A3 Unity and diversity: Organisms Flashcards
Why is variation between organisms considered a defining feature of life?
Because no two organisms are exactly alike, even within a species. Genetic variation ensures adaptability and evolution, and is essential for natural selection to occur.
What is the binomial system for naming organisms?
A two-part Latin name: the genus (capitalized) and the species (lowercase). E.g., Homo sapiens.
Why is it sometimes hard to distinguish between populations and species?
Because non-interbreeding populations may be in the process of speciation. They may still share traits or gene flow, making it hard to draw a clear line.
How does chromosome number vary between plant and animal species?
It varies widely—even between closely related species. Chromosome number doesn’t correlate with complexity.
What contributes to the diversity of eukaryotic genomes?
Eukaryotes have:
Introns
Regulatory sequences
Repetitive DNA
Multiple chromosomes
This allows for more complex gene regulation and variation.
What is a dichotomous key, and how is it made?
A series of paired questions that lead to the identification of an organism.
Best developed by engaging with local species and observing physical traits.
(Think “Does it have leaves? Yes/No → Go to Step 2.”)
Why do we need classification systems for organisms?
To organize the diversity of life, understand relationships, and make communication about species clear and consistent across languages and regions.
Why is classifying organisms into traditional taxa sometimes difficult?
Organisms may have traits from multiple groups
Horizontal gene transfer (esp. in prokaryotes) blurs lines
Evolutionary relationships don’t always match physical traits
What is a clade?
A group of organisms that share a common ancestor and have shared derived characteristics.
Clades can include living and extinct species.
What is a cladogram?
A branching diagram showing evolutionary relationships between clades, based on shared traits or molecular data.
What’s the difference between a karyotype and a karyogram?
Karyotype: the number and type of chromosomes in a cell
Karyogram: the visual display of those chromosomes arranged in pairs
Why do we now classify organisms into three domains?
rRNA base sequences showed fundamental genetic differences.
This led to the three-domain model:
Bacteria
Archaea
Eukarya
Archaea turned out to be more different from bacteria than expected
