21 1 Plant Cells and Tissues KEY CONCEPT

21. 1 Plant Cells and Tissues KEY CONCEPT Plants have specialized cells and tissue systems.

21. 1 Plant Cells and Tissues Plant tissues are made of three basic cell types. • Parenchyma cells are the most common plant cell type. – store starch, oils and water – help heal wounds to the plant – have thin flexible walls

21. 1 Plant Cells and Tissues • Collenchyma cells provide support to a growing plant. – they are strong and flexible. – celery strings are strands of collenchyma. – they have unevenly thick cell walls.

21. 1 Plant Cells and Tissues • Sclerenchyma cells are the strongest plant cell type. – second cell wall hardened by lignin – die when they reach maturity – used by humans to make linen and rope

21. 1 Plant Cells and Tissues Plant organs are made of three tissue systems. • Dermal tissue covers the outside of a plant. – protects the plant – secretes cuticle of leaves – forms outer bark of trees

21. 1 Plant Cells and Tissues • Ground tissue is found inside a plant. – provides support – stores materials in roots and stems – most commonly made of parenchyma

21. 1 Plant Cells and Tissues • Vascular tissue transports water, minerals and organic compounds. – two networks of hollow tubes stem – xylem transports water and minerals – phloem transports photosynthetic products leaf root

21. 1 Plant Cells and Tissues • The cohesion-tension theory explains water movement. – Plants passively transport water through the xylem. – Cohesion is the tendency of water molecules to bond with each other. – Adhesion is the tendency of water molecules to bond with other substances.

21. 1 Plant Cells and Tissues • Water travels from roots to the top of trees. – absorption occurs at roots – cohesion and adhesion in xylem – transpiration at leaves

21. 1 Plant Cells and Tissues • Transpiration is the loss of water vapor through leaves. – water vapor exits leaf stomata – helps pull water to the top branches

21. 1 Plant Cells and Tissues Roots anchor plants and absorb mineral nutrients from soil. • Roots provide many functions. – support the plant – absorb, transport, and store nutrients – root hairs help absorption

21. 1 Plant Cells and Tissues • There are several parts of a root. – root cap covers the tip – apical meristem is an area of growth – vascular cylinder contains xylem and phloem vascular cylinder apical meristem root cap

21. 1 Plant Cells and Tissues Stems support plants, transport materials, and provide storage. • Stems have many functions. – support leaves and flowers – house most of the vascular system – store water – grow underground for storage – form new plants Strawberry stolons

21. 1 Plant Cells and Tissues • Primary growth increases a plant’s length. • Secondary growth increases a plant’s width.

21. 1 Plant Cells and Tissues Most leaves share some similar structures. • The blade is usually broad and flat. – collects sunlight for photosynthesis – connects to the stem by a petiole blade petiole

21. 1 Plant Cells and Tissues • Mesophyll is between the leaf’s dermal tissue layers. cuticle upper epidermis palisade mesophyll spongy mesophyll lower epidermis

21. 1 Plant Cells and Tissues • Guard cells surround each stoma. – Stomata open and close when guard cells change shape. – When stomata are open, water evaporates and gas exchanges. – Stomata close at night and when plant loses too much water. guard cells stoma

21. 1 Plant Cells and Tissues • Leaves may be simple, compound, or double compound. Simple leaf Compound leaf Double compound leaf

21. 1 Plant Cells and Tissues • Leaf veins may be parallel or pinnate. Parallel veins Pinnate veins

21. 1 Plant Cells and Tissues • Leaf margins may be toothed, entire, or lobed. Toothed margin Entire margin Lobed margin

21. 1 Plant Cells and Tissues • Leaves have many adaptations. – for extreme temperatures, ex: pine needles

21. 1 Plant Cells and Tissues • Leaves have many adaptations. – for extreme temperatures, ex: pine needles – for water loss, ex: cactus spines

21. 1 Plant Cells and Tissues • Leaves have many adaptations. – for extreme temperatures, ex: pine needles – for water loss, ex: cactus spines – for aquatic environments, ex: water lily – for getting food, ex: Venus’ flytrap