U1: Transpiration is the inevitable
consequence of gas exchange in the leaf
transpiration= loss of water vapor from the leaves
and stems of plants
Factors affecting transpiration rate
Humidity
High humidity= low rate of transpiration
wind
moves water away from the stomata
increasing the rate of transpiration
CO2
stomata open and close
based on CO2 concentration
lowers rate of transpiration
Sunlight
light opens guard cells
increased rate of transpiration
Temperature
heat increases rate of evaporation
increase rate of transpiration
Guard Cells
Controls the stomata
from opening or closing
stomata
CO2 and H2O can enter or leave the cell here
use trigger pressure to open or close stomata
when there is a lot of water the guard cells
budge and open the stomata
U2: Plants transport water from the roots to the
leaves to replace losses from respiration.
water evaporates from the leaves
water loss causes leaf to draw more water from the spongy
mesophyll into the air space
this causes the spongy mesophyll to draw water from the
end of the xylem
then due to water being weakly attracted to each other due to
hydrogen bonding (COHESION) the water gets sucked up from the
bottom of the xylem
U3: The cohesive property of water and the structure
of the xylem vessels allow transport under tension.
cohesive properties
water holds together which allows for water
to travel up the xylem, against gravity
xylem provides support
to the plant
xylem is reinforced by rings of lignin
U4: The adhesive property of water and evaporation generate
tension forces in leaf cell walls.
U5: Active uptake of mineral ions in the roots causes
absorption of water by osmosis
since there is a greater concentration of mineral ions in the roots
than water in the soil active transport is needed using ATP
since the concentration of mineral ions is increasing in the roots the water
concentration decreases causing water to enter the roots by osmosis
plants have a mutualistic relationship with fungi. There gains are a
higher absorptive capacity for water and mineral nutrients due to the
funguses large surface area
Application
A1: Adaptions of plants in deserts and in
saline soils for water conservation
Plants have adapted to reduce water
loss in dry environments
waxy leaves
have a waxy cuticle on both the upper
and lower epidermis of the leaves
waxy layer repels water loss
through both epidermises.
Firs and Pines
needles as leaves reduces surface area
thick waxy cuticle
sunken stomata to limit exposer
no lower epidermis
Succulent
needles as leaves to
reduce surface area
water is stored in fleshy stem
metabolic adaptions
CAM
reduces water loss by opening pores at night
but closing them during the day
A2: Models of water transport in xylem using simple
apparatus including blotting or filter paper, porous pots
and capillary tubing
Skill
S1: Draw the structure of primary xylem vessels in
sections of stems based on microscope images
S2: Measurement of transpiration using photometers. (Practical 7)
factors affecting rate of transpiration
leaf surface area
thickness of epidermis and cuticle
stomatal frequency
stomatal size
stomatal position
Abiotic factors
S3: Design of an experiment to test hypotheses about the effect of
temperature or humidity on transpiration rates.
Nature of Science: Use models as represebtatiobs of the real world-
mechanisms unvolved in water transport in the xylem can be investigated
using apparatus and materials that show similarities in structure to plant
tissues