1. 9.1 Plant Structure & Growth
Topic 9 Plant Science

2. Plant Structure & Growth
 9.1.1 Draw and label plan diagrams to show the distribution
of tissues in the stem and leaf of a dicotyledonous plant.
(Either sunflower, bean or another dicotyledonous plant with
similar tissue distribution should be used).
 Note that plan diagrams show distribution of tissues (for
example, xylem, phloem) and do not show individual cells.
They are sometimes called “low power” diagrams.

3. Plant Structure & Growth
 9.1.2 Outline three differences between the structures of
dicotyledonous and monocotyledonous plants.
 Teachers should emphasize three differences between
monocotyledonous and dicotyledonous plants (examples
include: parallel versus net-like venation in leaves,
distribution of vascular tissue in stems, number of
cotyledons, floral organs in multiples of 3 in
monocotyledonous versus 4 or 5 in dicotyledonous, fibrous
adventitious roots in monocotyledonous versus tap root with
lateral branches in dicotyledonous).

4. Plant Structure & Growth
 9.1.3 Explain the relationship between the distribution of
tissues in the leaf and the functions of these tissues.
 This should be restricted to dicotyledonous plants. The
functions should include: absorption of light, gas exchange,
support, water conservation, and the transport of water and
products of photosynthesis.
 9.1.4 Identify modifications of roots, stems and leaves for
different functions:
 bulbs, stem tubers, storage roots and tendrils.

5. Plant Structure & Growth
 9.1.5 State that dicotyledonous plants have apical and lateral
meristems.
 Apical meristems are sometimes referred to as primary
meristems, and lateral meristems as cambium. Meristems
generate new cells for growth of the plant.
 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.

6. Plant Classification
 There are FOUR main groups of plants.
 These can be easily identified by studying their
external structure:
 Phylum Bryophyta
 Bryophytes (mosses and liverworts)
 Phylum Filicinophyta
 Ferns
 Phylum Coniferophyta
 Conifers
 Phylum Angiospermatophyta
 Angiosperms (flowering plants)

7. Angiospermophytes - Flowering Plants
 Highly variable structure;
 Tiny herbaceous to large trees
 They have roots, stems and leaves
 An advanced vascular system
 Can form woody tissue
 Can grow up to 100m in height
 Seeds are produced
 Seeds develop from ovules inside ovaries. The ovaries are
part of flowers. Fruits develop from the ovaries to
disperse the seeds.

8. Angiospermophytes - Flowering
Plants

9. Monocotyledons and Dicotyledons
 Angiosperms can be divided onto two classes.
 Classification depends upon the number of seed leaves
(cotyledons) which they have in their seeds.
 The TWO classes are:
 Monocotyledons
 One seed leaf
 Leaves usually have parallel veins
 Includes: grasses, cereals
 Dicotyledons
 Two seed leaves
 Leaves are usually net veined
 Often grow to a large size: most trees, roses, many garden plants

10. Monocotyledons and Dicotyledons
 The IBO guide states:
 Teachers should emphasize three differences between
monocotyledonous and dicotyledonous plants (examples
include: parallel versus net-like venation in leaves,
distribution of vascular tissue in stems, number of
cotyledons, floral organs in multiples of 3 in
monocotyledonous versus 4 or 5 in dicotyledonous,
fibrous adventitious roots in monocotyledonous versus
tap root with lateral branches in dicotyledonous).

11. Structure of a Dicotyledons Plant
 Roots:
 Root hairs for absorbing
water and mineral nutrients.
 Stem:
 Transportation of water
from the roots to the leaves
 Transportation of the sugars
from the leaves to the roots
 Leaves:
 Main site of photosynthesis
 Buds (terminal and axillary)
 Site of new growth

12. Root Structure of a Dicotyledon Plant
 Plants absorb potassium, phosphate, nitrates and other mineral ions
from the soil
 The concentration of these ions is much higher inside the roots, so
they are absorbed by active transport.
 Root hairs provide a large surface are for mineral ion uptake.
 Because of the high solute concentration in root cells, water moves
into the roots cells by osmosis.
 Most of the water absorbed by the roots is drawn by the transpiration
pull into the xylem vessels in the centre of the root.
 To reach the xylem, water has to cross the cortex.
 There are two routes for the water to take to reach the xylem vessels:
 The symplastic route
 Water moves from cell to cell via the cytoplasm
 The apoplastic route
 Water moves along the cell walls

13. Root Structure of a Dicotyledon Plant

14. Root Structure of a Dicotyledon Plant

15. Stem Structure of a Dicotyledon Plant
 Stems connect the leaves, roots and the flowers of plants
 They transport materials between them using xylem and
phloem tissue.
 Xylem transports water and dissolved nutrients
 Phloem transports the products of photosynthesis
 Stems support the aerial parts of the plant
 Xylem tissue provides support especially in woody stems
 In dicotyledonous plants, the vascular bundles are
arranged in a ring around the outer part of the stem
 Xylem on the inside.
 Phloem on the outside.

16. Stem Structure of a Dicotyledon Plant

17. Stem Structure of a Dicotyledon Plant

18. Leaf Structure of Dicotyledon Plant

19. Leaf Structure of Dicotyledon Plant

20. Leaf Structure of Dicotyledon Plant

21. Modifications of roots, stems & leaves
 Tendrils are usually specialized stems or leaves that are
used by climbing plants for support, attachment and
cellular invasion by parasitic plants, generally by twining
around suitable hosts.

22. Food Storage in Plants
 Bulbs, stem tubers & storage roots are used for food
storage.
 Many plants develop a food storage organ in which food
is stored.
 Examples include:
 potatoes, carrots, corms, bulbs
 The steps in food storage are:
 Photosynthesis in the leaves produce glucose.
 The sugars are translocated in the phloem from the leaves to the
storage organ.
 The sugars are converted into starch, proteins and other organic
compounds for storage.

23. Food Storage in Plants
Ref: IB Biology, OSC

24. Meristems
 9.1.5 State that dicotyledonous plants have apical and lateral
meristems.
 Apical meristems are sometimes referred to as primary
meristems, and lateral meristems as cambium. Meristems
generate new cells for growth of the plant.
 9.1.6 Compare growth due to apical and lateral meristems in
dicotyledonous plants.
 See your notes for explanation

25. Phototropism
 9.1.7 Explain the role of auxin in phototropism as an
example of the control of plant growth.
 See your notes for explanation

26. IBO guide:
 9.1.1 Draw and label plan diagrams to show the distribution
of tissues in the stem and leaf of a dicotyledonous plant.
(Either sunflower, bean or another dicotyledonous plant with
similar tissue distribution should be used).
 Note that plan diagrams show distribution of tissues (for
example, xylem, phloem) and do not show individual cells.
They are sometimes called “lowpower” diagrams.

27. IBO guide:
 9.1.2 Outline three differences between the structures of
dicotyledonous and monocotyledonous plants.
 Teachers should emphasize three differences between
monocotyledonous and dicotyledonous plants (examples
include: parallel versus net-like venation in leaves,
distribution of vascular tissue in stems, number of
cotyledons, floral organs in multiples of 3 in
monocotyledonous versus 4 or 5 in dicotyledonous, fibrous
adventitious roots in monocotyledonous versus tap root with
lateral branches in dicotyledonous).

28. IBO guide:
 9.1.3 Explain the relationship between the distribution of
tissues in the leaf and the functions of these tissues.
 This should be restricted to dicotyledonous plants. The
functions should include: absorption of light, gas exchange,
support, water conservation, and the transport of water and
products of photosynthesis.
 9.1.4 Identify modifications of roots, stems and leaves for
different functions:
 bulbs, stem tubers, storage roots and tendrils.

29. IBO guide:
 9.1.5 State that dicotyledonous plants have apical and lateral
meristems.
 Apical meristems are sometimes referred to as primary
meristems, and lateral meristems as cambium. Meristems
generate new cells for growth of the plant.
 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.