Chapter 1: Previous Year Paper - 2021 (Term- I)

Time allowed: 2 hours Maximum Marks: 40

General Instructions:

Read the following instructions very carefully and strictly follow them:

1. This question paper comprises 15 questions. All questions are compulsory. (ii) (iii) (iv) (v) (vi) 1. 2. 3. 4.

2. This question paper is divided into three sections Section A, B and C.

3. SECTION A: Questions No. 1 to 7 are short answer type questions. Each question carries 2 marks.

4. Section B: Questions No. 8 to 13 are also short answer type questions. Each question carries 3 marks.

5. Section C: Questions No. 14 and 15 are case-based questions. Each question carries 4 marks.

6. Internal choices have been provided in some questions. Only one of the alternatives has to be attempted.

SECTION A

1. a.) Write the molecular formula of the following carbon compounds:

(i) Methane

Answer. The molecular formula of methane is CH4.

(ii) Propane

Answer: The molecular formula of propane is C³H8.

b.) Carbon compounds have low melting and boiling points. Why?

Answer: Carbon compounds, particularly hydrocarbons, tend to have low melting and boiling points because:

i. They generally consist of molecules held together by weak intermolecular forces like van der Waals forces (dispersion forces).

ii. These forces are much weaker compared to covalent or ionic bonds, meaning less energy is required to break these forces and change the state of the compound (solid to liquid or liquid to gas).

2. The electrons in the atoms of two elements X and Y are distributed in three shells having 1 and 7 electrons respectively in their outermost shells.

(a) Write the group numbers of these elements in the Modern Periodic Table.

Answer: X: Since element X has 1 electron in its outermost shell, it belongs to Group 1 (alkali metals) of the Modern Periodic Table.

Y: Since element Y has 7 electrons in its outermost shell, it belongs to Group 17 (halogens) of the Modern Periodic Table.

(b) Write the molecular formula of the compound formed when X and Y combine with each other.

Answer: Element X (Group 1) will lose 1 electron to become positively charged (cation), and element Y (Group 17) will gain 1 electron to become negatively charged (anion).

Therefore, they will combine in a 1:1 ratio to form a neutral compound. The molecular formula of the compound formed is XY.

(c) Which of the two is electropositive?

Answer: Element X is electropositive. Electropositive elements tend to lose electrons easily. Since X has 1 electron in its outermost shell, it will likely lose that electron and form a cation, making it electropositive.

Element Y, on the other hand, is electronegative, as it tends to gain electrons to complete its outer shell.

3. a) Which of the following flowers will have higher possibility of self-pollination?

Mustard, Papaya, Watermelon, Hibiscus

Answer: Mustard flowers have a higher possibility of self-pollination due to their structure, while papaya, watermelon, and hibiscus mainly rely on cross-pollination.

b) List the two reproductive parts of a bisexual flower.

Answer: Stamens (Male reproductive part) and Pistil (Female reproductive part)

4. Which one of the two multicellular organisms - Spirogyra and Planaria reproduces by regeneration and why? Give an example of any other organism which can also reproduce by the same process.

Answer: Planaria reproduces by regeneration. This means that if a part of the body is lost or damaged, Planaria can regenerate the lost part and form a new organism. This is possible due to the high regenerative ability of Planaria's cells, which can divide and differentiate into different cell types.

Spirogyra, on the other hand, is a filamentous-algae that reproduces primarily through fragmentation, where parts of the filaments break off and grow into new individuals. While Spirogyra can regenerate, it does not exhibit the same level of regenerative capability as Planaria.

Example of another organism that reproduces by regeneration:

Starfish: If a starfish loses a limb, it can regenerate the lost limb and sometimes even regenerate a whole new starfish from a part of the body.

5.(a) What is variation? List two main reasons that may lead to variation in a population.

Answer: Variation refers to the differences in characteristics or traits within a population of organisms. It can occur in physical appearance, behavior, or genetic makeup, among other factors. This variation is essential for the process of natural selection and evolution.

Two main reasons that may lead to variation in a population are:

i. Genetic Mutation: Mutations are random changes in an organism's DNA sequence. These can introduce new traits into a population, which may be beneficial, neutral, or harmful. Over time, beneficial mutations may be passed down to future generations.

ii. Sexual Reproduction: During sexual reproduction, genetic material from two different parents combines, leading to offspring with unique genetic combinations. This shuffling of genes increases genetic diversity in a population.

OR

(b) (i) In a cross between violet flowered plants and white flowered plants, state the characteristics of the plants obtained in the F¹ progeny.

Answer: In a cross between violet-flowered plants and white-flowered plants, assuming the flower color is determined by a simple Mendelian inheritance pattern where violet (V) is dominant over white (v), the characteristics of the F¹ progeny would be as follows:

Genotype: The F¹ progeny will inherit one allele for flower color from each parent. If the violet-flowered plant is homozygous dominant (VV) and the white-flowered plant is homozygous recessive (vv), all F¹ progeny will have the genotype Vv.

Phenotype: Since violet (V) is dominant over white (v), all F¹ progeny will have violet flowers. They will exhibit the dominant trait despite carrying one recessive allele for white flowers.

Therefore, all F¹ plants will have violet flowers, but they will be heterozygous (Vv) for the flower color gene.

(ii) If the plants of F¹ progeny are self-pollinated, then what would be observed in the plants of F² progeny?

Answer: If the F¹ progeny plants (which are heterozygous Vv) are self-pollinated, the resulting F² progeny will exhibit a 3:1 phenotypic ratio for flower color, with the following observations:

Genotypic ratio: The F² progeny will inherit one allele from each parent. Since the F¹ plants are Vv (heterozygous), the cross would be:

Vv × Vv.

This will produce the following possible genotypes:

VV (homozygous dominant)

Vv (heterozygous)

vv (homozygous recessive)

The genotypic ratio in the F² progeny will be:

1 VV: 2 Vv: 1 vv.

Phenotypic ratio: Since violet (V) is dominant over white (v), both VV and Vv will result in violet flowers, while only vv will result in white flowers.

The phenotypic ratio will therefore be:

3 violet-flowered plants: 1 white-flowered plant.

Thus, the F² progeny will show a 3:1 ratio of violet-flowered to white-flowered plants.

(iii) If 100 plants are produced in Fo progeny, then how many plants will show the recessive trait?

Answer: In the F² progeny, the recessive trait (white flowers) will only appear in plants with the vv genotype. Based on the 3:1 phenotypic ratio (3 violet-flowered plants for every 1 white-flowered plant), we can calculate the number of plants that will show the recessive trait in a population of 100 plants.

Since one out of every four plants is expected to have the vv genotype (which results in white flowers), the number of plants showing the recessive trait in a population of 100 will be:

Number of recessive trait plants=1/4×100=25

So, 25 plants in the F² progeny will show the recessive trait (white flowers).

6. (a) (i) Name and state the rule to determine the direction of force experienced by a current carrying straight conductor placed in a uniform magnetic field which is perpendicular to it.

Answer: The rule used to determine the direction of the force experienced by a current-carrying straight conductor placed in a uniform magnetic field that is perpendicular to it is Fleming's Left-Hand Rule.

This rule states that if you stretch the thumb, index finger, and middle finger of your left hand so that they are perpendicular to each other, then:

i. Thumb: represents the direction of the force (motion of the conductor).

ii. Index Finger: represents the direction of the magnetic field (from North to South).

iii. Middle Finger: represents the direction of the current (flow of electrons in the conductor).

When you align your hand in this way, the direction of the force experienced by the conductor will be in the direction of the thumb.

(ii) An alpha particle while passing through a magnetic field gets projected towards...