The big idea: Millions of species have been discovered, named and described, but many more are still to be discovered.
The points to remember
- About 2 million species have been named and described so far.
- Estimates of the total are much higher: one well-known study estimated about 8.7 million.
- Thousands of new species are still described every year.
- Most unknown species are small (insects, fungi, microbes) or live in hard-to-reach places, such as the deep sea and tropical forests.
- So the true number of species on Earth is not known.
Real example: beetles: About 400,000 species of beetle have been described, more than any other group of animals, and scientists expect many more are still waiting to be found.
Do not overstate what is known:
Not 'all species are known': It is wrong to say that all species, or nearly all, have been discovered. Many more remain to be found.
Free preview
This is the free notes preview
You're reading the free notes. Aimnova Pro unlocks the full study experience — and you can try it with your first topic free to keep:
- FlashcardsLock in vocabulary and key terms with spaced repetition.
- Practice questionsAnswer exam-style questions and get instant AI marking.
- Mock exams & past-paper vaultSit full mocks and see exactly how examiners award marks.
- Personalised study planA daily plan built around your exam date and weak areas.
Start Studying Free Full access to Aimnova Pro · cancel anytime
The big idea: Evidence from fossils suggests that there are more species alive on Earth today than at any time in the past.
The points to remember
- Fossils show which kinds of organisms lived at each time in the past.
- Counted over 540 million years, the number of groups has risen overall.
- There were five mass extinctions: sharp falls when many species died out quickly.
- After each one, new species evolved and diversity recovered, then rose higher.
- So biodiversity today is the highest the fossil record shows.
Remember it as: Five falls, but the line ends highest.
Real example: after the dinosaurs: The mass extinction 66 million years ago ended the dinosaurs, apart from the birds. Afterwards mammals and birds evolved into many new species.
Read the graph the right way:
Not 'the same as in the past': Biodiversity has not stayed the same, and it has not only fallen. The fossil record shows a rise with five sharp dips.
Feeling unprepared for exams?
Get a clear study plan, practice with real questions, and know exactly where you stand before exam day. No more guessing.
Get Exam Ready FreeYour first topic is free to keep • No credit card required
The big idea: Classification is pattern recognition: the same observations can be classified in different ways, so species counts differ.
The points to remember
- Scientists group organisms by looking for patterns in their features and DNA.
- Splitters treat small differences as important, so they recognise more species.
- Lumpers treat small differences as variation within one species, so they recognise fewer.
- The observations are the same: only the way they are classified differs.
- So the number of species in a group can change without anything new being found.
Remember it as: Splitters split, lumpers lump.
Real example: African elephants: African elephants were long counted as one species. Using body shape and DNA, the forest elephant and the savanna elephant are now treated as two species, each assessed separately for conservation.
Use the words correctly:
Not a mistake: When two scientists count different numbers of species in a group, neither has to be wrong. They classify the same observations in different ways.
How it is tested: Paper 1A: which statement about species numbers is supported by evidence. Paper 1B or 2: read a fossil-record graph, or explain why the total number of species is not known.
IB-style questionOutline[2 marks]
A graph of the fossil record shows the number of families of marine animals over the last 540 million years, with five sharp falls. Outline what the fossil record shows about the number of species alive today compared with the past.
Model answer plan
See the answer broken into clear points, with guidance on how each point earns marks.
Supported by evidence: Only two claims are supported: many species are still unknown, and more species are alive now than at any time in the past.