Life 103- week 7
Life 103- week 7 LIFE 103
Popular in Biology of Organisms-Animals and Plants
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This 6 page Class Notes was uploaded by Alexis Darling on Friday March 4, 2016. The Class Notes belongs to LIFE 103 at Colorado State University taught by Jennifer L Neuwald; Tanya Anne Dewey in Fall 2016. Since its upload, it has received 6 views. For similar materials see Biology of Organisms-Animals and Plants in Biology at Colorado State University.
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Date Created: 03/04/16
Soil Soil horizons are the different layers of soil. Focus on the A horizon because plants get most water and minerals from this upper layer, even if they have a deep taproot. Topsoil= the A horizon: made up of minerals, living organisms, and humus. ● Mineral compounds: ○ Inorganic cations; these positively charged ions adhere to the negative soil particles, preventing them from leaching (washed out of soil by ground water), but for a plant to absorb them they must be dissolved into the soil solution. Therefore cation exchange is the process by which plant roots release H+or CO + 2 (which reacts with H 2to form H ions) to displace the cations that were stuck to the negative soil so that the cations dissolve into the soil solution for plant uptake. + In other words the H ions bump the minerals off the soil particles and into solution for plant access. 3 *Negatively charged ions (POan4NO 3 do not adhere to soil particles and therefore are easily lost by leaching ○ Organic humus; decaying organic material which creates a crumbly soil that is great at retaining water and air pockets ● Living organisms: ○ bacteria, fungi (the 2 main components), protists, worms, insects, plant roots, etc; all help to mix the soil and decompose Plant Nutrition Three keys for growth and life cycle: soil, water, and air. ❖ Water makes up 8090% of living mass ❖ 96% of dry mass is derived from CO 2 ransformed in photosynthesis) ❖ 4% of dry mass is from inorganic elements taken from the soil ● While more than 50 elements are used, only 17 and essential: ○ 9 macronutrients needed in large amounts (ex: K to open stoma (by + pumping K in, water flows in by osmosis and guard cells press against each other and increase diameter of opening)) ○ 8 micronutrients needed in small amounts; most are required for certain enzymes to functioncalled enzyme cofactors Mutualistic Relationships ❖ Plants and soil microbes: ➢ Dead plants supply energy for microbes ➢ Living roots secrete nutrients which support close by microbes ➢ Microbes release growthstimulating chemicals for plants ➢ Microbes prevent root disease by antibiotic production ➢ Microbes absorb toxic metals and work so more nutrients are in an available form ❖ Plants and bacteria: + ➢ Plants can only utilize NH 4or NO3(not atmospheric nitrogen); therefore... ➢ Nitrogen fixation= conversion of atmospheric N gas to NH + 3 ➢ From NH 3 ammonifying bacteria turn it to NH4 or nitrifying bacteria turn it to NO3 ➢ One tight mutualistic relationship in the nitrogen cycle is Rhizobium bacteria in legume roots: forms nodules swellings caused by bacterial growth inside the plant root walls so that bacteria receive sugar and a protected, anaerobic environment while the plant has a constant supply of fixed nitrogen for access ❖ Plants and fungi: ➢ Fungus gets sugar, host plant gets increased surface area on roots and growth factors which stimulate root branching ➢ Mycorrhizae a) Ectomycorrhizae fungal hyphae between plant root cells (through extracellular space) b) Arbuscular mycorrhizae hyphae form arbuscules (‘tiny trees’) inside plant cells ~Epiphytes although they grow on plants, they obtain their own water from rain ~Parasitic plants grow on other plants and absorb sugars and minerals from the host ~Carnivorous plants still photosynthetic but consume insects for nitrogen supply (adaptation to live in areas with little nitrogen in soil) Angiosperm Reproduction mostly a review) ~Stamen= filament (stalk) + anther (where pollen is produced) ~Carpel= stigma (sticky to capture pollen) + style (stalk) + ovary Pollen transfer (anther to stigma) by wind, water, or animals ● If by wind, the anthers release huge amounts of pollen to increase chances of fertilization. ● If by animals, flower structure is designed to attract certain animal pollinators and their shape has evolved with animal body shapes to make sure a specific pollinator can access and deposit the most pollen. ○ Bees→ sweet smelling and bright flowers (many have nectar guides; UV markings to draw bee to proper spot) ○ Moths→ white or yellow flowers ○ Bats→ fragrant, nectarfilled flowers, light colored like moths because they go out at night; white or yellow stands out the most ○ Butterflies→ brightly colored and fragrant flowers ○ Birds→ red or yellow, large, nectarfilled flowers lacking smell (because birds have poor olfactory sense) ○ Flies→ flowers that smell like rotten meat Double Fertilization: Steps: stigma captures a pollen grain, pollen tube grows through style, enters through micropyle to ovary, releases 2 sperm; one to fertilize egg (forms zygote), one to combine with the 2 polar nuclei (forms triploid endosperm (for food storage)) Dormancy: Seed dehydrates (still within seed coat) to enter this state of no growth or metabolic activity so that it can germinate at a later time of a more advantageous environment. In a state of dormancy, most seeds remain viable for 12 years; some only a few days, others centuries. Environmental cues required to break dormancy: ○ animal digestion ○ temperature changes ○ light changes ○ fire ○ water Structure: ● Cotyledons the seed leaves; make up the main fleshy part of a seed ● Hypocotyl between cotyledons and radicle ● Radicle embryonic root; the end tip of the projection Radicle comes out first to anchor plant in the ground, then growth pushes the hypocotyl out of the ground as a hook shape, and finally the hypocotyl pulls the cotyledon out of the ground. Energy for these initial stages (before capable of photosynthesis) comes from the endosperm… In most monocots the endosperm stores the nutrients the whole time and continues to after germination. Therefore they only need thin cotyledons. In most eudicots, the storage of the endosperm is transferred into the cotyledons prior to germination, leading them to have thick cotyledons. Reproduction: Sexual reproduction results in greater genetic diversity and allows for evolutionary adaptation, but not all seedlings survive and it requires energy to produce seeds. Asexual reproduction results in clones, therefore they are all vulnerable to extinction if there is a harmful change in environment (ex: new fungus or disease) yet they are more successful in a stable environment as they have no need to spend energy on seeds. Fragmentation type of asexual reproduction in which the parent separates into smaller parts that all grow into whole plants of their own Adventitious shoots type of asexual reproduction, come from a parent root system then form separate shoot system Also benefits of self pollination include the assurance that each ovulate will become a seed because it is not dependant on a pollinator (more risky). Dioecious species have male and female parts on separate plants to ensure pollination from a different plant. Breeding and Genetic Engineering: ~Hybridization breeders use this method to bring new genes into a species Could be through artificial selectio humans choose what reproduces. ~Transgenic organisms must be engineered; they express a gene obtained from a completely different species These methods can improve the nutritional quality and increase the quantity of food, specifically for impoverished areas. examples: (for nutrition)Golden Rice contains more vitamin A Transgenic Cassava more betacarotene and iron (for quantity)production of Bt toxin which kills insect pests can tolerate herbicides or resist diseases The debate: possible impact on environment allergens could be transferred gene spread to weeds (create superweeds resistant to herbicides) Plant Responses ~Cell signal processingreception stimulus is detected by receptor proteins that change shape transduction “second messengers” pass on the signals amplified response cell activities are regulated; usually by increased activity of certain enzymes Internal Signals: ~Plant hormones produced in low concentrations, transported throughout plant from the specific part where each is produced, bind to certain receptors and result in responses ● Auxins elongate: ○ produced in apical buds (the tips of shoots) and move down stem to regulate young shoots ○ activates proton pumps which move H + ions outside of cell membrane; enzymes are activated by the low pH; which weaken cell walls, allowing elongation ■ Applications: if supplied to a cut leaf or plant part, that single part can be stimulated to develop adventitious roots, giving rise to clones ■ But overdose can kill ● Cytokinins cause cytokinesis: ○ produced in tissues of active growth (roots, embryos, fruits) ○ control cell division and differentiation and apical dominance (axillary bud growth suppressed) ● Gibberellins germinate: ○ produced in young leaves and roots ○ contribute to cell elongation, growth of leaves, stems, and fruit, and control seed germination; ○ After imbibition (water taken into seed), gibberellins released to signal seed to digest starch so that sugar is made available for energy to grow ● Ethylene takes away the green: ○ produced during times of stress (lack or excess of water, mechanical injury, infection) or to grow around an obstacle ○ Leads to t riple response a) slowing of elongation b) thickening of stem (to be stronger) c) horizontal growth (to get around barrier) ○ Also controls ripening ethylene stimulates fruit to ripen and ripening fruit releases more ethylene (gas) ■ Applications: Fruit producers can harvest fruit while green, then store it in circulating CO2 til ready to be put out then add ethylene External Signals: Light Plants detect presence, direction, intensity, and wavelength of light with photoreceptors. 2 groups of photoreceptors: ● Bluelight photoreceptors ● Phytochromes : These pigments regulate when a seed germinates and shade avoidance responses ○ Seed germination: small seeds have little energy reserves, so they remain dormant until the most optimal conditions are assured ○ Shade avoidance: leaves near the bottom of the forest receive farred light→ need to grow taller to access better light conditions, leaves in the canopy absorb red light→ grow wider to shade competition growing beneath them
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