Text Handout on IB Plant Objective 9.3 & 9.4 Growth & Reproduction in Plants
9.3 Objectives for Growth in Plants
9.3.1 Undifferentiated Cells in the Meristems of plants allow indeterminate growth.
9.3.2 Mitosis and cell division in the shoot apex provide cells needed for the extension of the stem
and the development of leaves.
9.3.3 Plant hormones control growth in the shoot apex.
9.3.4 Plant shoots respond to the environment by tropisms.
9.3.5 Auxin efflux pumps can set up concentration gradients of auxin in plant tissue.
9.3.6 Auxin influences cell growth rates by changing the pattern of gene expression.
Text Questions: Remember that you are responsible to show me work for the underlined sections.
9.3.1 #1- Revisit page 760. Draw and label the diagrams in figure 35.11. Explain why the secondary
phloem is on the inside of the primary phloem. Why is this not true for the secondary xylem? What
tissue is the origin of the secondary xylem? Now read page 763 column 2 ‘Tissue organization of stems’
especially paragraph 2 on page 764. Was the stem cross section that you drew in the Plant Tissue Lab
monocot or eudicot? Explain why you think so.
9.3.2- #2- Skim section 12.1-12.2 (on mitosis) on pg. 233-5. Draw and label the Diagrams in the center of
figure 12.7 on pages 236-7. However, DRAW THEM IN THE SHAPE OF THE PLANT CELLS ON PAGE 241.
Pay particular attention to the distinctions between Prophase and Prometaphase which will be new to
us all. How are they different? (Answer the chromosome questions (in yellow with a red question mark)
below the picture of Prometaphase). Read the captions under the onion cell pictures on page 241 and
label any differences you can distinguish. Draw the bottom of figure 12.10b (the formation of the cell
plate). How big is a micrometer?
#3. Draw a rough sketch of figure 35.16 on pg. 763. Label as in the figure but add where you think
mitosis will be the strongest. Draw a carrot pointing to this sketch and at the fat end draw figure 35.12.
Make sure the tip of the carrot (arrow) shows all the places where 35.16 can be found in figure 35.12.
9.3.3-Read Pg. 763 ‘Primary Growth of Shoots’. Skim pgs. 836-39 (general info about plant hormone
pathways) pay particular attention to the diagrams for understanding. (You will need this information to
understand Topic 9.4 as well.) Read pgs. 840 (especially first row of table on Auxin) to 845(whole
section on Auxin, cytokinins and gibberellin)
#4 Focusing on pg. 844 first, write a paragraph explaining in your own words how the combination of
auxin and cytokinins may influence Apical Dominance. Outline the evidence that supports direct control.
Why might there be questions about this hypothesis?
9.3.4. #5 Draw the control diagram at the top of Figure 39.5 on pg. 841.This is an example of a tropism.
Leave space for another diagram next to this picture. Draw a carrot pointing to the bending section of
the plant in figure 39.5 and Draw figure 39.7 at the fat end of the carrot. This figure explains Auxin’s
role in the Acid Growth Hypothesis. Where would the longer cell in figure 39.7 (pg. 843) be found on the
bending plant in figure 39.5? Show the location by labeling 39.5. with the elongated cells. Note the role
of proton pumps in the Acid Growth Hypothesis. How is acidity related to protons? Explain how an
increase in acidity could affect the hydrogen bonds holding the cellulose microfibrils together.
9.3.5-#6- Read the 2nd full paragraph on pg. 842. Explain in your own words what the polar transport of
Auxin is. Read Figure 39.6 on page 842. Draw a xylem parenchyma cell (explanation pg.758 top) Show
where auxin transport proteins would be found. Explain how the experiment shown in figure 39.6
worked.
9.3.6-#7-Review the section on auxin (840-843): making a t-chart, in column A list the name of each
protein this hormone activates, requires or suppresses. In column B list the activity of each protein if
known. How do cells make proteins? What must auxin be affecting if it is controlling the expression of
proteins? Using figure 39.4 as a model, substituting auxin for light in the diagram, redraw one possible
pathway for a protein on your t-chart.
9.4 Reproduction in Plants
9.4.1 Flowering involves a change in gene expression in the shoot apex.
9.4.2 The switch in flowering is a response to a change in light and dark periods in many plants.
9.4.3 Success in plant reproduction depends on pollination, fertilization and seed dispersal.
9.4.4 Most flowering plants use symbiotic relationships with pollinators in sexual reproduction.
Before writing read the first half of chapter 38 Angiosperm Reproduction and Biotechnology from pg.
815 to pg. 829, up to the section on totipotency. This will be a good overview of the concepts for this
section.
9.4.1 Now read page 774 and 775 in Chapter 39. First step, translate into your own words what the
proteins called transcription factors do that are switched on during flowering. These are the
products of the floral meristem identity genes. In your paragraph please include where the cells
that contain these genes are found? Next from the text on pg. 816, draw and label a diagram
showing the structure of a dicotyledonous animal-pollinated flower. Limit the diagram to sepal,
petal, anther, filament, stigma, style and ovary. Next to the names on your drawing describe the
function of each flower part.
9.4.2 Explain how flowering is controlled in long-day and short-day plants, including the role of
phytochrome (pg. 850). This specific explanation for day length flowering control can be found
on 852-854. In your explanation talk about Pr and Pfr. How are they different? It will be helpful
to look online for an image of phytochrome. Draw the image of both forms of the molecule
below your paragraph.
9.4.3
Distinguish between pollination, fertilization and seed dispersal. Skim pgs. 821-826
Pollination 635 and 818- List the various types found in the diagram on pg. 820-21
Fertilization pg. 640 and 818-19
Seed Dispersal 826 and Figure 38.12
Then:
Draw and label a diagram showing the internal structure of a dicotyledonous seed. Use the
diagram on page 823. Then depict germination structures either by reproducing the diagram on
pg. 845 or finding one of your own online. The Aleurione layer is shown but the Testa aka seed
coat is omitted on 845. Draw an outer layer on the diagram and label it as the seed coat or testa.
The embryo root is called the radicle in Campbell. Likewise the shoot is aka the epicotyl. The
stem is the hypocotyl. Label all. (the shoot is rising above the radicle). One of the parts of the
seed is the cotyledon. Look up what it does and describe it next to your diagram.
Continued below:
9.4.4 Write a paragraph describing the symbiotic interrelationships between the saguaro cactus and
its pollinators. The flower is depicted on page 821 in figure 38.5. Look online to add more detail. How
many different kinds of pollinators can you find? Use only well-cited source pages online. No citations?
Use those pages as pointer pages. You do not need to cite references as long as you paraphrase. Add a
sentence or two about any seed dispersal symbiosis that you find (name all animals by Genus and
species--scientific name).
Bonus Question from 9.1 Xylem Transport:
Objective 9.1.5 Reread pages 786-788 on mineral ion transport and fungal symbiosis water flow from page 810-811.
Draw figure 36.8 and combine the ideas from this figure with those Mycorrhizae (Fig. 37.13 on page 811). Now read
the Topsoil composition section on page 800 (both inorganic and organic). Add a drawing of figure 37.3 cation
exchange in the soil (including the root hair).