A2 Human Biology Unit 3

Text questions

P55/Q1		Bandro and the lesser bamboo lemur are able to produce fertile offspring, therefore, in spite of some differences between these two species (eg. different habitats which they occupy) bandro is often classified as a subspecies of the lemur.
P55/Q2		Prophase I.
P58/Q3		Geographical separation, habitat isolation.
P59/Q4		Allopatric speciation takes place when a given population is divided into 2 smaller populations as a result of a geographical separation. This separation usually makes interbreeding totally impossible. Sympatric speciation: geographical isolation does not occur, yet strong forces of natural selection bring about genetic differences between the two populations (which can, at least in theory, occasionally interbreed).
P60/Q5		Lycopersicon esculentum.
P63/Q6		Membrane-bound organelles, e.g. mitochondria, chloroplasts.
P64/Q7		The cell at the tip of a fungal hyphae is metabolically very active. A number of enzymes must be synthesised in the cell in order to control a number of metabolical processes taking place there. A large number of genes coding for the specific proteins, which make enzymes, are needed. These genes are parts of the DNA chain. Fragments of the DNA coding for these various proteins are stored inside the many nuclei there.
P67/Q8		Protoctista, Fungi, Plantae.

Assignment

P69/Q1

First, by pollinating yellow-flowered plants with pollen of the pink-flowered plants, a certain number of seeds should be produced. The seeds should be placed in soil and plants of F1 (which will grow from these seeds) should be pollinated using pollen produced by individuals of F1. If from this process of pollination some germinating seeds are produced, then this could be the evidence that yellow and pink-flowered plants belong to the same species (because they can interbreed and can produce fertile offspring).

P70/Q2

MM →	M*
	M**
FF →	F*	*FM - develops into embryo
	FF**	**FFM - develops into endosperm

P70/Q3

The double set of chromosomes (PP) delivered by the Primrose female parent to the nucleus of the endosperm (CPP) contains alleles which determine slow development of the endosperm compared with the other chromosomal composition (CCP).

Endosperm is a tissue which provides a food source for the development of embryo. If development of the endosperm is slow, consequently the development of the embryo will be slow or halted altogether. This takes place with the endosperm CPP (female parent - promrose). Hence only 1% of the seeds formed have embryos present.

P70/Q4

Primroses and cowslips are different species because interbreeding between them is very rare. Hybrids which sometimes result from this interbreeding are sterile.

Examinations

P71/Q1	a)	The fact that all the flies native to Hawaii belong only to one genus suggests that there is less variation amongst the flies living on the island. This could result from the isolation of the island from the Continent, hence much smaller chances of introducing new genes to the gene pool of the local populations of Drosophila. Inbreeding caused by crosses between closely related individuals living in closed population on the island will slow down the process of separation of the existing species into new genuses as a result of natural selection. It can also result from lower natural selection pressures acting on the genus Drosophila. Hence slow pace of evolution/differentiation of this genus into new ones.
	b)	Patches (A & B) of vegetation isolated by large areas of bare lava will differ slightly in terms of their abiotic and biotic factors. There is a genetic variation within the populations living in A and B. One genetic variant confers an advantage on the possessor(s) of a favourable allele of a gene. The possessor of the favourable allele will have more offspring than the possessor of only less favourable allele → the frequency of the favourable allele will increase in the population ("natural selection") → different phenotypes in A and B ("evolution").
	c)	Natural selection pressures on the British Isles were much higher than on Hawaii, where the environment was less harsh to the flies. As a result of more severe natural selection and faster evolution of the species of Drosophila in the British Isles, the number of genetical differences between once closely related species has increased so much, that they have evolved into different, new genuses.
P72/Q2	a)	(i) Family: Suidae (ii) Genus: Sus
	b)	Bush pigs and red river hogs may belong to the same species. In the natural environment they have interbred for many years. If their offspring were fertile then it would confirm the above statement.