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Chapter 36

Bio204-Chapter 36 detailed review.doc

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Ingo Ensminger

Chapter 36 – Detailed Review Plants exhibit indeterminate growth that means they keep on growing throughout their lives. 36.1: Plant Forms: Themes with Many Variations Plants use light energy (photons), CO from air and water (electron source) from 2 soil to make carbohydrates. Plants also use water to maintain normal pressure and volume by filling their cells. Plants also use nitrogen, potassium, magnesium and phosphorus to make macromolecules like nucleic acid, enzymes and phospholipids. Plants use two basic systems to get the resources needed for photosynthesis. • Root System: underground, anchors plant and takes in water and ions from soil • Shoot System: aboveground, harvest light and CO from air to make 2 sugars • Usually, the root and shoot system are connected by vascular tissue. Herbaceous plant (herb): seed plant that lacks wood and has short lived stem. The Root System includes: • Taproot: vertical section of underground root system • Lateral root: horizontal looking sections of underground root system • Diversity on 3 levels: morphological diversity, phenotypic plasticity (changes in individual root system over time) and modified roots for unusual functions Morphological Diversity • Root systems are diverse in shape and size • In prairie grassland ecosystems, grasses and herbaceous plants have root systems that are perennial (live for many years). If the aboveground portion dies in fire, winter or dry season, the plant can send up a new shoot system. o Root systems of prairies plants that live side by side can be very different.  Prairie grass have fibrous root systems  Prairies rose has a thick taproot that can store starch  Different plants have different root systems that penetrate the ground at different depths. The tips of the roots are where the most water and nutrient absorption occurs. • Natural Selection has favoured diversity in root systems among species that live in the same area to minimize water and nutrient competition. o Diversity in root systems of prairie plants has 2 important consequences  Different plant species can co-exist in the same area with less competition for soil resources since each type of root system is specialized in acquiring resources from different regions of the soil  Most individuals can withstand water stress during droughts Phenotypic Plasticity: changes in individual root or shoot system over time, depending on environment conditions that change throughout the course of time  Spruce trees that grow in wet soil which lacks oxygen have shallow root systems and the same tree growing in drier soil extends several meters deep into the ground. o Even genetically identical individuals have different looking root systems if growing in different types of environment  Roots actively grow in areas where resources are abundant and die back or do not grow in areas where resources are lacking or used up! Modified Roots Adventitious root: root that develops from the shoot system instead of the root system  Prop roots of corn brace the plant in windy weather  Mangroove plant grows in deoxygenated swamps but their root systems can conduct gas exchange through pneumatophores and grow upward instead of downward The Shoot System Consist of one or more stems – vertical aboveground structures Nodes: located on stems where leaves are attached Internodes exist between nodes Leaves: appendages that extend laterally from the stem and consist of photosynthetic organs Axillary bud: a bud forms between a leaf and stem and may develop into a branch if conditions are appropriate Apical bud: a bud at the tip of a bud or stem where growth extends the length of the stem or branch The shoot system is a repeating series of nodes, internodes, leaves, apical and axillary buds. After an initial period of growth, the plant grows by adding more parts rather than increasing the size of each part. Thus, the number of nodes, internodes and leaves increases as the plant grows. Morphological Diversity Shoot systems of different plants range in size. In habitats where light is scarce, plants invest more energy and resources in the growth of light gathering apparatus. The manners in which the branches are added to the shoot system (narrow angles, long internodes/wide angles, short internodes) affect the shape of the individual and its ability to compete for light. Variations in the size and shape of the shoot system are important: it allows plants of different species to harvest light and CO at 2ifferent locations, minimize competition and thrive in a wide array of habitat. Phenotypic Plasticity Shoot system also respond to variations in water, nutrient and light availability. Shoot systems can bend toward light if the plant is shaded on one side or grow more leaves and branches in regions exposed to more light. Shoot system grows in direction that maximizes the plant’s chance of capturing light. Extra-floral nectaries (EFN): produced by plants to attract and feed ants that attack herbivores who feed on the plants. • Plants respond to herbivore attack on their leaves by producing more EFN. Modified Shoots Not all stems acquire CO an2 photons for photosynthesis. • Enlarged Cactus stems store water and leaves are modified into spines for plant protection. • Stolons: aboveground modified stems that run over soil surface and produce roots and leaves • Rhizomes: underground stems store starch and aid in asexual reproduction by producing a new plant at each node • Tubers: underground swollen ends of rhizomes that store carbohydrate • Thorn: modified stems protect plants against herbivore attacks The Leaf Large surface area is site of photosynthesis Simple leaf has two parts: • Blade: expanded portion of leaf • Petiole: stalk of the leaf Exhibit diversities Morphological diversity Simple leaves have a blade and petiole. Compound leaves have the blade divided into smaller leaflets. Doubly compound leaves have leaflets divided into smaller ones. Needle – shaped leaves exist in deserts or northern habitats because • Reduce surface area to prevent water loss through transpiration • Less susceptible to wind damage Leaves can be • paired opposite to each other on a stem • alternate on either side of the stem • arranged in compact clusters at plant base Different plant species arrange their leaves in different arrangements to maximize the efficiency of the light captured. Phenotypic plasticity Leaves don’t grow cont
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