lecture 24-biology

lecture 24-biology - Lecture 24-Chapter 36: Resource...

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Lecture 24-Chapter 36: Resource Acquisition and Transport in Vascular Plants Underground Plants -enables to escape heat, but have to grow very slowly 36.1 L AND P LANTS A CQUIRE R ESOURCES B OTH A BOVE AND B ELOW G ROUND - algal ancestors of land plants absorbed water, minerals, and CO2 directly from the water …transport relatively simple since each cell was close to source of substances -earliest land plants were nonvascular plants that grew photosynthetic shoots above the shallow fresh water in which they lived…leafless shoots had waxy cuticles and few stomata which allowed them to avoid excessive water loss while still permitting gas exchange for photosynthesis -anchoring/absorbing assumed by base of stem or by threadlike rhizoids -as land plants evolved, competition for light, water, and nutrients increased…taller plants with broad, fat appendages had an advantage -increase in surface area, more evaporation…needed water more and more anchorage -favored production of multicellular branching roots …capable of efficient long distance transport of water, minerals and products of photosynthesis extensive root and shoot system which carry out long distance transport ( xylem: water and minerals from roots shoots… phloem: photosynthesis products -through stomata , leaves take in CO2 and release O2 …sugars are produced by photosynthesis… transpiration from leaves creates force within leaves that pulls xylem sap upward - phloem sap can flow both ways between shoots and roots. It moves from sites of sugar production (usually leaves) or storage (usually roots) to sites of sugar use or storage - roots exchange gases with the air spaces of soil, taking in O2, and discharging CO2 -water and minerals in the soil are absorbed by roots - water and minerals are transported upward from roots to shoots as xylem sap -adaptations: must get most light while losing least water Shoot Architecture and Light Capture -stems serve as supporting structures for leaves and as conduits for transport of water and nutrients -leaf size/structure: outward diversity we see in plant form -largest leaves found in rain forests and smallest are found in dry or very cold environments were liquid is scarce and evaporate loss from leaves is more problematic - phyllotaxy : arrangement of leaves on a stem is an architectural feature of immense importance in light capture -dettermiend by sshoot apical meristem and specificto each species (may have one leaf per node or two) -most angiosperms have alternate phyllotaxy with leaves arranged in an ascending spiral around the stem, each successive leaf emerging about 137.5 degrees from the site of previous one -plant features that reduce self shading increase light capture (leaf area index): ratio of total upper leaf surface of a single plant or an entire crop divded by the surface area of the land on which the plant or crop grows -values up to 7 are common for many mature crops and little benefit to higher than value…and
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This note was uploaded on 03/03/2010 for the course BIOG 1101 taught by Professor N/a during the Fall '10 term at Cornell.

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lecture 24-biology - Lecture 24-Chapter 36: Resource...

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