Lab on Roots Flashcards
What percentage of plants form mutualistic realtionships with fungi?
90%
What are mycorrhizae?
mutualistic fungi that line in or around plant roots (means fungus root)
What does the fungi gain from the mutualistic realtionship with roots?
products of photosynthesis
What does the root gain from the mutualistic relationship with fungi?
phosphorus and other minerals.
Why are most species of orchid difficult to cultivate?
the corresponding fungus is hard to obtain.
What is present in fungal walls that corresponds to the cellulose in plant walls?
Chitin (stains blue)
Fungal hyphae that are endomycorrhizae enter…
the cells of the cortex.
hyphae in ectocorrhizae grow only…
between the cells of the cortex.
In terrestrial systems, the nutrient that most commonly limits plant growth is….
nitrogen (triple bonded and hard to break.)
With what can a plant form a mutualistic relationship that allows the plant to receive nitrogen in a usable form?
bacteria (prokaryotes)
What are the small bulges of prokaryotes on the outside of roots called?
root nodules
What are the functions of roots?
most importantly anchorage and absorption, with other functions like storage, hormone production, and can be modified for purposes including support, aeration, propagation and parasitism.
What is the primary root?
the first root that emerges from the seed in germination.
In most plats, the primary root develops into what?
the taproot, which becomes central in the plant’s root system and continues to be most prominent throughout the life of the plant.
Taproot systems are common in which class of species?
dicots
What replaces the primary root in monocots?
adventitious roots develop into a fibrous root system where no one root is dominant.
What are adventitious roots?
roots that develop from a structure other than another root (ex: from the stem)
All roots on grasses are…
adventitious.
What are aerial roots?
adventitious roots that originate from above ground structures.
What are epiphytes?
plants that grow on other plants.
What is the velamen?
the white, spongy material which is a multiple epidermis that helps the root retain water in epiphytes.
What are pneumatophores?
negatively gravitropic roots that provide ventilation to a submerged root system.
pneumatophores are often referred to as…
knees.
What are lenticels?
areas of periderm that facilitate gas exchange.
The parasitic plant dodder is incapable of photosynthesis. How does it gather those nutrients?
it sinks a haustorium into the stem of another plant where it taps into the xylem and phloem.
What is a haustorium?
a modified root of a parasitic plant used to reach the xylem and phloem for nutrient absorption.
What are the three regions of growth in a root called?
- region of cell division
- region of elongation
- region of maturation
The region of cell division is located where?
at the end of the root (where cells are still dividing) and where patterns of root growth are being established.
the majority of cells in a mature root come from which tissue system?
the ground tissue system
What marks the region of elongation?
the point where the first sieve elements mature.
While some cell division continues, what is primarily happening in the region of elongation?
the cells are growing in size.
Most of the root length increase occurs in which region?
the region of elongation.
Where does the region of maturation begin?
where the first xylem tracheary elements mature.
Why is it safe for root hairs to extend into the soil in the region of maturation?
there is no more elongation occurring, which means the root hairs won’t be destroyed by the root pushing through the soil.
The region of maturation is also called what?
the root hair zone.
What are root hairs?
extensions of epidermal cells that function to increase root surface area for absorption.
What produces the root cap?
preclinical divisions of the apical meristem.
What is the root cap?
a structure that protects the root apex as it bores through the soil.
What happens to the cells of the root cap as the root pushes through the soil?
they are sloughed off.
What is the stele?
the vascular cylinder in a root or stem.
what is a protostele?
seen in dicot roots, this is a solid core of vascular cylinder.
What is a syphonostele?
seen in monocot roots, it is the pith of parenchymal cells in the center of the stele.
the cortex belongs to what tissue system?
ground tissue system
What is the exodermis?
the outermost layer of the cortex in roots
True or false. the exodermis is part of the dermal tissue system.
False. despite its name, it is part of the ground tissue system.
how can you differentiate between exodermal cells and the rest of the cortex?
exodermal cells are tightly packed compared to the cortex.
Most of the cortex is made up of what kind of cells?
loosely arranged parenchymal cells.
Why are air spaces common between cells in the root?
they allow for aeration of the root.
What is the endodermis?
the inner most layer of the cortex which is tightly packed and often have secondary cell walls.
What is the function of the endodermis?
it regulates water entry into the stele.
The central vascular cylinder in the root is the….
stele.
The stele arises from which tissue system?
the vascular tissue system.
What is the pericycle?
the outermost layer of the stele.
What is the function of the pericycle?
it gives rise to lateral roots and participates in secondary thickening of roots.
True or false. Xylem cells have secondary walls.
true.
What tissue system gives rise to the pith in roots (not stems)?
the vascular tissue system.
Where do lateral roots originate?
in the pericycle.
Early in development, what do lateral roots form?
their own dermal, vascular, and ground tissue systems.
What are the two secondary meristems in roots?
the vascular cambium and the cork cambium.
True or false. the secondary meristems of roots and stems have different ontogenetic origins.
True.
Where does the vascular cambium form?
between the primary xylem and primary phloem.
List the steps of secondary growth in roots.
- vascular cambium forms a ring around the primary xylem in the center of the stele.
- it produces secondary xylem toward the outside and secondary phloem growing inward.
- successive divisions push the vascular cambium outward, and the primary xylem and phloem are pushed farther away from each other while all other tissues are pushed outward.
- the cortex and epidermis are torn away and lost, and the primary phloem remains but is crushed and likely not recognizable in older sections.
the cork cambium is formed from what?
pericycle cells.
What do divisions of the cork cambium produce?
the periderm
What is the the periderm made of?
mostly cork.
What is the function of the periderm?
replaces the epidermis and protects the secondarily-enlarged root.
True or false. Roots with secondary thickenings are more complex than primary roots.
True
True or false. bacteria live inside the plant root.
True.
What do bacteria provide the plant root?
reduced usable nitrogen compounds.
What does the plant provide bacteria with?
a safe place to grow and photosynthetic products.
What do we call bacteria that live inside plant root cells?
they are bacteroids, and function less like independent organisms and more like organelles.
Why is the inside of a root nodule pink?
the type of hemoglobin, called leghemoglobin contains iron, which gives the nodule the pinkish color.
