Plant Tissue Systems

how does a plant tissue system form?

the new cells originating from the meristems are differentiated to perform specialized functions and form a plant tissue system

what do the cells forming plant tissue systems undergo and when do they undergo it? therefore what does this mean?

-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 is the definition of a tissue?

a tissue consists of group of one or more cell types which carries out specialized function(s)

what type of plants have 3 main tissue systems and what are they?

vascular plants have 3 main tissues systems. they are;

-dermal tissue system

-ground tissue system

-vascular tissue system

define dermal tissue system

this is the outer protective covering of plants

give an example of a dermal tissue system and describe it

eg:- Epidermis

-the 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 trichomes?

epidermal outgrowths such as hairs and glands

what are the functions of epidermis?

-defense against physical damage and pathogens

-cuticle helps to prevent water loss

-root hairs involve in absorption of water and minerals

-guard cells help gaseous exchange

-trichomes (epidermal outgrowths such as hairs and glands). hair like trichomes reduce water loss, shiny hairs reflect excess light. 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 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 do ground tissues include?

ground tissues include cells specialized for functions such as storage, photosynthesis, support and short distance transport

what are the main types of cells present in ground tissue? how many are there?

three main types of cells are present in ground tissue. they are:

-parenchyma cells

-collenchyma cells

-sclerenchyma cells

what are some features of 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 is the function of leucoplasts?

store starch

what are the functions of parenchyma cells?

-perform most of the metabolic functions of the plants (eg:- synthesis of various organic products)

-storage (eg:- 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 property of parenchyma cells is important to plants and humans on separate occasions?

-the ability to divide and differentiate under suitable conditions

-for plants: for wound repair

-for humans: for tissue culture practices

what are 2 similarities of collenchyma cells and parenchyma cells?

-both have only primary cell wall

-both are living cells

what are some properties of collenchyma cells?

-they are generally elongated

-they have thicker primary walls than parenchyma cells

-their walls are unevenly thickened (by cellulose)

-young dicot 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 are the functions of collenchyma cells?

-give mechanical support to leaves and stems without restraining grow

state some general properties 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 2 types of sclerenchyma cells?

sclereids and fibers

what are the features of 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 (eg:- nut shells, seed coats and flesh of course fruit)

what are the features of fibers?

fibers are usually grouped in strands. they are long, slender and tapered. used commercially to obtain fibers. (eg:- coconut husk fiber, hemp fibers)

what are the functions of sclerenchyma cells?

sclereids and fibers are specialized to provide support and strength

what are the vascular tissues?

xylem and phloem

what do xylem tissues consist of and in what plants?

it consists of vessel elements, tracheids, fibers and parenchyma cells in angiosperms and some gymnosperms

what are the characteristics of xylem tissues?

-it consists of vessel elements, tracheids, fibers 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 transport

what are some properties of 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 ends 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 some properties 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 do phloem tissues consist of and in what plants?

sieve tube elements, companion cells, parenchyma cells and fibers in angiosperms

what are sieve cells?

in seedless vascular plants and gymnosperms, sieve tube elements and companion cells are absent and instead of sieve tube elements, long narrow cells called sieve cells are present in these plants

what are some features of phloem tissues?

-it consist of sieve tube elements, companion cells, parenchyma cells and fibers in a 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.

what is a sieve tube?

chains of sieve tube elements are aligned to form sieve tubes

what is a sieve plate and function?

the end walls between sieve tube elements contain porous plate called sieve plate. it allows the movement of fluid from one sieve element to the next

what are some features of sieve tube elements?

-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 fluid from one sieve element to the next

what are some features of 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