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Unity and diversity - Diversity of organisms

Grade 12IBBiology

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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Classification in biology involves grouping organisms based on shared characteristics. The hierarchical system includes eight main levels: Domain, Kingdom, Phylum, Class, Order, Family, Genus, and Species. The mnemonic 'Dear King Philip Came Over For Good Soup' is often used.

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The binomial system of nomenclature, developed by Carl Linnaeus, uses two names: the Genus (capitalized) and the species (lowercase), both written in italics (e.g., HomoHomo sapienssapiens).

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All organisms are classified into three domains: ArchaeaArchaea (prokaryotic extremophiles), EubacteriaEubacteria (true bacteria), and EukaryotaEukaryota (organisms with membrane-bound organelles).

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Cladistics is a method of classification that groups organisms based on evolutionary ancestry. A 'clade' is a group of organisms that have evolved from a common ancestor, often identified using DNADNA base sequences or amino acid sequences in proteins.

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Evidence for evolution and diversity can be found in homologous structures (similar anatomy, different function, e.g., pentadactyl limb) and analogous structures (different anatomy, similar function due to convergent evolution).

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Molecular clocks rely on the mutation rate of DNADNA or protein sequences. The number of differences between two species can be used to estimate the time since they shared a common ancestor, where T∝ΔmT \propto \Delta m (time is proportional to the number of mutations).

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Simpson’s Diversity Index (DD) is a measure used to quantify the biodiversity of a habitat, taking into account both species richness and species evenness.

📐Formulae

D=1−∑n(n−1)N(N−1)D = 1 - \frac{\sum n(n - 1)}{N(N - 1)}

N=Total number of organisms of all speciesN = \text{Total number of organisms of all species}

n=Number of individuals of a particular speciesn = \text{Number of individuals of a particular species}

💡Examples

Problem 1:

Calculate the Simpson's Diversity Index (DD) for a community containing three species with the following populations: Species A (n=10n=10), Species B (n=15n=15), and Species C (n=5n=5).

Solution:

First, find the total population NN: N=10+15+5=30N = 10 + 15 + 5 = 30 Next, calculate ∑n(n−1)\sum n(n-1): Species A: 10×(10−1)=90\text{Species A: } 10 \times (10 - 1) = 90 Species B: 15×(15−1)=210\text{Species B: } 15 \times (15 - 1) = 210 Species C: 5×(5−1)=20\text{Species C: } 5 \times (5 - 1) = 20 ∑n(n−1)=90+210+20=320\sum n(n-1) = 90 + 210 + 20 = 320 Now, calculate N(N−1)N(N-1): 30×29=87030 \times 29 = 870 Finally, apply the formula: D=1−320870D = 1 - \frac{320}{870} D≈1−0.368=0.632D \approx 1 - 0.368 = 0.632

Explanation:

A Simpson's Diversity Index value closer to 11 indicates high biodiversity, while a value closer to 00 indicates low biodiversity. In this case, 0.6320.632 suggests moderate to high diversity.

Problem 2:

Two species of birds show a 2%2\% difference in their mitochondrial DNADNA sequences. If the estimated mutation rate is 1%1\% every 1,000,0001,000,000 years, calculate the time since these two species shared a common ancestor.

Solution:

Difference=2%\text{Difference} = 2\% Rate=1%/106 years\text{Rate} = 1\% / 10^6 \text{ years} Time=2%1%×10−6\text{Time} = \frac{2\%}{1\% \times 10^{-6}} Time=2×106 years\text{Time} = 2 \times 10^6 \text{ years}

Explanation:

Using the molecular clock hypothesis, we divide the total genetic divergence by the mutation rate to estimate the evolutionary separation time.