PLANT TISSUES
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2.1
Meristematic tissue
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2.2
Plant tissues can be divided into meristematic tissue and permanent tissue.
Meristematic tissue is actively dividing tissue in which new cells are formed by
mitosis. The cells are not differentiated to perform a specific function.
Permanent tissue is already differentiated to perform a specific function and
includes xylem, phloem, parenchyma, collenchyma, sclerenchyma and
epidermis.
Apical meristem is found near the tips of roots and stems and are responsible
for growth in length.
Lateral meristem is found between the xylem and phloem in a dicotelydonous
plant, and it makes the plant grows thicker.
Permanent tissue
Type of tissue
Structure
Function/s
Epidermis
• Forms the
outer layer
around roots,
stems and
leaves.
• Brick-shaped
and in a
single layer
• Cells are
transparent
with no
intercellular
air spaces.
• Protects
the
underlying tissues
from injury.
• Cuticle prevents
water-loss
in
leaves and stems.
• Transparent
epidermis allows
sunlight through
for photosynthesis.
Type of tissue
Structure
• Epidermis of
leaves and
stems are
covered with
a waxy layer,
the cuticle.
• Specialised
epidermal
cells are root
hairs and
guard cells.
Function/s
Illustration
Illustration
Parenchyma
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Sclerenchyma •
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Collenchyma
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Xylem
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Large with
• Stores food and
water
thin cell walls
• Produces
Large
carbohydrates
intercellular
through
spaces
photosynthesis
Large
• Intercellular
vacuoles
spaces allow for
Cells contain
gaseous
chloroplasts in
exchange
leaves and
stems
Cells
are
• Provides the plant
dead and
with structure and
hollow
support
Contain
lignin • Two
types
i.e.
sclereids
and
fibres
Unevenly
• Provides
thickened
mechanical
cells with
support to the
cellulose
plant
Most
thickenings
occur in the
corners of the
cell walls
Cells
are • Transport water
and mineral salts
elongated
from the roots to
Contains no
the rest of the
living material
plant
Cell
walls
thickened by • Serves as
strengthening
lignin
and support
Consists
of
tissue
xylem vessels
and tracheids
Type of tissue
Phloem
Structure
• Living,
elongated
cells without
thickened
walls
• Consists of
sieve tubes
and
companion
cells
Function/s
Illustration
• Transport organic
substances from
the leaves to the
rest of the plant
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ORGANS
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3.1
An organ is a group of tissues that perform a specific function.
Leaf Structure
Leaf section
Structure
Functions
Epidermis
Covers upper and lower
surfaces of the leaf.
Transparent and do not
contain chloroplasts.
Waxy cuticle covers the
epidermis. Lower
epidermal cells contain
stomata
Protects the underlying
tissues.
Cuticle reduces excessive
moisture loss.
Allow light through for
photosynthesis.
Stomata are responsible
for gaseous exchange
into and out of leaf
Mesophyll
(Palisade and spongy
mesophyll)
Palisade cells: elongated
cells under the upper
epidermis. Contain large
amount of chloroplasts.
No intercellular air spaces
between the cells. Cell
walls are thin.
Palisade cells are primarily
responsible for
photosynthesis
Spongy cells: round
parenchyma cells with
large intercellular air
Spongy cells are also
responsible for
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Leaf section
Vascular bundles
Structure
Functions
spaces. Contain
chloroplasts.
photosynthesis and
gaseous exchange
Xylem and phloem
Xylem transports water
and dissolved mineral salts
to the mesophyll cells
Phloem transports
produced organic
nutrients to other parts of
the plant.
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SUPPORT AND TRANSPORT
SYSTEMS IN PLANTS
ANATOMY OF
DICOTELYDONOUS PLANTS
4.1.1 Internal structure of a root
When the cross section of a young dicotyledonous root (refer to diagram below) is
studied, three regions can be distinguished i.e. the epidermis, cortex and the central
cylinder:
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The epidermis forms the outer layer of the root and contain finger-like
outgrowths, the root hairs.
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The cortex consists of parenchyma cells with large intercellular air spaces.
The inner-most layer of the cortex consists of a single layer of cells called the
endodermis.
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The radial and transverse walls of the endodermis contain thickened strips
known as the Casparian strips
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The central cylinder: under the epidermis there are thin-walled cells called the
pericycle. On the inside of the pericycle is the vascular tissue that consists of
xylem and phloem.
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Internal structure of a stem:
When the cross section of a young dicotyledonous stem (refer to diagram below) is
studied, three regions can be distinguished i.e. the epidermis, cortex and the central
cylinder:
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The epidermis forms the outer layer of the stem.
The cortex consists of collenchyma, parenchyma and endodermis.
The central cylinder: Xylem and phloem occur in vascular bundles in the stem.
The xylem is on the inside and the phloem on the outside. A layer of
meristematic tissue, the cambium, occurs between the xylem and phloem.
Cambium makes secondary thickening possible.
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The central region of the stem is the pith and consists of parenchyma cells.
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4.1.3 Uptake of water and mineral salts by the roots:
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The water potential of the soil water is higher (contains less dissolved
substances) than the water potential of the cell sap in the vacuoles of the root
hair
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Water molecules move by osmosis through the permeable cell wall, through
the selectively permeable cell membrane, cytoplasm and selectively
permeable tonoplast into the vacuole of the root hair.
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The vacuole swells and the pressure within the root hair increases. The pressure
that builds up in the vacuole is called, turgor pressure.
4.1.4 Movement of water from the root hair to the xylem of the root:
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The water potential in the root hair is now higher than in the adjacent
parenchyma cells in the cortex of the root.
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Water moves in two ways to the xylem of the root:
 The main route that water takes is from cell to cell by osmosis – this
is a slow process
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 Water can also move through the cell walls and intercellular air
spaces between the cells by diffusion – this is a faster process
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When water reaches the endodermis, with Casparian strips, it cannot
pass through the cell walls of these cells. Water now moves through the
passage cells of the endodermis through the pericycle to the root xylem.
4.1.5 Upward movement of water from the xylem of the root to the leaves of the
plant:
pieliemanjaro
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Revise the cross-section through the leaf.
The three forces involved in the upward movement of water in a plant is:
capillarity, root pressure and transpiration pull. Refer to the list of definitions and
textbook and study the sections on capillarity and root pressure. Transpiration
pull is the main force that draws water upwards in a plant.
The water potential in the intercellular air spaces of the mesophyll cells
decreases as water vapour is lost through the stomata of the leaves.
Water molecules diffuse from the cell walls of the mesophyll cells into the air
spaces
The water potential of the mesophyll cell walls is now lower than that of the cell
sap of the mesophyll cells
This water potential gradient extends back to the leaf xylem.
Tension builds up and a suction force develops at the top of the stem xylem,
which pulls water up from the root xylem. A column of water is pulled upwards.
Therefore, the water that was lost through the leaves by transpiration is
replaced by the absorbed water from the soil through the root hairs.
4.1.6 The translocation of manufactured food from the leaves to other parts of the
plant:
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Translocation is the movement of substances e.g. sugars (sucrose) that are
produced in the leaves during photosynthesis to other part of the plant. These
substances are transported by the phloem from the leaves to the stems and
the roots.
4.1.7. TRANSPIRATION:
Transpiration is the loss of water vapour through the aerial parts of the plant
mainly through the stomata.
4.1.7.1 Relationship between water loss and the structure of a leaf:
The smaller the leaves, the smaller the surface area for evaporation.
Thorns and hairs on a leaf limit transpiration.
Leaves with stomata mainly on the lower side of the leaf or leaves with sunken
stomata will limit transpiration.
4.1.7.2 External factors influencing transpiration:
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High temperatures increase the rate of transpiration.
Higher light intensity will increase the rate of transpiration.
High humidity will decrease the rate of transpiration.
Wind will increase the rate of transpiration.
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Activity 1
1.2
The diagram below shows a cross section through a dicotyledonous root.
1.2.1 Identify part:
(a)
(b)
A
B
(1)
(1)
1.2.2 Give the LETTER and NAME of the part that:
(a)
(b)
(c)
(d)
gives rise to side/lateral roots
transports organic food in the plant
stores starch in the root
(2)
transports water in the plant
(2)
(2)
(2)
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1.3
The diagram shows a cross section of a dicotyledonous leaf.
1.3.1 Give the LETTER of the part that:
(a) is transparent and impermeable to water.
b) transports water and mineral salts.
(1)
(1)
1.3.2 What are parts C and D collectively called?
(1)
*1.3.3 Tabulate ONE structural difference between parts B and F.
(3)
* 1.3.4 Explain TWO ways in which part C is structurally adapted for its function of
photosynthesis.
(4)
1.4
The graphs below show the transpiration rates under different environmental
conditions.
*1.4.1 Describe the relationship between the temperature and transpiration rate in
GRAPH A.
(4)
*1.4.2 Explain the shape of the graph at point X in GRAPH B.
1.5
The diagram represents the pathway of water through the root.
(3)
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*1.5.1 If it has rained recently, give the LETTER in the diagram where the water
potential will be the highest?
(1)
*1.5.2 Name TWO structural suitabilities of the root hair for the function of water
absorption.
(2)
1.5.3 Which LETTER in the diagram refers to the endodermis?
(1)
1.5.4 Which special feature is present in the endodermis to control the pathway of
water to the part labelled D?
(1)
1.5.5 Name THREE forces responsible for the upward movement of water through
tissue D.
(3)
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An investigation was carried out to study the effect of light intensity on the
rate of water loss through the leaves of a plant.
1.6
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Apparatus X (shown in the diagram below) was used to measure the rate of
water loss from the leaves at several light intensities.
At each light intensity, the apparatus was left for 15 minutes before starting
measurements.
The water loss was recorded in the dark and at four different light intensities.
The results of this investigation are shown in the table below.
*1.6.1 State a hypothesis for this investigation.
(2)
*1.6.2 State the dependent variable in the above investigation.
(1)
*1.6.3 Predict what would be the effect on the results if the investigation was carried
out at a lower temperature.
(1)
*7.6.4 State ONE way in which the reliability of the results obtained at each light
intensity could have been improved.
(1)