Plant cell needs cell wall whereas animal cell do not because the plants need rigid structure so that they can grow up and out . All cells have cell membranes, and the membranes are flexible. So animal cells can have various shapes, but plant cells only have the shapes of their cell walls.
If it is always expressed it is dominant, also dominant allele is a possible answer. If it is not expressed unless both alleles are the same, it is recessive.
Earths climate Is changing by global temperature rise, Warming oceans, shrinking Ice sheets, glacial retreat, decrease snow cover, sea level rise, declining Arctic sea ice, extreme events, and ocean acidification
A. Yes is correct.
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Let us look at the what, why and how of studying extreme places like the deep earth and the deep space. Scientists need to figure out as to 'what' they want to look at such places, be it a new exotic creature or bio-genesis (birth of life). Unless there are several testable hypothesis constructed, such a study cannot begin. The 'why' aspect deals with the purpose of such research and expeditions. Is it of any use to the humans, or will it improve our current understanding of a phenomenon? The 'how' aspect deals with the technology and the economic assistance that can help in undertaking such a research. All these are the challenges that needed to be thoroughly considered to make such a research or expedition possible.