Chap 37

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Acid precipitation carries excess H⁺ into the soil, releasing cation minerals and washing them away .

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Carnivorous plants live in acid bogs where soils are poor in nitrogen and other minerals. Various insect traps consist of modified leaves usually equipped with glands that secrete digestive enzymes.

Venus' flytrap Triggered by electrical impulses from sensory hairs, two leaf lobes close in half a second. Despite its common name, Dionaea muscipula usually catches ants and grasshoppers. Pitcher plants Nepenthes, Sarracenia, and other genera have water-filled funnels. The insects drown and are digested by enzymes. Sundews Sundews (genus Drosera) exude a sticky fluid that glitters like dew. Insects get stuck to the leaf hairs, which enfold the prey.

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This tropical fern grows on rocks, cliffs, and trees. It has two types of fronds: branched fronds resembling antlers and circular fronds which forms a basket that collects rain and debris. Roots grow into this basket to absorb water and minerals.

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Parasitic plants.

Mistletoe, a photosynthetic parasite. Mistletoe (genus Phoradendron) lives as a parasite on oaks and other trees. Dodder, a nonphotosynthetic parasite. Dodder (genus Cuscuta), the orange "strings" on this pickleweed, draws its nutrients from the host. The transverse section shows a haustorium tapping the host's phloem. Indian pipe, a nonphotosynthetic parasite. This species (Monotropa uniflora) absorbs nutrients from the fungal hyphae of mycorrhizae of green plants.

Parasitic plants.
Mistletoe, a photosynthetic parasite. Mistletoe (genus Phoradendron) lives as a parasite on oaks and other trees.		Dodder, a nonphotosynthetic parasite. Dodder (genus Cuscuta), the orange "strings" on this pickleweed, draws its nutrients from the host. The transverse section shows a haustorium tapping the host's phloem.		Indian pipe, a nonphotosynthetic parasite. This species (Monotropa uniflora) absorbs nutrients from the fungal hyphae of mycorrhizae of green plants.

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Development of a soybean root nodule.

Root hairs form an infection thread by invagination of the plasma membrane.
Rhizobium bacteria penetrate the infection thread, and form bacteroids within vesicles of root cells.
Cortex and pericycle cells fuse, forming a nodule.
The nodule develops vascular tissue that facilitate exchange of materials between bacteria and the plant

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APPLICATION In hydroponic culture, plants are grown in mineral solutions without soil. One use of hydroponic culture is to identify essential elements in plants.

TECHNIQUE Plant roots are bathed in aerated solutions of known mineral composition. Aerating the water provides the roots with oxygen for cellular respiration. A particular mineral, such as potassium, can be omitted to test whether it is essential.

RESULTS If the omitted mineral is essential, mineral deficiency symptoms occur, such as stunted growth and discolored leaves. Deficiencies of different elements may have different symptoms, which can aid in diagnosing mineral deficiencies in soil.

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Hydroponic culture

APPLICATION Hydroponic culture, where plants are grown in mineral solutions without soil, can be used to identify essential elements in plants.

TECHNIQUE Plant roots are bathed in aerated solutions of known mineral composition. A particular mineral, such as potassium, can be omitted to test whether it is essential.

RESULTS If the omitted mineral is essential, mineral deficiency symptoms occur, such as stunted growth and discolored leaves.

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Common mineral deficiencies in maize leaves.

Phosphate–deficient plants have reddish purple margins, particularly in young leaves.

Potassium–deficient plants exhibit “firing,” or drying, along tips and margins of older leaves.

Nitrogen deficiency is evident in a yellowing that starts at the tip and moves along the midrib of older leaves.

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Deficiency warnings from “smart” plants.. Some plants have been genetically modified to signal an impending nutrient deficiency before irreparable damage or stunting occurs. For example, after laboratory treatments, the research plant Arabidopsis develops a blue color in response to an imminent phosphate deficiency.

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Ectomycorrhizae. The mycelium (mass of branching hyphae) forms a dense sheath ("mantle") over the surface of the root. The hyphae extend into the soil, absorbing water and minerals.

Hyphae also extend into the extracellular spaces of the root cortex, forming a "Hartig net", providing extensive surface area for nutrient exchange between the fungus and its host plant.

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Endomycorrhizae. Hyphae digest small patches of the root cell walls, then grow into a tube formed by invagination of the root cell's membrane, analogous to poking a finger into a balloon.

Within the root cortex, extensive branching of hyphae forms arbuscules, providing an enormous surface area for nutrient swapping .

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The role of soil bacteria in the nitrogen nutrition of plants. Ammonium is made available to plants by two types of soil bacteria: those that fix atmospheric N₂ (nitrogen-fixing bacteria) and those that decompose organic material (ammonifying bacteria).

Plants absorb mainly nitrate, produced from ammonium by nitrifying bacteria, from the soil.

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Plants in the Leguminoceae (Fabaceae) family, such as this pea, have root nodules containing Rhizobium (“root living”) bacteria, which fix nitrogen and obtain photosynthetic products from the plant. A cell from a root nodule of soybean is filled with bacteroids in vesicles.

Plants in the Leguminoceae (Fabaceae) family, such as this `pea`, have root nodules containing Rhizobium (“root living”) bacteria, which fix nitrogen and obtain photosynthetic products from the plant.		A cell from a root nodule of `soybean` is filled with bacteroids in vesicles.

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Root and shoot systems of a pea seedling.

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The uptake of nutrients by a plant: a review. From CO₂, O₂, H₂O, and minerals, the plant produces all of its own organic material .

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Soil horizons.

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The availability of soil water and minerals.

Soil water. Some water in the soil is held by hydrophilic soil particles and cannot be absorbed by the root. Cation exchange in soil. Hydrogen ions (H⁺) help make nutrients available by displacing positively charged minerals (cations such as Ca²⁺) that were bound to the surface of negatively charged soil particles. Plants contribute H⁺ by secreting it from root hairs and also by cellular respiration: CO₂ reacts with H₂O to form carbonic acid (H₂CO3) in the soil, whichdissociates to add H⁺

Carnivorous plants live in acid bogs where soils are poor in nitrogen and other minerals. Various insect traps consist of modified leaves usually equipped with glands that secrete digestive enzymes.
Venus' flytrap Triggered by electrical impulses from sensory hairs, two leaf lobes close in half a second. Despite its common name, Dionaea muscipula usually catches ants and grasshoppers.		Pitcher plants Nepenthes, Sarracenia, and other genera have water-filled funnels. The insects drown and are digested by enzymes.		Sundews Sundews (genus Drosera) exude a sticky fluid that glitters like dew. Insects get stuck to the leaf hairs, which enfold the prey.