Biology 2nd Paper (Zoology) · Classes 11-12 · Chapter 1

Animal Diversity and the Start of Classification.

Two people of one species have different hair colour. A forest holds tigers, deer and monkeys side by side. A desert looks nothing like a wetland. We call all three “diversity”, yet they are not the same thing. This note teaches you to tell them apart, and shows how people first began to sort animals into groups, starting with Aristotle.

1. Animal diversity and its three kinds

The genetic, species and ecological differences seen among all the aquatic, land and flying animals of the earth are called animal diversity.

Animal diversity is of three kinds: genetic diversity, species diversity and ecosystem diversity. Below are six situations. Pick one up, then drop it in the right box.

2. The three kinds, a little closer

Genetic diversity is the degree of difference in genetic material among the members of one species in a given ecosystem. It is also called intraspecific diversity.

It matters. A species with high genetic diversity adapts better to a changing environment and is less likely to become extinct.

The number of different species living together in one region at one time and forming an ecological community is species diversity. It is the basic level of biodiversity.

Biodiversity is higher in the tropics than in deserts and polar regions because nutrients and climate are favourable there: moderate temperature, enough light and enough rain.

A region with high species diversity is called a biodiversity hotspot.

Ecosystem diversity is the variation among the species of communities in different ecosystems that are linked by energy flow and nutrient cycling. Examples of ecosystems are grassland, forest, desert and wetland.

3. Aristotle's first division

The Greek philosopher Aristotle (384-322 BC) set out to make zoology a separate branch of science, so he is called the father of zoology. He was also the first to try to classify the animal world.

He split animals into two groups: red-blooded vertebrates, called Enaima, and animals without red blood, the invertebrates, called Anaima. Later, by the way they reproduce, Enaima were divided into oviparous (egg-laying: fish, amphibians, reptiles, birds) and viviparous (bearing live young: mammals). Open the tree and see.

4. The first bases of classification

Outer features alone soon stopped being enough. Habitat, genetics, cell and tissue science, embryology and internal organ structure all came to count as reasons for animal differences.

In classification, the features given priority are body size, structure, symmetry, segmentation, body cavity, sex and life cycle.

By body size, animals are of two kinds: micro-animals, which cannot be seen without a microscope, such as Trichodina anabasi; and macro-animals, which are visible to the naked eye, such as Cavia porcellus, the guinea pig.

By grade of cellular organisation, the animal world falls into four groups: cellular, cell-tissue, tissue-organ and organ-system grade.

Cellular grade: some cells specialise for a task, some for reproduction, some for gathering food, a kind of division of labour. Porifera have this grade.

Cell-tissue grade: similar cells are arranged in a set pattern to form tissue. Cnidaria show it.

Tissue-organ grade: several tissues join to make organs. It first appears in Platyhelminthes: eye spots, proboscis, reproductive organs. Examples are the tapeworm Taenia and the liver fluke Fasciola.

Organ-system grade: organs combine into systems, such as respiration, circulation and digestion. Most phyla show it. It first appeared in the marine Nemertean group.

By way of living, animals are of two kinds. Free-living animals move about independently, like the pigeon Columba livia. Parasitic animals absorb food from another animal's body, like the liver fluke Fasciola hepatica. One question settles it: is there a host?

5. Check yourself

Three questions in the exam's style. The first is on the definitions.

In the second, work out which kind of diversity is meant.

For the last, remember Aristotle or the grades of organisation.

The whole note on seven cards.

Source: Biology 2nd Paper (Zoology), Classes 11-12 (NCTB), Chapter 1 “Animal Diversity and Classification”, the “Animal Diversity and the Start of Classification” part.