Day 65 Plants and Fungi

For almost the first 2 billion years of earths existence, land was lifeless.

Fossil evidence show that about 1.2 billion years ago cyanobacteria and protists existed on land

But it has only been within the last 500 million years (470 million) that plants and fungi crept onto land

By 385 million years ago land plant species that could grow tall enough to make forests finally appeared on earth.

There are very few plants in the ocean

-Most marine photosynthetic organisms are protists

-Like the algae (seaweeds, kelp, algae)

The move to land started with a type of algae that can live for short periods of time out of water called a Charophyte

-Some Charophytes live in shallow water. Whenever an organism lives in shallow water it faces the risk of drying out. If the water level evaporates the Charophyte will be faced with periods of drying. Due to natural selection the Charophytes that had adaptations to survive dry periods are the ones that survived.

-One of the Charophyte adaptations is called a sporopollenin. It is a durable polymer that prevents exposed zygotes from drying out.

-The adaptations of Charophytes is what led to land plants. The hardest obstetrical to overcome for organisms to move onto land was avoiding drying out. Even if the organism was able to avoid desication the zygotes would still dry out. It was not until zygote adaptations

List of adaptations in land plants

-Alternation of generations

-Walled spores produced in sporangia - The sporophyte stage of a plant life cycle has multicellular organs called sporangia that produce spores.

-Sporopollenin is a polymer that makes the walls of the spores resistant to dry environments

-Apical meristems - is a type of cell division that takes place at the root tips that allow the plant to grow and spread

-Cuticle- A waxy cuticle on the leaves of plants prevent the plant from drying out

-Stomata- help the plant with photosynthesis by allowing air in and out of the leaves

Types of Land Plants

The Bryophytes are the non-vascular land plants

-There are three clades of bryophytes

-Liverworts, mosses, and hornworts

-The earliest fossils of bryophites date back to 470 million years ago

-Bryophites do not have roots, instead they have rhizoids

-Rhizoids anchor bryophites to the ground but cannot absorb water like roots can

-Bryophites have a dominant gametophyte generation and need water to reproduce

-They do not have seeds but instead have sperm

The Ferns were the first vascular land plants allowing plants to grow tall

-Ferns still did not have seeds so they need to maintain a moist environment

-Ferns are the first land plants to move to a dominant sporophyte generation

-The gametophyte generation is small but independent

The seed plants evolved the adaptations to conquer land.

Plant groups by gametophyte or sporophyte generations

Once seeds evolved then plants could invade land without drying out.

-There are two types of seed plants

-Gymnosperms and Angiosperms

-Gymnosperm means naked sperm (have no ovum)

-Angiosperm means covered sperm (have an ovum)

Gymnosperms were probably first in their evolution. The gymnosperms are the pine trees known as conifers. Most of these trees and plants are evergreens

Angiosperms have flowers. The flower holds the eggs in an ovum. 95% of all plants and trees on earth are angiosperms.

There were millions of years on earth where giant ferns ruled and trees had not yet evolved. Once wood evolved trees began to take over. their strong trunks allowed them to grow higher into the light. There was no organism on earth that could digest wood. For 100 million years trees fell and piled up without being decomposed. This was the carboniferous period. This is where all of our oil comes from. Eventually through mutations fungi and bacteria became able to break down wood.