topic nine Flashcards
what is transpiration
the loss of water vapour through the leaves, stems, and other above-ground parts of the plant.
stomatta purpose
opening and closing of guard cells
spongy mesophyll allows
large sa and moist surface necessary for gases to be exchanged
cross section of a leaf
why is it importnant to lower the conc of oxygen gas during photosynthesis
it is a competitive inhibitor of a key enzyme rubisco
transpiration occurs
mainly through open stomata
what does a CAM metabolsim do
store carbon dioxide at night so that stoamta can be close during the day
why are stomata closed at night
to conserve water
what does the xylem transport
water and dissolved minerals from the roots to all other parts of the plant
When stomata are open, the water that is lost must constantly be replaced or the plant will…
dry out
what are the walls of xylem strengthened with
ligin, a complex polymer that binds with cellulose to provide great strength and rigidity to the cell walls. The woody tissue made from lignified xylem can support plants many metres tall. Lignin also allows the xylem vessels to withstand the forces involved in transpiration without collapsing. Lignin can be deposited throughout the cell walls or as rings or spirals inside the xylem vessels.
structure of xylem
dead at maturity
hollow narrow tubes
structure of primary xylem vessel
how is transpiration passive
The cellulose in mesophyll cell walls is hydrophilic and water adheres to it, creating a film of water on the surface of the cells. When water vapour diffuses out of the stomata, the internal air spaces of the leaf become less humid. Water then evaporates from the moist mesophyll cell walls into the air spaces. water is cohesive so pulls other water up
Lignin provides strength to cell walls by binding with
cellulose.
the pathway most water follows from roots to the outside atmosphere?
Root xylem → stem xylem → leaf xylem → mesophyll cell wall → leaf air spaces → water vapour lost to the atmosphere.
what do root hair cells have that actively transports mineral ions from the surrounding water into the cytoplasm of the cell against the conc grad
protein pumps
what allows water to move into the plant cells via osmosis
the high conc of mineral ions in the cytoplasm whcih can reach 100x the conc outside the cell
Water uptake through osmosis in root hairs.
what are xerophytes
plants that have adapted to live in conditions where liquid water is difficult ot obtain
adv of thick waxy cuticle in dry conditions
Reduces non-stomatal transpiration rate because the cuticle is hydrophobic and creates a barrier to prevent water loss.
adv of fewer stoamta in dry conditions
Reduces transpiration rate by having fewer openings in the leaf.
adv of stomata in sunken pits
Reduces transpiration rate by allowing moisture (humidity) to build up near stomata.
adv of fine hairs along underside of leaf
Reduces transpiration rate by retaining a layer of moisture near the stomata.
adv of CAM physiology (crassulacean acid metabolism)
Reduces transpiration rate enormously because stomata close during the day. Stomata open at night to collect and store carbon dioxide, when darkness and cooler temperatures reduce evaporation. During the day, pre-collected carbon dioxide allows photosynthesis to occur without water loss.
adv of Reduced air spaces in leaf mesophyll
Reduces transpiration rate due to reduced surface area for evaporation.
adv of Few/small leaves, or photosynthesis moved into stem
Reduces transpiration rate because there is reduced surface area for light to strike and water to evaporate.
adv of Curled or rolled leaves in dry coniditons
Reduces transpiration rate because there is reduced surface area for water loss and there can be production of humid areas by the stomata.
adv of water storage tissue in dry condiitons
Increased water storage when water is available. Succulent plants have tissues in stems or leaves adapted to store large amounts of water; other plants store water in tubers.
adv of deep, highly branched roots in dry cond
Increased ability to take up water because deep roots may reach a lower water table beyond the dry soil. Branched roots provide increased surface area for water absorption.
what are halophytes
plants that have adapted to grow in areas with high salinity, such as along an ocean shoreline or in certain swamps and marshes.
adv of salt storage in vacuoles in saline cond
Compartmentalises salt in vacuoles, thus protecting cellular organelles and enzymes from damage by high salt concentration.
adv of high conc of org solutes in saline environemtns
Increases osmolarity by having a high concentration of sugars and other solutes, thus water can still enter by osmosis.
adv of Salt storage glands in leaf in saline cond
Accumulates salt in a limited area by filling the salt glands until they release salt crystals onto the leaf surface where they will fall off or be dissolved in rain.
adv of leaf abcission in saline cond
Removes salt by breaking off leaves with toxic levels of salt and letting them fall from the plant.
adv of Selectively permeable membrane in root cells in saline cond
Excludes salt by having no ion channels to allow passage of Na + and Cl - , and/or has active transport pumps to remove the ions.
adv of xerophytic adaptations in saline cond
Conserves water by having few stomata, water storage tissue, thick cuticle and other adaptations listed in Table 1 .
internal factors affecting rate of transpiration
Root to shoot ratio
Surface area of leaves
Number of stomata per unit leaf area
Leaf structure, for example, the presence of hair or thick waxy cuticle.
external factors affecting rate of transpiration
Light
Wind
Temperature
Humidity
Water availability.
effect of light on transpiration
As light intensity increases , the rate of transpiration increases .
Stomata are closed in the dark, but as light intensity increases stomata open and allow water vapour to escape from the air spaces of the leaves. Therefore, bright sunlight increases the rate of transpiration. Photons also provide energy for evaporation .
efect of wind on transpiration
As wind velocity increases , the rate of transpiration increases .
In low wind conditions, the air underneath leaf becomes increasingly humid. This reduces the water vapour concentration gradient from the leaf’s air spaces to the outside air, and so reduces the rate of transpiration. As wind speed increases, the humid air is blown away more quickly and is replaced by drier air, which increases the rate of transpiration due to the increased concentration gradient for water vapour. However, if the wind speed reaches a critical level, the stomata may close to reduce the rate of transpiration.
effect of temperature on transpiration
As temperature increases, the rate of transpiration increases .
Higher temperatures provide more energy for evaporation of water from the cell walls and decrease the humidity of the external atmosphere. However, if the temperature gets too high for enzymes to function efficiently, the stomata may close and the transpiration rate may fall.
effect of humidity on transpiration
As humidity increases , the rate of transpiration decreases .
Humidity refers to the percentage of water vapour present in the atmosphere. When the air surrounding a leaf is dry (low humidity), the concentration gradient for diffusion of water vapour from the air spaces within the leaf to the outside is steep and transpiration occurs quickly.
phloem consists of coumns of living cells called
sieve tubes
each cell in a sieve tube is called a
sieve element
what do sieve elements contain
limited cytoplasm with a few mitochondria and other organelles, but the nucleus, vacuole, cytoskeleton, and many other structures are broken down.
how are sieve cells and companion cells connected
pores called plasmodesmata
what are sieve elements filled with
phloem sap
what is phloem sap
combination of water, dissolved sucrose nd other carbs, amino acids, proteins and mienrals and plant hormones
phloem structure
function of reduced organelles in sieve elements
Absence of cell structures (including nucleus, cytoskeleton, golgi, ribosomes and vacuole) frees the lumen to conduct a large volume of sap
function of Companion cells in sieve elemtns
Metabolic support cells (containing all the standard organelles) provide biomolecules (e.g. enzymes) necessary to maintain life functions in the sieve elements
function of plasmodesmata in sieve elements
Openings between the sieve elements and companion cells allow communication and support from companion cells
function of sieve plate in sieve elements
Pores through the horizontal cells that join sieve elements allow sap to flow freely
function of cell membrane in sieve elements
Presence of a fully functional cell membrane in sieve elements that contains specialised protein pumps provides the structures needed to control the composition of sap
what do sources do
produce more sugars than needed
what do sinks do
need more sugars than producded
wehre are the xylem and phloem in a dicot stem
next to eachother
The phloem is closer to the surface of the stem. The phloem tubes are narrower than the xylem.
where are the yxlem and phloem in monocot stems and roots
In monocot roots, the xylem is not an ‘X’ shape but rather forms a ring slightly inside the phloem ring. In monocots, vascular bundles are scattered throughout the stem rather than forming a ring, although the phloem still always faces the outside.
structure of apical meristem
what will absorbing a red photon do
convert Pr to Pfr
how is Pfr converted to Pr
Pfr slowly and spontaneously changes to Pr in darkness. Pfr can also be rapidly converted to Pr by exposure to far-red light (photons with a wavelength of about 730 nm).
labelled structure of a seed
