Adaptations for transport: Plants Flashcards
write the word equation for photosynthesis
carbon dioxide + water to glucose + oxygen
what is different about plants’ transport systems compared to animals?
they have two separate transport systems instead of transporting water mineral ions and organic molecules together
how is water and mineral ion transported in plants?
photosynthetic cells in the leaf need water and mineral ions which are available only in the soil so the transport of water and mineral ions from the roots to the leaves is essential
these molecules are transported upwards in hollow tubes formed by dead cells called xylem tissue
how are photosynthates transported?
glucose produced during photosynthesis is used to make sucrose and amino acids
these molecules must be moved from the leaves to other organs of the plant
photosynthates are transported upwards and downwards in phloem tissue (bi-directional movement)
where is the vascular tissue in the leaf?
vascular bundle (xylem and phloem) arranged as a vein or midrib
where is the vascular tissue found in the stem?
vascular bundles arranged around the periphery of the stem
where is the vascular tissue found in the root?
arranged in the centre of the root and together with the endodermis and pericycle is called the stele. there are no vascular bundles in the root
how are mineral ions like NO3- and water transported to the root?
they are actively transported from the soil to the root which lowers the water potential inside the root hair cell so water also enters by osmosis
where is the energy for active transport coming from to aid the transport of mineral ions?
oxygen enters the roots from the soil to be used in aerobic respiration, providing ATP for active transport
why do waterlogged soils struggle to uptake ions to roots?
they lack oxygen
how does the uptake of water and mineral ions happen across the root?
they travel through the root cells of the cortex to the endodermis down a water potential gradient
what are three routes of the transport of water across the root?
symplast
apoplast
vacuolar
define the apoplast pathway
water is taken up by the root hair cell and moves across the cortex by cohesion via the cell walls
define the symplast pathway
water moves from the cytoplasm of one cell to the next by osmosis via plasmodesmata
define the vacuolar pathway
water can move via the cytoplasm and vacuoles
describe the route of water and mineral ions into the xylem. there are 6 points
the cell walls of all endodermal cells contain a Casparian strip made of a waxy substance called suberin that is impermeable to water molecules and mineral ions, meaning the apoplast pathway is blocked at this point
water and mineral ions from the apoplast pathway are forced across the cell membrane into the symplast pathway
active transport is needed to move ions into the cytoplasm of the endodermal cells
mineral ions then diffuse in the pericycle and then into the xylem
therefore the only way that water and mineral ions can pass through the endodermis to the pericycle and into the xylem is by the symplast pathway
water follows by osmosis down a water potential gradient
why is the Casparian strip beneficial to the plant?
it gives the plant greater control over which ions can enter the xylem and are transported to the rest of the plant
how is hydrostatic pressure generated in the root and what effect does it have on water?
when water moves from the endodermal cells of the root and into the xylem by osmosis, this generates hydrostatic pressure and forces water a small distance up the xylem
how would cyanide result in a reduction in root pressure? reference the Casparian strip
Casparian strip stops apoplast pathway
cyanide is a respiratory inhibitor
movement of ions into the xylem requires active transport
water potential in the xylem is not reduced so there is less root pressure
why does the plant need to control the entry of mineral ions into the xylem?
some mineral ions are toxic
how does the plant ensure toxic ions can’t enter the cells?
Casparian strip forces ions to cross the membrane into the symplast pathway by active transport and the Casparian strip is very impermeable
also there are no transport proteins in the membrane
why do plants need to absorb nitrates from the soil?
required for synthesis of amino acids and nucleotides(DNA, RNA, ATP)
nitrogenous base and proteins
name some other mineral ions absorbed by plants and state their uses
potassium ions for opening stomata
magnesium ions for constituent of chlorophyll
PO4 3- or phosphate ions for synthesis of phospholipids and constituent of nucleotides
calcium is a structural component in plant cell walls
give 2 features of root hair cells that are adaptations for uptake and mineral ions
large surface area for absorption of water and mineral ions
large numbers of mitochondria to generate ATP for active transport of ions
define transpiration
the evaporation of water from inside the leaves through the stomata and into the atmosphere
describe the transpiration stream
water is absorbed by the root hair cells by osmosis
water moves through the root tissue into the xylem and is transported up the xylem in the plant stem to the leaf by cohesion
water is transported by osmosis from the xylem in the leaf to the cells of the spongy mesophyll where it evaporates from the surface of the cells into the air spaces
water vapour then diffuses from the air spaces out of the leaf through the stomata down a water potential gradient
define cohesion
water molecules are attracted to each other by hydrogen bonds
define adhesion
water molecules are attracted to the hydrophilic lining of the lignified xylem vessel walls
how does water travel up the xylem to the leaves of the plant using cohesion tension theory? (transpiration pull)
as water vapour diffuses out of the stomata of the leaf by transpiration, water molecules are drawn up from behind to replace those lost
water molecules are drawn across the leaf and up the xylem and this is possible because of cohesion between water molecules due to hydrogen bonds and adhesion between water molecules and the xylem vessel walls
this upward movement of water creates tension on the xylem vessel walls
what are two other processes that help water move up the xylem a small amount?
capillarity - the forces of adhesion and cohesion allow water molecules to rise up the narrow tubes for a short distance which is useful in small plants
root pressure
why is capillarity not useful in large trees?
it’s useful for small plants and not in larger plants because after a short distance capillary action is opposed by gravity
what increases the rate of respiration?
any factor that increases the water potential gradient between the water vapour in the leaf and surrounding atmosphere
what are four factors the rate of transpiration is increased by?
temperature
wind speed
humidity
light intensity
explain each of the 4 factors that increase rate of transpiration
temperature -
rise in temperature increases the kinetic energy of the water molecules and increases the rate of evaporation and diffusion of the water vapour into the atmosphere
water potential is also lower in high temperatures which increases the water potential gradient
wind speed -
still air results in a layer of water vapour around the stomata of a leaf
this reduces the water potential gradient between the outside and inside of the leaf
air movement blows away the diffusion shell and increases the rate of transpiration from the leaf
humidity -
water potential gradient inside and out of the leaf decreases when there is more water vapour in the atmosphere
usually, there is a steep water potential gradient between the inside of the leaf and the atmosphere as the leaf is saturated with water vapour
light intensity -
light causes stomata to open to allow gas exchange for photosynthesis
what is a potometer?
this apparatus measures the rate of uptake of water by the shoot which indicates the rate of transpiration
give the labels for the set up of the potometer
beaker with water
air bubble in capillary tube
graduated scale in mm along the capillary tube
tap
reservoir of water
bung
plant cutting/leafy shoot
why is the rate of uptake only an estimate of the transpiration rate?
some water is used by the plant as a reactant in photosynthesis