Download Unit 14 Plants Introduction and Evolution Notes

PLANT INTRODUCTION AND EVOLUTION
Mosses may be similar to some of the first plants that lived on land.
Probably evolved from green algae that lived in ancient swamps and oceans.
One of the challenges plants were faced with when they moved to land was the need for
water.
They evolved a variety of adaptations for obtaining and conserving water.
Roots of Giant Redwoods obtain water from deep underground reservoirs.
Waxy covering on the leaves of a Magnolia tree help retain moisture.
Individual Moss plants are usually no more than a few cm high.
Most of their parts are only one cell thick.
Giant Redwoods have circumferences up to 30m
Height of 90+ meters.
ADAPTING TO LIFE ON LAND
Plants provide: food, shelter, and oxygen
ORIGIN OF PLANTS
Plant = a multicellular eukaryote, with cells surrounded by cell walls made of cellulose
and with a waxy waterproof coating called a cuticle.
A billion years ago = no plants
Land was barren except for some algae at the edges of inland seas and oceans.
Shallow waters that covered much of Earth’s surface were teeming with bacteria, algae,
and other Protists.
Simple animals such as: corals, sponges, jellyfish, and worms.
Among these organisms were Green Algae
1st plants began to appear approx 500mya
May have looked like present day mosses.
Moss-like plants are pioneer species = convert rock to dirt
May have helped lead the way for other plants by being among the first soil builders.
No fossil record of 1st land plants
Tissues to delicate and decayed too easily
Earliest fossils = Psilophytes (still exist today)
All plants probably evolved from filamentous Green Algae
This algae dwelt in the ancient oceans.
Both have cell walls with cellulose
Both have same types of chlorophyll
Both store food in the form of starch
ADAPTATIONS OF PLANTS
Life on land has advantages as well as challenges
A filamentous Green Alga floating in a pond doesn’t need to conserve water.
The alga is completely immersed in a bath of water and dissolved nutrients.
It can absorb these directly into its cells.
For most land plants, the only available supply of water and minerals is in the soil.
Only the portion of the plant that penetrates the soil can absorb these nutrients.
Algae reproduces by releasing unprotected gametes into the water.
Fertilization and development take place here.
Gametes of most land plants are protected from drying out by a waterproof covering of
thick walled cells.
Land plants must also withstand the forces of wind and weather.
Must be able to grow upright against gravity.
Over the past 500 million years plants have developed a huge variety of adaptations that
reflect the challenges and advantages of living on land.
CUTICLE:
They have developed ways to prevent water loss.
Surface of apple, maple leaf, or stem of a houseplant = smooth and slightly slippery
Cuticle = a protective waxy layer that covers most fruits, leaves, and stems.
Waxes and oils are lipids = do not dissolve in water
Helps to prevent the water in plants tissue from evaporating
Stomata = openings in the cuticle of the leaf.
Allow exchange of gases.
Pores of stomata open during the day (photosynthesis)
Release water and oxygen
Take in the CO2 needed
During the night, these openings partly close down to prevent too much water loss.
Although the plant is coated with a waxy cuticle, plants lose up to 90% of the water they
contain through these openings in the epidermis (outer layer of cells).
LEAVES:
All the cells of a filamentous Green Alga carry out photosynthesis.
But in most land plants, the leaves are the only organs that do this.
Leaf = a broad, flat organ of a plant that traps sunlight energy for photosynthesis.
Also exchange gases through stomata
Leaves are supported by the stem and grow upward for sunlight.
They have both and upper and lower surface.
ROOTS:
Root = a plant organ that absorbs water and minerals from the soil, transports them to
the stem, and anchors the plant to the ground.
Plants depend on the soil as primary source for water and other nutrients.
Some roots (radish and sweet potato) also accumulate starch reserves and function as
organs of storage.
Mosses and their relatives have rhizoids rather than roots.
Usually only one cell thick and do not extend far into the soil.
STEM:
Water moves from the roots of a tree to its leaves.
Sugars produced in the leaves move to the roots.
Both occur through the stem.
A stem provides structural support for upright growth
Contains tissues for transporting food, water, and other materials from one part of the
plant to another.
May also serve as organs for food storage.
Green stems contain chlorophyll and takes part in photosynthesis.
Vascular Plants = plants that posses vascular tissues.
The stems of most plants contain vascular tissues made up of tubelike, elongated cells
through which water, food, and other materials are transported.
Most familiar plants = Pine and Maple tree, Ferns, Rhododendrons, Rye grass, Ivy and
Sunflowers, etc……
Nonvascular Plants = do not have vascular tissue
Mosses and several other small less familiar plants
Tissues are usually no more than a few cells thick.
Water and nutrients travel from cell to cell by osmosis and diffusion.
Evolution of vascular plants was a major importance in enabling plants to survive in so
many habitats.
Vascular plants can live further away from water.
Because vascular tissues include thickened cells called “fibers”.
Fibers = help support the upright growth
Can grow much larger than nonvascular.
REPRODUCTIVE STRATEGIES:
Adaptations include evolution of spores and seeds.
These structures protect the zygote or embryo
They also keep them from drying out before mature/ right conditions.
Seed = contains an embryo, along with a food supply and is covered by a protective coat.
Spore = consists only of a single haploid cell with a hard outer wall.
In spore-releasing plants (mosses and ferns) the sperm swim through a film of water to
reach the egg.
In seed-producing plants (conifers and flowering plants) sperm are able to reach the egg
without swimming through a film of water.
This difference explains why non-seed plants require moister habitats than most seeds
producers do.
ALTERNATIONS OF GENERATIONS
The lives of all plants consist of 2 alternating stages or generations.
1. Gamete Generation
- Responsible for the development of gametes
- All cells of the gametophyte, include the gametes are haploid (n)
2. Sporophyte Generation
- Responsible for the production of spores
-
All cells of sporophytes are diploid (2n)
Spores are produced by meiosis and are haploid (n)
All plant life cycles include the production of spores
In non-seed plants (ferns) the spores have hard outer coverings and are released directly
into the environment.
They will then grow into gametophytes.
In other plants (conifer, flowering) the spores are retained by the parent plant and develop
into gametophytes of only a few cells retained within the sporophytes.
Usually called seed producing plants.
Release the new sporophytes into the environment in the forms of seeds.
PHYLOGENY OF PLANTS
Many changes have taken place since the first plants became adapted to life on land.
Landmasses have moved from place to place (plate tectonics)
Climates have changed
Bodies of water have formed and disappeared.
100’s of thousands of plant species have evolved.
Countless numbers have became extinct as conditions have changed.
Plants have adaptations that enable them to survive in almost every type of environments
on Earth.
Taxonomist recognize 10 Divisions:
5 Non-Seed Plant Divisions:
Bryophyta = mosses and liverworts
Psilophyta = leafless stems
Lycophyta = Club mosses
Sphenophyta = Horsetails
Pterophyta = Ferns
5 Seed Producing Divisions:
Cycadophyta = Palmtree looking
Gnetophyta =
Ginkgophyta = Ginko biloba
Coniferophyta = Pine, Fir, Cypress, Redwood
Anthophyta = Flowering plants (larges/most diverse group)