Transcript An Introduction to Plant Diversity

Lesson Overview
What is a Plant?
Lesson Overview
An Introduction to
Plant Diversity
Lesson Overview
What is a Plant?
THINK ABOUT IT
Plants have adapted so well to so many environments that they dominate
much of the surface of our planet.
Lesson Overview
What is a Plant?
The Plant Kingdom
Plants are classified as members of the kingdom Plantae.
Plants are eukaryotes that have cell walls containing cellulose and carry out
photosynthesis using chlorophyll a and b.
Lesson Overview
What is a Plant?
What Plants Need
All plants have the same basic
needs: sunlight, a way to exchange
gases with the surrounding air,
water, and minerals.
Lesson Overview
What is a Plant?
Sunlight
Plants use the energy from
sunlight to carry out
photosynthesis.
Leaves are typically broad and flat
and are arranged on the stem so
as to maximize light absorption.
Lesson Overview
What is a Plant?
Gas Exchange
Plants require oxygen to support
cellular respiration, as well as
carbon dioxide to carry out
photosynthesis.
Plants must exchange these gases
with the atmosphere and the soil
without losing excessive amounts
of water through evaporation.
Lesson Overview
What is a Plant?
Water and Minerals
Land plants have evolved
structures that limit water loss and
speed the uptake of water from
the ground.
Minerals are nutrients in the soil
that are needed for plant growth.
Lesson Overview
What is a Plant?
Many plants have specialized
tissues that carry water and
nutrients upward from the soil and
distribute the products of
photosynthesis throughout the
plant body.
Lesson Overview
What is a Plant?
Origins in the Water
The ancestors of today’s land plants were water-dwelling organisms similar to
today’s green algae.
Although not as large and complex as many plants, green algae have cell walls and
photosynthetic pigments that are identical to those of plants. Green algae also
have reproductive cycles that are similar to plants.
Studies of the genomes of green algae suggest that they are so closely related to
other plants that they should be considered part of the plant kingdom.
Lesson Overview
What is a Plant?
An Overview of the Plant Kingdom
The relationship of plant groups is shown below
Lesson Overview
What is a Plant?
The Plant Life Cycle
The life cycle of land plants has two alternating phases, a diploid (2N) phase and a
haploid (N) phase.
The shift between the haploid phase–a cell that contains half the genetic
information with only one copy of each chromosome, and the diploid phase –a cell
that contains two copies of each chromosome. This is known as the alternation of
generations, as shown in the figure.
Lesson Overview
What is a Plant?
The Plant Life Cycle
The multicellular diploid phase is known as the sporophyte, or spore-producing
plant.
Lesson Overview
What is a Plant?
The Plant Life Cycle
The multicellular haploid phase is known as the gametophyte, or gameteproducing plant.
Lesson Overview
What is a Plant?
Trends in Plant Evolution
An important trend in plant evolution is the reduction in size of the gametophyte
and the increasing size of the sporophyte.
Lesson Overview
What is a Plant?
The First Plants
Green algae are mostly aquatic. They are found in fresh and salt water, and in
some moist areas on land.
Ancient green algae shared the ocean floor with corals and sponges.
Green algae absorb moisture and nutrients directly from their surroundings
and do not contain the specialized tissues found in other plants.
Lesson Overview
What is a Plant?
Multicellularity
Green algae can form colonies.
Spirogyra forms long threadlike colonies called filaments.
Lesson Overview
What is a Plant?
Multicellularity
Volvox colonies consist of as few as 500 to as many as 50,000 cells arranged to
form hollow spheres.
Volvox shows some cell specialization and straddles the fence between
colonial and multicellular life.
Lesson Overview
What is a Plant?
Mosses and Other Bryophytes
Mosses, hornworts, and liverworts all belong to a group of plants known
as bryophytes.
Bryophytes have specialized reproductive organs enclosed by other, nonreproductive cells.
Bryophytes show a higher degree of cell specialization than do the green
algae and were among the first plants to become established on land.
Lesson Overview
What is a Plant?
Mosses and Other Bryophytes
Mosses have a waxy, protective
coating that makes it possible for
them to resist drying, and thin
filaments known as rhizoids that
anchor them to the soil. Rhizoids
also absorb water and minerals
from the soil.
Lesson Overview
What is a Plant?
Why Bryophytes Are Small
Bryophytes do not make lignin, a substance that hardens cell walls, and do
not contain true vascular tissue. Because of this, bryophytes cannot
support a tall plant body against the pull of gravity.
Lesson Overview
What is a Plant?
Vascular Plants
About 420 million years ago, plants for the first time were able to grow
high above the ground.
Fossil evidence shows these plants were the first to have a transport
system with true vascular tissue. Vascular tissue carries water and
nutrients much more efficiently than does any tissue found in bryophytes.
Lesson Overview
What is a Plant?
Evolution of a Transport System
Vascular plants are known as tracheophytes, after a specialized type of
water-conducting cell they contain. These cells, called tracheids, are
hollow tubelike cells with thick cell walls strengthened by lignin.
Tracheids are found in xylem, a tissue that carries water upward from the
roots to every part of a plant.
Lesson Overview
What is a Plant?
Evolution of a Transport System
Vascular plants also have a second transport tissue called phloem that
transports solutions of nutrients and carbohydrates produced by
photosynthesis.
Lesson Overview
What is a Plant?
Seedless Vascular Plants
Among the seedless vascular plants alive today are three phyla commonly
known as club mosses, horsetails, and ferns. The most numerous of these
are the ferns.
Lesson Overview
What is a Plant?
Seedless Vascular Plants
Ferns have true vascular tissues, strong roots, creeping or underground
stems called rhizomes, and large leaves called fronds, shown in the figure.
Ferns can thrive in areas with little light and are most abundant in wet
habitats.
Lesson Overview
What is a Plant?
The Importance of Seeds
A seed is a plant embryo and a food supply, encased in a protective covering. The
living plant within a seed is diploid and represents the early developmental stage
of the sporophyte phase of the plant life cycle.
Lesson Overview
What is a Plant?
The First Seed Plants
Today’s seed plants are all descended from common ancestors.
The fossil record indicates that ancestors of seed plants evolved new adaptations
that enabled them to survive on dry land.
Lesson Overview
What is a Plant?
Cones and Flowers
In seed plants, the male gametophytes and the female gametophytes grow and
mature directly within the sporophyte. The gametophytes usually develop in
reproductive structures known as cones or flowers.
Nearly all gymnosperms bear their seeds directly on the scales of cones.
Flowering plants, or angiosperms, bear their seeds in flowers inside a layer of
tissue that protects the seed.
Lesson Overview
What is a Plant?
Pollen
In seed plants, the entire male gametophyte is contained in a tiny structure called
a pollen grain.
Pollen grains are carried to the female reproductive structure by wind or animals
such as insects.
The transfer of pollen from the male reproductive structure to the female
reproductive structure is called pollination.
Lesson Overview
What is a Plant?
Flowering
Plants
Flowers and Fruits
The origin of flowering plants is the most recent among the origins of all plant
phyla.
Flowering plants originated on land and soon came to dominate Earth’s plant life.
Lesson Overview
What is a Plant?
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.
Lesson Overview
What is a Plant?
Flowering
Plants
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.
Lesson Overview
What is a Plant?
Flowering
Plants
Advantages of Fruits
After pollination, the ovary develops into a fruit, a structure containing one
or more matured ovaries. The wall of the fruit helps disperse the seeds
contained inside it. The development of the multiple ovaries of a blackberry
flower into the cluster of fruits that make up one berry is shown.
Lesson Overview
What is a Plant?
Flowering
Plants
Advantages of Fruits
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.
Lesson Overview
What is a Plant?
Flowering
Plants
Angiosperm Classification
When an animal For many years, flowering plants were classified according to the
number of seed leaves, or cotyledons, in their embryos. Those with one seed leaf
were called monocots. Those with two seed leaves were called dicots.
Lesson Overview
What is a Plant?
Flowering
Plants
Monocots and Dicots
The differences between monocots and dicots include the distribution of vascular
tissue in stems, roots, and leaves, and the number of petals per flower.
Lesson Overview
What is a Plant?
Flowering
Plants
Monocots and Dicots
The characteristics of monocots and dicots are compared in the table below.