Topic 9: Plant Science Modified from S. Taylor, S. Frander and L. Ferguson

9.1.2 Outline 3 differences between the structures of dicotyledonous plants and monocotyledonous plants

9.1.1 Draw and label plant diagrams to show the distribution of tissues in the stem and leaf of a dicotyledonous plant.

Distribution of Tissues in Stem and Leaf of Dichotyledonous Plants Epidermis surrounds and contain stem/leaf organ and vascular tissue; outer layer of wax coated cells that provide protection. Xylem is vascular tissue used in water transport. Phloem is vascular tissue used in organic solutes transport. Pith is the center of dicot plant stems; in some plants it breaks down forming a hollow stem, while in older woody plants it is filled with rigid xylem wood fiber. Cambium are the single-celled layer of meristematic (dividing) tissues that continually divides to form phloem tissues toward the outside and xylem tissues toward the inside. Cell division of the cambium tissues adds width to the stem. Cortex is the primary tissues of a stem externally bound by the epidermis and internally by the phloem. Info from

Tissue Organization of Leaves The epidermis in leaves is interrupted by stomata, which allow CO 2 exchange between the air and the photosynthetic cells in a leaf Each stomatal pore is flanked by two guard cells, which regulate its opening and closing The ground tissue in a leaf, called mesophyll, is sandwiched between the upper and lower epidermis

Fig Key to labels Dermal Ground Vascular Cuticle Sclerenchyma fibers Stoma Bundle- sheath cell Xylem Phloem (a) Cutaway drawing of leaf tissues Guard cells Vein Cuticle Lower epidermis Spongy mesophyll Palisade mesophyll Upper epidermis Guard cells Stomatal pore Surface view of a spiderwort (Tradescantia) leaf (LM) Epidermal cell (b) 50 µm 100 µm VeinAir spacesGuard cells Cross section of a lilac (Syringa)) leaf (LM) (c)

Below the palisade mesophyll in the upper part of the leaf is loosely arranged spongy mesophyll, where gas exchange occurs The vascular tissue of each leaf is continuous with the vascular tissue of the stem Veins are the leaf’s vascular bundles and function as the leaf’s skeleton Each vein in a leaf is enclosed by a protective bundle sheath Tissue Organization of Leaves

9.1.3 Explain the relationship between the distribution of tissues in the leaf and the functions of these tissues. Absorption of light—parenchyma chloroplasts (ground tissue) Gas exchange stomata in epidermis--(controlled by epidermis guard cells) (dermal) Water conservation--cuticle produced by epidermis (and guard cells ) (dermal) Transport of water—xylem (vascular tissue) Transport of products of photosynthesis—phloem (vascular tissue)

9.1.4 Identify modifications of roots, stems and leaves for different functions: bulbs, stem tubers, storage roots and tendrils Bulbs are vertical, underground shoots consisting mostly of the swollen bases of leaves that store food Stem tubers are the swollen ends of underground stems that are specialized for storing food.

9.1.4 Identify modifications of roots, stems and leaves for different functions: bulbs, stem tubers, storage roots and tendrils Storage roots are taproots that store food. The plant consumes this food during flowering and fruit production. Tendrils modified stems or leaves as seen in climbing plants; provide flexible support

9.1.5 State that dicotyledonous plants have apical and lateral meristems Meristem—plant tissue that remains embryonic for the life of the plant, allowing for growth throughout life, since they divide by mitosis Compare growth due to apical and lateral meristems in dicotyledonous plants. Apical –primary (vertical) growth --enables plant to reach light Lateral--secondary (lateral) growth; form from cambium --replaces epidermis with bark --adds new vascular rings each year

Meristems generate cells for new organs A plant can grow throughout its life; this is called indeterminate growth Some plant organs cease to grow at a certain size; this is called determinate growth – Annuals complete their life cycle in a year or less – Biennials require two growing seasons – Perennials live for many years Meristems are perpetually embryonic tissue and allow for indeterminate growth Apical meristems are located at the tips of roots and shoots and at the axillary buds of shoots Apical meristems elongate shoots and roots, a process called primary growth

Secondary growth adds girth to stems and roots in woody plants Secondary growth occurs in stems and roots of woody plants but rarely in leaves The secondary plant body consists of the tissues produced by the vascular cambium and cork cambium Secondary growth is characteristic of gymnosperms and many eudicots, but not monocots Lateral meristems add thickness to woody plants, a process called secondary growth There are two lateral meristems: the vascular cambium and the cork cambium The vascular cambium adds layers of vascular tissue called secondary xylem (wood) and secondary phloem The cork cambium replaces the epidermis with periderm, which is thicker and tougher

Fig Shoot tip (shoot apical meristem and young leaves) Lateral meristems: Axillary bud meristem Vascular cambium Cork cambium Root apical meristems Primary growth in stems Epidermis Cortex Primary phloem Primary xylem Pith Secondary growth in stems Periderm Cork cambium Cortex Primary phloem Secondary phloem Pith Primary xylem Secondary xylem Vascular cambium

9.1.7 Explain the role of auxin in phototropism as an example of control of plant growth Auxin—a plant hormone that controls growth Tropism—a plant response to an external stimulus Phototropism—a plant response to light Proteins called phototropins absorb light and bind to receptors that stimulate transcription of (growth)elongation genes in the cells, with the most auxin produced in the shaded cells.