Taxonomic Hierarchy: PECTAA Class 11 Biology, Punjab Board

A school has classes, sections and rolls. A name in the school record tells you exactly where a student sits. Biologists do the same for living things. Eight levels, from the biggest group to the smallest, place any organism in one line.

Chapter 1 of the PECTAA Biology 11 book is Biodiversity and Classification. Section 1.2 gives the taxonomic hierarchy. This note covers it for FSc Part 1 (1st year, Class 11) students in Lahore, Faisalabad, Sargodha, Rawalpindi, Multan, Gujranwala and the other Punjab boards. Gujrat district comes under the Gujranwala board. PECTAA writes the books. Your own board sets your paper.

What to know

The book says the hierarchy helps scientists to sort and understand the relationships between different forms of life. Each level is a taxon (plural taxa). The levels, from highest to lowest, are:

1. Domain. The highest level of classification. There are three: Archaea, Bacteria and Eukarya.
2. Kingdom. One of the highest ranks, just below domain. It groups forms of life that share fundamental characteristics. In domain Eukarya the book names the kingdoms Animalia, Plantae, Fungi and Protista.
3. Phylum. The next level below kingdom. Organisms in a phylum share a basic body structure and important structural features. Book example: in kingdom Animalia, phylum Chordata includes animals with a notochord, such as mammals, birds, reptiles, amphibians and fish.
4. Class. Divides a phylum by more specific common traits. Book example: in Chordata, class Mammalia includes animals with hair and mammary glands.
5. Order. Groups the organisms of a class by further shared characteristics. Book example: in Mammalia, order Primates, with large brains and opposable thumbs.
6. Family. Groups by more precise common attributes. Book example: in Primates, family Hominidae.
7. Genus. A more specific rank in a family. It groups species that are very closely related and often look alike. Book example: genus Homo in family Hominidae.
8. Species. The most specific level. It stands for a single type of organism. Members of a species can interbreed and produce fertile offspring. Book example: Homo sapiens.

Key points

The book gives a table that follows three organisms through every level.

Read the table in two ways.

• Down a column. Each step narrows the group. Domain Eukarya holds all four eukaryote kingdoms, while Passer domesticus is one species.
• Across a row. The human and the sparrow are the same down to phylum, then they differ. The onion is different from kingdom onward.

The species name has two parts: the genus, then the species word. The book table shows it as two words, for example Passer domesticus.

Where the hierarchy starts. Section 1.1 explains that the old five-kingdom system put prokaryotes together in kingdom Monera. The three-domain system splits them into Archaea and Bacteria and keeps all eukaryotes in Eukarya.

Worked examples

Example 1. Place the sparrow in the hierarchy, using the book table.

1. Domain Eukarya, kingdom Animalia.
2. Phylum Chordata, class Aves.
3. Order Passeriformes, family Passeridae.
4. Genus Passer, species Passer domesticus.

Example 2. The book says species are the most specific level. Which level is broader, genus or family?

1. A family contains genera.
2. A genus contains species.
3. So family is broader than genus.

Example 3. Two organisms are in the same class but in different orders. Are they in the same phylum?

1. The classes sit inside a phylum, so the same class means the same phylum.
2. Yes, they are in the same phylum, and in the same kingdom and domain too.

Example 4. Find where the human and the onion first differ in the book table.

1. Both are in domain Eukarya.
2. At kingdom, the human is in Animalia and the onion is in Plantae.
3. So they first differ at kingdom.

Common mistakes in the exam

1. Writing the levels in the wrong order. The order is domain, kingdom, phylum, class, order, family, genus, species.
2. Starting at kingdom. In this book domain is above kingdom.
3. Saying there are four domains. There are three.
4. Writing the species name as one word. It is genus plus species word, such as Allium cepa.
5. Mixing up order and class. Class is the broader level. Order sits inside a class.
6. Giving "can interbreed" only. The book says members interbreed and produce fertile offspring.

Exam technique

• Answer a "write the hierarchy" question as a numbered list. The list shows the order.
• Add one book example next to each level when marks allow it.
• For a table question, copy the rank names in the left column first.
• Check your board's notice for the sections in your paper.

Practice questions

1. Write the three domains. Answer: Archaea, Bacteria and Eukarya.
2. In which phylum does the book place the sparrow? Answer: Chordata.
3. Which is the class of the onion in the book table? Answer: Monocots.
4. Define species as the book does. Answer: The most specific level of classification, representing a single type of organism. Members can interbreed and produce fertile offspring.
5. Give the order and the family of Homo sapiens. Answer: Order Primates and family Hominidae.

Ready to practise this? Continue in 1st Year Biology.