Key to questions from Lab Manual 3: Stems
1. Primary growth is longitudinal—it contributes to the overall length and height of the root and shoot systems. Secondary growth is lateral growth, which contributes to the girth (or thickening) of the stem or root.
2. The three primary meristems are the protoderm giving rise to the epidermis, the procambium which gives rise to the vascular tissue, and the ground meristem which gives rise to the ground tissues (pith + cortex).
3. Vascular bundles in monocots are arranged in scattered bundles throughout the cortex, whereas in dicots vascular bundles are arranged in a ring around a central portion of the ground tissues called the pith.
4. Bundle caps are composed of sclerenchyma fibers.
5. Differences between the xylem and the phloem tissues include:
- the xylem is more extensive than the phloem, i.e. the xylem’s tissue system is larger than the phloem’s.
- the xylem has reinforced cell walls that are considerably thicker than the phloem cell walls.
- the xylem is composed of vessel elements and tracheids, whereas the phloem is
made up of sieve tube members and companion cells
- xylem cells are much larger than cells that make up the phloem. Phloem cells are
also more irregularly shaped than the cells within the xylem.
6. Stems have a variety of different functions including support of photosynthetic organs, transport of water and nutrients to the leaves, transport of sugars to the roots, storage of sugars, and production of new living tissue (meristems).
Key to questions from Lab Manual 5: Roots
1. The chief function of root hairs is to absorb water from the soil surrounding the root.
2. Root hairs increase the surface area of the root, allowing for more contact with the soil which provides a greater opportunity for water uptake.
3. The pericycle gives rise to the lateral roots in tissues with secondary growth. In roots, tissues derived from the pericycle also develop into the cork cambium which gives rise to the phelloderm and the cork layers of the root.
4. The root cortex is involve in sugar storage and the transport of water to the vascular cylinder.
5. If root hairs developed directly above the meristematic region in roots, they would be in the roots region of elongation. Because the cells in this region are actively elongating, the laterally anchored root hairs would be torn off as the cells expanded, pushing the root tip deeper into the soil.
6. Four differences between monocot and dicot roots include:
- Monocots typically do not have secondary thickenings, whereas dicots often do
- Monocots have a ring of vascular bundles, whereas dicots have a solid stele with a three or four pronged xylem with phloem occurring between the prongs
- Monocots have a fibrous root system, while dicots usually have a tap root
- Monocot root systems develop from the stem and are considered adventitious, while dicot roots develop from the radicle that gives rise to the primary root in dicots
7. Three (or four) differences between dicot roots and stems are:
- In roots, the cortex takes up lots of the root’s diameter, while in stems it is only present as the outer ring
- The cortex in roots is used to store starch granules, whereas in stems these granules are less prevalent
- Roots have an obvious endodermal layer that is reinforced with the casparian strip, stems do no have this tissue layer.
- In roots, vasculature is in the center of the structure, whereas in stems the vascular bundles are arranged in a ring.
8. The Tilia root and stem are different in that the root has no pith, its cortex gets sloughed off as it develops, and the secondary phloem is less organized than that of the stem.
9. Two contrasting features of the monocot root and monocot stem are:
- In the roots, the endodermis is clearly visible, whereas the stem doesn’t have an endodermis
- The vasculature of the root is contained within the vascular cylinder, whereas in the stem the vascular bundles are scattered throughout the ground tissue.
10. A lateral root develops from the pericycle, whereas a lateral branch develops from an axillary bud.
Key to questions from Lab Manual 6: Leaves
1. A leaflet (part of a compound leaf) can be distinguished from a leaf by looking at the petiole, or the portion of the leaf that actually attaches to the stem. If a single blade is connected to the petiole, then the blade is considered a leaf. If there are multiple mini-blades branching off of a single petiole, then they are leaflets.
2. The mesophyll of a corn leaf lacks the palisade layer of spongy mesophyll, whereas the mesophyll of a lilac leaf has this layer.
3. Three types of special adaptations of the xerophyte leaves are:
- a thick cuticle to protect against water loss and to reflect excess light
- a hypodermis which is a tissue layer capable of storing water
- sunken stomata present in small cavities called stomatal crypts that are surrounded by trichomes to reduce water loss
4. Distinguishing between monocots and dicots:
In terms of roots, monocots will not have any kinds of secondary thickenings, and therefore never produce woody roots. Internally, their roots would also be arranged in bundles within the vascular cylinder while dicot vasculature occurs as a solid stele with a multi-pronged xylem. Monocot vasculature also takes up more of the root diameter than dicot vasculature.
In terms of stems, monocots have a scattered arrangement of vascular bundles, while dicots have vascular bundles arranged in a ring. Monocots do not have a pith, while dicots can and typically do possess a pith.
Leaves of monocots do not possess a distinct palisade layer, whereas most dicots do. And externally, monocots have parallel venation, while dicots have a net-like venation pattern, either palmate or pinnate in nature.