Iron-deficiency anemia can cause fatigue (tiredness), shortness of breath, chest pain, and other symptoms. Severe iron-deficiency anemia can lead to heart problems, infections, problems with growth and development in children, and other complications.
Semantics is the study of meaning. It is a wide subject within the general study of language. An understanding of semantics is essential to the study of language acquisition (how language users acquire a sense of meaning, as speakers and writers, listeners and readers) and of language change (how meanings alter over time).
A topic is a particular issue or idea that serves as the subject of a paragraph, essay, report, or speech. The primary topic of a paragraph may be expressed in a topic sentence. The main topic of an essay, report, or speech may be expressed in a thesis sentence. An essay topic, say Kirszner and Mandell, should be narrow enough so that you can write about it within your page limit.