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25-3 Plant Adaptations
Photo Credit: ©Dr. Paul A. Zahl/Photo Researchers, Inc.
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Aquatic Plants
Aquatic Plants
To take in sufficient oxygen, many aquatic plants have tissues with large air-filled spaces through which oxygen can diffuse.
Mangroves have specialized air roots with air spaces in them. These spaces conduct air down to the buried roots, allowing root tissues to respire normally.
Bald cypress trees grow structures called knees, which protrude above the water. The knees bring oxygen-rich air down to the roots.
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Aquatic Plants
The reproductive adaptations of aquatic plants include seeds that float in water and delay germination for long periods.
Many aquatic plants grow quickly after germination, extending the growing shoot above the water’s surface.
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Salt-Tolerant Plants
Salt-Tolerant Plants
When plant roots take in dissolved minerals, a difference in concentration of water molecules is created between root cells and the surrounding soil.
This causes water to enter the root cells by osmosis.
For plants in salt water, this means taking in much more salt than the plant can use.
The roots are adapted to salt concentrations that would quickly destroy root hairs on most plants.
The leaves of these plants have specialized cells that pump salt out of the plant tissues and onto the leaf surfaces, where it is washed off by rain.
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Desert Plants
Desert Plants
Plants that live in the desert biome are called xerophytes.
Xerophytes must tolerate a variety of extreme conditions, including strong winds, daytime heat, sandy soil, and infrequent rain.
Plant adaptations to a desert climate include extensive roots, reduced leaves, and thick stems that can store water.
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Desert Plants
Cactuses have root systems that spread out for long distances just beneath the soil surface or reach deep down into the soil.
To reduce water loss due to transpiration, cactus leaves have been reduced to thin, sharp spines and they have thick green stems that carry out photosynthesis and are adapted to store water.
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Desert Plants
The stems of cactuses swell during rainy periods and shrivel during dry spells, when the plants are forced to use up their water reserves.
Seeds of many desert plants can remain dormant for years, germinating only when sufficient moisture guarantees them a chance for survival.
When rain does come, the plants mature, flower, and seed in a matter of weeks or even days, before the water disappears.
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8. Nutritional Specialists
Plants that have specialized features for obtaining nutrients include carnivorous plants and parasites.
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9. Nutritional Specialists
Carnivorous Plants
Some plants that live in wet and acidic environments with little or no nitrogen present obtain nutrients using specialized leaves that trap and digest insects.
The leaf secretes enzymes that digest the insect and release nitrogen for the plant to use.
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10. Nutritional Specialists
The best known of the carnivorous plants is the Venus’ flytrap.
Carnivorous plants, such as the Venus’ flytrap, digest insects—and occasionally frogs—as a source of nutrients. Photo Credit: Sean Morris/©Oxford Scientific Films
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11. Nutritional Specialists
Parasites
Some plants extract water and nutrients directly from a host plant.
Like all parasites, these plants harm their host organisms and sometimes even pose a serious threat to other species.
The dodder plant Cuscuta is a parasitic plant that grows directly into the vascular tissue of its host. There, it extracts nutrients and water.
Mistletoe grows as a parasite on many plants, including conifers in the western United States.
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Epiphytes
Epiphytes
Epiphytes are plants that are not rooted in soil but instead grow directly on the bodies of other plants.
Most are found in the tropical rain forest biome, but they also grow in other moist biomes.
Epiphytes are not parasites.
They gather their own moisture, generally from rainfall, and produce their own food.
One of the most common epiphytes is Spanish moss, which is not a moss but a bromeliad.
Over half of orchids are epiphytes.
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Chemical Defenses
Chemical Defenses
Plants are an important source of food for insects.
Many plants defend themselves against insect attack by manufacturing compounds that have powerful effects on animals.
Some of these chemicals are poisons that can be lethal if eaten.
Others act as insect hormones, disrupting normal development and preventing insects from reproducing.
These chemicals include those used in aspirin, nicotine, codeine, and other drugs or medicines.
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