Outline the cell theory.

Annotate the electron micrograph of the Escherichia coli cell with the function of the indicated structure.

Calculate the magnification of the electron micrograph.

Explain the role of the following enzymes in DNA replication.
Helicase

Explain the role of the following enzymes in DNA replication.
DNA ligase

a. living things are composed of cells;
b. cells are the basic/smallest unit of life;
c. cells come from pre-existing cells;
Do not accept cells are the “smallest organisms”.
Do not accept “cells are the building blocks” of life on its own.

attachment to surfaces / holds bacteria together / conjugation
Do not accept “exchange material” on its own.
If more than one function is given, mark the first answer only.

× 15 000 (accept answers in the range of × 14 000 to × 16 000)

helicase: unwinds /unzips the DNA (into two strands) / breaks H bonds;

DNA ligase: joins/seals the nick between the (Okazaki) fragments;

Most students earned these marks. A small number demonstrated knowledge of the properties of cells but seemed to be unfamiliar with the cell theory itself.

A number failed to state a correct function. The pilus plays a role in adhering to surfaces and in bacterial conjugation. A number annotated the picture with the name of the structure without stating a function.

About half of candidates correctly answered this question. A number were making order of magnitude errors such as writing 150 000x and 1500x. Some were unfamiliar with the interpretation of the metric prefix.

Most were able to explain the function of helicase.

Similar to primase, the mechanism of action of ligase was very rarely accurately described, most limiting it to bond formation between Okazaki fragments, not acknowledging that ligase has a role on the leading strand as well.