Biodiversity & Classification

What is Biodiversity?

Biodiversity (biological diversity) refers to the variety of life on Earth at all its levels. Scientists recognise three main levels of biodiversity:

Genetic diversity — variation in the genetic information (DNA) within a species. For example, not all lions look identical; individuals carry different gene variants.
Species diversity — the number and variety of different species in an area. A coral reef has far higher species diversity than a wheat field.
Ecosystem diversity — the variety of different ecosystems (habitats and communities) across the planet, from rainforests to deserts.

South Africa is one of the world's most biodiverse countries. The Cape Floristic Region (CFR) in the Western Cape is a global biodiversity hotspot containing roughly 9 000 plant species — about 70% of which are found nowhere else on Earth (endemic species). Kruger National Park supports the "Big Five" and thousands of other species across its 20 000 km² savanna ecosystem.

Why does Biodiversity Matter?

Ecosystem stability: More species means more resilient ecosystems — if one species is lost, others can fill its role.
Food security: Wild plants provide genetic material for breeding disease-resistant crops.
Medicine: Many medicines (aspirin, penicillin, anti-malarials) were originally derived from wild organisms.
Ecosystem services: Clean water, clean air, pollination, and soil fertility all depend on biodiversity.
Cultural and aesthetic value: Many South African communities and eco-tourism depend on natural biodiversity.

Threats to Biodiversity

Threat	Description	SA Example
Habitat loss	Natural areas converted to farmland, cities, mines	Lowland fynbos destroyed by urban development around Cape Town
Invasive species	Non-native species outcompete indigenous species	Australian wattle and pine plantations invading fynbos; largemouth bass in rivers
Pollution	Chemical runoff, plastic, and acid mine drainage harm ecosystems	Acid mine drainage killing aquatic life in Witwatersrand rivers
Climate change	Shifting rainfall and temperatures push species out of their ranges	Fynbos biome projected to shrink dramatically under warming scenarios
Overexploitation	Overhunting, overfishing, and illegal trade	Rhino poaching; abalone poaching on the Cape coast

Classification of Living Things

Scientists use taxonomy to group and name organisms. The modern classification system was developed by Carl Linnaeus (18th century). Organisms are grouped by shared characteristics — today, mainly by evolutionary (genetic) relationships.

The classification hierarchy (from broadest to most specific):

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

Mnemonic: "King Philip Came Over For Good Soup"

The Five Kingdoms

🦠

Monera

Bacteria, blue-green algae. Prokaryotes — no nucleus.

🔬

Protista

Amoeba, Paramecium, algae. Mostly single-celled eukaryotes.

🍄

Fungi

Mushrooms, moulds, yeast. Absorb nutrients from dead matter.

🌿

Plantae

Mosses, ferns, flowering plants. Photosynthetic, cell walls.

🐾

Animalia

Insects, fish, birds, mammals. Multicellular, heterotrophic.

Binomial Nomenclature

Every species is given a unique two-part scientific name (binomial nomenclature), following rules set by Linnaeus:

The first part is the Genus name — always capitalised.
The second part is the species name — always lowercase.
The full name is written in italics (or underlined when handwritten).

Examples:
Homo sapiens — modern humans
Panthera leo — lion
Protea cynaroides — King Protea (South Africa's national flower)
Acinonyx jubatus — cheetah

Dichotomous Keys

A dichotomous key is a tool scientists use to identify an unknown organism. It works by presenting a series of paired statements — at each step, you choose the one that applies, and follow the path until you reach the organism's identity.

"Dichotomous" means "split into two" — each question has exactly two choices (YES or NO, or Choice A vs Choice B). Dichotomous keys can be used to identify plants, animals, rocks, fungi, and more.

Try the interactive dichotomous key game in the Explore tab — classify 5 different organisms!

Answer all questions in your exercise book. Draw diagrams where asked. Use correct scientific names where required.

Question 1 · (3 marks)

Define the three levels of biodiversity (genetic, species, and ecosystem). Give one example of each.

Question 2 · (5 marks)

South Africa is considered a biodiversity hotspot. (a) Name ONE region in South Africa that is a global biodiversity hotspot and state why it is significant. (b) Describe THREE threats to biodiversity in South Africa and explain how each threat causes harm.

Question 3 · (7 marks)

List the seven levels of biological classification from broadest to most specific. Write the mnemonic used to remember them. Then classify the lion (Panthera leo) as completely as you can — use your lesson notes and knowledge.

Question 4 · (4 marks)

Explain the rules of binomial nomenclature. Write the scientific names of TWO South African organisms, demonstrating the correct format.

Question 5 · (4 marks)

Explain what a dichotomous key is and how it is used. Construct a simple dichotomous key that could be used to distinguish between these four organisms: mushroom, oak tree, eagle, bacterium. Show your key as a series of numbered paired questions.

Question 6 · (2 marks)

What is the difference between a prokaryote and a eukaryote? Which kingdom contains prokaryotes?

Question 7 · (6 marks)

A group of Grade 7 learners carried out a biodiversity survey. In each habitat, they marked out an identical 100 m² survey area, counted every living organism they found, and recorded how many different species those organisms belonged to:

Habitat	Total number of organisms counted	Number of different species found
Grassland	140	12
Pond edge	95	18
Paved schoolyard	60	3

(a) Which habitat has the highest species DIVERSITY? Explain your answer using the data in the table — do not simply pick the habitat with the most organisms. (b) Calculate the number of species found per 100 organisms counted in each habitat (species ÷ organisms × 100), and use these values to rank the three habitats from most to least diverse. (c) The grassland has more total organisms than the pond edge, yet the pond edge is more diverse. Explain why total organism count alone is not a good measure of biodiversity. (d) Suggest ONE reason why the paved schoolyard has such low species diversity.

Biodiversity & Classification

What is Biodiversity?

Why does Biodiversity Matter?

Threats to Biodiversity

Classification of Living Things

The Five Kingdoms

Binomial Nomenclature

Dichotomous Keys

Classification Explorer