Transcript 20.1 Origins of Plant Life

20.1 Origins of Plant Life
KEY CONCEPT
Plant life began in the water and became adapted to
land.
20.1 Origins of Plant Life
Land plants evolved from green algae.
• Plants and green algae have many common traits.
– both are photosynthetic eukaryotes
– both have the same types of chlorophyll
– both use starch as a storage product
– both have cell walls with cellulose
20.1 Origins of Plant Life
• Genetic analysis points to the common ancestor of all
plants.
– extinct green algae species in class Charophyceae
– modern charophyceans common in lakes and ponds
20.1 Origins of Plant Life
• Important plant characteristics likely originated in
charophyceans.
– multicellular body allowing for specialization of
cells and tissues
– cell division that allows for chemical communication
between cells
– reproduction involving sperm swimming to egg
20.1 Origins of Plant Life
• True plants evolved through natural selection.
– Ancestral charophyceans lived in areas of shallow
water.
– Those that could survive longer dry periods were
favored.
– First true plants probably grew at edges of water.
– True plants have embryos that develop while attached
to female parent.
20.1 Origins of Plant Life
• True plants evolved through natural selection.
20.1 Origins of Plant Life
Plants have adaptations that allow them to live on land.
• Challenges of living on land have selected for certain
plant adaptations.
• A cuticle allows plants to retain moisture.
– waxy, waterproof layer
– holds moisture in
20.1 Origins of Plant Life
• Stomata are tiny holes in the cuticle.
stoma
– can open and close
– allow air to move in and out
20.1 Origins of Plant Life
• A vascular system allows resources to move to different
parts of the plant.
– collection of specialized tissues
– brings water and mineral nutrients up from roots
– disperses sugars from the leaves
– allows plants to grow higher off the ground
water
and
mineral
nutrients
sugars
20.1 Origins of Plant Life
• Lignin allows plants to grow upright.
lignin
plant cells
– hardens cell walls of some vascular tissues
– provides stiffness to stems
20.1 Origins of Plant Life
• Pollen grains allow for reproduction without free-standing
water.
– pollen grains contain a cell
that divides to form sperm
– pollen can be carried by
wind or animals to female
structures
20.1 Origins of Plant Life
• A seed is a storage device for a plant embryo.
– seed coats protect
embryos from drying
wind and sunlight
– embryo develops
when environment is
favorable
20.1 Origins of Plant Life
Plants evolve with other organisms in their environment.
• Plants and other organisms can share a mutualistic
relationship.
– a mutualism is an interaction in which two species
benefit
– plant roots and certain fungi and bacteria
– flowering plants and their animal pollinators
20.1 Origins of Plant Life
• Plants have adaptations that prevent animals from eating
them.
– spines and thorns
– defensive chemicals