Question

1. Discuss how the following innovations, which first appeared in Gymnosperms have freed plants from dependence upon water for sexual reproduction and allowed Gymnosperms to dominate the world’s vegetation until they were replaced by Angiosperms.

a) The pollen grain with its pollen tube.

b) The ovule and the seed.

2A. List and describe the xerophytic adaptations of the pine needle.

Answer 1

Dear student

I'll try to be short and simple , to help you understand the concept.

1. Initially, the gymnosperms , like liverworts and ferns depended mainly on the water as a source/medium for sexual reproduction.

With years of evolution, the adaptation to seeds and pollens were predominant. This helped them to dominate the world for centuries, until the angiosprems came into existence.

They had certain adaptations, that helped the existence of seeds and its viability in the harsh climatic conditions. Starting with the layers of hard coats that enclose the seed(s). This reduced their dependency on water. The seeds could remain in dormant situation as long as they required. When favourable conditions return, they develop into diploid Sporophytes.  

The very first adaptations were the formation of cupules, where the ovules were protected and formed true seeds .

The evolution of seeds , ensured that, it could be dispersed into far away places my means of wind , water or even carried away by animals. This ensured less competition with the parent or sibling plants for resources.  

The pollens were mainly the male gamete part of the plants , that were adapted to produce in larger numbers. Much reduced in size . This happened to promote more easy dispersion purposes. Easily blown with the wind or air. These can be also transported by pollinators (animals that usually unknowingly carry the pollens on their backs/body and lead to the female pollen receptors).

These adaptations ensured modifications such that dissication/destruction of seeds or pollens do not occur.  

2A. The xerophytic adaptation of Pinus starts with its basic cone like structure. This helps them to shed off snow from the branches, exposing the leaves for photosynthesis.

They have adapted to winter seasons , with short growth time. Every year they grow a new whorl of leaves from the nain branch , called the Candle.

The needle like leaves ,fasicles , to ensure the least mositure loss, as the exposed surface area is reduced.

The leaves have sunken stomata , to further prevent water loss.

They also seem to have a waxy coating on the leaves, that makes the cuticle layer.

I hope this could help you.  

Until next time, Best Wishes.