20.1 Origins of Plant Life - Clinton Public School District

20.1 Origins of Plant Life

Bell Ringer

• Read the info on p611, then answer the following questions.

• 1-Based on the question on page 611, what form do you think this domination takes?

• 2-What are some important plants in the US? • 3-What value do other plants have?


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


• Green algae is a photosynthetic eukaryote• It is a plant like protist• It has pigments that give various types of algae their

distinct colors

Land plants evolved from green algae.

20.1 Origins of Plant Life• 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


• Genetic analysis points to the common ancestor of all plants.– extinct green algae species in class Charophyceae– modern charophyceans common in freshwater habitats like lakes and ponds.


Question

• What evidence suggests that green algae are close relatives of land plants?


Bell Ringer

• Look at figure 20.2 on page 613. Answer the following questions:

• 1-What is the common ancestor of all plants?• 2-What is the first category of plants to evolve from

the ancestral line (in # 1)• 3-When did the flowering plant lineage diverge from

the cone-bearing plant lineage?


• 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


– Ancestral charophyceans lived in areas of shallow water.

– Those that could survive longer dry periods were favored.

– Like mosses they relied on droplets of water that brought sperm to eggs to produce the next generation.

– Also have a simple structure similar to that of moss, keeping low to the ground to retain moisture


-First true plants probably grew at edges of water.

-True plants have embryos that develop while attached to female parent.


• True plants evolved through natural selection.


• Challenges of living on land have selected for certain plant adaptations.

• Unlike land plants algae are constantly surrounded by water. – Needed for photosynthesis– Buoyancy supports weight – Allow reproduction and dispersal– Prevents from drying out


• A cuticle allows plants to retain moisture.– waxy, waterproof layer– holds moisture in

Plants have adaptations that allow them to live on land.


• Stomata are tiny holes in the cuticle.

stoma

– can open and close– allow air to move in and out

Without stomata movement of air would be prevented by the cuticle


• A vascular system allows resources to move to different parts of the plant.

sugars

water and mineral nutrients

– 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


• Lignin allows plants to grow upright.

– hardens cell walls of some vascular tissues– provides stiffness to stems – Allows plants to retain upright structure

plant cells

lignin


• Plant height is limited by the ability of a plant to support it’s own weight.


• Pollen and seeds are adaptations that allow seed plants to reproduce completely free of water.


• 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


• 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


Bell Ringer

• Some scientist think that certain species of green algae should be in the kingdom Plantae. What reasons might these scientist use to defend their position?

• Do you agree or disagree? Why?


• Plants have coevolved with other terrestrial organisms for millions of years

• Some of these relationships are cooperative while others have evolved between plants species and the animals that eat them.

Plants evolve with other organisms in their environment.

20.1 Origins of Plant Life• 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

- Ex: hawk mouth and orchid


• Plants have adaptations that prevent animals from eating them. – spines and thorns

– Ex: Roses, cactus


• Chemicals– Some insects use defensive chemicals produced by

plants to their advantage.- Ex: larvae of monarch butterflies feed exclusively on

milkweed species. Milkweed plants produce a chemical that makes monarch larvae, adults, and even eggs taste bad to potential predators.

Plants have adaptations that prevent animals from eating them.


Question

• What do pollen and seeds allow plants to do on land?


• What do stomata and cuticles allow plants to do?


• What does lignin help plants do?


• What does a vascular system allow plants to do?

20.1 Origins of Plant Life - Clinton Public School District

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