Question

List and describe in detail the 5 derived characters of land plants, and explain how they were useful adaptations for life on land.

It is believed that the coelacanths and lung fish represent a crucial link between other fish and tetrapods. What is the major feature in these fish that supports this hypothesis?

Answer 1

Land plants are multicellular organisms that can be distinguished from other living things by a number of characteristics.

The adaptations and characteristics of land plants include: 1) waxy cuticle, 2) stomata, 3) roots, 4) symbiotic association with mycorrhizal fungi and 5) alternations of generations.

1. Waxy cuticle: A waxy cuticle that covers the outer surface of the plant protects against radiation damage from UV light and prevents drying out through evaporation.
2. Stomata (singular: stoma): Stomata are minute pores which allow for exchange of gasses (such as oxygen and carbon dioxide) between the plant cells and the environment. Except liverwort stomata are present in all land plants.
3. Roots (or root-like structures): Roots anchor plants to the soil and serve as conduits for water absorption. All land plants have true roots except Bryophytes (mosses, liverworts and hornworts). Bryophytes have root-like structures called rhizoids that anchor them to their substrate but are not involved in water absorption.
4. Symbiotic association with mycorrhizal fungi: A symbiotic association is the relationship between two interacting organisms and an organism is benefited which will be mutualistic, commensalistic or parasitic. Symbiotic association with mycorhizal fungi are closely associated with approximately 80% of all land plant species and provide additional surface area for absorption of both water and nutrients from the soil. The fungi share these resources with the plant roots and the plant shares photosynthetic sugar products with the fungi.
5. Alternation of generations: All land plants reproduce via the alternation of generations life cycle, where both the haploid and the diploid stage of an organism are multicellular.  The haploid multicellular form, known as a gametophyte, is followed in the life cycle sequence by a multicellular diploid form  the sporophyte. which includes both a multicellular haploid stage and a multicellular diploid stage. Why is this an adaptation to life on land because it also occurs in some green algae, which are aquatic but share a common ancestor with all land plants.

It is believed that Coelacanths and lung fish represent a crucial link between other fish and tetrapods. The major feature in these fish that supports this hypothesis is "their fins have skeletal and muscular structures similar to amphibian limbs".