Botany - Plant Tissues

**This chapter is an extremely important foundation for future chapters in this course. If you don’t learn this material now, you’ll be struggling for the rest of the semester.**

I. Overview of plant growth and structure

A. Primary Growth—growth of ___________________________

1. The resulting tissues are called primary tissues

a. In botany, primary always refers to the first year’s growth.

2. In annuals (that live only one year) this is the only type of growth.

3. In perennials, this is the first year’s growth and the growth of elongation every subsequent year of the plant’s life.

4. Primary tissues – arise from the primary meristems (apical, axillary, and intercalary)

a. Include epidermis, ground tissues, primary xylem, and primary phloem

B. Secondary Growth—increase in ___________________________ (width, i.e. woody growth)

1. The resulting tissues are called secondary tissues

a. Primary tissues (produced the first year) are replaced by

secondary tissues in subsequent years in perennials.

2. Secondary tissues – arise from lateral (secondary) meristems (vascular cambium and cork cambium)

a. Includes secondary xylem, secondary phloem, and bark

C. Plant organs: ___________________________________________

II. Plant Meristems

A. ___________________________ are undifferentiated, embryonic tissue present throughout the life of the plant. These cells can differentiate/mature into any other type of cell.

1. Only type of plant tissue which actively divides.

2. All other plant tissues are derived from meristematic tissues.

B. There are 2 main types of meristems

1. ___________________________ Meristems – located at the tips of shoots and roots that cause increases in length

a. Apical mersitems – located at the tips of shoots and roots

b. Axillary meristems – located in the leaf axils

c. Intercalary meristems – produce increases in length in grasses

2. ___________________________ (Secondary) Meristems – located toward the exterior of stems and roots that cause increases in girth

a. Vascular Cambium – produces secondary vascular tissues (secondary phloem and secondary xylem)

b. Cork Cambium – replaces the epidermis with bark

Meristems produce plant tissues

C. The Primary Meristems

1. ___________________________ meristems - mass of rapidly dividing cells, found at tips of roots and shoots. These meristems produce increases in length.

a. Also produces embryonic buds and leaves

b. Produces three ___________________________: (which produce primary tissues)

1. ___________________________ – develops into the dermal system

2. ___________________________ – develops into the ground tissues

3. ___________________________ – develops into the vascular tissues and the vascular cambium

2. ___________________________ meristems – produces lateral (side) branches, found in the leaf axils

3. ___________________________ meristems – produces increases in length along the distance of a stem in many monocots (particularly ___________________________) and in horsetails.

a. They are usually found near ________________________ (leaf attachment points)

D. The ___________________________ (Secondary) Meristems – usually found only in plants with secondary growth, in other words in ___________________________ plants (they live year after year). These meristems produce increases in girth and produce wood. These meristems form a cylinder that runs the length of the roots and stems. These meristematic cells of the vascular cambium are called initials.

1. ____________________________________ – a meristem sandwiched between the xylem (toward the inside of the stem) and the phloem (toward the outside of the stem) that will produce the secondary xylem and phloem.

a. Secondary xylem – will become annual (growth) rings in the stem.

b. Secondary phloem – will replace the previous year’s phloem.

1. The old phloem is crushed by this process and becomes part of the bark

2. ____________________________________ – a meristem located externally to the vascular cambium, sandwiched between the cortex and the periderm.

a. Responsible for producing cork cells which replace the epidermal cells of primary growth and make of the bulk of ___________________________

Reminder about Plant Tissues:

Simple plant tissues = have only one cell type	Complex plant tissues = 2+ cell types
· Parenchyma · Collenchyma · Sclerenchyma · Secretory Tissues · Epidermis	· Xylem · Phloem · Periderm

III. Simple Plant Tissues – consist of only one type of cell

Parenchyma

Collenchyma

Sclerenchyma (circled)

A. ___________________________ - relatively undifferentiated tissue composed of large, isodiametric cells.

1. This tissue makes up the ___________________________ (cortex & pith).

2. Usually used for ___________________________, but may support the roles of other cells.

3. The cells are alive when functional.

4. Types of parenchyma

a. ___________________________ – usually found in aquatic plants, aerenchyma is parenchyma with large air spaces between the cells

b. ___________________________ – mainly found in leaves, chlorenchyma is parenchyma that has chloroplasts

c.___________________________ - specialized parenchyma with long cytoplasmic extensions, used for transferring materials between cells

B. ___________________________ - similar to parenchyma cells, but with thickened, often irregular primary cell walls.

1. Used for structural support and protection of plant parts.

a. Produces flexible support found in plant leaves & floral parts

b. Provides strength to growing plant organs

2. Cells are alive when functional

C. ___________________________ - highly specialized cells that have thick, lignified secondary cell walls.

1. Used for _____________________________________________

2. Cells are dead when functional

3. Types of sclerenchyma

a. ___________________________ - isodiametric cells, usually scattered throughout other tissues

1. give pears their gritty texture

b. Stone cells - groups of sclereids found in specific areas of plants

c.___________________________ - thin, elongated cells which are associated with other tissues

1. Fibers are often used in industry to make textiles (e.g. cotton)

D. Secretory Tissues - Composed of secretory cells that produce hormones and other substances which are exported from the cells

1. e.g. nectar, oils, mucilage, latex, resins, etc.

E. ___________________________ - Consists of roughly rectangular cells, usually one cell thick.

1. The epidermis is the outermost covering of annual plants and first-season perennial plants.

2. Most epidermal cells secrete a waxy cuticle to help decrease water loss by evaporation.

3. Structures associated with the epidermis

a. ___________________________ – cytoplasmic extensions from root epidermal cells that have increased surface are for the absorption of water.

Cross section diagram of a dicot root

Electron microscope view of root epidermis (note the root hairs)

b. Leaf hairs - similar to root hairs, but usually have the function of warding off herbivores

c.___________________________- specialized cells that form ___________________________ (openings in the epidermis which allow gas exchange with the deeper tissues and the outside)

1. Guard cells are the only epidermal cells that have chloroplasts.

Leaf epidermis with epidermal hairs

Microscope view of leaf stomata

d. Gland cells - modified epidermal cells that secrete substances

IV. Complex Plant Tissues—consist of two or more cell types that have similar functions

A. ___________________________ - carries water from the roots to the rest of the plant

1. ___________________________ – carries water longitudinally (up the plant)

a. Similar in appearance to fibers, but longer and wider

b. Secondary walls contain pits (holes that extend through the cell walls & allow the passage of water)

c.Usually overlap at the ends where pit pairs occur

d. Dead when functional

2. ___________________________- same function as tracheids—carries water longitudinally (up the plant)

a. Evolutionary more advanced than tracheids

1. Typically found in angiosperms (flowering plants) and not in simpler plants like gymnosperms

b. Usually shorter and wider than tracheids with thinner secondary cell walls

c.Cells have open areas at the ends where they join other vessel elements to form long tubes called vessels

d. Dead when functional

3. ___________________________ (a.k.a. ray parenchyma) - living parenchyma cells which transport water laterally (to the side)

a. Ray parenchyma is long-lived and alive when functional

b. Ray initials in the vascular cambium produce the xylem rays

4. Fibers – support and protect the other cell types

B. ___________________________—tissue that conducts carbohydrates (food) from the photosynthetic

parts of the plant to the rest of the plant. All phloem cells, except fibers are alive

when functional.

1. ________________________________________- elongated cells that are laid end to end to form long sieve tubes.

a. They do not have large openings like vessel elements

b. Instead, they have porous sieve plates through which plasmodesmata pass

c. They lose their nuclei at maturity so they cannot perform their normal cell metabolism

a. This means they won’t be using a lot of the food that are carrying to other plant cells, but they also can’t take care of themselves.

2. ________________________________________ - parenchyma cells that physiologically support the sieve-tube cells

3. Phloem rays - similar to xylem rays; used for lateral conduction

4. Phloem fibers - support and protect the other phloem cells

C. ___________________________ - the major constituent of bark. The periderm is produced by the cork cambium.

1. ___________________________—boxlike cells with cell walls impregnated with ___________________________ (a fatty substance that waterproofs the cells). Dead when functional.

2. ___________________________ —pockets of loose parenchyma that allow gas exchange through the bark

3. ___________________________ —consists of all of the cells from the secondary phloem to the outside of the plant