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Evolution of Plants
The Nitrogen Cycle
• Matter is recycled in the environment within and between ecosystems.
• All organisms require nitrogen to make amino acids, which are used to
build proteins and nucleic acids, which combine to form DNA and RNA.
The Nitrogen Cycle
• Although nitrogen gas is the most abundant form of nitrogen on Earth, only
certain types of bacteria that live in the soil and on the roots of legumes can
use this form directly.
• The bacteria convert nitrogen gas into ammonia, in a process known as
nitrogen fixation.
The Nitrogen Cycle
• Other soil bacteria convert fixed nitrogen into nitrates and nitrites
that plants can use to make proteins and nucleic acids.
• Heterotrophs eat the plants and reuse nitrogen to make their own
nitrogen-containing compounds.
The First Land Plants
• The greatest challenge that early land
plants faced was obtaining water.
• They met this challenge by growing
close to the ground in damp locations.
• Fossils suggest the first true plants
were still dependent on water to
complete their life cycles.
• One of the earliest fossil vascular
plants was Cooksonia, shown here.
The First Land Plants
• Several groups of plants evolved
from the first land plants.
• One group developed into
mosses (Bryophytes).
• Another lineage gave rise to
ferns, cone-bearing plants, and
flowering plants.
An Overview of the Plant Kingdom
• Botanists divide the plant kingdom into five major groups based on four
important features: embryo formation, specialized water-conducting
tissues, seeds, and flowers.
Vascular Plants
• Vascular tissue—xylem and
phloem—make it possible for
vascular plants to move fluids
through their bodies against the
force of gravity.
Vascular Plants
• Vascular plants are known as
tracheophytes, after a
specialized type of waterconducting cell they contain.
• These cells, called tracheids, are
hollow tubelike cells with thick
cell walls strengthened by lignin.
Lignin Trivia!
In 2007, lignin extracted from shrubby
willow was successfully used to produce
expanded polyurethane foam.[14]
Xylem
• Tracheids are found in xylem,
a tissue that carries water
upward from the roots to
every part of a plant.
• Xylem  water
Phloem
• Vascular plants also have a
second transport tissue
called phloem that
transports solutions of
nutrients and carbohydrates
produced by photosynthesis.
• Phloem  Food
Seedless Vascular Plants
• Examples: Club mosses,
horsetails, and ferns. Most
are ferns.
• Ferns can thrive in areas with
little light and are most
abundant in wet habitats.
• Need this habitat to
reproduce: animation
Short Answer #8
Explain two advantages
that vascular tissue gave
plants.
The Importance of Seeds
• Every seed contains a living
plant ready to sprout as soon
as it encounters the proper
conditions for growth.
• The production of seeds has
been one key to the ability of
plants to colonize even the
driest environments on land.
Seed Plants
• Do you eat plant embryos??
• A seed is a plant embryo and
a food supply, encased in a
protective covering.
Cones and Flowers
• In seed plants, the male
gametophytes (sex cells) and the
female gametophytes grow and
mature directly within the
sporophyte (adult plant cells).
• The gametophytes usually
develop in reproductive
structures known as cones or
flowers. And they can have both
male and female organs!
Cones and Flowers
• Nearly all gymnosperms
bear their seeds directly on
the scales of cones.
Cones and Flowers
• Flowering plants, or
angiosperms, bear their
seeds in flowers inside a
layer of tissue that protects
the seed.
Pollen
• In seed plants, the entire male
gametophyte is contained in a tiny
structure called a pollen grain.
• Pollen grains deliver sperm to the
female reproductive structure by
wind or animals such as insects.
• The transfer of pollen from the
male parts to the female parts is
called pollination.
Pollen
• Pollen in
gymnosperms
must be carried by
the wind.
Pollen
• Pollen in
angiosperms is
mostly carried by
insects and larger
animals.
Seeds
• After fertilization, the zygote
contained within a seed grows
into a tiny plant—the
sporophyte embryo.
• A tough seed coat surrounds
and protects the embryo and
keeps the contents of the seed
from drying out.
Seeds
• The embryo begins to grow
when conditions are right. It
does this by using nutrients
from the stored food supply
until it can carry out
photosynthesis on its own.
Which of the following includes a plant embryo,
a food supply, and a protective covering?
A) pollen grain
B) spore
C) seed
D) gametophyte
During pollination in seed plants, pollen
grains
A) swim to female reproductive structures through water.
B) must be carried from a male cone or flower to a female cone or
flower.
C) carry zygotes to the female structures, which form the seeds.
D) are carried to female reproductive structures by wind or animals.
The gametophytes of gymnosperms are found
inside reproductive structures called
A) flowers.
B) cones.
C) embryos.
D) ovules.
Angiosperms
• Angiosperms –
flowering plants
Flowers and Fruits
• Angiosperms develop unique reproductive organs known as flowers,
shown in the figure.
• Flowers contain ovaries, which surround and protect seeds.
Advantages of Flowers
• Flowers are an evolutionary
advantage to plants because
they attract animals that carry
pollen with them to the next
flower they visit.
• This means of pollination is
much more efficient than the
wind pollination of most
gymnosperms.
Fruit
• After pollination, the
ovary develops into a
fruit, a structure
containing one or more
matured ovaries.
Fruit
• When an animal eats a fleshy
fruit, seeds from the fruit
enter the animal’s digestive
system. By the time the
seeds leave the digestive
system, the animal may have
traveled many kilometers.
• By using fruit, flowering
plants increase the ranges
they inhabit.
Short Answer #7
Describe two advantages that
gymnosperms have over bryophytes
(nonvascular land plants) and two
advantages that angiosperms have over
gymnosperms.
Cotyledons
• Seed leaves in their
embryo
o Monocot – 1 seed leaf
o Dicot – 2 seed leaves
Angiosperm Classification
• Scientific classification places the monocots into a single group
but places the dicots in different categories.
Monocots and Dicots
• The characteristics of monocots and dicots are compared in
the table below.
Woody and Herbaceous Plants
• Woody plants are made
primarily of cells with thick
cell walls that support the
plant body.
• Herbaceous plants have
stems that are smooth and
nonwoody.
Annuals, Biennials and Perennials
Angiosperms produce seeds inside
protective structures called
A) pollen grains.
B) cones.
C) ovaries.
D) petals.
Flowering plants that grow, flower,
produce seeds, and die in one year
are called
A) annuals.
B) dicots.
C) perennials.
D) biennials.