Back to topics

What do blood-type letters and signs mean?

A blood donor card stamped with 'O+' or 'AB-' is shorthand for two separate molecular ID systems on the surface of red blood cells. The letters A, B, and O describe the presence or absence of specific sugar antigens, while the plus or minus sign usually records the presence or absence of the RhD antigen, critical clues for preventing a dangerous immune reaction during a transfusion.

3–5 min

Questions you could explore

  • Why does O not mean that a red blood cell has no antigens at all?
  • What do the ABO letters describe, and what does the positive or negative sign add?

Start reading

  • American Red CrossBlood Types

    The American Red Cross explains ABO and Rh labels and notes that careful typing and cross-matching matter for transfusion.

Ready to try your ideas aloud?

Your topic carries over. Record up to 2½ minutes, depending on your plan.

Health and the body

Daylight and the body's clock

Even in a room with no clocks, your body follows an internal roughly 24-hour schedule of sleepiness, hunger, and alertness. Those internal daily rhythms respond to outside cues, with morning and evening light helping reset and coordinate the body's master clock.

3–5 min

Daylight and the body's clock

Health and the body3–5 minEven in a room with no clocks, your body follows an internal roughly 24-hour schedule of sleepiness, hunger, and alertness. Those internal daily rhythms respond to outside cues, with morning and evening light helping reset and coordinate the body's master clock.

Health and the body

How vaccines build immune memory

The first time the immune system encounters an unfamiliar antigen, building a response takes time. Vaccines help develop recognition and memory before a later encounter with a pathogen. Different types introduce antigens or instructions for making them in different ways, offering a starting point for exploring how immune memory works.

4–5 min

How vaccines build immune memory

Health and the body4–5 minThe first time the immune system encounters an unfamiliar antigen, building a response takes time. Vaccines help develop recognition and memory before a later encounter with a pathogen. Different types introduce antigens or instructions for making them in different ways, offering a starting point for exploring how immune memory works.

Health and the body

Antibiotics and the viruses they cannot treat

Antibiotics can treat certain bacterial infections, but they do not treat the viruses that cause a common cold. Because bacteria are living cells with their own metabolic machinery and viruses are tiny genetic packages that hijack your cells, an antibiotic that disables bacteria has no matching target in the viruses that cause a cold.

2–3 min

Antibiotics and the viruses they cannot treat

Health and the body2–3 minAntibiotics can treat certain bacterial infections, but they do not treat the viruses that cause a common cold. Because bacteria are living cells with their own metabolic machinery and viruses are tiny genetic packages that hijack your cells, an antibiotic that disables bacteria has no matching target in the viruses that cause a cold.

What do blood-type letters and signs mean? | Speech Topic | speaking.app