plants acquire these from the soil through its roots
carbon dioxide
a plant acquires this through the open stomata of the leaves. as this enters the leaves, oxygen and water vapor exit the leaves.
oxygen and water vapor
as carbon dioxide enters the leaves, these leave the leaves
light
a plant acquires this from the sun
hydroponic culture
a plant is grown without soil, in a mineral solution. a tube "aerates" the culture by pumping oxygen (needed for aerobic respiration) into the mineral solution
essential nutrient
a nutrient that a plant is unable to complete its life cycle without; a plant would die without it. there are 17
macronutrients
elements that plants require in relatively large amounts. there are nine: carbon, oxygen, hydrogen, nitrogen, potassium, calcium, magnesium, phosphorus, and sulfur
micronutrients
elements that plants need only small amounts of. there are eight: chlorine, iron, manganese, boron, zinc, copper, nickel, and molybdenum
mineral deficiency symptom
a symptom (depending on the function of the element) that occurs when an essential element is not present in adequate quantities
mobile nutrient
a nutrient that moves about freely in the plant. younger parts of the plant are more effective at drawing in nutrients in short supply than older parts of the plant. therefore, with these, deficiency symptoms will first appear on the older parts of the plant
immobile nutrient
does not freely move about the plant. because older parts of the plant might have an adequate supply of the immobile nutrient, it is the younger parts of the plant that exhibit deficiency symptoms first
nitrogen deficiency
results in leaves yellow from the tip to the center. it exhibits chlorosis of all its leaves
potassium deficiency
results in leaves with edges that are colored in a "firing" pattern with yellows and reds
phosphate deficiency
results in leaves with reddish-purple edges, particularly in the younger leaves
texture
characteristic of the soil which is a major contributor to a plants success; the general structure of the soil. this largely depends on the size of the soil's particles
composition
characteristic of the soil which is a major contributor to a plants success; refers to the inorganic and organic components present in the soil
soil
the eventual product of the breakdown of solid rock, due to wind, water, and even chemicals secreted by animals
topsoil
what we think of as soil; contains particles resulting from the breakdown of solid rock, living organisms, and humus
sand
the largest particle (2.0 mm to 0.02 mm in diameter). it does not adhere to water because it is not charged
silt
the second-largest particle (.02 mm to .002 mm in diameter). it does not adhere to water because it is not charged
clay
the smallest particle (smaller than 0.002 mm in diameter) clay adheres to water because it has a slight negative charge
humus
partially decayed organic material, including material formed by bacteria and fungi on dead organisms, fallen leaves, and feces
horizons
visible soil layers
O horizon
the soil horizon that contains only organic material
A horizon
the soil horizon- known as topsoil- that is most important for plant growth. minerals are leached from this horizon
B horizon
this soil horizon is where minerals and clay from above are deposited. it contains little organic material; plants do not generally have roots that make it past this horizon
C horizon
this is the soil horizon that consists only of unconsolidated rock
anions
negatively charged ions, such as nitrate (NO3-), phosphate (H2PO4-), and sulfate (SO4 2-). they are bound only loosely to the soil particles, so they are released and absorbed by the plant easily
cations
positively charged ions, such as calcium (Ca 2+), magnesium (Mg 2+), and potassium (K+). these ions are bound much more tightly to soil particles, so they are not easily released and absorbed. rather, the root hairs take up these cations by exchanging hydrogen ions (H+) for them. these hydrogen ions are formed when water and carbon dioxide released by the root after cellular respiration come together to form carbonic acid. dissociation of the acid leads to the release of hydrogen ions.
sustainable agriculture
minimizing the damage due to human abuse of the land. if properly used, soil is a renewable resource that may not ever be depleted
organic fertilizers
a type of fertilizer consist of decomposing organic material (fishmeal, manure, or compost)
commercially produced fertilizers
fertilizers which contain minerals either prepared through industrial processes or mined. rich in nitrogen, phosphorus, and potassium
"smart plant"
a genetically engineered plant that tells its cultivator when it needs fertilizer. the plant has a promoter sequence that binds to RNA polymerase when the phosphorus content is low. The RNA polymerase causes the transcription of a gene that leads to the production of a blue pigment. when a farmer notices the blue, he realizes the phosphorus content of the plants is getting low and he should add fertilizer, reducing the need to over-fertilize in order to ensure that one's plants do not die
irrigation
watering plants; it can change the nature of the soil forever. salts remain in the soil even after water has evaporated, and the soil can become too salty because the water potential of the soil solution becomes negative, inhibiting water uptake by the roots. drip irrigation and the development of new plants that require less water minimize the depletion of water resources and the risk of salinization due to irrigation.
soil reclamation
involves converting soil unfit for agriculture into soil fit for agriculture. traditional methods involved simply removing the contaminated soil. a new method is phytoremediation
phytoremediation
a biological method that uses plants to extract and contaminate pollutants in the soil. once the plants have grown and extracted the pollutants, they are removed and destroyed. the remaining land is pollutant-free and for cultivation
nitrogen
the element that makes the greatest contribution to plant growth and crop yields. plants use this element to make nucleic acids, proteins, chlorophyll, and other organic molecules
nitrogen-fixing bacteria
fix atmospheric nitrogen (N2), converting it to ammonium (NH 4+)
converts the majority of ammonium from nitrogen-fixing bacteria and ammonifying bacteria into nitrate (NO3-)
denitrifying bacteria
converts nitrate (NO3-) back into gaseous nitrogen (N2), which is lost to the atmosphere
mutualistic relationships
relationships that benefit both organisms; includes symbiotic nitrogen fixation and mycorrhizae
one-sided relationships
relationships that benefit just one organism, at the expense of the other; includes epiphytes, parasitic plants, and carnivorous plants
nodules
plant cells that have been infected with nitrogen-fixing bacteria. the bacteria inside these are contained within the root cell's vesicles, and are called bacteroids. these cells are nonphotosynthetic, so the environment is largely anaerobic (a requirement for nitrogen fixation)
bacteroids
the bacteria inside the nodules contained within the root cell's vesicles
flavonoid
a chemical signals emitted by the root, which infects surrounding cells in the soil and attracts the appropriate bacterial strain. the bacterial strain then emits a signal that stimulates the root hairs to elongate and curve.
infection thread
the membrane of the root hair, stimulated by the bacterial strain, that invaginates and allows the bacteria into the root hair. the bacteria then penetrate the cortex, which divides and sends the bacteria deeper into the root. eventually a nodule forms as affected regions of the cortex and pericycle fuse. vascular tissue then forms, providing a path by which substances can flow to an from the nodule.
crop rotation
a practice in which a non-legume is planted a piece of land one year, and then a legume is planted on the same land the next year. in this manner, the non-legume crop can take advantage of the nitrogen left behind by the legumes, which produce a significant amount of nitrogen due to mutualistic relationships with nitrogen-fixing bacteria
mycorrhizae
modified roots that consist of a mutualistic combination of fungi and roots. the fungus spreads out over a large surface area, promoting the uptake of water and minerals for the host plant. the host plant, in turn, supplies the fungus with sugar- the plant's photosynthetic produce. the majority of plants today form mycorrhizae, which is thought to have been an evolutionary adaptation that helped the earliest terrestrial plants survive on land
ectomycorrhizae
a kind of mycorrhizae in which the mycelium forms a mantle over the root's surface. fungal hyphae extend into the soil from the mantle. this increases the surface area and promotes the uptake of water and minerals. the fungale hyphae of ectomycorrhizae grow into the root's cortex, forming a network in the apoplast through which the fungus exchanges nutrients with the plants
mantle
a dense sheath over the root's surface
apoplast
extracellular space through which the fungus exchanges nutrients with the plants
endomycorrhizae
the more common kind of mycorrhizae; without a mantle over the root's surface. fungal hyphae extend into the soil from the root instead of the mantle. these hyphae are microscopic., they digest small patches in the walls of the root cell and extend into it, penetrating the cell walls of cells in the cortex but not the plasma membrane or cytoplasm. some hyphae form arbuscules ("little trees")
arbuscules
"little trees" - branches that increase the hyphal surface area and promote nutrient transfer
epiphyte
anchors itself on the branches or trunks of other organisms, absorbing water and minerals from the rain through its leaves instead of its roots. they do not get their nutrition from their host plant; they can nourish themselves
parasitic plants
these do not always nourish themselves; they absorb sugar and minerals from their hosts
carnivorous plants
these kill and digest small animals (such as insects) to obtain nitrogen and other necessary minerals. these are adaptations made by plants that live in environments where the soil lacks essential elements such as nitrogen
