Plant Diversity – Part 2
Chapter 22, sections 4-5
Seed Plants
• When you picture a plant, you probably think
of it growing from a seed. However, seeds are
actually a relatively new innovation, which
has allowed plants to become as successful as
they have worldwide.
Seed Plants
Seed plants are divided into two groups:
•Gymnosperms - plants where seeds are found
relatively exposed, in cones
– Includes conifers such as pines and spruces, as well as
cycads, ginkoes, and gnetophytes
•Angiosperms - flowering plants, where the seeds
are covered by a layer of tissue, such as a fruit, to
protect them
– Includes grasses, flowering trees and shrubs, and all
flowers
Reproduction
• Seed plants do not require water for
fertilization to occur, which allows them to
live in a much broader range of habitats than
ferns and mosses can.
• The adaptations which allow fertilization to
occur without water include: flowers or
cones, the transfer of sperm by pollination,
and the protection of embryos in seeds.
Cones and Flowers
• The gametophytes of seed plants grow inside
reproductive structures of the sporophyte
generation.
Cones
• In gymnosperms
these structures are
cones, which are the
seed bearing
structures of these
plants.
Flowers
• In angiosperms, the gametophytes are found
in the reproductive structures - flowers.
Pollen
• In seed plants the entire male gametophyte is
found inside a tiny structure called a pollen
grain.
• The sperm of these plants do not need to
swim through water to fertilize the eggs.
– The entire pollen grain is carried to the female
reproductive structure by wind, water, insects, or
small animals – this is known as pollination.
Seeds
• A seed is the embryo of the plant, which is
encased in a protective coating and
surrounding by a food supply.
Seeds
• The embryo is a very early stage of
development of the diploid sporophyte. The
embryo stops growing while it is still very
small, and remains dormant in this condition
for weeks, months, or even years, only
germinating when conditions are right again.
Seed Banks
Food Supply
• The food supply in the seed provides food to the
embryo as it grows. When the seed germinates and
the embryo begins to grow again, it uses the
nutrients and energy from the stored food supply,
until it can produce it’s own food through
photosynthesis.
Seed Coat
• A seed coat surrounds and protects the
embryo and prevents it from drying out.
Seed Structures
• Some seeds also have special structures to
help it to be dispersed to new habitats. This
can include “wings” to help it blow in the
wind, textures or tiny hooks so the seed can
attach to the fur or feathers of animals, or the
seeds are contained in fleshy tissues (fruit) to
encourage animals to eat them and disperse
the seeds.
How Seeds Travel
Evolution of Seed Plants
• Mosses and ferns thrived and were diversifying,
300-400 million years ago. At this time many
habitats were much wetter than they are today.
• Over time the climate changed however,
becoming drier, making it harder for seedless
plants to survive and reproduce.
• Many species of mosses and ferns became
extinct, and were replaced by seed plants that
could live in drier conditions.
Evolution of Seed Plants
• The earliest seed plants resembled ferns – we
have fossils of these plants from 360 million
years ago.
Gymnosperms
• Gymnosperms all reproduce with seeds that are
exposed; the word gymnosperm means “naked
seed.” Current groups of gymnosperms include
conifers, cycads, ginkgoes, and gnetophytes.
Conifers
• Conifers are the most common gymnosperms,
with over 500 species alive today. This group
includes pines, spruces, firs, cedars, sequoias,
redwoods, junipers, and yews.
Conifers
• Some can live to be very
old (the bristlecone pine
can live for more than
4000 years), and some
can grow to be
extremely tall (redwoods
can grow to over 100m).
Cycads
• Cycads are unique palm-like plants, which use large
cones to reproduce. They first appeared in the
Triassic period (225 million years ago), and huge
forests of cycads were common during the age of
dinosaurs.
Cycads
• Today only 9 groups of cycads still exist, and
most are much smaller than those ancient
varieties.
• Cycads make good houseplants, and they are
found naturally in tropical and subtropical
locations such as Mexico, the West Indies,
Florida, and parts of Asia, Africa, and
Australia.
Ginkoes
• Ginkgo trees were also
very common during the
age of dinosaurs, but
there is only 1 species
left today: Ginkgo biloba.
Ginkgos may be some of
the oldest seed plants,
and they seem to have
changed very little over
time.
Ginkgoes
• Ginkgoes were often cultivated in ancient China,
where they were planted near temples. Today they
are commonly used as shade trees in urban areas in
the US and Canada, since they are quite resistant to
air pollution.
Gnetophytes
• Gnetophytes are fairly odd plants, which seem
to be the most closely related to angiosperms
of all the gymnosperm groups. There are
about 70 species of this group alive today,
though they were common in the Cretaceous
period (145 mya).
Gnetophytes
• One of the best-known gnetophytes is the plant
Welwitschia, which grows in the Namibian desert,
and has only 2 leaves which grow continuously
throughout its lifespan.
Ecology of Conifers
• Conifers thrive in a wide variety of habitats in
many biomes – from mountains and boreal
forests, in sandy soils, and in temperate
rainforests.
• Conifer leaves have special adaptations for dry
conditions. Scientists suggest that when
conifers were evolving 250 million years ago,
the climate conditions were dry and cool.
Adaptations for Dry Conditions
• To deal with these conditions, conifers evolved
long, thin leaves that we call needles.
– This shape reduces the surface area where water
can be lost through evaporation.
• There is also a thick, waxy coating on the
needles, to further reduce water loss.
• The openings (stomata) that allow for gas
exchange, are found in cavities below the
surface of the leaves.
Evergreens
• Most conifers are
“evergreens” – trees that
retain their leaves
throughout the year. The
needles stay on the tree for
2-14 years, and new ones
gradually replace older
needles, rather than turning
over all at once.
Exceptions
• Larches (tamaracks) and bald-cypresses are
exceptions – they lose their needles every fall.
Homework
• Textbook Reading
– Section 22-4 (pgs 564-568)
• Questions 1-3 (pg 568)
• Notebook Quiz on Chap 22 on Friday
• We’ll watch the video of the Guest Speaker on
Friday
Demonstration
• Osmosis - a process by which molecules of a
solvent (usually water) tend to pass through a
semipermeable membrane from a less concentrated
solution into a more concentrated one, thus
equalizing the concentrations on each side of the
membrane.
• Diffusion - the gradual intermingling of substances
by the natural movement of their particles.
Angiosperms
• Flowering plants first
appeared during the
Cretaceous period (135
million years ago), which
makes them the youngest
group of plants. They
quickly dominated Earth’s
plant life – flowering plants
are the vast majority of
living plant species.
Flowers
• Flowers are the unique reproductive organs
used by Angiosperms. Flowers give
angiosperms an advantage by attracting
animals such as bees, moths, hummingbirds,
or bats, who then transport pollen from
flower to flower. This type of pollination is
much more efficient than the wind pollination
used by gymnosperms.
Flowers
• Flowers contain ovaries, which surround and protect
seeds. This is what gives angiosperms their name –
angiosperm means “enclosed seed.” The ovary
develops into a fruit after pollination, protecting the
seed and helping with its dispersal.
Fruit
• A fruit is a wall of tissue
surrounding the seed, and it
is another reason
angiosperms have been so
successful.
• When an animal eats the
fruit, the seeds pass through
the digestive system
Fruit
• The seeds pass through the digestive tract
unharmed and are deposited far from the
original plant
– This helps to drastically increase the range of
flowering plants by spreading their seeds over
hundreds of square kilometers.
Diversity of Angiosperms
• Angiosperms are an incredibly diverse group
of plants. There are multiple ways to break up
all angiosperms into groups. It’s important to
remember that these different sets of
categories overlap each other (example: an
iris is a monocot, but also a herbaceous
perennial).
Monocots & Dicots
• The monocots and dicots are the two classes
within the angiosperms.
• They are named for the number of seed
leaves in the plant embryo
– Monocots have 1 cotyledon, dicots have 2
cotyledons
Monocots & Dicots
• There are several other differences between
these two groups:
• Vein arrangement in leaves
– Monocots have parallel veins
– Dicots have branched veins
Monocots & Dicots
• Flower parts
– Monocots have multiples of 3
– Dicots have multiples of 4 or 5
Monocots & Dicots
• Arrangement of vascular bundles in stems
– Monocots – scattered throughout stem
– Dicots – bundles in a ring
Monocots & Dicots
• Root-types
– Monocots have fibrous roots
– Dicots have a taproot
Monocots vs Dicots
Monocots & Dicots
• Examples:
– Monocots: corn, wheat, lilies, orchids, palms
– Dicots: roses, clover, tomatoes, oaks, and daisies
Woody & Herbaceous
• Another way to divide up angiosperms is by
the characteristics of their stems – whether
they are woody or not. Woody plants have
cells with thick cell walls to support the plant
body.
• Woody plants include shrubs, trees, and vines.
Woody
• Shrubs are smaller
than trees and have
multiple stems coming
up form the roots, in
contrast to one main
stem (trunk) as in a
tree.
– Examples: blueberries,
roses, and hawthorn
Woody
• Vines have long, flexible stems.
– Examples: grapes and ivy
Herbaceous
• Herbaceous plants have
stems that are smooth
and non-woody, and
these plants are generally
much smaller than woody
plants.
– Examples: dandelions,
petunias, and sunflowers
Annuals, Biennials, & Perennials
• Some plants grow, flower, and die in a single
year. Other types of plants will regrow the
next spring.
• Plants can be categorized by their life spans
into three groups – annuals, biennials, and
perennials.
Annuals
• Annuals - flowering plants which grow from
seed to maturity, flower, produce seeds, and
die, all in one growing season
– Examples: marigolds, petunias, pansies, wheat,
cucumbers
Biennials
• Biennials – flowering plants that complete
their life cycle in two years.
• The first year they germinate and grow roots,
short stems, and sometimes leaves.
• In the second year they grow new stems,
leaves, then flowers and seeds. Once the
flowers produce seeds, the plant dies.
– Examples: evening primrose, parsley, celery,
foxglove
Perennials
• Perennials – any flowering plant that lives for
more than two years.
• Most perennials live many years.
• Some perennials are herbaceous (peonies,
asparagus, and many grasses), but most
perennials are woody plants, such as palm
trees, sagebrush, maple trees, and
honeysuckle.
Demonstration
• Osmosis - a process by which molecules of a
solvent (usually water) tend to pass through a
semipermeable membrane from a less concentrated
solution into a more concentrated one, thus
equalizing the concentrations on each side of the
membrane.
• Diffusion - the gradual intermingling of substances
by the natural movement of their particles.
Homework
• Read Section 22-5 (pgs 569-572)
– Questions 1-3
• Lots of Article Analyses are still missing!
• Notebook Quiz tomorrow
– This whole chapter
Great Summary Video
• https://www.youtube.com/watch?v=X4L3r_XJ
W0I (8 min)
Crash Course: Vascular Plants
• https://www.youtube.com/watch?v=h9oDTM
XM7M8&noredirect=1 (12 min)
Notebook Quiz
• 15 min (timed)
• Open book to your notes/logbook
– No textbooks or photocopies of textbooks
• Remember your name!
• Put in the yellow folder when finished
• When done – do something SILENTLY!
Guest Speaker Videos
• Sub – please see folder of videos on the USB
key