Plants Cell
cell wall
cytoplasm
vacuole
cell
membrane
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
- Turgor
plant cell put in distilled water
net water movement into the cell by osmosis
plant cell
contains solutes
water potential lower
than pure water
vacuole and cytoplasm swells

cytoplasm is pushed against cell wall
turgor
turgor is present because:
cell wall is rigid and strong,
cell bursting is prevented
hydrostatic pressure
develops inside the cell
tendency of the cell to give
out water increases
water potential increases
When water potential of cell
= water potential of water
Turgor occur (cell cannot take in
any water) the cell is turgid
Water Relations of Plant
- Plasmolysis
plant cell in
concentrated solution
net water movement out
of the cell by osmosis
vacuole and
cytoplasm shrink
The whole phenomenon
is called plasmolysis and
cell is plasmolysed
flaccid
cytoplasm is torn away
from cell wall
Turgidity of Plant Cells
vacuole
enlarged
cell membrane separated
cell wall from cell wall
vacuole
cytoplasm
very small
plasmolysed cell
turgid cell
(in hypertonic sol)
(in hypotonic sol.)
solution here is the same
as the external solution
Cells in Different Solutions
Solution Concentration
hypotonic
hypertonic
animal cells
haemolysis
(e.g. RBC)
plant cells
turgid
shrink
plasmolysis
(cell is flaccid)
To Investigate the Effects of
Sucrose Solution and Tap Water
on Epidermal Cells of Red Onion
Scale Leaf or Rhoeo Discolor
Leaf
fleshy scale leaf of
red onion bulb
filter paper
forceps
epidermis
What do you observe when the epidermal strip is
placed in the concentrated sucrose solution ?
Ans: The coloured cytoplasm shrinks.
fleshy scale leaf of
red onion bulb
filter paper
forceps
epidermis
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
filter paper
forceps
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
filter paper
forceps
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.
Effects of Concentrated
Sucrose Solution and Tap
Water on Raw Potato Strips
petri dish
20% surcose solution
water
raw potato
strips
A
B
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
20% surcose solution
water
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.
Transpiration
 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 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 that
Water is Given Off During
Transpiration
polythene
bag
A
B
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
B
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
B
What conclusions can you draw from the results ?
Ans: We can conclude that a leafy shoot gives off water
during transpiration.
To Measure the Rate of
Transpiration by Using a
Simple Potometer
graduated
capillary tube
leafy shoot
reservoir
tap
air/water
meniscus
What are the environmental conditions under which
transpiration occurs quickly ?
Ans: It is under dry, warm and windy conditions.
graduated
capillary tube
leafy shoot
reservoir
tap
air/water
meniscus
Does this apparatus give you an accurate measurement of
the rate of transpiration ?
Ans: In
No.addition,
It is because
it is too
it only
small
measures
to fit thethe
whole
rateroot
of water
system
uptake
and
thisby
may
theaffect
leafy shoot
the rate
… of water uptake.
graduated
capillary tube
leafy shoot
reservoir
tap
air/water
meniscus
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.
graduated
capillary tube
leafy shoot
reservoir
tap
air/water
meniscus
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.
Environmental Factors Affecting
the Rate of Transpiration
There are five environmental factors which affect
the rate of transpiration. They are:
(I) Light Intensity
(IV) Wind Speed
(II) Temperature
(V) Water Supply
(III) Humidity
Light 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
Temperature
temperature
rate of evaporation
of water from
mesophyll cells
relative humidity of
air outside leaf
rate of diffusion of water
vapour from intercellular
space in leaf to outside
Humidity
humidity
rate of
outside
transpiration
it makes the diffusion gradient of water
vapour from moist intercellular space of a
leaf to the external atmosphere steeper

Wind Speed & Water Supply
wind blows
lack of water
water vapour around
soil dries, plant wilts
the leaf sweeps away
and stomata close
transpiration rate
INCREASES
transpiration rate
DECREASES
Stomata
 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 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
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 Investigate
Stomatal Distribution in a
Leaf by Using Cobalt
Chloride Paper
cobalt chloride paper
sellotape
Obtain a potted plant. Using sellotape stick a small square
of 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.
cobalt chloride paper
sellotape
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.
To Observe the Release of
Air Bubbles from Leaves
placed in Hot Water
forceps
hot water
leaf
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.
Structure of Root
Root 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
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
reduction of effective pressure at the top
of xylem vessel
water flows upwards from roots continuously
flow of water through plant: transpiration stream
tension produced to draw up water:
transpiration pull
Transverse Transport
of Water to 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 ~
Functions of Transport System
in Angiosperms
 carries water and mineral salts from the
roots to the mesophyll cells of the leaves
for photosynthesis by xylem
carries foods made in the leaves by
photosynthesis to other cells of the plant
by phloem
 xylem and phloem are together called
vascular bundles
Arrangement of Conducting
Tissues 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
- to resist the strong pulling force
from the wind blowing the shoot
 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 bending force
produced by wind
 in leaves
- vascular bundles are often called veins in
which xylem lies above the phloem
Xylem
 consists of long tubular vessels
 each vessel is made up of many dead cells
which are hollow and joined end to end
 the end walls of the cells have disappeared
and so a long and open tube is formed
 xylem vessels run from the root, through the
stem and finally branch out into every leaf of
the plant
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
Phloem
 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
Sieve Tubes and Vessels
Sieve Tubes
living cells
smaller diameter
walls relatively thin,
flexible, composed of
cellulose
Vessels
dead cells
larger diameter
walls relatively thick,
hard, strengthened by
rings of lignin
Comparison between
Sieve Tubes and Vessels
Sieve Tubes
the lumens of mature
cells are filled with
cytoplasm
end walls of adjacent
sieve tubes from
sieve plates
Vessels
the lumens of
mature cells are
empty
end walls of adjacent
vessels cells
break down
Upward Transportation of Water
and Mineral Salts
• root pressure
• capillarity
• by transpiration pull
Transpiration 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 Nutrients
 translocation is the process of transporting
the manufactured carbohydrates in
photosynthesis via phloem from the leaves
to other parts of the plant
~ End ~