Lecture 6 Flashcards
Functions of Roots
•Water uptake
•Nutrient capture
•Anchorage into soil
•Roots hold soil together
•Root nodules can fix nitrogen into soils
•The rhizosphere
Where do the best fodsilized roots comes from
Rhynie Chert a 407 million year old site in Scotland
Where did roots evolve from
Sporophytes
In Devonian period c. 410 million years ago
The evolution of roots emerged as a consequence of what
the differentiation of underground stems (rhizomes) into two specialized organs:
Describe the am two specialised organs formed from differentiation of underground stems (rhizomes)
(i)thicker perennial stems that form conduits to distribute water and nutrients, serve as stores and support above-ground structures; and
(ii) thinner, longer structures to absorb water and nutrients.
Where did root hairs possibly evolve from
Rhizoids of earlier plants to increase the volume of substrate available for exploitation
Subsequent evolution of roots has yielded much- branched axes down to how many μM
40 μM
What is the limit of 40 μM in branched axes of roots set by
Long distance transport constraints
The association of roots with fungi from the start enabled what
better uptake of nutrients from a larger volume of substrate
What does chemical weathering consume
CO2
Roots with fully integrated vascular systems were essential to evolution of large plants and tall tree trunks for what
Water transport
Bio mechanical strength
Example of positive feedback
Bigger plants need deeper soils
Plants contribute to the formation of souls by decomposition leading to deeper soils
When a seed germinates what is the first structure to appear
The root / radicle
Other roots that branch out from the primary root are called what
Secondary roots
What are the stages of seed germination
- Imbibition: Seeds absorb moisture and swell until the seed coat bursts
- The radicle pushes through the seed coat downwards into the soil
- Primary roots begin to develop and the hypocotyl forms a hook that straightens out, pulling the cotyledons above ground
- The primary leaves begin unfolding and the stem elongates.
- The true leaves completely emerge and the cotyledons
eventually fall off.
What is Imbibition
Seeds absorb moisture and swell until the seed coat bursts
Write a short note on Monocots
a flowering plant with an embryo that bears a single cotyledon (seed leaf). Monocotyledons constitute the smaller of the two great divisions of flowering plants, and typically have elongated stalkless leaves with parallel veins (e.g. grasses, lilies, palms,orchids).
Write a short note on Dicots
a flowering plant with an embryo that bears two cotyledons (seed leaves). Dicotyledons constitute the larger of the two great divisions of flowering plants, and typically have broad stalked leaves with net-like veins (e.g. daisies,bean,spinach ,rosehawthorns, oaks).
What increases the surface area of the root
Tiny root hairs
root cap lines from what cell
Apical cells to tissues in more mature parts of the roots
What is a protostele
Solid cylinder of xylem
Example of storage roots
carrot (Daucus carota),
sugar beet (Beta vulgaris),
sweet potato (Ipomoea batatas)
yams (Dioscorea spp.)
What are storage roots
Roots adapted to store products photosynthesised in the shoot
Products are synthesised above ground and transported to root in phloem where they reside until needed to complete life cycle
Example of Air roots
Mangroves
Cypress Knees
What are air roots also known as
Pneumarophores
What are air roots
In some trees that live in swamps
grow above the surface of the water and allow oxygen to be transported to the inner cortex of the root system, and CO2 to escape from the root interior.
Name the primary structure in Air roots/ Pneumatophores that allow gas exchange
Lenticels
What are Buttress roots
vertically flattened roots that project out of the ground and lower trunk at the base of large trees.
What are Prop/Stilt roots
adventitious roots that develop on a trunk or lower branch that begin as aerial roots but eventually grow into a substrate of some type;
Function of Prop/Stilt roots
Provide mechanical support having good compression or tensile properties to help support trees at their bases
What are Adventitious roots
roots that arise from anything other than the radicle
What do Tap root and Fibrous roots systems arise from
The Radicle
