How do Organisms Reproduce? - Class 10 Science - Chapter 7 - Notes, NCERT Solutions & Extra Questions
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Notes - How do Organisms Reproduce? | Class 10 NCERT | Science
Reproduction is a fundamental process for the continuation and survival of all living organisms. Understanding the different modes of reproduction, DNA copying, and the importance of variation is crucial for Class 10 students. This comprehensive guide covers the essential points of how organisms reproduce, ensuring you excel in your exams.
Types of Reproduction
Asexual Reproduction
Asexual reproduction involves a single organism producing offspring without the involvement of gametes. This mode of reproduction is common in unicellular organisms and certain plants and animals.
Binary Fission
Binary fission is a form of asexual reproduction where a unicellular organism divides into two equal parts. This method is common in organisms like amoebas.
Multiple Fission
In multiple fission, an organism divides into many daughter cells simultaneously. This method is observed in the malarial parasite, Plasmodium.
Budding
In budding, a new individual grows from a certain part of the parent organism and eventually detaches to become an independent organism. Yeast and Hydra use this method.
Fragmentation
Fragmentation occurs when an organism breaks into several pieces, each of which grows into a new organism. This is common in organisms like Spirogyra.
Spore Formation
Spore formation is a method where specialized reproductive units called spores develop into new individuals under favourable conditions. Bread mold (Rhizopus) uses this method.
Vegetative Propagation
Vegetative propagation is a form of asexual reproduction where new plants grow from parts of the parent plant, such as roots, stems, or leaves. This method is used in potatoes, sugarcane, roses, and more.
Tissue CultureTissue culture involves growing new plants from small pieces of plant tissue in a controlled environment. This technique is especially useful for growing disease-free plants.
Sexual Reproduction
Sexual reproduction involves the fusion of male and female gametes, resulting in offspring with genetic variation. This process is crucial for the adaptation and evolution of species.
Sexual Reproduction in Flowering Plants
The reproductive parts of flowering plants are located in the flower. The male part, called stamen, produces pollen grains, while the female part, called pistil, contains ovules. Pollination is the transfer of pollen from the stamen to the stigma, leading to fertilization and the formation of seeds.
Sexual Reproduction in Humans
In humans, the male and female reproductive systems are involved in producing gametes and facilitating fertilization.
Male Reproductive System
The male reproductive system includes the testes, which produce sperm, and the vas deferens, which transports sperm. Secretions from glands like the seminal vesicles and prostate gland provide nutrition and ease the transport of sperm.
Female Reproductive System
The female reproductive system includes the ovaries, which produce eggs, fallopian tubes for egg transport, the uterus for nurturing the embryo, and the vagina.
During fertilization, a sperm and an egg combine to form a zygote, which develops into an embryo and eventually a fetus. The mother's uterus supports this development.
DNA Copying and Variation
Significance of DNA Copying
DNA copying is crucial for the inheritance of traits from parents to offspring. This process ensures that the new generation has similar body designs and functions.
Importance of Variation
Variation is vital for the survival and evolution of species. It allows organisms to adapt to changing environments and enhances their chances of survival.
Reproductive Health and Contraception
Understanding Puberty
Puberty is the stage when the human body undergoes several changes to reach sexual maturity. These changes include the development of secondary sexual characteristics and the maturation of reproductive organs.
Methods of Contraception
Contraception methods help prevent unwanted pregnancies and the transmission of sexually transmitted diseases (STDs). Common methods include:
Barrier Methods: Condoms prevent sperm from reaching the egg.
Hormonal Methods: Pills regulate hormone levels to prevent egg release.
Intrauterine Devices (IUDs): Copper-T devices prevent fertilization.
Surgical Methods: Vasectomy and tubectomy block the pathways of sperm and eggs, respectively.
Conclusion
Understanding the various modes of reproduction, the significance of DNA copying, and the importance of variation is essential for Class 10 students. This knowledge not only helps in exams but also in understanding the fundamentals of biology and the continuity of life.
Frequently Asked Questions
What is reproduction and why is it important for organisms?
Reproduction is the biological process by which new individual organisms are produced. It is essential for the survival and continuation of species.
How does reproduction differ from other life processes like nutrition and respiration?
Unlike nutrition and respiration, which are vital for the survival of an individual organism, reproduction is crucial for the continuation of the species.
What is DNA copying, and why is it crucial in reproduction?
DNA copying ensures that the genetic information is passed on from parent to offspring, maintaining the species' characteristics.
What are the two main types of reproduction?
The two main types are asexual and sexual reproduction.
How do unicellular organisms reproduce?
Unicellular organisms typically reproduce asexually through methods like binary fission and multiple fission.
What is binary fission, and how is it different from multiple fission?
Binary fission involves the division of a unicellular organism into two equal parts, while multiple fission involves dividing into many daughter cells simultaneously.
What is budding, and how does it occur in organisms like Hydra?
In budding, a new individual grows from the parent organism and detaches to become independent. In Hydra, buds form and grow into new individuals.
What is fragmentation, and which organisms use this mode of reproduction?
Fragmentation involves breaking an organism into pieces, each growing into a new individual. This method is used by organisms like Spirogyra.
How does spore formation work in fungi like bread mold?
Spore formation involves producing reproductive cells (spores) that can grow into new individuals under favourable conditions.
What is vegetative propagation, and why is it important in plants?
Vegetative propagation uses parts of plants to grow new plants. It is important for growing genetically identical plants quickly.
How does tissue culture work?
Tissue culture involves growing new plants from small pieces of plant tissue in a controlled environment, ensuring disease-free plants.
What is the significance of sexual reproduction over asexual reproduction?
Sexual reproduction introduces genetic variation, which is crucial for adaptation and evolution.
What are the male and female reproductive systems in humans?
The male system includes testes, vas deferens, and associated glands. The female system includes ovaries, fallopian tubes, uterus, and vagina.
How does fertilization occur in flowering plants?
Pollen from the stamen transfers to the stigma, leading to fertilization and seed formation.
What changes occur in human bodies during puberty?
Changes include the development of secondary sexual characteristics, maturation of reproductive organs, and emotional changes.
What methods of contraception are available to avoid pregnancy?
Methods include barrier methods (condoms), hormonal pills, IUDs (Copper-T), and surgical methods (vasectomy and tubectomy).
Why is variation important in reproduction?
Variation allows organisms to adapt to changing environments and increases the chances of survival.
How does regeneration differ from other forms of reproduction?
Regeneration involves regrowing lost parts, which can lead to the formation of new individuals in some species, unlike other methods where a complete new individual is formed initially.
What are the advantages and disadvantages of asexual and sexual reproduction?
Asexual reproduction is fast and does not require a mate, but lacks genetic variation. Sexual reproduction introduces variation but is a slower process requiring mates.
How do environmental changes impact reproductive processes?
Environmental changes can affect the availability of mates, the viability of offspring, and the overall success of reproduction.
With this comprehensive guide, you are now well-prepared to understand the various aspects of how organisms reproduce, ensuring you have the knowledge to excel in your Class 10 exams.
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Asexual reproduction takes place through budding in
(a) Amoeba.
(b) Yeast.
(c) Plasmodium.
(d) Leishmania.
Asexual reproduction through budding takes place in (b) Yeast. In yeast, the budding process involves the formation of a bud, which is a small outgrowth on the parent yeast cell. This bud then enlarges, matures, and eventually detaches from the parent cell to become an independent yeast cell. This type of asexual reproduction allows for rapid multiplication and is a common way for yeast to propagate.
Which of the following is not a part of the female reproductive system in human beings?
(a) Ovary
(b) Uterus
(c) Vas deferens
(d) Fallopian tube
(c) Vas deferens is not a part of the female reproductive system in human beings. The vas deferens is part of the male reproductive system, where it transports sperm from the epididymis in preparation for ejaculation.
The anther contains
(a) sepals.
(b) ovules.
(c) pistil.
(d) pollen grains.
The anther is a part of a flower's stamen and contains:
(d) pollen grains.
The anther is responsible for producing and releasing pollen, which is essential for the process of fertilization in plants. Sepals, ovules, and the pistil are different parts of a flower. Sepals protect the developing bud; the ovule is contained within the ovary, and the pistil is the female reproductive part of a flower, which includes the stigma, style, and ovary.
What are the advantages of sexual reproduction over asexual reproduction?
Sexual reproduction has several advantages over asexual reproduction:
Genetic Diversity: Sexual reproduction combines genetic material from two parents, resulting in offspring with unique genetic combinations. This diversity is crucial for adaptation and survival in changing environments, as it increases the likelihood of some offspring being better suited to new challenges.
Evolutionary Adaptation: The genetic variation produced by sexual reproduction can accelerate evolution. Variants better adapted to their environment are more likely to survive and reproduce, leading to rapid evolutionary changes.
Disease Resistance: The genetic diversity from sexual reproduction can make populations more resilient to diseases. If some individuals are genetically resistant to a particular pathogen, the species is less likely to be wiped out by disease.
Elimination of Harmful Genes: Sexual reproduction allows harmful genes to be potentially masked or eliminated over generations through recombination and selection processes.
In essence, the primary advantage of sexual reproduction is its ability to generate genetic diversity, which is a key factor in the adaptability and long-term survival of species.
What are the functions performed by the testis in human beings?
The testes in human beings have several key functions, primarily:
Production of sperm (spermatogenesis): Testes are responsible for the generation of male gametes, known as sperm, necessary for reproduction.
Production of hormones: They also produce hormones such as testosterone, which is essential for the development of male secondary sexual characteristics and the maintenance of healthy reproductive tissues.
Why does menstruation occur?
Menstruation is a natural biological process that occurs as part of the female reproductive cycle. It involves the shedding of the uterine lining (endometrium) when pregnancy does not occur. Each month, the body prepares for a potential pregnancy. The ovaries release an egg (a process called ovulation), and the uterine lining thickens to support a potential fertilized egg. If the egg is not fertilized by sperm, pregnancy does not happen, and the body sheds the thickened lining through the vagina. This shedding results in menstrual bleeding. Menstruation is a key part of the menstrual cycle, which typically lasts between 21 to 35 days. This cycle is crucial for reproductive health and signifies a woman's fertility.
Draw a labelled diagram of the longitudinal section of a flower.
Peduncle: The stalk of the flower.
Receptacle: The part of the stem that holds the flower.
Sepals: These are the outer parts of the flower (collectively called the calyx) that protect the flower when it is a bud.
Petals: These are the parts of the flower that are often colorful and attract pollinators (collectively called the corolla).
Stamens: These are the male reproductive parts and are made up of the anther and the filament.
Anther: This is the part of the stamen that produces pollen.
Filament: It holds the anther up to position it for pollination.
Pistil or Carpel: This is the female reproductive part, which includes the stigma, the style, and the ovary.
Stigma: The top part of the pistil that receives pollen.
Style: The neck or stalk that leads down from the stigma to the ovary.
Ovary: This contains the ovules (future seeds).
Ovule: These are contained within the ovary and, once fertilized, will develop into seeds.
What are the different methods of contraception?
There are several methods of contraception designed to avoid pregnancy, which can be categorized into the following:
Mechanical barriers: This method involves creating a barrier so that sperm cannot reach the egg. Examples include condoms used on the penis and similar devices used in the vagina.
Hormonal contraceptives: These contraceptives work by altering the body's hormonal balance to prevent the release of eggs and thus avoid fertilization. These are usually taken orally as pills but can cause side effects due to the hormonal changes they induce.
Intrauterine devices (IUDs): Devices such as the loop or the copper-T are placed in the uterus to prevent pregnancy. They can sometimes cause side effects like irritation of the uterus.
Surgical methods: These involve blocking the vas deferens in males, which prevents the transfer of sperm, or blocking the fallopian tube in females, which prevents the egg from reaching the uterus, thus preventing fertilization.
How are the modes for reproduction different in unicellular and multicellular organisms?
In unicellular organisms, reproduction often occurs through asexual methods, such as binary fission, budding, or spore formation. These processes lead to the creation of offspring that are genetically identical to the parent, ensuring rapid population growth under favorable conditions. Multicellular organisms, on the other hand, can reproduce both asexually and sexually. Asexual reproduction in multicellular organisms, such as fragmentation or vegetative propagation in plants, also produces genetically identical offspring. However, sexual reproduction, involving the fusion of gametes (sperm and egg) from two parents, introduces genetic diversity. This diversity is crucial for the survival and evolution of species, enabling them to adapt to changing environments and resist diseases more effectively.
How does reproduction help in providing stability to populations of species?
Reproduction is a fundamental biological process that ensures the continuity of species over generations. It plays a critical role in providing stability to populations of species through several mechanisms:
Genetic Diversity: Reproduction, especially sexual reproduction, creates genetic variation among offspring. This diversity is crucial for a species' ability to adapt to changing environments, resist diseases, and reduce the chances of genetic defects, ensuring a healthier and more resilient population.
Population Maintenance: Through reproduction, species can maintain or increase their population size, compensating for mortality due to predation, disease, or aging. This balance between birth and death rates is essential for the long-term survival and stability of a species.
Adaptation and Evolution: Reproduction allows for the passing of advantageous traits to subsequent generations, facilitating adaptation to environmental changes over time. This evolutionary process helps species to thrive in diverse habitats and conditions, contributing to the ecological balance and stability of ecosystems.
In summary, reproduction is vital for the survival, adaptation, and evolution of species, ensuring their stability and continuity within ecosystems.
What could be the reasons for adopting contraceptive methods?
The adoption of contraceptive methods is driven by a variety of reasons, primarily to control when and if individuals or couples wish to have children. Family planning is a key reason, allowing for the spacing of pregnancies and enabling couples to decide the size of their family. It aids in maintaining the health and well-being of both the mother and child by avoiding unplanned pregnancies and reducing the risks associated with childbirth at very young or older ages. Contraceptive methods are also used to manage certain medical conditions, such as PCOS (Polycystic Ovary Syndrome) and endometriosis, which can be alleviated through hormonal contraceptives. Additionally, they serve a critical role in preventing the transmission of sexually transmitted infections (STIs), including HIV, when barrier methods like condoms are used. By providing control over reproductive health, contraceptives empower individuals, especially women, enhancing their autonomy and ability to participate more fully in society and the economy.
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State how the sperm is structurally adapted to reach and penetrate the ovum.
The sperm is structurally specialized to efficiently reach and penetrate the ovum:
Tail functionality: The sperm is equipped with a tail that acts as a propeller, enabling the sperm to move forward towards the ovum.
Energy supply in the mid-piece: The mid-piece of the sperm contains a high concentration of mitochondria. These mitochondria generate the necessary energy required for the tail's movement through ATP (adenosine triphosphate).
Acrosome's role in the head: The head of the sperm houses the acrosome, a specialized structure similar to a lysosome. The acrosome contains enzymes that break down the outer membrane of the ovum, allowing the sperm to penetrate it.
Entry during fertilization: It is primarily the head and the middle piece of the sperm that enter the ovum to achieve fertilization, each contributing essential genetic material and energetic support, respectively.
Through these adaptations, the sperm is effectively equipped to reach the ovum and facilitate fertilization.
During mitosis, homologous chromosomes pair up and separate.
A) True
B) False
The correct answer is B) False.
During mitosis, homologous chromosomes do not pair up; this is a characteristic of meiosis. In mitosis, each chromosome duplicates during DNA replication but does not engage in pairing or genetic recombination with its homologous partner. This pairing and recombination is a process specific to meiosis, contributing to genetic diversity in the resulting gametes.
The Okazaki fragments in DNA chain growth:
A) polymerize in the 5'-3' direction and explain 3'-5' DNA replication.
B) result in transcription.
C) polymerize in the 3'-to-5' direction and forms replication fork.
D) prove the semi-conservative nature of DNA replication.
The correct option is A: polymerize in the $5'$-$3'$ direction and explain $3'$-$5'$ DNA replication. The lagging strand in DNA replication is synthesized in the direction of $3'$ to $5'$, but nucleotides themselves are added in the direction from $5'$ to $3'$. This apparent contradiction is resolved by utilizing RNA primers, which are placed at regular intervals along the strand. Between these primers, short sequences of DNA are synthesized; these sequences are known as Okazaki fragments. Each Okazaki fragment polymerizes in the $5'$-$3'$ direction, elucidating the mechanism behind $3'$-$5'$ DNA replication.
Functional megaspore in an angiosperm develops into:
A. Endosperm
B. Embryo sac
C. Embryo
D. Ovule
The correct option is B. Embryo sac
In angiosperms, the functional megaspore is the initial cell that forms the female gametophyte. It undergoes three rounds of mitosis resulting in a structure called the embryo sac, which ultimately contains eight nuclei and seven cells. This structure is crucial for fertilization and subsequent development of the seed.
Explain pollination.
Pollination is the process of transferring pollen grains from the male anther of a flower to the female stigma. This transfer is crucial as it enables plants to reproduce by creating seeds. These seeds carry genetic information needed to grow new plants. This process is essential for the continuation of plant species, allowing them to produce offspring for subsequent generations.
The diagram below illustrates the change that occurred in the frequency of phenotypes in an insect population over 10 generations. A probable explanation for this change would be that over time there was:
A) a decrease in the adaptive value of gene a
B) an increase in the adaptive value of gene a
C) an increase in the population of this insect
D) a decrease in the mutation rate of gene A
The correct option is B) an increase in the adaptive value of gene a.
In population genetics, it's observed that traits benefiting a species tend to become more prevalent over time. In this scenario, the increase in frequency of a particular phenotype (e.g., spots on the insects) suggests that these spots likely provide a camouflage advantage. Consequently, the gene 'a', which influences this trait, has had an increase in its adaptive value in the population over the generations. This environmental favorability leads to a higher occurrence of the gene in the population.
The testes in humans are present outside the body in the scrotal sacs because sperm develops at around 35 degrees Celsius, which is slightly less than the normal body temperature.
A) True
B) False
The correct answer is A) True.
Testes are located outside the body within the scrotal sacs primarily because the ideal temperature for sperm production is around 35 degrees Celsius, which is 2-3 degrees Celsius lower than the normal body temperature. The scrotal sacs dynamically adjust their surface area to help maintain a constant temperature optimal for sperm development.
What is not true about asexual reproduction?
A. It does not involve union of gametes.
B. It involves only one parental organism.
C. It involves two organisms of different sexes.
D. There is no mixing of genetic materials of two individuals.
The correct option is C. It involves two organisms of different sexes.
Asexual reproduction is defined by the characteristic where a single parent produces offspring without the involvement of gamete fusion. Unlike sexual reproduction, there is no formation of gametes, and no fertilization occurs, meaning there is no contribution from a second parent of a different sex.
Indicate whether the following statements are True (T) or False (F). Binary fission is a method of asexual reproduction. ()
The statement "Binary fission is a method of asexual reproduction" is True (T).
Asexual reproduction involves only one parent, resulting in offspring that are genetically identical to the parent. Binary fission is indeed a form of asexual reproduction wherein an organism replicates its DNA and divides into two parts, each one developing into a separate individual. This method is typical in prokaryotic organisms such as bacteria.
Which is the key feature for the members of a species?
A) Ability to interbreed
B) Similar size
C) Almost the same genotype
D) Similar appearance
The correct answer is A) Ability to interbreed.
A species is defined as a group of living organisms that consist of similar individuals capable of exchanging genes or interbreeding. This ability ensures that they are reproductively isolated from other groups.
The clones are developed by nuclear transfer into the host cell.
A. induced
B. natural
C. molecular
D. therapeutic
The correct answer is A. induced
Induced clones are developed through the process of nuclear transfer into a host cell. This method is an artificial technique used to create identical organisms by transferring nuclear genetic material.
Which among the following are correct statements about cloning?
A. Dolly is a clone of Finn Dorsett sheep.
B. Cow was the first mammal to be cloned.
C. Cloning is a process by which the exact copy of an organism is produced.
D. Cell was collected from the mammary gland of a male Finn Dorsett sheep.
The correct statements regarding cloning are:
A: Dolly is a clone of Finn Dorsett sheep.
C: Cloning is a process by which the exact copy of an organism is produced.
Explanation:
Cloning refers to the method in which an identical copy of a cell, part, or a complete organism is produced. This includes not only simple organisms, but animals and plants as well.
The significant achievement of cloning a mammal was marked by the creation of Dolly the sheep, who was born on July 5th, 1996. This event was led by Ian Wilmut and his team, marking her as the first successfully cloned mammal.
In the case of Dolly, cloning involved taking a cell from the mammary gland of a female Finn Dorsett sheep, which is significant because it highlights the donor was female, which makes statement D incorrect.
Note that Dolly's cloning was pivotal in the field of genetics, underscoring the potential of cloning technology and its implications for genetics and medicine.
Arrange the following events in DNA replication (top to bottom):
A. DNA unwinds
B. Strands separate
C. Strands scanned
D. New strands made
E. Copies created
The process of DNA replication involves several critical steps, each building on the previous one to ensure accurate copying of genetic information. Here’s the sequence of events:
DNA Unwinds: The double-helix structure of DNA unwinds to expose the strands for replication.
Strands Separate: The unwound strands then separate, making the individual single strands accessible for the replication machinery.
Strands Scanned: Each of the separated strands is scanned for any issues that might interfere with the replication process.
New Strands Made: New strands are synthesized using the original strands as templates, ensuring the genetic code is accurately copied.
Copies Created: The end result is the creation of two complete sets of DNA, each consisting of one original strand and one new strand.
This sequence ensures that the genetic information is duplicated accurately and efficiently, ready for cell division.
Why do organisms reproduce at the expense of energy even though reproduction is not as vital as respiration, excretion, etc.?
A. It's a basic instinct which cannot be avoided.
B. To continue their species.
C. To generate more energy and efficiency in the life processes.
D. To make organisms more vulnerable to natural changes.
The correct answer is B - To continue their species.
Reproduction, unlike vital processes such as respiration, digestion, and circulation, is not directly essential for an individual organism's survival. However, it involves significant energy consumption. Despite this, organisms engage in reproduction primarily to ensure the survival and continuation of their species in the biosphere.
Protein helping in opening of DNA double helix in front of replication fork is: a. DNA gyrase b. DNA polymerase I c. DNA ligase d. DNA topoisomerase
The correct answer to the question is:
a. DNA gyrase
DNA gyrase is an enzyme that plays a crucial role in the process of DNA replication by assisting in the opening of the DNA double helix ahead of the replication fork, thus facilitating the unwinding necessary for replication to occur. This enzyme specifically relieves the strain of unwinding by introducing negative supercoils into the DNA, making it a vital component in the replication machinery.
Binary fission describes the type of reproduction where the organism divides to form: (a) many spores (b) two daughters (c) many buds (d) two hyphae
The correct answer is (b) two daughters.
In binary fission, a single-celled organism divides into two daughter cells that are identical to the parent cell. This process is common among prokaryotes such as bacteria.
Not all living things reproduce.
A) True
B) False
The correct answer is A) True.
It is a common misconception that all living things reproduce. In reality, certain individual organisms, due to defects, conditions, or artificial modifications, may not reproduce. For example, sterile animals and seedless plants cannot reproduce. Hence, while reproduction is a characteristic of living species as a whole, not every individual necessarily has the capability to reproduce.
Formation of RNA over the template of DNA is:
A) Replication B) Translation C) Transversion D) Transcription
The correct answer is D) Transcription.
Transcription refers to the process where RNA is formed from a DNA template.
Genetic recombination due to crossing over of broken segments of chromatids occurs in the __________ stage of prophase I of meiosis.
A. Diplotene B. Leptotene C. Pachytene D. Zygotene
The correct answer is C. Pachytene.
In the Pachytene stage of prophase I in meiosis, the homologous chromosomes align very closely along their lengths. At this juncture, the chromatids often break and exchange segments, a process known as crossing over. This exchange promotes genetic recombination, which is crucial for the genetic diversity seen in sexually reproducing organisms. The points where the chromatids crossover are called chiasmata, and these visible structures highlight the physical crossing over and exchange of genetic material.
Hydra reproduce by which of the following methods of asexual reproduction?
A) Binary fission
B) Fragmentation
C) Budding
D) Both B and C
The correct answer is D) Both B and C.
Hydra can reproduce through budding and fragmentation, which are both forms of asexual reproduction:
In budding, Hydra forms an outgrowth due to repeated cell division at a specific site of the parent body. This outgrowth, known as a bud, develops into a tiny individual. Upon maturity, the bud detaches from the parent body and functions as a new, independent individual.
Fragmentation occurs when the body of a Hydra breaks into separate pieces, each called a fragment. Each fragment then grows and matures into a fully grown adult Hydra capable of reproduction.
It's important to note that binary fission, another form of asexual reproduction, involves a parent cell dividing into two halves, with each half growing rapidly into an adult. Examples include organisms like Amoeba and Paramecium, but this process does not occur in Hydra.
What is budding? Explain with an example. [2 MARKS]
Explanation:
Budding is a form of asexual reproduction, distinguished by the development of a new organism from an outgrowth or bud on the body of the parent. During this process, a bud forms which is initially a small protrusion. As the bud grows, it develops the attributes resembling those of the parent organism. Eventually, the mature bud detaches from the parent body and becomes an independent new organism, or in some scenarios, the bud remains physically connected, leading to colonial growths.
Example:
A typical example of budding can be found in yeast. In yeast cells, the budding process begins with the formulation of a small bud on the parent yeast cell. This bud then enlarges, matures, and finally separates to form a new yeast cell that is genetically identical to the parent. The image below illustrates budding in yeast:
In summary, budding is an efficient means of reproduction in certain organisms like yeast, allowing rapid colonization and proliferation under suitable conditions.
DNA polymerases are generally used in DNA replication.
A) To cut the helix at certain places.
B) For proofreading.
C) For breaking and joining pieces of one DNA strand.
D) For adding carbonyl compound.
The correct answer is B) For proofreading.
Proofreading is a crucial function of DNA polymerases during DNA synthesis. It involves the enzyme checking each newly added nucleotide against the template strand to ensure correct base pairing. If a mismatch is detected, DNA polymerase has the ability to excise the incorrect nucleotide in the direction from $3'$ to $5'$. This error-correction process helps maintain the accuracy and integrity of the DNA sequence being replicated.
What are the factors leading to speciation? How do these factors lead to speciation?
Factors Leading to Speciation
Speciation is the process through which new species are formed from preexisting ones. Several factors contribute to speciation:
Geographical Barrier
Natural Selection
Genetic Drift
Large Mutation
Let's examine how each of these factors leads to the formation of new species:
Geographical Barrier
Geographical Isolation occurs when a species or a group of individuals becomes isolated from others by a physical barrier such as a river, mountain, or glacier.
This isolation results in reproductive isolation, preventing interbreeding between the separated groups.
Over time, this reproductive isolation due to geographical barriers can lead to the evolution of new species.
Natural Selection
Natural selection is the process where nature selects individuals that can survive most effectively in a particular environment due to the presence of beneficial traits.
These variations make certain individuals more fit to survive environmental stresses.
Natural selection leads to the survival and reproduction of these well-suited varieties while less suited ones perish, eventually resulting in the formation of new species.
Genetic Drift
Genetic drift refers to the sudden change in the frequency of alleles within a given population.
This random change in allele frequencies can significantly impact the genetic makeup of a population, potentially leading to the emergence of new species.
Large Mutation
Mutation involves any change in the DNA.
Significant changes (large mutations) in DNA can lead to substantial genetic differences, allowing for the development of new species.
In conclusion, the interplay of geographical barriers, natural selection, genetic drift, and large mutations drives the evolution of new species from preexisting ones through various mechanisms of isolation, selection, and genetic variation.
What is mitosis in brief and how is the process happening in sexual reproduction?
Understanding Mitosis and its Role in Sexual Reproduction
Mitosis is a type of cell division in which a single cell (the parent) divides to produce two genetically identical daughter cells. This division ensures each daughter cell receives an identical set of chromosomes. Within the cell cycle, mitosis is the phase where the DNA in the cell's nucleus is divided into two equal sets of chromosomes.
Mitosis in Context of Sexual Reproduction
In sexual reproduction, two reproductive cells known as gametes come together through the process of fertilization. These gametes are formed through a specialized type of cell division called meiosis, which reduces the chromosome number by half. This ensures that when gametes fuse, the resulting cell restores the proper diploid chromosome number.
Haploid ($ n $) Cells: Gametes containing a single set of chromosomes.
Diploid ($ 2n $) Cells: Somatic (body) cells having two sets of chromosomes.
When fertilization occurs, the fusion of haploid gametes reconstructs the diploid chromosome number in the zygote, the first cell of a new individual.
Human Life Cycle
In humans, haploid gametes created via meiosis came together to form a diploid zygote. This zygote then undergoes mitosis repeatedly to grow and develop into an adult human. The cycle continues when the adult generates new haploid gametes, starting the reproductive process anew.
By maintaining the balance between meiosis and mitosis, organisms ensure genetic stability while allowing for genetic diversity through sexual reproduction.
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