BIOL 1108 Lab Week 5: Plant Anatomy & Growth

Three organs of the plant body

Stems, roots, and leaves

What is the "shoot" of a plant?

The stem and its leaves

Key features of leaf

-cuticle

-stomata (opened and closed by guard cells)

-columnar mesophyll cells

-spongy mesophyll cells

Cuticle

A water-impermeable, thin waxy layer which covers both the upper and lower surfaces of the leaf.

What is just to the inside of the cuticle?

A single layer of epidermis cells.

Stomata

The openings in leaves that allow moisture and gases to be exchanged with the environment.

Guard Cells

Open and close stomata

Columnar Mesophyll Cells

Long upright orientation of the cells near the upper surface. They are responsible for absorbing light

Spongy Mesophyll Cells

Below the columnar mesophyll cells and closer to the bottom surface of the leaf and have much larger air gaps positioned around them. Allows CO2 to easily spread throughout the leaf tissue

Key features of a privet leaf cross section

-upper epidermis

-mesophyll

-lower epidermis

-central vein/vascular bundle

Key features of stem

-epidermis

-cortex

-vascular bundles

-xylem

-phloem

-pith

Epidermis

Outermost layer of cells

Cortex

A layer of cells just beneath the epidermis

Vascular Bundles

Found distributed at regular intervals around the stem. Comprised of xylem and phloem tissues.

Xylem of stem

Has lignin, a rigid substance that helps physically support the plant (stains red). Transports water throughout the entire plant, pulling water from soil.

Phloem of stem

Adjacent to the xylem but on the side of the vascular bundle closest to the outside of the stem. It transports carbohydrates to the non-photosynthetic portions of the plant.

Pith

In the center of the stem, are large, thin walled cell and store water inside of their vacuoles

Cross section of Medicago stem

Key features of root anatomy

-epidermis

-cortex

-endodermis

-stele

-pericycle

-xylem

-phloem

Epidermis of root

Outermost layer of the cell. It bears root hairs, which hold the root in place and increase the surface area available for absorption

Endodermis

Circular band of cells that surround the central vascular tissues. Suberin prevents water and minerals from diffusing out of the vascular bundles.

Stele

All the tissue inside the endodermis including the pericycle, xylem, and phloem

Pericycle

The layer of undifferentiated cells directly inside the endodermis.

Xylem of root

Forms cross shaped mass in the center of the root.

Phloem in root

Found in bundles around the periphery of the star shaped xylem

Cross section of root

-endodermis

-pericycle

-xylem

-phloem

-cambium

Key features of the shoot apical meristem

The shoot apical meristem is a relatively small dome-shaped mass of cells at the apex of the stem.

The leaf primordial (developing leaves) occur in pairs on opposite sides of the stem and protect the apical meristem

The axillary bud primordia are lumps of small, dark cells that will become the apical meristems for lateral shoots.

Key features of the longitudinal section for shoot section

-apical meristem

-leaf primordia

-procambium

-axillary buds

Key features of the root apical meristem

-root cap

-zone of cell division

-zone of elongation

-zone of maturation

Key features of the longitudinal section for root section

-area of maturation

-area of elongation

-area of cell division

-root cap

-apical meristem

Zones of growth of root apical meristem

-zone of cell division

-zone of elongation

-zone of maturation

cross section of lateral root formation

-cortex

-epidermis

-pericycle

-endodermis

-developing lateral root

Key features of secondary growth

-Lateral Meristems which are:

-Vascular Cambium

-Cork Cambium

Vascular Cambium

Produces secondary xylem toward the center of the stem and secondary phloem towards the outside. Located in between the primary xylem and primary phloem

Tilia Slide

-cork

-cortex

-secondary phloem

-vascular cambium

-secondary xylem

Cork Cambium

Primarily adds cells to the outside of the stem, creating a protective layer. Cork is not the same as bark.

Bark

Outermost covering of the tree or plant, including everything external to the vascular cambium, including the phloem, cortex, and cork.

Lenticels

Splits in the outer protective layer (bark) allow for gas exchange with the environment.

How does a tree grow?

Primary Growth affects the vertical growth with the production of new leaves, stems, and roots

Secondary Growth increases the girth

The cambial tissues involved are the vascular and cork cambium in secondary growth

The primary vascular tissue includes primary phloem and primary xylem

The secondary vascular tissue includes the secondary phloem, which grows between the secondary xylem and secondary phloem.

Secondary Growth

Occurs by increasing the girth of the plant through the action of the Lateral Meristems, which include the Vascular Cambium and the Cork Cambium

Primary Growth

The production of new leaves, stems, and roots resulting in the vertical growth of the plant. It occurs in specialized regions called apical meristems. These are regions in which cell division and growth occurs continuously.

Cambial Tissues Involved

Vascular Cambium and Cork Cambium

Primary and Secondary Vascular Tissue

The primary vascular tissue includes primary phloem and primary xylem

The secondary vascular tissue includes the secondary phloem, which grows between the secondary xylem and secondary phloem.

Modifications and Variations of Leaves

-needle or scale leaves

-spines

-succulents

-leaf tendrils

-storage organs

-trichome

-floatation

-carnivorous

Needle or scale leaves

Typically seen in plants that keep there leaves all year long, the reduced size and surface area allows for better water retention in dry environments (pines spruce fir juniper cedar)

Spines

Mechanical defense structures that deter herbivores looking to consume the plant for water (cacti, holly)

succulents

Thick fleshy leaves that retain moisture due to a low surface-to-volume ratio (sedum, jade, aloe)

leaf tendrils

spirally coiled structures sensitive to touch. Coil for additional support for the plant body when something touches it (sweet pea, wild pea)

Storage Organs

Thick, fleshy scale-like leaves that store either water or nutrients (onion, tulip, lily)

Trichome

hairlike projections that extend from a plant's epidermis. some are glandular and produce secretions (geranium, tomato, begonia)

floatation

expanded airspaces in mesophyll of the leaf that provide buoyancy (water lily, water hyacinth)

carnivorous

traps insects allowing for plant growth in nitrogen and nutrient poor soil. (Venus fly trap, pitcher plant)

Modifications and Variations of Stems

-stem tuber

-rhizome

-stolon

-bulb

-corm

-stem tendril

stem tuber

fleshy underground stem used as starch storage, grow shallowly in soil (potato, yam)

rhizome

a horizontal, underground stem that produces new shoots and roots from its nodes (hops, ginger, iris)

stolon

shoot that grows along ground, producing roots at its nodes (strawberry)

Bulb

short stem with fleshy leaves or leaf bases that function as food storage organs during dormancy (onion, tulip, lily)

Corm

Short, hard underground stem that serves as storage to help plant survive adverse environmental conditions (crocus, banana)

stem tendril

thin, spiral coiling stem that attaches to nearby surfaces to support the plant body (grape, passiflora)

Modifications and Variations of Roots

-taproot

-fibrous

-aerial

-prop/stilt

-root tuber

taproot

large, central root, tending to be straight and thick. May have smaller roots branching from the large central one (dandelion, welwitschia)

Fibrous

Thin branching roots (grass, ferns, coconut palm)

Aerial

Above ground roots, which may take in water and or nutrients directly from the air (ivy, orchids)

Prop/stilt

Structural roots capable of holding up shoots that might otherwise fall over (corn, sugarcane, banyan tree)

root tuber

similar to a stem tuber, these are thickened storage organs that develop from lateral roots. Tend to grow deeper into the soil than do stem tubers. (sweet potato, dahlia)