Plant bio exam 2 quiz 1

How did coevolution with animals drive angiosperm diversification?

Pollinators (insects, birds) drove flower adaptations for fertilization, while animals dispersing fruits and seeds helped species expand quickly into new habitats.

What is the classic example of coevolution between a flower and a pollinator mentioned in the notes?

Darwin’s Orchid (Angraecum sesquipetale) and Morgan’s Sphinx moth (Xanthopan morganii). The orchid has a 35 cm nectar tube, and the moth has a proboscis long enough to reach the nectar.

What chemical compounds are responsible for floral scent in the Darwin’s Orchid example?

Large amounts of aldoximes, which are degradation products of amino acids (leucine, phenylalanine, valine, isoleucine).

What are the “Archaic Features” of early flowers?

• No distinct sepals and petals (tepals).

• Free, unspecialized carpels.

• Indefinite number of flower parts.

• Radial symmetry.

What are the “Modern Features” of flowers?

• Distinct sepals and petals (can be fused).

• Closed carpels (stigma, style, ovary).

• Definite number and fewer flower parts.

• Radial or bilateral symmetry

What is the difference between the sporophyte and gametophyte generations in land plant evolution

The diploid sporophyte became the predominant life form, while the gametophyte was reduced in size and became non-self-sustaining, dependent on the sporophyte for sexual reproduction.

What is “Double Fertilization” in angiosperms?

A process where:

1. A 2n sperm fertilizes the egg to form a 2n zygote (embryo).

2. A 2n sperm fertilizes the central cell to form a 3n endosperm (nutrient source).

What develops from the ovule and the ovary after fertilization?

The ovule develops into the seed, and the ovary develops into the fruit.

What are the three main axes/parts of the developing embryo?

1. Radicle: Embryonic root.

2. Epicotyl: Embryonic stem.

3. Hypocotyl: The root/shoot junction.

What is the function of the suspensor in embryo development?

It provides nutrients to the developing embryo and then dies.

What are the three layers of the fruit wall (pericarp)?

1. Exocarp: Outer layer (skin/peel).

2. Mesocarp: Middle layer (flesh).

3. Endocarp: Innermost layer (can be tough or thin)

What happens to the fruit tissue during ripening?

Starch is broken down and converted into fructose, and cell walls are broken down to make the tissue softer.

What are the four external factors required for seed germination?

1. Water: Activates enzymes, digests stored food, and leaches inhibitors (in desert plants).

2. Oxygen: Required for aerobic respiration.

3. Temperature: Optimum range is 25–30°C.

4. Fire/Smoke: Karrikins in smoke trigger signaling pathways.

What are the internal hormonal factors controlling germination?

The ratio of Abscisic Acid (inhibits germination/maintains dormancy) to Gibberellins (promotes germination).

What is “After-Ripening”?

Enzymatic and biochemical changes that occur in the seed during dormancy (often triggered by low temperatures) prior to germination, involving low metabolic activity.

What is the key difference between plant and animal growth?

Plants continually make new organs (leaves, roots, flowers) as they grow, whereas animal growth is generally determinate.

Growth:

Irreversible increase in size (cell division + enlargement).

Morphogenesis:

Acquisition of a particular shape or form.

Differentiation

Process by which identical cells become different from one another.

What are the three primary meristems and what do they become?

Protoderm, ground meristem, procambium

Protoderm →

Epidermis (Dermal tissue system).

Ground Meristem →

Ground tissues: Parenchyma, Collenchyma, Sclerenchyma (Ground tissue system).

Procambium →

Primary Xylem and Primary Phloem (Vascular tissue system).

What is the difference in leaf venation between Eudicots and Monocots?

• Eudicots: Netted (reticulate) venation.

• Monocots: Parallel venation.

Why is Brassica oleracea significant in the study of plant form?

It demonstrates how domestication alters plant form; broccoli, cauliflower, kale, and cabbage are all the same species but have dramatically different structures due to selective breeding.

What was the significance of “Dwarf Plants” in the Green Revolution?

Dwarfing genes altered plant height, which likely improved crop yields by preventing lodging and redirecting energy, though the notes emphasize that understanding these genetic/physiological changes aids crop breeding.

What are the characteristics and functions of Parenchyma cells?

• Alive at maturity.

• Have primary walls and intercellular spaces.

• Functions: Photosynthesis, storage, and secretion.

What are the characteristics and functions of Collenchyma cells?

• Alive at maturity.

• Have uneven primary walls but no intercellular spaces.

• Function: Provide structural support in young tissues.

What are the characteristics and functions of Sclerenchyma cells?

• Dead at maturity.

• Have thickened cell walls.

• Function: Provide structural support (often to vascular bundles).

What is the structure of Xylem?

Hollow, thickened conducting cells (tracheids, vessels)

Tracheids:

• Found in gymnosperms; narrow, up to 1 cm long, perforated by complex pit membranes.

Vessels

Found in angiosperms; made of vessel elements that are wide, short, have simple pit membranes, and open/perforated end walls.

What is the structure of Phloem?

Hollow but living conducting cells.

What are the two primary functions of roots?

1. Anchorage

2. Absorption (of water and minerals)

What other functions can roots serve?

Food storage, clonal regeneration, and forming associations with bacteria (nitrogen fixation) or fungi (nutrient absorption)

What is the function of Root Hairs?

They are tubular extensions of epidermal cells that greatly increase surface area for efficient uptake of water and minerals. They also aid in associations with nitrogen-fixing bacteria and mycorrhizal fungi.

What is the function of the Cortex in roots?

It occupies the greatest area of the root. In storage roots, it stores starch. Under flooding, it can form aerenchyma (airspaces) to reduce respiration needs when oxygen is limited.

What is the Endodermis and what is its function?

The innermost layer of the cortex in mature roots. Except for passage cells, it is covered by lignin and suberin (Casparian strip) to regulate the radial movement of water and nutrients into the vascular cylinder.

What is the Exodermis?

In some mature roots, the outer layer of the cortex forms the exodermis, which accumulates lignin (for support) or suberin (for waterproofing).

What is the difference between Monocot and Eudicot root vascular structures?

• Monocots: Many xylem and phloem elements with a pith in the center.

• Eudicots: (Implied by contrast) Typically have a solid core of xylem without a large central pith.

• Note: In both, phloem and xylem alternate within the stele, enclosed by pericycle cells.

What is the function of the Root Cap?

It protects the Root Apical Meristem (RAM) and produces mucilage to aid in soil penetration.

What is the Quiescent Center (QC)?

A group of stem cells in the RAM that keep dividing but do not differentiate. They serve as the source for surrounding stem cells.

How do cells differentiate in the root meristem?

Through asymmetric cell division. As cells move away from the QC, they enter the elongation zone (where expansion dominates) and eventually differentiate into mature tissues.

How is the fate of Cortex vs. Endodermis determined?

Via the transcription factor Shortroot (SHR):

Transcription factor Shortroot production

1. SHR is produced in the stele and diffuses into the endodermis.

2. In the endodermis, SHR binds to Scarecrow (SCR).

3. This sequesters SHR, preventing it from moving into the cortex.

4. This initiates a feedback loop that induces endodermal fate and prevents cortical fate in that layer.

What is “De-differentiation” in the context of root branching?

The process by which somatic cells reactivate the cell cycle to develop new organs (like lateral roots). This often involves pericycle cells dedifferentiating.

What is the difference between Eudicot and Monocot root systems?

• Eudicots: Have a taproot system. The primary root grows downward and gives rise to lateral (branch) roots.

• Monocots: Have a fibrous (crown/nodal) root system. Roots are initiated from the nodes of the stem, and the primary root often does not dominate the adult system.

What are adventitious roots?

Roots that form from non-root tissues, such as stems. They help with anchorage, develop after damage, and are used in vegetative propagation.

Why are fine roots (feeder roots) ecologically significant?

• They account for ~33% of global annual net productivity in terrestrial systems.

• They are replaced every few months, contributing significantly to carbon reserves in the soil.

What constitutes secondary growth in roots and stems?

1. Secondary Vascular Tissues: Xylem and Phloem produced by the Vascular Cambium.

2. Periderm (Cork): Produced by the Cork Cambium.

What is Totipotency?

The capacity of an individual cell to proliferate and produce all the differentiated cells of the whole organism.

How can a single cultured plant cell regenerate an entire plant?

Through Somatic Embryogenesis or Organogenesis.

How does plant development differ from animal development?

Plants can make new organs throughout their entire life cycle, whereas animal development is generally determinate.

What allows plants to continuously produce new organs?

The active maintenance of stem cell pools in the apical regions (Root and Shoot Apical Meristems).

What signals determine stem cell differentiation?

Positional and hormonal signals.

What structures give rise to diverse root systems?

The Root Apical Meristem (RAM) and lateral meristems (like the vascular cambium).