KEY CONCEPT Plants have specialized cells and tissue systems.

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

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.

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

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

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

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

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.

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

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

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

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

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

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

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

Mesophyll is between the leaf’s dermal tissue layers. cuticle upper epidermis palisade mesophyll spongy mesophyll lower epidermis

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

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

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

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

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

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

Plants can respond to light, touch, gravity, and seasonal changes. Phototropism is the tendency of a plant to grow toward light. auxins build up on shaded side of stem cells on shaded side lengthen causes stem to bend toward light

Thigmotropism is a plant’s response to touchlike stimuli. climbing plants and vines plants that grow in direction of constant wind Thigmotropism A plant turns and bends in response to contact with an object.

Gravitropism is a plant’s response to Earth’s gravitational pull. positive gravitropism is downward growth (roots) negative gravitropism is upward growth (shoots) Gravitropism Plant stems grow upward, against gravity.

Photoperiodism is a response to the changing lengths of day and night. triggers some plants to flower (see below) triggers fall colors/winter dormancy of deciduous trees Photoperiodism A plant moves its leaves during the day.