Plant Structure, Growth, and Development

Page
4

plate

Vessel

element

Vessel elements, with

perforated end walls

Tracheids

Pits

Tracheids and vessels

(colorized SEM)

Vessel

Tracheids

100 µm

Slide 29

The two types of water-conducting cells, tracheids and vessel elements, are dead at maturity

Tracheids are found in the xylem of all vascular plants.

Vessel elements are common to most angiosperms and a few gymnosperms.

Vessel elements align end to end to form long micropipes called vessels.

Water-Conducting Cells of the Xylem

Slide 30

Differentiated Plant Cells

Sieve-tube element (left)

and companion cell:

cross section (TEM)

3 µm

Sieve-tube elements:

longitudinal view (LM)

Sieve plate

Companion

cells

Sieve-tube

elements

Plasmodesma

Sieve

plate

Nucleus of

companion

cells

Sieve-tube elements:

longitudinal view

Sieve plate with pores (SEM)

10 µm

30 µm

Slide 31

Sugar-Conducting Cells of the Phloem

Sieve-tube elements are alive at functional maturity, though they lack organelles.

Sieve plates are the porous end walls that allow fluid to flow between cells along the sieve tube.

Each sieve-tube element has a companion cell whose nucleus and ribosomes serve both cells.

Slide 32

Sieve-tube elements:

longitudinal view (LM)

Sieve plate

Companion

cells

Sieve-tube

elements

30 µm

Slide 33

Sieve-tube

element

Plasmodesma

Sieve

plate

Nucleus of

companion

cells

Sieve-tube elements:

longitudinal view

Sieve plate with pores (SEM)

10 µm

Slide 34

Concept 35.2: Meristems generate cells for new organs

A plant can grow throughout its life; this is called indeterminate growth.

Some plant organs cease to grow at a certain size; this is called determinate growth.

Annuals complete their life cycle in a year or less.

Biennials require two growing seasons.

Perennials live for many years.

Slide 35

Meristems are growth regions - have perpetual embryonic tissue that allows for indeterminate growth.

Apical meristems are located at the tips of roots and shoots and at the axillary buds of shoots.

Apical meristems elongate shoots and roots, a process called primary growth.

Slide 36