List two distinguishing characteristics of Chordates and explain the importance of a dichotomous key in biology.

3. State two distinguished characteristics found only in phylum Chordata (2 marks).

• Presence of a notochord at some stage of their life cycle.
• Presence of a dorsal hollow nerve cord.
• Presence of pharyngeal slits at some stage of their life cycle.
• Presence of a post-anal tail at some stage of their life cycle.

4. What is the importance of a dichotomous key in the study of biology? (1 mk) A dichotomous key is important for identifying and classifying organisms based on their observable characteristics.

5. The diagram below illustrates a common fresh lake inhabiting organism. Study it and answer the following questions.

a) Name the class to which the organism belong (1 mk).
The organism (fish) belongs to the class Pisces.

b) Give three reasons for your answer in (a) above (3 mks).

• It has a streamlined body for movement in water.
• It possesses fins for propulsion and steering.
• It has scales covering its body.
• It breathes using gills.

6. The diagram below represent a bacterium cell.

• Name the kingdom to which the bacterium belong (1 mk). The bacterium belongs to the kingdom Monera.

• State two distinguishing characteristics of the members of the kingdom named above. (2 mks)

• They are prokaryotic, meaning they lack a true nucleus and other membrane-bound organelles.

• They are unicellular organisms.

• Their genetic material (DNA) is circular and not enclosed in a nucleus.

• They reproduce primarily by binary fission.