If a dihybrid f1 plant is self fertilized, what proportion of progeny will have the same phenotype as the f1 parent? what proportion will be true-breeding? what proportion will be heterozygous at one or both loci?

 If a dihybrid F1 plant, self-fertilizes, the F2 progeny will have two types of phenotypes. One would be the dominant trait phenotype for both the alleles, which would be possessed by 3/4th of the population.
Other would be recessive trait phenotype for both the alleles, which would be possessed by 1/4th of the population. 
One fourth of the population would be true-breeding for the dominant traits.
Half of the population would be heterozygous for both traits and would have dominant phenotype
Rest one-fourth population would be homozygous for both recessive traits

Centriole.centrioles are present in animal cells but are usually absent in plant cells.

It depends on the surface of the levels. the rougher the surface, the greater is the frictional force. for rougher surfaces, you would need to exert greater force to move the object. the concept is that, you must overcome the frictional force in order to bring the object into motion. this is the reason why we add lubricants to the joints so they could easily move. this answer was on