Plant form and function Flashcards
Tissue
A tissue is a group of 1 or more cell types carrying out specialized functions
What are primary meristems
Apical
Intercalary
Axillary bud
Intra fascicular cambium
What are secondary meristems
Inter fascicular cambium
Cork cambium
During differentiation process, they undergo changes in
cytoplasm, organelles and cell wall
Dermal tissue system
Outer covering of the plant e.g; Epidermis
Protective covering in leaves, stems and roots of primary plant body
Tightly packed single cell layer
Usually covered by a cuticle which is a waxy epidermal covering found at aerial parts
Specialized cells such as root hairs,trichomes and guard cells
Functions of ground tissue system
Storage
Photosynthesis
Support
Short distance transport
Parenchyma cells
Living evem at functional maturity
Cells have primary cell walls which are relatively thin and flexible and most of the cells lack secondary cell walls
Central vacuole present
Parenchyma cells functions
Perform most of the metabolic functions of the plant
E.g: photosynthesis fibre
Storage - some cells contains leucoplasts( plastids) in which starch is stored
Most of the parenchyma cells retain the ability to divide and differenciate under suitable conditions. This ability is important in wound repair and tissue culture practises.
Collencyma cells
Generally elongated
They have thicker primary cell walls than parenchyma and cell walls are unevenly thickned with cellulose
Young petioles and stems often have strands of collenchyma just beneath the epidermis
Living even at functional maturity
Collencyma functions
Giving mechanical support to stems and leaves without restraining growth
Sclerenchyama cells
They produce secondary cell walls after cell elongation
Secondary cell walls are thickned by a large amount of lignin
Dead at maturity
2 types of cells known as sclerides and fibers
Sclerenchyma functions
Sclerides and fibers are specialized to provide strength and support
Sclereids
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
Fibers
Fibers are usually grouped in strands. They are long, slender and tapered. Used commercially to obtain fibers. e.g: coconut husk fiber, hemp fibers
Xylem
Consist of vessel elements, tracheids, fibers and parenchyma
Vessel elements and tracheids mainly conduct water
They are dead at functional maturity
Fibers give mechanical strength
Parenchyma involves in storage and in radial transport
Vessel elements
Found in all angiosperms and some gymnosperms only(Gnetum). Cylindrical and long. Shorter and wider than fibers and have thinner walls than tracheids which are thickened by lignin. They provide support to prevent collapse under tension during water transport.
End walls are perforated with perforation plates while other walls are interrupted by pits. Form xylem vessel by aligning end to end through perforation through which water moves freely.
Phloem
Consist of sieve tube elements, parenchyma, companion cells and fibers.
Sieve tube elements are not found in seedless vascular plants and gymnosperms instead long narrow cells called sieve cells are present.
Sieve tube elements
Lacks a nucleus, ribosomes, distinct vacuole and cytoskeletal structures
Cytoplasm is restricted to a thin pheripheral layer
Porus plate known as the sieve plate is found at end walls
Companion cells
Non conducting cells and are found alongside each sieve tube element. Nucleus and ribosomes serves to adjacent sieve tube elements by forming numerous plasmodesmata
Some companion cells involves in phloem loading and phloem unloading.
indeterminate growth
Plants continue growth throughout the life known as indeterminate growth.
Characteristics of meristematic cells
Living
roughly isodiametric
are structurally and functionally undifferentiated
central nucleus
dense cytoplasm
ability to multiply
During secondary growth cells in the pericycle converts to
Cork cambium
Radial and collateral vascular bundles
If xylem and phloem are not found in the same place (not connected) and have different radii it is known as an radial vascular bundle. Dicot and monocot roots contain radial vascular bundles.
If xylem and phloem are connected it is referred as collateral vascular bundles. Monocot and dicot stems contains collateral vascular bundles.
Exarch and endarch xylems
Early devoloped xylem is the protoxylem while the later developed xylem is the metaxylem
If the protoxylem is found outer to the metaxylem that is if inward growth of the xylem is present such a xylem is known as an exarch xylem. Found in monocot and dicot roots
And if the protoxylem is found inner to the metaxylem (outward growth) is is known as endarch xylem. Found in monocot and dicot stems.
Closed and open vascular bundles
If the primary meristem of intra fascicular cambium is present between the xylem and the phloem it is known as an open vascular bundle
Secondary growth
Increase in diameter of of stems and roots due to the new cells produced by lateral meristems
Periderm consist of
Cork cambium and the cork tissue
What acts as stomata during gaseous exchange of secondary stems
Lenticells
Bark consists of
Bark is all tissues out of the vascular cambium which consists of secondary phloem and periderm ( cork cambium and cork tissue)
Heart wood and sap wood
The secondary xylem no longer transporting water or minerals is known as the heart wood
Newest layers of the secondary xylem which still transports xylem sap is known as sapwood
Hard wood and soft wood
Secondary xylem of dicot angiosperms is known as hard wood while wood of gymnosperms is known as the soft wood.
Role of ABA in stomatal closure
ABA is produced in leaves and roots in response to water deficiency and leads to the closure of stomata by removing K ions. This prevents wilting of the plant.
In dicot leaves, stomata are found mainly in the
Lower epidermis
Only epidermal cells containing chloroplasts
Guard cells
Which mesophyll cells contain lower chloroplast
Spongy mesophyll
Differences between monocot leaves and dicot leaves in relation to the gaseous exchange
Monocot leaves contains stomata on both lower and upper epidermis while in dicot leaves stomata are mainly found in the lower epidermis
There is no distinction in the mesophyll layer of monocot leaves
Vascular cylinders (veins) are arranged in net like venation in dicot leaves while parallel venation is seen in monocot leaves
Structure of stomata
Stomata are microscopic pores surrounded by guard cells which are specialized epidermal cells containing chloroplast. They are typically bean shaped in angiosperms and contains walls of uneven thickness. Inner walls are thicker and relatively inelastic. Some of the microfibrils radially arrange to form inelastic hoops around the guard cells.
In plants gaseous exchange is possible via
stomata and lenticels
Gases can be exchanged via the cuticle as well
Role of ABA in stomatal closure in drought
• ABA is produced in roots and leaves in response to water deficiency.
• Production of ABA leads to close the stomata by removal of K+in guard cells.
• This prevents the wilting of the plant.
Factors affecting stomatal action
Light stimulates accumulation of K+ in guard cells
Decrease in CO2 concentration in substomatal cavity lead to open stomata
Internal clock in the guard cells
Environmental stresses
Collenchyma tissues are absent in
Roots
