Plant Science Exam 2

Uniformitarianism

The geological principle that forces and processes operating **today are the same** as those that operated in the past (Gradual change).

Plate Tectonics

The unifying model explaining continental movement, accounting for **mountain ranges, volcanoes, and earthquakes**.

Fossils supporting Pangea

Fossils of the **Glossopteris** fern and the reptile **Lystrosaurus** found across Southern Hemisphere continents.

Embryophytes (470 MYA) Key Feature

The **Embryo** (zygote protected by the female gametophyte), which is essential for survival on land.

Alternation of Generations

The life cycle stage alternating between a **Haploid Gametophyte** (makes gametes) and a **Diploid Sporophyte** (makes spores).

Sporopollenin and Cuticle

Dessication-resistant compounds that prevent **water loss** in early land plants.

Seed Plants (380 MYA) Key Features

**Heterospory** (producing two spore sizes) and the use of the **Seed** as the primary agent of dispersal.

Domestication Syndrome

A collection of phenotypic traits distinguishing domesticated plants from wild relatives (e.g., **loss of seed dormancy**, larger fruits, synchronous flowering).

Cultivation vs Domestication

**Cultivation** is the human care of plants. **Domestication** involves selection and genetic change leading to traits useful to humans.

Centers of Origin

Geographic areas (e.g., Vavilov's 8 centers) where the **greatest genetic diversity** of a crop's wild relatives is found.

r-selection

Life history strategy characterized by **short life, early reproduction, high fecundity** (many offspring), and low parental investment.

K-selection

Life history strategy characterized by **long life, late reproduction, low fecundity** (few offspring), and high parental investment.

Hermaphroditism

Flowers that contain **both male and female** gametes.

Monoecious

Plants that have **separate male and female flowers** on the **same individual**.

Dioecious

Plants that have individuals that are **either male or female** (separate male and female plants).

Macroenvironment

The large-scale environmental factors (e.g., **elevation, latitude, regional temperature**) dealt with by a population.

Microenvironment

Localized changes in environmental factors (e.g., **light availability, moisture, nutrients**) dealt with by individuals.

Biomes

Large-scale vegetation types (e.g., Tundra, Taiga, Tropical Forest) determined primarily by **climate (temperature and precipitation)**.

Abiotic Stress vs Biotic Stress

**Abiotic** stress is from non-living factors (e.g., drought, cold). **Biotic** stress is from living organisms (e.g., herbivory, infection).

Optimal Growing Conditions

Environmental conditions that allow a plant to reach its **maximum growth and reproductive capacity**.

Noxa

An environmental factor that causes stress at **any concentration or intensity**, with **no optimum range** (e.g., heavy metals, pollutants).

Latent life

A state of **suspended growth** and metabolism (dormancy) that allows an organism to survive harsh conditions.

Mesophiles

Organisms (including most plants) that thrive in **moderate temperatures** (between 15°C and 45°C).

Hardening

The physiological process by which a plant increases its resistance to cold temperatures after **gradual exposure** to them.

Floristic Kingdoms

Large **taxonomic groupings** reflecting shared **geological and evolutionary history** (e.g., Holarctic, African, Australian).

Rosette (Cold Temp Adapt.)

A compact, circular arrangement of leaves close to the ground to **protect the apical meristem** from freezing wind and cold.

Sun vs Shade leaves

**Sun leaves** are smaller and thicker to maximize light use; **Shade leaves** are larger and thinner to maximize light interception.

Pulvini

**Joint-like structures** at the base of leaves/leaflets that allow plants to **change leaf position** to track the sun (heliotropism).

Stolons

Above-ground, horizontal stems that **spread a plant** by forming new plants at the nodes (e.g., strawberry runners).

Buttress roots

**Wedge-shaped, tall and wide roots** that provide support to **shallow-rooted trees** in tropical forests.

Epiphytes

Plants that grow on other plants (often trees) for support; they get water/nutrients from the **air and rain**, not the host plant.

Water Potential (Psi)

The **potential energy of water** per unit volume; determines the direction of water movement in a plant.

Water Potential Formula

Psi = Psi_s + Psi_p + Psi_m + Psi_g (Osmotic + Pressure + Matric + Gravitational potentials).

Matric Potential (Psi_m)

The potential energy associated with **water binding to surfaces** (e.g., cell walls, soil particles).

Xerophytes

Plants adapted to **dry** environments, often having thick cuticles, sunken stomata, or CAM.

Aerenchyma

Specialized tissue with **large air spaces** that transports oxygen from the shoot to the submerged roots.

Hypoxia

A condition where tissues (e.g., submerged roots) experience **low oxygen** concentrations.

ROL Barrier

**Radial Oxygen Loss (ROL) barrier**, which seals the epidermis of roots to **prevent oxygen from leaking** into the surrounding anoxic soil.

Thorns

Sharp defense structures that are modified **stems** (shoots).

Spines

Sharp defense structures that are modified **leaves**.

Prickles

Sharp defense structures that are modified **epidermal outgrowths** (like hairs).

Trichomes

Small, hair-like structures on the leaf surface that can **deter small insects** or aid in temperature regulation.

Secondary Compounds

Chemicals not required for basic metabolism but used primarily for **defense** (e.g., against herbivory or pathogens).

Terpenoids

A class of secondary compounds that includes **essential oils** (e.g., mint, pine resin) used for defense.

Alkaloids

A class of nitrogen-containing, **bitter** secondary compounds that are often **toxic** (e.g., caffeine, nicotine, morphine).

Biotroph (Pathogen Strategy)

A pathogen that keeps host cells **alive** and feeds off them over an extended period (obligate parasite).

Necrotroph (Pathogen Strategy)

A pathogen that **kills** host cells and feeds on the dead tissue.

Hypersensitive Response (HR)

A rapid, localized, and deliberate **death of host cells** around the site of infection to prevent pathogen spread.

Raphides (Cellular Defense)

**Needle-like calcium oxalate crystals** that tear the mouthparts of herbivores upon ingestion.

Coevolution

The reciprocal evolutionary change between a plant and a specific herbivore, resulting in **highly specialized defense/attack traits**.

Auxins (Main Function)

Responsible for **Apical Dominance**, cell enlargement, lateral root formation, and **Tropisms**.

Abscisic Acid (Main Function)

The primary stress hormone; causes **stomata to close** and encourages **seed dormancy**.

Ethylene (Main Function)

A gaseous hormone that promotes **fruit ripening** and **senescence** (aging).

Auxins vs Cytokinins (Differentiation)

Balance controls **cell differentiation**: High Auxin/Low Cytokinin promotes **root** formation; Low Auxin/High Cytokinin promotes **shoot** formation.

Phytochromes (Pr vs Pfr)

**Pr** (Red light) is the inactive form; **Pfr** (Far-red light) is the **active form** that triggers responses like germination.

Etiolation

**Pale, elongated, spindly growth** that occurs when a plant is grown in the dark, as it attempts to find light.

Thigmotropism

A **directional growth response** to **touch** or physical contact (e.g., a tendril wrapping around a support).

Statoliths

**Gravity-sensing starch granules** found in root cap cells that signal the direction of gravity, enabling **Geotropism**.

Population Density

The number of individuals per unit of area (e.g., 125 lizards per hectare).

Mark-Recapture Formula

N = (M1 * M2) / R, where N is total population size, M1 is the number first marked, M2 is the number captured in the second sample, and R is the number of marked individuals recaptured.

Mark-Recapture Calculation

A researcher initially marks 80 snails. In the second sample, she catches 60 snails, 12 of which are marked. What is the estimated population size (N)?

Exponential Growth

A pattern where the population’s growth rate increases in proportion to its current size (J-shaped curve).

Logistic Growth

A pattern of growth that levels off as the population approaches its **carrying capacity (K)** (S-shaped curve).

Logistic Growth Maximum Rate

If a Logistic Growth curve levels off at 500 individuals, at which population size will the **maximum sustained growth rate** occur?

Optimal Foraging Formula

E_net = E_gross / (S + H)

Marginal value theorem

Predicts how long an animal should **stay in a food patch** before the rate of energy gain drops below the average for the habitat.

Dilution effect

The reduction in an **individual’s predation risk** as a consequence of living in a larger group.

Dilution Effect Calculation

100 individuals are in a group, and a predator captures one individual per attack. What is the probability that any single individual is captured in an attack?