IB Biology Topic A4.2.2 Comparisons Between Current Number of Species on Earth and Past Levels of Biodiversity Revision Notes (SL/HL)

IB Biology Topic A4.2.2 Comparisons Between Current Number of Species on Earth and Past Levels of Biodiversity Revision Notes (SL/HL) | RevisionDojo

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Counting Species: Why We Still Do Not Know How Many Exist

Scientists have formally described fewer than 2 million species.
This is almost certainly a small fraction of the true total.
Estimates for eukaryotes alone range from 2 to 10 million species.
Prokaryotes likely number in the billions, but their diversity makes them hard to classify.
Three factors explain the uncertainty:
1. Inaccessible habitats: many species live in the deep ocean or rainforest canopy, where sampling is hard.
2. Cryptic species: they look identical to known species but are genetically distinct.
3. Unculturable microbes: most microorganisms cannot yet be grown in a lab, so their diversity is largely unknown.

Tip

DNA barcoding identifies species by comparing short, standard gene sequences.
It is especially useful for telling apart cryptic species that look identical under a microscope.

The Fossil Record: Biodiversity Has Risen and Crashed Repeatedly

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Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris.
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Counting Species: Why We Still Do Not Know How Many Exist

Scientists have formally described fewer than 2 million species.
This is almost certainly a small fraction of the true total.
Estimates for eukaryotes alone range from 2 to 10 million species.
Prokaryotes likely number in the billions, but their diversity makes them hard to classify.
Three factors explain the uncertainty:
1. Inaccessible habitats: many species live in the deep ocean or rainforest canopy, where sampling is hard.
2. Cryptic species: they look identical to known species but are genetically distinct.
3. Unculturable microbes: most microorganisms cannot yet be grown in a lab, so their diversity is largely unknown.

Tip

DNA barcoding identifies species by comparing short, standard gene sequences.
It is especially useful for telling apart cryptic species that look identical under a microscope.

The Fossil Record: Biodiversity Has Risen and Crashed Repeatedly

Definition

Paywall

(on a website) an arrangement whereby access is restricted to users who have paid to subscribe to the site.

anim nostrud sit dolore minim proident quis fugiat velit et eiusmod nulla quis nulla mollit dolor sunt culpa aliqua

Duis aute irure dolor in reprehenderit

Note

Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam quis nostrud exercitation.

Excepteur sint occaecat cupidatat non proident

Tip

Lorem ipsum dolor sit amet, consectetur adipiscing elit.
Sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.
Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris.
Duis aute irure dolor in reprehenderit in voluptate velit esse cillum.

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A - Unity and Diversity9 subtopics

B - Form and Function10 subtopics

C - Interaction and Interdependence9 subtopics

D - Continuity and Change12 subtopics

IB Biology Topic A4.2.2: Comparisons Between Current Number of Species on Earth and Past Levels of Biodiversity Notes

Counting Species: Why We Still Do Not Know How Many Exist

The Fossil Record: Biodiversity Has Risen and Crashed Repeatedly

anim nostrud sit dolore minim proident quis fugiat velit et eiusmod nulla quis nulla mollit dolor sunt culpa aliqua

Duis aute irure dolor in reprehenderit

Excepteur sint occaecat cupidatat non proident

Unlock the rest of this chapter with a free account

Counting Species: Why We Still Do Not Know How Many Exist

The Fossil Record: Biodiversity Has Risen and Crashed Repeatedly

anim nostrud sit dolore minim proident quis fugiat velit et eiusmod nulla quis nulla mollit dolor sunt culpa aliqua

Duis aute irure dolor in reprehenderit

Excepteur sint occaecat cupidatat non proident

Unlock the rest of this chapter with a free account

A - Unity and Diversity9 subtopics

B - Form and Function10 subtopics

C - Interaction and Interdependence9 subtopics

D - Continuity and Change12 subtopics