Practise IB Biology SL D4.1 by tracing heritable variation and changing selection pressures through survival, reproduction and shifts in population traits.
Insect pollinators are vital to maintaining the biodiversity of ecosystems, but they are threatened by some human actions. Some pollinators, such as honey bees (Apis mellifera), produce honey, which is rich in glucose.
Explain how a plant species may evolve by natural selection over a long period to produce insect-pollinated flowers.
a. variation exists within a species / OWTTE;
b. mutation generates variation/new alleles;
c. meiosis/sexual reproduction generates variation (new combinations of alleles);
d. example of flower's trait to be selected for in this context;
e. (natural selection is caused by) selection pressures / changes in the environment / due to competition for pollinators / pollination;
f. flowers that have an advantageous characteristic attract more insects;
g. (plants with attractive flowers are) more likely to be pollinated/reproduce;
h. pass on the new allele / combination of alleles/heritable trait;
i. allele frequency increases over many generations;
j. eventually different populations of this species can no longer produce fertile offspring/new species formed;
For d. Award anywhere in response and allow examples including bright petals / enclosed anthers / enclosed stigma / sticky pollen. Also accept suggestions such as odour / colour that is particularly attractive to bees.
For g. to j. Accept converse - i.e. individuals without the advantageous characteristic are less likely to reproduce and pass on their alleles, so alleles conferring a disadvantage are selected against.
For g. do not accept survival.
7 max
Explain how sexual reproduction can eventually lead to evolution in offspring.
offspring vary in traits;
variation results from sexual reproduction;
independent assortment of alleles (during meiosis of spermatogenesis/ oogenesis) contributes to variation;
meiosis is the cellular process that produces gametes;
crossing over (during meiosis) increases variation;
fertilization (combination of different genomes) contributes to variation;
more offspring may be produced than the environment can hold;
struggle for existence can occur;
offspring whose traits best adapt them to environment will survive/survival of fittest;
change in environment will lead to survivors with new/different traits;
correct use of term natural selection/selective pressure;
variation is heritable / over time more offspring born with new trait;
change in gene pool;
when entire population (of a species) exhibits new trait, evolution has occurred;
Outline how overpopulation of a species in a given environment may lead to evolution.
more are born than can survive;
there is variety/variability in the offspring;
competition for resources / struggle for survival / selection pressure;
only the most able/adapted survive / survival of the fittest;
the survivors reproduce and pass on genes;
genes of less able/adapted are eliminated / change in the gene pool;
natural selection occurs;