Plants: Lecture 4 Flashcards
What are plant cell walls made of?
They are mostly composed of cellulose, a polysaccharide of glucose units.
- The cell wall is outside of the cell membrane, and stabilizes the plant.
How are the microfibrils lined up?
The microfibrils are lined up like sheets to compose the cell wall.
What are the kinds of cell wall?
There are 2 kinds:
Primary Wall: thin, in all cells
Secondary Wall: thicker, in some cells for extra strength.
Functions of cell wall?
- Determines and maintains shape
- Provides support and mechanical strength (allows tallness)
- Prevents cell membrane from bursting
- Controls rate and direction of cell growth and regulates cell volume
- Responsible for the plant architectural design
- Physical barrier to pathogens and water (suberized/waxy cells)
- Carbohydrate (starch) storage and reused in metabolic processes (seeds)
What are the three kinds of polysaccharides in the cell wall?
- Cellulose
- Hemicellulose
- Pectin
Function of Cellulose?
Polymer chain of up to 25,000 glucose molecules
- roughly 36 chains bond to make microfibril
Hemicellulose function?
They are cross-linking glycans that bond with the cellulose.
Function of pectin?
A jellylike glue in the cell wall.
What is the middle lamella?
It is the material between cells, made up of pectic substances.
Which cell wall is made first?
The primary wall is made first, and the secondary is made second, accounting for why it is on the inside of the primary wall.
What do plasmodesmata do?
They allow cytoplasm and other materials to move between cells easily
What are the three tissue systems in vascular plants?
- Dermal tissue
- Vascular tissue
- Ground tissue
What is dermal tissue?
A single layer that secretes cuticle (waxy)
What is vascular tissue?
Composed of the xylem and phloem: support and supply
- moves fluid around the plant
Ground tissue?
All tissue other than dermal and vascular: the bulk of the young plant, filling space between dermal and vascular tissues, mostly parenchyma cells, storage, photosynthesis, and support.
Types of dermal tissue?
The epidermis
Types of ground tissue?
- Parenchyma
- Collenchyma
- Sclerenchyma
Types of vascular tissues?
- Tracheids and vessel elements
- Sieve elements
What are epidermal cells and where are they located?
They are the outermost cells and made up of a single layer (sheet) covering leaves, stems and roots of non-woody plants or plant parts.
Functions of epidermal cells?
- Waterproofing the cells
- Protection from pathogens (viruses, bacteria, fungi).
- Other specialized roles (Hairs/trichomes in roots stems and leaves, Make nectar in nectary for flowers, Guard cells for gas exchange controlling opening and closing of cells during photosynthesis).
What is the cuticle, and what is it formed by?
The cuticle is formed by the epidermal cells, the outermost part being impregnated with wax. It is made of one layer of cells
- It protects against water loss, pathogens, and UV radiation.
Wax on a chamomile petal?
Chamomile flowers have a layer of wax that is arranged on the petal, making them reflect light and be white.
Pitcher plant?
Wax is arranged in one direction so that prey is caught and unable to climb back up. The lower areas have acid to kill the flies.
What are secretory trichomes?
Aromatic plants and those containing liquids because of oils in the epidermal layer.
- Mint Trichome: more than 1 cell
- Oregano: 8 cells containing aromatic oils
- Stinging nettle trichome: 1 cell containing fluid to release into victims.
- Cannabis: contains THC oils
- Marjoram: 2 small trichomes containing oil and those that hinder crawling insects.
Nectary?
Floral nectary are made by the epidermal cells - which make nectar
Parenchyma cells?
The most general cells or highly specialized. They are important for many metabolic processes such as food storage, photosynthesis, storage, and secretion.
Features of parenchyma cells?
- A type of ground tissue (stems and roots)
- Usually lack a secondary strength wall
- They are often able ti divide and differentiate at maturity (fully developed)
Examples of parenchyma cells?
- Fruit flesh
- Endosperm
- Pith and cortex of stems and roots
- Chloroplast laden cells inside the leaves.
Other examples of parenchyma cells?
A single cell in a plant
- Marigold petals
- Elongated parenchyma cells
Collenchyma cells?
They provide support, especially in young and growing organs that are stiffer.
Features of Collenchyma cells?
- A type of ground tissue
- Have a thick and uneven primary wall (easily identifiable)
- No secondary wall
- Always occur just below the epidermis
- Often occur in strands
- Alive at maturity: can continue to elongate
Collenchyma Example?
- Celery leaf midrib and petiole
- The ribs we feel on a celery stalk are each underlaid by a strand of collenchyma.
- This is why we see uneven cell walls on a photo of celery cross-section
Sclerenchyma cells?
They are hard cells. They are supportive cells and protect the cells that are no longer elongating.
Features of Sclerenchyma cells?
- A type of ground tissue
- Thick secondary wall with lignin (a rigid polymer)
- Cannot elongate at maturity (may be dead)
- 2 forms: fibers and sclereids.
Examples of sclerenchyma fibers?
They are thick cells, which line up to make a string/fiber.
- Jute fibers make up burlap
- Hemp is also made into fabric/fibers
Examples of sclereids?
- They make pears gritty because they are hard cells
- They make the hard nutshell of an acorn.
- Water lily leaves would make it taste bad and sharp if you bit into it.
What are tracheids and vessel elements?
They are the water conducting cells of the xylem.
- They are the support and supply of water and minerals from soil, moving them to the plants and making them able to be tall.
Features of tracheids and vessel elements?
- Dead at maturity and still functional
- Secondary wall is lignified and often spiral
- There are two kinds: Tracheids and Vessel elements.
- They are a type of vascular tissue: all vascular plants have tracheids.
Shape of tracheids vs. vessel elements?
Tracheids are tapered and long
Vessel elements are stacked and shorter.
What are pits?
They are the way that water and minerals flow from the soil into the plant.
- Holes in the secondary wall where only primary wall remains
- Allow water passage through cell
- In both tracheids and vessel elements
What is lignin?
It is what gives wood its wooden characteristic.
- A class of complex organic polymers (not a polysaccharide)
- It is the second most abundant natural polymer, after cellulose
Where is lignin deposited?
It is deposited in secondary cell walls; filling spaces and binds cellulose, hemicellulose and pectin. This gives the cell strength.
Where can lignin occur?
It gives strength to wood and bark.
- It can occur in cell walls of non-woody plants like palm trees, bamboo, wheat and straw.
Human uses of lignin?
Wood: 20-33% lignin by dry weight
Rope, clothing, rugs…. sclerenchyma fibers
Paper: lignin is removed leaving cellulose.
Artificial vanillin: real vanillin is from vanilla orchid.
Sieve-tube elements?
They are the sugar conducting cells of the phloem.
- They transport sugars (sucrose) an other organic compounds like hormones and minerals.
Features of Sieve-Tube elements?
- A type of vascular tissues
- Alive at maturity
- Typically with a companion cell (parenchyma)
Where do plants grow from?
Plants grow from meristems. They grow from bottom to to, with newer tissues being at the top.
What are meristems?
- The ultimate source of all parts of the mature sporophyte
- They are undifferentiated
- They will forever retain the ability to divide.
- A meristem cell will create a daughter cell that will then divide at a much higher rate to become some type of specialized cell.
Apical meristems?
There is a root and shoot apical meristem, which makes up most of the primary growth.
-They are the source of primary growth in shoot and root.
Lateral meristems?
These are in woody trees, and are the vascular cambium and cork cambium. They are secondary growth.
What do the three tissue systems arise from?
The three tissue systems (dermal, vascular, ground) arise from 3 new meristems, made by the apical meristem.
What meristems do apical meristems make?
- Protoderm makes dermal tissue
- Procambium makes vascular tissue
- Ground meristem makes ground tissue.
Where are the youngest tissues?
The youngest tissues are at the shoot tip.
Young stems: shoots?
Eudicots have vascular bundle arranged in rings
monocots have scattered vascular bundle.
Root Primary growth?
Once they stop elongating, they form root hairs.
Root hairs increase surface area how?
A 4 month old rye plant has:
- 14 billion root hairs
- Surface area of 400 square meters
- Placed end to end make length less than 10,000 km
What is the endodermis?
the innermost layer of cortex. The presence of this is how we know it is a root.
Roots?
Eudicot: xylem is an x and phloem is the rest of the vascular cylinder
Monocot: xylem is inside of the small circles in the vascular cylinder and phloem is the outside.
What is the stele/vascular cylinder?
This is the cells that are within the endodermis, which arise from the pro cambium
What are lateral roots?
It originates in the pericycle (outermost layer of vascular cylinder) and grows out through the cortex and epidermis.
What is the cross section and longitudinal section?
Cross section - original root
Longitudinal section - lateral
What do root caps do?
They protect the root
What do root hairs do?
They are epidermal cels and in crease the absorption area
What does the endodermis do?
The innermost layer of cortex and surround the vascular cylinder
What does the vascular cylinder (stele)?
Center of the root, containing the vascular tissues (xylem and phloem) and some ground tissues
What does the pericycle do?
It is between the vascular cylinder and endodermis, the origin of lateral roots
What do roots do?
They absorb water and minerals, nothing else.
