.
ii- Cytokinesis

Karyokinesis: It is the division of nucleus, which involves further four stages or phases.
1- Prophase.
2- Metaphase.
3- Anaphase.
4- Telophase.

Prophase: Prophase includes the following characters.
1. During early stages of cell cycle, Chromosome are not clearly visible even with electron microscope in early prophase.
2. As prophase proceeds, fine threads of chromosomes appear, as network called as chromatin
3. Later on chromosomes get condensed and become visible consisting of two chromatids attached at the point called centromere.
4. In the late prophase, nuclear membrane starts to disappear and nucleolus also disappear. .
5. Finally, all the nuclear material gets free in cytoplasm and mitotic apparatus starts to originate



Mitotic Apparatus: Aster and spindle are collectively known as mitotic apparatus. There are three different types of fibers.
1- Continuous fibers: The fiber which are running from pole to pole.
2- Discontinuous fibers: The fiber which are running from pole to central region or central plate.
3- Astral fibers: The fiber which are short fibers radiating from centrioles and remain at poles.
1. In the begining of this stage. nuclear membrane is completely disappeared and nuclear material arranged themselves in cytoplasm.
2. In this phase. chromosomes become more prominent and the region of centromere known as Kinetochore appeared with the special fibers known as kinetochore fibers.
3. The choromosomes arrange themselves on equatorial plane with spindle fiber radiating from poles.
1. The spindle fiber that attached with kinetochore start to contract and move towards the pole.
2. As the result of contraction. chromatids become detached at the point of centromere and now served as chromosome.
3. At the end. Chromosomes pulled tOI the oppos.te poles by further contraction of fibers.
1. This is the last phase of karyokinesis and is known as reverse of prophase.
2. Chromosomes starts to coiling and forming a chromatin network. In the late telophase. two daughter nuclei are formed.
3. Nuclear membrane is reappear. and nucleolus and other organelles start to reappear.

Cytoplaasmic division of a plant as bought about by cell plateformation

Cytoplaasmic division of a plant as bought about by cell plateformation

ii- Cytokinesis: It is the division of cytoelasm, as a result of which two daughter cells are formed.

1. During late telophase the astral microtubules send signals to equatorial region of the cell.
2. At this point actin and myosin are activated that form contractile ring.
3. Later on cleavage furrows developed at the center that deepers towards the centre of the cell and finally two daughter cells are formed.
1. In plant cells, in the late telophase, cellulose particles gethered in the center of the cell and form vessicles originated from golgi bodies known as phragmoplast.
2. These phragmoplast fused to form phragmophase at the end of telophase.
3. Later on these membranous vessicles fused completely and become the plasma membrane of daughter cell and then synthesis of cell wall occurs outer to plasma membrane. ‘
Conclusion of Mitosis: As a result of mitosis, two daughter diploid cells arise from the division of diploid mother cells. In this division chromosome number in daughter cells remain constant as in mother cells.
OR Define Sex-linked inheritance. Discuss Sex-linked inheritance in humans.
In human beings there are 23 pairs of chromosomes. Out of which 22 pairs of chromosomes are autosomes and the remaining 23rd pair is morphologically different in male and femal is called sex-chromosome. There are about 200 genes present on X-chromosome. There are two most popular sex-linked traits found in human beings i.e., colourblindness and haemophilia.
Colour-Blindness: It is a sex-linked inheritance found in human beings. In this condition colour blind person cannot distinguish red colour from green. It is more common in males and rare in females. There are some possible results of various crosses.
N= normal
n= colour blind
Cross:1 Colour Blind Male Vs Normal Female:







Posted on December 31, 2015 in 2nd Year 2015 Karachi Board Past Papers

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