Life 103 Week 7
Life 103 Week 7 LIFE 103
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This 4 page Class Notes was uploaded by Caroline Hurlbut 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 12 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
Angiosperm Reproduction & Biotechnology • key features of angiosperm life cycle —ﬂowers —fruits —double fertilization • ﬂowers have 4 ﬂoral organs that are modiﬁed leaves —carpels —stamens —petals —sepals • stamen - male reproductive structure that consists of a ﬁlament stalk with a sac called an anther where pollen is produced • carpel - female reproductive structure that consists of an ovary at the base and a style leading up to a stigma where pollen is received • transfer of pollen can be done by water, wind, or animals (most commonly animals) • bees are the most important insect pollinators • double fertilization - 2 sperm deposited into embryo sac —one sperm fertilizes egg—>zygote —other sperm combines with central cell (has 2 polar nuclei)—>triploid food- storing endosperm (3n) • endosperm is thin in monocots and thick in eudicots • a seed has 3 ploidys —integument (seed coat)=2n —endosperm=3n —embryo=2n • structure of mature seed —embryo, food supply, seed coat —seed dehydrates as it matures and enters state of dormancy—>increases chance seed germinates at advantageous time/place —breaking of dormancy often requires speciﬁc environmental cues A. animal digestion B. temp or light changes C. ﬁre D. water —embryo consists of embryonic axis below cotyledons (hypocotyl, terminates in the radicle) attached to 2 ﬂeshy cotyledons (seed leaves) • seed germination and development —germination depends on imbibition, the uptake of water by dry seeds —radicle emerges ﬁrst to anchor plant • sexual reproduction - increases genetic variation, evolutionarily advantageous but only a fraction of seedlings survive • asexual reproduction - genetically identical organisms, no need for pollinator and can be beneﬁcial to successful plant in stable environment —fragmentation is common form of asexual reproduction —in some species a parent plant’s root system gives rise to adventitious shoots that become separate shoot systems • some ﬂowers self-fertilize to ensure every ovule will develop into a seed • dioecious species have staminate and carpellate ﬂowers on separate plants • people modify crops by breeding and genetic engineering (artiﬁcial selection) —hybridization common in nature used by breeders to introduce new genes —genetically modiﬁed plants may increase quality and quantity of food worldwide —some plants have been modiﬁed to be resistant to insects and certain diseases —golden rice is transgenic modiﬁed crop that puts vitamin A in rice —most serious concern is introduced genes escaping into related weeds through hybridization—>superweeds Soil & Plant Nutrition • plants obtain most of their water and minerals from upper layers of soil • soil is stratiﬁed into layers called soil horizons —A horizon (topsoil): mineral particles, living organisms, humus —B horizon —C horizon • soil solution - water and dissolved minerals in pores between soil particles • components of topsoil —inorganic A. cations (ex. K^+, Ca^2+) adhere to negatively charged soil—>prevents leaching out of soil through groundwater B. cation exchange - cations displaced from soil by other cations and enter soil solution C. anions (ex. PO4^3-, NO3^-) don’t bind with soil particles and are lost to leaching —organic A. humus - decaying organic matter—>builds crumbly but still porous soil, provides nutrients B. bacteria, fungi, algae, and other living organisms • 80-90% of a plant’s fresh mass is water while 96% of a plant’s dry mass is CO2 assimilated into carbs during photosynthesis • 17 essential elements, chemical elements required for a plant’s life cycle —9 of these are macronutrients that are needed in large amounts —remaining 8 are micronutrients, which are mostly enzyme cofactors • plants and soil microbes have mutualistic relationship —microbes depend on plant nutrients and help plant by stimulating growth, producing antibiotics, and increasing nutrient availability • nitrogen cycle —nitrogen is important limiting nutrient for plant growth —can be absorbed in the form of NO3^- or NH4^+ —nitrogen ﬁxation: conversion of nitrogen from N2 to NH3 —symbiotic relationships with nitrogen-ﬁxing Rhizobium bacteria provide ﬁxed nitrogen for some plants (legumes) • root nodules on a legume —nodules are composed of plant cells infected by Rhizobium bacteria —inside vesicles of nodule the bacteria assume a form called bacteroids —plant obtains ﬁxed nitrogen from Rhizobium, Rhizobium obtains sugar and anaerobic environment • fungi and plant nutrition —fungi and plant roots have mycorrhizal relationships —fungus gets sugar and plant gets increased surface area for water and mineral absorption as well as growth factors secreted by fungi to stimulate root growth and branching • 2 types of mycorrhizae —ectomycorrhizae —arbuscular mycorrhizae • unusual plant adaptations —epiphytes: grow on other plants but get own nutrients —parasitic plants: tap into roots and get nutrients from other organisms —*carnivorous plants: photosynthetic but obtain nitrogen by killing and digesting mostly insects
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