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Biology
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2. 22–1 Introduction to Plants
Photo Credit: © Terry Donnelly/Dembinsky Photo Associates
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What Is a Plant?
What Is a Plant?
Plants are multicellular eukaryotes that have cell walls made of cellulose.
Plants develop from multicellular embryos and carry out photosynthesis using the green pigments chlorophyll a and b.
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The Plant Life Cycle
Alternation of Generations
All plants have a life cycle with alternation of generations, in which the haploid gametophyte phase alternates with the diploid sporophyte phase.
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The Plant Life Cycle
During the two phases of the life cycle, mitosis and meiosis alternate to produce the two types of reproductive cells—gametes and spores.
The diploid (2N) phase is called the sporophyte, or spore-producing plant.
The haploid (N) phase is called the gametophyte, or gamete-producing plant.
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6. What Plants Need to Survive
In order to survive, plants need:
sunlight
water and minerals
gas exchange
transport of water and nutrients throughout the plant body
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Early Plants
The first plants evolved from an organism similar to the multicellular green algae living today.
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Early Plants
The oldest known plant fossils, about 450 million years old, are similar to today’s mosses.
They had a simple structure and grew close to the ground.
One of the earliest fossil vascular plants was Cooksonia, which looked similar to mosses living today.
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9. Overview of the Plant Kingdom
Plants are divided into four groups based on these features:
water-conducting tissues
seeds
flowers
Plants are also classified by other features, including reproductive structures and body plan.
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10. Overview of the Plant Kingdom
Evolutionary Relationships Among Plants
Flowering plants
Cone-bearing plants
Ferns and their relatives
Flowers; Seeds enclosed in fruit
Mosses and their relatives
This cladogram shows the evolutionary relationships among the various groups of plants. The four main groups of living plants are mosses and their relatives, ferns and their relatives, cone-bearing plants, and flowering plants.
Seeds
Water-conducting (vascular) tissue
Green algae ancestor
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22–1
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22–1
Most plants alive today are
cone-bearing.
flowering.
ferns.
mosses.
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22–1
The two phases of a plant's life cycle are referred to as
alternation of generations.
spontaneous generation.
biogenesis.
sexual and asexual.
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22–1
Which statement accurately describes a way that plants meet their basic needs?
Plants take in carbon dioxide from soil through their roots.
Plants obtain the energy for photosynthesis from sunlight.
Plants obtain minerals by exchanging gases with the atmosphere.
Plants absorb water through their broad, flat leaves.
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22–1
The first group of plants to evolve from green algae were the
cone-bearing plants.
ferns.
mosses.
flowering plants.
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22–1
The diploid phase of the plant life cycle is known as the
sporophyte.
gametophyte.
egg.
spore.
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17. END OF SECTION