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Jennifer Kim

Period 6

26a

I. Plant Nutrition and Soil

a. In the 17th century, a Dutch-man named Jean-Baptiste Van Helmont tested a hypothesis that was

said by the ancient Greeks; created an experiment where he planted a tree that weighed 5 lb in a

large pot containing 200 lb of soil; he water the plants regularly for 5 years and later re-weighed it andfound that the plant weighed 170 lbs and the soil weighed only a few ounces less than 200 lbs.

he concluded that the weight of the plant was increased because of the water that it was fed

b. Water is an important nutrient for the plant

water and carbon dioxide combine in a plant when sunlight is present; water and carbon dioxide to-

gether produces carbohydrates, which is the chief organic matter of plants

roots carry on cellular respiration, which is a process that uses oxygen and gives off carbon dioxide

A. Essential Inorganic Nutrients

a. approximately 95% of a typical plants dry weight is carbon, hydrogen, and oxygen because theses

are the elements that are found in most organic compounds, such as carbohydrates

carbon dioxide supplies carbon, and water supplies hydrogen and oxygen is found in the organic

compounds of a plant

b. plants require an intake of minerals as well

mineral-> an inorganic substance usually containing two or more elements

a nutrient is essential if it has an identifiable role, not other nutrient can substitute and fulfill the

same role, and a deficiency of this nutrient causes a plant to die without completing its life cycle

essential nutrients are divided into macronutrients and micronutrients according to their relative con-

centrations in plant tissue

c. beneficial nutrients-> another category of elements taken up by plants; either required for or en-

hance the growth of a particular plant

B. Determination of Essential Nutrients

a. When a plant is burned, its nitrogen component is given off as ammonia and other gases, but most

other essential minerals remain in the ash.

water culture, or hydroponics-> method for determining the mineral requirements of a plant; allows

plants to grow well if they are supplied with all the nutrients they need; more successful for macronu-

trients than micronutrients

for micronutrients, the water and mineral salts must be absolutely pure, but purity is difficult to obtainbecause even instruments and glassware can introduce micronutrients

C. Soil

a. Plats acquire carbon when carbon dioxide diffuses into leaves through stomata; oxygen can enter

from the air, but all of the other essential nutrients are absorbed by roots from the soil

b. terrestrial life is dependent on the quality of the soil and the ability of soil to provide plants with the

nutrients they need

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Jennifer Kim

Period 6

1) Soil Formation

a. Soil formation begins with the weathering of rock in the Earths crust; weathering first breaks down

rock to rubble and then to soil in particles

there is the mechanical mechanism, such as the freeze-thaw cycle of ice, or the chemical effect,

such as acidic rain washing away soluble components of rock or when oxygen combines with the ironof the rocks

b. organisms also play a role in the formation of soil

decaying organic matter, called humus begins to accumulate when the remains of grasses, herbs,

and soil animals die and decompose mostly by bacteria and fungi

humus supplies nutrients to plants, and its acidity also leaches minerals from rock

c. building soil takes a long time

2) The Nutritional Function of Soil

a. soil-> mixture of mineral particles, decaying organic material, living organism, air, and water, which

together support the growth of plants

its best if the soil contains particles of different sizes because only then will there be spaces for air;

roots take up oxygen from air spaces and ideally, water clings to particles by capillary action and does

not fill the spaces

-Mineral Particles

a. mineral particles vary in size: sand particles are the largest; silt particles have an intermediate size,

and clay particles are the smallest; soils are a mixture of these three types of particles

because sandy soils have many large particles, they have large spaces, and the water easily drains

readily through the particles, but sandy soils, a soil composed mostly of clay particles have small spa-

ces that fill completely with water

b. Clay particles are negative, and they can retain positively charged minerals, preventing these min-

erals from being washed away by leaching

Plants exchange hydrogen ions for these minerals when they take them up; if rain is acidic, its hy-

drogen ions displace positive mineral ions and cause them to drain away, which is why acid rain kills

trees

c. a combination of sand, silt, and clay particles, called loam, sufficiently retains water and nutrients

while still allowing the drainage necessary to provide air spaces

-Humusa. humus-> mixes with the top layer of soil particles and increases the benefits of soil

b. humus causes soil to have a loose, crumbly texture that allows water to soak in without doing away

with air spaces

swells when it absorbs water and shrinks as it dries; helps aerate soil

c. soil that contains humus is nutritious for plants; acidic; retains positively charged minerals until

plants take them up

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Jennifer Kim

Period 6

when the organic material in is broken down by bacteria and fungi, inorganic nutrients are returned

to plants

recycling of nutrients is a major characteristic of ecosystems

-Living Organisms

a. small plants play a major role in he formation of soil from bare rock; due to the process of succes-sion, larger plants eventually become dominant in certain ecosystems

the roots of larger plants penetrate soil even to the cracks in bedrock; slowly opens up soil layers,

allowing water, air, and animals to follow

b. the largest of the soil animals disturb and mix the soil by burrowing, but smaller animals ingest fine

soil particles and deposit them on the surface as worm casts

some earthworms also loosen and aerate the soil; a range of soil animals help break down leaves

and other plant remains by eating them

c. the microorganisms in soil, such as protozoans, fungi, algae, and bacteria, are responsible for the

final decomposition of organic remains in humus to inorganic nutrients

plants are unable to make atmospheric nitrogen and that soil bacteria play an important nutrient role

because they make nitrate available to plants

d. insects may improve the properties of soil, but they are also major crop pests when they feed on

plant roots

3) Soil Profiles

a. soil profile-> vertical section from the ground surface to the unaltered rock below; has parallel lay-

ers known as horizons

mature soil normally has three horizons

A horizon consists mainly of litter and humus, although most of the soluble chemicals may have

been leached away; upper most layer

B horizon has little or no organic matter but does not contain the inorganic nutrients leached from

the A horizon

C horizon is a layer of weathered and shattered rock

b. because the parental material(rock) and climate differ in various parts of the biosphere, the soil pro-

file varies according to the particular ecosystem

soils formed in grasslands tend to have a deep A horizon built up from decaying grasses over many

years, but because of limited rain, there has been little leaching into the B horizon4) Soil Erosion

a. soil erosions occur when water or wind carry soil away to a new location

deforestation(removal of trees) and desertification (increase in deserts due to overgrazing and over-

farming marginal lands) contribute to the occurrence of erosion, and so do poor farming practices in

general

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Jennifer Kim

Period 6

b. fertilizers and pesticides, carried by eroding soil into groundwater and rivers, are threatening hu-

man health so to make up for the loss of soils due to erosion, more energy is used to apply more fer-

tilizers and pesticides to crops

c. coastal wetlands are important as nurseries for many species of organisms and as protection

against storm surge from hurricanesII. Water and Mineral Uptake

a. the pathways for water and mineral uptake and transport in a plant are the same; water along with

minerals can enter the root of a flowering plant form the soil simply by passing between the porous

cell walls

Casparian strip-> a band of suberin and lignin bordering four sides of root endodermal cells; forces

water to enter endodermal cells

water an enter epidermal cells at their root hairs and then progress through cells across the cortex

and endodermis of a root by means of cytoplasmic strands within plasmodesmata; water enters root

cells when they have a lower osmotic pressure than the soil solution

b. minerals are actively taken up by plant cells

plants can take up minerals until they are many times more concentrated in the plant than in the sur-

rounding medium; following their uptake by root cells, minerals move into xylem and are transported

into leaves by the upward movement of water and along the way, minerals can exit xylem and enter

those cells that require them and some even eventually reach leaf cells

minerals must cross a selectively permeable plasma membrane when hey exit xylem and enter liv-

ing cells

c. ions cannot cross the plasma membrane because they are unable to enter the nonpolar phase of

the lipid bilayer

long been known that plant cells expend energy to actively take up and concentrate mineral ions

if roots are deprived of oxygen or are poisoned so that cellular respiration cannot occur, mineral ion

uptake is diminished; energy of ATP required for mineral ion transport, but not directly

plasma membrane pump, called a proton pump, hydrolyzes ATP and uses the energy released to

transport hydrogen ions out of the cell and so sets up an electrochemical gradient that drives positive-

ly charged ions through a channel protein into the cell; negatively charged mineral ions are transport-

ed by carrier proteins

1) Adaptations of Roots for Mineral Uptakea. rhizobium bacteria-> can fix atmospheric nitrogen; break the bond and reduce nitrogen to NH4+ for

incorporation into organic compounds ; bacteria live in root nodules and are supplied with carbohy-

drates by the host plant and then the bacteria furnish their host with nitrogen compounds

b. mycorrhizal association-> involves fungi and almost all plant root

ectomycorrhizae form a mantle that is exterior to the root, and they grow between cell walls; can

penetrate cell walls

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Jennifer Kim

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the fungus increases the surface area available for mineral and water uptake and breaks down or-

ganic matter, releasing nutrients that the plant can use and then the root furnishes the fungus with

sugars and amino acids

plants are extremely dependent on mycorrhizae; nonphotosynthetic plants use their mycorrhizae to

extract nutrients from nearby treesc. some plants have poorly developed roots or no roots at all because minerals and water are sup-

plied by other mechanisms

epiphytes-> air plants; do not grow in soil but on larger plants, which give them support; do not re-

ceive nutrients from their host

some have roots that absorb moisture from the atmosphere, and many catch rain and minerals in

special pockets at the base of their leaves