BIOLOGY · Stage 7 · Chapter 1: Classification and Life
Biology 1.10 Moving classification forwards
5 min read 6 parts Lesson 10 of 11
Lesson summary
1.10 Moving classification forwards — Alhussan International Academy — Biology (Stages 7–9) notes: Explain how modern classification uses new evidence such as genetic material and why classification schemes change.Early classification — in the 1700s Linnaeus and other biologists …
- Appearance can mislead
- Scientific understanding develops
- Better microscopes
- Advantage of genetic evidence
- Evolutionary tree
- Convergent evolution
Section 1 of 6From appearance to evidence
- Early classification
- in the 1700s Linnaeus and other biologists grouped organisms by what they looked like.
- They recorded the number of limbs or body parts, how an organism breathed or reproduced, and its colours, patterns and sizes.
- Careful observation like this is still important in classification today.
- Appearance can mislead
- organisms that look alike are not always closely related.
- Dolphins look like fish but are mammals.
- Unrelated desert plants can look alike because they adapted to similar conditions.
- Scientific understanding develops
- ideas are tested against evidence and changed when new evidence requires it.
Section 2 of 6Microscopes and genetic material
1Better microscopes3 points
- they showed the inside of cells and revealed big differences between groups.
- Bacteria have no nucleus, while animal, plant and fungal cells do.
- This led to bacteria being separated from the rest of life.
2Genetic material3 points
- all living organisms, even viruses, contain genetic material that carries the instructions for making new organisms.
- Scientists compare genetic material from different organisms to see whether they are the same species.
- Closely related organisms share more of their DNA than distant relatives, so DNA acts as a record of ancestry.
3Advantage of genetic evidence3 points
- species can be identified without trying to breed them.
- Two different species cannot breed to produce fertile offspring, which was the old test.
- It also allows classification of microscopic organisms that have few visible features.
Section 3 of 6Evolutionary trees and domains
- Evolutionary tree
- a branching diagram in which each branch point represents a common ancestor.
- The closer two organisms are on the tree, the more recently they shared an ancestor.
- Convergent evolution
- DNA comparison shows that some organisms that look alike evolved separately.
- DNA comparison also shows that some animals that look different are close relatives.
- Three-domain system
- Bacteria, Archaea and Eukarya, based on genetic differences.
- The Eukarya include animals, plants, fungi and protoctists.
- A natural group
- it should include an ancestor and all its descendants, so classification reflects evolution.
Section 4 of 6Case study: the clouded leopard
- Original naming
- clouded leopards were given the name Neofelis nebulosa.
- (tree tigers in Borneo, mint leopards in Southern China)
- For many years biologists thought the animals in both countries were one species.
- clouded leopards were given the name Neofelis nebulosa.
- Genetic analysis
- the genetic material of the Borneo and Chinese animals was as different as that of lions and tigers.
- The Borneo animals were given a new scientific name, Neofelis diardi.
- Conclusion
- genetic evidence lets biologists decide whether organisms are the same species or only look very similar.
Section 5 of 6Biodiversity and measuring change
- Biodiversity = the variety of living organisms, measured for the whole world or for a small area such as a school yard.
- Species must be identified by classification before biodiversity can be measured.
- Importance of biodiversity
- it is healthy for the world, for example for the soil that grows crops and for the plants that produce oxygen.
- Measuring change
- counting species in an area at different times shows whether biodiversity is changing.
- 50 species now compared with 49 twenty years ago shows a stable, probably healthy area.
- 50 species now compared with 100 twenty years ago is a big loss and a cause for concern.
- Why classification matters
- it shows which species exist so that action can be taken to look after them.
Section 6 of 6Why classification keeps changing
- New discoveries
- new species are still being found, especially in oceans, soils and rainforests.
- New evidence
- it can move a species to a different group.
- Earlier work
- scientists used the best methods they had, and each generation builds on the last.
- Shared data
- teams from many countries share data in databases, which also lets scientists check each other's work.
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