Lecture AP Biology Chapter 38, 39 Angiosperm reproduction Plant responses to internal and external signals

Chapter 38
Angiosperm Reproduction


Angiosperms have 3 unique F eatures:
F lowers
2. F ruits
3. Double
F ertilization (by
2 sperm)
1.


REPRODUCTIVE VARIATIONS




Pollination : transfer pollen from anther to stigma





Some plants are self-pollinated
Cross-pollinated plants:
◦ Self-incompatibility: plant rejects own pollen or closely related plant
◦ Maximize genetic variation

Stigma

Stigma

Anther
with
pollen

Pin flower

Thrum flower

“Pin” and “thrum” flower types reduce self-fertilization


The development of a plant embryo


Fruit






Egg cell  plant embryo
Ovules inside ovary  seeds
Ripe ovary  fruit
Fruit protects enclosed seed(s)
Aids in dispersal by water, wind, or animals

Seeds
Mature seed  dormancy (resting)
◦

Low metabolic rate

◦

Growth & development suspended

◦

Resumes growth when environmental conditions suitable for germination




Germination
Seed take up water (imbibition)  trigger
metabolic changes to begin growth



◦


Root develops  shoot emerges  leaves expand
& turn green (photosynthesis)

Very hazardous for plants due to vulnerability
 Predators, parasites, wind


Plant Reproduction
Sexual

Asexual
(Vegetative Reproduction)

Flower  Seeds

Runners, bulbs, grafts, cuttings
vegetative (grass), fragmentation,
test-tube cloning

Genetic diversity

Clones

More complex & hazardous for
seedlings

Simpler (no pollinator needed)

Advantage in unstable
environments

Suited for stable environments

Asexual
reproduction in
aspen trees

Test-tube cloning
of carrots


Humans Modify Crops



Artificial selection of plants for breeding
Plant Biotechnology:
◦ Genetically modified organisms

 “Golden Rice”: engineered to produce betacarotene (Vit. A)
 Bt corn: transgenic – expresses Bt (bacteria)
gene  produces protein toxic to insects
◦ Biofuels – reduce CO2 emissions

 Biodiesel: vegetable oils
 Bioethanol: convert cellulose into ethanol


Chapter 39
Plant Responses to Internal and External Signals

Experiments with Light and the coleoptile


Excised tip placed
on agar block
Growth-promoting
chemical diffuses
into agar block

Cells on darker side
elongate faster than
cells on brighter side
AUXIN = chemical
messenger that
stimulates cell
elongation

Control

Control
(agar block
lacking
chemical)
has no
effect

Agar block
with chemical
stimulates growth
Offset blocks

cause curvature


Important plant hormones :
1. Auxin – stimulate cell elongation  phototropism &
gravitropism (high concentrations = herbicide)
2. Cytokinins – cell division (cytokinesis) &
differentiation
3. Gibberellins – stem elongation, leaf growth,
germination, flowering, fruit development
4. Abscisic Acid – slows growth; closes stomata during
H2O stress; promote dormancy
5. Ethylene – promote fruit ripening (positive feedback!);
involved in apoptosis (shed leaves, death of annuals)


The effects of gibberellin on stem elongation
and fruit growth


Ethylene Gas: Fruit Ripening

Canister of ethylene gas to ripen
bananas in shipping container

Untreated tomatoes vs. Ethylene
treatment


Plant Movement

1.

2.

Tropisms: growth responses  SLOW
 Phototropism – light (auxin)
 Gravitropism – gravity (auxin)

 Thigmotropism – touch
Turgor movement: allow plant to make relatively
rapid & reversible responses
 Venus fly trap, mimosa leaves, “sleep”
movement


Positive gravitropism in roots: the statolith
hypothesis.


Thigmotropism: rapid turgor movements by
Mimosa plant  action potentials


Plant Responses to Light
Plants can detect direction, intensity, & wavelenth of
light
 Phytochromes: light receptors, absorbs mostly red light


◦ Regulate seed germination, shade avoidance