Biology: Topic-wise Test- 3 - NEET MCQ

In a test cross:

• The organism with the dominant trait is always crossed with an organism with the recessive trait. 
• If any offspring show the recessive trait, the unknown genotype is heterozygous. 
• If all the offspring have the dominant trait, the unknown genotype is homozygous dominant.

Fig: The test cross

Hence, the correct option is A

NCERT Reference: Topic INHERITANCE OF ONE GENE of chapter "Principles of Inheritance and Variation"  of NCERT.

Autolysis, caused by the lysosomal enzymes, plays a role in the disappearance of tail during the metam orphosis of frog's tadpole, and in softening of gum tissue to allow eruption of teeth in vertebrates. For autolysis, enzymes of primaryly so somes are  released from the cell. Autolysis occur in ageing, dead and diseased cells.

One full turn of the helical strand would involve ten steps or ten base pairs. The pitch would be 34Å.

G0-phase

Explanation: The G0 phase, also known as the "resting phase," is a period in the cell cycle where cells are metabolically active but not actively dividing. During this phase, cells are considered to be in an invisible or quiescent state because they are not involved in cell division or preparation for cell division. The G0 phase can be temporary, with cells returning to the cell cycle to divide, or it can be permanent, such as in the case of some differentiated cells that no longer divide.

A plant cell has rigid wall on the outside. It has plastids and a centrally located large vacuole. All of these are absent in an animal cell.

Ribosomes are naked ribonucleoprotein protoplasmic particles (RNP) which function as a site for protein synthesis.

• Since the yellow seeds are dominant to green, the allele for yellow seeds should be represented with upper case letter while the one for green seeds should be written in lower case letter.
• Let's suppose that the allele for yellow seed is Y and that for green seeds is y. Hence the genotype of the heterozygous yellow seeded plant will be "Yy" and that for green seeded plant will be "yy" (as the recessive allele is expressed only in homozygous conditions).
• The cross between heterozygous yellow seeded plant and green seeded plant will produce 50% yellow seeded plants and 50% green seeded plants.

Hence, the correct option is C

NCERT Reference: Topic " INHERITANCE OF ONE GENE” for basic understanding of this cross from chapter " Principles of Inheritance and Variation"

The number of substrate molecules changed per minute by a molecule of enzyme is called turn over number. Higher the turn over number more effective is the enzyme.

Correct option is B)
Peroxisomes are found in photosynthetic cells and perform photorespiration. They also take part in lipid metabolism. Lysosomes are the cell's garbage disposal system and not the peroxisomes.
So, Statement 1 is correct and statement 2 is incorrect.

• The cell wall of plants is a rigid structure that provides tensile strength to the plants and provides them with support.
• They, therefore, provide the plant cells with support and protect them from mechanical damage.
• The cell walls mediate cell adhesion in plant cells.
• It has narrow pores through which fine strands of cytoplasm are able to pass.
• The nucleus regulates the cell cycle.

The best stage to count the number and study the morphology of chromosomes is during metaphase. During metaphase, the chromosomes are condensed and highly visible, making it easier to count and study their structure. The chromosomes are also lined up at the equatorial plane of the cell, which makes it easier to observe them under a microscope.

Metaphase is a stage in the process of cell division known as mitosis, during which the cell's nucleus divides into two identical daughter nuclei. At this stage, the chromosomes, which contain the cell's genetic material, are visible under a microscope as thin, elongated structures. They are arranged in pairs, with one chromosome from each pair being inherited by each daughter nucleus.

By counting the number of chromosomes and studying their morphology (shape, size, and structure), scientists can learn more about the genetic makeup of an organism and how it may be affected by various factors, such as environmental conditions or genetic mutations.

Chromosomes appeared beaded during the leptotene stage of the prophase of meiosis I, also the longest stage of meiosis cell division.
Chromatin materials start condensing after that stage.

The mechanism of distributing chromosomes by centriole pairs to the daughter cells is called astral division. This kind of division occurs in animal cells.

Fig: Image showing Astral Division

• The father of a colour blind female must be colour blind.
• The mother has to be at least a carrier. This is possible if the maternal grandfather was colour blind [remember criss-cross].

Hence, the correct option is B.

NCERT Reference: Topic- Colour Blindness of chapter "Principles of Inheritance and Variation" of NCERT.

The cytoskeleton in a cell is involved in functions like mechanical support, motility, maintenance of the shape of the cell.

Pachytene: During the third substage of meiosis, the chromosomes continue to condense. Crossing over takes place at this stage and at each point of crossing over a chiasma is formed (singular: chiasma) between non-sister chromatids of homologous chromosomes.

Fig: Stages of Prophase I of Meiosis

In meiosis I, during pachytene, crossing over occurs between the non-sister chromatids of the homologous chromosomes. The exchange of genetic material (DNA) between the non-sister chromatids of the homologous chromosomes is known as crossing over. It leads to the recombination of genetic material which involves a mutual exchange of the corresponding segments of non-sister chromatids of homologous chromosomes. It takes place by breakage and reunion of chromatid segments.

Since, in mitosis the number of chromosomes in the parent and progeny cells is the same, it is also called as equational division.

All living organisms are composed of cells and products of cells.all cells arise from pre-existing cells.

Bivalent or tetrad formation takes place during the zygotene stage of prophase I, after synapsis has occurred and homologous chromosomes form pairs. However, the bivalent is distinct only in the next stage, pachytene.

• There are 20 naturally occurring amino acids.
• All the amino acids except glycine are chiral. Amino acids are classified as acidic, basic or neutral based on the relative number of amino and carboxylic groups.
• Amino acids are classified as essential amino acids and non-essential based on whether they are synthesized in the body or not.

In plants, cytokinesis or division of cytoplasm occurs due to the formation of the cell plate.

In animals, cytokinesis occurs due to the formation of constriction in the middle cell membrane.

In monohybrid and dihybrid cross F₂ generation is obtained by selfing of F₁ hybrids as male and female.

Fig: Monohybrid cross showing F₁ and F₂ generation

Hence, the correct option is B

NCERT Reference: Topic " INHERITANCE OF ONE GENE " of chapter Principles of Inheritance and Variation" of NCERT

• Mendel studied the common garden pea plant, Pisum sativum because it was easy to cultivate and had a relatively short life cycle of 3 months. The plant exhibited discontinuous characteristics such as flower colour and pea texture.
• Owing to its anatomy, it was easy to control the self-pollination of the plant and cross-fertilization between desired parents could be accomplished artificially.
• The presence of pure breeding varieties and easily visible contrasting characters and presence of F₁ fertile hybrids were the additional advantageous characters for which Mendel choose garden pea as experimental material. 

Hence, the correct option is C

NCERT Reference: Topic “MENDEL’S LAWS OF INHERITANCE” of chapter "Principles of Inheritance and Variation" of NCERT

The SER provides surface for the synthesis of  including phospholipids, cholesterol, steroid hormones and hormones, adrenal corticoid hormones), ascorbic acid are visual pigments.

Homologous chromosomes are two similar chromosomes of each type present in diploid cells.
During meiosis homologous chromosomes separate from each other.

• In Snapdragon flower, cross between true-breeding white and red coloured flower produce pink coloured flower in the F1 generation.
• This happens due to the incomplete dominance of alleles over the other.

Hence, the correct option is A.
NCERT Reference: Topic -  Incomplete Dominance of chapter "Principles of Inheritance and Variation" of NCERT.

• tRNA has an anticodon loop that has bases complementary to the code, it also has an amino acid acceptor end by which it binds to amino acids.
• The site lies at the 3' end opposite the anticodon in tRNAs are specific for each amino acid.

Fig: tRNA binding site 
Hence, the correct option is C.
NCERT Reference: Page no. 114 of topic “6.6.2 tRNA– the Adapter Molecule” of chapter 6.

Chemically, ribosomes consist of two parts, proteins and rRNA. Proteins are both structural and enzymatic.

• In a dihybrid cross, two new kinds of plants with new traits are formed. This is possible only when all traits assort independently and recombine to form a new combination.
• Mendel found that each pair of alleles segregates independently of the other pairs of alleles during gamete formation. 
• This is known as the Law of independent assortment and hence it can be proved by the dihybrid cross.

Hence, the correct option is C

NCERT Reference: Topic " Law of Independent Assortment " of chapter "Principles of Inheritance and Variation"  of NCERT