Assessment Statement
 9.1.1 Draw and label plan diagrams to show the distribution of
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tissues in the stem and leaf of a dicotyledonous plant.
9.1.2 Outline three differences between the structures of
dicotyledonous and monocotyledonous plants.
9.1.3 Explain the relationship between the distribution of
tissues in the leaf and the functions of these tissues.
9.1.4 Identify modifications of roots, stems and leaves for
different functions: bulbs, stem tubers, storage roots and
tendrils.
9.1.5 State that dicotyledonous plants have apical and lateral
meristems.
9.1.6 Compare growth due to apical and lateral meristems in
dicotyledonous plants.
9.1.7 Explain the role of auxin in phototropism as an example of
the control of plant growth.
Draw a labelled plan diagram to show the distribution
of tissues in the stem of a dicotyledonous plant
Structure
Function
Epidermis
Thin layer of cells for protection
Xylem
For transport of water & mineral ions
Phloem
For translocation of organic nutrients such as amino acids &
sucrose
Pith
Storage and support
Cambium
layer of actively dividing cells (lateral meristem ) for the
secondary growth
Cortex
Packaging tissue for storage and support
Draw a labelled plan diagram to show the distribution
of tissues in the leaf of a dicotyledonous plant.
Differences between the structures of
dicotyledonous & monocotyledonous plants
Monocotyledons
Dicotyledons
Parallel veins in narrow leaves
Branching, net-like veins in
broad leaves
Embryo has ONE cotyledon
Embryo has TWO cotyledons
Flower parts (sepals & petals)
arranged in threes
Flower parts (sepals & petals)
arranged in fours or fives
Fibrous adventitious roots
Tap root with lateral branches
Vascular bundles scatted
throughout the cortex
E.g. maize, wheat, oat
Vascular bundles arranged in a
ring around edge
E.g. bean, daisy, sunflower, pea
Relationship between the distribution of
tissues in the leaf & their functions
Relationship between the distribution of
tissues in the leaf & their functions
 palisade cells contain lots of
 waxy cuticle to prevent
chloroplasts for absorbing light
energy
 palisade cells arranged “end-on”
to ensure each cell receives
maximum amount of light
 no chloroplasts in upper
epidermis to ensure light
reaches palisade layer
 chloroplasts present in spongy
mesophyll cells to ‘mop up’ any
unused light
excessive water loss from
epidermal cells by evaporation
 air spaces in spongy mesophyll
layer to ensure adequate supply
of CO2 to photosynthesizing
cells and ease of removal of O2
 stomata located on leaf lower
surface to allow gases in and
out of leaf
 presence of vascular bundle to
supply water from roots & for
removal of products of
photosynthesis
Modifications of roots, stems and
leaves for different functions
Bulbs
 bulbs are underground
storage structures that
contain reserves of
nutrients to ensure
survival from season to
season
 consists of layers of
fleshy leaf bases closely
packed on a short stem
 the leaf cells are packed
with starch grains &
other nutrients
 E.g. onion, garlic
Stem tubers
 stem tubers are swollen
tip of rhizome or
underground stem
 they store carbohydrate
for growth of new plants
during the next season
 the cortex cells in the
stem are packed with
starch grains & other
nutrients
 E.g. Irish potato
Storage roots
 storage roots contain
stores of carbohydrate
for the plant to use later
 they are usually swollen
tap roots (primary roots)
 the cortex cells in the
root are packed with
starch grains & other
nutrients
 e.g. carrot, sweet potato
Tendrils
 tendrils are modified
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leaves
tendrils are slender stemlike structure to curl
around to a support
they are sensitive to
touch, so faster growth
occurs on the opposite
side
tendrils help support the
plant
E.g. vine, ivy
Apical and lateral meristems
 plants grow at meristems i.e.
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regions of unspecialised cells
that retains ability to divide &
differentiate into any type of cells
after cytokinesis, one daughter
cell differentiates & the other
remains in the meristem
dicotyledonous plants have
apical & lateral meristems
apical meristems, are found at
the tips of shoot & root, they
result in growth in length of the
plant – primary growth
lateral meristems, are found at
the tips of cambium in the
vascular bundles, they result in
increase the diameter or girth of
the plant – secondary growth
Phototropism
 phototropism is plant's
response to directional light
by either growing towards it
or away from it
 there are two types of
phototropism:
 positive phototropism, i.e.
growth of a plant’s shoot
towards light, putting the
leaves in a better position for
photosynthesis
 negative phototropism, i.e.
growth of a plant's roots away
from light
 phototropic responses are
controlled by auxins, plant
growth hormones
Role of auxin in phototropism
 auxin is a plant hormone produced by the tip of
the shoot (stem)
 auxin causes transport of hydrogen ions (H+)
from cytoplasm to cell wall
 decrease in pH due to H+ pumping breaks
bonds between cell wall fibres, making cell walls
flexible & extensible
 auxin makes cells enlarge, elongate & grow
 gene expression is also altered by auxin to
promote cell growth
 in positive phototropism, growth occur towards
the source of light
 shoot tip senses the direction of brightest light,
auxin are moved to side of stem with least light
i.e. darker side
 higher concentration of auxin causes cells on
dark side to elongate & grow faster than on the
illuminated side - hence the shoot bends
towards the source of light
 any questions on plant
structure & growth
 Thank you