Plant Tissue Systems Flashcards
What is a tissue?
A tissue consists of a group of one or more cell types which carry out specialized function(s)
Name the 3 main tissue systems of vascular plants
- Dermal tissue system
- Vascular Tissue system
- Ground Tissue System
Where do cells undergo changes in during differentiation?
Cytoplasm
Cell wall
Organelles
What is the dermal tissue system?
It is the outer protective covering of plants
Ex: Epidermis
Write the features of the epidermis
- Protective layer in 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 the epidermis
- Epidermis in the older regions of stems and roots is replaced by a protective layer called periderm after secondary growth
What is the cuticle?
A waxy, epidermal coating in aerial parts of the plant
What specialized cells are found in the epidermis?
Guard cells
Root hair cells
Trichomes
What is the periderm?
A thick and tough covering formed after secondary growth, replacing the epidermis in older regions of stems and roots
What are the functions of epidermis?
- Defense against physical damage and pathogens
- Cuticle helps prevent water loss
- Root hairs involve in absorption of water and mineral ions
- Guard cells help gaseous exchange
- Hair like trichomes reduce water loss, shiny hairs reflect excess light
- Some trichomes secrete chemicals involved in defense against insects/ pathogens/herbivores
What is the function of cuticle?
Helps prevent water loss
What is the function of root hairs?
Absorption of water and mineral ions
What is the function of guard cells?
Gaseous exchange
What are trichomes?
Epidermal outgrowths such as hairs and glands
What are the functions of trichomes?
- Hair like trichomes reduce water loss
- Shiny hairs reflect excess light
- Some trichomes secrete chemicals involved in defense against insects/ pathogens/herbivores
Describe ground tissue system
- Ground tissue fills the gap between dermal tissue and vascular tissue
- They mainly consist of cortex (outside the vascular cylinder) and pith (inner to vascular cylinder)
- The ground tissue includes cells specialized for functions such as storage, support, short distance transport and photosynthesis
- There are 3 main types of cells present in the ground tissue.
- Parenchyma Cells
- Collenchyma Cells
- Sclerenchyma Cells
What are the 2 main parts of the ground tissue?
cortex (outside the vascular cylinder)
pith (inner to vascular cylinder)
What are the functions of the specialized cells in the ground tissue?
storage, support, short distance transport and photosynthesis
What are the 3 main types of cells present in ground tissue?
- Parenchyma Cells
- Collenchyma Cells
- Sclerenchyma Cells
What is the function of ground tissue system?
Ground tissue fills the gap between dermal tissue and vascular tissue
Describe parenchyma cells
- Living even at functional maturity
- Mature cells have relatively thin and flexible primary cell walls, and most cells lack secondary cell walls
- They have a large central vacuole
Describe the cell wall of parenchyma cells
- Mature cells have relatively thin and flexible primary cell walls
- Most cells lack secondary cell walls
What are the functions of parenchyma cells?
- Performs most metabolic functions of plants (ex: synthesis of various organic products)
- Storage (some cells in root and stem contain plastids (leucoplasts) which can store starch)
- Most 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 ability of parenchyma cells is important for wound repair
- Most parenchyma cells retain the ability to divide and differentiate under suitable conditions. This ability is important in wound repair
Write the functions of leucoplasts of parenchyma cells
Storing starch
What is a metabolic function performed by parenchyma cells?
Synthesis of various organic products
Describe collenchyma cells
- They are generally elongated
- They have thicker primary cell walls than parenchyma cells
- Their walls are unevenly thickened
- Young stems and petioles often have strands of collenchyma just below the epidermis
- Even at functional maturity, they are living, flexible, elongating, with stems and leaves they support
Describe the cell walls of collenchyma cells
- They have thicker primary cell walls than parenchyma cells
- Their walls are unevenly thickened
Where are collenchyma cells found?
Young stems and petioles often have strands of collenchyma just below the epidermis
What are the functions of collenchyma cells?
- Give mechanical support to leaves and stems without restraining growth
Describe sclerenchyma cells
- Secondary cell walls are produced after cell elongation
- They have secondary cell walls thickened by a large amount of lignin
- They are dead cells at maturity
- There are 2 types of sclerenchyma cells:
- Sclereids
- Fibers
What are the 2 types of sclerenchyma cells?
- Sclereids
- Fibers
Describe the cell walls of sclerenchyma cells
- Secondary cell walls are produced after cell elongation
- They have secondary cell walls thickened by a large amount of lignin
Describe sclereids
- Shorter and wider than fibers and irregular in shape
- They have very thick lignified secondary cell walls
- They’re found in places where growth has stopped
Ex: Nut shells, seed coats, flesh of coarse fruits
What’s the structure of sclereids?
- Shorter and wider than fibers and irregular in shape
- They have very thick lignified secondary cell walls
Where are sclereids found?
In places where growth has stopped
Ex: Nut shells, seed coats, flesh of coarse fruits
Describe the cell walls of sclereids
- They have very thick lignified secondary cell walls
What are the places of sclereids where growth has stopped?
Nut shells, seed coats, flesh of coarse fruits
Describe sclerenchyma fibers
- Usually grouped in strands
- They are long, slender and tapered
- Used commercially to obtain fibers
Ex: Coconut Husk Fiber, Hemp Fiber
What’s the structure of sclerenchyma fibers?
Long, slender and tapered.
Give examples for sclerenchyma fibers
Coconut Husk Fibers
Hemp Fibers
What’s the function of sclerenchyma cells?
- Sclereids and fibers are specialized to provide strength and support
What are the 2 main vascular tissues?
Xylem
Phloem
Describe the xylem tissue
- It consists of
- Vessel elements
- Tracheids
- Fibers
- Parenchyma cells
- These tissues are found in angiosperms and some gymnosperms
- Vessel elements and tracheids are dead at functional maturity. They mainly conduct water.
- Fibers give mechanical strength
- Parenchyma cells function in storage and radial transportation
Where are xylem tissues found?
In angiosperms and some gymnosperms
What are the functions of each cell in xylem tissues?
Vessel elements and tracheids - They mainly conduct water
Fibers - Give mechanical strength
Parenchyma cells - Function in storage and radial transportation
What’s the function of vessel elements and tracheids in xylem tissues?
They mainly conduct water
What’s the function of fibers in xylem tissues?
Giving mechanical strength
What’s the function of parenchyma cells in xylem tissues?
Storage and radial transportation
Describe vessel elements of xylem tissue
- 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 the tension of water transport.
- Perforation plates are present at the end walls of vessel elements. Other walls are interrupted by pits
- They form xylem vessels by aligning end to end with perforation plates. Water flows freely through perforation plates
What plants contain vessel elements?
All angiosperms and some gymnosperms
Describe the structure of vessel elements
- They are cylindrical and long
- They are wider, shorter, and have thinner walls than tracheids
What’s the function of secondary cell walls of vessel elements of xylem tissues?
They provide support to prevent collapse under tension of water transport
Describe the perforation plates of vessel elements
- Perforation plates are present at the end walls of vessel elements. Other walls are interrupted by pits
- They form xylem vessels by aligning end to end with perforation plates. Water flows freely through perforation plates
Describe 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 plants are tracheids found in?
All vascular plants
Describe the structure of tracheids of xylem tissues
Long, thin cells with tapering ends
What’s the function of pits in tracheids?
Water moves from end-to-end through pits
Describe the phloem tissue
- It consists of
1. Sieve tube elements
2. Companion cells
3. Parenchyma cells
4. Fibers - Only found in angiosperms
- Except fibers, all 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 cells do the phloem tissue consist of?
- Sieve tube elements
- Companion cells
- Parenchyma cells
- Fibers
What plants are phloem tissues found in?
Angiosperms
Which cells in phloem tissue are living?
Except fibers, all other phloem cells are living cells
In what plants are sieve tube elements and companion cells absent?
In seedless vascular plants and gymnosperms
In seedless vascular plants and gymnosperms, what cells are present instead of sieve tube elements?
Long, narrow cells called sieve cells
Describe sieve tube elements
- Sieve tube elements lack
1. Nucleus
2. Ribosomes
3. A distinct vacuole
4. Cytoskeletal elements - The cytoplasm is reduced into a thin, peripheral layer
- Absence of these organelles allow nutrients to pass more freely.
- Chains of sieve tube elements are aligned to form sieve tubes
- The end walls between sieve tube elements contain porous plates called sieve plates
- Sieve plates allow the movement of fluid from one sieve element to the next
Why are there an absence of organelles in sieve tube elements?
To allow nutrients to pass more freely
Write the adaptations of sieve tube elements to help nutrients pass more freely through them
- Lacking nucleus, ribosomes, a distinct vacuole and cytoskeletal elements
- The cytoplasm being reduced to a thin peripheral layer
What are sieve plates?
The end walls between sieve tube elements contain porous plates called sieve plates
Write the function of sieve plates
Sieve plates allow the movement of fluid from one sieve element to the next
How are sieve tube elements aligned to form sieve tubes?
Chains of sieve tube elements are aligned to form sieve tubes
Describe companion cells
- They are non-conducting cells
- They are found alongside in each sieve tube elements and connects with sieve tube elements by numerous plasmodesmata
- Nucleus and ribosomes of these cells also serve to adjacent sieve tube elements
- Some companion cells in leaves help in phloem loading and in other organs unloading
What’s the location of companion cells?
They are found alongside in each sieve tube elements and connects with sieve tube elements by numerous plasmodesmata
Write the functions of companion cells
- Nucleus and ribosomes of these cells also serve to adjacent sieve tube elements
- Some companion cells in leaves help in phloem loading and in other organs unloading
