Water potential (the potential energy of water) at a given location is determined by _____.
the force of gravity on the water
the presence or absence of cell walls
physical pressure on water and the amount of solutes dissolved in it
the nature of solutes dissolved in water
answer
physical pressure on water and the amount of solutes dissolved in it
question
How do plants that are adapted to dry and salty soils tolerate the low water potential in the environment?
By increasing transpiration
By lowering the solute potential inside their cells
By wilting during daytime
By keeping their stomata closed all the time
answer
By lowering the solute potential inside their cells
question
What would happen if this cell were moved from pure water to a seawater solution?
Water would move in and out of the cell at the same rate.
Water would move into the cell.
Water would move out of the cell.
Water would not move in or out of the cell.
answer
Water would move out of the cell.
question
How would the solute potential of recently irrigated agricultural soil change from the morning to the middle of the afternoon on a hot dry summer day?
Greatly decreased solute potential over the day
No difference: agricultural soils contain high levels of salt that will not affect solute potential.
No difference: soil maintains only one solute potential.
Greatly increased solute potential over the day
answer
Greatly decreased solute potential over the day
question
What is the force behind the process known as "transpiration" in plants?
Water is absorbed into the roots through root hairs.
Water is absorbed into the leaves through stomata.
Carbon dioxide is absorbed through stomata.
Cohesion-tension
answer
Cohesion-tension
question
When water moves from soil into the vascular tissues inside the root, it can take three possible pathways. Of these, the apoplastic route is _____.
through plasmodesmata
through aquaporins on the plasma membrane
by active diffusion across the plasma membrane
between cells and through cell walls
answer
between cells and through cell walls
question
When would you observe a positive root pressure?
During hot and sunny days
During heavy transpiration
When the water potential inside the root is very low
During guttation
answer
During guttation
question
The transport of a water column up a very tall tree can be explained by _____.
cohesive and adhesive forces of the water column under evaporative tension
gravitational pull
root pressure that pushes water up
positive pressure in xylem that pushes water up
answer
cohesive and adhesive forces of the water column under evaporative tension
question
What might occur if a mutation reduced the water-repellent quality of suberin?
The apoplastic route of water travel would halt.
The transmembrane route of water travel would halt.
The symplastic route of water travel would halt.
The apoplastic route of water travel into the root xylem would be allowed.
answer
The apoplastic route of water travel into the root xylem would be allowed.
question
In which of the following conditions would transpiration be expected to be highest?
When it is raining
When stomata are closed
A cloudy humid day
A hot, dry, and windy day
answer
A hot, dry, and windy day
question
The flow of xylem from root to leaf in a tall tree is principally due to ________________.
root pressure, the buildup of pressure in a root due to its intake of water
an increase in water potential in the leaves due to evaporation
an increase in solutes in the leaf
a decrease in water potential in the leaves due to evaporation
answer
a decrease in water potential in the leaves due to evaporation
question
Some plants growing in arid climates have small leaves and thick waxy cuticles on the upper epidermis. This is an adaptation for _____.
increasing water absorption
decreasing water breakdown in photosynthesis
increasing transpiration
decreasing water loss from leaves
answer
decreasing water loss from leaves
question
The water potential of phloem sap is lowest in which of the following situations?
Near leaves in midsummer
Near roots in winter
Near roots at the start of spring
Near leaves at the start of spring
answer
Near leaves at the start of spring
question
Which of the following plant organs may act as a source for translocation of sugars inside a plant?
Young growing leaves
Mature leaves
Any non-green tissue
Developing flowers
answer
Mature leaves
question
According to the pressure-flow hypothesis, what mechanism causes the movement of phloem sap from sources to sink tissues?
Solute potential differences between source and sink
Root pressure
Pressure potential differences between source and sink
Transpirational pull from the leaves
answer
Pressure potential differences between source and sink
question
Imagine a plant without phloem. For sugars to move from one region of the plant to another, what must happen?
It would be impossible for sugars to move.
The sugars would be actively transported from cell to cell.
The sugars must be loaded into tracheids and vessel elements instead.
The sugars will passively move down a concentration gradient.
answer
The sugars would be actively transported from cell to cell.
question
According to the pressure-flow hypothesis, which direction are sucrose and water flowing in the phloem when roots are sources and leaves are sinks?
According to the pressure-flow hypothesis, which direction are sucrose and water flowing in the phloem when roots are sources and leaves are sinks? See Section 35.4 (Page 739) .
Water flows down the stem, and sucrose flows up the stem.
Water flows up the stem and sucrose flows down the stem.
Water and sucrose flow up the stem.
Water and sucrose flow down the stem.
answer
Water and sucrose flow up the stem.
question
Sieve cells have no nuclei and few organelles because _______________.
they only live a few days.
they don't have any function
they can specialize in simple, cytoplasmic based metabolism
this arrangement facilitates the efficient unimpeded transport of phloem sap
answer
this arrangement facilitates the efficient unimpeded transport of phloem sap
question
You add copper supplements to a potted plant and see normal, but not enhanced, growth. Why not?
You add copper supplements to a potted plant and see normal, but not enhanced, growth. Why not? See Section 36.1 (Page 749) .
Small amounts of copper are toxic to plants.
Not enough supplement was added.
Levels of copper in the soil were already at sufficient levels.
Copper is not an essential nutrient.
answer
Levels of copper in the soil were already at sufficient levels.
question
What makes a nutrient an essential nutrient to plants?
It is needed in large quantities by all plants.
It is part of photosynthetic structures.
It is required for photosynthesis or respiration.
It is required for normal growth and reproduction.
answer
It is required for normal growth and reproduction.
question
What defines a micronutrient?
It is needed in very minute quantities.
The effects are essential but are very small and hard to detect.
It is a very small molecule or atom.
It is needed only by microscopic organisms.
answer
It is needed in very minute quantities.
question
If you grew a plant with labeled atoms of carbon, nitrogen, hydrogen, and oxygen, which of these sources would dominate the mass of the plant?
Labeled carbon and hydrogen from nutrients in the soil
Labeled carbon and oxygen from carbon dioxide
Labeled nitrogen and hydrogen from nutrients in the soil
Labeled oxygen and hydrogen from water
answer
Labeled carbon and oxygen from carbon dioxide
question
The ability of plant roots to penetrate through soil is determined by which of the following?
Soil's water-holding capacity
Soil pH
Soil nutrient levels
Soil texture
answer
Soil texture
question
Moderate soil acidity means there are protons in the soil. Protons increase the availability of nutrients to plants by _____.
promoting cation exchange
leaching away cations from soil after heavy rains
promoting cellular respiration in root cells
increasing cation binding to soil particles
answer
promoting cation exchange
question
How do plants influence the uptake of cations such as magnesium involving cation exchange?
By releasing nutrients
By releasing CO2
By releasing water
By releasing electrons
answer
By releasing CO2
question
Root hairs absorb nutrients from soil against the nutrient concentration gradient. To achieve this, root hairs use _____.
facilitated diffusion
proton pumps
direct diffusion
osmosis
answer
proton pumps
question
Anions are repelled, not attracted, by the electric gradient established by the proton pumps. How do plants absorb anions?
By cotransport proteins
By diffusion
By vacuoles
By active transport proteins that require ATP
answer
By cotransport proteins
question
How do proton pumps impact potassium uptake?
They increase positive charge within the cell to attract potassium ions.
Protons bind to potassium to move through cation channels.
They decrease positive charge within the cell to attract potassium ions.
They increase space within the cell to make room for potassium ions.
answer
They decrease positive charge within the cell to attract potassium ions.
question
How would poisoning proton pumps impact anion uptake?
It would decrease the uptake of anions by passive diffusion.
It would have no effect; most anions utilize ATP-driven pumps for uptake.
It would increase the uptake of anions via cotransport with protons.
It would decrease the uptake of anions via cotransport with protons.
answer
It would decrease the uptake of anions via cotransport with protons.
question
A molecule binds and blocks a potassium channel in a plant cell membrane. What would be its effects?
Potassium uptake would be blocked because the proton pump would no longer work.
Potassium uptake would be unchanged since uptake is by active transport by pumps.
Potassium uptake would be blocked since potassium ions enter cells through facilitated diffusion.
Potassium uptake would be unchanged since potassium readily crosses through the cell membrane's lipid bilayer.
answer
Potassium uptake would be blocked since potassium ions enter cells through facilitated diffusion.
question
In which environment do you least expect to find nitrogen-fixing bacteria?
Where nitrogen is rare, while other essential nutrients are plentiful
Where nitrogen and other essential nutrients are rare
Where nitrogen and other essential nutrients are plentiful
Where nitrogen is plentiful, while other essential nutrients are rare
answer
Where nitrogen is plentiful, while other essential nutrients are rare
question
What is biological nitrogen fixation?
The conversion of nitrogen gas into ammonia, nitrate, or nitrite by microbes
The absorption of nitrate ions by plant roots
The conversion of nitrogen gas into ammonium ions inside root cells
The exclusion of excess nitrate ions from plant roots
answer
The conversion of nitrogen gas into ammonia, nitrate, or nitrite by microbes
question
Legume plant roots are colonized by _____ to form root nodules.
epiphytes
ectomycorrhizae
rhizobia
node factors
answer
rhizobia
question
If a plant grows on another plant and depends on this plant for all its nutritional needs, including sugars, nutrients, and water, it can most specifically be called a(n) _____.
epiphytic plant
symbiotic plant
parasitic plant
infectious plant
answer
parasitic plant
question
Carnivorous plants trap and digest insects to overcome _____
nitrogen deficiency in low-nitrogen soils
lack of water in arid environments
excess digestive enzyme activity inside the cells
infectious diseases transmitted by insects
answer
nitrogen deficiency in low-nitrogen soils
question
Where would you add bars to the small tree to indicate the evolution of multicellularity?
Within the branch that includes both animals and choanoflagellates
One on each of the branches of animals, choanoflagellates, and fungi
At the base of tree before the split into the fungi and animal/choanoflagellate clades
Within the branch of Animalia and within the branch of fungi
answer
Within the branch of Animalia and within the branch of fungi
question
In your body, the inside "tube" within a "tube" is derived from the _____.
mesoderm
ectoderm
endoderm
epidermis
answer
endoderm
question
Which of the following is evidence that supports the hypothesis that sponges are the sister group to all other animals?
Sponges share many genes in common with other animals.
Sponges share many characteristics with choanoflagellates.
Some sponges have a true epithelium.
Sponges contain microRNAs.
answer
Sponges share many characteristics with choanoflagellates.
question
In your body, the outside "tube" that surrounds a cavity and inner "tube" is derived from the ________.
mesoderm
endoderm
ectoderm
muscle
answer
ectoderm
question
Which phylum includes the most basal lineages of animals?
Ctenophora
Chordata
Cnidaria
Porifera
answer
Porifera
question
Why was the evolution of a coelom a critically important innovation for animals?
The coelom made it possible for animals to colonize land.
The coelom separates vertebrates from invertebrates.
The coelom gives rise to a complex nervous system.
The coelom can act as a hydrostatic skeleton.
answer
The coelom can act as a hydrostatic skeleton
question
The basic bilaterian body form plan can be thought of as simply _____.
a series of boxes
a tube within a tube
several joined rings
many concentric circles
answer
a tube within a tube
question
What is the relationship between choanoflagellates and animals?
Choanoflagellates are a phylum of animals.
Choanoflagellates are a basal lineage among the animals.
Choanoflagellates are considered an outgroup to the animal lineages.
Choanoflagellates are ancestral to animals.
answer
Choanoflagellates are considered an outgroup to the animal lineages
question
The phyla Porifera, Cnidaria, and Ctenophora are ________.
very similar when it come to movement
very similar when it comes to feeding
the most recent of all animal lineages
the most ancient of all animal lineages
answer
the most ancient of all animal lineages
question
Key traits in animals
answer
1. they are multicellular eukaryotes
2. they move under their own power
3. except sponges, they have both nerve (neurons) and muscle cells.
4. they are heterotrophs meaning they rely on other organisms for food.
5. they are the largest predators, herbivores, and detrivores.
question
3 Germ Layers
answer
1. endoderm gives rise to the lining of digestive track. (gut, anus, etc.)
2. mesoderm gives rise to circulatory system, muscles, and internal structures such as bone and organs.
3. ectoderm gives rise to skin and nervous system
question
diploblasts
answer
have two germ layers- ectoderm, and endoderm.
cnidaria, and ctenophora
question
triploblasts
answer
have 3 germ layers- endoderm, mesoderm, and ectoderm.
all animals other than cnidarians and ctenophores.
all triploblasts have cephalization + bilateral symmetry = very successful.
question
radial symmetry
answer
at least 2 planes of symmetry.
cnidarians, ctenophores, and sponges.
all diploblasts are radially symmetrical
have nerve cells organized into nerve net
question
bilateral symmetry
answer
single plane of symmetry with long narrow bodies.
most other animals.
all triploblasts (except echnioderms) are bilaterally symmetrical
a tube within a tube
question
cephalization
answer
a true head where structures for feeding, sensing, & processing information are concentrated.
locating & capturing food is more efficient when movement is directed by head(brain) & powered by bilateral body
question
tube within a tube
answer
inner tube: gut with mouth & anus on either end
outer tube: forms nervous system & skin
mesoderm (in between): forms circulatory system, organs, and muscles.
question
coelom
answer
enclosed, fluid filled body cavity between the tubes.
creates a container for circulation of oxygen & nutrients.
creates hydrostatic skeleton (allows soft bodied animals to move without limbs or fins) which gave organisms the ability to move in search of food.
question
coelomate
answer
a triploblast with a coelom.
question
acoelomate
answer
a triploblast without a coelom.
question
pseudomate
answer
a triploblast that retains a coelom without a mesodermal lining.
1. dermal tissue system
2. ground tissue system
3. vascular tissue system
question
epidermal cells
answer
secrete cuticle (hydrophobic waxy layer that cover shoots, protecting leaves, & reducing water loss
question
trichomes
answer
hair like appendages, various functions:
1. keep plant cool & protect against damaging sunlight
2. minimize water loss
3. regulate gas exchange in shoots
4. provide barbs or toxins to protect from herbivores
question
three cell types in the ground tissue system
answer
1. parenchyma
2. collenchyma
3. sclerenchyma
question
parenchyma
answer
spherical, thin walled, living- metabolizing tissue
located throughout the plant
functions: photosynthesis & respiration, storage, regeneration
most abundant & versatile plant cells. primary site of photosynthesis in leaves. mainly store starch in roots
many are totipotent (can continue to divide & develop into a mature plant) which helps in repair of wounds & reproduction.
question
collenchyma
answer
elongated cells with unevenly thickened cell walls, alive at maturity
located beneath the epidermis in young stems & in leaf veins
functions: flexible support system
have primary cell walls that can continue to expand & lengthen as they provide flexible support to growing regions of shoots.
question
sclerenchyma
answer
primary and secondary cell walls, dead at functional maturity.
located at fibers in wood, bark, leaves, stems and also in sclereids in fruits and seeds
function is to provide structural support
secondary cell wall consists of tough and rigid lignin as well as cellulose.
question
xylem
answer
made up of tracheids & vessel elements
water conducting cells; move water through plant
perforations & pits found on sides & ends assist in conduction of water
question
phloem
answer
function to transport sugars, amino acids, hormones, and toxins through specialized parenchyma cells called sieve tube elements
question
sieve tube element
answer
long, thin cells that are alive at maturity.
have perforated ends called sieve plates, lack nuclei, chloroplasts, and other organelles.
connected by plants. have few organelles
question
companion cells
answer
connected to the sieve-tube element via plasmodesmata.
provide sieve-tube elements with the molecules that keep them alive.
help to load and unload carbohydrates from the sieve-tube elements.
question
meristems
answer
populations of undifferentiated cells that retain ability to undergo mitosis.
question
apical meristems
answer
found at tip of each root & shoot; responsible for primary growth.
question
root cap
answer
protects apical meristem; senses gravity to determine growth direction & secretes lubricant.
question
primary root system organization
answer
root cap
zone of cellular division
zone of cellular elongation
zone of cellular maturity
question
secondary growth
answer
increases width of roots & shoots, increasing amount of conducting tissue available & providing increased structural support
produces wood & occurs in species that have cambium + apical meristems
question
cambium
answer
forms cylinder that runs length of root, trunk, or branch.
site of secondary growth
question
primary growth
answer
makes the plant taller ad the roots longer.
leads to non-woody, herbaceous stems
question
3 types of primary meristematic cells
answer
protoderm gives rise to dermal tissue or epidermis
ground meristem gives rise to ground tissue system
procambium gives rise to the vascular tissue system
question
different types of cambrium
answer
vascular cambium and cork cambium
question
vascular cambria
answer
secondary meristem located between the primary xylem and primary phloem
produces secondary xylem and phloem.
produces conducting parenchyma cells in rays to transport water and nutrients laterally through large stems
question
secondary phloem
answer
functions in sugar transport and forms the outer layer of tree trunks (bark)
question
secondary xylem
answer
functions in water transport and makes up wood
question
cork cambria
answer
secondary meristem, located near the perimeter of the stem that REPLACES the epidermis and forms bark.
produces cork cells (that replace the original epidermal cells) with lenticels (opening that allow gas exchange)
question
transpiration
answer
occurs when 2 conditions are met:
(1) stomata are open, usually during the day when photosynthesis is occurring.
(2) the air in the environment is drier than the air inside the leaves
plants replace the water losst by transpiration with water that is absorbed by the roots. PASSIVE; does not require ATP.
question
water potential
answer
the potential energy that water has in a particular situation compared to the potential energy of pure water at atmospheric pressure at the same temperature.
water always flows from areas of high water potential to areas of low potential.
measured in units called megapascals
question
water potential gradient
answer
water potential gradient between leaves and roots
usually high potential in soil; low potential in air
to move UP plant water moves DOWN water-potential gradient that exists between soil, tissues, & atmosphere
question
3 pathways water is transported through root cortex
Why is the transport of phloem sap considered an active process?
Transpiration is driven by the energy in sunlight.
Energy is used to transport sucrose into companion cells near sources, against a concentration gradient.
Phloem sap is able to move down through a plant with the force of gravity.
The manufacture of sucrose via photosynthesis is driven by the energy in sunlight.
answer
Energy is used to transport sucrose into companion cells near sources, against a concentration gradient.
question
Salt is used to melt snow and keep roads clear during the winter in many cities. Land adjacent to de-iced roads often ends up with a high concentration of salt in the soil. Explain why plants growing near salted roads may appear wilted in the spring.
answer
The high concentration of solutes in the soil, formed from the salt and melting snow, would result in a low water potential in the soil. This would make it difficult for plants growing in that region to absorb water.
question
symplastic route
answer
is inside the plasma membranes.
the symplast consists of the cytosol and the continuous connections through cells via plasmodesmata.
question
transmembrane route
answer
is based on flow through aquaporin proteins- water channels located in the plasma membranes of many cells.
Some water may also diffuse directly across plasma membrane.
question
apoplastic route
answer
is outside the plasma membranes.
the aploplast consists of cel walls, which are porous, and the spaces that exist between cells.
water moving along the apoplastic route must eventually pass through the cytoplasm of the endodermal cells before entering xylem
question
casparian strip
answer
a narrow band of wax secreted from the the tightly packed endodermal cells
composed mainly of suberin
important because it blocks the apoplastic route by preventing water from moving through the walls of the endodermal cells & into vascular tissue.
for water & solutes to get to vascular tissue they must move through the cytoplasm of an endodermal cell.
ESSENTIAL for root pressure to develop
question
suberin
answer
forms a waterproof barrier where endodermal cells contact each other.
(makes up casparian strip)
question
endodermal cell
answer
acts as gatekeepers by regulating what enters the xylem
question
root pressure
answer
positive pressure of xylem sap in the vascular tissue of roots. generated during the night as a result of the accumlation of ions from the soil and subsequent osmotic movement of water into the xylem.
question
guttation
answer
excretiojn of watter droplets from plant leaves.
caused by root pressure
question
capillary action
answer
movement of water up a narrow tube.
occurs in response to 3 forces:
1. adhesion
2. cohesion
3. surface tension
question
adhesion
answer
molecular attraction among unlike molecules.
through hydrogen bonding
water interacts with a solid substrate (like glass or walls of capillary tube) and water molecules are pulled upwards as they bond to eachother and adhere to the side of the tube.
question
cohesion
answer
the molecular attraction among like molecules such as the hydrogen bonding that occurs in water molecules.
the upward pull by adhesion is transmitted to the rest of the column, which rises against the pull of gravity.
question
meniscus
answer
concave surface boundary
forms at most air-water interfaces.
form because adhesion and cohesion pull water molecules along side tube, while gravity pulls the water surface down in the middle
question
surface tension
answer
a force that exists among water molecules at an air-water interface.
question
cohesion-tension theory
answer
water is pulled from roots to the tops of trees along a water-potential gradient, via forces generated by transpiration at leaf surfaces.
relies on cohesion and tension
question
transmission of pulling force from leaf surface to the root
answer
is possible because
1. xylem forms a continuous network from roots to leaves so there are continuous columns of water throughout the plant
2. all of the water molecules are bonded to eachother through hydrogen bonds (cohesion)
question
bulk flow
answer
a mass movement of molecules along a pressure gradient
question
trichomes
answer
hairlike extensions of epidermal cells shield pits from the atmosphere
slow loss of water vapor from stomata by creating a layer of still air surrounding the somata
question
adaptations for limiting water loss
answer
needlelike leaves generally expose less surface area. present in species adapted to water limited habitats
broad leaves with large surface area. present in species adapted to wetter habitats.
question
CAM & C4 photosynthesis
answer
allow plants to increase CO2 concentrations in their leaves and conserve water
CAM plants open stomata at night to store the CO2 that diffuses into their tissues by adding carbon dioxide molecules to organic compounds
can grow with stomata closed during day
question
translocation
answer
movement of sugars by bulk flow in multiple directions throughout a plant- specifically from sources to sinks
question
source
answer
is a tissue where sugar enters the phloem
during growing season: mature leaves & stems that are producing sugar in excess of own needs
early in growing season: storage cells in roots and stems
question
sink
answer
a tissue where sugar exits the phloem
during growing season: apical meristems, lateral meristems, developing leaves, flowers, developing seeds & fruits, and storage cells.
early in growing season: developing leaves
question
sugar transport
answer
mature leaves acting as sources send sugar to tissues on the same side of the plant.
leaves on upper part of stem send sugar to apical meristems but leaves on the lower part of the plant send sugar to roots.
question
pressure flow hypothesis
answer
states that events at source tissues and sink tissues create a pressure potential gradient in phloem.
The water in phloem sap moves down this pressure gradient and sugar molecules are carried along by bulk flow
question
passive transport
answer
when ions or molecules move across a plasma membrane by diffusion- along their electrochemical gradient.
doesnt require energy
question
two types of membrane proteins
answer
facilitate the passive diffusion of specific ions or molecules
1. channel proteins form pores that selectively admit certain ions
2. carrier proteins undergo a conformational change that transports specific molecules across the lipid bilayer
question
facilitated diffusion
answer
responsible by channels and carriers
question
active transport
answer
ions or molecules move across a plasma membrane against their electrochemical gradient.
cells must expend energy in form of ATP to move solutes to unfavorable direction
question
pumps
answer
proteins that change shape when they bind ATP or phosphate group from ATP.
As they move pumps transport ions or molecules against electrochemical gradient
question
cotransporters
answer
a transmembrane protein that facilitates diffusion of an ion down its previously established electrochemical gradient and uses the energy of that process to transport some other substance in the same/opposite direction against its gradient.
aka secondary transporter
question
two types of cotransporters
answer
1. symporters: transport solutes against a concentration gradient, using energy released when a different solute moves in the same direction along its electrochemical gradient.
2. antiporters: the solute being transported against its concentration gradient moves in the direction opposite that of the solute moving down its concentration gradient.
question
essential nutrient
answer
element or compound required for normal growth and reproduction - plant cannot complete life cycle without it
17 are essential. 3 are: carbon, hydrogen, oxygen. others are mineral nutrients
question
macronutrients
answer
elements that plants need relatively large quantities of from soil
very important:
nitrogen, phosphorus, potassium
question
limiting nutrients
answer
availability limits plant growth
question
micrnonutrients
answer
nutrients that are only needed in small quantities
need small amounts, but still necessary.
question
mobile nutrients
answer
elements that are readily transported from older leaves to younger leaves when they are in short supply- so older leaves deteriorate first when these elements are scarce
question
immobile nutrients
answer
iron or calcium
stay in older leaves. when they are in short supply younger leaves are the first to show deficiency symptoms
question
hydroponic growth
answer
takes place in liquid cultures, without soil, so researches can precisely control availability of each nutrient.
question
weathering
answer
the forces applied by rain, running water, temperature changes, and wind which continually breaks tiny pieces off large rocks.
question
humus
answer
decaying organic matter
question
texture
answer
proportions of gravel, sand, silt and clay
question
importance of texture
answer
1. affects the ability of roots to penetrate and obtain water & nutrients, as well as anchor & support the plant body
2. affects a soil's ability to hold water and make it available to plants. (water usually sticks to clay & silt, but runs through sand & gravel)
3. texture and water content dictate the oxygen available for cellular respiration. oxygen used by root cells is found in air pockets among soil particles.
question
soil erosion
answer
occurs when soil is carried away from a site by wind or water. occurs naturally like when rivers cut away at their banks and carry material downstream.
question
sustainable agriculture
answer
techniques that maintain long-term soil quality and productivity.
farmers can reduce soil loss by:
1. planting rows of trees as windbreaks
2. using techniques that minimize amount of plowing and tilling needed to control weeds
3. planting crops in strips that follow the contour of hillsides
question
what factors affect nutrient availability
answer
elements required for plant growth are found in the soil as ions.
question
type of ions present in soil
answer
1. anions
2. cations
question
anions
answer
ions with negative charges
usually dissolve in soil water, interact with molecules via hydrogen bonding.
exception: phosphate ions, can form insoluble complexes with iron aluminum, calcium, or other positively charged cations
since exist as solutes they are readily available for plant absorption.
question
leaching
answer
loss of nutrients via the movement of soils.
happens to anions.
question
cations
answer
ions with positive charges.
dissolve in soil water but are not as readily available as anions.
interact with negative charges found on 2 types of soil particles:
1. organic matter that is rich in negatively charges organic acids
2. the surfaces of clay particles that are rich in mineral anions
resist leaching but difficult for plants to absorb because of strong bonds to clay
question
role of soil ph
answer
soils with low pH have a relatively high concentration of hydrogen ions and are acidic
soils with high pH contain relatively few hydrogen ions and are basic or alkaline.
MOST plants thrive in soils with neutral pH. (6-7)
question
cation exchange
answer
release of cations, such as magnesium and calcium from soil particles, by protons in acidic soil water. released cations are available for uptake by plants
occurs when protons or other soluble cations bind to negative charges on soil particles and cause bound cations (magnesium or calcium) to be released from the soil.
question
nutrient uptake
answer
most occurs just above growing root tip in zone of maturation. the root hairs of epidermal cells dramatically increase surface area available for nutrient and water absorption.
root hairs are so efficient that they create a zone of nutrient depletion.
question
electrochemical gradient
answer
established by proton pumps. drives the import of essential ions into cells.
these proteins are found in the plasma membranes at root of epidermal and cortex cells.
proton pumps in roots transport protons to the exterior of cells.
question
proton pumps
answer
uses energy in ATP to accumulate protons outside of the cell
leads to concentration gradient that favors proton movement into the cell
leads to voltage or charge difference across the membrane; exterior more positive.
electrical gradient produced by proton pumps is enough to attract cations into cell despite concentration gradients
question
membrane potential
answer
a difference in electric charge across a cell membrane; form of potential energy
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