Lecture 6: Plant Structure & Function Flashcards
Know: - 3 tissue types - the cells for each - the 2 organ systems - primary growth - secondary growth - meristems in both kinds of growth - where xylems and phloems form
Describe the primary cell wall of plants
The primary cell wall of plants is found in all plant types.
It is forms a layer on the outside of the plasma membrane and is secreted by the plasma membrane. It is composed of cellulose and protects the cell while providing some structural support. Because it is made from cellulose, it is flexible and more permeable than the membrane.
Describe the secondary cell wall of plants
Only SOME plants have cells with secondary cell walls. This is a second layer that surrounds the cell (closer to the cell), secreted by the plasma membrane after the primary cell wall.
The secondary cell wall provides greater protection and structural support as it is composed of cellulose and the rigid molecule, LIGNIN. Lignin is not flexible or permeable.
What is lignin? Which plant cell wall contains it?
Lignin is a molecule that makes woody stems rigid. The secondary cell wall is composed of lignin and cellulose.
Describe the plasmodesmata
Plasmodesmata are the small channels lined with plasma membrane between cell walls that connect different cells. The plasmodesmata allows for the movement of cytoplasm that can carry molecules or organelles (like chloroplasts that move in response to light) between different cells.
Describe turgor pressure
When the central vacuole of a plant cell fills with water, it expands and exerts a force from the inside of the cell against the primary cell wall. Since the primary cell wall is made of flexible cellulose, the cell expands slightly.
Where is water stored inside a plant cell that expands?
Inside the central vacuole
T or F: Turgor pressure provides some structural support? Even for some non-vascular plants and herbaceous non-woody plants?
TRUE because the cells are filled and expanded to their maximum they become rigid and structurally supportive. Turgor pressure is the reason moss doesn’t look like seaweed outside of water.
What is the opposite of turgid?
Flaccid. When a plant does not have enough water and becomes wilted, the cells are flaccid.
What are the 3 tissue systems that plant cells are organized into? Briefly describe each.
- Dermal tissue system: the external covering of the plant
- Vascular tissue system: the transport system within plants that moves water, nutrients, and sugars.
- Ground tissue system: tissues that are neither vascular or dermal. This system functions in storage, photosynthesis, and support.
The dermal tissue system is located in the ____? which is the _____ tissue layer in plants?
The dermal tissue system is located in the EPIDERMIS which is the OUTER TISSUE LAYER in plants
The epidermis (or dermal tissue system) is composed of which 3 cells? What are their functions?
- Epidermal cells: produce the WAXY CUTICLE that protects the cell from water loss.
- Guard cells: are located in shoots to form the stomata that allow for gas exchange. The guard cells control the opening and closing of the stomata.
- Root hairs: are not actual cells, but are an extension of the epidermal cells. Their main function is to absorb nutrients and water by increasing the surface area of the plant. They also help minimally in structural support.
The ground tissue system is composed of which 3 cells?
- Parenchyma cells
- Collenchyma cells
- Sclerenchyma cells
Describe the parenchyma cells. Which tissue system do they belong to?
The parenchyma cells are part of the ground tissue system.
They are LIVING, thin, flexible cells that perform MOST METABOLIC FUNCTIONS of the plant (including photosynthesis).
Describe the collenchyma cells? Which tissue system do they belong to?
The collenchyma cells are part of the ground tissue system.
They are LIVING cells that have irregularly thickened cell walls to provide some flexible structural support. More so than the parenchyma cells.
Describe the sclerenchyma cells? Which tissue system do they belong to? Are they dead or alive at functional maturity, why?
The sclerenchyma cells belong to the ground tissue system.
They are DEAD at functional maturity in order to perform their job more efficiently. They are VERY RIGID cells due to their secondary cell wall that contains lignin to provide STRUCTURAL SUPPORT.
They are dead at maturity because once they have produced their secondary cell wall, the cell wall can perform the functions this cell needs to do (provide structural support).
Which of the 3 ground tissue cells has a secondary cell wall? why?
The sclerenchyma cells have a secondary cell wall because their main function is to provide structural support to the plant. the secondary cell wall contains lignin and therefore is extremely rigid.
The vascular tissue system is composed of which 2 tissues? Function of each?
- Xylem tissue transports water and mineral nutrients throughout the plant body.
- Phloem tissue transports sugars made from photosynthesis around the plant body.
The vascular tissue system is composed of which 4 cells? and to which tissue do the cells belong?
Composed of…
Xylem tissue:
- tracheids
- Vessel elements
Phloem tissue:
- sieve tube elements
- companion cells
What is the structure and function of tracheid cells? Which tissue and which tissue system do they belong? Alive or dead at maturity? why?
Tracheid cells are located in the xylem tissue of the vascular tissue system.
STRUCTURE: they are long, thin tube-like cells that contain lignified secondary cell walls.
FUNCTION: to move water through the plant body, but they are water tight cells so they contain pits (specific openings) to allow water to move between cells.
They are DEAD at functional maturity so their containments can disintegrate and the tube can become hollow and more efficient at transferring water.
What is the structure and function of vessel element cells? To which system and tissue system do they belong? Are they alive or dead at maturity?
Vessel element cells are located in the xylem tissues of the vascular tissue system.
STRUCTURE: they are wider and shorter than tracheid cells and are connected from end to end lengthwise to form long tubes. They have pits and perforations at cell ends to allow water to flow more efficiently.
They are dead at maturity because they have a secondary cell wall, so their inside containments can disintegrate and they can become hollow and more efficient at moving water.
FUNCTION: to transport water throughout the plant
T or F: Tracheids are more efficient at transferring water than vessel elements?
FALSE. Vessel elements are more efficient at transferring water through plant bodies because they are wider and have large perforations AND pits, rather than just pits and thin tubes.
T or F: Tracheids and vessel elements are both dead at functional maturity?
TRUE to allow for more efficient water transfer through the hollow tubes that are supported by the secondary cell wall they produce.
What is the structure and function of the sieve tube element cells? to which tissue and tissue system do they belong? are they alive or dead at maturity?
The sieve tube elements are located in the phloem tissue of the vascular tissue system.
STRUCTURE: They do not have secondary cell walls, a nucleus, ribosomes or a vacuole.
FUNCTION: they connect to one another by their sieve plates (like perforations) to transport sugars (dissolved in water) throughout the body of the plant. Since they are alive at maturity, their perforations are plasmodesmata (functioning plasma membrane between different cells) to transfer the sugars.
How do sieve tube elements function if they do not contain a nucleus, ribosomes, or a central vacuole?
They have COMPANION CELLS! that consist of all the organelles needed for life and are connected via plasmodesmata to the sieve tube elements to transfer them the proteins they need for life.
