Viruses are made of one or more nuclei acid molecules surrounded by a coat protein or capsid. So the core of the virus will contain the viral genome. Some viruses' capsid maybe enclosed with an envelope derived from the host cell (the cell that the virus is infecting), and this envelope is also derived from the host cell membrane.
The main difference between a plant cell and the animal cell is the presence of cell wall.
In the plant cell, the cell wall is present, but in the animal cell, the cell wall is absent.
Hence, in the onion cells, the cell wall around the cell would be clearly visible, whereas in the case of cheek cell, the cell would only be lined by a cell membrane, a cell wall would not be present.
Further, the plant cell would have the chloroplast, as they perform photosynthesis, but the animal cell would not have chloroplast. Unlike animal cell, the central vacuole in the plant cell is bigger and clearly visible.
The density of an object determines whether it will float or sink in another substance. An object will float if it is less dense than the liquid it is placed in. An object will sink if it is more dense than the liquid it is placed in.
So an object denser than water will sink
Genetic variation can be caused by mutation (which can create entirely new alleles in a population), random mating, random fertilization, and recombination between homologous chromosomes during meiosis (which reshuffles alleles within an organism's offspring
