What is the cause of the differences found among individuals of the same species?

How many pairs of chromosomes are there in a human cell (in $pairs$)?

$(a)$ Differentiate between:
$(i)$ Homologous organs and Analogous organs
$(ii)$ Pollination and Fertilisation
$(b)$ What do fossils tell us about the process of evolution?

$A$ pea plant with blue colour flower denoted by $BB$ is cross-bred with a pea plant with white flower denoted by $ww$.
$(a)$ What is the expected colour of the flowers in their $F_{1}$ progeny?
$(b)$ What will be the percentage of plants bearing white flower in $F_{2}$ generation,when the flowers of $F_{1}$ plants were selfed?
$(c)$ State the expected ratio of the genotypes $BB$ and $Bw$ in the $F_{2}$ progeny.

When Mendel crossed a tall plant with a dwarf plant,what was the ratio of dwarf plants in the $F_{2}$ generation (in $, \%$)?

In which organisms is a higher degree of variation observed?