Exam 4

How does structure fit function in vascular plants at the organ level?

Leaves provide surface area for absorbing sunlight and exchanging gases, stems support and elevate the leaves to maximize photosynthesis, and roots anchor the plants while also absorbing water and mineral

How does structure fit function in vascular plants at the tissue level?

Dermal tissue protects the organs, vascular tissue provides support and transports resources, while ground tissue includes cells that carry out photosynthesis and store sugars

How does structure fit function in vascular plants at the cellular level?

Photosynthetic cells contain chloroplasts that convert sunlight into chemical energy, tube-shaped cells transport resources (water, minerals, sugars), and cells with root hairs near root tips increase root surface area to aid in absorbing water and minerals

Cell

The fundamental unit of life

Tissue

Group of cells consisting of one or more cell types that together, perform a specific function

Organ

Consists of several types of tissues that carry out particular functions.

Organ System

A collection of organs, that together, perform specific functions

Organism

The collection of cells, tissues, organs, and organ systems leading to a functioning living being

How does the morphology of a vascular plant reflect its evolutionary history?

Vascular plants reflect the two different environments it lives in: underground and above ground. This leads to the purpose of the two main systems: the root system and the shoot system.

Root System

The parts of vascular plants that reside underground. Usually responsible for water/mineral absorption and anchoring the plant. Can also be used for storage and reproduction in some plants.

Shoot System

The parts of vascular plants that are above ground. Consists of the leaves, stems, and (if applicable) flowers. Used for photosynthesis.

Root

Organ that anchors a vascular plant in the soil, absorbs minerals and water, and stores reserves.

Primary Root

Originates the the seed embryo, making it the first root; branches to include lateral roots.

Lateral Roots

The roots that develop from the primary root.

Taproot System

Tall, erect plants with large shoot masses usually have this kind of root system. The system consists of one main vertical root that usually develops from the primary root. This main root does not play as large a role in absorption, but facilitates in anchorage.

Taproot

The main root in a taproot system. Derived from the primary root and does not play as much a role as lateral roots in absorption. Facilitates anchorage and can be specialized for food storage.

Fibrous Root System

Root system found in small vascular plants or those that have a trailing growth habit making it more susceptible to grazing animals. This system is a thick mat of slender roots that spread out. The primary root dies early and does not become a taproot.

Adventitious Roots

The small roots that emerge from the stem in fibrous root systems.

Root Hairs

Thin, finger-like extensions of root epidermal cells that greatly increase the surface area of the root system’s surface area.

Buttress Roots

Aerial extensions of lateral surface roots that provide stability in shallow-rooted organisms.

Prop Roots

Modified aerial, adventitious roots that grow downward to provide support for heavy branches.

Storage Roots

A specialized underground organ that undergoes modifications during its development to store nutrients and is often used as food.

Pneumatophores

Specialized root structures that grow out from the water surface and facilitate the aeration necessary for root respiration in hydrophytic trees.

Strangling Aerial Roots

Aerial roots that eventually engulf the plant they support.

Stems

Plant organ bearing leaves and buds with the chief function being to elongate and orient the shoot in a way that maximized photosynthesis.

Nodes

The points at which leaves are attached on a stem.

Internode

The space between nodes on a stem.

Apical Bud

The type of bud located at the top (apex) of the plant, particularly at the very tip of the main stem.

Axillary Bud

The bud that is a precursor to a branch of lateral shoot.

Leaf

The main photosynthetic organ; intercepts light, exchanges gasses, dissipates heat, and defends against herbivores and pthogens.

What is the difference between the vein arrangement in monocots compared to dicots?

Monocots’ veins are arranged in parallel veins of equal diameter, while dicot veins are arranged in a “net like” manner of differing widths.

Simple Leaf

A leaf with a single, undivided blade

Compound Leaf

A leaf where the blade (surface), consists of multiple leaflets. The leaflets do not have axillary buds at their base.

How many types of tissue does a plant have? What are they?

There are three types: the dermal tissue, the vascular tissue, and the ground tissue.

Dermal Tissue

The outer protective covering of the plant (the “skin” of the plant).

Dermal Tissue in Leaves vs. Roots vs. Woody Plants

In leaves, dermal tissue is a waxy epidermal structure known as the cuticle.

In roots and small non-woody plants, the dermal tissue is the epidermis, or a layer of tightly packed cells.

In woody plants, the dermal tissue is thick and protective and called the periderm

Guard Cells

Specialized epidermal cells that control gaseous exchange via the stomata.

Trichomes

Specialized cells in shoots that reduce water loss, reflect excess light, and defend against insects.

List the three important specialized epidermal cells

Root hair cells, guard cells, and trichomes

Vascular Tissue

Tissue in plants that facilitates the transport of materials through the plant and that also provides mechanical support. Can be divided into two types of tissue: xylem and phloem.

Xylem

Vascular tissue that conducts water and dissolved minerals upward from roots to shoots.

Phloem

Vascular tissue that transports sugars (product of photosynthesis) from mature leaves to roots and young leaves.

Stele

The term for the collective vascular tissue of a root or stem. Also known as the vascular cylinder. It is surrounded by the endodermis and typically consists of xylem and phloem, which transport water, nutrients, and sugars throughout the plant.

Stele in Angiosperms

The root stele is a solid central vascular cylinder of xylem and phloem, while the stems and leaves have vascular bundles, with separate strands containing xylem and phloem.

Ground Tissue

Tissue that is neither dermal nor vascular and is specialized for different functions (storage, photosynthesis, support, etc.)

Pith

Ground tissue internal to the vascular tissue.

Cortex

Ground tissue external to the vascular tissue. In roots, this stores carbohydrates, transports water and salts to the center of the root, ad allows for the extracellular diffusion of water, minerals, and oxygen.

Stomata

Pores in the epidermis of leaves that function in the exchange of gases with the atmosphere.

Indeterminate Growth

The ability to grow through one’s life. Plants often exhibit this.

Meristems

The reason plants exhibit indeterminate growth. Theses cells divide, leading to new cells that elongate and become differentiated.

Determinate Growth

The type of growth where an organism stops growing after reaching a certain size.

What are the two main types of meristems?

Apical and lateral meristems

Apical Meristems

Located at the root and shoot tips and provide cells that enable primary growth.

Primary Growth

Allows roots to extend throughout the soil and shoots to increase exposure to light. In non-woody plants, it produces almost the entire plant body.

Secondary Growth

A growth in thickness (circumference) made possible by lateral meristems (vascular and cork cambium). Often exhibited in woody plants.

Lateral Meristems

Meristems that allow for growth in thickness. These meristems include the vascular cambium and the cork cambium.

Vascular Cambium

A cylinder of meristematic cells, one cell thick, that is wholly responsible for the production of secondary xylem and phloem. Located outside the pith and primary xylem and to the inside of the primary phloem and cortex.

Cork Cambium

In secondary growth, this replaces the epidermis with a thicker, tougher periderm.

Primary Meristems

Cells displaced from meristems may divide several more times as they mature, giving rise to the following tissues: the protoderm, ground meristem, and the procambium, which are collectively known as this. These tissues are responsible for producing the mature dermal, ground, and vascular tissues of roots and shoots.

Primary Growth

Growth in length caused by cell division in apical meristems. In herbaceous plants, almost the entire plant grows via this type of growth.

Root Zones for Primary Growth

1. Zone of Cell Division:

- The Zone of Cell Division encompasses the region housing the root apical meristem (RAM) and its progeny. Here, rapid cell division occurs, driven by the RAM's activity, leading to the production of stem cells.

2. Root Cap:

- Positioned at the tip of the root, the Root Cap serves as a multifunctional shield. It protects the other zones and the root from the abrasive soil. Through the secretion of a polysaccharide slime, the Root Cap facilitates soil lubrication, easing the root's passage through the substrate.

3. Zone of Elongation:

- Following the Root Cap, the Zone of Elongation is where most of the growth occurs as root cells elongate. As this occurs, the three primary meristems become more evident.

4. Zone of Differentiation:

- As cells transit from the Zone of Elongation to the Zone of Differentiation, they undergo differentiation and become their distinct cell types: protoderm, ground meristem, and procambium.

Protoderm

The outermost primary meristem developed in root primary growth. This gives rise to the epidermis and the root hairs.

Ground Meristem

The middle layer of primary meristem developed during root primary growth. This gives rise to mature ground tissue. This is mostly parenchyma cell and is found in the cortex.

Endodermis

This is the innermost layer of the cortex. It is a cylinder one cell thick that forms the boundary with the vascular cylinder and acts as a selective barrier that regulates passage of substances from the soil into the vascular cylinder.

Procambium

Gives rise to the vascular cylinder, consisting of xylem and phloem, surrounded by the a cell layer called a pericycle.

Differences in Roots of Dicots vs. Monocots

In dicots, xylem has a star-like appearance in the cross section, while the phloem is in the indentations of the “star”

In monocots, Vascular tissue consists of a core of undifferentiated parenchyma cells surrounded by a ring of alternating xylem and phloem cells.

How do lateral roots (branch roots) form?

Lateral roots arise from meristematically active regions of the pericycle. The lateral roots will then push through outer tissues until they emerge from the established root.

Primary Growth of Shoots

Shoots grow in length at the apical bud, located at the top of the shoot. The apical bud contains the shoot apical meristems and leaf primordia. The shoot apical meristems are where the cells divide and remain, while the leaf primordia give rise to young leaves in order to generate enough photosynthesis to keep the plant growing. Axillary buds are also developed as a way to ensure the plant’s survival if the apical bud is ever unable to continue cell divisions. The closer an axillary bud is to the apical bud, the more inhibited it is due to apical dominance.

Primary Growth of Roots

Roots undergo primary growth primarily at the root tip, where the root apical meristem (RAM) is located. The RAM continuously produces new cells, driving root elongation and the penetration of the root into the soil. As the root extends, it develops root hairs, which increase surface area for absorption of water and nutrients. Additionally, the root cap protects the delicate RAM and secretes substances to aid in soil penetration. This continuous growth at the root tip enables the plant to explore and exploit soil resources efficiently.

What covers the leaf epidermis and why?

A waxy cuticle because it greatly reduces water loss.

The majority of root growth occurs in the zone of elongation, which pushes the root tip farther into the soil.

True

The apical meristem of the root is covered by a protective layer called the ___________

root cap

Leaf Growth and Anatomy

Leaves develop from leaf primordia, which are located at the apical bud of a shoot. They are covered by waxy cuticles to reduce water loss, except where stomata are located. They also contain mesophyll

Stomata

“Pores” in leaves that allow exchange of CO2 and O2 between the surrounding area and photosynthetic cells inside the leaf. The term refers to the pore or the entire complex consisting of the pore flanked by guard cells.

Guard Cells

Specialized epidermal cells that flank stomata and regulate the opening and closing of the pore.

All gymnosperm species and many dicot species undergo secondary growth, but this process is unusual in monocots. Secondary growth is also rare in leaves.

True

Primary and secondary growth occur simultaneously in woody plants. But secondary growth increases the diameter of stems and roots where primary growth has ceased.

True

What is the order of layers in a woody plant after secondary growth?

From outer to inner: periderm (cork cambium & cork), primary phloem, secondary phloem, vascular cambium, secondary xylem, primary xylem, pith

How does the stem thicken during secondary growth?

It does this as the vascular cambium forms the secondary xylem to the inside and secondary phloem to the outside. As a result, the vascular cambium forms exterior to the primary xylem and interior to the primary phloem.

What happens as the stem thickens during secondary growth?

- Vascular Cambium: This meristem layer produces new cells that become wood (xylem) towards the center and bark (phloem) towards the outside. The continuous activity of the vascular cambium adds rings of wood and bark, making the stem thicker over time.

- Cork Cambium: Found in the outer cortex, it generates cork cells externally, forming the protective outer bark, and phelloderm cells internally. As the cork cambium produces more cork cells, the outer bark thickens, offering protection against physical damage and environmental stress.

Result: This dual process of adding layers of wood internally and cork externally strengthens the stem and provides protection, essential for the longevity and resilience of woody plants.

What is bark as it relates to secondary growth?

Bark includes all tissues external to the vascular cambium (secondary phloem and cork).

Describe the layers of a tree.

As trees age, the older layers of the secondary xylem no longer function and are called heartwood because they are closer to the center. The newer (and functional) secondary xylem is the sapwood because it transports xylem sap.

What are growth rings?

Secondary xylem produced in a different season. The secondary xylem produced in the spring (early wood) appears different from that produced in summer (late wood)

What are the benefits of small plants?

1. Easy to anchor in soil

2. Easy to absorb water and nutrients throughout transport

3. Easy to control water evaporation

What are the benefits of tall plants?

1. Can assess more sunlight

2. Bigger roots for stronger anchorage

3. Vascular tissue for efficient long-distance transport

Why do plants compete for height?

They need to grow tall to avoid shading by neighboring plants.

Why is there so much variation in branching patterns?

Because plants need to use the limited resources where it is needed most. If most of the energy goes into branching, less energy will be available for growing tall, and vice versa.

What is the correlation between water availability and leaf size? Why is there a correlation like this?

Species with big leaves typically live in tropical rainforests and ones with small leaves usually live in dry and/or cold environments. This is because bigger leaves need more water for filling the internal space, but in a dry environment, liquid water is more scarce.

Phyllotaxy

The arrangement of leaves on a stem. This is determined by the shoot apical meristem and is specific to each species.

Most angiosperms have opposite phyllotaxy.

False; Most angiosperms have alternate phyllotaxy, with leaves arranged in an ascending spiral around the stem.

List the three types of leaf phyllotaxy.

Opposite, alternate, whorled

Describe the phyllotaxy of angiosperms.

Most angiosperms have alternate phyllotaxy, with leaves arranged in an ascending spiral around the stem, each successive leaf emerging about 137.5 degrees from the site of the previous one.

How does leaf orientation affect light capture?

Some plants have horizontally oriented leaves, while others have vertically oriented ones. If the sunlight is mild, the leaves will stay horizontal to maximize light capture. However, if it is intense, their orientation becomes vertical to reduce light capture.

What happens when there are many layers of vegetation in a plant?

The shading of the lower leaves is so great that they photosynthesize less than they respire. The nonproductive leaves or branches then undergo programmed cell death and shed. This is known as self-pruning.

How many major pathways of transport are there in plants? What are they?

Three; the apoplastic, symplastic, and transmembrane pathways.

Aploplast

Consists of everything outside the plasma membrane in plant cells, including cell walls and extracurricular spaces.

Symplast

Consists of the entire mass of cytosol of all the living cells in a plant, as well as the plasmodesmata, the cytoplasmic channels that interconnect the cells.

Which ONE of the following is NOT a strategy used by plants to maximize light capture directly?

A. Plants develop a wide variety of shoot architectures depending on environmental conditions.

B. Leaf size and structure vary significantly in response to different environmental conditions.

C. Leaf orientation adjusts as different times during the day.

D. Older branches are naturally shed from old trees.

D. Older branches are naturally shed from old trees

Plants do not develop a wide variety of shoot architectures depending on environmental conditons.

False; Typically, taller plants require thick stems for greater vascular flow, but vines are an exception.

When plants need to minimize water loss, stomata close and photosynthesis stops.

True