VII. SEXUAL REPRODUCTION IN ANGIOSPERMS
A. Benefits of Sexual Reproduction
1. increases genetic diversity of a population (and thus the species)
a. increases the probability that there will be phenotypic variation in the population
Q: Explain why genetic diversity is an advantage.
A: __________________________________________________________________________
__________________________________________________________________________
Q: Explain why genetic diversity is not a guarantee of phenotypic variation, particularly in very
small populations and over the very short term.
A: __________________________________________________________________________
__________________________________________________________________________
B. Flower Structure
Figure 44. The parts of a complete flower.
http://www.flmnh.ufl.edu/flowerpower/fgpimages/floweryellow.jpg
Figure 45. Formation of male and female gametophytes.
http://www.mhhe.com/biosci/genbio/raven6b/graphics/raven06b/other/raven06_42.pdf
1. Male structures and their functions
a. anther: produces pollen by meiosis
b. pollen: the immature male gametophyte, will mature when if it receives stimulation
from the stigma, carries the generative cell/nucleus and the tube cell nucleus
c. filament: structure that supports the anther
d. stamen: anther + filament
2. Female structures and their functions
a. ovary: contains the ovule(s)
b. ovule: produces the egg cell by meiosis, when mature will have 8 haploid nuclei,
one of which is the egg cell nucleus, 2 others (called the polar nuclei) when
fertilized will develop into the endosperm of the seed
c. stigma: produces a sugary substance that the pollen can stick to and stimulates
growth of the pollen tube and division of the generative nucleus
d. style: supports the stigma
e. carpel: stigma + style
f. pistil: one or more carpels
3. Other flower parts
a. petal: (usually) colourful, leaf-like structure(s) surrounding the reproductive parts
b. corolla: all of the petals
c. sepal: modified leaves that protect the petals and reproductive structures when the
bud is first forming
d. calyx: all of the sepals
C. Pollination, Fertilization, Seed Formation and Fruit Formation
Here is an animation:
http://content.bfwpub.com/webroot_pubcontent/Content/BCS_3/Sadava_9e/Animated%20Tutor
ials/life9e_3801_double_fert.html
Figure 46. Pollination and fertilization.
http://content.bfwpub.com/webroot_pubcontent/Content/BCS_3/Sadava_9e/Interactive%20Su
mmaries/3810.html
1. pollination: transfer of pollen from the anther to the stigma
a. occurs by wind or by animal pollinators
i. the flower has evolved with potential pollinators (coevolution)
ii. characteristics such as scent, nectar, petal markings can aid in attracting animal
pollinators or direct the pollinators towards the nectar or pollen
2. fertilization: the fusion of nuclei
a. angiosperms have double fertilization (2 fusion events occur)
Figure 47. Pollination and fertilization in an angiosperm.
http://content.bfwpub.com/webroot_pubcontent/Content/BCS_3/Sadava_9e/Interactive%20Su
mmaries/3810.html
3. the pollen grain lands on the stigma
4. the pollen tube grows towards the embryo sac and the generative nucleus divides by
mitosis to form two sperm nuclei
5. one sperm nucleus fuses with the egg cell to produce the diploid (2n) zygote
a. the zygote will divide by mitosis to produce the embryo (diploid sporophyte)
6. the second sperm nucleus fuses with the 2 polar nuclei to produce a triploid (3n) cell
a. this cell will divide to produce the endospem
7. following pollination and fertilization, ovules develop into seeds and the ovary will
develop into the fruit
D. Control of flowering
Here is an animation:
http://content.bfwpub.com/webroot_pubcontent/Content/BCS_3/Sadava_9e/Animated%20Tutor
ials/life9e_3802_eff_day_night.html
1. photoperiodism: the phenomenon where plant flowering is controlled by exposure to
light (dark really!)
a. short-day (long-night) plants: plants that flower when the length of darkness is
longer than a critical time length
i. e.g. chrysanthemums, poinsettias, morning glory
b. long-day (short-night) plants: plants that flower when the length of darkness is
shorter than a critical time length
i. spinach, sugar beet
c. day-neutral plants: plants whose flowering is not controlled by photoperiod
2. The role of phytochrome
a. phytochrome exists in 2 forms
i. one is called Pr because it absorbs red light (about 660nm) and gets converted
into PFr during the day
ii. one is called PFr because it absorbs far-red light (about 730nm) and gets
converted back to Pr during the night
a. promotes flowering in long-day plants and inhibits it in short-day plants
b. sunlight is richer in red light so Pr gets converted into PFr
i. low PFr promotes flowering in short-day plants
ii. high PFr promotes flowering in long-day plants
E. Seed structure
1. seed coat (testa): from the hardened ovule
2. embryo: baby plant
a. epicotyl: the embryonic stem above the cotyledon(s)
b. hypocotyl: the embryonic stem below the cotyledon(s)
c. radicle: the embryonic root
d. plumule: the embryonic shoot (leaves and stems)
e. cotyledon(s): the “seed leaf (leaves”, contains the endosperm which is food for the
developing embryo
f. micropyle: small pore in the seed coat for absorption of water
Figure 48. Structure of a dicotyledonous seed.
http://www.bio.miami.edu/dana/pix/seed_structure.gif
3. germination: the emergence of the radical from the seed coat
a. seed absorbs water through the micropyle
i. water moves through the tissue by osmosis
ii. activates hormones and enzymes
iii. causes seed to swell and seed coat to burst
iv. metabolism = chemical reactions so require water
v. activates giberellin
a. activates amylase production in the endosperm so that starch is converted
to maltose
b. maltose is converted to glucose
c. glucose is used by the embryo
b. requires oxygen
c. requires a suitable temperature
d. may require additional environmental signals such as specific wavelengths of light,
changes in temperature etc.
4. Importance of seeds
a. allow the embryo to remain dormant until conditions are favourable for growth
i. abscisic acid inhibits starch breakdown and is important for establishing
dormancy
b. protect the embryo from the environment
c. provide food for the developing embryo until it is capable of photosynthesis
d. aid in dispersal of the offspring away from the parent plant
i. minimizes competition
5. Importance of fruits
a. aid in seed dispersal
i. may be adapted to attract animals that will ingest them without harming the
seeds
ii. may be adapted to stick onto animals that will then transport the fruit away
from the parent plant
iii. may be buried (and forgotten) by animals
iv. may be adapted to be carried by the wind
v. may be adapted to float on water
VIII. PLANT HORMONES
A. Hormones specifically mentioned in the IB syllabus: auxin, abscisic acid, giberellin,
phytochrome
Table 4. Plant hormones and their functions.
http://www.phs.d211.org/science/filipekcj/AP%20Biology/PowerPoint/39_Lecture_Presentation.p
df
Selected botany terms:
For a comprehensive glossary: http://extension.oregonstate.edu/mg/botany/glossary.html
1. complete flower: has 4 layers of parts
2. incomplete flower: lacking 1 or more of the 4 layers of parts
3. perfect flower: has both male and female parts
4. imperfect flower: only male or female parts
5. monoecious plant: has both male and female imperfect flowers on the individual plant
6. dioecious plant: has only male or female imperfect flowers on the individual plant
7. herbaceous: refers to plants that are non-woody and have shoot systems that die down
during the winter
8. annual: refers to a plant that goes through its entire life cycle within one year and then dies;
no secondary growth occurs
9. perennial: refers to a plant that lives for multiple years
Online review activities etc.:
1. http://www.phschool.com/science/biology_place/biocoach/plants/intro.html
2. Plant anatomy and nutrient transport:
http://wps.prenhall.com/esm_audesirk_bloe_7/17/4459/1141600.cw/index.html
3. Plant reproduction and development:
http://wps.prenhall.com/esm_audesirk_bloe_7/17/4459/1141677.cw/index.html
References:
1. http://www.mhhe.com/biosci/genbio/maderbiology7/student/olc/chap36-outline.mhtml
2. http://leavingbio.net/FLOWERING%20PLANTS.htm#stemsfunctions
3. http://www.emc.maricopa.edu/faculty/farabee/biobk/BioBookPLANTANATII.html
4. http://www.emc.maricopa.edu/faculty/farabee/biobk/biobookplantanat.html
5. http://www.mhhe.com/biosci/genbio/maderbiology7/student/olc/chap36-outline.mhtml
6. http://biology.clc.uc.edu/courses/bioall/plant%20families.htm
7. http://www.uic.edu/classes/bios/bios100/lectures/pl_anat.htm
8. http://www.doctortee.com/dsu/tiftickjian/plant-anat/xylem.html
9. http://ib.berkeley.edu/courses/bio1b/plantsfall08/pdfs/Carlson11_StructureFunction2.pdf
10. http://scidiv.bellevuecollege.edu/rkr/biology213/lectures/pdfs/secondarygrowth213.pdf
11.
http://bcs.whfreeman.com/thelifewire9e/default.asp#542578__591489__
12. For lots of detail about secondary growth:
http://plantphys.info/plant_biology/secondary.shtml
13.http://bcs.whfreeman.com/thelifewire9e/default.asp#542578__591499__
14.http://www.mhhe.com/biosci/genbio/raven6b/graphics/raven06b/other/raven06_39.pdf
15.http://www.rsc.org/learnchemistry/content/filerepository/CMP/00/001/060/Transport%20in%20flowering%20plant
s.pdf
16. http://bcs.whfreeman.com/thelifewire9e/default.asp#542578__591529__
17. http://www.gothamsci.com/APBio/chapt37_lecture.pdf
Here is an article that goes into a lot of detail on plant nomenclature and taxonomy (I have not
read it yet):
http://www.vcru.wisc.edu/spoonerlab/pdf/Spooner%20et%20al.,%20taxonomy%20paper.pdf
Associations:
The American Society of Plant Taxonomists: http://www.aspt.net/index.php