BIOLOGY TOKPunctuated Equilibrium

1. Evolution proceeds rapidly in bursts for short periods of time, intermittent with

long periods of stability In periods of stability organisms become well suited to the environment, with

natural selection acting to maintain characteristics Equilibrium is punctuated by a rapid environmental change (e.g. volcanic

eruption, meteor impact) which leads to directional selection Gaps in the fossil record and the lack of intermediate forms for many species

support this theory Strata in the fossil record that show the appearance of many new species

following a mass extinction support this theory

2. The development of stomach ulcers and stomach cancer is example of paradigm shift.

3.

Polyploidy is a condition in which an organism has more than two complete sets of chromosomes in all somatic cells (i.e. > diploid)

It is far more common in plant species as they lack separate sexes and are capable of asexual reproduction (self-pollination)

It may occur as a result of the failure of a meiotic cell to undergo cytokinesis (so chromosome replication occurs minus cell division)

Consequently gametes are diploid (2n) and resulting offspring are tetraploid (4n) 

Because tetraploid offspring can no longer mate with diploid organisms (triploid offspring tend to be infertile), speciation has occurred.