A 3.1 HL Diversity of organism Flashcards
What is a dichotomous key?
A dichotomous key is a (usually written) device constructed from a series of highly organized statements arranged into couplets. It’s a tool used in fieldwork to aid in identification of organisms and is composed of a series of questions or statements based on physical characteristics of organisms concerned. Each question has only two possible answers – usually stating whether a feature or characteristic is present in organism or not
What is a couplet?
A couplet consists of two descriptions which should represent mutually exclusive choices (often it is a particular combination of characteristics that determines the difference).
What must each couplet contain?
Each couplet only expects two answers to each question
(YES or NO).
Why does breeding between two close species some times lead to infertile hybrids?
It’s suspected that one of reasons breeding between some closely related species don’t usually result in a fertile offspring is due to a mismatch in chromosome number. When a donkey that has 62 chromosomes is bred with a horse that has 64, they each pass half to their offspring. This means that offspring would end up with an uneven number of chromosomes, & this is thought to play a part in making it infertile.
Why does the biological species concept not work for asexual organisms?
Using this concept, those individuals won’t be classified as a species as they aren’t capable of interbreeding & producing fertile offspring. Prokaryotes reproduce asexually in process of binary fission. One bacterial cell grows & eventually splits into 2 identical cells. Another example, genus Hydra, a group of freshwater species related to jellyfish, anemones & coral. Hydra reproduce asexually through a process known as budding, where an offspring, genetically identical to the parent, is grown on parent organism & buds off once large enough.
Why has horizontal gene transfer further confused our understanding of how species are defined and represents another major exception to the biological species concept?
Prokaryotes are also capable of horizontal gene transfer. This is a phenomenon where genetic material is exchanged between individuals rather than passed on from one generation to next. This has led to a huge amount of genetic variation among prokaryotes that otherwise may have little due to their method of asexual reproduction.
Why are dichotomous keys helpful?
In field, a dichotomous key of local species being investigated will allow you to more easily identify any specimens collected or observed.
How can genetics be used to identify species?
Recently, developments in gene technologies have allowed for new techniques to be created to quickly and easily identify species and measure biodiversity.
What is one method using genetics to identify a species?
One of these methods is DNA barcoding where an unknown specimen or environmental sample, often water or soil, is collected and DNA is extracted. From this sample certain specific DNA sequences are identified, creating a unique ‘barcode’ for that specimen. The sequences used have been selected because they show much more variation between species than they do within species. The barcode of the specimen can then be compared with a catalogue of barcodes that allows for identification of the species.
Why is using the DNA barcoding method useful?
Using this method, environmental assessments which are concerned with particular species are able to determine whether that species is present without having to observe the organism itself. In the case of elusive, endangered species, this is quite significant. DNA barcoding can also assist in the measuring of biodiversity, a key environmental indicator of ecosystem health and sustainability. This technique has numerous other potential uses, including testing food for microorganism contamination, identifying species in different stages of their life cycle, identifying species from partial specimens and even analysing stomach contents to see what organisms have been consumed.
