State the main function of
(i) Guard cells.
(ii) Thrombocytes.
(iii) Chordae tendineae.
(iv) beta-cells of pancreas.
(v) Cerebrospinal fluid.

Explanation

### Step-by-Step Solution:

1. **Guard Cells**:
- Guard cells are specialized cells located in the epidermis of leaves, surrounding the stomatal pores.
- **Main Function**: They regulate the opening and closing of stomatal pores, facilitating gas exchange (like oxygen and carbon dioxide) and controlling water loss through transpiration.

2. **Thrombocytes**:
- Thrombocytes, also known as platelets, are small cell fragments found in the blood.
...