Ch 23- Roots, Stems, and Leaves
• Cells of seed plant are organized into different
tissues and organs
• Principal organs of seed plants- roots, stems,
leaves
• Roots- absorb water and dissolved nutrients,
anchor plants in ground
• Stems- supports, transports, and protects plant
• Leaves- broad, flat surfaces where photosynthesis
takes place
Plant Tissue Systems
• What are the principal tissues of seed plants?
– Dermal, vascular, ground
• Dermal tissue- “skin” of plant, outermost layer
– Consist of epidermal cells
– Cuticle- thick waxy coating that protects against water loss
– Trichomes- tiny projections that protects the leaf, gives
fuzzy appearance
– Root hair cells- provide large amount of surface area, aids
in water absorption
– Guard cells- regulate water loss and gas exchange on
underside of leaves
• Vascular tissue- plants “bloodstream” that transports water
and nutrients throughout plant
• What specialized cells make up vascular tissue
– Xylem and phloem- made up of networks of hollow connected
cells that carry fluids throughout plant
• Xylem- made up of tracheids and vessel elements, transfers
water throughout plant
– Tracheids- long, narrow cells with walls that resist pressure, die
when mature
– Vessel element- cell that forms part of continuous tube in which
water can move, die when mature
• Phloem- made up of sieve tube elements and companion
cells, transfer nutrients throughout cell
– Sieve tube elements- cell that is joined end to end to form sieve
tubes
– Companion cells- cell that surrounds sieve tube elements
• Ground tissue- cells that lie between dermal
and vascular tissue, cell walls vary in thickness
– Parenchyma- cell with thin cell wall and large
central vacuole
– Collenchyma-cell with strong, flexible cell wall,
helps support larger plants
– Sclerenchyma- cell with extremely thick, rigid cell
wall that makes ground tissue tough and strong
• What are the functions of the three types of
cells?
Plant Growth and Meristematic Tissue
• Meristems- clusters of tissue, responsible for
continuing growth throughout plant’s life
• Meristematic tissue- found only in tips of shoots
and roots, responsible for plant growth
• Apical meristem- group of undifferentiated cells
that divide to produce increased length of stems
and roots
• How does meristematic tissue differ from other
plant tissue?
– Only plant tissue that produces new cells by mitosis
Sec 2- Roots
• 2 main types of roots- taproots and fibrous roots
• Taproot- primary root grows long and thick,
secondary root remains small
– Mainly in dicots
– Carrots, oak trees, dandelions
• Fibrous- branch of roots where no single root
grows larger than rest
– Mainly in monocots
– Grasses
Root Structure and Growth
• Roots contains dermal, vascular, and ground tissue
• Root consists of central vascular cylinder surrounded by ground
tissue and epidermis
• Root hair- tiny projection from epidermis
• Cortex- spongy layer of ground tissue just inside epidermis
• Endodermis- layer of cells that completely encloses vascular tissue
• Vascular cylinder- central region of root that includes vascular tissue
• Root cap- tough structure that protects a root as it forces its way
through surface
• What are the different functions of roots?
– Anchor plant in ground, absorb water and nutrients
Sec 3- Stems
• What are the main functions of stems?
– Produce leaves, branches, and flowers
– Hold leaves up to sunlight, transport substances
between roots and leaves
• Stems made up of dermal, vascular, and ground
tissue
– Surrounded by epidermal cells with waxy protective
coating
– Contains nodes- where leaves are attached,
internodes- regions between nodes, and budsundeveloped tissue that produces new stems and
leaves
• How do monocot and dicot stems differ?
– Monocots- vascular bundles are scattered throughout
stem
– Dicots- vascular bundles arranged in ring
• Pith- parenchyma cells inside ring of vascular tissue
• How do primary growth and secondary growth occur in
stems?
– Primary growth- growth that occurs at end of plant,
increases plant in length.
• Produces by cell division in apical meristem
• Takes place in all seed plants
– Secondary growth- growth in which stems increase in
width
• Takes place in lateral meristematic tissue- vascular cambium and
cork cambium
• Vascular cambium- produces vascular tissues and increases the
thickness of stems over time
• Cork cambium- produces the outer covering of stems
• Formation of wood
– Heartwood- older xylem near center of stem, no
longer conducts water, usually darkens with age
– Sapwood- surrounds heartwood, active in fluid
transport, lighter in color
• Tree rings indicate weather conditions, and
age
• Bark- phloem, cork cambium, and cork
– Protects tree
Sec 4- Leaves
• Leaf structure- ideal for absorbing light and carrying out
photosynthesis
– Blades- thin, flattened sections of leaves
– Petiole- thin stalk that attaches blade to stem
• Leaf function- carry out photosynthesis
– Mesophyll- tissue that makes up most of leaf, performs most of
plant’s photosynthesis
– Palisade mesophyll- layer of tall, column shaped mesophyll cells
just under epidermis of leaf
– Spongy mesophyll- loose tissue beneath the palisade layer of a
leaf
– Stomata- openings on underside of leaf, allow carbon dioxide
and oxygen to diffuse into and out of leaf
– Guard cells- controls opening and closing of stomata
• Transpiration- loss of water through its leaves
• How does gas exchange take place in a leaf?
– Plants regulate the opening and closing of their
stomata to balance water loss with rates of
photosynthesis
Sec 5- Transport in Plants