Internal Organization of Stems Flashcards
What is the Epidermis?
A protective single layer of parenchyma cells on the outermost layer of the plant.
What is the function of the epidermis?
Aids in interchanging materials from the outside of the cell to the inside
Protects the plant from fungi and bacteria invasion
Prevents water loss
What is the substance that covers the epidermis?
A waterproof cutin builds up on the surface of the epidermis making a waxy layer or waxy cuticle
What is the waxy cuticle?
A waterproof layer of cutin on the surface of the epidermis which prevent desiccation and gas exchange from everywhere but the stomata.
What is a stomatal pore?
An opening on the underside of the leaf which allows for gas exchange.
What are Guard cells?
These are cells that surround the stomatal pore controlling its size and therefore gas exchange.
How do guard cells function?
These cells swell by absorbing water which allows the stomatal pore to be open allowing CO2 and O2 to be exchanged and water to leave.
What happens when the water level is low?
The guard cells are unable to stay open and so the pore is closed
When are the guard cells closed?
The guard cells close at sunset and during water stress
What are trichomes?
These are the projections from epidermal cells or hairs
What is the function of trichomes?
Primary function is protection
- Deter herbivores
- Minimize water loss
- Protect from over exposure to sunlight (shade underlyinh cells)
What is the Cortex?
The cortex is under the epidermis and is made up of parenchyma and collenchyma
What is Aerenchyma?
This is cortex with loosely packed cells and large intercellular spaces.
What are the two types of vascular tissue in the plant?
Xylem and phloem
What are vascular tissue responsible for?
Transporting materials throughout the plant.
What is the xylem vessel made up of?
The xylem vessel is made up of two types of conducting sclerenchyma: tracheids and vessel elements. These are dead cells at maturity
What is a tracheary element?
This is the name of mature conducting sclerenchyma
How does the tracheary element develop?
1- The young parenchyma cell goes through one cycle of mitosis and is arrested in G0.
2- The cell then begins to grow and elongate becoming longer and narrower and soon the secondary wall is deposited to re-enforce the thin primary wall.
3- The cell then dies and the protoplasm degenerates leaving a hollow tube
4- Areas on the primary wall remain without any secondary wall so that water can enter and exit the elements as the secondary wall is impermeable to water
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Where does the xylem get its strength from?
The secondary cell wall
Annualar thickening
Simplest of the tracheary elements
Only a small amount of secondary wall is present
Organized into ring
Does not provide a lot of strength
Helical thickening
The secondary wall is 1 to 3 rings in the primary cell wall
Scalariform
Scalariform thickening is stronger as the extensive secondary wall underlies most of the inner surface of the primary wall (ladder-like pattern)
Reticulate
Secondary wall is deposited in a mesh-like manner
Bordered pits
Area in the primary wall that do not have secondary wall are weak points which allow for water to pass through. They are surrounded by extra secondary wall material.
Pit membranes
The primary walls and middle lamella between the two pits
Pit pairs
Aligned set of pits
How does water move through the vessel elements?
Vessel elements are vertically stacked and the ends of the cells are removed so there is a continuous tube called perforations allow water to move with less friction than the tracheids.
What is a vessel?
A stack of vessel elements. They absorb water from the parenchyma cells
Tracheids
These are cells that have a primary and secondary wall. Die at maturity and have pits along their side wall for lateral transfer.
Perforations
These are formed at the last stage of differentiation where often an entire end of the cell wall is digested creating a large opening.
What is something all plants with vascular tissue have in common?
Tracheids
Which type of plant only has vessel elements? WHy?
Flowering plants to transport water long distances from root to stem
Which plant only has tracheids?
Conifers
What are the 2 types of conducting elements in phloem?
Sieve element members and sieve cells
What does sieve element refer to?
Sieve element member or sieve cells
What do Phloem develop from?
Develop from parenchyma cells that remain metabolically active at maturity.
Sieve pores
These are enlarged plasmodesmata
Sieve areas
A collection of sieve pores in one place
Sieve cell
These are cells which have a similar structure to tracheids but they have seive areas distributed along their cell surface
Sieve element members
These are cells which have sieve plates with large pores at both ends of the cell and are stacked on top of each other in a vertical column.
More effective way of transporting phloem sap
What is unusual about sieve elements?
Their nucleus degenerates so there is no complex metabolism and they remain alive but neighboring cells exert nuclear controlled.
What cells are sieve cells associate with?
Albuminous cells
What cells are sieve element members?
Companion cells
What is the function of companion cells and albuminous cells?
They are involved in loading and unloading sugars into the sieve elements
Structure of neighboring cells?
Smaller than the sieve elements
Prominent nucleus
Dense cytoplasm filled with ribosomes
large plasmodesmata
How are conducting cells connected to the controlling cells?
Walls between conducting cells and controlling cells have a lot of complex passages that are sieve areas on the conducting side and large plasmodesmata on the controlling side
