Biodiversity (biological diversity) is the enormous variety of living organisms on the Earth — from microscopic algae and bacteria to giant trees, from glowing jellyfish to soaring eagles — together with the variety of habitats they live in, from the snow-clad Himalayas to the coral reefs of the Andaman Sea.

It exists at three levels:

• Species diversity — the number of different kinds of organisms.
• Genetic diversity — variation within a species (e.g. many crop varieties).
• Habitat/ecosystem diversity — forests, deserts, wetlands, reefs and so on.

It is essential for life: ocean algae release most of our oxygen, fungi and bacteria recycle waste into soil nutrients, and bees, birds and bats pollinate flowers — keeping ecosystems stable.

Grouping organisms by shared characteristics turns millions of confusing species into an organised, systematic picture. It lets us:

• Compare and identify organisms quickly by common features.
• See relationships — similar features suggest a common ancestor.
• Study life logically, like books arranged in a library.
• Apply knowledge to conservation, ecosystem management and farming.

Scientists move from broad, visible features to finer ones:

1. External features — shape, size, body organisation
2. Mode of nutrition — autotrophic or heterotrophic
3. Internal structures — skeleton, organs, tissues
4. Cell structure — unicellular/multicellular, prokaryote/eukaryote, cell wall
5. Ecological role — producer, consumer, decomposer
6. Reproduction — sexual and/or asexual
7. Genetic similarity — likeness of DNA

Plants are mainly grouped by body complexity, vascular tissue and seeds/flowers; animals by features such as the presence or absence of a notochord and their level of body organisation.

Knowing crops, pests and helpful organisms precisely improves farming:

• Crop varieties — choosing drought-tolerant, pest-resistant types keeps the diversity that reduces crop-failure risk.
• Pest management — identifying insects tells us which protect crops and which damage them.
• Helpful microbes — classifying bacteria like Rhizobium (fixes nitrogen) boosts soil fertility.
• Sustainable farming — understanding relationships supports balanced, eco-friendly practices.

The same animals can be grouped differently depending on the criterion chosen — that is the key idea:

Because one organism (the tiger) fits several groups at once, a fixed, systematic basis is needed — leading to classification.

Yes — very likely. When organisms share fundamental features (cell structure, body plan, DNA), the simplest explanation is that they inherited them from a shared ancestor.

E.g. all mammals have hair and feed young with milk; tiger and lion (genus Panthera) share skull structure and the ability to roar. The more features shared, the closer the common ancestor — which is why DNA similarity is a strong modern criterion.

By using biological classification and binomial nomenclature. Each species gets a unique two-part scientific name and a place in the hierarchy (Kingdom → … → Species). This lets scientists worldwide record, compare and refer to species without confusion, and group similar ones (e.g. all four hornbills in one family).

Despite the shared hornbill body plan, they differ in fine features:

• Body size (e.g. the Great Hornbill is much larger).
• Colour and pattern of plumage, neck and throat.
• Shape, size and colour of the casque on the beak, and the beak itself.
• Calls, habitat and the type/size of tree and fruit used.

Hornbills nest only in large, old trees with cavities. If they vanished:

• Hornbills would lose nesting sites and could fail to breed, so populations fall.
• As key seed dispersers, their decline would reduce regeneration of fruit trees.
• The whole food web linked to them would be disturbed, lowering the forest’s biodiversity.

Whittaker’s system uses four main criteria:

1. Cell type — prokaryote or eukaryote (true nucleus or not)
2. Cell structure — cell wall present/absent (chitin vs cellulose)
3. Level of organisation — unicellular or multicellular
4. Mode of nutrition / ecological role — autotroph, heterotroph; producer, consumer, decomposer

The flow chart shows how these sort all life into the five kingdoms:

Both appear as single-celled prokaryotes (no true nucleus) — Kingdom Monera.

• Cells are tiny and simple; genetic material lies free in the cytoplasm.
• Bacteria occur in many shapes and live everywhere — soil, water, air, hot springs, even inside us.
• Cyanobacteria are autotrophic and photosynthesise.

Some bacteria are pathogens, but many are useful (Lactobacillus, Rhizobium); gut bacteria of ruminants help make biogas, and some break down pollutants.

After a week, a drop under the microscope shows tiny moving organisms — protists such as Amoeba, Paramecium and Euglena.

These are single-celled eukaryotes (Kingdom Protista) living in water/moist places; some autotrophic, some heterotrophic, many moving by cilia or flagella.

Safety: the infusion smells bad — wear a lab coat, mask and gloves, and autoclave before discarding.

In a unicellular organism one cell is a complete body; its organelles act like organs:

• Cell membrane → exchange of gases/materials
• Food vacuoles → digestion · Contractile vacuole → excretion
• Cilia/flagella → movement · Nucleus → control & reproduction

Because the cell is tiny, materials diffuse quickly, so one cell manages everything. Large multicellular bodies instead use division of labour among specialised cells, tissues and organs.

Bryophytes (mosses, Marchantia) form flat green mats. Compared with ordinary leaves:

• Their leaf-like parts are simple, only a few cells thick, not true leaves (no proper veins).
• They have no true roots, stems, leaves or vascular tissue.
• They attach by thread-like rhizoids and need a film of water to reproduce.

Because they need water for reproduction they are the “amphibians of the plant kingdom.”

First seen in pteridophytes (ferns): vascular tissue (xylem & phloem) and true roots, stems and leaves, which absorb and transport water internally, so the plant no longer needs a wet surface for transport.

But ferns (and bryophytes) still need water for reproduction, because male cells must swim to the female cells — so they remain tied to moist conditions for fertilisation.

In a tall plant, water from roots must travel a long way up to the leaves and food must travel down — too slow for simple diffusion.

So tall plants need vascular tissues: xylem carries water/minerals up, phloem carries food. These pipelines allow efficient long-distance transport, letting ferns, gymnosperms and angiosperms grow large.

Seeds protect the embryo, store food and allow fertilisation without water (as in gymnosperms), so seed plants survive in dry and cold regions.

Fruits (angiosperms) protect seeds and disperse them far by wind, water, insects, birds or animals. Together they let plants colonise a wide range of new environments — making angiosperms the most widespread group.

Both have xylem and phloem, so both transport water and food. The difference is in arrangement and complexity:

• Fern (pteridophyte): vascular tissue is simpler/primitive, with basic bundle arrangement and little secondary growth.
• Sunflower (angiosperm): bundles are more organised, arranged in a regular ring, often with cambium for further growth.

Leaf venation sorts flowering plants into two groups:

Broad reticulate dicot leaves capture sunlight efficiently; narrow parallel monocot leaves bend in wind and resist drying — venation reflects adaptation.

From algae to angiosperms, plants gradually evolved transport tissue → seeds → flowers & fruits, steadily conquering land.

The beetle’s exoskeleton (rigid chitin covering) gives advantages the soft earthworm lacks:

• Protection from predators and injury.
• Prevents water loss, so it can live in dry, exposed places on land.
• Supports powerful muscles for walking and flight.
• Provides shape and support on land.

This is a key reason arthropods are the most successful land animals.

It means more than the number of species. It includes three connected levels:

• Genetic diversity — variation within a species.
• Species diversity — the variety of organisms.
• Ecosystem/habitat diversity — varied habitats and the interactions within them.

I would record the standard criteria, broad to fine:

• Cell type — prokaryote or eukaryote (Monera vs the rest).
• Number of cells — unicellular or multicellular.
• Cell wall — present/absent and its material.
• Mode of nutrition — autotroph or heterotroph.
• Body organisation, movement, symmetry, and notochord/backbone (for animals).

Why: these reliably place it in the correct kingdom and reveal its relationships.

Every cell carries DNA, the inherited instructions for growth and function. Comparing DNA reveals similarities invisible from outside.

Organisms with similar DNA share a common ancestry, so genetic studies show true evolutionary relationships more accurately than external features — leading to refined systems like the three-domain classification.

Climate change alters temperature, rainfall and habitats:

• Habitat loss — melting ice, droughts or floods destroy homes.
• Range shifts & timing — species migrate; flowering may fall out of sync with pollinators.
• Extinction — species that can’t adapt disappear, and dependents decline too.
• Disturbed food webs, reducing overall biodiversity.