Root Physiology Flashcards
What are the two main types of root system?
Tap roots
- have a primary root which is the longest and thickest, lateral roots branch from the primary root
Fibrous roots
- adventitious roots branching from the radicle and stem, no main root.
What is a eudicot?
Most plants and trees, legumes etc. Have a tap root.
What is a monocot?
Grass, plam trees etc, have fibrous roots.
What is a rhizome?
Rhizomes are modified stems growing horizontally in the soil. They are probably the ancestors of roots.
What are the layers of a cell wall?
- Middle lamella (formed during cell division, mostly pectin)
- Primary cell wall (mostly cellulose, hemicelulose and pectin)
- Secondary cell wall (formed after cell growth in specialised cell types, lignin instead of pectin, so stronger)
What are the 3 types of plant tissue?
- Ground tissue
- Vascular tissue
- Dermal tissue
What are the types of ground tissue? (bonus: which one is in roots)
- Sclerenchyma
- Collenchyma
- Parenchyma (in roots)
What are types of vascular tissue?
- Xylem
- Phloem
What are the types of dermal tissue?
- Epidermis
- Periderm
What is parenchyma?
Parenchyma cells have thin primary walls.
Parenchyma tissue contains intercellular air spaces.
Most plant organs contain parenchyma tissue (“bulk”).
What are the 4 main zones found in a root? (from bottom to top)
- root cap
- zone of cell division
- zone of elongation
- zone of cell differentiation
What are the 3 radial layers found in roots and what are they used for?
Epidermis: absorption
Cortex: bulk of the root
Stele: transport
What is the Casparian strip?
A diffusion barrier between the cortex and the endodermis, described as an internal skin.
Hydrophobic plug between cells: forces passage through cytoplasm (selective)
What is the function of the root cap?
Shield, sensor, steer
How does the root cap detect gravity.
Amylopasts, which contain starch in a very high density, are heavy. They fall to the bottom of the root cap, giving the root direction.
Where to root hairs get produced and where are thy found?
Produced in the zone of elongation, they are found in the younger parts of the root as they only live for 1 to 3 weeks.
Where and how do lateral roots form?
They are formed in the zone of cell differentiation.
They start growing from the pericycle to connect the new vascular tissue to existing vascular tissue.
How do roots provide anchorage?
- resistance to uprooting
- resistance to overturning
What are the main components of soil?
- minerals
- organic matter
- water and air
What are the macro nutrients?
- potassium
- nitrogen
- phosphorus
- sulfur
- magnesium
- calcium
What are the mirco nutrients?
- iron
- nickel
- manganese
- copper
- molybdenum
- boron
- chloride
- zinc
What are Mycorrhizae, what do they do?
Plant symbiotic fungi, they facilitate access to nutrients in exchange for carbohydrates.
What are ectomycorrhizal fungi?
Live outside root cells, found in 3% of land plants.
What are endomycorrhizal fungi?
Develop within the root cortex cells, found in 80% of land plants.
Describe the symbiotic relationship some plants have to get fixed nitrogen?
Nitrogen fixing bacteria (rhizobia) are hosted in root nodules where they fix nitrogen (N2 + 3H2 -> 2NH3) in exchange for carbohydrates and a sheltered environment.
Occurs in legumes.
What might be the difference between the root system irrigated and non irrigated plants?
Non irrigated: expanded roots horizontally to catch rainfall near soil surface
Irrigated: have the resources to forage deeper in the ground for nutrients
What is the plasmodesmata?
Plasmodesmata allow transport of macromolecules between adjacent cells. The desmotubule in the centre of the plasdesma connects the endoplasmic reticula.
What are the 3 pathways nutrients and water can be transported to the xylem?
Apoplastic: through extracellular space (mostly cell wall)
Symplastic: through cells, using plasmodesmata
Transcellular: through cells, using transporters
What are 3 types of specialized root?
Storage - e.g. sweet potato for starch or wild cucumber for water
Parasitic - e.g. haustorial roots attack to the host and drain nutrients from it vascular system
Aerial - e.g. prop roots (around stem or branches) or velamen roots for aerial plants
