State the name of a bacterium responsible for TB in humans.
Fig. 4.1 shows a scanning electron micrograph of bacteria that cause TB. Calculate the true length of the bacterial cell in Fig. 4.1 along the line X-Y. Write the formula you will use in the box. Give your answer in micrometres ($\mu\text{m}$) to two significant figures.
Bacteria are single-celled prokaryotes with diameters of $1\text{-}5\,\mu\text{m}$. State two other structural characteristics that show a cell is prokaryotic.
A student used the data in Fig. 4.2 to predict that measures to control the spread of HIV will decrease the number of deaths from TB. Discuss whether the data in Fig. 4.2 support this prediction.
In healthy people, T-helper cell numbers range from 500 to 1200 cells per $\text{cm}^3$ of blood. In untreated people infected with HIV, T-helper cell numbers can fall to below 200 cells per $\text{cm}^3$ of blood. Explain why a low T-helper cell count makes it more likely that untreated people infected with HIV will die if they also have TB.