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Plants CellPlants Cell
cell wall cytoplasm
cell membrane
vacuole
cell wall freely permeable so it lets
most of molecules to go
through
osmosis does not occur
cell membrane
beneath cell wall
selectively permeable
Water Relations of Plant Water Relations of Plant - Turgor - Turgor
plant cell put in distilled water
plant cell contains solutes
water potential lower than pure
water
net water movement into the cell by osmosis
vacuole and cytoplasm swells
cell wall is rigid and strong, cell bursting is
prevented
turgor is present because: turgor
hydrostatic pressure develops inside the cell
cytoplasm is pushed against cell wall
tendency of the cell to give out water increases
water potential increases When water potential of cell
= water potential of waterTurgor occur (cell cannot take in
any water) the cell is turgid
Water Relations of Plant Water Relations of Plant - Plasmolysis - Plasmolysis
plant cell in concentrated
solution
net water movement out of the cell by
osmosis
vacuole and cytoplasm shrink
cytoplasm is torn away from cell wall
flaccid
The whole phenomenon is called plasmolysis and
cell is plasmolysed
Turgidity of Plant CellsTurgidity of Plant Cells
turgid cell(in hypotonic sol.)
plasmolysed cell(in hypertonic sol)
cell wall
cytoplasm
vacuoleenlarged
solution here is the same as the external solution
cell membrane separated from cell wall vacuole
very small
Cells in Different Cells in Different SolutionsSolutions
Solution Concentration
animal cells(e.g. RBC)
plant cells
hypotonic hypertonic
haemolysis
turgid
shrink
plasmolysis(cell is flaccid)
To Investigate the Effects To Investigate the Effects of Sucrose Solution and of Sucrose Solution and Tap Water on Epidermal Tap Water on Epidermal Cells of Red Onion Scale Cells of Red Onion Scale Leaf or Leaf or Rhoeo Discolor Rhoeo Discolor
LeafLeaf
fleshy scale leaf of red onion
bulb forceps
filter paper
epidermis
What do you observe when the epidermal strip is placed in the concentrated sucrose solution ?Ans: The coloured cytoplasm shrinks.
Explain your observation.Ans: When the piece of epidermis is placed in
concentrated solution, cells lose water by osmosis as the cells have a higher water potential than the sugar solution.
fleshy scale leaf of red onion
bulb forceps
filter paper
epidermis
What has happened to the cells in tap water ?Ans: The coloured cytoplasm swells and cells
become turgid.
fleshy scale leaf of red onion
bulb forceps
filter paper
epidermis
Explain your answer.Ans: When the piece of epidermis is placed in
tap water, cells gain water by osmosis as the surrounding tap water has a higher water potential than the cells.
fleshy scale leaf of red onion
bulb forceps
filter paper
epidermis
Effects of Effects of Concentrated Concentrated
Sucrose Solution and Sucrose Solution and Tap Water on Raw Tap Water on Raw
Potato StripsPotato Strips
What has happened to the potato strips ?Ans: Potato strip A increases in both weight
and length while potato strip B decreases in both weight and length.
petri dish
water20% surcose solution
raw potato strips
A B
Explain your answer.Ans: For potato strip A, it gains water by
osmosis so both of its weight and length increase but for potato strip B, it loses water by osmosis so its weight and length decrease.
petri dish
water20% surcose solution
raw potato strips
A B
TranspirationTranspiration
an evaporation of water in form of
water vapour from the surface of
plant to atmosphere
it mainly takes place in leaves
where there are some openings
called stomata
more water loses from the lower
surface of the leaf than the upper
one as more stomata present on
the lower surface it also happens in lenticels and
cuticle
Transpiration in LeavesTranspiration in Leaves
a thin film of moisture is covered
with each mesophyll cell
the moisture evaporates from
mesophyll cells into intercellular
spaces and diffuses out of stomata
into atmosphere
water potential of cells losing water
decreases so they draw water from
deeper cells in the leaf by osmosis.
This in turn, draws water in xylem
vessels into leaf to replace the loss
Experiment to Show Experiment to Show that Water is Given that Water is Given
Off During Off During TranspirationTranspiration
What do you observe in the polythene bags ?Ans: The one enclosing plant A becomes
misty while nothing can be noticed in the one enclosing plant B.
polythene bag
A BB
How can you show that it is water ?Ans: We can use anhydrous cobalt chloride
paper to test it. It will turn the paper from blue to pink or we can use anhydrous copper sulphate. Water will turn it from white to blue.
polythene bag
A BB
What conclusions can you draw from the results ?Ans: We can conclude that a leafy shoot gives
off water during transpiration.
polythene bag
A BB
To Measure the Rate To Measure the Rate of Transpiration by of Transpiration by
Using a Simple Using a Simple PotometerPotometer
What are the environmental conditions under which transpiration occurs quickly ?Ans: It is under dry, warm and windy
conditions.
air/water meniscus
graduated capillary tube
reservoir
leafy shoot
tap
Does this apparatus give you an accurate measurement of the rate of transpiration ?Ans: No. It is because it only measures the rate
of water uptake by the leafy shoot … Ans: In addition, it is too small to fit the whole
root system and this may affect the rate of water uptake.
air/water meniscus
graduated capillary tube
reservoir
leafy shoot
tap
Sometimes you may introduce an air bubble into the capillary tube. State the advantage of this method.Ans: Movement of the air bubble is easier to
observe than that of air/water meniscus.
air/water meniscus
graduated capillary tube
reservoir
leafy shoot
tap
Sometimes you may introduce an air bubble into the capillary tube. State the disadvantage of this method.Ans: Friction between the capillary wall and
the bubble may affect the movement of bubble.
air/water meniscus
graduated capillary tube
reservoir
leafy shoot
tap
Environmental Factors Environmental Factors Affecting the Rate of Affecting the Rate of
TranspirationTranspirationThere are five environmental factors
which affect the rate of transpiration.
They are:
(I) Light Intensity
(II) Temperature
(III) Humidity
(IV) Wind Speed
(V) Water Supply
Light IntensityLight Intensity
stomata open in light, so plants can
get enough carbon dioxide from
atmosphere for carrying out
photosynthesis
light will increase temperature so
increases the rate of transpiration
TemperatureTemperature
temperatur
erelative humidity of air outside
leaf
rate of evaporation of
water from mesophyll cells
rate of diffusion of water vapour from intercellular space in leaf to outside
HumidityHumidity
humidity
outside
rate of
transpiration
it makes the diffusion gradient of
water vapour from moist
intercellular space of a leaf to the
external atmosphere steeper
Wind Speed & Water SupplyWind Speed & Water Supplywind
blows
water vapour around
the leaf sweeps
awaytranspiration
rateINCREASES
lack of water
soil dries, plant wilts
and stomata
close
transpiration
rateDECREAS
ES
StomataStomata stomata are pores in the epidermis
which gaseous exchange takes
place during photosynthesis (or
respiration)
find mainly in lower epidermis of
dicotyledonous leaves and stems
Guard CellsGuard Cells each stomata is surrounded
by two guard cells
which possess
chloroplasts
its inner wall is thicker than
outer wall
it is kidney-shaped
guard cell
stoma
Distribution of Stomata Distribution of Stomata in Leaves in Leaves
normal plants
mainly on the lower surface of leaves
floating plants
mainly on the upper surface
leaves may also have air sacs to keep them afloat so they can carry out gaseous exchange
submerged aquatic plants
no stomata (not required since gaseous
exchange can be carried out by
diffusion though the leave surface)
no cuticle (the primary function of
cuticle is to prevent excess water
transpiration which is not present in
aquatic plants)
Experiment to Experiment to Investigate Stomatal Investigate Stomatal Distribution in a Leaf Distribution in a Leaf
by Using Cobalt by Using Cobalt Chloride PaperChloride Paper
cobalt chloride paper
sellotape
Obtain a potted plant. Using sellotape stick a small squareof anhydrous cobalt chloride paper onto each surface of a leaf of the plant. Record the time taken for the cobalt chloride paper on each surface of the leaf to turn pink.
Which piece of cobalt chloride paper turns pink first? Ans: The piece of cobalt chloride paper
attached to the lower epidermis of the leaf turns pink first.
cobalt chloride paper
sellotape
Explain your answer.
Ans: It is because more stomata are present in the lower epidermis.
cobalt chloride paper
sellotape
Why is it important to handle cobalt chloride paper with forceps? Ans: It is because there is moisture on human
fingers so the paper may turn pink before sticking onto the surfaces of leaves.
cobalt chloride paper
sellotape
To Observe the To Observe the Release of Air Release of Air
Bubbles from Leaves Bubbles from Leaves placed in Hot Waterplaced in Hot Water
Which surface has more air bubbles coming off?Ans: There are more air bubbles appear on
the lower surface of the leaf.
forceps
hot water
leaf
Where does the air come from?Ans: It is in the air spaces between the
mesophyll cells in leaf which expands on heating and passes out through stomata of the leaf.
forceps
hot water
leaf
What does the result show?Ans: The result shows that more stomata are
present on the lower epidermis of the leaf.
forceps
hot water
leaf
Structure of RootStructure of RootRoot Cap
a protective layer at the very tip of root
to protect the delicate cells of root from being damaged as the root grows down through the soil
Epidermis
cover the rest of root
absence of cuticle so water can enter
Growing Point
behind root cap
cells are capable of active division
Region of Elongation
more elongated than cells in growing
point and have large vacuoles
Region of Root Hair
little way behind root tip
root hair are thin-walled extension
of epidermal cells of root
increase surface area for uptake of
water and mineral salts
Vascular Tissue
further from the tip of root
contain xylem and phloem
xylem transport absorbed water to
every part of plant
Absorption of Soil Water Absorption of Soil Water by Root Hairs by Root Hairs
soil water is a dilute solution of salts
which is more dilute than cell sap and
cytoplasm in root hair
water will pass by osmosis into root hair
through cell wall and cell membrane
transpiration occurs in leaves so water is continuously removed
from the plant
flow of water through plant: transpiration stream tension produced to draw up water:
transpiration pull
reduction of effective pressure at the top of xylem vessel
water flows upwards from roots continuously
Transverse Transport Transverse Transport of Water to of Water to
Xylem Xylem epidermal cells gain water by
osmosis
NOTE: some water may travel inwards along or between cell walls without entering cytoplasm or vacuole of each cortical cell
cytoplasm and cell sap have higher water
potential than neighbouring cortical cells
water travels by osmosis
inwards from cell to cell
~ ~ End End ~~
Functions of Transport Functions of Transport System System
in Angiospermsin Angiosperms carries water and mineral salts
from the roots to the
mesophyll cells of the leaves for
photosynthesis by xylem
xylem and phloem are together
called vascular bundles
carries foods made in the leaves
by photosynthesis to other cells
of the plant by phloem
Arrangement of Conducting Arrangement of Conducting Tissues in AngiospermsTissues in Angiosperms
in root
- close to central position in which
xylem is found in the centre in a
star-like arrangement and
phloem lies between the radial arms
of the xylem
in stem
- close to the epidermis where the
conducting tissues are arranged
in a ring near the outside edge, with
phloem lying outside and
xylem inside
- to resist the strong pulling force
from the wind blowing the shoot
- to resist the strong bending force
produced by wind
in leaves
- vascular bundles are often called
veins in which xylem lies
above the phloem
XylemXylem consists of long tubular vessels
each vessel is made up of many dead cells
which are hollow and joined end to end
xylem vessels run from the root,
through the stem and finally branch
out into every leaf of the plant
the end walls of the cells have disappeared
and so a long and open tube is formed
xylem vessels contain no cytoplasm
or nuclei
to prevent xylem from collapsing, they
have thick cell walls made of cellulose
and strengthened by rings of a
woody substance called lignin
PhloemPhloem made up of tube cells called sieve tubes
which are living cells joined end to end by
perforated horizontal walls called sieve plate
the perforations allow dissolved substances to
flow through them so food made in the leaves
can be carried to other parts of the plant
sieve tubes contain cytoplasm but
no nuclei and they do not
have lignin in their cell walls
each sieve tube has a companion cell
next to it. The companion cell does
have a nucleus and contain many
other organelles
Comparison between Comparison between Sieve Tubes and Sieve Tubes and
VesselsVesselsSieve Tubes
Vessels
living cells dead cells
smaller diameter
larger diameter
walls relatively thin, flexible, composed of
cellulose
walls relatively thick, hard,
strengthened by rings of lignin
Comparison between Comparison between Sieve Tubes and Sieve Tubes and
VesselsVesselsSieve Tubes
Vessels
the lumens of mature cells are
filled with cytoplasm
the lumens of mature cells are empty
end walls of adjacent sieve
tubes from sieve plates
end walls of adjacent vessels
cells break down
Upward Transportation of Water Upward Transportation of Water and Mineral Saltsand Mineral Salts
• root pressure
• capillarity
• by transpiration pull
Transpiration PullTranspiration Pull most of the water rising up in the xylem of the stem is pulled up by this
during transpiration, water is continually removed from the top of xylem
vessels to supply cells in the leaves so pressure at the top of xylem
reduces and water flows up
Transport of Organic Transport of Organic NutrientsNutrients
translocation is the process of
transporting the manufactured
carbohydrates in photosynthesis via
phloem from the leaves to other parts
of the plant
~ ~ EndEnd ~~