the plant kingdom evolution from water to land. primitive plants were “aquatic” – lived in...
TRANSCRIPT
The Plant Kingdom
Evolution from Water to Land
Primitive Plants Were “aquatic” – lived in water
If salt water, we use the term “marine” It is believed that land plants evolved from
simple, algae-like, aquatic plants. We think plants and algae are closely related because they both: Have the same kind of chlorophyll Store their food as starch Have cellulose in their cell walls
WHY did ancestral plants live in the water? Prevents them from drying out They don’t need roots to soak up water Reproductive gametes can easily swim
from male to female sex organs No need for strong structures
to hold them up… buoyancy
of water supports them
Characteristics of Plants multicellular photosynthetic adapted for living
primarily on land non-motile (motile
means capable of motion)
Cell walls composed of cellulose
Have chloroplasts with chloropyll
Food
stored as
starch
Alternation of Generations All plants show ALTERNATION OF
GENERATIONS in their life cycles 2 stages:
Sporophyte stage (diploid cells) Gametophyte stage (results from meiosis and
produces haploid gametes)
In trees, the part we see is the sporophyte. The gametophyte is very small and internal.
How are plants classified? There are 300 000 – 500 000 classified
plants on earth. They are divided into 2 groups, according to adaptations for life on land: Non vascular plants (mosses, liverworts and
hornworts) smaller, and dependent on moist conditions to live
Vascular plants (trees, shrubs, grasses) live on the land
Non Vascular Plants Mosses need water for
reproduction – male gamete swims to female gamete through water
Do not have true roots, stems or leaves, but have structures similar to vascular plants
Stay small in size because diffusion is how they get their water and nutrients – every cell must be near water source.
See this site for a picture.
Moss
Moss Life Cycle
Life Cycle of Moss gametophyte stage – consists of cells that are haploid (n).
some gametophyte cells produce eggs; others produce sperm. In a moist environment water carries the sperm to the
eggs. Fertilization diploid (2n) zygote grows into a
structure called a sporophyte and remains on the female gametophyte
sporophyte generation is diploid and produces haploid spores through meiosis
haploid spores land on moist ground -- grow into a gametophyte
Vascular Plants These include all land plants
Gymnosperms (cone-bearing plants) Angiosperms (flowering plants)
In the vascular plants, the sporophyte is the dominant generation
The gametophyte is found inside the seeds of the plant.
Angiosperms &
Gymnosperms
have highly
specialized
reproductive
structures,
producing the
embryo (the gam-
etophyte)
protected inside
seeds….
These seeds are fertilized inside the female parts of a flower…
Advanced water and nutrient carrying tissues, XYLEM & PHLOEM:
Cross section Longitudinal section
Specialized
Leaves
Specialized Leaves: Conifer needle cross section
Openings called stomata reduce water loss while allowing for gas exchange….
Summary of Plant Adaptations for Life on Land: Roots allow for water absorption from deep
in the soil when rainfall is scarce Protective mechanisms prevent water loss
– cuticle (waxy coating) on leaves, shape of leaves (ie. Needles)
Strong stems and structures to hold the plant up against gravity--necessary without the buoyancy of water to hold the plant up.
Summary continued… Stomata, pores in the leaves, allow for gases
to enter or exit the interior of the leaf (plants use CO2 and give off O2)
Water is “sucked up” in xylem tubes, and nutrients are transported in phloem tubes to parts of the plant that don’t photosynthesize, so the need for small plant bodies for the sake of diffusion is reduced
Summary continued… Thickened cell walls for rigid support Extreme fluctuations in temperature,
humidity, sunlight and wind require adaptations as well. Cacti, evergreen trees, prairie grasses and shrubs all have adapted by means of water storage tissues, modified leaves to reduce water loss, etc.
The End