Soil pH is a measure of the acid content of the soil. The graph shows the tolerance of earthworms to soil pH. The graph is titled Tolerance. It plots population on the vertical axis against a range of environmental variable on the horizontal axis. The shape of the curve is like a bell, and extends from the lower limit of tolerance to the upper limit. In a meadow where earthworms live in the soil, the pH gradually decreases from the optimum range into the zone of stress. What is the MOST LIKELY effect on the earthworm population?

The pH of the soil, which is a measure of the acidity of the soil, governs to a large extent what is suited to and will grow well on a particular soil. Thus, agricultural crops, many of which go on to become our food, require soils in a particular pH range in order to produce their best yields. Both garden and wild flowers have a pH range in which they grow best. Similarly most organisms that live in the soil will operate in soils in a pH range that suits them. For example, one of the most common species of earthworms,has a strong preference for soils with a pH above 5.5 to just over 7.0. Other species of earthworm such as Allolobophora longa can tolerate pHs less than 5.5 but only down to about 4.5. Below pH 4.5 in Western Europe at least, there are usually few earthworms in the soil. pH also has an important effect on the availability of plant nutrients. Several nutrients become less available at the lower end of the pH range, i.e. below pH 5.5 and the availability of a few tails off significantly at pHs above 7.5. It is important that those who use the soil for purposes that depend on soil nutrients should be aware of the best pH range for key nutrients.

Explanation:

d is the answer

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answers are:

lysogenic     viral dna merges with host cell dna

lysogenic     no symptoms

lytic               viral dna takes over

lysogenic     virus does not destroy host cell

lytic               virus destroys host cell

lytic               induces symptoms of viral infection

lysogenic       cell reproduces and spreads provirus