Biology Semester II

Sections:

Introduction |  Section 1 | Section 2 | Section 3

Section One:

Part 1 | Part 2 | Part 3 | Part 4 | Part 5 | Part 6 | Part 7 | Part 8

Biology: Plant Organs, Tissues, and Cells: Part Three The leaf consists of the generally flat blade, one or more leaf veins, a petiole, and usually an axillary bud. The petiole is the stalk that connects the leaf blade to the plant stem. It can be long (as in celery and bok choy) or short (as in cabbage and lettuce). Leaves may be simple or compound. Simple leaves have a single subdivision or leaflet. Compound leaves have more than one leaflet. Leaves attach to stems at nodes (internodes are the spaces between nodes).   Left: Leaf showing blade and petiole. Right: Roses, illustrating nodes where leaves attach, and internodes between the nodes. Plants carry out sexual reproduction inside a specialized structure known as a sporangium. Meiosis occurs within the sporangium, producing spores. Ferns and other free sporing plants produce and release spores as part of their sexual reproduction process. Seed plants retain the female spore, which becomes the seed. Most seed plants produce cones, modified leaves that carry either the sporangia or seeds. Flowers are a collection of sterile and reproductive tissue produced by the flowering plants (a group of seed plants). Oh yes, we do eat flowers! Broccoli and cauliflower are tiny flower buds that we eat before they open. Left: Iris and Right: flower showing petals and other flower parts. At meristems, plant cells are formed by mitosis and develop into cell types. The different cell types are grouped to form different plant tissues. Plants have only three tissue types: dermal, ground, and vascular. Dermal tissue covers the outer surface of herbaceous, or soft-stemmed, plants. This tissue is composed of epidermal cells, which are closely-packed cells that secrete a waxy cuticle to aid in the prevention of water loss. The ground tissue makes up most of the primary (soft tissue) plant body. Parenchyma, collenchyma, and sclerenchyma cells are common in the ground tissue. Vascular tissue transports food, water, hormones, and minerals within the plant. Vascular tissue includes xylem, phloem, and cambium tissues. A meristem is a region of localized mitosis that produces new plant cells. Apical meristems exist at the tip of the shoot or root. New cells produced here increase the length or height of the plant. Lateral meristems occur in cylinders that surround the stem and extend nearly the entire length of the plant. A cambium is a lateral meristem tissue that usually produces secondary growth. This type of growth increases the plant’s diameter rather than its length. Vascular cambium produces wood; cork cambium gives rise to a tree’s bark. Onion root tip.   Tissue Type Cells Produced By: Function(s) of Tissue (and  Cell Type) Dermal Apical and Root Meristems Coverage of surface and protection (Epidermal Cells, Trichomes) Exchange of gases (Guard Cells) Absorption of water and mineral nutrients (Root hairs) Ground Apical and Root Meristems     Cork Cambium Storage (Parenchyma) Photosynthesis (Parenchyma) Comprising the bulk of the plant’s primary body (Parenchyma) Support (Collenchyma and Sclerenchyma) Waterproofing of a woody stem (Cork) Vascular Apical and Root Meristems     Vascular Cambium Transport of water and mineral nutrient upward within the plant, support (Xylem) Transport of food and water throughout the plant body (Phloem) Lateral transport (Parenchyma in the xylem and/or phloem areas) Secondary Xylem (wood) and Secondary Phloem (a major part of the bark) Table showing the three types of plant tissues, the cells that compose each tissue type, and the function of each tissue type. Now go on to the next part.

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