Consider the following statements about pollen grains and identify the correct ones.
I. Pollen grains are typically spherical and measure between 25–50 micrometers in diameter.
II. The outer wall of a pollen grain, known as the exine, is made of cellulose and is highly resistant to environmental factors. 
III. Sporopollenin, a component of the exine, is one of the most resistant organic materials, able to withstand high temperatures and harsh chemical conditions.
IV. Germ pores in the pollen grain exine are areas where sporopollenin is absent and plays a crucial role in the pollen grain's ability to fertilise.
V. The inner wall of the pollen grain, called the intine, is made up of sporopollenin.
VI. A mature pollen grain typically contains two cells: a large vegetative cell and a smaller generative cell.