Introductory Plant Biology Ninth Edition Kingsley Stern Chapter
Introductory Plant Biology Ninth Edition Kingsley Stern Chapter 5 Image Slides* *See Power. Point Lecture Outline for a complete, ready-made presentation integrating art and lecture notes. 1 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.
Chapter 5 Roots
Root function • Anchor plant to soil • absorb water and minerals in solution 3
How roots develop • Embryo- an immature plant • Radicle- first root that grows out of an embryo 4
2 types of mature roots 1. Taproot- large major root - pine trees, carrots 2. Fibrous roots- many branched roots; Adventitious roots- roots that develop from stem, leaf, etc. 5
Fig. 5. 1 6
Root development in flowering plants 1. Dicotyledon- have 2 “seed leaves” - have taproots from which secondary roots develop - ex. Peas and carrots 2. Monocotyledon-have 1 “seed leaf” - have fibrous roots - ex. Corn and rice 7
Root structure; 4 regions 1. Root cap- thimble-shaped mass of parenchyma cells - Protects the root from damage as it pushes through the dirt - Dictysomes produce slimy substance to help root move - Functions in the perception of gravity 8
4 root regions cont. 2. Region of cell division- composed of apical meristem in the center of the root tip - produces surrounding root cap 9
3 types of meristem from apical meristem 1. Protoderm- forms epidermis 2. Ground meristem- forms cortex 3. Procambium- forms primary xylem and phloem 10
4 root regions cont. 3. Regions of elongation- 1 cm from root tip - cells grow longer and wider - no further increase in cell size takes place above this region 11
4 root regions cont. 4. Region of maturation/differentiation or “root hair zone” 12
Fig. 5. 2 13
Cells and Tissues of Region of Maturation • Root hairs - absorb water & minerals - hold tightly to soil - increase surface area - not separate cells; extensions of specialized epidermal cells - up to 250, 000/in 2 14
Fig. 5. 4 b 15
Cells/Tissues cont. • Cortex- parenchyma cells that lie between epidermis and inner tissues; stores food 16
Cells/Tissues cont. • Endodermis- separates cortex from vascular tissue - Consists of a single-layer cylinder of cells -Casparian strips- “mortar” of suberin around endodermis cells 17
Cells/Tissues cont. • Endodermis cont. • Casparian strips- force all water and dissolved substances to pass through the plasma membrane or plasmodesmata of the endodermis - this regulates types of minerals absorbed 18
Fig. 5. 5 19
Cells/Tissues cont. • Vascular cylinder- inside area of endodermis - pericycle- parenchyma cells that give rise to lateral vascular cambium and lateral roots - primary xylem- central core; usually 4 arms - branch roots grow opposite of arms 20
Cells/Tissues cont. • Phloem- forms between xylem arms • Vascular cambium- develops between xylem and phloem • Cork cambium- woody plants only - arises outside vascular cambium - generally not found in monocots 21
Fig. 5. 6 22
Tissue Development 23
Specialized Roots • Food storage roots- sweet potatoes, carrots • Large number of parenchyma cells form in branch roots • Store carbohydrates 24
Specialized Roots • Water-storage roots- pumpkin family roots - plants store water in roots when water supply in soil is low 25
Specialized Roots • Propagative roots- adventitious buds- buds appearing in places other than the stem - buds develop into aerial stems called suckers, with rootlets at base - found in cherry, apple, pear trees 26
Specialized Roots • Aerial roots- may support plant in high wind; aid in climbing • Contractile roots- pull plant deeper into the soil • Buttress roots- add stability 28
Fig. 5. 12 29
Fig. 5. 13 30
Fig. 5. 14 31
Specialized Roots • Parasitic roots- mistletoe - haustoria-(sing. haustorium) projections that develop along stem in contact with host - penetrate outer tissue and connect with host’s vascular tissue 32
Mycorrhizae • mycorrhizae- fungus roots - fungus grows on roots; can’t grow beyond Casparian strip - absorb phosphorus, water and minerals for the plant - fungus lives on plant’s sugar - ex. of mutualism 33
Fig. 5. 16 ab 35
Root Nodules • root nodules- small swelling on roots filled with N 2 -fixing bacteria - found in Legumes 36
Fig. 5. 17 37
Human Relevance of Roots • food; carrots, sugar beets, turnips rutabagas, parsnips, horseradishes, sweet potatoes • spices- sassafras, sarsaparilla, licorice • dyes • drugs • insecticides 38
Soil • several types of sand, rocks, pebbles, clay, silt, small animals, bacteria, fungi • Humus- decomposed organic matter 39
Soil texture and mineral composition • sand silt- small particles • clay- colloid-suspension of particles that are larger than molecules, but do not settle out of fluid • loam-mixture of sand, clay organic matter - agricultural soil- 40% silt, 40% sand, 20% clay 40
Minerals in soil • include- O 2, H 2, Si, Al, Fe, K, Ca, Mg, Na 42
Soil p. H • Some plants thrive in acidic conditions, others basic • liming- adding Ca or Mg to make soil basic • basic soil can be made more acidic by adding S or N 2 45
Fig. 5. 4 a 47
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