Five kingdoms — cell type, wall, nutrition
Every kingdom is eukaryotic except Bacteria, which are prokaryotic — unicellular, no true nucleus, wall not cellulose. Animals: no cell wall, heterotrophic (ingest), multicellular. Plants: cellulose wall, autotrophic, multicellular. Fungi: wall not cellulose (chitin/glucan), saprotrophic or parasitic, mostly multicellular — yeast is unicellular. Protoctists: mainly unicellular, wall and nutrition variable. All five share the same genetic code (DNA).
Vertebrates — five classes, four features
All vertebrates are chordates with a vertebral column. Fish: wet scales, eggs in water (external fertilisation), gills, ectothermic. Amphibians: moist smooth skin, eggs in water, gills as larvae then lungs and skin, ectothermic. Reptiles: dry scaly skin, leathery-shelled eggs on land, lungs, ectothermic. Birds: feathers, hard-shelled eggs on land, lungs, endothermic. Mammals: hair or fur, live young suckled on milk, lungs, endothermic.
Arthropods — one phylum, four subgroups
Every arthropod has an exoskeleton, jointed limbs and a segmented body, so those never identify a subgroup. Insects: 3 pairs of legs, 3 body regions (head, thorax, abdomen), 1 pair of antennae, usually 2 pairs of wings. Arachnids: 4 pairs of legs, 2 regions (cephalothorax, abdomen), no antennae or wings. Crustaceans: 5 or more pairs of legs, 2 pairs of antennae, mainly aquatic. Myriapods: many legs and segments, 1 pair of antennae.
Drawn from real examiner reports.
Exoskeleton, not "skin" or "shell"
The hard outer covering of an arthropod is the exoskeleton. Mark schemes reject "skin" — that is the soft covering of a vertebrate — and "shell", which implies a separate structure the animal sits inside. Use the exact term: it is worth a mark on its own when a question asks you to name the covering.
Flagged s23 P31 Q1c
Arachnids: eight legs, two regions
Arachnids have eight legs (four pairs), two body regions (cephalothorax and abdomen), no antennae and no wings; insects have six legs and three regions. Antennae alone never settle it — myriapods also have one pair and crustaceans have two pairs, so only "none" points to an arachnid.
Flagged w22 P42 Q3a · s23 P31 Q1
A kingdom is not a class
The hierarchy runs kingdom → phylum → class → order → family → genus → species. Asked for the kingdom of a cat, the answer is Animalia — "mammal" is a class and "vertebrate" a sub-phylum, so both score zero. The reverse loses marks too: writing "animal" when a vertebrate group is asked for.
Flagged s22 P41 Q1a · w22 P31 Q1 · s23 P31 Q1c
Viruses are non-living — no kingdom
A virus is a protein coat around a nucleic acid (DNA or RNA), with no cell membrane, cytoplasm or ribosomes. It reproduces only inside a host cell and is smaller than a bacterium. Because it is non-living it belongs to none of the five kingdoms — never Prokaryotae. HIV is a virus, not a bacterium.
Flagged s22 P31 Q2b i (HIV called a bacterium)
Bacteria are prokaryotes
Bacterial DNA floats free in the cytoplasm — there is no true membrane-bound nucleus, and that is what makes bacteria prokaryotes. Every other kingdom (animals, plants, fungi, protoctists) is eukaryotic. Bacteria do have a cell wall, but it is not cellulose, so "has a cell wall" never means "plant".
Jointed limbs ≠ insects only
An exoskeleton, jointed limbs and a segmented body are shared by every arthropod — arachnids, crustaceans and myriapods have them too. Offering either as the reason an organism is an insect scores nothing. To name an insect you must give six legs (three pairs) and three body regions: head, thorax and abdomen.
Flagged w22 P42 Q3a · s23 P31 Q1
Identify, then justify with a named feature
Run the decision chain: not cellular → virus (no kingdom); no true nucleus → bacteria; cellulose wall and autotrophic → plant; non-cellulose wall and absorbs food → fungus; no wall and ingests food → animal; eukaryotic and unicellular → protoctist. Then quote the feature that placed it — "it has special features" scores zero.
Arthropods: count legs, then regions
Confirm the exoskeleton and jointed limbs to fix the phylum, then count. Six legs and three body regions → insect. Eight legs and two body regions → arachnid. Many legs with two pairs of antennae → crustacean. Many segments with many pairs of legs → myriapod.
Spores or seeds decides fern vs flower
Ferns and flowering plants are both multicellular, vascular (xylem and phloem) and have cellulose cell walls, so those are similarities, not differences. Ferns bear spores on the underside of their fronds and never form flowers or seeds; flowering plants form seeds enclosed in a fruit that develops from a flower.
MCQ traps: wrong rank, shared feature
Reptiles are ectothermic — only birds and mammals are endothermic. Amphibians have moist, smooth skin; dry, scaly skin is a reptile. Fungi placed in the plant kingdom is always wrong (wall not cellulose, no photosynthesis). Reject any option that offers a shared arthropod feature as a subgroup identifier.
Kingdom: the broadest classification group. All living organisms are placed in one of five kingdoms (animals, plants, fungi, bacteria/prokaryotae, protoctists). Viruses are non-living and belong to no kingdom.
Prokaryote: a cell with no true membrane-bound nucleus — the genetic material (DNA) floats freely in the cytoplasm. Only bacteria are prokaryotes.
Eukaryote: a cell with a true nucleus enclosed in a membrane. Animals, plants, fungi and protoctists are all eukaryotes.
Autotrophic: able to produce organic molecules from inorganic raw materials using an energy source (e.g. photosynthesis in plants).
Heterotrophic: obtains organic molecules by consuming other organisms.
Saprotrophic: feeds by secreting enzymes onto dead organic matter and absorbing the soluble products (the feeding mode of fungi).
Define prokaryote. Which kingdom is prokaryotic?
State three features that are used to classify an organism as a plant rather than an animal or fungus.
