Exam practice

The two-kingdom system put prokaryotes with eukaryotes, unicellular organisms with multicellular ones, and fungi (with no chlorophyll) with green plants, and some organisms, like Euglena, fitted in neither kingdom. The five-kingdom system separates organisms by the type of cell, the number of cells, the cell wall, the mode of nutrition and their role in the ecosystem, so organisms that are really alike are grouped together. That shows their natural relationships better.

Most fungi have no chlorophyll and can’t make their own food. They absorb their food from dead and decaying organic matter, such as rotting wood, dung and old bread. An organism that feeds on dead and decaying matter is called a saprophyte (saprotroph), so fungi are called saprophytes.

Monerans are prokaryotes: their cells have no proper nucleus and no membrane-bound organelles, and their DNA lies loose in the cytoplasm. Protists are eukaryotes: their cells have a true nucleus with a nuclear membrane and organelles such as mitochondria, and they reproduce both asexually and sexually. Eukaryotic cells evolved later than prokaryotic ones and are more complex, so protists are considered more advanced.

It is the system of giving every species a scientific name of two words, started by Carolus Linnaeus. The first word is the genus (generic name), beginning with a capital letter; the second is the species (specific name), beginning with a small letter. The name is printed in italics or underlined when handwritten. Example: Homo sapiens (human), where Homo is the genus and sapiens the species. The same name is used by scientists all over the world.

Human: Homo sapiens. Garden pea: Pisum sativum. Mustard: Brassica campestris. Leopard: Panthera pardus.

A species is a group of similar organisms that can breed with each other and produce fertile young; it is the smallest unit of classification. A genus is a group of closely related species with many features in common; it comes just below the family. For example, the tiger (Panthera tigris), the lion (Panthera leo) and the leopard (Panthera pardus) are three species of one genus, Panthera. In a scientific name, the genus is the first word and the species the second.

Draw the chart as in Figure 2.2: living things → prokaryotic (Monera) or eukaryotic; eukaryotic → unicellular (Protista) or multicellular; multicellular → no cell wall (Animalia) or cell wall; cell wall → autotrophic (Plantae) or heterotrophic (Fungi).
Examples: Monera: bacteria such as Rhizobium, blue-green algae such as Nostoc. Protista: Amoeba, Euglena. Fungi: mushroom, Mucor. Plantae: fern, mustard. Animalia: earthworm, human.

1. They are prokaryotic, unicellular microorganisms.
2. The cell has no definite nucleus; the DNA lies in the cytoplasm.
3. There are no membrane-bound organelles.
4. Many survive in harsh conditions.
5. They may be autotrophic, parasitic, saprophytic or symbiotic.
6. There are three types: archaebacteria (e.g. Pyrolobus), eubacteria (e.g. Rhizobium, Clostridium) and cyanobacteria (e.g. Nostoc, Anabaena).

1. They are eukaryotes: the cell has a true nucleus.
2. Most are unicellular, with their organelles inside a cell membrane.
3. They move by pseudopodia, cilia or flagella.
4. Some make their own food, some take in food, and some are parasites.
5. They reproduce both asexually and sexually.
6. They are animal-like (Amoeba, Paramecium), plant-like (Euglena, diatoms) or fungus-like (slime molds).

1. They have no chlorophyll; most are multicellular, some unicellular (yeast).
2. Most are saprotrophic, absorbing food from dead and decaying matter.
3. The body is a thallus, not divided into root, stem and leaf, made of a mycelium of hyphae.
4. The cell wall is made of chitin, and food is stored as glycogen.
5. They reproduce asexually and sexually, mostly by spores.
6. By nutrition they are saprotrophic (Mucor, mushroom), parasitic (Puccinia) or symbiotic (the fungus in a lichen).

Examples: mushroom, Mucor, yeast, Penicillium.

The taxa form a ladder: kingdom → phylum → class → order → family → genus → species. Each taxon is part of the one above it and contains the ones below it. The higher the taxon, the more kinds of organisms it includes and the fewer features they share; the lower the taxon, the fewer kinds, and the more alike they are.
Example (human): kingdom Animalia includes all animals; phylum Chordata only animals with a notochord; class Mammalia only those that feed their young on milk; order Primates only lemurs, monkeys, apes and humans; family Hominidae only the great apes and humans; genus Homo only humans; species sapiens only us. So organisms that share a lower taxon, like the human and the chimpanzee (same family), are closer relatives than those that share only a higher one, like the human and the cow (same class).

A. Rhizopus (bread mold): kingdom Fungi. No chlorophyll; body a mycelium of hyphae, with root-like rhizoids; reproduces by spores formed in black sporangia.
B. Mucor: kingdom Fungi. No chlorophyll, saprotrophic (grows on bread and roti); body a mycelium of hyphae; round sporangia full of spores on upright stalks.
C. Nostoc (a blue-green alga): kingdom Monera. Prokaryotic cells with no true nucleus; cells joined in bead-like chains with some larger, thick-walled cells (heterocysts) that fix nitrogen; has chlorophyll and makes its own food.
D. Paramecium: kingdom Protista. Unicellular and eukaryotic; slipper-shaped, covered with cilia for swimming; takes in food through a groove (oral groove).