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plant adaptations for life on land

-early life on land was perfect for plants
-there was an abundance of sunlight and carbon dioxide
-there were very few pathogens and plant-eating animals
-certain key adaptions needed to take place in order for plants to be able to live on dry land
-these are key differences that seperate multicellular algae which are also, photosynthetic, multicellular, and eukaryotic from plants


key differences in between plants and algae include

-anchored but have no rigid tissues
-supported by the surrounding water
-the entire body of algae obtains minerals and CO2, directly from the water
-nearly the entire organisms has access to light and can photosynthesize
-flagellated sperm swim to the egg for fertilization to occur
-offspring are also dispersed by water
-surrounded by air and not water, must have a mechanism of maintaining water within cells
-must be able to obtain nutrients and resources from both soil and air
-must be able to support the body in a non-bouyant medium
-must have a mechanism to reproduce and disperse offspring without water


plant adaptions on land include

1. maintaining moisture:
2. obtaining resources from two very different environments
3. supporting plant body
4. reproduction and dispersal


two types of vascular tissue

1. xylem: functions to move water and minerals UP from the roots
-composed of dead and living cells
2. phloem: functions to move sugars both UP and DOWN the plant
-composed of only living cells


maintaining moisture

-the proportions of land plants that are above ground are covered with a waxy cuticle that functions to prevent water loss
-CO2 and O2 cannot diffuse across this cuticle so pores within the leaf called stromata function in gas exchange
-surrounding cells regulate the opening and closing of the stromata
-usually stromata are open during sunlight hours allowing gas exchange
-stromata are closed during darkness in order to prevent water loss


obtaining resources from two very different environments

-plants must obtain chemicals from both the soil and the air
-water and nutrients are typically found within the soil
-light and CO2 are found above ground
-roots, stems, and leaves help fulfill these varied requirements
1. roots
-provide anchorage
-absorb water and mineral nutrients from the soil
2. stems and leaves
-contain leaves which capture CO2 from the air and light from the sun
-enable photosynthesis
-apical meristems growth producing regions that are found near the tips of both roots and stems
-elongation and branching act to maximize exposure to resources found within the soil and air
-most but not all plants have vascular tissues
-vascular tissues are a network of thick walled cells that are joined into small tubes that extend throughout the plant body
-the few plant types which are avascular (lack transport system) are severely restricted in height (ex mosses)
-this is because they have very limited means to distribute water and minerals from the soil to the leaves


supporting the plant body

-plants must be able to hold themselves up against the force of gravity
-cell walls of some plant cells are thickened and reinforced by a chemical called ligin
-the absence of ligin containing cell walls in mosses and other avascular plants is another height limitation


reproduction and dispersal

-plants must be able to keep their gametes and developing embryos from drying out in the air
-much like the earliest land plants, mosses and ferns still produce gametes within male and female gametangia
-male gametes are released and swim to the female gametangium where the egg remains
-this requires water therefor mosses and ferns are only able to reproduce in moist environments
-pines and flowering plants have pollen grains
-pollen grains are structures that contain the sperm producing cells
-these are brought close to the egg by the wind and animals
-this does not require moisture
-all plants have fertilized egg (zygote) develop into an embryo while still attached to the parent plant
-the embryo is multi-cellular and dependent called an embryophyte
-this is a key difference between plants and algae
-all plant life cycles involve an alternating haploid and diploid lifecycles



structures made of protective jacket of cells surrounding the gamete producing cells


the haploid generation produces

eggs and sperm


the diploid generation produces

spores within a structure called a sporangium



-spores can develop into a new organism without fusing to another cell
-onlu mosses and ferns still rely on spores for dispersal
-pines and flowering plants use seeds to disperse their offspring



-are elaborate embryo containing structures that protect the embryo from elements and are dispersed by wind or animals
-plants that do not use seeds to disperse their offspring are referred to as seedless plants
-mosses and ferns are seedless plants


seedless, avacular plants were the first to arise and are collectively referred to as

-ex) mosses
-lack true roots and leaves
-they resemble all other plants because they have apical meristems and embryos that develop while attached to the parent plant
-because they dont have lignified cell walls they cannot grow very tall
-they are often found in spongy mats which retain water
-they may also be found growing in dense mats


vascular plants

-have lignified vascular tissues
-provide strong support allowing them to stand straight and grow tall on land
-two primary groups:
-seedless vascular plants
-seeded vascular plants


seedless vascular plants

-include the ferns
-these are well developed roots and stems
-common in forests but are most diverse in the tropics
-some can grow several meters tall
-they do not require moisture for reproduction much like the mosses
-they disperse their offspring as spores carried through the air


seeded vascular plants

-these account for more than 90% of all species of living plants
-seeds and pollen imporved the ability of plants to live within diverse habitats on land
-seeds contain an embryo and food supply contained within a protective coating
-package of survival
-facilities the dispersal of plant embryos over wide distances
-pollen brings sperm producing cells into close contact with egg-producing parts
-water is not necessary for fertilization
-pollen is able to travel large distances
-there are two main groups of seeded plants:
1. gymnosperms
2. angiosperms



-the earliest lineage of seeded plants
-gymno means naked and refers to the fact that seeds are not produced in specialized chambers
-the largest group of gymnosperms are the conifers
-consist mainly of cone bearing trees
ex) pine



-the most recent episode in plant evolution
-these are flowering plants
-angio means container and refers to the fact that the seed is produced within a specialized chamber
-flowers are complex reproductive structures that develop seeds within protective chambers


four key adaptions for life on land

1. dependent embryos are present in all plants
2. lignified vascular tissues mark a lineage that gave rise to most vascular plants
3. seeds are found on all gymnosperms and angiosperms
-these dominate the plant kingdom today
4. flowers are markers of the angiosperm lingeage


haploid and diploid generations alternate

-in contrast to humans which have diploid life cycle, plants have an alternating life cycle
-haploid and diploid stages are distinct
1. the gametophtye is the haploid generation of a plant and produces gametes
2. the sporophte is the diploid generation of the plant and produces spores


stages of the plant life cycle

1. haploid (n) gametophyte plants produce gametes (sperm and egg) by mitosis
2. fertilization produces a diploid (2n) zygote
3. the zygote divides by mitosis and develops into a multicellular diploid sporophyte plants
4. the sporophyte produces haploid spores by meiosis
5. spore then develops by mitosis into a multicellular, haploid gametophyte
* this life cycle appears to have evolved independently in plants