What is the author urging the reader to do?

Rise and do the work proper to a human being (He reminds himself he was made "for action or exertion," not to lie warm in bed.)

Why does the author mention plants, birds, ants, and bees?

As examples of beings that do their natural work without complaint (They all "work together to put in order their several parts of the universe," a model for doing one's own natural work.)

What excuse for staying in bed does the author consider and reject?

That staying warm is more pleasant (He raises "But this is more pleasant" and rejects it by asking whether he exists merely to take pleasure.)

As used here, "exertion" most nearly means:

effort and hard work (He asks whether he exists for pleasure "and not at all for action or exertion." Exertion is effortful work, the opposite of lying warm in the bed-clothes.)

On Rising in the Morning: Level 4 Reading Comprehension Questions

In the morning when thou risest unwillingly, let this thought be present: I am rising to the work of a human being. Why then am I dissatisfied if I am going to do the things for which I exist and for which I was brought into the world? Or have I been made for this, to lie in the bed-clothes and keep myself warm? But this is more pleasant.

Dost thou exist then to take thy pleasure, and not at all for action or exertion? Dost thou not see the little plants, the little birds, the ants, the spiders, the bees working together to put in order their several parts of the universe? And art thou unwilling to do the work of a human being, and dost thou not make haste to do that which is according to thy nature?

Source: Marcus Aurelius, Meditations (c. 170 AD). Marcus Aurelius, Meditations, Book V, trans. George Long (1862). Public domain.

Comprehension questions