Kingdom Plantae
All plants are thought to have evolved from an
ancestor of plant-like protists over 400 million
years ago. Plant-like protists are also called
phytoplankton or algae. They are not
considered plants because:
• Algae are mostly unicellular
• May form colonies, but do not form tissues
• Do not develop from an embryo
Features which distinguish plants from protists
•
•
•
•
•
multicellular
photosynthetic
food storage molecule - amylose starch
structural polysaccharide - cellulose
life cycle - alternation of generations
– diploid sporophyte
– haploid gametophyte
• produce multicellular embryo protected in
multicellular haploid tissue which differs from
green algae.
Major adaptations of terrestrial plants
• the development of a waxy cuticle (to prevent water loss or dessication)
Major adaptations of terrestrial plants
• The development of microscopic pores called stomata (to allow gases such
as CO2 and O2 in and out through the cuticle)
Major adaptations of terrestrial plants
• differentiation of parts into
distinct tissues such as leaves and
stems (a feature of mosses and
vascular plants but to a much
lesser extent the liverworts and
hornworts)
Specialized Plant Tissues
Tissue System
and Its Functions
Dermal Tissue System
• protection
• prevention of water loss
Ground Tissue System
• photosynthesis
• food storage
• regeneration
• support
• protection
Vascular Tissue System
• transport of water/minerals
• transport of food
Component Tissues
Epidermis
Periderm
Parenchyma tissue
Collenchyma tissue
Sclerenchyma tissue
Xylem tissue
Phloem tissue
Location of Tissue
Systems
Major adaptations of terrestrial plants
• Development of vascular systems
(to efficiently transport water and
nutrients)
Leaf structure
•
Specialization of above and below ground tissues (e.g., the development of leaves for
efficient collection of sunlight energy or of roots specialized for nutrient transport as well
as support)
Root structure
•
Development of secondary growth (to allow the formation of thick structures as opposed
to simply long, thin ones which grow only at either end)
•
Development of
reproductive strategies
which did not depend on
the existence of standing
water (e.g., pollen, seeds,
flowers)
Major adaptations of terrestrial plants
•
Decrease in the conspicuousness of the gametophyte and an increase in the
conspicuousness of the sporophyte (i.e. alternation of generations)
Alternation of Generations
• Most plants display a life cycle that alternates
between haploid and diploid phases
• The haploid stage is generated by meiosis and is
called the gametophyte (gamete-producing plant)
• The diploid stage is generated by fertilization and
is called the sporophyte (spore-producing plant)
• A general pattern in plant evolution has been
from early plants which had a dominant haploid
stage to more recent plants which have a more
dominant diploid stage.