When Chapter 29: Green Plants
--Green plants consist of green algae and land plants
--Before the evolution of land plants, only bacteria, archaea, and single-celled protists lived.
--Green algae, although traditionally considered protists, are studied with green plants bc (1) they are the closest
living relative to land plants (monophyletc group with them) (2) the transition from aquatic to terrestrial life
occurred when land plants evolved from green algae
--Land plants were the first organisms that could grow with their tissues exposed to air instead of being partially
submerged in water. (mutually beneficial relationships bw fungi and plants colonized land first) This enabled
multicellular organisms to occupy dry land.
Why do biologists study the Green Plants?
Plants provide ecosystem services—they alter the landscape in a beneficial way. (
all the organisms in a particular area and physical traits of atmosphere, precipitation, sunlight,
soil, nutrients etc.)
Plants produce oxygen
Photosynthesis removes electrons from water and reduces carbon dioxide and
makes sugars. Oxygen is a by-product. (oxygenic photosynthesis evolved in
cyanobacteria and made an oxygen-rich atmosphere)
Plants build soil
Plant parts are decomposed (worms, fungi, bacteria, archaea, protists, etc) and
these decomposers add organic matter to the soil.
Plants hold soil
Roots hold soil and its nutrients in place. (Wind and water erosion results in
Plants hold water
Plant tissues take up and hold water.
Forests, prairies, wetlands prevent rain from quickly running off a landscape bc:
leaves soften fall of rain, roots hold soil, plant organic matter builds the soil’s
(In contrast, deforested areas have streams that flood,
then dry up completely)
Plants moderate the local climate
Shade lowers temperature and increases relative humidity.
Reduce the impact of winds that dry and cool the landscape. (in contrast, when
plants are removed for people, habitats are dryer and have extreme temperature
Plants provide food!!
Plants are the key to the carbon cycle on land (just like bacteria/protists are the key for
ocean carbon cyces)
Plants fix more carbon dioxide than they produce. Deforestation results in higher
carbon levels, which results in global warming.
Plants provide humans with food, fuel, fiber, building material, and medicines
—actively select individuals with the largest and most nutritious plant
parts year after year for reproduction.
Wood and coal as fuel
Cotton and other fibers for clothes, towels, etc
Woody plants for lumber, papermaking. It is stronger than other materials
Drugs made from plants. Plants make these compounds to repel insects and animals.