PROYECTOS SOCIALES Y EMPODERAMIENTO SOCIAL
ESTRUCTURACIÓN DE PROYECTOS SOCIALES, Y SU INCIDENCIA SOBRE LOS NIVELES DE PARTICIPACIÓN Y EMPODERAMIENTO EN LOS
4.4.1 Análisis de los mecanismos actuales
Internally, a root consist of an outer cylinder and an inner central cylinder or stele. A transverse section of a root (fig. 2.11) shows the following arrangement of tissues from the circumference to the centre.
• Piliferous layer
• Cortex, includes the endodermis Outer Cylinder Pericycle
• Vascular tissue and pith Inner Cylinder or Stele
The outer cylinder consists of a wide zone of loosely packed, thin-walled parenchyma bound on the outside by a single-cell thick piliferous layer. Roots hairs arise from young cells of the piliferous layer. The endodermis is the innermost layer of the cortex. It is made up of a single-cell thick layer of barrel-shaped cells. Each cell is encircled by a thick waxy band.
Figure 2.11
taleieroUs
cortex endodermi
pericycl pith xyle bundle
phloe bundle
Differences Between Monocotyledons and Dicotylecons — Morphology of Angiosperms — Roots System 99
The stele consists of vascular tissue made up of alternate phloem and xylem bundles arranged in a ring.
Usually, there are more vascular bundles in a monocotyledonous root than a dicotyledonous one. The pericycle which bounds the vascular tissue on the outer side is a one- or two cell thick layer of thin-walled cells. The pith which is large in monocotyledonous roots is composed of thin-walled parenchyma. In most dicotyledonous roots, the xylem fills up the centre of the stele, forming a centrally supporting column.
The main supporting tissues in roots are xylem and the turgid parenchyma which makes up the cortex
Note:
Cambium, a meristematic tissue which gives rise to secondary growth, appears in older dicotyledonous roots but is completely absent in monocotyledonous roots (Fig. 2.11).
'transverse section of a dicotyledonous root
(diagrammatic) 'transverse section of a monocotyledonous
root (diagrammatic)
Briefly describe the internal structure of a root.
Angiosperms as a group of plants has a lot of biological and economic importance to man. Angiosperms which comprises of dicotyledonous and monocotyledonous plants can be sources of food, raw materials, for industries and sources of income to the farmer. Therefore their study should be intensified.
In this unit, we have learnt that;
i.
Angiosperms comprises of monocotyledonous and dicotyledonous plants
ii
Monocotyledons bear seeds with one cotyledon each, while dicotyledons have two cotyledons
iiiThe vascular bundles of the stem of monocotyledons are scattered, while that of dicotyledons are in a
regular pattern.
iv. Monocotyledons do not undergo secondary growth because of the absence of cambium cells, while dicotyledons usually undergo secondary growth because of the presence of cambium cells.
v. Roots can be modified for support, storage and for climbing.
Write short notes on the following;
a. Monocotyledon (2 marks) b. Dicotyledon (2 marks) c. Prop roots (2 marks) d. Breathing roots (2 marks)
ld - - lo - Umeh (1996) College Biology - Publisher, Ltd., Benin City.
rojini T. Ramalingam (2001). Modern Biology - African - Feb Publisher, Benin City
Volume 2: Flowering Plants
Page
1.0 Introduction 102
2.0 Objectives 102
3.0 Sterns 102
3.1 Types of Stems 102
3.1.1 Woody Stems 103
3.1.2 Herbaceous Stems 103
3.1.3 Monocotyledonous Stems 103
3.1.4 Other Types of Stems 103
3.1.5 Leaning Stems 103
3.1.6 Creeping Stems 103
3.1.7 Modified Stems 103
3.2 The Internal Anatomy of the Stem 107
3.3 Functions of Stems 108
3.4 Leaves 108
3.4.1 Leaf Shape 108
3.4.2 Forms of Leaves 109
3.4.3 Types of Compound Leaves 110
3.5 Arrangement of Leaves 111
3.6 The Internal Anatomy of a Leaf 113
3.7 Functions of Leaves 113
3.8 Flowers 113
3.9 Seeds and Fruits 117
4.0 Conclusion 122
5.0 Summary 122
6.0 Tutor MarkedAssignment 123
7.0 Further Reading and other Resources 123
1 01
Shoot system is the part of the plant which grows above the soil except the modified aerials roots. Shoot system can also be defined as that part of the plant which develops from the plumule of the embryo, normally appears above ground (at least at some stage in development) and bears the leaves, buds, flowers and possibly other appendages. There seems to be no other way to distinguish morphology between a root system and a shoot system except by reference to appendages such as leaves and flowers, which are never borne by roots.
The shoot system consists of two main organs:- (1)
stem
and (2) the leaves. During the reproductive stage, flowers and fruits may be seen on different branches of the stem.By the end of this unit, you should be able to;
i. explain the types of stems
n. explain the various types and purposes of stem modification iii. list the functions of stems
iv. explain the internal anatomy of a stem v. explain the various forms of leaves vi. list the functions of leaves
vii. list the four floral leaves of a flower
viii. explain the types of fruits.
The stem is the ascending portion of the axis of the plant, developing directly from the plumule, and bears leaves, branches and flowers. When young, it is normally green in colour.
A stem consists of nodes and internodes alternating throughout its length. It is more or less cylindrical in appearance and ends in a terminal bud. Nodes are the slightly enlarged portion of the stem from which leaves and buds arise. The buds occur on the axis of leaves and sometimes develop into branches and flowers. An internode is the portion between two successive nodes. The terminal bud consists of actively dividing cells (meristematic cells). All the young tissues of the shoot system develop from these meristematic cells. Newly formed leaves can be seen covering the terminal buds.
Stems are either erect, decumbent, procumbent, prostrate or creeping.
Stem can be smooth, hairy or rough They can bear roots or not.