KEY CONCEPT Plants have specialized cells and tissue systems.

KEY CONCEPTPlants have specialized cells and tissue systems.

Parenchyma cells are the most common plant cell type. store starch, oils andwater help heal wounds tothe plant have thin flexible walls Plant tissues are made of three basic cell types.

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

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

Dermal tissue covers the outside of a plant. protects the plant secretes cuticle of leaves forms outer bark of trees Plant organs are made of three tissue systems.

provides support stores materials in roots and stems most commonly made of parenchyma • Ground tissue is found inside a plant.

two networks of hollow tubes xylem transports water and minerals phloem transports photosynthetic products stem leaf root • Vascular tissue transports water, minerals and organic compounds.

KEY CONCEPT 20-2 The vascular system allows for the transport of water, minerals, and sugars.

Xylem contains specialized cells. vessel elements are short and wide tracheid cells are long and narrow xylem cells die at maturity tracheid vessel element Water and dissolved minerals move through xylem.

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

absorption occurs at roots • Water travels from roots to the top of trees. • cohesion and adhesion in xylem • transpiration at leaves

water vapor exits leaf stomata helps pull water to the top branches • Transpiration is the loss of water vapor through leaves.

Phloem contains specialized cells. sieve tube elements have holes at ends companion cells help sieve tube elements unlike xylem, phloem tissue is alive Phloem carries sugars from photosynthesis throughout the plant.

plants actively transport sugar from the source sugar flows to the sink due to pressure differences • The Pressure-flow model explains sugar movement. phloem xylem sugars Water moves from the xylem into the phloem by osmosis, due to the higher concentration of the sugars in the phloem. The water flow helps move sugars through the phloem. 2 Sugars move from their source, such as photosynthesizing leaves, into the phloem. 1 water The sugars move into the sink, such as root or fruit, where the are stored. 3

KEY CONCEPT 21.3 Roots and stems form the support system of vascular plants.

Roots provide many functions. support the plant absorb, transport, and store nutrients root hairs help absorption Roots anchor plants and absorb mineral nutrients from soil.

There are several parts of a root. root cap • root cap covers the tip

There are several parts of a root. apical meristem • 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 • There are several parts of a root. vascular cylinder • There are several parts of a root. • root cap covers the tip • apical meristem is an area of growth

Fibrous root systems have fine branches. • There are two main types of roots. Taproot Fibrous root • Taproot systems have one main root.

Stems have many functions. support leaves and flowers house most of the vascular system store water Baobab trees Cactus Stems support plants, transport materials, and provide storage.

grow underground for storage Ginger rhizomes Potato tubers 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 Strawberry stolons Stems support plants, transport materials, and provide storage. • Stems have many functions. • support leaves and flowers • house most of the vascular system • store water • form new plants

Some stems are herbaceous and conduct photosynthesis.

Some stems can be woody, and form protective bark.

Secondary growth increases a plant’s width. • Primary growth increases a plant’s length.

Tree rings help determine the age of a tree. bark bands heartwood one year of growth sapwood

KEY CONCEPTLeaves absorb light and carry out photosynthesis.

The blade is usually broad and flat. collects sunlight for photosynthesis connects to the stem by a petiole blade petiole Most leaves share some similar structures.

Mesophyll is between the leaf’s dermal tissue layers. cuticle upper epidermis palisademesophyll spongymesophyll lowerepidermis

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. stoma guard cells • Guard cells surround each stoma.

Leaves may be simple, compound, or double compound. Compound leaf Simple leaf Double compound leaf

Leaf veins may be parallel or pinnate. Parallel veins Pinnate veins

Leaf margins may be toothed, entire, or lobed. Toothed margin Entire margin Lobed margin

cuticle upper epidermis palisademesophyll xylem spongymesophyll phloem lowerepidermis stomata Most leaves are specialized systems for photosynthesis. • There are two types of mesophyll cells. • both types contain chloroplasts • palisade mesophyll absorbs sunlight • spongy mesophyll connects to stomata

Leaves have many adaptations. • for extreme temperatures, ex: pine needles

Leaves have many adaptations. • for extreme temperatures, ex: pine needles • for water loss,ex: cactus spines

for aquatic environments, ex: water lily • Leaves have many adaptations. • for extreme temperatures, ex: pine needles • for water loss,ex: cactus spines

for aquatic environments, ex: water lily • Leaves have many adaptations. • for extreme temperatures, ex: pine needles • for water loss,ex: cactus spines • for getting food,ex: Venus’ flytrap

KEY CONCEPT Plants have specialized cells and tissue systems.