Pollen grains are generally spherical,measuring about

Which cell is involved in the formation of the pollen tube?

The type of fossil pollen grains present in the area may be helpful in the exploration of

Which substance provides protection to pollen grains against high temperatures?

Which of the following statements is false regarding the exine of pollen grains?

Complete the following flow chart:
Pollen Mother cell $\to$ Pollen tetrad $\to$ Pollen grain $\to$ Vegetative cell
Pollen Mother cell $\to$ Pollen tetrad $\to$ Pollen grain $\to$ ..........