transition between charophytes and liverworts hornwarts mosses from water to land BIOLOGICAL DIVERSITY CHAPTER 30 PLANTS 11 10 o most ancestral What is a Plant autotrophic o photosynthesis for carbon and energy needs o selective pressure has enhanced this process chlorophyll different types pigments enhance energy production heterotrophic autotrophic o ex venus fly traps o a few plants that are strictly heterotrophic tend to be parasites on other plants get all energy phosphorus carbon from their host plants complex life cycles o alteration of generations o cell walls see below increases rigidity of cell increase of support have ranges of cellulose and lignin polysaccharides compose cell wall o multicellular o eukaryotic chloroplasts and mitochondria Plant Evolution another billion years after the oldest definite fossils for eukaryotes for land plants to emerge o likely derived from aquatic protists best hypothesis out there green algae charophytes chlorophytes Chara uni multicellular Ulva closest living relative of land plants based on genome analysis Water Land Challenges water to land transition was very difficult to make o many things selected for in aquatic organisms that would not be helpful on land o water has a free floating environment o land has a gravity based environment capturing water o root systems have capacity to absorb water from the environment around them roots are the core of how plants capture water how plants without roots capture water o rhizoid retaining water o hydrophobic waxy coatings on the leaves stems hydrophobic repels water from passing through coming out of the plant o storage in roots structural stability o gravity o rigid cell walls lignin structural carbohydrates cellulose result is woody tissues o issues with how large a plant can grow driven by structural stability plants were really small to begin with cellulose and lignin based cell walls allowed for extended growth nutrient uptake o in water there is a viable uptake of carbon nitrogen and phosphorus o on land plants have to look harder for those C N and P nutrients symbiosis relationships with nitrogen fixing bacteria roots for uptake facing herbivores eating live plant tissues and granivores eating grains or seeds o needed to evolve new ways to resolve that issue will die without enough living tissue toxin creations secondary compounds compounds toxic to those ingesting them thorns spines shells for seeds o reduces drying and desiccation of those seeds grasses that enhance growth when faced with herbivory seasonal change o going into an environment with extremes temperatures dormancy winter extreme growth spring hibernation and rapid growth o abiotic factors Basic Plant Life Cycle background info o goal is to adapt life cycles to alternating periods of dormancy shutting down plant o common to all plants as well as to multicellular green brown and red algae o terminology number of chromosomes for an organism chromosome number diploid humans have 46 chromosomes including sex chromosomes total number of chromosomes 46 for humans represented as 2n o 2n n chromosomes from mom n chromosomes from dad o 2n n MOM egg n DAD sperm GAMETES o each parent provides a haploid number of chromosomes o 2n embryo haploid always half of the diploid number 23 for humans represented by n gametes are ALWAYS haploid o unicellular o n gamete o plants have independent haploid and diploid life stages haploid and diploid can live on their own leads to alteration of generations alternation of generations o haploid n o diploid 2n o circular loop gametophyte haploid produces egg n and sperm n fertilization is the joining of egg n and sperm n o 2n zygote o 2n embryo o 2n sporophyte diploid sporophyte goes to sporangia o sporangia to spore mother cell 2n o through meiosis the mother cell 2n goes to spores n o spore goes once again into a gametophyte o sporophytes are only present for a short time and is an independent life stage n alternations of generations gets more complicated with different groups Earliest Land Plants Charopytes to Bryophtes bryophyta o likely came from charophytes o three subgroups mosses hornworts liverworts o do not have true roots rhizoids holds plant in place anchor capacity to absorb water o act like a sponge o no vascularization directly proportional to blood vessels in humans does not go through specific vessels water is drawn into plant along a single long cell really defines this group no way of moving water and nutrients around significant selective pressure small organisms o grow closer to the water source require moist wet habitat associated with lakes streams wetlands saturated soils etc leaf like spikes gametophyte stage of life dominant and longest life stage very simple aggregation of cells o no true leaves o limited in habitats o hornworts bryophyta gametophyte is at the base sporophyte is the horn spike part mutualistic relationship with cyanobacteria symbiotic relationship cyanobacteria are nitrogen fixers live in hornwort tissues o fertilizer for the hornworts atmospheric nitrogen gas into ammonia plant growth as plant undergoes photosynthesis carbon and cellulose produced is shared with the cyanobacteria hornworts have capacity to grow in places they would otherwise not be able to o liverworts gametophyte in the base basil looking sporophyte comes out of the top Dominant Lifecycles gametophytes become less dominant from bryophytes to flowering plants sporophyte becomes more dominant from bryophytes to flowering plants Tracheophytes Bryophytes to all other plants begin to see vascularization and rooting o dates back to 420 million years ago o cooksonia sp earliest plant that possessed vascularization vascular system o internal plumbing in the shoots stems o present in roots o present in leaves o two distinct parts below ground roots roots growing into nutrient ground organic matter take up nutrients and water through root hairs above ground leaves shoots stems water and nutrients are moved up the plant and spreads into different tissues xylem associated with moving water and dissolved minerals o moves strictly upward o once water gets to the leaves the plant can release it through transpiration an aspect of respiration that occurs through small leave openings stomata stomata mouth like openings that can open and close release water vapor gas exchange carbon dioxide and oxygen surrounding the stomata is the cuticle waxy structure that prevents water loss from all other surface
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