22. 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
23. • 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
30. Stamen
• Male reproductive
structure of flower, Anther
made of 2 parts
• Filament – long,
thin, stalk that
supports the anther
• Anther – makes Filament
pollen grains
Anther + Filament = Stamen
36. 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
37. Q: What kind of symbiotic
relationship is this?
A: Mutualism
38. 25 – 1 Hormones and Plant Growth
• In plants, the division, maturation,
and development of cells are
controlled by a group of chemicals
called hormones
39. Hormones
• A substance that is produced in
one part of the organism and
affects another part of the same
organism
40. Target Cell
• The portion of an
organism affected
by a particular
hormone
41. Auxins
• Discovered by Charles Darwin
and his son
• They were trying to explain
phototropism
47. 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
48.
49. 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
55. 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
58. 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
59. 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