Plant organisation 2.0 Flashcards
what do phloem cells consist of?
living cells
how are the sieve tubes specialised for transport?
they have no nuclei
describe the structure of a sieve tube
-each sieve tube has a perforated end so its cytoplasm connects one cell to the next.
how are sucrose and amino acids translocated within the sieve tubes?
through their cytoplasm
what does transport of substances in the phloem require?
energy
what do the companion cells do to provide the energy needed to transport substances?
attach to each sieve tube to provide this energy
what type of transport process happens within the xylem and phloem?
xylem = physical/ passive process
phloem = active process
what happens to water when plants open their stomata to let CO2 in? (2)
what is this process called?
-water on the surface of spongy and palisade mesophyll cells evaporates
-and diffuses out of the leaf.
-transpiration
where is water drawn from to replace the water lost from the leaves?
the xylem
what is between the water molecules which makes them strongly attracted to one another?
because of what?
strong cohesion between the molecules
-because of hydrogen bonding
describe the growth of root hair cells
they grow between soil particles and absorb water and minerals from the soil.
which 4 factors affect transpiration?
temperature
humidity
air movement
light intensity
what would need to happen to the temperature in order to increase transpiration rate?
increase it
why would an increase in temperature increase transpiration rate? (3)
Increases molecular movement so that:
-more water molecules evaporate from cell surfaces
-the rate of diffusion of water molecules from the leaf is increased
what would need to happen to the humidity in order to increase transpiration rate?
decrease it
why does a decrease in humidity increase transpiration rate? (2)
-reduces the concentration of water molecules outside the leaf
-diffusion of water from the leaf increases
what would need to happen to the air movement in order to increase transpiration rate?
increase it
why does an increase in air movement increase transpiration rate?
-removes water vapour from leaf surfaces
-more water diffuses from the leaf because a high concentration gradient is maintained
what would need to happen to the light intensity in order to increase transpiration rate?
increase it
why does an increase in light intensity increase transpiration rate?
-Increases the rate of photosynthesis
-stomata open so that water diffuses out of the leaf
what can the stems of cacti store which makes them well adapted to their environment?
they can store water
why are the root systems of cacti beneficial? (2)
Widespread or very deep root systems
-that can collect water from a large area or from very deep underground.
why are the spines of cacti beneficial?
they are modified leaves
what are the features of modified leaves & how are they useful? (2)
-minimise the surface area and so reduce water loss.
-protect the cacti from animals that might eat them.
what are the leaves (spines) of cacti adapted to have?
-why?
Very thick, waxy cuticle
-to reduce water loss by evaporation.
what do cacti have a reduced number of across their spines?
-why?
Reduced number of stomata
-to reduce water loss by transpiration.
describe the movement of sucrose from where it is made to sinks: (6)
-sucrose moves from source into sieve tubes via active transport
-energy is provided by the companion cells (attached to sieve)
-water moves into the top of phloem from nearby xylem by osmosis
-water moves from high conc in xylem to low conc in phloem
-pushes sucrose towards sinks (up or down)
-sucrose enters sink cells by diffusion or active transport (depending on concentration levels)
