Plant Science (Ciencia De Plantas) - Ib (Ingles)

Topic 9 Plant Science

9.1.1 Draw and label plan diagrams to show the distribution of tissues in the stem and leaf of a dicotyledonous plant.
These are low power diagrams that show the distribution of the different tissue types. Cell structure is not required for this syllabus statement.
Stem cross section (Helianthus spp)
Tissue types of the plant stem:
* Epidermis: surface of thestem made of a number of layers often with a waxy cuticle to reduce waterloss.
* Cortex Tissue: Forming a cylinder of tissue around the outer edge of the stem. Often contains cells with secondary thickening in the cell walls which provides additional support.
* Vascular bundle: contains xylem, phloem and cambium tissue.
* Xylem: a longitudinal set of tubes that conduct water from theroots upward through the stem to the leaves.
* Phloem (sieve elements) transports sap through the plant tissue in a number of possible directions.
* Vascular cambium is a type of lateral meristem that forms a vertical cylinder in the stem. The cambium produces the secondary xylem and phloem through cell division in the vertical plane.
* In the centre of the stem can be found the pithtissue composed of thin walled cells called parenchyma. In some plants this section can degenerate to leave a hollow stem.
 

Cell diagram for comparison (the syllabus requires you know the tissue diagram)

 
Leaf section:
* Cuticle is a waxy layer which reduces water loss through the upper epidermis.
* Upper epidermis is a flattened layer of cell that forms the surface of the leafand makes the cuticle.
* Palisade Layer: This is the main photosynthetic region of the leaf.
* Vascular bundle: contains the transport system and vascular meristem tissue (x-xylem, p-phloem).
* Spongy mesophyll: contains spaces that allows the movement of gases and water through the leaf tissue..
* Lower epidermis: bottom surface layer of tissues which contains the guard cellsthat form each stoma.
 9.1.2 Outline three differences between the structures of dicotyledonous and monocotyledonous plants.

Time out for some TOK:
Take a walk around your garden or local park and using the table above classify into Monocotyledon and Dicotyledon plant. In doing so you will be following in the foot steps of John Ray(1627-1705). These differences first published in "Method ofplants' 1682 by John Ray. Geoffrey Keynes described Ray's work as 'epoch-making piece of work' of 'historical significance'. Ray's work was so far ahead of its time that its importance was not recognised until very much later. Students of history should not the dates of Ray's life and consider the historical significance of this time in England (Charles II and the Act of Uniformity). Ray is alsocredited with one of the earliest attempt to define a species. His definition (look it up) was an early version (more than 300 years ahead) of the modern ( but very similar to) definitions provided by Ernst Mayr.
Discussion: which other scientist or scientific concepts (at the time of their publication) were not recognised as they were so a far ahead of the rest of contemporary thinking. Illustrations of the differences between monocotyledon and dicotyledonous

 
(a) The fibrous branching roots of the monocotyledon
(b) The tap root structure with lateral roots of the dicotyledon .
9.1.3 Explain the relationship between the distribution of tissues in the leaf and the functions of these tissues.
Tissues:
(a) Phloem transports the products of photosynthesis (sugars, amino acids).(b) Xylem transports water and minerals into the leaf tissue from the stem and roots.
(c) Epidermis produces a waxy cuticle for the conservation of water.
(d) Palisade layer which is the main photosynthetic region.
(e) Spongy layer creates the spaces and surfaces for the movement of water and gases.
(f) Lower epidermis contains the stomatal pores which allow gas exchange with the leaf.
The...