IB Biology A3.1 Diversity of Organisms

Flashcards covering SL and HL content for IB Biology Topic A3.1: Diversity of Organisms, including variation, taxonomy, species concepts, chromosome numbers, karyotyping, genome size, sequencing, and eDNA.

What is biological variation?

Variation refers to the differences in physical, genetic, or physiological traits between individual organisms.

How does variation within a single species compare to variation between different species?

There is variation within a single species, but there is significantly more variation between different species.

Who is known as the Father of Taxonomy, and how did he classify organisms?

Carolus Linnaeus developed a classification system based on morphology, which relies on observable physical traits of organisms.

What is the morphological species concept?

A species concept that defines a species as a group of individuals that are morphologically similar to each other and morphologically distinct from other species.

How are scientific names formatted under Linnaeus's system of binomial nomenclature?

The first part of the name identifies the genus (capitalized), and the second part distinguishes the species (lowercase). The full name is written in italics or underlined.

Based on their binomial names shown in the image, which two reef shark species are most closely related?

Carcharhinus melanopterus (Black-tip reef shark) and Carcharhinus perezi (Caribbean reef shark) are most closely related because they belong to the same genus (Carcharhinus).

What is the definition of a species according to the biological species concept?

A species is a group of organisms capable of interbreeding with each other to produce fertile offspring.

Besides morphology and interbreeding, what other characteristics can be used to classify organisms into species?

Ecological niche, DNA sequence comparisons, types of metabolic molecules produced (such as carbon dioxide vs. methane or hydrogen gas), and evolutionary lineage from fossils.

What is a population in biological terms?

A group of organisms of the same species living in the same place at the same time.

Why can it be an arbitrary decision whether two geographically isolated populations belong to the same or different species?

Because speciation is a gradual process of trait divergence between reproductively isolated populations, and since they do not meet in nature, their ability to interbreed cannot be observed naturally.

What are the diploid chromosome numbers of humans (Homo sapiens) and chimpanzees (Pan troglodytes)?

Humans have $46$ chromosomes ($23$ pairs), while chimpanzees have $48$ chromosomes ($24$ pairs).

What are the diploid chromosome numbers of Jack Jumper ants (Myrmecia pilosula) and Black mulberry plants (Morus nigra)?

Jack Jumper ants have a diploid chromosome number of $2$, whereas Black mulberry plants have a diploid chromosome number of $308$.

What is the distinction between a karyotype and a karyogram?

A karyotype is the total number and type of chromosomes present in a cell, whereas a karyogram is a photo or diagram of chromosomes organized into homologous pairs by size and structure.

Which three structural features shown in the diagram are used to identify homologous chromosomes during karyotyping?

Length, placement of centromere, and banding pattern.

What chromosomal abnormality and sex are depicted in this karyogram?

The karyogram represents a male (one X and one Y chromosome) with Trisomy 18 (Edward's Syndrome), indicated by three copies of Chromosome 18.

What hypothesis explains why humans have $23$ pairs of chromosomes while chimpanzees have $24$ pairs?

The hypothesis states that human Chromosome 2 formed from the fusion of two ancestral chromosomes (corresponding to chimpanzee Chromosomes 2A and 2B) after human ancestors diverged from their common ancestor with chimpanzees.

What evidence supports the hypothesis that human Chromosome 2 originated from the fusion of two primate chromosomes?

Human Chromosome 2 matches chimpanzee Chromosomes 2A and 2B in total length, gene sequence, and banding pattern, and contains a vestigial telomere sequence internal to the chromosome at the proposed fusion site.

What is a genome?

A genome is the entire set of genetic information of an organism.

What constitutes the human genome?

The $22$ pairs of autosomes, the $2$ sex chromosomes in the cell nucleus, and the chromosome inside mitochondria.

What are single-nucleotide polymorphisms (SNPs)?

Single-base substitution mutations that produce variations in DNA sequence among individuals within the same species.

How is genome size measured, and what are its standard unit conversions?

Genome size is measured by the total amount of DNA in nitrogen base pairs ($\text{bp}$), using units such as kilobases ($1\,\text{kb} = 1,000\,\text{bp}$), megabases ($1\,\text{Mb} = 1,000,000\,\text{bp}$), or gigabases ($1\,\text{Gb} = 1,000,000,000\,\text{bp}$).

What are the genome sizes of Influenza A virus, Escherichia coli, Drosophila melanogaster, Homo sapiens, and Picea sitchensis?

Influenza A virus: $13.2\,\text{kb}$; E. coli: $5.6\,\text{Mb}$; Drosophila melanogaster: $143.7\,\text{Mb}$; Homo sapiens: $3.1\,\text{Gb}$; Picea sitchensis: $20.5\,\text{Gb}$.

How does genome size relate to organism complexity across different biological groups?

Prokaryotes have larger genomes than viruses, and eukaryotes generally have larger genomes than prokaryotes. However, among eukaryotes, genome size varies wildly and does not directly correlate with complexity.

What is personalized medicine, and how does whole genome sequencing enable it?

Personalized medicine uses an individual's specific genetic profile obtained through genome sequencing to select targeted, effective medical treatments and minimize adverse side effects.

What are two limitations of applying the biological species concept to certain groups of organisms?

It cannot be applied to asexually reproducing species (which do not interbreed) or to bacteria that undergo horizontal gene transfer across species boundaries without sexual reproduction.

Why is cross-breeding between species with different chromosome numbers unlikely to produce fertile offspring?

Because homologous chromosomes cannot pair up correctly during meiotic cell division, leading to failure of functional gamete formation.

What is a dichotomous key?

A classification tool consisting of a series of paired choices based on observable physical traits that guides the user to identify an unknown organism.

What is a DNA barcode, and how is environmental DNA (eDNA) used in biodiversity studies?

A DNA barcode is a unique sequence used to identify a species. eDNA collected directly from environmental samples (such as soil or water) is barcoded and compared to reference databases to rapidly measure ecosystem biodiversity.