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

Chapter 38 and 39 provides knowledge of angiosperm reproduction Plant responses to internal and external signals. In this chapter, the following content will be discussed: Types of fruit, plant peproduction, experiments with light and the coleoptile, ethylene gas: fruit ripening, plant movement, plant responses to light, plant responses to stress.

Chapter 38

Angiosperm Reproduction

Angiosperms have 3 unique

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

Pin flower

Anther with pollen

Thrum flower

“Pin” and “thrum” flower types reduce

self-fertilization

The development of a plant embryo

Egg cell  plant embryoplant embryo

Ovules inside ovary  seedsseeds

Ripe ovaryovary  fruitfruit

Fruit protects enclosed seed(s)

Aids in dispersal by water, wind,

or animals

Mature seed  dormancy (resting)

◦ Low metabolic rate

◦ Growth & development suspended

◦ Resumes growth when

environmental conditions suitable for 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

Sexual (Vegetative Asexual

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

Plant Reproduction

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 beta-carotene (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

Agar block with chemical stimulates growth Offset blocks cause curvature

Control (agar block lacking chemical) has no effect Control

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

SLOW

 Phototropism – light (auxin)

 Gravitropism – gravity (auxin)

 Thigmotropism – touch

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

Biological Clocks

Circadian rhythm: biological clocks

 Persist w/o environmental cues

Photoperiodism: physiological

response to the relative length of

night & day (i.e flowering)

nights are long (mums, poinsettia)

are short (spinach, iris, veggies)

photoperiod (tomatoes, rice,

dandelions)

How does

interrupting

the dark

period with a brief exposure

to light affect flowering?

Plant responses to

stress

3 Excess Salt:

denaturation

(↑unsat fatty acids, ↑fluidity)

6. Herbivores:

 physical (thorns)

 chemicals (garlic, mint)

 recruit predatory animals (parasitoid

wasps)

7. Pathogens:

 1st line of defense = epidermis

 2nd line = pathogen recognition,

host-specific