BIOL 1030 Lecture Notes - Pericycle, Monocotyledon, Mycelium
7 May 2018
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Lecture 28: Angiosperm seeds
Seed is mostly dormant, when mature will dry, dehydrate to lower metabolism and suspend
growth. When the conditions are right, the seed will germinate and be able to develop an
embryo. Dormancy allows the embryo to survive when growth is not ideal. !
Overwintering, when winter lasts for longer than ‘usual’, the seed requires an extended cold
period to break enforced dormancy. !
Drought is also resisted, the seed will require a certain amount of water (threshold to be
surpassed in order for germination to occur. This increases the chance of survival and times
seed development for periods when water is not lacking. !
The minimum requirements for a seed to survive, include:
Water, for rehydration of the seed and to increase metabolism for cell enlargement!
Oxygen, for respiration (generation of ATP), often oxygen is low in concentration in water (need
to find a balance)!
Optimum temperature for enzymes, the exact temperature depends on the plants habitat;
with cooler areas ~10 degrees celsius, and more tropical areas ~20 degrees celsius. !
-Primary growth root: initials (cells dividing); RAM and derivatives (~1mm)!
•Indeterminate growth
-Derivatives enlarge in zone of elongation; the root cap pushes deeper into the soil!
-Zone of maturation, where mature primary tissues, root hairs in root!
-Zone of differentiation, tissues specialize to from functional systems!
Root functions:!
-Anchorage of the plant body
-Water and material uptake by the root hairs; absorption in the tubular epidermal!
•Asymbiosis with mycorrhizae, a fungus root that is a mutualistic association between the
roots of the plant and the fungal mycelia!
•With lichens, the fungal main body and algal cells!
-Storage of organic nutrients; starch (for root cortex), ground tissue!
-Transport mechanism
•Xylem: root to shoot system that is the unidirectional transport of water and minerals!
•Phloem: movement of sugars within the plant body, bidirectional !
-Sugars produced in photosynthesis: shoot to root!
-Stored sugars: root to shoot!
-Starch in cortex moved for SAM growth: root to shoot!
The root hairs first play a role in absorption and then serve as anchorage after they are no
longer living.!
Cross-section: dicot root in zone of maturation; inner primary xylem, then primary phloem, then
the pericycle (initiates RAM), enclosed by the endodermis (boundary of stele, vascular tissue)
the future RAM on the outside (for a lateral root), the cortex and then the outer root hairs.!
Cross-section: monocots, do not have a distinct shaped xylem or phloem, with a central pith;
not secondary growth (there is a lack of organization).
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Document Summary
Seed is mostly dormant, when mature will dry, dehydrate to lower metabolism and suspend growth. When the conditions are right, the seed will germinate and be able to develop an embryo. Dormancy allows the embryo to survive when growth is not ideal. Overwintering, when winter lasts for longer than usual", the seed requires an extended cold period to break enforced dormancy. Drought is also resisted, the seed will require a certain amount of water (threshold to be surpassed in order for germination to occur. This increases the chance of survival and times seed development for periods when water is not lacking. The minimum requirements for a seed to survive, include: Water, for rehydration of the seed and to increase metabolism for cell enlargement. Oxygen, for respiration (generation of atp), often oxygen is low in concentration in water (need to nd a balance)
