What is a Plant

1
What is a Plant?

• Plants are multicellular eukaryotes that have
  cell walls made of cellulose.
• They develop from multicellular embryos and carry
  out photosynthesis using the green pigments
  chlorophyll a and b
• Plants are so different from animals that
  sometimes there is a tendency to think of them as
  not being alive
• However, plants are alive, everywhere, and highly
  successful

2
The Plant Life Cycle

• Plants have life cycles that are characterized by
  alternation of generations
• In this life cycle, the haploid gametophyte phase
  alternates with the diploid sporophyte phase
• A gametophyte is a haploid, or gamete-producing,
  phase of an organism
• A sporophyte is a diploid, or spore-producing,
  phase of an organism

3
Alternation of Generations Life Cycle
4
What Plants Need to Survive

• The lives of plants revolve around the need for
• Sunlight
• Water minerals
• Gas exchange
• Movement of water nutrients throughout the
  plant body

5
Early Plants

• The first plants evolved from an organism much
  like the multicellular green algae living today
• However, the evolution of plants favored species
  that were more resistant to the drying rays of
  the sun

6
Overview of the Plant Kingdom

• The great majority of plants alive today are
  angiosperms (the flowering plants)

Cone-bearing plants760 species
Ferns andtheir relatives11,000 species
Floweringplants235,000 species
Mosses andtheir relatives15,600 species
7
The Nonvascular Plants - Bryophytes

• Mosses and their relatives are generally called
  Bryophytes (nonvascular plants)
• THEY HAVE NO ROOTS, STEMS, OR LEAVES
• They have a life cycle that depends on water for
  reproduction
• They lack vascular tissue and therefore must grow
  low to the ground
• Groups of Bryophytes include
• Mosses
• Liverworts
• Hornworts

8
Mosses

• The most common bryophytes are mosses
• They grow abundantly in areas with water
• They can tolerate cold climates well
• They do not have true roots, stems, or leaves
  instead, they have rhizoids (long, thin cells)
  that anchor them to the ground

9
Liverworts

• Liverworts are Bryophytes that produce gametes in
  structures that look like little green umbrellas
  during sexual reproduction
• Liverworts can also reproduce asexually by means
  of gemmae (small cup-like spheres that contain
  haploid cells)

SEXUAL
ASEXUAL
10
Hornworts

• Hornworts are generally found only in soil that
  is damp nearly year round
• Their gametophytes look like those of liverworts

11
Evolution of Vascular Tissue

• What happened to allow plants to grow taller than
  mosses?
• Fossil evidence shows that these plants contained
  vascular tissue tissue that is specialized to
  conduct water and nutrients through the body of a
  plant

12
Vascular Tissue

• The first vascular plants had a new type of cell
  that was specialized to conduct water
• Tracheids are the cells found in xylem, a form of
  tissue that carries water upward from the roots
  to every part of a plant
• Phloem transports solutions of nutrients and
  carbohydrates produced by photosynthesis
• Lignin is a substance produced by plants that
  makes cell walls rigid
• Both forms of vascular tissue, xylem and phloem,
  can move fluids throughout the plant body against
  the force of gravity

13
Seedless Vascular Plants

• Seedless vascular plants include
• club mosses
• horsetails
• ferns
• These plants HAVE true roots, leaves, and stems
• ROOTS underground organs that absorb water
  minerals
• LEAVES photosynthetic organs
• STEMS supporting structures that connect roots
  and leaves

14
Club Mosses

• These are small plants that live in moist
  woodlands and near streambeds and marshes
• Lycopodium is the most common club moss today
  it looks like a mini pine tree

15
Horsetails

• The only living genus of horsetails is Equisetum
• Its leaves are arranged in distinctive whorls at
  joints along the stem

16
Ferns

• Ferns are members of the phylum Pterophyta
• They have creeping or underground stems called
  rhizomes and large leaves called fronds
• They are most abundant in wet habitats

frond
rhizome
roots
17
Life Cycle of Ferns
18
Seed Plants

• Over millions of years, plants with the ability
  to forms seeds became the most dominant group of
  photosynthetic organisms on land
• Seed plants are divided into 2 groups
• Gymnosperms bear seed directly on cones
• Conifers
• Cycads
• Ginkos
• Gnetophytes
• Angiosperms flowering plants that bear their
  seeds within a layer of tissue that protects the
  seed
• Grasses
• Flowering trees and shrubs
• All flowers

19
Reproduction Free From Water

• Adaptations that allow seed plants to reproduce
  without water include
• flowers or cones
• the transfer of sperm by pollination
• the protection of embryos in seeds

20
Cones Flowers

• The gametophytes of seed plants grow and mature
  within sporophyte structures called cones or
  flowers
• Cones are the seed-bearing structures of
  gymnosperms
• Flowers are the seed-bearing structures of
  angiosperms

21
Pollen

• In seed plants, the entire male gametophyte is
  contained in a tiny structure called a pollen
  grain
• The pollen grain is carried to the female
  gametophyte by wind, insects, birds, small
  animals, or bats
• The transfer of pollen from the male gametophyte
  to the female gametophyte is called pollination

22
Seeds

• A seed is an embryo of a plant that is encased in
  a protective covering and surrounded by a food
  supply
• An embryo is the early developmental stage of the
  sporophyte plant
• The seed coat surrounds and protects the embryo
  and keeps the contents of the seed from drying
  out
• After fertilization, the zygote contained within
  a seed grows into a tiny plant the embryo

23
Seeds
24
Gymnosperms Cone Bearers

• Gymnosperms include
• Gnetophytes
• Cycads
• Ginkoes
• Conifers

25
Gnetophytes

• Welwitschia, an inhabitant of the Namibian desert
  in southwestern Africa, is one of the most
  remarkable gnetophytes
• it has 2 huge leathery leaves which can grow
  continuously and spread across the ground

26
Cycads

• Cycads are members of the phylum Cycadophyta
• They are palm-like plants that reproduce with
  large cones
• They can be found in all tropical and subtropical
  zones around the world

27
Ginkgoes

• Today, the phylum Ginkgophyta contains only one
  living species, Ginkgo biloba (the maiden-hair
  tree)

• Cultivated and protected in China by monks
• the male species of this tree is often planted in
  urban settings in the US, where their resistance
  to air pollution make them popular shade trees
• The female tree smells like vomit

28
Conifers

• Conifers are by far the most common gymnosperms
• The phylum Coniferophyta includes
• Pines
• Spruces
• Firs
• Cedars
• Sequoias
• Redwoods
• Yews

29
Conifers

• Conifers thrive in a wide variety of habitats
• Mountains, sandy soil, cool, moist areas
• Conifers have leaves that are long and thin
  which reduces the surface area from which water
  can be lost by evaporation
• They also have a thick, waxy layer that covers
  their leaves again to reduce water loss
• Most conifers are evergreens meaning they
  retain their leaves year round

30
Angiosperms Flowering Plants

• Angiosperm means enclosed seed
• Angiosperms have unique reproductive organs known
  as flowers
• Flowers attract pollinators, which makes
  spreading seeds more efficient than the wind
  pollination of most gymnosperms
• Flowers contain ovaries, which surround and
  protect the seeds
• After pollination, the ovary develops into a
  fruit, which protects the seed and aids dispersal
• Fruit is a thick wall of tissue and another
  reason why angiosperms are successful the fruit
  attacts herbivores which eat the fruit and then
  spread the seeds

31
Diversity of Angiosperms

• Angiosperms are an incredibly diverse group that
  includes
• Monocots and dicots
• Woody and herbaceous plants
• Annuals, biennials, and perennials

32
Monocots and Dicots

• Monocots and dicots are named for the number of
  seed leaves, or cotyledons, in the plant embryo
• Monocots have one seed leaf and dicots have two

33
Characteristics of Monocots Dicots
34
Woody Herbaceous Plants

• Flowering plants can be subdivided into various
  groups according to the characteristics of their
  stems
• Woody plants are made primarily of cells with
  thick walls that support the plant body
• Trees
• Shrubs
• Vines
• Herbaceous plants do not produce wood as they
  grow, but rather they have stems that are smooth
• Dandelions
• Zinnias
• petunias

35
Annuals, Bennials, Perennials

• There are 3 categories of plant life spans
• Annual flowering plants that complete a life
  cycle within one growing season
• Marigolds, pansies, zinnias, cucumbers
• Biennial flowering plants that complete their
  life cycle in 2 years
• Primrose, parsley, celery
• Perennial flowering plants that live for more
  than 2 years
• Peonies, asparagus, grasses