<p>Answers</p><p>Activity 29/30.1 What Major Events Occurred in the Evolution of the Plant Kingdom?</p><p>Construct a concept map that describes the early evolution of plant life on Earth. Be sure to include relationships among all the organisms and factors in the list on the next page. Keep in mind that there are many ways to construct a concept map.</p><p> Begin by writing each term on a separate Post-it note or piece of paper.  Then organize the terms into a map that indicates how the terms are associated or related.  Draw lines between terms and add action phrases to the lines that indicate how the terms are related</p><p>Here is an example:</p><p>If you are doing this activity in small groups in class, explain your map to another group of students when you finish it.</p><p>Copyright © Pearson Education, Inc., publishing as Benjamin Cummings</p><p>182 TERMS: bryophytes pteridophytes lycophytes endosymbiont anaerobic bacteria cyanobacteria (blue- green algae) chloroplast mitochondria vascular tissue waxy cuticle charophyceans chlorophytes alternation of generations megaspore microspore nonvascular plants seedless seeds angiosperm gymnosperm flowers xylem phloem microphyll megaphyll spore gametophyte sporophyte egg gametangia root stem flagellated sperm archegonium antheridium pollen grain ovule</p><p>Copyright © Pearson Education, Inc., publishing as Benjamin Cummings</p><p>183 Use the understanding you gained from constructing the concept map to answer the questions.</p><p>1. Describe the major problems ancestral land plants had to overcome before they could make the transition from water to land. Water was less available on land, and most of the available water was not on the surface. In addition, desiccation (water loss) was a problem in the atmosphere. On land, there were greater variations than in the ocean—for example, in environmental temperature and chemistry. On land, new types of transport mechanisms were required—for example, for food, water, gametes, and so on. Water was no longer available to support the plants’ “bodies” against gravity. In water, most of the ultraviolet light is filtered out in the first few centimeters of the water column. On land, the higher UV levels could easily bleach chlorophyll and damage or mutate nucleic acids.</p><p>2. Describe the major solutions to the problems in question 1 that can be found in today’s land plants. In other words, what mutations occurred that allowed organisms to make the transition to land? To reduce evaporative loss, a waxy cuticle covers the surface of cells in contact with the environment. Flavonoids, pigments that selectively filter UV light, are found in all land plants. Sporopollenin evolved to form resistant walls on land spores to protect them from desiccation.</p><p>Copyright © Pearson Education, Inc., publishing as Benjamin Cummings</p><p>184 To protect haploid gametes against both desiccation and UV light, all land plants have protected gametangia (for example, in archegonia or antheridia in lower plants). This feature must have evolved prior to or concomitant with the move onto land. Air spaces and guard cells with associated stomata provide additional protection against desiccation while also allowing for gas exchange in photosynthesis. The evolution of lignin added structural support to cells and supported them against gravity. Subsequent evolution of xylem and phloem allowed for greater efficiency in food and water transport. The seed, with its waxy coating and low water content, enabled the next generation of embryos to withstand environmental fluctuations in water availability and temperature until conditions were suitable for germination.</p><p>Copyright © Pearson Education, Inc., publishing as Benjamin Cummings</p><p>185</p>