State the main function of the following:

(i) Chordae tendineae play a vital role in holding the atrioventricular valves in place while the heart is pumping blood.

(ii) Lymphocytes produce antibodies which kill or neutralise the germs or the poisons from them.

(iii) The Seminiferous tubules produce sperms by the process called spermatogenesis.

(iv) The thylakoid membranes of a chloroplast are the site of light reactions of photosynthesis as the pigment chlorophyll is contained in the walls of thylakoids.

(v) Secrete insulin that helps to lower the level of glucose in blood.