Can you explain these briefly....???

Question

1.)The biological species concept is easily applicable to plants and animals but not to primitive organisms like bacteria...

2.) Not all structural or physical similarities indicate close phylogenetic relationship.

Answer 1

1.  The biological species concept says that a species is a group of interbreeding organisms.  Bacteria reproduce asexually most of the time.  So, if a bacterial cell only ever reproduces by itself, how would we know if it is a member of a species with other individuals if we only used the biological species concept?

2.  There is  both convergent and divergent evolution.  In convergent evolution, two species that have similar selective pressures to overcome will somtimes have similar adaptations to deal with it.  For example, sharks, bony fish, and dolphins all have a dorsal fin.  That doesn't mean they are all closely related, it means they have similar lifestyles that need adaptations to help them control their stability while swimming and they all converged on the same trait.

Answer 2

The biological species concept defines a species as members of populations that actually or potentially interbreed in nature, not according to similarity of appearance. Although appearance is helpful in identifying species, it does not define species.

Organisms may appear to be alike and be different species. For example, Western meadowlarks (Sturnella neglecta) and Eastern meadowlarks (Sturnella magna) look almost identical to one another, yet do not interbreed with each other—thus, they are separate species according to this definition.

Organisms may look different and yet be the same species. For example, look at these ants. You might think that they are distantly related species. In fact, they are sisters—two ants of the species Pheidole barbata, fulfilling different roles in the same colony.

Many characteristics can vary within a single species. For example, the plant hydrangea may have pink “flowers”—they’re actually modified leaves—or blue “flowers.” But that doesn’t mean that we should classify the two forms as different species. In fact, you could cause a blue-“flowered” plant to become a pink-“flowered” plant just by changing the pH of the soil and the amount of aluminum taken up by the plant.

now as i mentioned breeding is imp it is 4 this reason that this concept is not applicale 2 primitive organisms like bacteria

Many organisms reproduce asexually, so we do not know whether they fit the concept or not. For example, bacteria usually clone themselves, and even when they do go through something like sexual reproduction, they do not exchange genes the way that most prokaryotes do.

This objection may apply even to "advanced" creatures. For example, some lizards and salamanders do not (ever) have sexual reproduction. Their populations are all females, and they lay eggs which have never been fertilized, and hatch as females which carry on the cycle. Among plants, asexual reproduction is even easier, as many plants reproduce by budding. Strawberries and Bermuda grass are easy examples, but dandelions also reproduce without s*x, and redwoods can

WELL AS 4 THE SECOND ANS

Merely sharing common features is not enough since they may derive from different evolutionary causes:

Homology

This is what we want. The feature is shared because it derives directly from a common ancestor. For example the bony features of the forelimbs in vertebrates

Parallelism

The similar feature occurs in different species, but it is not present in their immediate common ancestor. For example, anteater-like features in various different mammalian lineages (# diagram P.211). These shared features are very much functional adaptations.

Convergence

Similar to parallelism, but the ancestral lineages differed for a considerable period of time. For example vertebrate and octopus eyes, or the hydrodynamic morphology of marine predators from the widely separated fish, reptile and mammalian classes (# diagram P.40).

Practice

Obviously, homologies are what we need to consider to reconstruct phylogenies. However, they are not always easily separated from the other 2 (together often referred to as analogy). Consider the convergence example: the shape of the pectoral fins in these animals is very similar due to convergence. However, there is a great deal of homology there two. Especially between the reptile and the mammal due to a common land vertebrate ancestor.