ch 9 Flashcards
functions of xylem vessel
-transport water and mineral ions from the roots to the stem and leaves
-provides structural support to the plants
adaptations of xylem vessel to their function [2]
-cells joined end to end, no cross walls to form long continuous tubes , which allows water to flow easily
-has thick cell wall nade of cellulose and lignin to withstand hydrostatic pressure, and prevent collapsing
function of phloem [2]
translocate sucrose and amino acids, allow bidirectional movement of food from source to sink
difference between the vascular bundle in root and stem [2]
in root it is single and central but in stem it is multiple and peripheral
differences (not vascular bundle related) between the transverse section in root and stem [2]
- root has root hair cells
-root has endodermis
define vascular bundles
it is the collective name for xylem and phloem, they are found throughout the root,stem and leaves
describe the journey of water from the soil up to the leaves [3]
-root hair cell absorbs water from soil
-water then moves by osmosis along the cells of the root till it reaches the root xylem
…90% of the water pass across the cell walls of the cell because cellulose is fully permeable
..10% of water pass through the cytoplasm and vacuole \
- all of the water eventually reach the root xylem to ascend up to stem and leaf xylem, this is achieved by the transpiration pull
importance of transpiration [2]
- help in ascend of water from soil up to the leaves
-cooling down the plant
define transpiration
it is the loss of water vapour from the surface of the leaves through stomata
explain : transpiration pull [4]
-water molecules are held together by forces of attraction between them called cohesion
- transpiration occurs where water vapour diffuses from the air spaces, inside the leaf to outside through stomata
- water lost from the leaf by transpiration, will be replaced by another water from the leaf’s xylem causing a decrease in pressure of water in the leaf xylem
-this will create a pressure gradient between root xylem and leaf xylem, so water ascends from high hydrostatic pressure at root xylem to low hydrostatic pressure st leaf xylem
state the steps of transpiration [2]
- evaporation, liquid water evaporates from spongy cells to air space
-diffusion, water vapour diffuses from high conc in air spaces to low conc
in atomspheric air through stomata
state the internal factors that affect transpiration [4]
- thickness of cuticles:
thick cuticle -> less transpiration
-number of stomata
more stomata -> more transpiration
-surface area of the leaf
larger surface area -> more transpiration
-air spaces inside leaf :
more air spaces -> more transpiration
state and explain the external factors that affect transpiration [4]
-light : more light -> more transpiration because more opens the stomata
- temperature : more temp -> more transpiration because inc. in temp increases the kinetic energy of water molecules so they evaporate and diffuse faster from the mesophyll cells
- wind speed : more wind speed -> more transpiration, because the wind removes the water vapour from the surface of the leaf which increases the diffusion gradient so more diffusion
-humidity : more humidity -> less transpiration , because the increased humidity means more water vapour in air surronding leaf so less diffusion gradient
when does a plant wilt
if the amount of water a plant loses from its leaves is greater than the amount of water that is available in the soil to travel into the plant through its roots then wilting will occur
how does a plant wilt
the plant becomes soft and droops because the cell wall becomes flaccid and no longer able to support the plant
what is potometer
apparatus used to measure the water uptake by plant which is nearly equal to water loss by transpiration
mechanism of potometer
water is lost from the leaves by transpiration, so it is replaced by water drawn from the capillary tube to xylem vessels in plant, the rate of transpiration is determined by measuring the distance moved by water along the capillary tube per unit time ( bigger distance, more transpiration)
how should the plant be adjusted before placing it in potometer
slant cut in stem to avoid getting an air bubble in xylem and blocking it
how should the external factors be set for showing their effect by potometer [5]
- inc temp -> heater
-dec temp -> AC
-light intensity -> lamp
-wind speed -> fan
-humidity -> surronding the potometer by plastic bag
why do some people consider the use of potometer inaccurate
mot all water is used for transpiration some water is used for :
- solvent for metabolic reactions
-in cell turgidity to support the plant
-to build cell components such as cyyoplasm and vacuole
define translocation
the movement of manfactured food (sucrose and amino acids) in phloem vessels from source to sink using energy
what is the direction of translocation dependant on [2]
- growth stage of plant
-time of year
what is meant by source in translocation
-part of the plant that releases sucrose or amino acids
what is meant by sink in translocation
part of plant that use or store sucrose or amino acids
