But some bacterium always lives in surroundings with the same concentration of dissolved substances as in their own cytoplasm. what structure do these bacteria not need? (fourth paragraph of subsection implies the answer)

Periplasmic space

Explanation:

The periplasmic space is a colloidal layer that contains a large amount of hydrolytic and other enzymes that direct essential nutrients to the plasma membrane transport proteins, preventing them from spreading back to the outside. For this reason, bacteria living in environments with the same concentration of dissolved substances as in their own cytoplasm need the periplasmic space to prevent the loss of structures to the external environment.

The periplasmic space contains antibiotic inactivating enzymes, chemoreceptors (sensors that help the cell to detect changes in the environment) and oligosaccharides that appear to help the bacteria resist the molarity of the environment.

In the periplasmic space of many Gram-negative bacteria, between the cell wall and the phospholipid layer of the outer membrane there are lipoproteins that would assist in anchoring the outer membrane to the cell wall.

amber has allowed scientists to study dna that has been preserved over millions of years.