What is caused by the harmful effects of certain microorganisms?

Options

A. Fermentation of glucose
B. Food poisoning in humans
C. Heart disease in humans
D. Production of antibiotics

Explanation

### Step-by-Step Solution

1. **Understanding Microorganisms**: Microorganisms are tiny organisms that cannot be seen with the naked eye. They can be beneficial or harmful to humans and the environment.

2. **Identifying Harmful Effects**: Among the options given, we need to identify which one describes a harmful effect caused by certain microorganisms.

3. **Analyzing the Options**:
- **Option A: Fermentation of Glucose**: This is a process carried out by yeast and is beneficial for producing bread and alcohol. Therefore, it is not harmful.
- **Option B: Food Poisoning in Humans**: Certain bacteria, such as Clostridium botulinum, can cause food poisoning, which is indeed a harmful effect.
- **Option C: Heart Diseases in Humans**: Microorganisms do not directly cause heart diseases, so this option is not correct.
- **Option D: Production of Antibiotics**: While some microorganisms produce antibiotics, this is a beneficial effect, not harmful.

4. **Conclusion**: The only option that describes a harmful effect caused by microorganisms is **Option B: Food poisoning in humans**.

### Final Answer
The harmful effect caused by certain microorganisms is **food poisoning in humans**.

---