2. Draw and label plan diagrams to show
the distribution of tissues in the stem
and leaf of a dicotyledonous plant.
Carissa Fletcher
3. Structure Function
Cuticle Waterproof layer
Epidermis Transparent but protective layer.
Xylem (vascular bundle) Support and water transport
Phloem (vasular bundle) Products of photosynthesis transported
by this tissue.
Sclerenchyma These are dead cells with a large
component of lignin – again for
structure.
Carissa Fletcher
4. Plant classification
All plants on earth have
been classified into the
following phylum;
• bryophyta,
• filicinophyta,
coniferophyta and
• angiospermophyta.
Carissa Fletcher
5. Angiosperms or flowering plants have traditionally been
classified into two further groups; dicots and monocots (these
are some examples of the morphological differences).
Carissa Fletcher
6. Explain the relationship between the
distribution of tissues in the leaf and
the functions of these tissues.
Carissa Fletcher
7. The epidermis is the
outer layer of cells
covering the leaf.
The epidermis serves
several functions:
1. protection against
water loss, regulation of
gas exchange,
2. secretion of metabolic
compounds,
3. (in some species)
absorption of water
Epidermis tissue
contains; epidermal
cells, guard cells,
subsidiary cells, and
epidermal hairs
(trichomes).
Carissa Fletcher
8. The epidermis is covered with pores called stomata, part of a stoma
complex consisting of a pore surrounded on each side by chloroplast-
containing guard cells, and two to four subsidiary cells that lack
chloroplasts.
The stoma complex regulates the exchange of gases and water vapour
between the outside air and the interior of the leaf.
Typically, the stomata are more numerous over the (lower) epidermis
than the (upper) epidermis.
Carissa Fletcher
9. - Thecylindrical shape of palisade cells allows a large amount of light to be
absorbed by the chloroplasts.
- Beneath the palisade mesophyll are the spongy mesophyll cells,
irregularly-shaped cells that having many intercellular spaces to allow the
passage of gases, such as the intake of carbon dioxide for photosynthesis
to take place.
- positioned towards the upper surface of the leaf and contain the largest
number of chloroplasts per cell in plants.
- they have a very large surface area in order for them to absorb more light
during photosynthesis
Carissa Fletcher
10. Midrib
Many dicots also have a large
midrib. This contains the vascular
bundle of xylem and phloem
tissue.
Veins
A small network of veins is found
throughout the leaf. These ensure
that no cell is far from a xylem
phloem vessel. All cells have a
constant supply of water and can
have their sugars removed after
photosynthesis.
Carissa Fletcher
12. Modifications of plant structures
A bulb is an
underground vertical
shoot that has
modified leaves (or
thickened leaf bases)
that are used as food
storage organs by a
dormant plant.
Carissa Fletcher
13. Tubers are various types of modified plant structures that
are enlarged to store nutrients.
They are used by plants to survive the winter or dry months
and provide energy and nutrients for re growth during
the next growing season
They are a means of asexual reproduction
Two different groups of tubers are: stem tubers, and root
tubers.
A stem tuber forms from thickened rhizomes.
The tops or sides of the tuber produce shoots that grow into
typical stems and leaves and the under sides produce
roots.
They tend to form at the sides of the parent plant and are
most often located near the soil surface. E.g. a potato
A tuberous root or storage root, is a modified lateral root.
enlarged to function as a storage organ.
The enlarged area of the root-tuber, or storage root, can be
produced at the end, or middle of a root, or involve the
entire root.
It is thus different in origin but similar in function and
appearance to a stem tuber. Examples of plants with
notable tuberous roots include the sweet potato,
cassava.
Carissa Fletcher
14. A Tendril is a specialised
stem, leaf or petiole with a
threadlike shape that is used
by climbing plants for support
and attachment, generally by
twining around whatever it
touches. They can be formed
from modified shoots,
modified leaves, or auxiliary
branches
Carissa Fletcher
15. Plant growth and meristems
• Plants have regions of Meristems are analogous with STEM
cells called meristems.
CELLS in humans.
• These are undifferentiated
embroyonic tissue that is
plueripotent cells
• In dicotyledons there are
apical meristems. These
are growing tips that will
form first of all a root and
a shoot. There are also
auxillary that form from
leaf axials.
• The region 1 in the
photograph on the left is
the apical meristem
Carissa Fletcher
17. The vascular cambium is a lateral
meristem (causing the diameter of the plant
to grow) in the vascular tissue of plants.
The vascular cambium is the source of
both the secondary xylem (inwards,
towards the pith) and the secondary
phloem (outwards), and is located between
these tissues in the stem and root.
The vascular cambium is a type of
meristem - tissue consisting of embryonic
(incompletely differentiated) cells from
which other (more differentiated) plant
tissues originate.
Carissa Fletcher
18. Auxins are a class of plant growth
substances or plant hormone.
Auxins
Auxins have an essential role in
coordination of many growth and
behavioral processes in the plant
life cycle.
They typically act in concert with, or
in opposition to other plant
hormones.
For example, the ratio of auxin to
cytokinin in certain plant tissues
determines initiation of root
versus shoot buds.
Thus a plant can (as a whole) react
to external conditions and adjust
to them, without requiring a
nervous system.
Carissa Fletcher
20. The role of auxin in phototropism
Phototropism is directional growth in which the direction of growth is
determined by the direction of the light source. In other words, it is the
growth and response to a light stimulus.
The cells on the plant that are farthest from the light have a chemical called
auxin that reacts when phototropism occurs.
This causes the plant to have elongated cells on the farthest side from the
light.
Phototropism in plants such as Arabidopsis thaliana is directed by blue light
receptors called phototropins
Other photosensitive receptors in plants include phytochromes that sense
red light.
Auxins have many roles but in this respect, auxins are responsible for
expelling protons (by activating proton pumps) which decreases pH in
the cells on the dark side of the plant.
This acidification of the cell wall region activates enzymes known as
expansins which break bonds in the cell wall structure, making the cell
walls less rigid.
In addition, the acidic environment causes disruption of hydrogen bonds in
the cellulose that makes up the cell wall.
The decrease in cell wall strength causes cells to swell, exerting the
mechanical pressure that drives phototropic movement.
Carissa Fletcher
