Unit 8 Review Flashcards
Transpiration (including how the structure of the xylem aids in the process)
Transpiration is the loss of water (vapor) from plant leaves (and stems)
- Water in spongy mesophyll evaporates out of stomata (down concentration gradient) - stomata open for gas exchange for photosynthesis
- Water is bonded to other water molecules (cohesion) in a chain ALL the way down the xylem of the plant
- Water in xylem “pulled” upward and new water molecules enter roots (negative pressure)
- Water molecules also hydrogen bind to xylem tissue (adhesion), which facilitates transpiration due to its cells lacking a membrane (water enters freely), layer of inner dead cells (continuous tube), outer layer contains pores (water moves through to leaves easily), and lignin rings (strengthen tissue); Transpiration rates measured using POTOMETERS (measure meniscus movement in tubing and divide by time))
Long, hollow tube - interconnected dead cells - cells form TRACHEIDS (tapered ends connected by pits - found in all vascular plants)
Cellulose in cell walls is polar (adhesion with water) and is THICKENED (support against inward pressure/ pressure resistance - cell walls lignified for this too (lignin deposits - deposited in circular arrangements = annular vessels, or in helical arrangements = spiral vessels)
In angiosperms, xylem cells also form vessel elements - cell walls are fused to form one, long, continuous tube =FASTER rates
The movement of energy and nutrients through ecosystems.
- Energy and nutrients travel from producers to consumers to decomposers.
- Energy transformations are not 100% efficient – only ~10% of the energy available at one trophic level (from one organism) gets passed on to the next
- Not all ingested food is absorbed, not all of an organism is eaten, heat loss (MOST due to CELLULAR RESPIRATION)
- Heat cannot be transformed into usable forms (once heat = “lost”), therefore energy losses restrict food chain lengths and limit amount of biomass at higher trophic levels
- Energy must constantly be replenished in ecosystems (sunlight)
- Nutrients are always RECYCLED in ecosystems (organisms die and their complex, organic molecules are broken down into simple substances by saprotrophs, which are returned to the soil etc. to be taken up/ made into complex organic molecules again by plants, which are passed on to consumers to decomposers and the cycle continues…)
Carbon Cycle
-Photosynthesis: CO2 removed from atmosphere/ water by plants; “fixed” to make organic compounds (sugars, proteins, lipids) = largest flux
-Feeding: Heterotrophs obtain organic compounds by feeding
-Cellular respiration: Organisms break down organic compounds to release energy (and release CO2 and heat as byproducts)
-Decomposition (aerobic): Saprotrophs break down organic material and release CO2 (and carbon to soil, air, etc.)
-Decomposition (anaerobic): Methanogenic archaeans breakdown organic compounds and release methane (CH4) which forms deposits underground or is oxidized to CO2 and H2O in atmosphere
-Saprotrophs inhibited by anaerobic conditions and organic acids produced in anaerobic conditions (lower pH) and organic matter not fully decomposed forms peat (in waterlogged soils) - compressed peat can form COAL (fossil fuel)
Note: Compressed, fossilized partially decomposed (anaerobic) marine remains form oil and natural gas
-Combustion: Burning of fossil fuels/ biofuels releases CO2 into atmosphere (significant increases in CO2 in atmosphere)
-Bodies of Water: CO2 dissolves in bodies of water (diffusion) and combines with H2O to form carbonic acid. Carbonic acids dissociate into carbonate ions and hydrogen ions. Hydrogen ions lower pH (acidic). Carbonate ions used by molluscs and corals for shells/ exoskeletons (which can compact to form limestone rock). Increased temps and lower pH cause corals to expel symbiotic algae (bleaching) and cause LESS carbonate ions to be incorporated into shells and exoskeletons
Process of Natural Selection
- Within populations there exist genetic (heritable) variations (mutations, meiosis, sexual reproduction)
- Populations tend to produce more offspring than the environment can support (leading to competition)
- Environmental pressures allow only those organisms best adapted to the environment to survive and reproduce = differential reproductive success (Note: survivors pass on their genes for their favorable traits/ adaptations)
- Over many generations, there is a change in allele frequencies of gene pool of population due to differential reproduction (survival of the fittest)
Process of Speciation
SPECIATION: The formation of a new species (no longer able to interbreed/ produce fertile offspring)
New species form due to reproductive isolation (gene pools become separated by barriers that prevent interbreeding).
Gene pools change due to genetic drift (random/ chance events) or natural selection (environmental pressures). Genetic drift = higher in smaller populations (faster change due to less genetic variation); occurs due to population bottlenecks (a large scale event reduces population by an order of magnitude > 50%) or the founder effect (small portion of original population breaks away/ separates from original)
Speciation can be allopatric or sympatric.
Allopatric speciation: GEOGRAPHIC barriers (rivers, mountains, volcanoes etc.) prevent interbreeding (and exposure to different environmental conditions causes gradual divergence/ change in allele frequencies)
Sympatric speciation: REPRODUCTIVE barriers (not physical barriers) prevent interbreeding. Can be temporal (different timing in reproductive cycles/ periods/ activities so no interbreeding) or behavioral (incompatible courtship behaviors so no interbreeding)
-Sympatric speciation can be caused by polyploidy: meiotic failure results in gametes with extra SETS of chromosomes
-More common in plants because can self-pollinate/ reproduce asexually (ex: Allium)- can happen in only one generation (polyploid plants usually larger/ more disease resistant/ have increased longevity)
Methods of used by roots to absorb water and mineral ions
Diffusion: flow down a concentration gradient into root
Fungal hyphae: symbiotic relationship (fungus absorbs minerals for plant in exchange for sugars)
Mass flow: water flows into plant INTO high solute concentrations by osmosis (creates negative pressure in soil around root); minerals hydrogen bond to water and move passively with water into plant
Active transport: Protein pumps in root cells (lots of mitochondria) actively transport mineral ions against concentration gradient (like potassium ions) OR *Protein pumps actively pump H+ ions into surrounding soil (these bind to negatively charged ions in soil and diffuse back into root with H+ ions); displaces (forces out) positively charged minerals from clay so they can be absorbed (diffusion) into root cells – this is INDIRECT active transport
Abiotic factors that affect transpiration rates
- Light: Increases rate of transpiration (more light = more photosynthesis/ gas exchange, more heat – more open stomata)
- Temperature: Increases rate of transpiration (more evaporation to keep cool)
- Wind: Increases rate of transpiration (evaporating water removed faster, so more water diffuses out of leaf)
- Humidity: Decreases rate of transpiration (more water in air = decreased concentration gradient = less diffusion)
- Soil Water: Less soil water = decreased transpiration
- CO2 levels in air: MORE CO2 in air = decreased transpiration (stomata do NOT need to be open as much to get CO2 in)
Biotic factors that affect transpiration rates
Guard Cells and the hormone abscisic acid regulate transpiration by opening and closing stomata
- When dehydrated, mesophyll cells release abscisic acid, causes guard cells (around stomata) to LOSE potassium, water follows by osmosis, decreasing water pressure/making guard cells flaccid = closing stomata
- K+ ions actively transported into guard cells, water follows by osmosis, guard cells turgid = opens stomata
The use of potometers to measure transpiration rates
Transpiration rates measured using POTOMETERS (measure meniscus movement in tubing and divide by time))
Adaptations of xerophytes
Xerophytes are plants adapted to dry climates
naturally higher transpiration rates (high temps/ low humidity), so they have adaptations to decrease transpirational water loss
Reduced/ rolled leaves (↓ surface area)
Stomata: Reduced numbers, closed during day (CAM plants), one side of leaf only (prevent water loss)
Thicker waxy leaf cuticles
Low growth (decreasing wind/ light exposure; C4 plants – take in CO2 faster so stomata do not open as long
(Note: not all xerophytes have low growth, CAM, or C4 photosynthesis!)
Translocation (including how the structure of the phloem aids in the process)
*Sugars (as sucrose)/ amino acids actively transported by companion cells into phloem tissue (called sieve tubes) at leaves/ stems (SOURCE) Water diffuses from xylem into phloem (creating sap) Sap volume/ pressure drives sap downward (mass flow) Companion cells actively transport organic molecules (sugar stored as starch) into “SINK” (fruit, seeds, roots) and water moves back into xylem (osmosis) Sieve tubes (phloem tissue) = 2 types of cells: 1. Sieve elements - long/narrow and joined together to form long tube; anucleate; thick/rigid cell walls to withstand high pressure; connected by sieve plates (have pores); 2. Companion cells - loading and unloading of organic compounds from sieve tubes; increased surface area; lots of mitochondria and transport proteins; plasmodesmata (connect cytoplasm to sieve elements)
The use of aphids to measure translocation rates
Plants grown with radioactively labeled CO2 (incorporated into sugars)
Aphids placed along stem length to feed; stylets into phloem then severed
Sap flows out; analyzed for radioactive sugars and rates calculated
Diagram a half view of an animal pollinated flower
*Look at slideshow
Diagram a seed and know the functions of each structure
*Look at slideshow
Role of auxin
Auxin CHANGES PATTERNS OF GENE EXPRESSION (shoot apical meristem), and stimulates mitosis and cell elongation - causes stem growth, development of leaves (leaf primordia) and flowers
Auxin INHIBITS lateral buds (apical dominance) - promotes vertical growth
Auxin promotes PHOTOTROPISM in shoot apex (positive tropism - shoot apex grows TOWARD the light) - normally distributed evenly in plant stems, but if one side of plant receives more light: auxin efflux pumps actively transport auxin to SHADED side of plant (higher concentration); auxin CHANGES PATTERNS OF GENE EXPRESSION (expansion genes upregulated = increased cell wall elasticity) and activates proton pumps (H+ ions pumped to cell walls, decreasing pH, loosening cellulose fibers by breaking bonds between them) - cells ELONGATE on shaded side, causing shoot apex to grow TOWARD the light
