Ch. 35 Plant anatomy and growth
Talking about angiosperms (flowering plants).
- not “primitive” mosses, ferns, hornworts, liverworts that don’t have vascular tissue
- not gymnosperms - the conifers (have some differences)
- angiosperms are by far the most diverse and widespread plants
General
- terrestrial plant must inhabit two very different environments, air and soil and draw nutrients from each, so parts are evolved to be efficient at that
o air is exposed to air and sun
o soil not, but access to water and minerals
- so plant structure divided into two parts (Fig. 35.3)
o shoot system – stems and leaves and flowers
o root system – roots
- neither survives without the other
o shoots do photosynthesis, make ATP and sugars
o roots furnish water and minerals
o so must be ways to transport stuff among roots and shoots
Roots
- taproots – single large primary root with less prominent lateral roots (dandelion, carrot)
- fibrous roots – many thin roots equal in diameter (grasses)
- both have root hairs – to increase surface volume (Fig. 35.22)
Stems
- part of shoot system
- alternating nodes (points where leaf attached) and internodes (between leaves) (Fig. 35.11)
- at angle formed between each leaf and stem is lateral bud
o most lateral buds inactive, but if activated can form a branch
- at the top of the stem (and at tip of each branch) is the terminal bud
o may form flower
- diversity of stems
o Cacti – stem is primarily water storage organ
o Tubers – underground stem that is primarily for carbohydrate storage (like potato)
Leaves
- flattened part is blade (Fig. 35.12)
- stalk is the petiole
- leaf types
o grass has no petiole
o simple – a single blade
o compound – many blades
- leaf morphology is genetically defined and highly characteristic of a species
- leaves can be highly modified (Fig. 35.15)
o flowers
o cactus spines
Plant cells
- have rigid primary wall made mostly of cellulose (carbohydrate)
- may have secondary wall inside of primary
o can have different molecules (lignin in wood, waxy suberin in cork)
- plant cell cytosol is connected through holes in cell wall called plasmodesmata
Plant cell types (Table 35.2 has some of this)
o meristem
o undifferentiated like stem cells in animals
o totipotent, can give rise to all other cell types
o self-renewing, can give rise to more meristem cells
o parenchyma
§ thin walls, usually only primary wall
§ perform most metabolic functions of the plant
· photosynthesis
· storage
· packing and support
o collenchyma
§ thicker primary walls
§ provide support to plants that are not woody
§ celery strings are collenchyma
o sclerenchyma
§ thick cell wall, often have secondary wall
§ very rigid
§ used for support
§ often functions only when cell is dead
· wood
· nuts
Plant tissue systems
- meristematic
o rapidly growing, undifferentiated cells
- dermal
o outer covering of plant
o one cell layer thick
o specialized according to what organ it is in
§ root epidermal specialized for water and mineral absorption
§ stem and leaf epidermal cells secrete cuticle – waxy covering
o always serve as a barrier between outside world and inside plant
- vascular tissue
o xylem and phloem
o for transport
o xylem
§ function is to transport water and dissolved minerals
§ cells are dead when functional
§ tracheids are long cylindrical cells connected by lots of pits
· when cell does programmed cell death, wall stays and many form tube connected by pits
· all vascular plants have these
§ vessel elements
· only in angiosperms
· when cells die the ends disintigrate, leaving a tube
o phloem
§ function is to transport sugars and other organic compounds
§ cells are cylindrical
§ at maturity, cell loses nucleus and some other organelles and cytoplasm is around periphery, but cell stays alive
§ between cells is remnants of cells wall, looks like a sieve
§ called a sieve plate
§ sometimes called sieve tubes
§ each cell has companion cell which has nucleus, ribosomes, etc, helps keep sieve tube cell alive
- ground tissue
o storage
o support
o photosynthesis