Tobin and Dusheck: Asking About Life, 3E__________ Chapter 22 Copyright 2005 Brooks/Cole Thomson Learning Chapter 22 How Did Plants Adapt to Dry Land?

Copyright 2005—Brooks/Cole—Thomson Learning

Tobin and Dusheck: Asking About Life, 3E __________ Chapter 22

Chapter 22

How Did Plants Adapt to Dry

Land?



Key Questions• How did plants adapt to life on land?• How do bryophytes survive on land

without vascular tissues?• What are the advantages of a

vascular system?• How are seeds an adaptation to a

dry, terrestrial environment?• What roles do flowers and fruits play

in angiosperm reproduction?



What Is a Plant?

• Multicellular organism that performs photosynthesis and develops from an embryo

• Almost all live on land• Descendants of protists• Land invasion depended on

evolution of different structures



Land Adaptations• Waxy cuticle — reduces water

loss• Ability to absorb water from a

variety of sources• Enclosed reproductive organs,

called gametangia, in which gametes form

• Enclosed sporangia in which spores form



Identify Different Plant Types

• Identify as many different plants as you can. How are they different from one another?



Vascular vs. Nonvascular• Vascular or

tracheophytes• Have pipelike

tissues that conduct water

• Grow large• Examples: fir

trees, ferns

• Nonvascular or bryophytes

• Lack a vascular system

• Much smaller• Less diverse



The Divisions of Plants



Evolution of Plants



Plant Evolution• Evidence comes from fossils and

comparisons with living species• First plants evolved from a

common ancestor that resembled a green alga

• Vascular plants predate nonvascular plants

• First seedless plants — Carboniferous Period



Kingdom Plantae



Angiosperm Evolution

• Angiosperms — flowering plants• First fossils — about 125 million

years ago• Evolved from gymnosperms —

plants that have no fruits or flowers

• Many adaptations



Mosses, Liverworts and Hornworts

• Nonvascular Plants or bryophytes

• Depend on free standing water for photosynthesis and fertilization



Bryophyte Characteristics

• All parts of their bodies are adapted to absorb water

• This gives them a spongy feel• Exhibit alternation of generations

— a sexual life cycle in which haploid and diploid phases are both multicellular



Life Cycle of a Moss



Vascular Plants



Vascular Plants• Called tracheophytes• Have division of labor with separate

transport systems for water (xylem) and sugars (phloem)

• Diploid Phase dominates the life of the plant

• Seeds are protected by coat, and food is stored inside for germination



Seed-Lacking Tracheophytes

• 4 divisions that lack seeds:– Pterophytes (ferns)– Psilotophytes– Lycophytes– Equisetophytes



Life Cycle of a Fern



Life Cycle of a Fern

• A fern releases haploid spores• Spores mature into haploid

gametophytes• Gametophytes make sperm and

egg• Fusion of sperm and egg• Zygotes grow right out of the

gametophyte for a new fern



Lycophytes

• Have true roots, stems and simple leaves

• Also called lycopods

• Example: club mosses



Equisetophytes• Referred to as

horsetails• Have true roots,

stems and complex leaves

• Stems are jointed

• Outer cell walls are reinforced with silica



Reproduction in Seed Plants• Manage fertilization without water• Use a form of internal fertilization• Sperm and ovum fused, and

develop within the female gametophyte

• Seeds consist of a diploid zygote and a source of food encased in a seed coat



Gymnosperms

• Seed plants without flowers• Evergreen• Conifers produce male and

female gametophytes in cone-shaped strobili (the cones)

• Male and female cones on same tree



Life Cycle of a Pine



Cycads• Large-leafed

plants that look like palms

• No flowers or fruits

• Bear naked seeds

• Produce male and female strobili



Ginkgos• Either male or

female• Resemble

cycads in their life cycle

• Resemble conifers in their growth patterns



Uses of Flowers and Fruits

• Flowers ensure distribution of pollen through a variety of methods

• Fruits are mature ovaries that enclose and protect seeds

• Fruits usually enhance dispersal of seeds



Life Cycle of a Flowering Plant



Angiosperm Reproduction

• Flowers reproduce by means of double fertilization

• 2 sperm nuclei from the pollen grain fertilize 2 ova from the ovary

• A diploid zygote is formed and a triploid cell forms the endosperm



Flower Parts

• Stamen — anther and filament (male)

• Carpel — style and ovary (female)

• A corolla or petals and a calyx of sepals surround stamens and carpels

• Not all flowers have all parts



Key Concepts• A plant is a multicellular organism

that photosynthesizes and develops an embryo

• Nonvascular plants lack vascular tissues

• The vascular system enables plants to transport water and nutrients, to grow large, and to diversify

• Seeds allow plant to withstand dry environments

Documents

Tobin and Dusheck: Asking About Life, 3E__________ Chapter 22 Copyright 2005 Brooks/Cole Thomson Learning Chapter 22 How Did Plants Adapt to Dry Land?