Which of the following is a density-independent limiting factor?

D. Tornado.

Explanation:

A limiting factor can be defined as any environmental condition or force (resources) that is capable of affecting the growth rate, distribution and size of a population of living organisms within an ecosystem.

Basically, limiting factors are divided into two (2) main categories and these are;

I. Density-dependent limiting factor.

II. Density-independent limiting factor.

A density-independent limiting factor can be defined as the environmental factors which affect or limit the growth (size) of a population of living organisms irrespective of the population density i.e number of individual organism per unit area.

Some examples of density-independent limiting factors are earthquakes, flood, hurricane, tsunami, wildfire, volcanic eruptions, environmental pollutants, droughts etc.

Hence, a tornado is a density-independent limiting factor because it is abiotic and can kill all the living organisms irrespective of the population density.

we solve the problem using the hardy-wineberg equation.

let us start with the homozygous recessive proportion of individuals with sickle cell anaemia,

we have the proportion as q² = 0.25.

∴ q = 0.5 (frequency of hbs in population)

further,

solving for the frequency of normal cell by using the fact that,

p + q = 1

∴ p = 1 - 0.5 = 1 - 0.5 = 0.5

now we can calculate 2pq in p² + 2pq + q², which is the frequency for heterozygous carriers of sickle cell anaemia,

∴ 2pq = 2 x 0.5 x 0.5 = 0.5

and the homozygous normal cell individuals proportion is given by the expression,

∴ p² = 0.5² = 0.25

hence, the carriers for sickle cell anaemia are in proportion, 0.5, or 50%.