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GeneralClass 10CBSE

C2H5OH → C2H5Br (Ethyl bromide)

React ethanol with HBr (or PBr₃). The -OH group is protonated, making water a leaving group, and Br⁻ substitutes via SN2.

GeneralClass 10CBSE

Which is NOT a Union Territory? 

Mizoram is a full-fledged State of India (became the 23rd state on 20 February 1987). Chandigarh and Daman and Diu are Union Territories.India's 8 Union Territories (as of 2020):Union TerritoryCapital 1Delhi (NCT)New Delhi2ChandigarhChandigarh3PuducherryPuducherry4Jammu and KashmirSrinagar/Jammu5LadakhLeh6Andaman and Nicobar IslandsPort Blair7LakshadweepKavaratti8Dadra and Nagar Haveli and Daman and DiuDamanIndia now has 8 Union Territories (not 7 updated after 2019–2020 reorganisation). Part VIII (Articles 239–242) of the Constitution governs UTs.

GeneralClass 10CBSE

How do characteristics of mother and father get transmitted in a human embryo?

Characteristics are transmitted through genetic inheritance via chromosomes. The mother contributes 23 chromosomes through the egg and the father contributes 23 through the sperm. When they fuse at fertilisation, the embryo receives 46 chromosomes (23 pairs) half from each parent. Each chromosome carries thousands of genes that code for traits like eye colour, blood group, height, and skin tone.

ScienceClass 10CBSE

While humans have chromosomal sex determination, some organisms exhibit environmental sex determination. Give an example of an organism where sex is determined by environmental factors and briefly explain how it works.

An example of an organism where sex is determined by environmental factors is the green sea turtle (and many other reptile species like crocodiles and alligators). In green sea turtles, the sex of the hatchlings is determined by the temperature at which the eggs are incubated during a critical period of embryonic development. This phenomenon is known as Temperature-Dependent Sex Determination (TSD). High Incubation Temperatures: Typically produce female offspring. Low Incubation Temperatures: Typically produce male offspring. Intermediate Temperatures: Can produce a mix of both sexes. This means that the same genetic makeup can lead to either a male or a female, depending on the external environmental conditions experienced by the embryo. This is a significant contrast to chromosomal sex determination where sex is fixed at fertilization.

ScienceClass 10CBSE

In a dihybrid cross, if the F1 generation has genotype RrYy, what proportion of gametes produced by this F1 individual will carry the alleles 'RY'? Justify your answer based on Mendel's laws.

The F1 individual has the genotype RrYy. According to Mendel's Law of Independent Assortment, the alleles for different genes (in this case, R/r for seed shape and Y/y for seed color) assort independently of each other during gamete formation. This means that the segregation of R and r is independent of the segregation of Y and y. For the 'R' gene, the individual Rr will produce gametes with 'R' and 'r' alleles in equal proportions (1/2 R, 1/2 r). For the 'Y' gene, the individual Yy will produce gametes with 'Y' and 'y' alleles in equal proportions (1/2 Y, 1/2 y). To find the proportion of gametes carrying 'RY', we multiply the probabilities of inheriting 'R' and 'Y': P(R) = 1/2 P(Y) = 1/2 P(RY) = P(R) * P(Y) = (1/2) * (1/2) = 1/4 Therefore, 1/4 (or 25%) of the gametes produced by the RrYy individual will carry the alleles 'RY'. The other types of gametes (Ry, rY, ry) will also be produced in equal proportions of 1/4 each.

ScienceClass 10CBSE

Compare the amount of variation generated in a population through asexual reproduction versus sexual reproduction. Which mode of reproduction is more advantageous for evolution and why?

Variation in Asexual Reproduction: Asexual reproduction typically involves a single parent producing genetically identical offspring (clones). Variations in asexually reproducing organisms arise primarily due to random mutations during DNA replication. The rate of mutation is generally low, so the amount of variation generated in a population through asexual reproduction is very limited. Variation in Sexual Reproduction: Sexual reproduction involves the fusion of gametes from two parents, leading to a recombination of genetic material. Key processes like crossing over during meiosis, independent assortment of chromosomes, and random fertilization introduce a significant amount of genetic variation in each generation. Offspring are genetically unique, inheriting a novel combination of traits from both parents. Advantage for Evolution: Sexual reproduction is generally more advantageous for evolution. The high degree of variation generated through sexual reproduction provides a wider range of phenotypes for natural selection to act upon. In a changing environment, this increased genetic diversity makes it more likely that some individuals will possess traits that allow them to survive and reproduce, thus ensuring the adaptation and long-term survival of the species. While asexual reproduction is efficient in stable environments, its limited variation can make a species vulnerable to rapid environmental changes, potentially leading to extinction.

ScienceClass 10CBSE

Mendel used several contrasting characters in his pea plant experiments. List any four such contrasting characters and explain why pea plants were a good choice for his experiments.

Four contrasting characters Mendel studied in pea plants: 1. Stem Height: Tall vs. Dwarf 2. Seed Shape: Round vs. Wrinkled 3. Seed Color: Yellow vs. Green 4. Pod Shape: Inflated vs. Constricted 5. Pod Color: Green vs. Yellow 6. Flower Color: Purple vs. White 7. Flower Position: Axial vs. Terminal Reasons why pea plants were a good choice for Mendel's experiments: 1. Easily Cultivated: Pea plants are easy to grow and maintain in a garden setting. 2. Short Life Cycle: They have a relatively short generation time, allowing Mendel to observe multiple generations in a reasonable period. 3. Self-pollinating: Pea plants naturally self-pollinate, which allowed Mendel to obtain pure-breeding lines (homozygous for specific traits) easily. 4. Cross-pollination Possible: They can also be easily cross-pollinated artificially by hand, enabling controlled crosses between different parental plants. 5. Distinct Contrasting Traits: Pea plants exhibit several easily observable and distinct contrasting traits (e.g., tall vs. dwarf, round vs. wrinkled seeds) that were not blended in hybrids. 6. Large Number of Offspring: Each cross produced a large number of seeds, providing statistically significant data for analysis.

ScienceClass 10CBSE

Why is variation important for the survival of a species, especially in changing environmental conditions? Illustrate with an example.

Variation is crucial for the survival of a species because it provides the raw material for natural selection to act upon, allowing populations to adapt to changing environmental conditions.If all individuals in a population were genetically identical, a sudden change in the environment (e.g., a new disease, climate change, or a new predator) could potentially wipe out the entire species if no individual possessed a trait that allowed them to survive the change. With variation, some individuals might possess traits that make them better suited to the new conditions. These individuals are more likely to survive, reproduce, and pass on their advantageous traits to their offspring. Over time, the frequency of these beneficial traits increases in the population, leading to adaptation and the continued survival of the species. Example: Consider a population of insects living on a plant species. If a new pesticide is introduced that kills most of the insects, a few individuals might have a naturally occurring genetic variation that makes them resistant to the pesticide. These resistant insects will survive while others perish. They will then reproduce, and their offspring will inherit the resistance. Over several generations, the population will evolve to become largely resistant to the pesticide, ensuring the survival of the species despite the environmental challenge.

ScienceClass 10CBSE

Distinguish between acquired and inherited traits with two examples for each. Why are acquired traits generally not passed on to the next generation?

Acquired Traits: These are characteristics that an individual develops during its lifetime due to environmental influences, experiences, or lifestyle choices. They are not encoded in the organism's DNA and therefore cannot be passed on to offspring. Examples: 1. A person developing strong muscles through weightlifting. 2. A scar resulting from an injury. 3. Learning to play a musical instrument. 4. A change in skin color due to sun exposure. Inherited Traits: These are characteristics that are passed down from parents to their offspring through genes. They are encoded in the organism's DNA and are present from birth. Examples: 1. Eye color (e.g., blue eyes, brown eyes). 2. Hair color and texture (e.g., straight hair, curly hair). 3. Blood group (e.g., A, B, AB, O). 4. Genetic diseases like color blindness or hemophilia. Acquired traits are generally not passed on to the next generation because they involve changes to somatic (body) cells, not germ (reproductive) cells. Only the genetic information present in the germ cells (sperm and egg) is transmitted to the offspring. Changes in body cells, even if significant for the individual, do not alter the genetic code that will be inherited by the next generation.

ScienceClass 10CBSE

Describe the chromosomal mechanism of sex determination in humans. What are the possible combinations of chromosomes in the gametes produced by males and females, and how do these combinations lead to male or female offspring?

In humans, sex determination is primarily chromosomal, involving two sex chromosomes: X and Y. Females have two X chromosomes (XX), while males have one X and one Y chromosome (XY). Gamete Production: Females (XX): During meiosis, females produce only one type of gamete (egg) with respect to sex chromosomes, which always carries an X chromosome. Males (XY): During meiosis, males produce two types of gametes (sperm) in approximately equal proportions: half carry an X chromosome and half carry a Y chromosome. Offspring Determination: When fertilization occurs, the sex of the offspring is determined by the sperm that fertilizes the egg: If an egg (X) is fertilized by a sperm carrying an X chromosome, the resulting zygote will be XX, developing into a female. If an egg (X) is fertilized by a sperm carrying a Y chromosome, the resulting zygote will be XY, developing into a male. Therefore, it is the male parent who determines the sex of the offspring in humans.

ScienceClass 10CBSE

Differentiate between Mendel's Law of Segregation and Law of Independent Assortment. Explain each law with a suitable example from pea plant crosses.

Mendel's Law of Segregation states that during the formation of gametes, the two alleles for a heritable character separate (segregate) from each other such that each gamete carries only one allele for that character. When the egg and sperm unite, they bring together two alleles for each character.For example, in a monohybrid cross involving pea plants for stem height (Tall 'T' and dwarf 't'), a heterozygous parent (Tt) will produce gametes where 50% carry the 'T' allele and 50% carry the 't' allele. These alleles segregate during gamete formation. Mendel's Law of Independent Assortment states that during gamete formation, the alleles for different genes assort independently of each other. This means that the inheritance of one trait does not influence the inheritance of another trait, as long as the genes are located on different chromosomes or are far apart on the same chromosome. For example, in a dihybrid cross involving pea plants for seed shape (Round 'R' and wrinkled 'r') and seed color (Yellow 'Y' and green 'y'), the alleles for seed shape (R/r) will assort independently of the alleles for seed color (Y/y). A dihybrid parent (RrYy) will produce four types of gametes (RY, Ry, rY, ry) in equal proportions, demonstrating that the segregation of R and r is independent of the segregation of Y and y.

ScienceClass 10CBSE

Explain the concept of 'accumulation of variations' in a population during sexual reproduction, and how it contributes to evolution. Provide an example.

Accumulation of variations refers to the gradual build-up of small differences in traits within a population over generations. In sexual reproduction, variations arise due to processes like crossing over during meiosis, independent assortment of chromosomes, and random fertilization. Each new offspring inherits a unique combination of genes from its parents, leading to slight variations in their characteristics. These small, individual variations, when passed down and compounded over many generations, can lead to significant changes in the overall characteristics of a population. This continuous accumulation of variations provides the raw material for natural selection to act upon, driving the process of evolution. For example, consider a population of bacteria exposed to an antibiotic. Some bacteria might have a slight genetic variation that confers a small degree of resistance to the antibiotic. While this resistance might not be immediately obvious, if these slightly resistant bacteria survive and reproduce more effectively in the presence of the antibiotic, their offspring will inherit this variation. Over many generations, the accumulation of such advantageous variations can lead to a population that is largely resistant to the antibiotic, demonstrating evolution.

ScienceClass 10CBSE

Discuss the significance of the 'Law of Independent Assortment' in understanding genetic diversity. Provide an example to illustrate this law.

The Law of Independent Assortment states that alleles for different genes assort independently of one another during gamete formation. This means that the inheritance of one trait does not influence the inheritance of another trait, as long as the genes are located on different chromosomes or are far apart on the same chromosome. This law is crucial for understanding genetic diversity because it explains how new combinations of traits can arise in offspring that are not present in either parent. For example, in a dihybrid cross involving seed shape (Round/Wrinkled) and seed color (Yellow/Green), a parent with Round Yellow seeds (RRYY) and another with Wrinkled Green seeds (rryy) will produce F1 offspring that are all Round Yellow (RrYy). When these F1 individuals produce gametes, the alleles for seed shape (R/r) assort independently of the alleles for seed color (Y/y), leading to four possible gamete combinations (RY, Ry, rY, ry) in equal proportions. This independent assortment allows for a wide variety of phenotypic combinations in the F2 generation, contributing significantly to genetic variation within a population.

ScienceClass 10CBSE

A genetic cross involves a true-breeding plant with red flowers (RR) and a true-breeding plant with white flowers (rr). If red is dominant over white, what is the probability of obtaining white-flowered plants in the F2 generation?

First, the cross between RR and rr will produce an F1 generation that is entirely Rr (red flowers). When two F1 plants (Rr x Rr) are crossed, the F2 generation will have genotypes RR, Rr, and rr in a 1:2:1 ratio. The phenotypes will be 3 red (RR, Rr) : 1 white (rr). Therefore, the probability of obtaining white-flowered plants in the F2 generation is 1/4 or 25%.

ScienceClass 10CBSE

How does the environment sometimes influence sex determination in certain organisms, contrasting with the chromosomal mechanism in humans?

While humans and many other organisms use a chromosomal mechanism for sex determination, some species exhibit environmental sex determination. In these cases, external factors like temperature, pH, or social cues during development can influence whether an individual develops as male or female. For example, in many reptiles like crocodiles and turtles, the temperature at which eggs are incubated determines the sex of the hatchlings. Higher temperatures might lead to one sex, while lower temperatures lead to the other. This contrasts with humans where sex is fixed at fertilization by the combination of X and Y chromosomes, regardless of environmental conditions during gestation.

ScienceClass 10CBSE

Explain the Law of Segregation using an example of a monohybrid cross involving flower color in pea plants (Purple is dominant over white).

The Law of Segregation states that during the formation of gametes, the two alleles for a heritable character segregate (separate) from each other such that each gamete receives only one allele. For example, if we cross a pure-breeding purple-flowered pea plant (PP) with a pure-breeding white-flowered pea plant (pp), the F1 generation will all be heterozygous purple (Pp). When these F1 plants form gametes, the 'P' allele and the 'p' allele segregate, so that half the gametes will carry 'P' and half will carry 'p'. This segregation ensures that the recessive trait (white flowers) reappears in the F2 generation when two F1 individuals are crossed (Pp x Pp), resulting in a 3:1 phenotypic ratio (3 purple: 1 white).

ScienceClass 10CBSE

Consider a monohybrid cross between a homozygous dominant tall pea plant (TT) and a homozygous recessive dwarf pea plant (tt). What will be the genotype and phenotype of the F1 generation?

The homozygous dominant tall pea plant has genotype TT, and the homozygous recessive dwarf pea plant has genotype tt. The gametes produced by the tall plant will all carry the 'T' allele, and the gametes produced by the dwarf plant will all carry the 't' allele. When these are crossed, all offspring in the F1 generation will have the genotype Tt. Since 'T' (tallness) is dominant over 't' (dwarfness), the phenotype of all F1 offspring will be tall.

ScienceClass 10CBSE

Explain the concept of 'sex determination' in humans. What role do the X and Y chromosomes play in this process?

In humans, sex determination is primarily chromosomal. Females typically have two X chromosomes (XX), while males typically have one X and one Y chromosome (XY). During reproduction, the mother always contributes an X chromosome to the offspring. The father, however, can contribute either an X or a Y chromosome. If the father contributes an X chromosome, the offspring will be XX (female). If the father contributes a Y chromosome, the offspring will be XY (male). The presence or absence of the Y chromosome, specifically the SRY gene on it, is crucial in triggering the development of male characteristics.

ScienceClass 10CBSE

Differentiate between acquired and inherited traits, providing an example for each.

Acquired traits are characteristics that an organism develops during its lifetime in response to environmental influences or experiences. These traits are not encoded in the organism's DNA and therefore cannot be passed on to offspring. An example is a person developing strong muscles through exercise or learning to play a musical instrument. Inherited traits, on the other hand, are characteristics determined by an organism's genes, which are passed down from parents to offspring. These traits are encoded in the DNA and are heritable. An example is eye color, hair color, or genetic predispositions to certain diseases.

ScienceClass 10CBSE

Describe Gregor Mendel's experiment with pea plants that led to the formulation of the Law of Dominance. What specific observations supported this law?

Mendel's experiment for the Law of Dominance involved crossing pure-breeding tall pea plants with pure-breeding dwarf pea plants (P generation). He observed that all the offspring in the first filial (F1) generation were tall. When he self-pollinated these F1 tall plants, the second filial (F2) generation produced both tall and dwarf plants in a 3:1 ratio. The specific observation that supported the Law of Dominance was that in the F1 generation, only one of the parental traits (tallness) was expressed, while the other trait (dwarfness) remained hidden or masked. This indicated that one allele (for tallness) was dominant over the other (for dwarfness).

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