KEY CONCEPT Plant life began in the water and became adapted to land.

Plant Evolution

Plant Evolution• Land plants evolved from

green algae (450 mya)– Both have same type of

chlorophyll, store energy as starch, DNA similarities

• Green algae ancestor– Multicellular body– Cells w/ channels to

communicate– Reproduce w/ sperm &

egg• Early plants– Low growth (nonvascular)

• True plants evolved through natural selection. – True plants have embryos that develop while attached to female

parent.– 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.

Land plants had to overcomemany challenges. We’ll takea look at the adaptations…

Land Adaptations

stoma

• Challenge = Retaining Moisture– Early plants grew near waters edge

• Adaptation:– Cuticle: Waxy coating– Stomata: Pores to allow gas exchange

Land Adaptations

• Challenge = Transporting Resources• Adaptaion:– Vascular system: tissue to transport nutrients

• Up from the roots (ex: water)• Down from the leaves (ex: sugars)

– Allows taller growth

water

glucose

Land Adaptations

• Challenge = Growing Upright• Adaptation:– Large plants need to support own weight– Lignin: hardens cell wall; gives wood strength

• Challenge = Reproduction on Land• Adaptation:– Pollen: Allow for reproduction without free-standing water.

• Can be carried by wind/animals.– Seeds: Hard coated storage device for a plant embryo.• Protects embryos from drying wind and sunlight.

– Embryo then develops when environment is favorable.

Land Adaptations

Plant Ecology• Mutualistic relationships– Type of symbiosis where

both organisms benefit– Ex: Plants (provides living

space)/Bacteria (create nutrients)

– Ex: Plants (provide food)/Insects (help pollinate)

• Herbivore interactions– Defense adaptations– Spines, thorns, chemicals

REview1) What traits do plants and plant-like protista (algae) share?2) Name 4 adaptations that plants have for life on land.3) Which plant adaptation allows them to carry nutrients to great

heights?4) Which plant adaptation allows them to retain moisture?5) What is the purpose of lignin?6) Explain a symbiotic relationship between plants and other

organisms?7) How do plants protect themselves from predators?