A3.1 diversity of organisms

Question 1

variation between organisms

Answer 1

no two individuals are identical in all traits, patterns of variation are complex and a defining feature of life used to classify organisms.

Question 2

morphological concept of species

Answer 2

groups of organisms with shared traits, established by Carolus Linneaus.

Question 3

binomial naming system (nomenclature)

Answer 3

• first part of name is the genus (capital letter): genus is a group of closely related species
• second part of name is the species name (lowercase)
• written in italics
• universally recognized among biologists

Question 4

biological species concept

Answer 4

a group of organisms that can breed and produce fertile offspring

very difficult to apply in other groups of plants and animals:
- fertile offspring can be produced between members of different species.

• some organisms reproduce asexually and therefore do not breed
• extinct species where we do not have enough info to classify them from fossils

Question 5

speciation

Answer 5

the splitting of one species into two or more which happens gradually over a long period of time with populations becoming increasingly different in their traits.

speciation occurs due to reproductive isolation usually as a result of geographical isolation. The two populations adapt to different environments and therefore have different morphological traits.

It can therefore be an arbitrary decision as to whether two populations are regarded as the same species or not.

Question 6

human chromosome number

Answer 6

46 chromosomes

Question 7

chimpanzee chromosome number

Answer 7

48 chromosomes

Question 8

diploid cells and chromosomes

Answer 8

diploid cells are used to describe a nucleus that has chromosomes organized in homologous pairs (even number of chromosomes)

Question 9

the number of chromosomes as a characteristic

Answer 9

the number of chromosomes is a characteristic feature of members of a species

Question 10

karyograms

Answer 10

karyograms are photographs or diagrams in which the chromosomes of an organism are shown in homologous pairs of decreasing length

used to show a person’s karyotype which is the number and type of chromosomes present in a cell or organism.

to prepare a karyogram:
cells in metaphase of mitosis are examined microscopically

stains give chromosomes distinctive banding patterns

each chromosome has a centromere (constriction in the chromatids)

Question 11

evolution of chromosome 2

Answer 11

chimpanzees are the closest relatives of humans:
2 hypotheses:

1. a complete chromosome disappeared
2. at some point during evolution two chromosomes fused together

evidence:
- banding pattern of chromosome 2 in humans is similar to that of chromosome 12 and 13 in chimps

• chromosome 2 has an extra centromere and a region in the centre with the base sequence of telomeres

Question 12

falsification of hypotheses:

Answer 12

for a hypothesis to be scientific it must be testable

Question 13

hypothesis

Answer 13

a statement that is testable using the scientific hypothesis

Question 14

genome

Answer 14

all the genetic information of an organism, the entire base sequence of each of the DNA molecules.

Question 15

unity and diversity of genomes within species

Answer 15

organisms of the same species share most of their genome but variations such as single-nucleotide polymorphisms create diversity.

Question 15

single-nucleotide polymorphisms

Answer 15

positions in a gene where alternative bases may be present which diversify humans.

they are known as SNPs because at least 1% of individuals have a different base from the others

Question 16

the human genome project

Answer 16

• 1990-2003
• determined the order of all the bases in human DNA

Question 17

variation in genomes between species

Answer 17

1. variation in genome size: the quantity of DNA they have in their nuclei
2. variation in base sequence:

variation between species is much larger than variation within species

Question 18

current and potential future uses of whole genome sequencing

Answer 18

the speed of sequencing is increasing while the speed is decreasing.

current use: research into evolutionary relationships

potential uses: in future it may be possible to sequence everyone’s genome which would allow for personalized medicine to be created based on the specific genome of a person

Question 19

difficulties with the biological species concept (HL)

Answer 19

the biological species concept does not work well with groups of organisms that reproduce asexually or when genes can be transferred from one species to another.

• parthenogenesis (female stick insect reproduces without male)
• vegetative propagation: plants sending out runners that take roots near the original plant
• bacteria reproduce asexually through binary fission, no gametes produced
• horizontal gene transfer:
  plasmid transfer between donor bacterium and host bacterium can occur at multiple stages of their lifespan

this poses a challenge to the biological concept.

Question 20

chromosome number as a shared trait in species

Answer 20

cross-breeding between closely related species is unlikely to produce fertile offspring if parental chromosome numbers are different

e.g horse and donkey= infertile mule

Question 21

identifying species using DNA barcoding and environmental DNA

Answer 21

DNA barcodes are short sections of DNA from one gene, or max. several genes, that are distinctive enough to identify a species.

Environmental DNA is obtained from samples of water, soil or any other part of the abiotic environment.

a combination of these techniques can be used to indicate levels of biodiversity in an environment through the presence or absence of species as there is DNA from a wide diversity of organisms that have interacted with the sampled environment e.g skin, faeces.

+ rapid method of investigation of biodiversity
+ more accurate that studying it morphologically

• only gives indication of presence or absence of species, not population size
• does not tell us if the DNA is from living or dead organism
• soil components can interfere with the sequencing process creating inaccurate results