plant nutrition & transport ! Flashcards
upper epidermis
made up of a single layer of closely packed cells
no chloroplasts
covered by a layer of cuticle : transparent & waxy
- allows light to pass through
- prevents excessive water loss from upper epidermis
palisade mesophyll !
closely packed cells that are long & cylindrial
contains many chloroplasts : located near the top surface of leaf -> light is most abundant -> maximum absorption of light energy
spongy mesophyll !
cells are irregularly shaped
have lesser chloroplasts than palisade mesophyll cells
contains the vascular bundle (xylem & phloem tissues)
cells : covered in a thin layer of moisture
- for CO2 to dissolve in before diffusing into the cells
have numerous large intercellular air spaces among the cells
-allowing transport of water, sucrose & amino acids within the plants
lower epidermis !
consists of a single layer of closely packed cells
no chloroplasts : no photosynthesis
covered with a layer of cuticle : prevent excessive water loss
guard cells !
control size of stomata : regulate gaseous exchange between plant & surroundings
day : guard cells photosynthesis - convert light energy -> chemical energy
- chemical energy : pump K+ ions into the guard cells from neighbouring epidermal cells -> water potential of guard cells to decrease -> water from neighbouring epidermal cells enter guard cells by osmosis
- turgidity of guard cells increase -> becomes curved -> pulls stoma open
night : K+ ions diffuse out of guard cells to epidermal cells -> water potential of guard cells increase -> water leaves by osmosis
- turgidity decreases -> becomes flaccid -> stoma closes
carbon dioxide - entering leaves !
day : photosynthesis occurs
- CO2 : rapidly used up -> concentration is lower than atmospheric air -> diffusion gradient established
- surfaces of mesophyll cells : covered by thin film of moisture -> CO2 dissolves -> diffuse into cells
lamina!
large surface area : maximise absorption of sunlight for photosynthesis + allows rapid diffusion of CO2 to reach inner cells of leaf
thin : allowing for a shorter diffusion distance for gases during gaseous exchange
petiole !
positions lamina away from stem : allows lamina to absorb maximum sunlight & carry out gaseous exchange
veins !
allow transport of water & mineral salts to the cells in the lamina
transports manufactured food (glucose) from cells in the leaves to the other parts of the plant
main vein : gives off branches repeatedly -> forming network of fine veins
leaf arrangement !
organised around the stem in a regular pattern : grow in pairs
- opposite one another or singly in an alternative arrangement
- > ensures that the leaves are not blocking each other from sunlight
- > ensures that each leaf receives optimum light
photosynthesis formulas !
6CO2 + 12H20 (light energy & chlorophyll) -> C6 H12 O6 + 602 + 6H2O
carbon dioxide + water (light energy & chlorophyll) -> glucose + oxygen + water
conditions - photosynthesis !
light intensity presence of chloroplasts carbon dioxide suitable temperature water
light-dependent stage !
enzymes are involved
light energy : absorbed by chlorophyll in leaves & converted into chemical energy
12 H20 (photolysis of water) -> 6O2 + 24H
light-independent stage !
enzymes involved
does not require light energy
hydrogen atoms produced by light-dependent stage : used to reduce CO2 into glucose
limiting factors !
a factor that directly affects or limits a process if its quantity or concentration is altered
affects rate of photosynthesis !
- light intensity
- CO2 concentration
- temperature
pathway of water !
root hair : fine tubular outgrowth of an epidermal cell that grows between soil particles
- close contact with surrounding soil particles
soil particle : thin film of liquid surrounding it
cell sap in root hair cell : more concentrated due to presence of mineral salts
- lower water potential than soil solution -> water enters root hair by osmosis
entry of water : dilutes root hair cell cap
- 1st root hair cell : higher water potential than 2nd root hair cell -> water passes from 2nd to 3rd to cortex …
- process continues until water enters xylem vessels
root hair cell !
has numerous mitochondria : release energy from aerobic respiration
- allow uptake (active transport) of mineral salts
long narrow protrusion : increases surface area to volume ratio
- increases rate of absorption of water & mineral salts
large central vacuole with concentrated cell sap : creates water potential gradient for quicker movement of water molecules by osmosis
root pressure !
pressure resulting from the constant entry of water from the roots
root cells surrounding xylem causes water potential in xylem to lower -> water moves into xylem
capillary action !
tendency of water to move up very narrow capillary tubes
- forces of cohesion : attached by water molecules
- forces of adhesion : stick to wall
transpiration pull !
suction force caused by transpiration which results in water moving up the xylem against gravity
transpiration !
loss of water vapour from the aerial parts of the plant, especially through the stomata of the leaves
evaporation of water from cells in the leaf by transpiration
- removes latent heat of vaporisation -> cools the plant, preventing it from being scorched
water transported to the leaves can be used in photosynthesis
- keeps cells turgid
- replaces water lost by the cells
water movement in leaves !
water that moves out of the mesophyll cells : form a thin film of moisture around the cells
water from the thin film of moisture : evaporates to form water vapour in the intercellular air spaces
- water vapour : diffueses out of the stomata to the drier air outside the leaf - transpiration
movement of water out of the calls to replace the thin film of moisture that has evaporated
- causes the cell sap’s water potential to decreases
mesophyll cells : absorb water via osmosis from the cells deeper in the leaf
- results in the production of a suction force : transpiration pull
temperature - transpiration factors !
increase in temperature -> increases rate of evaporation of water from the cell surfaces -> increases water vapour in air spaces -> increase rate of transpiration
light intensity - transpiration factors !
presence of light : stomata size increases -> increased rate of evaporation of water -> increases rate of transpiration
absence of light : stomata size decreases -> decreased rate of evaporation of water -> decreases rate of transpiration
humidity - transpiration factors !
the drier / less humid the air outside the leaf is, the steeper the concentration gradient between leaf & atmosphere -> increases rate of transpiration
high humidity : lower vapour concentration gradient between leaf & atmosphere -> decreases rate of transpiration
wind - transpiration factors !
wind : blows away water vapour that accumulates outside the stomata
- helps maintain water vapour concentration gradient between the leaf & the atmosphere -> increases transpiration rate
still air : water vapour that diffuses out of the leaf makes the air outside the leaf more humid -> decreases transpiration rate
wilting !
occurs when rate of water loss (transpiration) exceeds rate of water absorption
vacuole + cytoplasm of plant cells : shrink
- plant cells : lose their turgor -> becomes flaccid
factors - wilting !
strong light -> increases rate of transpiration -> wilting occurs
too much fertiliser in soil : root hair cells -> higher water potential than surrounding soil solution -> water leaves the root hairs by osmosis -> wilting occurs
advanatages of wilting !
reduces rate of transpiration
prevents excessive water loss : guard cells are flaccid -> stomata closed -> lesser transpiration
cools plant down
- leaf folds up -> surface area to volume ratio decreases
disadvanatges - wilting !
stomata close : amount of CO2 decreases
leaves will droop :
- absorption of sunlight decreases -> photosynthesis decreases
- lesser surface area to volume ratio that is exposed to sunlight -> photosynthesis decreases
