Kingdom Plantae Like Animalia Is a Group of Multicellular Eukaryotic Organisms

Kingdom Plantae like Animalia is a group of multicellular eukaryotic organisms.

·  Plants face many of the same problems we have talked about for animals.

·  Plants must acquire energy and exchange matter; plants capture solar energy directly

·  Both plants and animals face similar challenges to living on land

Plant Structure and Growth-

Plant bodies are simple

·  only a few types of basic organs

·  roots with root hairs

·  stems

·  leaves

·  flowers + fruit

·  fewer cell types and tissue types than animals-names not stressed

·  all cells begin as parenchyma and differentiate into other types:

*  photosynthetic leaf cells (Fig 35.19a b)

*  phloem for transporting sugars

*  some cells become functional only when dead: xylem and fibers (note economic importance of these cell types)

· leaves modified in many different ways (fig 35.6)

·  for photosynthesis from sunny deserts to rainforest shade

·  as spines in cactus

·  tendrils in peas

·  as colorful signals to animals

Plant bodies are potentially immortal

· plants are rooted in place, but their growing tips continually explore new territory

· some shoots grow vertically and some grow horizontally

· meristems are sites of plant growth-sites of rapid cell division

· only two types of meristems in plants (fig 35.12):

·  apical meristems at ends of growing shoots-buds (fig 35.17)

*  primary growth—increases in length

*  generate plant form, i.e., leaf arrangement, lateral meristems

·  vascular cambium in a cylinder within the stems of woody plants (fig 35.23)

*  secondary growth—increases in diameter in woody plants

*  increase diameter through accumulation of xylem or wood

*  cambium cells are a meristem-zone of rapid cell division

*  cells to the inside differentiate into xylem

*  cells in the outside differentiate into phloem

*  cuticle and epidermis break up and are replaced by cork cambium

· growth of plants and animals different

·  modular vs unitary

*  continually add young modules at growing tips

*  trees that are rooted in one place eventually get old and die

*  plants that produce horizontal stems can live 1000’s of yrs, and continually move around

·  do plants perceive where they are?

*  receptors to light intensity and quality (pigments)

*  receptors for touch (?)

*  receptors for gravity (statoliths-starch grains settle to bottom of cells in roots)

·  do they respond to different conditions?

*  variety of hormones stimulated by different receptors that change growth

*  ex. pigments receive information on light environment; shade will stimulate longer spacers between leaves, light will stimulate leaves

*  ex. wind or touch stimulates plants to grow shorter, stouter bodies with more fibers and support in the stem

*  ex. roots can rapidly reorient their grow to gravitational pull

Vascular tissues are critical adaptations for terrestrial plants

·  As plants increase in size their surface area to volume increases

·  As plants move onto land, the moist cells inside the body must be protected from drying out

·  Plants evolve to do two things to solve this problem:

o  Produce a waxy cuticle on the surface of their epidermis that prevents water loss

o  Produce stomates to control entry and exit of gases

o  Circulate fluid and matter through their body in specialized vascular tissues

The most primitive plants lack a vascular system

·  Mosses (Phylum Bryophyta) lack waxy cuticle and vascular system

·  What are the consequences of no waxy cuticle and no vascular system?

o  Must live in moist locations

o  Must remain small

More advanced plants have waxy cuticle and vascular tissue

·  Phyla: Pteridophyta (Ferns), Gymnosperms (conifers) and Angiosperms (flowering plants)

TRANSPORT IN PLANTS

First need to list what plants need transported in terms of energy and matter (fig 36.1):

·  Energy: harvested directly from solar radiation by cells containing chloroplasts (Fig 35.19a,35-19b-Stomata.jpg, c)

o  Energy is transported through body in the form of sugars

·  Matter:

o  water is used in photosynthesis and lost from stomates

o  carbon dioxide is used in photosynthesis and brought in thru stomates

o  oxygen is used in mitochondria and is brought in thru stomates

o  carbon dioxide is lost from mitochondria and exits thru stomates or is reused in photosynthesis

o  oxygen is a by product of photosynthesis and is lost thru stomates

Water + dissolved nutrients move in xylem

· rootsàshoots in xylem

· driving force is loss of water thru stomates--transpiration

·  99% of water in roots is lost thru stomates

·  CO2 gain is linked to H2O loss

·  what causes stomates to open?

*  light

*  low CO2

·  what causes stomates to close

*  loss of turgor or water pressure

· cohesion-tension mechanism (transpiration movie)

·  water loss from cells in leaves to intercelluar space then thru stomates

·  provides negative pressure and pulls water out of xylem to replace water lost from leaf.

·  negative pressure gradient is maintained all the way to roots

·  properties of water important

*  cohesive due to hydrogen bonds

*  adhesive to sides of xylem elements

· evidence to support

·  1. xylem sap recedes from cut surface of stem-cut stems will wilt due just as siphon will stop if you get an air bubble in them

·  2. Stems shrink when transpiration is great

·  3. Water starts moving first in leaves in morning

· factors affecting transpiration

·  humidity

·  wind

·  temperature

·  light

Sugars move from sources to sinks in phloem

· sieve tubes run in bundles adjacent to xylem (fig 36.17)

· sources are sites where sugars are actively loaded into sieve tubes, i.e., photosynthetic leaves or storage

· sinks are sites where sugars are pulled out of sieve tubes and used, ie., growing tissues, storage organs, fruits, parasites

· phloem connects sinks and sources

· turgor pressure builds up at sources

· turgor pressure is reduced at sinks

· results in bulk flow

· resources can move in one direction one day, and reverse the next in phloem