Plant Structure and Function

What were the first ancestors of land plants? What time period?

Charophyceans (algae), Precambrian

What was the first group of land plants? Time period?

Bryophytes, Paleozoic, 475 mya

First vascular plants? Time period?

Pteridophytes, Paleozoic, 420 mya

First seed plants? Time period?

Gymnosperms, Mesozoic, 305 mya

First flowering plants? Time period?

Angiosperms, Mesozoic but mostly Cenozoic,

Evidence that Charophytes are closest relatives of land plants (7) – shared ancestral characteristics

(1) homologous chloroplast (2) homologous membranes for cell wall synthesis (3) homologous peroxisomes (4) homologous flagellated sperm (5) homologous phragmoplasts (6) spores (7) sporopollenin

Phragmoplasts

Rosette cellulose-synthesizing complex

Spores

Allow sexual reproduction

Sporopollenin

Molecular evidence, pollen can be used to identify

Shared derived characteristics of land plants (5) – not shared with Charophytes

(1) alternation of generations (2) multicellular, dependent embryos (3) walled spores produced in sporangia (4) multicellular gametangia (5) apical meristems

Tissue (4 types)

Group of cells consisting of one or more cell types that together perform a specialized function; meristematic , vascular, ground, dermal

Vascular tissue (3)

from pro cambium, carries out long-distance transport of material between roots and shoots; xylem, phloem, and stele

Xylem

Conveys water and dissolved minerals upward from roots to shoots; tracheid and vessel elements

Tracheid

Dead at maturity, water moves from cell to cell

Vessel Elements

Dead at maturity, most common in angiosperms, align end to end to form long vessels; hardened with lignin

Phloem

Transports organic nutrients from where they are made to where they are needed; sieve tubes, sieve plates, companion cells

Sieve tubes

Alive at maturity, lack organelles

Sieve plates

Porous end walls that allow fluid to flow between cells along sieve tube

Companion cells

Along with each sieve tube element, its nucleus and ribosomes serve both cells

Stele

Vascular tissue of stem or root; central vascular cylinder, vascular bundles

Central vascular cylinder

Angiosperms, has pericycle

Pericycle

Outermost layer in vascular cylinder where lateral roots arise

Vascular bundles

Stele of stems and leaves are divided into these strands of xylem and phloem; in eudicots they are arranged in a ring but in monocot stems they are scattered

Ground tissue

Includes cells specialized for storage, support, and photosynthesis; pith and cortex

Pith

Ground tissue internal to vascular tissue

Cortex

Ground tissue external to vascular tissue (mostly parenchyma cells); endodermis

Endodermis

Innermost layer of cortex that regulates passage of substances from soil into the vascular cylinder

Parenchyma cells

Thin primary cell walls, active (photosynthesis) with organelles and large vacuoles, lack secondary walls, least specialized, perform most metabolic functions, retain ability to divide and differentiate

Collenchyma cells

Grouped into strands and help support young parts of plant shoot, thick uneven primary cell walls, lack secondary walls, alive at maturity, petiole support, flexible support without restraining growth

Sclerenchyma cells

Rigid thick secondary cell walls, dead at maturity, support stem and leaf veins, hard coverings of fruit; sclereids and fibers

Sclereids

Short and irregular in shape, thick lignified secondary walls

Fibers

Long and slender and arranged in threads

Dermal

From protoderm, epidermis and periderm

Epidermis

In nonwoody plants, layer of tightly packed cells; cuticle, trichomes

Cuticle

Waxy coating that prevents water loss

Trichomes

Outgrowths of shoot epidermis that helps with insect defense, water loss (hairy)

Periderm

Woody plants, replaces epidermis in older regions of stems and roots

Organ (3)

Consists of several types of tissues that together carry out particular functions; roots, stems, leafs

Roots (4)

Anchor, absorb minerals and water, store carbs; taproot, lateral roots, root hairs, fibrous roots

Taproot

Main vertical root in eudicots and gymnosperms

Lateral roots (eudicots and gymnosperms)

Arise from taproot; eudicots and gymnosperms

Fibrous root system

Monocots; when taproot dies in embryonic stage this arises; adventitious roots and lateral roots

Adventitious roots

Arise from stems or leaves

Lateral roots (monocots)

Arise from adventitious roots

Root hairs

Where absorption of water and minerals occur, increases surface area

Nodes

Alternating system at which leaves are attached

Internodes

Stems between nodes

Axillary bud

Has potential to form a lateral shoot or branch if apical bud is removed

Apical bud

Located near shoot tip and causes elongation of young shoot

Apical dominance

Helps maintain dormancy in most axillary buds

Rhizomes

Horizontal shoot that grows just below surface; vertical shoos emerge from axillary buds on rhizome

Bulb

Vertical underground shoots consisting mostly of enlarged bases of leaves that store food (onion)

Stolons

Horizontal shoots that grow along the surface that allow the plant to reproduce asexually (strawberries)

Tubers

Enlarged ends of rhizomes or stolons specialized for storing food (potatoes)

Leaves

Main photosynthetic organ of most vascular plants

Blade

leaf

Petiole

Stalk that joins the leaf to a node of the stem

Veins

Vascular tissue of leaves, function as a skeleton enclosed by a protective bundle sheath

Parallel veins

Found in monocots

Branching veins

Found in eudicots

Stomata

Allow exchange of CO2 and O2 of epidermis

Guard cells

Regulate opening and closing of stomata

Mesophyll

Ground tissue between upper and lower epidermis

Palisade mesophyll

Upper part of leaf in eudicots

Spongy mesophyll

Lower part of leaf in eudicots; loose arrangement allows for gas exchange

Simple leaf

Single, undivided blade, some deeply lobed

Compound leaf

Blade consists of many leaflets, no axillary bud at base

Doubly compound leaf

Each leaflet is divided into smaller leaflets; allows for less tearing and resistance to pathogens

Tendrils

Cling and coil for support (peas, grapevines)

Spines

Spines of cacti are leaves that carry out photosynthesis in stems

Storage leaves

Succulents store water (ice plant)

Reproductive leaves

Succulents produce adventitious plantlets that fall off the leaf and take root in soil

Bracts

Surround a group of flowers to attract pollinators (poinsettia)

Indeterminate growth

Growth occurs throughout plant’s life

Determinate growth

Growth ceases after reaching a certain size, animal and some plant organs (leaves, thorns, flowers)

Annuals

Complete their life cycle in a year or less

Biennials

Require two growing seasons

Perennials

Live for many years

Which of the following is not a type of primary meristematic cell found in apical meristems?
Procambium
Ground meristem
Protoderm
Vascular cambium

Vascular cambium; The vascular cambium is a type of cell found in lateral (not apical) meristems and is involved in secondary (not primary) growth.

Which structure determines the direction of root growth by sensing gravity?
Mucigel
Pith
Root cap
Root hairs

Root cap; The root cap is a layer of protective cells that determines the direction of root growth by sensing gravity.

True or false? Plant growth involves both the production of new cells by mitosis and the expansion of cell volume.

True

Which of the following statements about the vascular cambium is true?
It is located between the primary xylem and cortex.
It is a type of apical meristem.
It is a layer of undifferentiated cells that develops into secondary xylem and phloem.
It develops into cork cells on the outside of the cortex.

It is a layer of undifferentiated cells that develops into secondary xylem and phloem; Vascular cambium is a type of lateral meristem that produces secondary xylem and phloem in a plant.

Why do plants need secondary growth?

To provide structural support for the plant

Which of the following parts of a plant remains on the plant even after several years of growth?
Primary phloem
Epidermis
Primary xylem
Cortex

Primary xylem; the primary xylem is located close to the pith of the plant and remains a part of the plant even after several years of growth.

True or false? Primary growth can occur at both the apical and lateral meristems at the tips of the roots and stems in a plant.

False; Primary growth results in increased length and occurs only at the apical meristems at the tips of the roots and stems in a plant.

Secondary growth NEVER occurs in _____.

Leaves

_____ provides cells for secondary growth.

Vascular cambium; Vascular cambium is lateral meristem that provides cells for secondary growth.

Vascular cambium forms wood toward the stem’s _____ and secondary phloem toward the stem’s _____.

Center… surface; Wood, or secondary xylem, is formed toward the stem’s center, and secondary phloem is formed toward the stem’s surface.

What is the function of cork?

insulation and waterproofing (stems and roots)

How is the supply of vascular cambium maintained?

By the division of its cells; When a vascular cambium cell divides, one cell differentiates and the other cell remains meristematic.

Cell division in the vascular cambium adds to the girth of a tree by adding new _____ to the layer’s interior and _____ to the layer’s exterior.

Xylem… phloem; The vascular cambium produces xylem at its interior and phloem at its exterior.

As the epidermis is pushed outward and sloughed off, it is replaced by tissues produced by the _____.

Cork cambium; The cork cambium produces the phelloderm, phellogen, and cork cells. These cells move outward to replace epidermal cells.

Cellular differentiation is responsible for _____.

One daughter cell becoming a sieve tube whereas the other becomes a companion cell; Cell differentiation occurs as different genes are switched on and off.

At which level in the hierarchy of plant structure is the polarity of a plant determined?

Cells; The first division of the one-celled zygote establishes the polarity of the future plant.

Cellular differentiation and morphogenesis in plants depends primarily on _____.

Regulation of gene expression; The DNA of all the somatic cells in a plant is the same. What changes during cell differentiation is which genes are turned on and which genes are turned off.

Root hairs are important to a plant because they _____.

Increase surface area for absorption; Root hairs are extensions of individual epidermal cells on the root surface, which increase the absorptive surface area of the root tremendously.

Which of the following is correctly matched with its tissue system?

Cortex… ground tissue system

Other than the transport of materials, what is another function that vascular tissue performs in a leaf?

The tissue functions as a skeleton that reinforces the shape of the leaf; Veins in leaves (vascular bundles) transport materials and provide support.

How do cells in a meristem differ from cells in other types of plant tissue?

They continue to divide; Meristem is embryonic tissue, and it retains the ability to divide.

The primary growth of a plant adds _____ and secondary growth adds _____.

Height… girth; Apical meristems elongate shoots and roots through primary growth. Lateral meristems add girth to woody plants through secondary growth.