Plant Science Exam 2

Catastrophism

Idea that changes to Earth’s crust happen because of sudden, violent events such as natural disasters and not gradual change, believed until the 1700s

Uniformitarianism

Theory that changes to Earth’s crust happen due to continuous and uniform process, founded by James Hutton in 1785

Continental Drift

Idea that the continents were once a whole mass of land called Pangea and have since drifted over geologic time, proposed by Alfred Wegener in 1912, Pangea is said to have broken up 200 mya.

Plate tectonics

Provided an explanation for Wegener’s lack of mechanism in his hypothesis, unifying model which accounts for origin of continents and oceans, mountain ranges, earthquakes, etc. 

Internal structure of Earth

Has a thermal gradient (hotter in the center)

• Inner core: solid due to high pressure

• Outer core: molten iron

• Mantle: mostly solid rock of iron and magnesium silicate (flows slowly)

• Crust: mostly granite (continents) and basalt (oceans)

• Lithosphere: crust and upper mantle which is broken into 20 plates that can move over plastic mantle

Fossils and genetic evidence for Pangea

There are matching fossil records that support Pangea, current distribution of taxa also supports. Example: Araucaria is a plant that is only in southern hemisphere

Age of Earth

4.5 billion years old (Ga)

Stromatolites

Earliest microfossils from 3.5 Ga

Cyanobacteria

Earliest evidence from 2.7-2.1 Ga and are disputed fossils

Algae-like plants

Showed up at 1 GaEm

Embryophytes

Land plants, appeared in mid-Ordovician period (470 mya)EM

Embryo

Zygote protected by female gametophyte and is essential for survival on land

Alternation of generations

Facilitated by:

• Haploid gametophyte (makes gametes)

• Diploid sporophyte (makes spores)

Sporopollenin and cuticle

Dessication-resistant compounds, prevents plant from becoming extremely dried out

Carpet bombing

Spores are major agents of dispersal, many spores released at once

Vascular plants

Seedless, appeared in late Silurian/early Devonian (about 420 mya)

Seed plants

Also vascular, appeared during Devonian (about 380 mya), seeds are agent of dispersal, characterized by:

• Heterospory - producing 2 kinds of spores

  • Megaspores - retained by sporophyte (protects embryo)

  • Microspores - travels to fertilize megaspore

Domestication syndrome

Selection by humans which has led to plants characterized by a set of phenotypic traits not adaptive in the wild, dependent on humans for survival

Landraces

Local variety of a domesticated plant, differ in adaptations to environments as well as culinary uses, Example: different kinds of maiz

Nikolai Vavilov

• One of first to note lower resilience of domesticated plants compared with wild relatives

• Proposed interbreeding

• Collected germplasm of domesticated + wild

• Identified 8 centers of origin for domestication

Centers of Origin

1. China (rice, soybeans, peach)

2. A) Indo-Malay (banana, coconut) B)Indo burma (mango, eggplant)

3. Central Asia (lentils, apples)

4. Fertile Crescent (oats, wheat, dates)

5. Mediterranean (olives, cabbage, mint)

6. Ethiopia (coffee, okra, sesame)

7. Mesoamerica (corn, chocolate, tomato)

8. A) Andes (potato, lima beans, corn) B) Chile (some potatoes strawberries)                                    C) Chaco-Pantal (cashew, rubber, pineapple)

Population

A group of freely interbreeding individuals of the same species in the same habitat, species can have multiple populations

Annual

Completes life cycle (seed to seed) within 1 year or less

Biennial

Tends to live for 2 years, 1st year grows roots and leaves, 2nd year long stems and flowers, dies after setting seed

Perennial

Lives several years and usually flowers several times, can be woody or survive underground (tubers)

Semelparous

Reproduces only once in its lifetime, includes annuals, biennials, and some perennials

Iteroparous

Reproduces many times during its life, includes most perennial plants

Hermaphroditism

Flowers with both male and female gametes

Monoecious

Plants with both male and female flowers

Dioecious

Plants with either male or female flowers

r selection

Many offspring, low investment, short life, most die before maturity, low individuality, etc.

K selection

Few offspring, long life, high investment, high individuality, etc.

Macroenvironment

Elevation, latitude, temperature, rainfall, etc. 

Microenvironment

Localized changes in light availability, moisture, nutrients, etc.

Taxonomic groupings that reflect geological and evolutionary history

• Holarctic

• South American

• African

• Indo-Pacific

• Australian

Biomes/types of vegetation

• Tundra: Small-sized plants adapted to short seasons

• Taiga: Conifer forests

• Deciduous forests: Broad-leaf temperate forests

• Grasslands: Praires, steppes, savannah, pampas

• Shrublands: Chaparral, scrub, etc.

• Desert: Plants are further apart than in shrublands

• Tropical forests: human and warm, peak diversity

Biotic factors

Result from interactions with other organisms, Example: herbivory, infection, symbiosis, etc.

Abiotic factors

Includes parameters (temperature, pH, humidity) and resources (light, water, minerals) that determine growth as well as others that can add stress (pollution)

Limiting factors

Can limit plant processes, can be caused by one environmental factor at suboptimal level

Stress

Occurs when essential factors (light, water, oxygen, nutrients) are at inappropriate levels

Environmental noxa

Factors that trigger stress at ANY concentration (heavy metals, pollutants, etc.)

State of latent life

A state which plants reach when intensity of stress factors is inappropriate where minimal life processes occur

Dormancy

Adapted latent life stage triggered by environmental cute, involves physiological changes

Avoidance strategy

Seeds and spores allow annual/ephemeral plants to avoid moments of highest environmental stress

Mesophiles

Require moderate temperatures to grow

Hardening

The process by which tolerable stress levels trigger the plant to prepare for extreme conditions

Changes in leaf when adapting to high temperatures

• Surface: hairs can reduce evaporation and reflect intense sunlight

• Size: smaller, thicker leaves help minimize effect of high light intensity

• Angle/position: some species (legume) can moves leaves to reduce exposure to sunlight

• Transpiration: increasing transpiration can help maintain the plant cooler than surrounding environment

• Shading: plants use some structures to protect others from direct sunlight

• Avoidance strategy: in hot environments, many species are short-lived annuals (ephemeral) avoiding worst conditions

Adaptations to cold temperatures

• Rosette/low growing plants: protected against weight of snow and environment warmer close to ground

• Evergreen plants: high concentrations of sugar in leaves acts as anti-freeze

• Deciduous plants: leave abscission and bud scales to protect axillary meristems

Photosynthesis

A process that requires carbon dioxide and water and reactants and produces sugars and oxygen, requires sunlight

Chlorophyll

Captures sunlight for photosynthesis, molecules located in the thylakoid membranes in the chloroplasts

Light as an environmental stressor

• Too low: not enough to cover plant’s metabolic requirements

• Too high: unused energy leads to oxidative stress

Pulvini

Join-like thickening at base of leaves (legumes) that allows for movement of leaves (this is how plants change the position of their leaves to adjust to light intensity!!)

• In ferns, mosses, and some seed plants chloroplasts move to different parts of the cell to adjust light intensity

Sun leaves

Smaller and thicker, with will-developed mesophyll and several layers of palisade cells, epidermal hairs might minimize excess sunlight

Shade leaves

Larger and more tender, with weakly developed mesophyll, epidermal cells might act as lenses to increase light capture

Mesophyll

Inner tissue of plant leaf, contains chloroplasts, primarily responsible for photosynthesis

Sun leaves at subcellular level

Chloroplast with small grant and few stromal thylakoids, photosystem: small proportion of antenna and many reaction centers

Shade leaves at sub cellular level

Chloroplast with large grant and many stromal thylakoids, photosystem: large proportion of antenna and few reaction centers

Stolons (runners) (spread)

Aboveground stems, emerge from crown and bend downwards, develop plantets where they touch the ground

Stoloniferous rhizomes (spread)

Belowground stems, upright shoots, develop from axillary buds in nodes, adventitious roots in underside

Suckers (spread)

Upright shoots growing from horizontal roots (aka “adventitious shoots)

Twiners (climb)

Stems of vines that grow in spiral around objects such as small trunks, supports itself

Tendrils (climb)

Modified leaf or short stem that wraps around objects they touch, provide support for main stem

Adhesive pads 

At tips of tendril-like short stems, allow plants to attach to walls

Supportive roots 

In soft, wet soils plants form these to help them grow taller

Buttress roots (growing tall)

Wedge-shaped, tall and wide, prevent shallow-rooted trees from falling over

Prop roots (growing tall)

adventitious/aerial roots that arise from the trunk (or large branches) and grow downwards to provide support in shifty conditions (ex: mangroves)

Epiphytes (stealing light)

Grow in wet areas, use their roots to grasp tree branches (instead of water absorption)

Lianas

Typically in rainforests, woody, creeping vines that spread through the canopy spreading their leaves to the sun

Raunkiaer’s approach

Proposed a sequence of life forms depending on how they protect their meristem