During the period of Cenozoic era, co-evolution between plants and animals species occur. It has been profound that certain plants and insects influence another in evolution, in a process known as mutualism where all organisms benefit from each other. They firstly evolve in the aquatic environment before they evolve on land.

Species that co evolve were single cell plant and multicelled eukaryote organism, the blue-green algae was the single cell plant which evolve on the sea. It was the first species to generate its own food in a process known as photosynthesis where sunlight and water are used; during this process oxygen is also generated. While animal cannot produce its own food, they depend direct or indirectly on plants for its survival, and for animal to be evolved on earth it is traced back to plant this show dependency of animal to plant.

The oxygen that the algae produce spread all over the aquatic environment, it began to fill the atmosphere and this made it possible for other organism to develop. Because of high concentration of oxygen produced by algae in the atmosphere, it tends to give access to animal species to evolve on land. Oxygen form part of ozone layer in the upper atmosphere which tends to block the dangerous ultraviolet rays of the sun, these rays was making it impossible for organism to live out of water. But it was simple for plant to survive on land because they can utilise the ultra violet rays into food.

Simplicity of plant to convert sunlight into food made it possible for plant to evolve on land, and the first plant to evolve on land was Mosses. This made it possible for other animal to evolve on land, because of the oxygen generated by plant which forms the ozone layer that block the ultraviolet which restrict life of organisms to exist on land.

Mutualisation which develop between plant species and animal species during co evolution influenced by the resource that one need to survive, plant release oxygen as by products which is used by animal for its survival while animal release carbon dioxide as by products which plant species use it during the process of photosynthesis. For each species to survive it have to depend on the other directly or indirectly.

This dependency between plant and animal species can be seen during reproduction, where plant depends on organism to transfer pollen grains to the female flowers. This helps the plant to reproduce and increase plant population, which is simple method to transfer pollen than wind pollination which need quality seed to be dispersed. While organisms benefit from plant through food and habitant for reproduction that the plant provides, mostly this happens to insects such as moth and bees.

Sometimes plant and organisms become total depend on each other, this happen when one insect only function to pollinate their pollen grains only and it find habitant on the same type of plant ‘s flower. Some become specific to that species only and they protect that species form herbivores. For example, species such as Yucca (Plant) and Moth(organism)they depend on each other yucca provide habitant for moth and allows it to reproduce on its flower where its larvae (caterpillar) live in developing ovary and eat yucca seeds, while moth function as the pollinator.

This mutualism can also be seen in the acacia trees and acacia ants, these ants are specifically depends on the acacia tree for foods. They tend to protect the acacia tree from the herbivores which feed on it and also prune the seeds of any plants that found under acacia tree. This ants sting the animal that feed on acacia or scratch on it, and the ants benefit from the substance that the acacia produce as a food.

In conclusion, plants and organisms depend on each other in a process known as mutualism where all benefit. plant play a role in bring life on earth as the primary producer of factors that sustain life, while animals generate carbon dioxide that sustain plants and also increase the population of plants in the process of reproduction, organisms function as the pollinator.
All in all most of the species in the environment depend directly or indirectly to the other.

References:

1. Kazlev.A.M. 2002, Plants, (Land plants) [Internet] 2003 April 28 [cited 2006 May 08].Available from: http://www.palaeos.com/Plants/default.htm

2. Kohler, S. Plants, [Internet] 2006 May 8, 14:30. UTC [cited 2006 May 07]. Available from: http://www.blueplanetbiomes.org/plants.htm