Plant Structure:

Cells, Tissues, Organs,

Meristems & Growth

Organization of the Plant Body

Shoot System (Mostly Above Ground) – Stems, leaves, buds, flowers, and fruit. The shoot system develops from the shoot apical meristem (SAM). Function of the shoot system is photosynthesis, reproduction, seed dispersal, support, and gas exchange.

Root System (Mostly Below Ground) –

Main root (primary) and branch roots. The root system develops from the root apical meristem (RAM). Function of the root system is anchorage, absorbs and transports minerals and water, and stores food.

Organ – several types of tissues that together carry out particular functions. A typical plant body contains basic organs: roots, stems, and leaves, and flowers. Organ systems in plants are the shoot system and Root System.

Plant Cells & TissuesMeristems – sites in the plant body where cells divide and where differentiation into

specialized cells and tissues are initiated. Meristematic areas are the source of new cells and tissues.

Tissues – a group of cells of similar structure that performs a special function. Tissues make up plant organs. Plant tissues are made up of living and dead cells.

1) Ground Tissue System

- Responsible for housekeeping functions (photosynthesis, storage and support).

- Most extensive tissue type.

- Simple tissues make up this tissue system.

- Tissue Types: Sclerenchyma, Collenchyma, and Parenchyma.

- Ground Tissue System is found in the mesophyll of leaves & pith (often internal to vascular tissue) & cortex (often external to vascular tissue) of young green stems.

- Ground Tissue System is found throughout the plant.

Three Tissue Systems Make Up the Plant Body

Leaf Cross Section Stem Cross Section Root Cross Section

Note: On the below cross sections, only ground tissues are circled with red dots.

A) Parenchyma Tissue (Cells)- Most common type of plant cell.

- Primary cell walls that are thin and flexible. Secondary cell walls are often absent but not all the time. If secondary wall is present, lignin makes up the secondary cell wall.

The Simple Tissues of the Ground Tissue System

Celery Parenchyma Pine _____________________

- Parenchyma cells perform most of the metabolic functions of a plant. This include photosynthesis, cellular respiration, and food storage.

- Mesophyll (Parenchyma) cells make up the bulk of leaf tissue and these cells have chloroplasts and photosynthesize and store water.

- In roots, parenchyma cells (in the cortex) contain plastids and store starch.

Parenchyma Tissue (Cells) continued.- When parenchyma cells are turgid, they give support to the plant.

- Most parenchyma cells can divide and differentiate into other types

of plant cells under certain conditions, such as during the repair of an injury. In the laboratory, an entire plant can be regenerated from a single parenchyma cell.

Impatiens sp.

The Simple Tissues of the Ground Tissue System

Celery Collenchyma

B) Collenchyma Tissue (Cells)- Supports “Strengthening tissue” young

stems and leaf petioles. These cells are right below the surface.

Collenchyma cell walls are thickened at the corners.

- Collenchyma cells have primary cell walls only.

- Mature collenchyma cells are alive and they elongate as stems and leaves grow.

- The “strings” of a stalk of celery consists of collenchyma cells.

C) Sclerenchyma Tissue (Cells)- Main function of sclerenchyma cells is to support the weight of the plant and

plant organs.

- Cells have rigid, thick primary and secondary cells walls.

- Secondary cells walls are thick with lignin providing strength.

- Sclerenchyma cells are dead at maturity.

The Simple Tissues of the Ground Tissue System

Sclerenchyma Cells from Geranium

Sclerenchyma Tissue (Cells) continued.- There are two types of sclerenchyma cells.

Impatiens sp.

FIBERS

Fibers are long, thin and fibrous-like and they usually occur in bundles. They are

used commercially to make rope and clothing (hemp) and flax fibers are used to make linen.

SCLEREIDS Sclereids look like sheets. They are short and

irregular in shape but very hard. They make up tough seed coats, nutshells

and pits. They give the pear its gritty texture.

Pear Sclereids

2) Vascular Tissue System - These are the conducting tissues, which transport water, nutrients and

sugar.

- Complex tissues make up this tissue system.

- Vascular tissue is often found in vascular bundles in a plant.

- Main Tissue Types: Xylem (Primary & Secondary), Phloem (Primary & Secondary), (Note: Primary is early growth and secondary is later growth.)

- Vascular Tissue System is found throughout the plant.

Leaf Cross Section Stem Cross Section Root Cross Section

Note: On the below cross sections, only vascular tissues are circled with red dots.

Three Tissue Systems Make Up the Plant Body

A) Xylem Tissue (Cells)- Xylem tissue transports water and minerals upwards from the roots.

- Xylem makes up wood and is not living at maturity. It needs to be dead and hollow for transport.

The Complex Tissues of the Vascular Tissue System

Primary Vascular Bundle of Sunflower Secondary Growth of Basswood Stem

Xylem Tissue (Cells) continued.Xylem is made up of 4 cells types: Tracheids, Vessel Members (Vessel

Elements), Fibers (Sclerenchyma cells) and Parenchyma cells.

Fibers (Sclerenchyma Cells), a simple tissue we discussed before from the ground tissue system, is present in the vascular tissue system helping in the support of xylem.

Parenchyma, a simple tissue we discussed before from the ground tissue system, is present in the vascular tissue system helping tracheids and vessel members with transport. Parenchyma cells are the only living cells in xylem tissue.

Tracheids and Vessel members are the cells that actually do the transport.

Tracheids are long, thin cells that overlap and are tapered at the ends. Water passes from one cell to another through pits, areas with no secondary cell wall. Because their secondary cell walls are hardened with lignin, tracheids function to support the plant as well as to transport nutrients and water.

Vessel Members are aligned end to end and differ from tracheids in that the ends are perforated to allow free flow through the vessel member. In other words, these cells are in a line and have openings at the ends of the cells to allow water transfer.

Seedless vascular plants (Ferns) and most gymnosperms (pine trees and relatives) have only tracheids; most angiosperms (flowering plants) have both tracheids and vessel members.

Xylem Tissue (Cells) continued.

Tracheids (Note: Overlapping and are tapered at the ends and are

connected by bordered pits)

Vessel Members (Note: Aligned end to end but they digest out end walls

forming a tube called a vessel)

Water

Flowing

Upwards

B) Phloem Tissue (Cells)- Phloem transports sugar (food) down through the plant originally from

photosynthesizing cells (often the leaves) by active transport.

The Complex Tissues of the Vascular Tissue System

Primary Vascular Bundle of Sunflower Secondary Growth of Basswood Stem

Phloem Tissue (Cells) continued.In flowering plants (angiosperms), the following cells make up phloem: Sieve

Tube Members (Sieve Tube Elements), Companion Cells, Parenchyma Cells, Fibers and Sclereids.

Fibers & Sclereids (Sclerenchyma Cells), a simple tissue we discussed before from the ground tissue system, may present in the vascular tissue system helping in the support of phloem.

Parenchyma, a simple tissue we discussed before from the ground tissue system, is present in the vascular tissue system helping phloem tissue in “unloading and loading” and also involved in storage.

Sieve tube members are the cells that actually do the transport.

Sieve Tube Members are the food-conducting cells. These cells are joined at their ends to form long sieve tubes (conducting elements of phloem). In contrast to conducting elements of xylem, these cells are alive at maturity but they lose organelles as they age in order to function as a tube. The end walls of sieve-tube members contain sieve plates (which have pores) to facilitate the flow of fluid from one cell to the next.

Companion Cells are connected by plasmodesmata to sieve tube members. Companion cells retain their organelles and they nurture sieve tube members by producing proteins and transporting these proteins to sieve tube members.

Phloem Tissue (Cells) continued.

Stem Phloem Tissue(Shown from side view)

Sugar Flowing Down

Phloem Tissue (Cells) continued.

Primary phloem in cucumber stem shown in cross

section.

Phloem Tissue (Cells) continued.In seedless vascular plants (Ferns) and gymnosperms (pine trees and

relatives), sieve cells rather than sieve-tube members are the conducting elements in phloem. Albuminous cells (parenchymna-like cells) act as companion cells to these sieve cells.

Pine Phloem(Shown from side view)

BIO 141 Botany with Laboratory

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