Some plants make large seeds (eg coconut palms), while some make numerous seeds (eg sunflowers). Why isn't there a plant that makes numerous, large seeds?

The correct answer is : Due to constraint or limitation in resource and energy availability.

Explanation:

The total energy of an organism is constant. It utilises this energy to carry out its growth, development, metabolism and reproduction. Although, a huge amount of energy is invested in the process of an organism's reproduction, the total energy invested is constant. So, if an organism, like coconut palm, produces large seeds, it is investing substantial amount of its resources for the production of each seed. Therefore, with a constant amount of energy available to it, it is capable of producing only a few number of large seeds. In the case of an organism like sunflower, it produces small seeds, so the amount of resources that it invests for the production of each seed is less. Hence, it can invest the rest of the available resources for the production of large number of seeds. Therefore, due to nutrient and energy constraint it is not possible for plants to produce numerous and large seeds.