Download Gymnosperms evolved seeds as a way to protect their young

Gymnosperms evolved seeds as a way
to protect their young
After mosses and ferns, the next group of plants to
evolve was the gymnosperms [JIM-nuh-sperms] . This
group includes pine trees and other conifers (conebearing plants ; see Figure 3 .8), as well as cycads and
ginkgos.
Gymnosperms were the first plants to evolve seeds,
structures in which plant embryos are encased in a protective covering and provided with a stored supply of
nutrients (Figure 3 .10) . Gymnosperms (gymno, "naked";
sperm, "seed") have seeds that are relatively unprotected compared with those of angiosperms, the next
major group of plants to arise . Gymnosperms were the
dominant plants 250 million years ago, and the evolution of seeds was probably an important part of their
success . Seeds provided nutrients that plant embryos
could use to grow before they were able to produce
their own food via photosynthesis . Seeds also provided
embryos with protection from drying or rotting and
from attack by predators.
Angiosperms produced the world's first flowers
Although typically we think of flowers when we think of
plants, flowering plants are a relatively recent development in the history of life . Today the flowering plants, or
angiosperms [Awjee-oh-sperms], are the most dominant
Light-gathering leaves
are the main site of
photosynthesis . Leaves
absorb carbon dioxide
through tiny openings.
A waxy covering
(cuticle) on leaves
and stems prevents
unnecessary
water loss by
evaporation .
Most plants possess vascular
tissues . The vascular system
transports water and minerals
throughout the plant and adds
to its sturdiness.
Flowers are the structures
in which reproduction takes
place and in which fruits
are produced.
Fruits contain the
young of the next
generation, the seeds . j
The stem provides
support and extends the
plant toward the sun.
Roots anchor plants
to the ground and
allow them to absorb
water and critical
nutrients from the soil.
and diverse group of plants on the planet, including
orchids, grasses, corn plants, and apple and maple trees.
Angiosperms produce seeds that are well protected (angio
means "vessel," referring to the tissues that encase the
plant's embryo).
Highly diverse in size and shape, angiosperms live
in a wide range of habitats—from mountaintops to
deserts to salty marshes and fresh water. Almost any
plant we can think of that is not a moss, a fern, or a
cone-producing tree is an angiosperm . The key to the
Figure 3 .9 The Basic Structures of a Plant
Shown here is a familiar garden vegetable, a pepper plant . Because it
is a member of the angiosperms, the last of the major plant groups to
evolve, all the evolutionary innovations that distinguish plants can be
shown on this one plant.
success of angiosperms, and their defining feature, is
the flower . Flowers are specialized structures for sexual
reproduction, or pollination, where the male and the
female gametes meet (Figure 3 .11).
Some flowers provide food, such as the sugary liquid
known as nectar, to attract animals to visit them and in
the process transport pollen (male gametes) from flower
to flower. The transported pollen can fertilize another
flower's ovules (structures containing female gametes).
Thus animals can provide a means of sexual reproduction between even very distant plants . Plants also use
wind to disperse their pollen from flower to flower.
People with hay fever are reacting to this method of
plant sex, which sends nose-irritating pollen blowing
through the air.
In addition to increasing the efficiency of fertilization
through flowers, angiosperms have evolved a variety of
ways to distribute their seeds to distant places in order
to get their young off to a good start . One of these is the
use of tasty fruits that attract animals . As the embryos
of some angiosperms are developing, the surrounding
ovary develops into a ripening fruit (see Figure 3 .11).
Animals eat the fruit and later excrete the seeds in their
feces . These nutrient-rich wastes provide a good place for
the seeds to begin life, often far from their parent plant
where they will not compete with that parent for water,
Chapter 3 Major Groups of Living Organisms
3.5
Figure 3 .12 Getting Around
Plants have evolved many ways of spreading to new areas. (a) A palm
tree seed in a coconut can float for hundreds of miles until it reaches
a new beach where it can take root and grow . (b) Some seeds have
wings (for example, maple "keys") or other structures (such as
dandelion fluff, shown here) that allow them to be carried by the
wind, sometimes over great distances .
nutrients, or light . But hitching a ride in an animal's gut
is not the only means plants have for overcoming their
immobility ; plant seeds have evolved many other ways to
travel (Figure 3 .12).
Plants are the basis of land ecosystems
and provide many valuable products
It is difficult to overstate the significance of plants . As
photosynthesizing organisms, plants use sunlight and
carbon dioxide to make sugars, food that they and the
organisms that eat them can use. Nearly all organisms
on land ultimately depend on plants for food, either
directly by eating plants or indirectly by eating other
organisms (such as animals) that eat plants or that eat
other organisms that eat plants, and so on . Many organisms live on or in plants, or on or in soils largely made up
of decomposed plants.
Flowering plants provide humans with materials such
as cotton for clothing and with pharmaceuticals such as
morphine. Essentially all agricultural crops are flowering plants, and the entire floral industry rests on the
reproductive structures of angiosperms . Gymnosperms
such as pines, spruces, and firs are the basis of forestry
industries, providing wood and paper.
As valuable as plants are when harvested, they are
also valuable when left in nature . By soaking up rainwater in their roots and other tissues, for example, plants
prevent runoff and erosion that can contaminate streams.
Plants also produce the crucial gas oxygen.
The Fungi : A World
of Decomposers
Most people are familiar with fungi as the
'BACTERIA' 'ARCHAEA)
mushrooms sliced on their pizza or sprouting from their lawns . However, the Fungi,
a kingdom within the domain Eukarya,
also includes yeasts (single-celled fungi)
and molds . In fact, the familiar mushroom
is just a small part of a fungus. Most fungal
'BACTERIA' (ARCHAEA)
EUKARYA
PROTISTA
(PLANTAE
FUNGI
tissues typically are woven through whatc2
ever substance—often the tissues of
another organism—the fungus is digesting and making its living from . Because fungal tissues
are largely hidden from view, fungi are among the most
poorly understood of the major groups of organisms.
Fungi can be costly to human society. They can cause
diseases, contaminate crops, rot food, and force us to
clean our bathrooms more often than we might like. Other
fungi are beneficial, providing us with pharmaceuticals,
including antibiotics such as penicillin . Yeasts such as
Saccharomyces cerevisiae [sAK-ah-roh-MICE-eez Bair-uhVEE-see-eye] can feed on sugars and produce two important products : alcohol and the gas carbon dioxide, both
crucial to the rising of bread and the brewing of beer.
Fungi also provide highly sought-after delicacies such as
truffles, whose underground growing locations can be
found only by specially trained dogs or pigs.
As Figure 3 .13 shows, the fungi are divided into three
distinct groups : zygomycetes, which evolved first,
ascomycetes, and basidiomycetes . Each group differs in—
and is named for—its unique reproductive structures.
Fungi play several roles in terrestrial ecosystems.
Many fungi are decomposers . Playing the role of garbage
processor and recycler, these fungi speed the return of
the nutrients in dead and dying organisms to the ecosystem. Some fungi are parasites (organisms that live in or
on other organisms and harm them), while others are
mutualists (organisms that benefit from, and provide
benefits to, the organisms they associate with) . Sometimes
the benefits and harms in these associations involve nutrition, sometimes not . Do not confuse these terms, however, with the categories of decomposer, consumer, and
producer, even though they describe how organisms get
their nutrition . Mutualist and parasite are a separate,
unrelated pair of words to describe whether organisms
are good or bad for the organisms they associate with.
For example, consumers can be mutualists or parasites;
likewise, mutualists can be consumers, producers, or
decomposers .
Chapter 3 Major Groups of Living Organism
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In humans, fungi can cause mild diseases such as athlete's foot . Fungal diseases can also be deadly, like the
pneumonia caused by the fungus Pneumocystis carinii
[woo-moh-szss-tiss kuh-REE-nee], the leading killer of
people suffering from AIDS . Fungi attack plants, too.
Ceratocystis ulmi [BARE-uh-toh-srss-tiss ooL-mee] causes
Dutch elm disease, which has nearly eliminated the elm
trees that once formed arching canopies over streets all
across the United States. Rusts and smuts are fungi that
attack crops . Still other fungi are specialized for eating
insects, and biologists are trying to use these fungi to kill
off insects that are crop pests (Figure 3.16).
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Some fungi live in beneficial associations with
other species
Some fungi are mutualists, living in association with
other organisms to their mutual benefit . One broad
group of mutualists—found in all three groups of fungi
(zygomycetes, ascomycetes, and basidiomycetes)—is
known as mycorrhizal [MY-koh-RYE-zul] fungi . These
species live in mutually beneficial associations with
plants . The fungi form thick, spongy mats of mycelium
on and in the plants' roots that help the plants absorb
more water and nutrients . The fungi receive sugars
and amino acids, the building blocks of proteins, from
the plants . More than 95 percent of ferns (and their
close relatives), gymnosperms, and angiosperms have
mycorrhizal fungi living in association with their roots.
Figure 3 .17 Mutua list Fungi
A lichen consists of an alga and a fungus intimately entwined In a
mutually beneficial association . This lichen, known as British soldiers
is shown growing on an old log.
For example, morels—a group of mushrooms highh
prized as food by some—are the reproductive structures of mycorrhizal fungi.
Another familiar fungal association is the lichen [akin], a lacy, orange or gray-green growth often seen on
tree trunks or rocks . A lichen is an association of an alga
(a photosynthetic protist, as we learned earlier) anda
fungus (Figure 3 .17) . Both ascomycetes and basidiomycetes are known to form lichens . The alga and fungus
in a lichen grow with their tissues intimately entwined,
allowing the fungus to receive sugars and other carbon
compounds from the alga . In return, the fungus produces
lichen acids, a mixture of chemicals that scientists believe
may function to protect both the fungus and the alga from
being eaten by predators.
3 .6
IBACTERIA] I ARCHAEAII
IBACTERIAL ARCHAEAL
ire 3.16 Fungal Parasites
e fungi are parasites, making their living by attacking the tissues
her living organisms . This beetle, a weevil in Ecuador, has been
1 by a Cordyceps [Koe-duh-seps] fungus, the stalks of which are
ring out of its back .
Unit 1 The Diversity of Life
The Animalia : Complex,
Diverse, and Mobile
EUKARYA
PROTISTA
PLANTAEI FUNGI ]
11
The Animalia, or the animals, are
a kingdom within the domain Eukarya . The Animalia is the most
familiar major group, and the one
to which humans belong. All animals are multicellular, and many
of them are quite complex . The
animals include flashy creatures
such as Bengal tigers, peacocks,
and you, as well as worms, sea
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stars, snails, insects, and other creatures that are less obviously animal-like, such as sponges and corals.
The sponges, the most ancient of animal lineages,
were the first to branch off the evolutionary tree (Figure
3 .18 on the next page) . Next to evolve were the cnidarians [nye-DARE-ee-uns] (including jellyfish, sea
anemones, and corals), and then the flatworms . The
next group to evolve was the protostomes, a group that
comprises more than 20 separate subgroups, including mollusks (such as snails and clams), annelids (segmented worms), and arthropods (including crustaceans,
spiders, and insects), the three shown in Figure 3 .18.
These three protostome groups are depicted branching
off together because it is unclear which of them evolved
from the others first . What is known is that they are
part of a single lineage descending from an ancestor
that branched off the tree after flatworms, but before
echinoderms [ee-KYE-noh-derms] . Next to evolve were
the echinoderms (sea stars and the like) and the vertebrates (animals with backbones, such as fish, birds,
and humans), both deuterostomes [ g oo-ter-oh-stomes].
Like all fungi and some bacteria and protists, animals
are consumers, making their living by eating the tissues
of other organisms, from which they derive both carbon
and energy. Animals differ from fungi and plants in that
animal cells do not have cell walls surrounding their
plasma membranes . Typically mobile and often in search
of either food or mates, animals have evolved a huge diversity in their ways of life.
Outgoing water
One type of specialized cell,
the collar cell, has a tail-like
appendage, known as a
flagellum, which keeps water
flowing through the sponge.
Collar cells also trap food and
pass it to other cells, which i
digest it.
Figure 3 .19
Sponges Have Specialized Cells but Lack Tissues
Sponges are loose associations of cells . Although some of these
cells are specialized, none are organized as tissues, as in most
other animals .
Animals evolved organs and organ systems
Animals evolved true tissues
Sponges are among the simplest of animals . They represent a time in the evolution of animals before tissues—
specialized, coordinated collections of cells—had evolved.
A sponge is a loose collection of cells (Figure 3 .19) . If it is
put through a sieve and broken apart into individual
cells, it will slowly reassemble as a whole sponge.
Widespread and highly successful, sponges feed on amoebas and other tiny organisms in their aquatic environment, filtering a ton of water just to get enough food to
grow an ounce.
One of the earliest animal groups to evolve true tissues
was the cnidarians . Their name—Cnidaria—comes from
the Greek word for "nettle," a stinging plant found on land.
Cnidarians are characterized by stinging cells they use
to immobilize prey and to protect themselves from predators. Like other cnidarians, jellyfish (Figure 3 .20) have
specialized nervous tissues, musclelike tissues, and digestive tissues. This specialization allows behavior—such as
gracefully and rapidly swimming away from predators—
that requires the coordination of many cells .
After tissues, the next level of complexity to evolve was
organs and organ systems . Recall that organs are body
parts composed of different tissues organized to carry
out specialized functions . Usually organs have a defined
boundary and a characteristic size and shape ; an example is the kidney.
An organ system is a collection of organs functioning
together to perform a specialized task . The human digestive system, for example, is an organ system that includes
the stomach as well as other digestive organs, such as the
pancreas, liver, and intestines . Flatworms, a group of fairly
simple wormlike animals, were one of the earliest groups
to evolve true organs and organ systems (Figure 3 .21).
Animals evolved complete body cavities
Still later in the history of this group, animals evolved a
complete body cavity—an interior space with a mouth at
one end and an anal opening at the other . The two distinct evolutionary lineages that exhibit such cavities are
the protostomes and the deuterostomes (see Figure 3 .18).
Protostomes include such animals as insects, worms, and
Chapter 3 Major Groups
of
Living Organisms
riew the tissue
wrs of a jellyfish .
I The endoderm is specialized to
facilitate digestion, discharging
proteins that break down food,
which is then taken up by the cells
f The mesoglea is
an inner layer of
jellylike material .
The tentacles contain specialized
stinging cells that are used to inject
poisons into prey and subdue them.
Figure 3 .20 Jellyfish Have True Tissue Layers
Cnidarians (including jellyfish) were one of the earliest groups to
evolve true tissues . These tissues include the ectoderm (ecto, "outer";
derm, "skin") and the endoderm (endo, "inner") . For clarity, these two
layers are color-coded blue and yellow, respectively . Sandwiched
between them is an inner (red) layer of secreted material known as the
mesoglea (meso, "middle" ; glee, "jelly") . In addition to serving as
nervous tissue, the ectoderm coordinates with the endoderm to
contract like muscle tissue . Tentacles bring food into the internal cavity
through a single opening, which serves as both a mouth and an anus.
Figure 3 .21 Flatworms Evolved Organs and Organ
Systems
One of several organ systems in the flatworm is the reproductive
system . It contains both male and female structures, since every
flatworm can function as both a male and a female . For clarity, we
have color-coded the female structures pink (ovary, oviduct, and
genital pore) and the male structures blue (penis and testis).
Unit 1 The Diversity of Life
snails. Deuterostomes include animals such as sea stars
(echinoderms) and all the animals with backbones (vertebrates), such as humans, fish, and birds.
The names for these two lineages refer to which of
the two openings in the early embryo becomes the
mouth . In protostomes (from proto, "first" ; stome,
"opening"), the mouth forms from the first opening to
develop, and the anus forms elsewhere later . hn
deuterostomes (deutero, "second"), the first opening
develops into the anus, while the second opening
becomes the mouth. This developmental difference has
led to radically different patterns of tissue organization in these two groups.
Animal body forms exhibit variations
on a few themes
Animals exhibit a great variety of shapes and sizes, many
of which are variations on a few basic body plans.
Arthropods (arthro, "jointed" ; pod, "foot") have a hard
outer skeleton called an exoskeleton (exo, "outer"), which
is made of chitin [KYE-tin], the same material found in the
cell walls of fungi.
One feature that has facilitated the evolution of arthropod bodies is their segmented body plan . Over time, individual body segments have evolved different combinations
of legs, antennae, and other specialized appendages,
resulting in a huge number of different types of animals,
some of them extremely successful . Probably the bestknown arthropod group is the insects (grasshoppers,
beetles, butterflies, and ants, among others), which have
six legs and live on land . Whereas prokaryotes dominate
Earth in sheer numbers of individuals, insects dominate
in number of species, having many more species than
any other group of organisms.
Other arthropod groups include the arachnids [uhRACK-nids] (spiders, scorpions, and ticks), which have
eight legs and also live on land ; the crustaceans (lobsters, shrimps, and crabs), which have ten or more legs
and live primarily in water ; and millipedes and centipedes, which live on land and have many more legs—
but less specialization—than the previously mentioned
groups . Arthropods are a wonderful illustration of how
evolution can modify a basic body plan to produce many
variations over time (Figure 3 .22) . Looking just at the
evolution of the last segment (the rear ends) of these
animals, one can see that the changes support a huge
variety of shapes and lifestyles . The last segment has
evolved into the delicate abdomen of a butterfly, the
piercing abdomen of a wasp (which has a huge structure
eat prey, avoid being captured, attract mates and care
for young, and migrate to new habitats . As we saw earlier,
animals are quite useful to immobile organisms, such as
plants, which have evolved ways to get animals to carry
their pollen and seeds.
Animals play key roles in ecosystems
and provide products for humans
Because they live by eating other organisms, and
because most are mobile, animals play many roles in
ecosystems . Most serve as consumers, preying on many
species of plants and animals . Some animals, such as
carrion beetles, serve as decomposers of dead animals.
Figure 3.22 Variations on a Theme
From a simple segmented body plan, arthropods have evolved a huge
diversity of forms and sizes . The millipede can be viewed as the
simplest form of these segmented animals, as all of its segments are
similar. As segments have evolved and diversified, a variety of
organisms have arisen, from lobster to swallowtail butterfly to
parasitoid wasp.
for inserting and laying eggs deep in another animal's
body), and the delicious tail of the lobster.
Such segmentation can also be seen in the annelids
(segmented worms ; see Figure 3 .18) . This group includes
the familiar earthworm, whose body is made up of a
repeated series of segments (Figure 3 .23a).
Vertebrates—animals with an internal backbone—
are also built on a (less obvious) segmented body plan
(Figure 3.23b) . The major vertebrate groups include fish,
amphibians (frogs and salamanders), reptiles (snakes,
lizards, turtles, and crocodiles), birds, and mammals
(including humans and kangaroos) . Like annelids and
arthropods, vertebrates illustrate how a variety of very
different forms can evolve from one basic body plan . The
front appendage of vertebrates has evolved as an arm in
humans, a wing in birds, a flipper in whales, an almost
nonexistent nub in snakes, and a front leg in salamanders and lizards.
Animals exhibit an astounding variety
of behaviors
Another fascinating characteristic of animals is their
ability to move, which allows for a wide range of behaviors . Animals have evolved varied ways to capture prey,
Test your knowledge
of the properties of
multicellular
eukaryotes .
(a)
(b)
Figure 3.23 Many Animals Are Segmented
Segmentation, a body plan in which segments repeat and often can
evolve independently of one another, is shown here in (a) an
earthworm (an annelid, or segmented worm), and (b) a vertebrate.
Chapter 3 Major Groups of Living Organisms