If 'reported' in the right light ... most anything can be considered photojournalism. How you shoot (treat) the subject matter is more important than what the subject matter may be. Photojournalism photographs are designed to report ... to tell a story.
Does the teacher want a photo story, (more than one photo illustrating a story), or a single photo illustrating a story?
An image of a single flower or a formal portrait of a person, generally wouldn't be considered photojournalism. But if you shot the flower as a story ... "The first bloom of Spring ..." or "Flowers of the Rose Parade ..." would be considered photojournalism. But ... your submission for your assignment will not have the advantage of text to explain the image. So you photo must also tell a story without text. S0 the second example of the formal portrait needs to show more than just the head and shoulders ... you need to shoot an environmental portrait which includes enough elements/info in the photo to let the viewer construct a story about the person.
Read a few newspapers (online is cheap) ... then emulate.
Photojournalism:
1) Hard News (police scanner stuff / fires / political / current events / et al;
2) Sports news;
3) Business/Finance news;
4) Entertainment/Arts news; and
5) Feature/Human Interest (Features can be anything of interest which isn't necessarily time-critical. In other words a story which can run, today ... or tomorrow ... or in a month.)
"1. Timing
The word news means exactly that - things which are new. Topics which are current are good news. Consumers are used to receiving the latest updates, and there is so much news about that old news is quickly discarded.
A story with only average interest needs to be told quickly if it is to be told at all. If it happened today, it's news. If the same thing happened last week, it's no longer interesting.
2. Significance
The number of people affected by the story is important. A plane crash in which hundreds of people died is more significant than a crash killing a dozen.
3. Proximity
Stories which happen near to us have more significance. The closer the story to home, the more newsworthy it is. For someone living in France, a major plane crash in the USA has a similar news value to a small plane crash near Paris.
Note that proximity doesn't have to mean geographical distance. Stories from countries with which we have a particular bond or similarity have the same effect. For example, Australians would be expected to relate more to a story from a distant Western nation than a story from a much closer Asian country.
4. Prominence
Famous people get more coverage just because they are famous. If you break your arm it won't make the news, but if the Queen of England breaks her arm it's big news.
5. Human Interest
Human interest stories are a bit of a special case. They often disregard the main rules of newsworthiness; for example, they don't date as quickly, they need not affect a large number of people, and it may not matter where in the world the story takes place.
Human interest stories appeal to emotion. They aim to evoke responses such as amusement or sadness. Television news programs often place a humorous or quirky story at the end of the show to finish on a feel-good note. Newspapers often have a dedicated area for offbeat or interesting items."