Principles of Biology BIOL 100C: Introductory Biology III Plant Cell Types Dr. P. Narguizian Fall 2012.

Principles of Biology

BIOL 100C:BIOL 100C:Introductory Biology IIIIntroductory Biology IIIPlant Cell Types

Dr. P. NarguizianFall 2012

Plants (Anatomy & Physiology)1) What are the differences between Non-vascular vs. Vascular plants (examples)?

2) Gymnosperms vs. Angiosperms?

3) Monocots vs. Eudicots (Dicots)?

4) What are the 3 basic plant organs (components & functions)?

5) What are the 3 plant tissue systems (components & functions)?

6) Roots vs. Shoots (components & functions)?

Plant Anatomy

BIOSKILL Plants have three basic organs: roots, stems, and leaves.

• Vascular plants exist in two distinct terrestrial environments at the same time-above ground (leaves and stems) and below ground (roots).

• Each part of a vascular plant contains cells grouped into tissues, which are collections of cells of one or more type that perform specific functions.

• A collection of tissues used for a particular process is called an organ. A plant's organs are its roots, stems, and leaves.

• A root anchors a plant in the ground and absorbs water and other nutrients from the soil. A plant's roots comprise its root system, which generally exists below ground.


Plant Anatomy

Figure 2 Root systems that grow above ground.

Not all roots are underground. When the roots of the tidal-growing red mangrove (a) are not standing in air, they are immersed in water.

Some scientists think the exposed roots help the trees take in oxygen. The buttress roots of the fig tree (b) add additional support to the tree. These types of roots are most common among trees that are grow in shallow soil, so cannot penetrate the ground deeply. Much like they do for the mass of a stone cathedral building, they provide additional support to the tree structure by attaching high on the tree trunk and extending in a tapered shape toward the ground..


Plant Anatomy


• There are two main types of root systems: taproot and fibrous root.

• The taproot system consists of a main root, the taproot, running vertically into the ground, with lateral roots growing out of the taproot.

• Taproots tend to be thick and sturdy, whereas the lateral roots that grow from them are often stringy and thin.


Plant Anatomy

Figure 3 Root systems: taproots and fibrous roots.

Taproot systems are structured with a single, thick main root, growing vertically down from the plant stem. A carrot (left) is a eudicot taproot that is also a common vegetable. In contrast, fibrous root systems are a collection of many smaller adventitious roots, all similar in size. Small green onions (right) are monocot plants with fibrous root systems.


Plant Anatomy


•Roots developing from the stem or from other unusual locations (such as leaves) are known as adventitious roots.

•In most monocots, the taproot dies early and many smaller roots of similar size emerge directly from the stem, developing into a fibrous root system.


Plant Anatomy

BIOSKILL Interpret Micrographs

•Root hairs are extensions of epidermal cells that lie just beyond the tip of the root.

•Root hairs infiltrate the spaces between soil particles and absorb the water by osmosis.

•Root hairs pump positive hydrogen ions into the soil and exchange them for the positive mineral ions.


Plant Anatomy

Figure 4 Root hairs.

Plants absorb water mostly through root hairs, which are extensions of epidermal cells.

Root hairs are tiny — only 80 to 1,500 micrometers in length.


Plant Anatomy

The stems and leaves of a plant are the shoot system.

• The main function of the leaves and stems-which together constitute a plant's shoot system-is harvesting sunlight.

• The stem of a vascular plant supports the plant, stores nutrients, generates new tissue, and makes and supports leaves.

• The stem of a vascular plant makes leaves at special sites called nodes. Between two nodes is a segment called an internode. Together, they make up the majority of the stem.

• In eudicots, the very tip of a stem, where most growth occurs, is called the apical bud.

• Branches develop from lateral buds called axillary buds, which grow at the upper angle between leaves and the stem.

• In most plants, the apical bud is dominant over the axillary buds. This phenomenon is called apical dominance.


Plant Anatomy

Figure 5 Shoot system.

The shoot system contains the stem and leaves.


Plant Anatomy

The stems and leaves of a plant are the shoot system.

• Leaves are the organs primarily responsible for photosynthesis, the process whereby plants use energy from sunlight, carbon dioxide, and water to make sugars.

• The blade is the part of the leaf that contains chloroplasts for photosynthesis and is usually flat and thin to maximize exposure to sunlight.

• The blade contains the stomata, which enable the plant to transpire and exchange gases with the atmosphere.

• The petiole is the part of the leaf near the node where the blade joins the stem.

• A simple leaf consists of a single blade, whereas a compound leaf has many divisions, known as leaflets.


Plant Anatomy

Figure 6 Leaf morphology.

A simple leaf possesses a single, undivided blade. The blade of a compound leaf has leaflets, arranged either singly or doubly.

Note that axillary buds form only where the petiole meets the stem, not in the leaflets.


Plant Anatomy

Exceptions to the rule.

•Leaves are not always used for photosynthesis, like in cacti, in which the stems do photosynthesis.

•The spines of cacti likely evolved from leaves, but they are nothing like the leaves of any other plant; mature spines are not even alive.


Plant Anatomy

Figure 7 Cacti spines.

In cacti, leaves have evolved into sharp spines. Notice that the stems display the characteristic green of photosynthetic tissue.


Plant Anatomy

Plant Tissues

All of the tissue in vascular plants consists of just three types-dermal, vascular, and ground.


Plant Anatomy

Figure 8 Plants are composed of three types of tissues.

Dermal tissues primarily protect a plant. Vascular tissues transport water, nutrients, and minerals.

Ground tissues are responsible for every other function in a plant, including metabolic processes, protection, and transport.


Plant Anatomy

Plant Tissues

• Ground tissue comprises the bulk of the plant and generally makes up the structures in between the dermal and vascular tissues.

• Ground tissue carries out most of the plant's metabolic processes, e.g., photosynthesis.

• Dermal tissue provides a protective covering for the roots, stems, and leaves, so it is found on the outside of plant organs.

• Vascular tissue serves to transport food, water, hormones, and minerals, so it is usually found in a plant's interior.


Plant Anatomy

Dermal tissues surround and protect plant organs.• In nonwoody plants, epidermal cells form a single, tightly packed layer

called the epidermis.

• Epidermal cells in leaves and stems secrete a waxy material called the cuticle, which coats the epidermis and prevents excessive water loss.

• In woody plants, a thicker, multilayered protective tissue called the periderm commonly replaces the epidermis in mature regions of roots and stems.

• Root hairs are extensions of epidermal cells in roots. Hair-like structures called trichomes are extensions of epidermal cells in leaves and stems.


Plant Anatomy

Figure 9 Trichomes.

In this SEM of a Nicotania benthamiana leaf, the trichomes extend from the tough epidermal cell layer on either side. Sandwiched in the middle are the photosynthetic cells.

At the far left is part of a vein (mv), which contains vascular tissue.


Plant Anatomy

Vascular tissue transports water, minerals, and sugars.

• The two main vascular tissues are xylem and phloem.

• Xylem tissue transports water and minerals from the roots to the shoots of a plant, moving from bottom to top, against gravity.

• Phloem tissue moves sugars from the leaves to the rest of the plant.

• Together, xylem and phloem tissues form cylindrically shaped bundles called vascular bundles, or stele.


Plant Anatomy

Figure 10 Vascular bundles in stem tissue.

This micrograph shows a cross section of a grape plant stem, with vascular bundles aligned side by side. Each vascular bundle contains adjacent xylem and phloem tissue.

Xylem tissue is the innermost red-stained layer, and phloem tissue is the thinner blue-stained layer. Vascular bundles are the main transport system of the plant stem. (Magnification = 116x).


Plant Anatomy

Figure 11 Xylem tissue.

Tracheids and vessel elements differ in shape. Tracheids are narrower, have tapered ends, and transport water and minerals between cells through bordered pits. Vessel elements (SEM at right) transport water and minerals vertically through pores.


Plant Anatomy

Ground tissue has multiple roles and contains diverse cells.

• The great majority of tissue in plants is ground tissue.

• In eudicots, ground tissue inside the ring of vascular bundles is commonly called the pith. Ground tissue exterior to the vascular bundles is called the cortex.

• The three types of ground tissue cells are parenchyma, collenchyma, and sclerenchyma.

• Parenchyma cells are the most common and versatile ground tissue cells. They have thin primary cell walls and usually lack secondary walls.


Plant Anatomy

Figure 12 Parenchymal cells.

Photosynthesis takes place in parenchymal cells. The green structures in these Arabidopsis cells are chloroplasts.


Plant Anatomy

Ground tissue has multiple roles and contains diverse cells.

• Collenchyma cells are thin, elongated cells with unevenly thickened walls that provide support and flexibility to growing regions of the plant, particularly in the stems and leaves.

• Sclerenchyma cells are the principle structural support in tissue that has ceased to grow in length.

• Many sclerenchyma cells are dead but retain their functionality because of their hard, thick secondary walls, which contain high amounts of lignin.

• Sclereids are short sclerenchyma cells that contain the most lignin and so are the hardest. These are the cells that form the outer covering of nuts and many fruit seeds.

• Fibers tend to be longer and more tapered in appearance than sclereids. They are often used commercially in the production of ropes and linen.


Principles of Biology BIOL 100C: Introductory Biology III Plant Cell Types Dr. P. Narguizian Fall 2012.

Documents

plants roots

ground roots

fibrous roots

types of roots

lateral roots

buttress roots

exposed roots

plant anatomy bioskill