Cell Biology Test - 19

The root tip cells of onion were used to test the potentially genotoxic effects of Alprazolam. The test was carried out according to Fiskesjö protocol (4, 11-12) with some modifications. Common onion (Allium cepa L.) has eight pairs of relatively large chromosomes (2n = 16) that allows for the easy detection of CAs.

Dinoflagellates are unicellularprotists which exhibit a great diversity of form. They possess condensed chromosomes even during interphase. Their nucleus is called as mesokaryon.

Astral body are formed of microtubules. Astral bodies are produced by centriole during cell division and attach with centromere of the chromosome.

Small disc-shaped structures at the surface of the centromeres are called kinetochores. These structures serve as the sites of attachment of spindle fibres (formed by the spindle fibres) to the chromosomes.

Human nerve cells do not divide after birth. The length of nerve cells increases with increase in body size but not the number of nerve cells.

During the G2 phase, proteins are synthesised in preparation for mitosis while cell growth continues.

If cytokinesis doesn't take place after karyokinesis, formation of daughter cells from the parent cell doesn't take place. The parent cell will have more than one nucleus, which are supposed to be present in daughter cells.

If it's a plant cell, cell plate formation doesn't take place.

If it's an animal cell, a furrow doesn't appear.

Cytokinesis means division of cytoplasm. So, the cytoplasmic division doesn't take place after the division of nucleus(karyokinesis).

Hence, the correct answer is Option D.

In plant cell, mitosis cell division is generally controlled by cytokinin hormone. Auxinis also required for cell division in plant.

Solution : 

The correct option is Option B.

The centromeres separate and the sister chromatids—now individual chromosomes—move toward the opposite poles of the cell. To replay the anaphase II animation, click the Replay button. The centromeres separate, and the two chromatids of each chromosome move to opposite poles on the spindle.

In Diploid cells, each homologous chromosome consists of one paternal and one maternal chromosomethat fuse together during fertilization of gametes.

The interphase, though called the resting phase, is the time during which the cell is preparing for divisionby undergoing both cell growth and DNA replication in an orderly manner.

Mitosis is also divided into four stages namely prophase, metaphase, anaphase and telophase.

During mitosis, Endoplasmic Reticulum (ER) and nucleolus begin to disappear at early prophase and these are not observed in late prophase. 

Meiosis cell division results into number of chromosome reduce to half, recombination of genes and formation of spores and gametes.

Polyploidy is the condition in which more than one set of chromosome is present in one cell. It is the property of increasing the number of chromosomes sets of the cell.

option C diploid somantic cells is correct answer. 

Explanation:-

In animals, mitotic cell division is only seen in the diploid somantic cells. 

Reason :- The plants can show mitosis divisions in both  haploid and diploid cells

At metaphase stage, the chromosome is made up of two sister chromatids, which are held together by the centromere.

In animal cell, cytokinesis takes place by furrow deepening centripetally and formation of two daughter cells. This method of cytokinesis is known as cleavage cytokinesis.

In telophase I, the nuclear membrane and nucleolus reappear.Meiosis II is similar to mitosis.

Egg yolk contains lampbrush chromosome where two homologous chromosomes with several chiasmata with several loop in chromatic region is found.

The quiescent stage (G0) of the cell cycle. Cells in this stage remainmetabolically active but no longer proliferate unless called on to do so.

During prophase, the chromosomes condense, the nucleolus disappears, and the nuclear envelope breaks down.

Colchicine is an alkaloid used in plant breeding for doubling of chromosomeby inhibiting cytokinesis. It is also called as mitotic poison.

Synapsis occur between two homologous chromosome during zygotene phase of prophase of meiosis I due to presence of synaptical complex between homologous chromosomes.

Number of chromosome changes during anaphase of meiosis I and amount of DNA content increaseduring S-phase of cell cycle.