Plant Tissues for Grade 10 Life Sciences

z
Aim of Lesson
At the end of this lesson you should be able to:
 Define basic terminology, such as xylem.
 Identify the relationship between the structure and function of the
tissues.
 Differentiate between meristematic and permanent tissue.
 Identify the structure and functions of the different parts of a
dicotyledonous leaf as an example of a plant organ.

z
Introduction
 You have studied cell structure and the functions of the different
organelles in Grade 9 and last term.
 You also studied the concept of a tissue as a group of similar
cells that are adapted for a particular function.

z
Plant tissue
Meristematic
tissue
Apical
Meristem
Lateral
Meristem
Permanent
tissue
Epidermis Ground tissue
Parenchyma Collenchyma Sclerenchyma
Vascular
tissue
Xylem Phloem

z
Plant tissues (Meristematic tissue)
 Meristematic tissue is actively dividing tissue in which new cells
are continually formed by mitosis. The cells are not yet
differentiated to perform a specific function.
 Differentiated: The process during which cells or tissues undergo a
change in size, shape and structure in order to perform specific
functions.

z
Meristematic tissues
 Apical meristem
 Consists of groups of undifferentiated stem cells that are found
near the tips (apex) of roots, stems and buds and are responsible
for growth in length by mitosis.
 Basic structure
 The cells of the apical meristem are relatively small and cube-shaped
with large, prominent nuclei and no intercellular spaces.
 Cell walls are thin and vacuoles are absent.

z
Meristematic cells of a stem tip

z
Meristematic tissues
 Functions of the apical meristem
 New cells that form through mitosis result in the primary growth (growth in length) of the plant.
 Lateral meristem
 Is found between the xylem and the phloem in the vascular bundles of dicotyledonous plants and
is known as cambium.
 Basic structure:
 Cambium cells are similar to those of the apical meristem, except that the cells are flatter and
slightly elongated.
 The cells have thicker cell walls than the cells of the apical meristem.
 NB! Sometimes a group of cells in the plant become meristematic (divide actively) for a
particular function, e.g. cells that form new cells to replace damaged and worn-out cells, or
cells that give rise to lateral roots. These cells are known as secondary meristematic
tissue

z
Plant tissues (Permanent tissue)
 Permanent tissue is tissue that is already differentiated to
perform a specific function. It includes epidermis, ground tissue
(parenchyma, sclerenchyma, collenchyma) and vascular tissue
(xylem and phloem).
 Epidermis
 The epidermis forms the outer layer around roots, stems and
leaves.

z
Epidermis
 Basic structure

z
Epidermis
 Epidermal cells are brick-shaped and arranged in a single layer.
 The cells are transparent and do not contain chloroplasts.
 There are no intercellular spaces between the cells.
 The epidermal cells of leaves and stems are covered by a waxy
layer, the cuticle, which repels water.
 The brick-shaped epidermal cells can be modified for specific
functions, for example into root hairs or the guard cells of a
stoma.

z
Epidermis
 Root hair cells
 Are specialised epidermal cells with thin-walled, hair-like
outgrowths.
 Root hairs increase the surface area of roots to maximise the
absorption of water and dissolved nutrients.
 A cuticle is absent so that roots can absorb water.
 A large central vacuole stores solutes to create a low water
potential that consistently draws water in by osmosis.

z
Epidermis
 Guard cells of a stoma
 Guard cells mainly occur in the epidermis of leaves.
 A stoma is formed by two bean-shaped guard cells.
 Between the two guard cells is an opening on the leaf surface
called the stomatal pore.
 Guard cells are the only epidermal cells that contain chloroplasts.

z
Epidermis
 Guard cells of a stoma
 The walls of the guard cells are unevenly thickened; they have a thin outer
wall and a thick inner wall. When water enters the guard cells by osmosis
during the day, they become turgid (swollen with water) and expand
unevenly. The stretching of the thin outer wall pulls the stomatal pore open.
 More stomata are often found on the lower surface of leaves to limit water
loss. Hydrophytes (water plants) float in water and thus their stomata are on
the upper surface.

z
Functions of the epidermis
 The epidermis protects the underlying tissues from injury and
desiccation (drying out).
 The cuticle prevents excessive moisture loss in leaves and stems.
 The transparent epidermis allows sunlight through for
photosynthesis.
 Root hairs absorb water and mineral salts from the soil.
 The guard cells of the stoma control the opening and closing of the
stomatal pore for gaseous exchange and transpiration (water loss).

z
Ground tissue
 Ground tissues fill the spaces between the epidermal tissue and
the vascular tissue.
 There are 3 types:
 Parenchyma
 Sclerenchyma
 Collenchyma

z
Ground tissue
 Parenchyma
 Parenchyma is the most abundant plant tissue.
 Basic structure
 Parenchyma cells are large with thin cell walls.
 Large intercellular spaces occur between the cells.
 The cells have large vacuoles.
 Stem and leaf parenchyma contain chloroplasts.

z
Parenchyma
 Functions
 Large vacuoles store food and water.
 Chlorenchyma produces carbohydrates through photosynthesis.
 Large intercellular spaces allow gaseous exchange to take place.
 The vacuole provides rigidity as a result of turgor pressure exerted
by the cell sap.

z
Sclerenchyma
 Are found in leaves, stems and fruit.
 The cell walls are evenly thickened with lignin.
 Each cell has a small lumen (cell cavity).
 Mature cells are dead and hollow (metabolically inactive).
 There are two types of cells: sclereids and fibres.
 Sclereids are more or less round in shape, e.g. stone cells.
 Fibres are more elongated.
 There are no intercellular spaces between the cells.

z
Sclerenchyma
 Functions
 Sclerenchyma serves as strengthening tissue.
 It provides rigid mechanical support to the plant.

z
Collenchyma
 Collenchyma usually occurs in young, growing herbaceous
stems just below the surface of the epidermal layer.
 The cell walls are unevenly thickened with cellulose.
 Most thickening occurs in the corners of the cell walls.
 There are small or no intercellular spaces between the cells.

z
Collenchyma
 Functions
 Collenchyma serves as strengthening tissue.
 It provides flexible mechanical support to some stems and leaves.

z
Vascular tissue
 Consists of xylem and phloem and forms the transport system of
the plant. Xylem and phloem occur in the roots, stems and
leaves.

z
Xylem
 Contains no living material and is regarded as dead tissue.
Xylem tissue mainly consists xylem vessels and tracheids.
 Xylem vessels (Basic structure):
 Xylem vessels consist of a series of elongated cells connected
end to end. The individual cells composing the xylem vessels are
called vessel elements.
 The individual cells do not contain cytoplasm and are therefore
empty and dead.
 The transverse walls (cross-walls) are perforated or have
disappeared completely to form a continuous tube.

z
Xylem
 The cellulose cell walls are thickened by lignin; however, the
entire wall is not evenly thickened, but lignin forms spiral, ring-
like or pitted (net) patterns.
 This uneven thickening provides additional strength and support
to the vessels in that they can stretch, remain open, flexible and
upright.
 In the thickened walls are pits that enable lateral transport
between the xylem vessels.
 In a cross-section, xylem vessels are round. Their round
structure provides additional strength and support.

z
Xylem (Tracheids)
 Basic structure
 Tracheids are elongated cells with tapered ends.
 Their cell walls are, as in the xylem vessels, thickened by lignin.
Pits connect adjacent cells for lateral transport of water.
 The tapered ends of the tracheids overlap and also contribute to
the strengthening of the tubes and to lateral transport.
 Water moves more slowly in the tracheids than in the xylem
vessels.

z
Xylem (Tracheids)
 Functions:
 Water and dissolved mineral salts are transported upwards by the
xylem tissue from the roots to the rest of the plant.
 Xylem serves as strengthening and support tissue for the plant.

z
Phloem
 Consists of living cells that, in contrast to xylem, do not contain
thickened cell walls. Phloem tissue mainly consists of sieve
tubes and companion cells.

z
Phloem (Sieve tubes)
 Basic structure
 Sieve tubes consist of elongated living cells that are joined to one
another end to end.
 The cross-walls between the continuous segments are perforated
and are called sieve plates.
 The cellulose cell walls of the sieve tubes are thin-walled and not
strengthened by lignin.
 Mature sieve tubes have no nucleus and are dependent on the
companion cells for their metabolic functions.

z
Phloem (Companion cells)
 Basic structure
 Companion cells have nuclei.
 Companion cells are responsible for performing all the metabolic
activities of the sieve tubes.

z
Phloem
 Functions
 Transport of produced organic nutrients from the leaves to the rest
of the plant.

Plant Tissues for Grade 10 Life Sciences

More Related Content

What's hot (20)

Similar to Plant Tissues for Grade 10 Life Sciences (20)

Recently uploaded (20)

Plant Tissues for Grade 10 Life Sciences