A3 - Diversity Of Organisms

Question 1

What is an organism in biological terms?

Answer 1

Any biological system that functions as an individual life form; all are composed of cells.

Question 2

What is a population?

Answer 2

A group of organisms of the same species living in the same area.

Question 3

What is a community in biology?

Answer 3

Populations of two or more different species occupying the same area at the same time.

Question 4

Define variation.

Answer 4

Differences between members of a group; it is a defining feature of life.

Question 5

What is discrete variation? Give an example.

Answer 5

Traits that can be put in distinct qualitative categories (no range), usually caused by one or few genes; e.g., blood type.

Shown with a bar chart.

Question 6

What is continuous variation? Give an example.

Answer 6

Traits that vary along a quantitative continuum, caused by interaction between many genes and the environment; e.g., height, body mass.

Shown with a histogram.

Question 7

What is intraspecies variation?

Answer 7

Variation within a species; it is inheritable.

Question 8

What causes genetic variation within a species?

Answer 8

1. Mutation (changes in DNA sequence)
2. Gene flow (movement of genes between populations)
3. Meiosis (formation of egg & sperm — allele combinations)
4. Sexual reproduction (random fertilization between egg & sperm)

Question 9

What is the role of natural selection in variation?

Answer 9

Genetic variation in a population leads to some organisms surviving better in their environment → those pass on beneficial traits → this process causes evolution via natural selection.

Question 10

What determines the amount of variation between species?

Answer 10

How closely related they are:
• Same species → less variation
• Different domains → most variation

Question 11

What is Linnaeus’ classification system hierarchy?

Answer 11

Domain → Kingdom → Phylum → Class → Order → Family → Genus → Species

Question 12

What is binomial nomenclature?

Answer 12

A system that uses two names to denote a species:
1. Genus (capitalized)
2. Species (lowercase)

Written in italics or underlined; Genus can be abbreviated (e.g., H. sapiens).

Question 13

What is the biological species concept (Ernst Mayr, 1942)?

Answer 13

A species is a group of actually or potentially interbreeding populations that are reproductively isolated from other such groups.

Question 14

What are some challenges to the biological species concept?

Answer 14

• Hybrids (e.g., mule = donkey + horse) can’t reproduce but still exist.
• Fertile hybrids (e.g., wholphin) don’t fit the definition.
• Variation across geographical ranges: same species may look/act differently.
• Asexual organisms don’t interbreed — concept is inapplicable.
• Practical difficulty: extinct species can’t be tested for interbreeding.

Question 15

What is divergence during speciation?

Answer 15

The process by which a genetically diverging population becomes hard to distinguish as a unique species — speciation = formation of new/distinct species over time.

Question 16

What does speciation require?

Answer 16

1. Reproductive isolation
2. Mutation
3. Natural selection

Question 17

Why is it difficult to distinguish species during speciation?

Answer 17

Because the decision is often arbitrary and subjective — there’s no clear cut-off.

Question 18

Define diploid and haploid.

Answer 18

• Diploid: 2 complete sets of chromosomes (e.g., somatic cells)
• Haploid: 1 complete set of chromosomes (e.g., gametes)

Question 19

How does chromosome number vary among species?

Answer 19

• It varies and reflects evolutionary changes.
• Same species = same chromosome number
• Different species = usually can’t interbreed
• Chromosome number is not linked to how “advanced” a species is

Example: Humans = 46, Chimpanzees = 48.

Question 20

What is a karyotype?

Answer 20

The process of organizing and visualizing chromosomes by staining and photographing them during mitosis; then classified by size, shape, and banding pattern.

Question 21

What is a karyogram?

Answer 21

An image showing all chromosomes in a cell arranged by size with homologous pairs matched.

Question 22

What features can be used to classify chromosomes?

Answer 22

• Length
• Centromere position
• Banding pattern

Question 23

Why do humans have 46 chromosomes while chimps have 48?

Answer 23

Two chimpanzee chromosomes (2a and 2b) fused in a common ancestor to form human chromosome 2.

Question 24

What is the evidence for the chromosome fusion hypothesis?

Answer 24

1. Chimp 12 + 13 = same total length as human 2
   
   2. Human 2 has a centromere where chimp 12’s was
   3. Banding on human 2 matches chimp 12 and 13
   4. Telomere DNA found in the middle of human 2 (fusion point)

Question 25

What is a genome?

Answer 25

All the genetic information of an organism.

Question 26

What is genome sequencing?

Answer 26

Identifying and recording the base sequence of an organism’s DNA.

Question 27

What are some current and future uses of genome sequencing?

Answer 27

• Becoming faster and cheaper (NGS = next-gen sequencing) • Used in personalized medicine • Phylogenetics (determining evolutionary relationships) • Grouping organisms by shared ancestry • Comparing extinct species or physically similar species • Determining evolutionary divergence.

Question 28

How is genome sequencing used in personalized medicine?

Answer 28

• Helps design treatments based on individual genes • Identifies genetic risks for specific diseases.

Question 29

Define speciation

Answer 29

Splitting of 1 species into 2 or more

Question 30

What determines genome size in eukaryotes?

Answer 30

Total mass of DNA in the nucleus

Question 31

In what units is genome size usually expressed?

Answer 31

in base pairs (bp) or megabase pairs (Mbp), where 1 Mbp = 10⁶ base pairs Units of mass — picograms (1pg = 10^-12g)

Question 32

What is the ‘C-value’ in genomics?

Answer 32

the haploid nuclear DNA content of an organism — the amount of DNA in a single set of chromosomes.

Question 33

How do genomes differ in unity and diversity across species?

Answer 33

Genomes vary in both size and base sequence between species.

Question 34

Is variation greater between or within species?

Answer 34

Variation in DNA is greater between species than within a species.

Question 35

How much DNA do humans share with each other and with chimpanzees?

Answer 35

Humans share 99.9% of their DNA with each other and around 99% with chimpanzees.

Question 36

Do humans and other organisms share the same genes?

Answer 36

Many coding genes are shared between species but are expressed differently in each organism.

Question 37

What is an SNP and why is it important?

Answer 37

A: An SNP (single nucleotide polymorphism) is a variation in one DNA base, and it contributes to genetic diversity within species.