21.4 Leaves TEKS 4B, 5B, 10B, 10C The student is expected to: 4B investigate and explain cellular processes, including homeostasis, energy conversions, transport of molecules, and synthesis of new molecules; 5B examine specialized cells, including roots, stems, and leaves of plants...; 10B describe the interactions that occur among systems that perform the functions of transport, reproduction, and response in plants; 10C analyze the levels of organization in biological systems and relate the levels to each other and to the whole system

21.4 Leaves TEKS 4B, 5B, 10B, 10C KEY CONCEPT Leaves absorb light and carry out photosynthesis.

21.4 Leaves TEKS 4B, 5B, 10B, 10C 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

21.4 Leaves TEKS 4B, 5B, 10B, 10C Mesophyll is between the leaf’s dermal tissue layers. cuticle upper epidermis palisade mesophyll spongy mesophyll lower epidermis

21.4 Leaves TEKS 4B, 5B, 10B, 10C –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 cellsstoma Guard cells surround each stoma.

21.4 Leaves TEKS 4B, 5B, 10B, 10C Leaves may be simple, compound, or double compound. Simple leaf Compound leaf Double compound leaf

21.4 Leaves TEKS 4B, 5B, 10B, 10C Leaf veins may be parallel or pinnate. Pinnate veins Parallel veins

21.4 Leaves TEKS 4B, 5B, 10B, 10C Leaf margins may be toothed, entire, or lobed. Toothed marginEntire marginLobed margin

21.4 Leaves TEKS 4B, 5B, 10B, 10C 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 xylem phloem cuticle upper epidermis palisade mesophyll spongy mesophyll stomata lower epidermis

21.4 Leaves TEKS 4B, 5B, 10B, 10C –for extreme temperatures, ex: pine needles Leaves have many adaptations.

21.4 Leaves TEKS 4B, 5B, 10B, 10C Leaves have many adaptations. –for extreme temperatures, ex: pine needles –for water loss, ex: cactus spines

21.4 Leaves TEKS 4B, 5B, 10B, 10C –for aquatic environments, ex: water lily Leaves have many adaptations. –for extreme temperatures, ex: pine needles –for water loss, ex: cactus spines

21.4 Leaves TEKS 4B, 5B, 10B, 10C –for aquatic environments, ex: water lily –for getting food, ex: Venus’ flytrap Leaves have many adaptations. –for extreme temperatures, ex: pine needles –for water loss, ex: cactus spines