The answer is both the first (Cause disease) and second (Cause algal blooms)
Explanation:
Protists may cause disease and even kill living things. Also, algal blooms are essentially protists but have chloroplasts- which plays a part in them being harmful.
Respiration occurs when glucose (sugar produced during photosynthesis) combines with oxygen to produce useable cellular energy. This energy is used to fuel growth and all of the normal cellular functions.
The first option. So they couldn't produce offspring. Mendel was cross pollinating the plants. While he was doing to that he found out about "The Principal Of Dominance" meaning some alleles are recessive while some are dominant.