04. Plant Form and Function Flashcards
What are the characteristics of meristems in plants?
• are living cells
• are isodiametric (roughly spherical)
• are structurally and functionally undifferentiated
• have a central nucleus
• have a dense cytoplasm
• have ability to multiply
What are three overlapping zones of the meristem?
• cell division
• cell elongation and
• differentiation
What are the three types of meristems?
- apical meristems
- lateral meristems
- intercalary meristems
What is the location of the apical meristem?
These meristems are located at root tips and shoot tip
What is the function of the apical meristem?
They add new cells that enable increase in length. This process is known as primary growth
What are the examples of vascular cambium?
secondary xylem
secondary phloem
Where can lateral meristem be found in?
They are found in woody plants
What is the function of lateral meristems’ cork cambium?
involve in the secondary growth in increasing circumference of roots and stems.
What does the vascular cambium produce?
secondary xylem and secondary phloem
What does the cork cambium produce?
cork cambium produces thick and tough periderm, replacing epidermis.
Where can the intercalary meristems be found?
Some monocots such as grasses show meristematic activity at the bases of stems and leaves (nodes).
What is the function of intercalary meristems?
They allow rapid regrowth in damaged leaves.
What are the features of the shoot apex
Found at tips of shoot apex
Protected by leaf primordial
Produces new cells only inwards
Features of the root apex?
Protected by root cap
Found at the tip of the root
Produce new cells both sides
outwards and inwards
Features of the root apex?
Protected by root cap
Found at the tip of the root
Produce new cells both sides
outwards and inwards
What do plant cells undergo during the differentiation process?
During differentiation process, they undergo
changes in cytoplasm, organelles and cell wall. Therefore, several types of plant cells
can be recognized according to their structure and function
What are the three tissue systems?
- dermal tissue systems
- ground tissue systems
- vascular tissue systems
What is the feature of dermal tissue system?
This is the outer protective covering of plants.
• Protective layer in the stems and roots of the primary plant body and leaves
• Tightly packed single cell layer
• Normally covered by a cuticle which is a waxy epidermal coating in aerial parts
• Specialized cells such as guard cells, trichomes and root hairs are also found in
epidermis
What are the functions of the epidermis?
• Defense against physical damage and pathogens
• Cuticle helps to prevent water loss
• Root hairs involve in absorption of water and mineral ions
• Guard cells help gaseous exchange
• Trichomes (epidermal outgrowths such as hairs and glands) ;
o hair like trichomes reduce water loss, shiny hairs reflect excess light
o Some trichomes secrete chemicals involved in defense against insects/
pathogens/ herbivores,
Epidermis in older regions of stems and roots is replaced by a protective layer called
periderm after the secondary growth
What is the location of the ground tissue?
Ground tissue fills the gap between dermal tissue and vascular tissue, mainly consists
of cortex (outer to vascular tissue) and pith (inner to vascular tissue).
What are the functions of the ground tissue?
storage, photosynthesis, support and
short distance transport.
What are the three main types of the ground tissues?
- parenchyma cells
- collenchyma cells
- sclerenchyma cells
What are the features of the parenchyma cells?
• Living even at functional maturity
• Mature cells have primary cell walls which are relatively thin, flexible and most
of the cells lack secondary walls
• They have a large central vacuole
What are the functions of the parenchyma cells?
Functions
• Perform most of the metabolic functions of the plants.
e.g. synthesis of various organic products
• Storage-
e.g. some cells in root and stems contain plastids (leucoplasts) which
store starch.
• Most of the parenchyma cells retain the ability to divide and differentiate under
suitable conditions. This ability is important in wound repair. These abilities also
make it possible to multiply and differentiate cells even from a single parenchyma
cell in tissue culture practices.
What are the features of the collenchyma cells?
• They are generally elongated
• They have thicker primary walls than parenchyma cells
• Their walls are unevenly thickened
• Young stems and petioles often have strands of collenchyma cells just below the
epidermis
• Even at functional maturity they are living, flexible and elongating with stems
and leaves they support
What is the function of the collenchyma cells?
Give mechanical support to leaves and stems without restraining growth
What are the features of sclerenchyma cells?
• Secondary cell walls are produced after cell elongation
• They have secondary cell walls thickened by large amount of lignin
• They are dead cells at maturity
What are the two types of sclerenchyma cells?
- sclereids
- fibers
What are the features of sclereids?
are shorter and wider than fibers and irregular in shape.
They have very thick lignified secondary cell walls.
They are found in places where growth has stopped e.g. nut shells, seed coats and flesh of coarse fruit.
What are the features of fibers?
are usually grouped in strands.
They are long, slender and tapered.
Used commercially to obtain fibers.
e.g: coconut husk fiber, hemp fibers
What are the features of sclereids?
They are shorter and wider than fibers and irregular in shape.
They have very thick lignified secondary cell walls.
They are found in places where growth has stopped e.g.
nut shells, seed coats and flesh of coarse fruit.
What are the features of fibers?
are usually grouped in strands.
They are long, slender and tapered.
Used commercially to obtain fibers. e.g: coconut husk fiber, hemp fibers
What are the sclerenchyma cell function?
Sclereids and fibers are specialized to provide support and strength.
What are the features of the xylem tissue?
• It consists of vessel elements, tracheids, fi bers and parenchyma cells in
angiosperms and some of the gymnosperms.
• Vessel elements and tracheids mainly conduct water.
• They are dead at functional maturity.
• Fibers give mechanical strength.
• Parenchyma functions in storage and in radial transportation.
What are the features of the vessel elements?
• In all angiosperms and some gymnosperms, contain vessel elements
• They are cylindrical and long.
• They are wider, shorter and have thinner walls than tracheids
• Secondary walls are thickened by lignin
• They provide support to prevent collapse under tension of water transport
• Perforation plates are present at end walls of vessel elements. Other walls are
interrupted by pits
• They form xylem vessel by aligning end to end with perforation plates
• Water flows freely through perforation plates
What are the features of tracheids?
• Found in all vascular plants
• Long, thin cells with tapering ends
• Secondary walls are thickened with lignin and often interrupted by pits
• Water moves from end to end through pits
• Thickening by lignin provides support to prevent collapse under water transport
What are the features of the phloem?
• It consist of sieve tube elements, companion cells, parenchyma cells and bers
in angiosperms
• Except fibers other phloem cells are living cells
• In seedless vascular plants and gymnosperms sieve tube elements and companion
cells are absent. Instead of sieve tube elements, long narrow cells called sieve
cells are present in these plants.
Where can we find the sieve cells?
In seedless vascular plants and gymnosperms
What are the features of the sieve tube element?
• Sieve tube elements lack nucleus, ribosomes, a distinct vacuole, and cytoskeletal
elements-
• cytoplasm reduced into a thin peripheral layer.
• Absence of these allow passing of nutrients more freely
• Chains of sieve tube elements are aligned to form sieve tubes
• The end walls between sieve tube elements contain porous plate called sieve
plate.
• Sieve plate allows movement of fl uid from one sieve element to the next.
What are the features of the companion cells?
• They are non-conducting cells.
• Found alongside in each sieve tube element and connects with sieve tube element
by numerous plasmodesmata
• Nucleus and ribosomes of these cells also serve to adjacent sieve tube element
• Some companion cells in leaves help in phloem loading and in other organs
unloading
What does the plant growth involve?
Growth involves irreversible increase of dry mass associated with the development of an organism.
Often it is associated with increase of cell number as a result of producing more cells from the meristem accompanied by cell elongation.
Plants continue growth throughout the life known as indeterminate growth.
Why are the distribution of monocot and dicot roots similar?
Apart of the distribution pattern of xylem and phloem tissue structures of both monocot
and dicot roots are more or less similar.
What is the function of the epidermis in the dicot root?
Epidermis protects inner parts while root hairs involve in the absorption
of water and minerals.
Describe the structure of the epidermis in dicot root
Outermost cell layer is epidermis. Cells have unicellular outgrowths called root
hairs.
Describe the structure of cortex of dicot root?
Between epidermis and vascular cylinder there is a ground tissue known as
cortex which is made up of mostly parenchyma cells with intercellular spaces.
What is the function of the cortex of dicot root?
Cortex mainly stores carbohydrates, and also transports water and minerals towards the endodermis.
Describe the structure of endodermis of dicot root
Innermost single cell layer of the cortex is the endodermis.
• Endodermis contains a suberin belt called casparian strip and no inter-cellular
spaces.
What is the function of the endodermis of dicot root?
Therefore, it blocks cortical apoplast from the vascular apoplast
Describe the structure of the pericycle in the dicot root?
Interior to endodermis there is a pericycle containing two or three parenchyma
cell layers.
What is the function of the pericycle of the dicot root?
These cells in dicot roots have meristematic function and involve in
the formation of lateral roots and secondary growth of the root.
Describe the location of the vascular tissue of the dicot root?
Inner to pericycle there is vascular tissues as a solid core. Xylem can be found in the middle and it is star shaped in a cross section of a dicot root.
Phloem is located in the groove between the arms of xylem.
Describe the vascular tissue of the monocot root
In monocot roots, vascular tissue consists of a central core of parenchyma cells
surrounded by a ring of alternating xylem and phloem
Describe the pericycle in the monocot root?
Pericycle in monocot roots is not meristematic
What is the function of the outermost epidermal cell layer of the dicot root?
The outermost epidermal cell layer protects inner parts from desiccation and infections
Name the special feature of the epidermis of the dicot stem?
The epidermis is interrupted by pores called stomata.
Collenchyma cells may also be present just beneath the epidermis to provide
strength.
Describe the structure of the monocot stem?
• Ground tissue of monocot shoot is not differentiated into cortex and pith
• The vascular bundles are scattered throughout the ground tissue in most monocot
stems.
• Each vascular bundle is surrounded by sclerenchyma. It consists of a xylem
tissue and a phloem tissue but no cambium inbetween xylem and phloem.
Describe the vascular bundle of the dicot stem?
• Vascular bundles arranged as a ring. Vascular bundle contains primary phloem
towards cortex primary xylem towards pith and in-between a cambium tissue.
• Outside vascular bundle, there is a cluster of sclerenchyma cell.
• Inner to vascular bundles large pith which is also made up of parenchyma cells
can be found.
What does the lateral shoots of the dicot stem develop from?
Lateral shoots develop from axillary buds
Structure of cortex of the dicot stem?
Interior to epidermis is cortex mostly containing parenchyma cells
Where does the secondary growth occur?
This occurs in stems and roots of woody perennial plants including, all
gymnosperms species and many dicot species.
What is the function of vascular cambium during secondary growth?
The vascular cambium adds secondary xylem (wood) towards primary xylem
and secondary phloem towards primary phloem, increasing vascular fl ow and
support for the shoots
Cork cambium structure in secondary growth and function?
The cork cambium produces tough thick covering consisting mainly of wax
impregnated cells that protect the stem from water loss and from invasion of
insects, bacteria and fungi.
