Plant Life Cycles CHAPTER 30

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Plant Life CyclesCHAPTER 30
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Animals vs. Plants
Plant Reproduction Animal Reproduction
Life cycle Alternation of generations No alternation of generations
Gametes Haploid gametes Haploid gametes
Spores Haploid spores No spores
Gametes made by Haploid gametophyte, by mitosis Diploid organism, by meiosis
Spores made by Diploid sporophyte, by meiosis No spores
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Alternation of Generations

• Plants have a double life cycle with two distinct
  forms
• Sporophyte diploid, produce haploid spores by
  meiosis.
• Gametophyte haploid, produce gametes by mitosis.

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Non-flowering plants

• Mosses, ferns, and related plants have motile,
  swimming sperm.
• What kind of environmental conditions would be
  required for reproduction in these plants?
• What kinds of limits does external reproduction
  impose on these plants?

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Life cycle of mosses

• Follow the link and write down in your notes 1
  page on the life cycle of mosses
• http//www.microview.org.uk/millennium/pages/moss_
  lifecycle.htm

http//www.sumanasinc.com/webcontent/animations/co
ntent/moss.html
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Moss Life Cycle
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Life cycle of ferns

• Ferns, unlike some other plants, do not flower in
  order to propagate. Instead, they reproduce
  sexually from spores.
• The life cycle of a fern is very different
  from the life cycle of many other plants.
• While many plants grow a mature adult form
  straight out of the seed, ferns have an
  intermediate stage, called a gametophyte, which
  then grows into a mature fern.
• There are two distinct stages in the life cycle
  of ferns. The first stage is that of the
  gametophyte.
• Spores are produced on the underside of mature
  plants. These will germinate and grow into
  small, heart-shaped plants called gametophytes.
• The gametophytes produce both sperm and egg
  cells, and will fertilize itself, or others. Once
  the fertilization occurs, the adult fern will
  begin growing.
• The second stage in the life cycle of a fern
  is the adult stage. The fertilized gametophytes
  begin to look like a mossy growth.

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Conifers

• Conifers (also non-flowering plants) have reduced
  gametophytes.
• Male gametophyte is contained in a dry pollen
  grain.
• Female gametophyte is a few cells inside of the
  structures that become the seed.

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Conifer life cycle
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Conifer pollination

• Conifers are wind-pollinated plants.
• Chance allows some pollen to land on the scales
  of female cones.
• Pollen germinates, grows a pollen tube into the
  egg to allow sperm to fertilize the egg.
• What are some advantages and disadvantages to
  wind pollination?

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Flowering Plant Reproduction
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Angiosperms (flowering plants)

• Plants that protect their seeds within the body
  of a fruit.
• Make up ¾s of all plants, including
• Trees, shrubs, herbs,
• grasses, water plants

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Structure of a Flower

• 1. Pistil
• 2. Stigma
• 3. Style
• 4. Ovary
• 5. Stamen
• 6. Filament
• 7. Anther
• 8. Petal
• 9. Sepal
• 10. Receptacle
• 11. Stem

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Male Reproductive Structure

• The stamen consists of two parts Anther and
  Filament
• The anther is where meiosis occurs to produce
  haploid pollen
• The filament is a stalk that supports the anther

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Female Reproductive Structure

• The pistil consists of the stigma, style and
  ovary
• The sticky stigma receives the pollen from the
  anther
• The pollen grows a tube down through the style
• Meiosis occurs in the ovary to produce haploid
  ovules

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Reproductive Structures

• Petals colourful
• structures that attract pollinators.

• Sepals surround and protect the flower bud.

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Pollination

• Wind, insects or other animals transfer pollen
  from the anther of one flower to the stigma of
  another
• Flowers vary depending on pollination mechanism

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Pollination Animation
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Pollination Vectors
Wind Pollination Dull, scentless flowers with
reduced petals
Bees/Butterfly Pollination Bright color,
nectaries, scent. They sip nectar, get pollen
on coats, transfer pollen from flower to flower
Bird Pollination Nectaries, bright colors,
tube-like flowers
Moth Pollination White petals, open at night
Fly PollinationRank odor, flesh colored petals
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• Pollen Grain

• Anther Sac

Pollen grains contain two haploid cells produced
through meiosis. 1- The Tube cell will grow
the pollen tube. 2- The Generative cell will
go through mitosis to create two sperm cells.
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Ovary
Each ovule within an ovary has a micropyle (an
opening for the pollen tube). The ovules
megasporangium undergo meiosis to produce four
haploid cells (3 die leaving 1 megaspore) The
megaspore undergoes mitosis 3 times to produce 8
haploid cells within the embryo sac.
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Fertilization

• After pollen lands on the stigma, a pollen tube
  grows down through the style to ovary
• Generative cell creates the two sperm nuclei
• Double fertilization occurs
• one sperm fertilizes the egg
• one sperm the two polar nuclei together

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Result of Double Fertilization

• The sperm nucleus and egg nucleus join to form a
  2n (diploid) embryo
• The other sperm nucleus and the two polar nuclei
  join to form a 3n (triploid) endosperm. The
  endosperm is the food supply for the embryo.
• First link

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Seed and Fruit Development

• After fertilization, the petals and sepals fall
  off flower
• Ovary ripens into a fruit
• The ovule develops into a seed

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Seed Dispersal Mechanisms-Allow plants to
colonize new areas and avoid shade of parent plant
Wind Dispersal - Flight mechanisms, like
parachutes, wings, etc. Ex. Dandelion, maples,
birch
Animal Dispersal - Fleshy fruits which animals
eat, drop undigested seeds in feces or burrs
which stick to animals coats
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Gravity Dispersal - Heavy nuts fall to ground and
roll ex. acorns
Water Dispersal - Plants near water create
floating fruits ex. coconuts
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Plant ResponsesCHAPTER 31

• How plants move and communicate

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Plant Hormones
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Plant Hormones

• Plant hormones can be divided into two classes
• Growth promoters Auxins, Gibberellins,
  Cytokinins
• Growth inhibitors Ethylene gas, Abscisic acid

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Growth promoters

• Hormones can promote plant growth in two ways
• Stimulating cell division in meristems to produce
  new cells.
• Stimulating elongation in cells.

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Auxins
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Auxin activity
Auxins stimulate genes in cells associated with
plant growth.
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Auxin roles

• Auxins carry out multiple roles having to do with
  plant growth including
• Tropisms
• Apical dominance
• Growth of adventitious roots
• Fruit growth

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Tropisms

• Tropisms are the growth of a plant toward or away
  from a stimulus, including
• Phototropism in response to light
• Gravitropism in response to gravity
• Thigmotropism in response to touch

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Nastic Movements
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Nastic movement in the sensitive plant (Mimosa
pudica)
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Hinge control in Venus Fly Trap - Nastic movement
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How it works

• Nastic movements are rapid, reversible movements
  in a plant.
• Electrical potentials across cell membranes,
  similar to those in our nerve cells, signal plant
  cells at the base of the Mimosa leaf to rapidly
  lose water. This causes the leaf to droop.

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Movies

• Sensitive Plant http//www.youtube.com/watch?vBV
  U1YuDjwd8
• Venus Fly Trap http//www.youtube.com/watch?vktI
  GVtKdgwofeaturerelated

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Other examples

• Sunflowers follow the sun during the day.
• Leaves of many plants turn to follow the sun.

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Day/Night length

• Some plants flower in response to the length of
  periods of darkness.
• Spring-blooming flowers are long night (short
  day) plants, while summer-blooming flowers are
  short night (long day) plants.
• Some plants are day-neutral.

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Plant Communication

• Plants communicate chemically.
• Injured plants send out chemical signals that may
• signal other plants to prepare for an attack.
• attract other insects that eat the insects that
  are attacking the plant.

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