Selected Plant Topics
Chapters 23 – 25
Specialized Tissues in Plants
23 -1
Seed Plant Structure • Three of the principal organs of
seed plants are roots, stems, and leaves
Roots• Absorb water and dissolved
nutrients
• Anchor plants in the ground
• Hold soil into place and prevent erosion
Stems• Support above ground parts of plant
• Transports nutrients
Leaves• Main photosynthetic systems
• Let in oxygen and carbon dioxide
Vascular Tissue• Forms a transport system that
moves water and nutrients throughout the plant
Types of vascular tissue
• Xylem – brings water and nutrients up from the roots
• Phloem – brings food down from the leaves
Leaf Structures and Functions
• Mesophyll – where photosynthesis happens
• Palisade mesophyll – closely packed, lots of chloroplasts
• Spongy mesophyll – loose tissue with many airspaces
• Stomata – pore-like openings in the underside of the leaf
• Allow CO2 and O2 to diffuse in and out of the leaf
Guard Cells• Control the opening and closing of
the stomata by responding to changes in water pressure
Transpiration• The loss of water through its
leaves
Gas Exchange• If stomata were kept open all the time, water
loss due to transpiration would so great that few plants would be able to take in enough water to survive.
• Plants keep their stomata open just enough to allow photosynthesis to take place but not so much that they lose too much water.
• The stomata open and close in response to changes in water pressure in the guard cells
• When pressure is high – stomata open
• When pressure is low – stomata close
Q: What time of day do you think stomata are open and why?
A: Daytime, cause that’s when photosynthesis happens
24 – 1 Reproduction with Cones and Flowers
Life Cycle of Gymnosperms
• Reproduction in gymnosperms takes place in cones
• Male cones produce – pollen grains
• Female cones produce – ovules
Structure of Flowers• Flowers are reproductive organs
that are composed of 4 kinds of specialized leaves
Sepals• Enclose the
bud before it opens, leaf-like
Petals• Brightly colored, attract insects to
flower
Stamen• Male reproductive
structure of flower, made of 2 parts
• Filament – long, thin, stalk that supports the anther
• Anther – makes pollen grains
Anther
Filament
Anther + Filament = Stamen
Pistil• Female reproductive structure,
made of 3 parts
Stigma• where pollen
grains land, sticky
Style• Connects stigma to ovary
Style
Ovary• swollen base of
the pistil where ovules are formed
Ovary
Pollination• Most gymnosperms and some
angiosperms are wind pollinated, whereas most angiosperms are pollinated by animals
• Insect pollination is beneficial to insects and other animals because it provides them with food
• Plants also benefit because this method of pollination is more efficient
Q: What kind of symbiotic relationship is this?A: Mutualism
25 – 1 Hormones and Plant Growth
• In plants, the division, maturation, and development of cells are controlled by a group of chemicals called hormones
Hormones
• A substance that is produced in one part of the organism and affects another part of the same organism
Target Cell• The portion of an
organism affected by a particular hormone
Auxins• Discovered by Charles Darwin
and his son
• They were trying to explain phototropism
Phototropism• The tendency for plants to grow
toward light
• Auxins are produced in the apical meristem and are transported downward into the rest of the plant
• They stimulate cell elongation
Gravitropism• The response of a plant to gravity
Auxin Like Weed Killers• High concentrations of auxins can
inhibit growth, so scientists have produced many auxin like compounds to be used as herbicide
• Ex.) Agent Orange
Cytokins• Plant hormones that stimulate cell
division, the growth of lateral buds and cause dormant seeds to sprout
• Cytokins often produce effects opposite to those of auxins
Gibberellins• Promote growth, particularly in
stems and fruits
Ethylene• Stimulate fruits to ripen
25 – 2 Plant Responses
tropisms• The response of plants to external
stimuli
• Ex.) gravitropism and photoperiodism
Thigmotropism• Growth in response to touch
Rapid Responses• Some plant responses do not
involve growth, they are so rapid it would be a mistake to call them tropisms
• Ex.) sensitive plant, venus fly trap
Sensitive Plant
Venus Fly trap
Photoperiodism• The way a plant responds to periods of
light and darkness• Short day plants – flower when days
are short• Long day plants – flower when days
are long• Photoperiodism in plants is responsible
for the timing of seasonal activities of plants
Dormancy • The period during which an
organism’s growth and activity decrease or stop
• As cold weather approaches deciduous plants turn off photosynthetic pathways, transport materials from leaves to roots, and seal leaves from the rest of the plant
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