Answer:
D
Explanation:
it just is i dont know y i just know it is D
Answer: It to activate
Explanation:Mount St. Helens, Washington, is the most active volcano in the Cascade Range. Its most recent series of eruptions began in 1980 when a large landslide and powerful explosive eruption created a large crater, and ended 6 years later after more than a dozen extrusions of lava built a dome in the crater.
Answer:
3. the absence of a cell wall in human cells
Explanation:
Animal cells do not have cell walls. Cell membranes separate the cytoplasm of the animal cells from the surroundings and maintain their interior. Plant cells have cellulosic cell walls. A cell wall surrounds the cell membrane of a plant cell. Cell walls serve to provide structural support and protect plant cells from pathogens. Cell walls also help keep excess water out of cells so they do not burst. Therefore, human cheek cells would not have cell walls while the onion cells would have cell walls made up of cellulose.
Answer:
The C. elegans embryo is a powerful model system for studying the mechanics of metazoan cell division. Its primary advantage is that the architecture of the syncytial gonad makes it possible to use RNAi to generate oocytes whose cytoplasm is reproducibly (typically >95%) depleted of targeted essential gene products via a process that does not depend exclusively on intrinsic protein turnover. The depleted oocytes can then be analyzed as they attempt their first mitotic division following fertilization. Here we outline the characteristics that contribute to the usefulness of the C. elegans embryo for cell division studies. We provide a timeline for the first embryonic mitosis and highlight some of its key features. We also summarize some of the recent discoveries made using this system, particularly in the areas of nuclear envelope assembly/ dissassembly, centrosome dynamics, formation of the mitotic spindle, kinetochore assembly, chromosome segregation, and cytokinesis.
1. The C. elegans embryo as a system to study cell division
The C. elegans embryo is a powerful model system for studying the mechanics of metazoan cell division. Its primary advantage is that the syncytial gonad makes it possible to use RNA interference (RNAi) to generate oocytes whose cytoplasm is reproducibly (>95%) depleted of targeted essential gene products. Introduction of dsRNA rapidly catalyzes the destruction of the corresponding mRNA in many different systems. However, depletion of pre-existing protein is generally a slow process that depends on the half-life of the targeted protein. In contrast, in the C. elegans gonad, the protein present when the dsRNA is introduced is depleted by the continual packaging of maternal cytoplasm into oocytes (Figure 1). Since depletion relies on the rate of embryo production instead of protein half-life, the kinetics tend to be similar for different targets. By 36-48 hours after introduction of the dsRNA, newly formed oocytes are typically >95% depleted of the target protein.
Explanation:
