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SBI3U Plants

Chapter 14.3 - Stems

Kristina Arvai

on 22 May 2013

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Transcript of SBI3U Plants

As mentioned, the main function of roots is to anchor the plant and to absorb nutrients and water. Roots may also store starch from sucrose produced by the leaves.

Most of the water and mineral absorption occurs through root hairs. Root hairs increase absorption of water and minerals by increasing the external surface area of the root. Chapter 14.3 :
The Stem Stem Growth Pattern Stolons: Aboveground horizontal stems that produce new plants asexually

Rhizomes: Underground horizontal stems, which may have enlarged sections called tubers that store starch (ex. potatoes)

Corm: Underground bulbous structures covered by papery leaves where nutrients are stored The Stem Stems and leaves constitute the shoot system. Stems move leaves toward the light and away from the shade of other plants or structures.

Stems must be strong to support the weight of leaves and to withstand the force of wind.

They must also conduct water, minerals, and nutrients between the roots and the leaves. Stem Epidermis The epidermis of a stem is a layer of cells that protects the inner tissues.

Like leaf epidermis, the epidermis of a young stem is covered by a cuticle and perforated by stomata.

In plants that live more than one growing season, the epidermis of the stem is replaced by a protective tissue known as periderm, which consists of nonliving cork cells. Stem Cortex and Pith The cortex is a layer of ground tissue between the epidermis and the vascular tissue of a plant. It is usually irregular in its shape and arrangement of cells.

The pith is a spongy ground tissue in the centre of stems and roots Monocot Dicot Vascular Tissue System: Xylem & Phloem Dermal Tissue System Chapter 14.3:
The Root The Root The main functions of roots are to anchor the plant and to absorb and conduct water and minerals.

There are two main patterns of root growth: taproot systems and fibrous root systems.

Taproot systems have a large main root known as a taproot that functions to "tap" deep sources of water. Most dicots and gymnosperms have a taproot system

Fibrous root systems have numerous small roots, which are most common in seedless vascular plants and monocots such as grasses. Root Functions Root Development In the root, the division, growth, and differentiation of cells can be traced linearly through three overlapping regions known as the zones of cell division (meristematic), elongation, and maturation.

The zone of cell division is a region of rapid mitosis of undifferentiated cells. The root cap protects this region as the root pushes between soil particles.

The zone of elongation is a region where cells elongate to force the root tip deeper into the soil

The zone of maturation is a region where cells begin specializing in structure and function into different cell types. Root hairs also develop from epidermal cells in this region. Root Lab MONOCOT MONOCOT Pith DICOT Ground Tissue System: Cortex & Pith Xylem Phloem Epidermis Cortex Vascular Cylinder Periderm Types of Plant Cells Plants begin as a single cell until cell division takes place through mitosis. Most of the mitosis takes place within meristematic cells, which are unspecialized cells that can divide indefinitely to produce new cells. Regions of these meristematic cells that produce new growth are called meristems.

There are two types of meristems:
1. apical meristems, which add length at the tips of stems and roots
2. lateral meristems, which add width to woody stems and roots

From these meristematic regions, new cells differentiate into specialized cells, which have specific structures and purposes. There are three types of differentiated cells:
1. parenchyma cells: general all-purpose cells that often fill space or provide structure
2. collenchyma cells: provide flexible support due to their cellulose thickened walls
3. sclerenchyma cells: provide rigid support due to their secondary walls hardened with lignin; these cells are dead at maturity Root Structure In examining cross sections of monocot and dicot roots, we see the tissues form cylinders. In monocot roots, the central cylinder (pith) is surrounded by alternating strands of xylem and phloem. In dicot roots they have a core of xylem in a lobe or star shape, which is surrounded by phloem.

The pericycle and the endodermis surround the vascular xylem and phloem tissue. The pericycle immediately encircles the vascular tissue and the endodermis encircles the pericycle.

The pericycle gives rise to lateral roots, while the endodermis functions to regulate the flow of substances between the cortex and the vascular tissue. plasmodesmata Vascular Cylinder *note starch grains within parenchyma Epidermis Water Uptake By Roots The root system serves to anchor the plant in the soil and meet water requirements of the plant. Water enters the root hairs, which provide an enormous surface area for absorption. From the root hairs, the water moves through the cortex, through the endodermis, and into the vascular cylinder. Once in the conducting elements of the xylem, the water moves upward through the root and stem and into the leaves. Recall the soil-plant-atmosphere pathway.

Water may follow one or more possible pathways to enter the vascular cylinder.
1. Apoplastic: via cell walls
2. Symplastic: from cell to cell via plasmodesmata
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