Gametogenesis, fertilization and early development MCQ Quiz in தமிழ் - Objective Question with Answer for Gametogenesis, fertilization and early development - இலவச PDF ஐப் பதிவிறக்கவும்

Concept:

• ​Gastrulation is defined as an early developmental process in which an embryo transforms from a one-dimensional layer of epithelial cells (blastula) and reorganizes into a multilayered and multidimensional structure called the gastrula.

Explanation:

• The blastulation phase continues with enlargement of the blastocele and formation of a spherical zygote.
• The gastrulation phase starts with spherical zygote invagination at its vegetal pole, where it invades the blastocele and gives rise to the archenteron.
• The opening of the archenteron is a blastopore in the rear end of the embryo. From then on, the inner archenteron begins to rotate anticlockwise

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   hence the correct answer is option 3

Concept:

• The mouth-like blastopore is the aperture of the archenteron.
• It begins to form during gastrulation.
• The second orifice of the blister might be the anus and the blister the mouth of an animal (second opening is called Deuterostome).

Explanation:

• After the zygote is formed, it divides through a process called cleavage and creates a structure known as a blastula.
• The "Blastocoel," a cavity filled with fluid, is located inside the hollow sphere known as the blastula.
• A layer of cells called "Blastoderm" surrounds this hollow.
• From this point on, the second stage of embryonic development, known as gastrilation, begins to take shape.
• The hollow sphere, or blastula, subsequently divides to form the "Gastrula" structure.
• It is made up of two or more layers of germinal layer cells.
• Three layers of cells make up this level.
• The blastula's cells rearrange to produce three primary layers during gastrulation.
• Each layer is referred to as the germ layer because it serves as the foundation for the development of various organ systems.
• Ectoderm, the outermost layer, is followed by the blastocoel cavity, and endoderm, the next layer, is followed by the archenteron cavity.
• A pore known as the "Blastopore" allows this gastrula chamber to communicate with the outside world.
• This portion of the gastrula may eventually grow into a mouth or an anus in some animals after they reach adulthood.

 

Concept:

• Cleavage describes the first cell division that occurs after fertilization, during the early stages of the embryo's development.
• Depending on how much yolk is in the egg, the cleavage can either be holoblastic (full cleavage) or meroblastic (incomplete cleavage).
• In general, cleavage in frog embryos is radially symmetrical and holoblastic, just like in echinoderms.
• The mesolecithal frog egg is large in yolk content. The vegetal pole and the animal pole are situated in the egg's opposing hemispheres.

Explanation:

•  Cleavage in most frog and salamander embryos is radially symmetrical and holoblastic, just like echinoderm cleavage.
• The amphibian egg, however, contains much more yolk.
• This yolk, which is concentrated in the vegetal hemisphere, is an impediment to cleavage.
• Thus, the first division begins at the animal pole and slowly extends down into the vegetal region.
•  In the axolotl salamander, the cleavage furrow extends through the animal hemisphere at a rate close to 1 mm per minute.
• The cleavage furrow bisects the gray crescent and then slows down to a mere 0.02–0.03 mm per minute as it approaches the vegetal pole.

Concept:

• Flowering plants (angiosperms) are the only organisms that undergo this type of double fertilization, which results in the development of both the embryo and the seed's prospective food source.

​Explanation:

Double fertilization

• In flowering plant reproduction, double fertilization refers to the fusion of the egg and sperm as well as the simultaneous fusion of a second sperm with the central cell bearing two polar nuclei.
• This leads to the formation of the endosperm (the seed's food-storage tissue).
• Because a sperm's fusion with the central cell, which resembles fertilization, occurs simultaneously with the actual fertilization—the fusion of a sperm with an egg—this is known as double fertilization.

Hence the correct answer is option 2: Central Cell.

The correct answer is Option 3 i.e. A and D

Key Points

• Organ are complex structure that is made up of many different tissues.
• Co-ordination in the formation of organ is achieved by one group of cells that change the behaviour, size, shape and mitotic fate of adjacent cells.
• This type of interaction between close cells and tissues that helps in differentiation of the tissue in organ is called proximate interaction or induction.
• Two components are involved in the proximate interaction- inducer and responder.

1. Inducer - this are type of tissue that produces a signal that results in changes in the cellular behaviour of the other tissue.
2. Responder- that tissue that is induced by the inducer is called responder.

• The ability of the responder tissue to respond to a specific inductive signal is called competence. 
• Competence is a passively acquired condition of the tissue.
• There are two types of cascade of induction: Reciprocal induction and sequential induction.

1. Reciprocal induction - In this induction, first inducer induces responder tissues, then one of the responder tissue induced inducer i.e., inducer becomes the induced.
2. Sequential induction - In this type of induction, first inducer secrete signal to the responder, the responder then send signal to other group of tissue.

Explanation:

• Inducer cells\tissue secreted proteins that binds to the receptor present on the respond tissue.
  • So, statement 'A' is correct.
• Response to inductive signals depends on competence of the responder cell. It is a passively acquire state of the responder cell\tissue.
  • So, statement 'B' is incorrect.
• In instructive interaction, the responding cells has a choice of fate, where in the presence of the inducer signal, responding tissue have one fate while in the absence of the inducer signal, responding tissue have alternate fate.
  • So, statement 'C' is incorrect.
• Lateral inhibition is a special type of induction process where the responding tissue originally has equivalent field of cells and after induction, the cells are differentiated into regular spaced pattern
  • So, statement 'D' is correct.

Hence, the correct answer is Option 3.

The correct answer is Option 2 i.e. Inner cell mass.

Key Points

• Stem cells are cells that have the ability to develop into many different cell types. 
• Different types of stem cells are as follows:
  1. Totipotent - These stem cells can differentiate into all possible cell types. The first dew cells after the division of the zygote are totipotent. 
  2. Pluripotent - These cells can differentiate into any type of cells. Early embryo cells are pluripotent.
  3. Multipotent - These cells can differentiate into a closely related family of cells. For example, hematopoietic stem cells can differentiates into red blood cells or white blood cells or platelets.
  4. Oligopotent - These cells can differentiate into a few types of cells 
  5. Unipotent - These can produce only one type of cell. Since they can renew themselves they are called stem cells. Example - adult muscle stem cells. 
• Embryonic stem cells are derived from the inner cell mass; they are the most potent stem cells as they can differentiate into all cell types.
• Embryonic stem cells are pluripotent and not totipotent because they cannot differentiate into extra-embryonic structures\organs.

Explanation:

• Blastocoel
  • Blastocoel is the fluid-filled cavity that is present in the blastulation stage of the embryo. It is also the first cavity formed during embryonic development. 
  • Since this is a cavity and not a tissue, hence, this is an incorrect option. 
• Inner cell mass
  • Inner cell mass (ICM) is the cellular mass found in the hollow interior of the blastocyst. 
  • It is the only pluripotent cell lineage in the entire blastocyst.
  • Hence, this is the correct option.
• Trophoectoderm
  • Trophoectoderm is the extra-embryonic structure that appears during early development and it gets attached to the uterine wall during implantation.
  • These later develop into trophoblast for the development of placenta.
  • Hence, trophoectoderm is essential for the implantation and for development of the placenta. It is differentiated cells with definite fate.
  • Hence, this is an incorrect option.
• Trophoendoderm
  • There is no such term as trophoendoderm.
  • Hence, this is an incorrect option.

Hence, the correct answer is Option 2.

The correct answer is All statements are correct

Explanation:

 

A. Sperm undergo acrosome reaction to penetrate the egg's zona pellucida.

• Correct: The acrosome reaction is a critical event in which enzymes are released from the acrosome, a cap-like structure over the anterior half of the sperm's head. These enzymes digest proteins and other components of the zona pellucida, the glycoprotein layer surrounding the egg, allowing the sperm to penetrate and reach the egg's plasma membrane.

B. The fusion of sperm and egg membranes triggers the completion of the egg's second meiotic division.

• Correct: The secondary oocyte is arrested in metaphase II of meiosis until fertilization. Upon fusion of the sperm with the egg's plasma membrane, intracellular signaling pathways are activated, leading to an influx of calcium ions. This calcium signal prompts the oocyte to resume and complete its second meiotic division, forming a mature ovum and a second polar body. This is crucial for producing a haploid egg ready to combine its genetic material with the sperm.

C. Cortical granules in the egg modify the zona pellucida post-fertilization to prevent polyspermy.

• Correct: Once a sperm successfully fuses with the egg, cortical granules (specialized secretory vesicles just under the egg's membrane) release their contents into the perivitelline space (the area between the plasma membrane and the zona pellucida) in a process called the cortical reaction. The enzymes released modify the zona pellucida, making it impenetrable to additional sperm, thereby preventing polyspermy (fertilization by more than one sperm), which would result in an abnormal number of chromosomes.

D. Capacitation is a biochemical change that sperm undergo in the female reproductive tract to gain the ability to fertilize an egg.

• Correct: Capacitation is a series of biochemical changes that sperm undergo after they enter the female reproductive tract. This process involves alterations to the sperm's plasma membrane and an increase in motility, preparing the sperm for the acrosome reaction and enhancing its ability to bind to and penetrate the zona pellucida. It is essential for successful fertilization, as capacitated sperm exhibit hyperactivated motility and are capable of undergoing the acrosome reaction.

E. The cortical reaction is initiated by the influx of calcium ions post-fusion of sperm and egg membranes.

• Correct: The fusion of sperm and egg membranes triggers a rapid increase in intracellular calcium levels within the egg. This calcium influx initiates the cortical reaction, causing the cortical granules to exocytose and release their contents. The enzymes and other substances released modify the zona pellucida to prevent additional sperm from binding and penetrating, thus ensuring monospermy (fertilization by a single sperm) and the correct genetic composition of the resulting zygote.

Conclusion: The correct answer is all statements are correct

 

The correct answers are 1) and 2)

Explanation:

• Danio rerio (Zebrafish):
  • Zebrafish embryos exhibit meroblastic cleavage, specifically discoidal cleavage. This type of cleavage occurs because the yolk is concentrated in one part of the egg, and only a portion of the egg undergoes cleavage, which results in the formation of a blastodisc.
• Gallus gallus (Chicken):
  • Chicken embryos also display meroblastic cleavage. Similar to zebrafish, chicken eggs have a large yolk, and cleavage occurs in a disc-like region (the blastoderm) on the yolk surface. This type of cleavage is essential for the development of the chick embryo.
• Synapta digita (Sea Cucumber):
  • Sea cucumbers exhibit holoblastic cleavage, where the cleavage furrow passes completely through the egg, resulting in equal division of the zygote, regardless of the presence of yolk.
• Xenopus laevis (Frog):
  • Frogs, including Xenopus laevis, exhibit holoblastic cleavage as well. Although frog eggs contain some yolk, the cleavage occurs throughout the entire egg, allowing for uniform cell division.

Additional Information: 

• Meroblastic Cleavage: This type of cleavage is characterized by incomplete division of the egg, primarily due to a large amount of yolk that inhibits cleavage furrows from passing through the entire egg. The resulting embryo consists of a small disc of cells atop a large yolk mass.
• Holoblastic Cleavage: In contrast, holoblastic cleavage involves the complete division of the egg, occurring in species with less yolk. This allows for uniform development of the embryo.

Chromosomes in Arabidopsis Plants: Arabidopsis plants are a model organism often used in plant genetics and molecular biology. They have 10 chromosomes, which means 5 pairs in their somatic (body) cells. This is crucial for understanding how many chromosomes are present in various cell types during the plant's life cycle.

Egg Cell Nucleus in the Female Gametophyte:
The egg cell is a type of gamete, which means it is involved in sexual reproduction.
In plants like Arabidopsis, the gametes are haploid, meaning they contain a single set of chromosomes.
Since the somatic cells of Arabidopsis have 10 chromosomes (5 pairs), the haploid cells, including the egg cell, will have half of this number, which is 5 chromosomes.

Generative Cell Nucleus in a Pollen Grain:
The generative cell within a pollen grain is responsible for producing sperm cells through division.
Like the egg cell, the generative cell is also haploid because it is involved in the process of fertilization, requiring haploid cells to merge and form a diploid zygote.
Therefore, the generative cell nucleus also contains 5 chromosomes.

Endosperm Nucleus:
The endosperm is a tissue produced inside the seeds of most flowering plants following fertilization. It surrounds the embryo and provides nutrition.
It is formed as a result of the fusion of a sperm cell with two nuclei in the female gametophyte, leading to a triploid cell (3 sets of chromosomes).
Given that each haploid set in Arabidopsis has 5 chromosomes, the triploid endosperm nucleus will have 3 times 5, equaling 15 chromosomes.

Fertilized Egg Nucleus:
The fertilized egg, or zygote, is formed when a sperm cell (haploid) fuses with an egg cell (haploid).
This fusion restores the diploid state, meaning the fertilized egg will have two sets of chromosomes.
Since each set has 5 chromosomes, the fertilized egg nucleus will have a total of 10 chromosomes (5 from the egg + 5 from the sperm).

Conclusion: Understanding the chromosome number in different cells of Arabidopsis is crucial for genetic studies and plant breeding. The haploid cells (egg and generative cells) contain 5 chromosomes each, the triploid endosperm has 15 chromosomes due to the fusion of three haploid nuclei, and the diploid fertilized egg goes back to having 10 chromosomes, reflecting the organism's somatic chromosome number.

The correct answer is Bindin in acrosomes and bindin receptors on egg vitelline membrane

Explanation:

Successful fertilization in sea urchins requires a highly specific interaction between proteins on the sperm and receptors on the egg.
This specificity ensures that sperm from the correct species fertilizes the egg, preventing cross-species fertilization.
The interaction involves specific binding proteins and receptors located on the sperm and egg membranes, which facilitate the fusion of sperm and egg.

Option 1: Bindin in acrosomes and bindin receptors on egg vitelline membrane: This is the correct answer. Bindin is a protein located in the acrosome of the sperm. During fertilization, bindin binds to bindin receptors on the egg's vitelline membrane, facilitating the fusion of the sperm and egg membranes.

Source: https://www.mdpi.com/2073-4409/11/19/298

• Option 2: Bindin in egg membrane and bindin receptors in acrosomes: This is incorrect. Bindin is located in the sperm's acrosome, not the egg membrane. The receptors for bindin are located on the egg's vitelline membrane, not in the sperm's acrosome.
• Option 3: Resact on egg jelly and bindin on sperm membrane: This is incorrect. Resact is a peptide released by the egg jelly, which acts as a chemoattractant for sperm. It does not directly interact with bindin. Bindin is involved in the actual binding process between the sperm and egg membranes.
• Option 4: Proteasomes on egg membranes and complex sugars on sperm membranes: This is incorrect. Proteasomes are protein complexes involved in degrading unneeded or damaged proteins within cells, not in the fertilization process. Complex sugars on sperm membranes do not specifically interact with proteasomes on egg membranes.