Question

5. d) Both plants and animals originated in aquatic environments, and eventually evolved to live on land. Describe a common challenge that both plants and animals faced in the move from an aquatic to a terrestrial environment, and new traits or modifications of traits that facilitated the evolution onto land. (10 points)

Answer 1

Q5) Desiccation or drying out is the common challenge faced by both plants and animals when they moved out of water, in aquatic system there was abundance of water but when they moved to land they faced shortage of water, both plants and animals faced the challenge to keep their body hydrated, besides this water used to help them in reproduction, in ample presence of water there was less chance of drying out of sperms and eggs or reproductive cells, water used to help them in the process of fertilization and movement of these reproductive cells.

To prevent from desiccation plants develop a waxy layer called cuticle which prevented water loss, also there is development of small pores on the surface of leaf which are called stomata, it helped them in the process of gaseous exchange and in preventing water loss. It helped in retaining water in the plant body depending on the weather condition, if climate is hot outside they used to remain closed to keep the water inside, but when the climate is colder they open up and allow gaseous exchange.

The development of vascular tissues in plants helped them in transporting water, nutrients and food material, they are of two types xylem and phloem, xylem used to help in conduction of water and nutrients from root to various parts of plant, phloem used to transport food from leaves to various plants parts. When they used to be in water vascular tissues were absent.

In plants embryos develops inside the female part after fertilization, but in case of algae or water plants they used to leave the embryo outside, on land they used to develop inside the plant body to prevent it from drying out.

Buoyancy of water used to give them support but on land they developed various structures like cell wall for support and help them to withstand the force of gravity. Plants on land developed various other structures like colored bracts etc. to attract insects and other sources for pollination. Pollination occurred by wind, insects, animals etc.

In case of animals to prevent desiccation they developed amniotic eggs, here egg developed an internal sac inside which it used to develop, this sac is used to prevent them from desiccation or drying out, the membrane allowed gaseous exchange but not water due to this the egg gets protection from drying out on land.

In case of arthropods there is development of exoskeleton, it is a bony external structure of the body which prevent water loss from body and help in supporting the body.

Land animals developed limbs which supported their body in withstanding the gravitational force and helped them in their movement because on land buoyancy of water is not there to support their body weight or in movement.

They developed kidneys which helped them in expelling waste material easily, excretory material is usually urea because it needs less water to expel it out, because water retention in body is the primary necessity of land animals.

Animals developed lungs instead of gills which they used to have in water, it helped them in gaseous exchange because air is abundant on land, and the pulmonary system help them in gaseous exchange. Also the circulatory system became more advanced based on the metabolic requirements of the body, gradually they developed from a two chambered heart as in case of fish to a four chambered heart in human beings with increasing metabolic activity of body. In land animals the lead less eye developed eye lid for protection from sunlight.

These are the various new traits or modification of traits developed in animals and plants to help them to adopt to the new environment that is from water to land.