Multicellular organization - Plants (Introduction)

Plants

-    multicelled, eukaryotic, photosynthetic autotrophs
-    life cycle of plants is characterized by alternation of generation
            o    gametophyte generation: cells of the plant body are haploid (n)
            o    sporophyte generation: cells of the plant body are diploid(2n)

Alternation of Generation

-    most live on land
-    300,000 species
-    Stabilize the soil they live in and provide a home for billions of insects and larger animals
-    Release O2 and absorb CO2
-    organized into two groups
          o    bryophytes
          o    tracheophytes

Bryophytes
-    non vascular plants ex. Mosses, liverworts and hornworts
-    primitive plants that lack transport vessel (xylem and phloem)
-    absorb H2O by diffusion from the air
-    flagellated sperm must swim through water to fertilize an egg.
-    Lack any lignin fortified tissue
-    Restricted to moist habitat and are tiny
-    Grow on rocks, soil and trees
-    Ex. Sphagnum or peat moss

Below are images of  different bryophytes

Below is an image of a moss sperm

Tracheophytes
-    have xylem and phloem for transport of nutrients
-    lignified transport vessels to support the plant
-    roots to absorb water while also anchoring and supporting the plant
-    leaves that increase the photosynthetic surface
-    life cycle with a dominant sporophyte generation
-    divided into two
            o    with seeds ex. gymnosperms and angiosperms
            o    without seeds ex. Ferns


Ferns
-    seedless plants
-    reproduce via spores instead of seeds
-    spores are homosporous that produce only one type of spore which then develops into a bisexual gametophyte.
-    Still restricted to moist habitats
-    Sperm is flagellated and must swim from male gametophyte (antheridium) to the female gametophyte (archegonium) to fertilize the egg.

Seed plants
-    heterosporous that produces two kinds of spores i.e megaspore and miscrospore
       o    megaspore – male gametophytes
       o    microspore – female gametophyte
-    sperm are not flagellated so do note require moist environment

homospory and heterospory

Gymnosperm
-    first seed plants to appear on earth
-    seeds are “naked” because they are not enclosed inside a fruit
-    seeds are exposed on modified leaves that form cones which are better adapted for a dry environment
-    other modifications include needle shaped leaves, thick, protective cuticle and relatively small surface area.
-    depend on wind pollination
-    Ex. Pines, firs, redwood, juniper and sequoia

Below is a picture of a naked pine seed

Below is an image of a Sequoia tree

Angiosperm
-    seed plants whose reproductive structures are flowers and fruits
-    most diverse plant specie including 90% of all plants
-    color and scent of a flower attracts animals that will carry pollen from one plant to another across distances
-    after pollination and fertilization the ovary becomes the fruit and the ovule becomes the seed.
-    The fruits protects the dormant seeds and aids their dispersal
-    There are two groups of angiosperms
         o    Monocots
         o    Dicots

 

Below are flowering plants