BIOL 002 - Exam 1

Using the four basic features of all homeostatic mechanisms, describe in general terms how your body would respond to an increase in blood sugar after you eat a candy bar.

- sense changes in specific internal and external conditions (stimuli) - communicate messages throughout organism - interpret and integrate messages to determine appropriate response - cause appropriate response if necessary *Your body would sense the increase in blood sugar *Then, the body would calm down/slow the heart rate, which would have increased due to the heightened blood sugar

Thimann and Skoog selected V. fabia (broad beans) for their experiments. What characteristics would make a particular species of plant a good choice for these experiments?

-Able to withstand tough weather circumstances -Have many apical/lateral buds -Strong root systems

Can you conclude from the results obtained by Zhang et al. that ABA in the leaf epidermis causes a plant's stomata to close? Why or why not?

-Increased ABA in dry roots is correlated with increased stomata closure - Experiment does NOT provide direct evidence that ABA causes stomata to close

Describe the role of hormones in homeostasis.

-Systemic Acquired Resistance -Response in changes to water levels -Growth & developmental responses *-ALL of these processes are responses to specific stimuli that allow plants to maintain homeostasis - ALL of these processes require communication signals (hormones)

Applying ABA to leaves...

....closes STOMATA the levels of ABA increase in leaves when their water content falls Closing stomata decreases water loss by evaporation

Scientists hypothesize that a hormone, which they call florigen, is produced in flowering plants and is important for the development of flowers. As we'll discuss later, length of daylight is an important signal for determining when some species of plants flower. In general terms, describe how florigen could promote flower development (i.e. describe the steps involved). What feature must all cells that respond to florigen share? List TWO ways that florigen could alter the behavior of target cells.

1) signal (stimulus) sensed by specific cells 2) causes specific hormone(s) to be produced and released 3) hormone travels throughout plant (via vascular tissue fluid)

Describe the components of the process of science and explain/describe the connections between the components.

1. Make observations 2. Pose question 3. Form hypotheses and predictions 4. Design hypothesis test (experiment) 5. Data collection & Analysis 6. Consult & communicate / Peer Review

PLANT HORMONES & THEIR RELATED PROCESSES 1. Systemic Acquired Resitance & _________________ 2. Drought Stress & ___________________ 3. Apical Dominance & __________________

1. Salicycic Acid 2. Absicic Acid (ABA) 3. Auxin

Select ALL light conditions that would inhibit flowering in a long-day (short-night) plant with a critical period of 12 hours. 14 hours of light, 4 hours of dark, a flash of red light, a flash of far-red light, 6 hours of dark 10 hours of light, 8 hours of dark, a flash of red light, a flash of far-red light, 6 hours of dark 8 hours of light and 16 hours of dark 10 hours of light, 8 hours of dark, a flash of red light, 6 hours of dark

10 hours of light, 8 hours of dark, a flash of red light, a flash of far-red light, 6 hours of dark 8 hours of light and 16 hours of dark Long-day (short-night) plants need fewer consecutive hours of darkness than their critical periods. Therefore, the plant will flower when it is exposed to a continuous period of darkness that is LESS than 12 hours. Red light is sensed as an interruption of darkness. Far-red light reverses the effects of red light.

Which of these light conditions would inhibit flowering in a short-day (long-night) plant with a critical period of 11 hours? 12 hours of light, 6 hours of dark, a flash of red light, a flash of far-red light, 6 hours of dark 12 hours of light, 6 hours of dark, a flash of red light, a flash of far-red light, a flash of red light, a flash of far-red light, 6 hours of dark 12 hours of light, 6 hours of dark, a flash of red light, 6 hours of dark

12 hours of light, 6 hours of dark, a flash of red light, 6 hours of dark Short-day (long-night) plants need more consecutive hours of darkness than their critical periods. Red light is sensed by plants as an interruption of darkness, and therefore shortens the length of the dark period in this light condition. This makes the number of consecutive hours of darkness sensed by the plant LESS than the critical period, so it will not flower. For the other conditions, the far-red light flashes reverse the effects of the red light, so the plant doesn't sense an interruption of darkness.

Select ALL the light conditions under which a long-day (short-night) plant with a critical period of 12 hours would flower 13 hours of light and 11 hours of dark 6 hours of light, 6 hours of dark, 11 hours of light, and 1 hour of dark 4 hours of light, 10 hours of dark, 6 hours of light, 4 hours of dark 11 hours of light and 13 hours of dark 2 hours of light, 14 hours of dark, 2 hours of light, 6 hours of dark

13 hours of light and 11 hours of dark 6 hours of light, 6 hours of dark, 11 hours of light, and 1 hour of dark 4 hours of light, 10 hours of dark, 6 hours of light, 4 hours of dark Long-day (short-night) plants need FEWER consecutive hours of darkness than their critical period. In this question, that means the plant would flower whenever it received fewer than 12 consecutive hours of darkness.

Explain why sample size is important to consider when evaluating/designing experiments. Many experiments involve only small samples. Propose one reason for why a scientist might choose to have a smaller or larger sample

A larger sample size tends to be more representative of a population, because it has a greater # of individuals. A smaller sample size can be easier to control in a lab due to there being less confounding variables, but may have more extreme results due to having a smaller #

List THREE things that affect the response caused in a particular type of target cell by a particular hormone.

A particular type of hormone can have different effects -on the same cell, depending on presence of other hormones -on the same cell, depending on concentration of that hormone -because different cell types have different receptor proteins for a particular hormone

What observations would provide evidence that a particular molecule functions as a signaling molecule to control flowering? (Hint - Think about where and under what conditions the molecule would be observed in a plant.)

An elevated amount of this molecule observed during the critical period of darkness for a flower?

Based on our discussions, write one example that illustrates that a particular plant hormone is involved in multiple processes, and one example that illustrates that most plant processes are controlled by multiple hormones.

An increase in ABA in dry roots its correlated with an increase in stomata exposure -Auxin does not inhibit lateral bud growth entirely (could be due to another hormone that's required)

Based on what you know about hormones, what are two challenges to developing an understanding of plant hormones and the processes in which they are involved?

An individual cell often has multiple types of hormone receptors Overall response depends on combination of hormone signals

Describe how auxin's redistribution (movement) from the lighter to the darker side of a seedling's tip is hypothesized to promote a seedling's growth towards light. Describe at least two other effects light could have on auxin that would cause a plant to grow towards light.

Auxin promotes growth of shoot cells by causing cell elongation = cels on the DARK side of a plant have HIGHER levels of auxin so that the plant bends toward the sun Growth inhibitors accumulate on the LIGHTER side of the seedling tips and move down seedlings to inhibit growth on the lighter side, while auxin distribution is unaffected

Auxin promotes growth of shoot cells by causing cell elongation. Based on this information, it is reasonable to predict that A. cells on the lighter side receive more auxin than cells on the darker side. B. cells on the darker side receive more auxin than cells on the lighter side. C. cellsonthedarkerandlightersidesreceiveequalamounts of auxin.

B. cells on the darker side receive more auxin than cells on the lighter side.

Why does it make sense that plants rely on gravity rather than light to ensure that roots grow downwards and shoots grow upwards

Because roots are underground, so they're not exposed to sunlight ever; also gravity can both effect roots & shoots, when sunlight can only affect shoots

Although a specific molecule has yet to be identified, scientists hypothesize that a hormone, which they call florigen, important for promoting flowering. In general terms, describe how florigen could act as a signaling molecule to promote flowering.

Communication signal (hormone) that "links" phytochrome activity to flowering response

An experiment is designed to test the hypothesis that taking vitamin C decreases the chance a person will catch a cold. The experimental group takes two vitamin C pills in the morning once a day for 10 days. Come up with an appropriate control group for the experiment.

Control: This group takes a placebo pill, or just a regular multivitamin

Explain why identifying a correlation between two things does NOT mean that one thing causes the other. See if you can find a news story that confuses correlation with causation.

Correlation DOES NOT equal causation You need to control the variables in a laboratory setting to see if X really does cause Y, and not just if they appear to be related

Explain the difference between short-day (long-night) and long-day (short-night) plants. Use the term "critical period" in your explanation.

Critical period: number of consecutive hours of darkness that determines flowering for a particular species - short-day (long-night) plants = MINIMUM # of hours (flower when length of DARKNESS is MORE than a certain # of hours) - long-day (short-night) plants = MAXIMUM # of hours (flower when length of DARKNESS is LESS than a certain # of hours) The number of consecutive hours of DARKNESS determines when short-day and long-day plants flower

Can you conclude from the results obtained by Zhang et al. that cells in dry roots produce more ABA than cells in wet roots? Why or why not?

Drying of roots leads to increased levels of ABA in the roots. It's CORRELATED, not directly producing.

Explain why Went included a group of decapitated seedlings with agar blocks that had been exposed to tips but left in the dark AND a group that received plain (untreated) agar blocks

Exposed to tips but left in dark = shows that the agar block & tips needed the light to function properly Plain agar blocks = different from treated agar blocks; shows that the agar itself is not affecting the plant direction

Current understanding of auxin

Growth substance isolated and identified as auxin - promotes growth by causing cell elongation auxin makes plant cell walls weaken in specific areas, which allows cells to swell with water and get longer -does NOT inhibit lateral bud growth in some plant species -data suggests does NOT enter or interact with cells of lateral buds

There's a _______________ concentration of auxin in cells of the lower portions of roots

HIGHER Why? Roots need to keep growing & spreading throughout the soil *Auxin INHIBITS growth of root cells but PROMOTES growth of shoot cells (ex. of how hormones can cause different responses in different types of cells)

Review the experiment performed by Zhang et al. to assess the effects of dry roots on ABA levels and stomata closure. Using a similar experiment, how could you assess the hypothesis that the amount of water received by the roots is directly related to the amount of ABA levels in roots (i.e. the less water a plant's roots get, the less ABA is present in the roots).

Have 10 plants (5 with no water, 5 with water). Measure the levels of ABA in the roots at the start to establish a baseline. Water (or not) periodically for 2 weeks. Then, measure the levels of ABA in the roots following the 2 week period and see if there has been any changes.

Write your own description/explanation of homeostasis.

Homeostasis: ability of an organism to keep internal conditions within a specific range - required for proper functioning of ALL organisms -dynamic process - internal conditions are NOT held constant Homeostatic mechanisms vary between organisms, but they do share a set of common features - sense changes in specific internal and external conditions (stimuli) - communicate messages throughout organism - interpret and integrate messages to determine appropriate response - cause appropriate response if necessary

The leaves of certain plant species fold up at night and then reopen at dawn. Explain why this is NOT an example of phototropism.

In cool air and darkness, the bottom-most petals of certain flowers grow at a faster rate than the upper-most petals, forcing the flowers shut.

Why is indeterminate growth beneficial for plants? Explain why indeterminate growth is NOT important for animals.

Indeterminate growth allows stationary organisms to respond to environmental changes throughout their lifetime (e.g. sudden increase in sunlight) Humans can easily pick up & move when they are threatened by a predator, so they do not need unlimited growth

Plants have well-developed induced defenses that allow them to defend against pathogen and herbivore attacks. In addition, plants have permanent defenses (e.g. thorns, toxins) that are always present. Which of the following explains a benefit of permanent defenses over induced defenses?

Induced defenses take time to initiate while permanent defenses are quicker Induced defenses are more specific than permanent defenses because they have evolved as specific responses triggered by particular pathogens. Permanent defenses are maintained in both the presence and absence of pathogens, and thus require more energy and resources than induced defenses. As illustrated by the experiments we discussed in class relating to systemic acquired resistance (SAR), induced defenses can provide "plant-wide" protection. Permanent defenses are beneficial because they are always present, and therefore offer immediate protection for a plant.

In addition to auxin, there is a substantial amount of evidence that indicates the hormone cytokinin is involved in apical dominance. Auxin produced by the tips of growing shoots inhibits lateral bud growth (directly or indirectly), while cytokinin has been shown to promote lateral bud growth. Which of the following would explain why it is beneficial for plants to have hormones that cause the opposite effect (inhibit vs. promote) on the same process?

It allows processes to be more finely tuned because the overall response depends on the relative amounts of each hormone present.

Using the four basic features of all homeostatic mechanisms, describe in general terms how a plant could respond to the placement of a barrier that prevents one side of a plant from receiving light.

It would move the bud to turn toward the light!

Although many studies indicate auxin inhibits lateral bud growth, there is also evidence to suggest auxin does NOT reach lateral bud cells. Results of recent analysis suggest that a hormone called strigolactone acts as a "second messenger" in apical dominance by directly inhibiting lateral bud growth in response to auxin. What observation would support this hypothesis?

Lateral bud growth is observed in plants that are able to produce auxin, but not strigoractone If strigolactone acts as a "second messenger" to inhibit lateral bud growth in response to auxin, then in the absence of strigolactone, auxin could not inhibit lateral bud growth.

MB #2: Salicylic acid is one of the hormones proposed to be important for systemic acquired resistance (SAR). Which of the following observations, if any, would suggest that salicylic acid is an important signaling molecule for SAR in response to infection by tobacco mosaic virus (TMV)?

Levels of salicylic acid increase in the vascular tissue fluid of a plant when a single leaf is infected with TMV. For salicylic acid to act as a signaling molecule and help promote whole-plant resistance in response to infection by TMV, it must be transmitted throughout the entire plant. As we discussed in class, molecules are transported in the fluid in a plant's vascular tissue. Observations of what occurs in response to other types of viruses cannot be directly applied to TMV. SAR is specific, it provides resistance against subsequent infection by the same pathogen. Simply observing increased resistance in upper leaves does not provide direct support that salicylic acid is important. If salicylic acid was only present in the infected leaves of a plant, there would be nothing to suggest that it is able to signal to other parts of the plant and cause changes that promote resistance to TMV.

Come up with at least two observations that would support the hypothesis: ABA produced by dry roots is transported to leaves where it causes stomata to close.

Measure the amount of ABA in the roots and see if the corresponding rate of water (stomata opening/closing) changes based on if the roots were watered/dried.

Of the results of an experiment do not support the hypothesis, does that mean that there was something wrong with the experiment?

No, it just means that the hypothesis was refuted; or, it could have been a "fluke" trial, and if repeated, different results could arise.

You set up a study to test the hypothesis a new herbal supplement decreases the duration of a cold. After you recruit volunteers, should you let them choose whether they want to be in the control or supplement group? Why or why not?

No; a blinded study ensures that biases will not interfere with the outcomes of the study, so the participants shouldn't know if they're receiving the condition or not

Describe the main ways in which plants respond to external stimuli.

Photoperiodism = developmental response due to changes in relative lengths of day & night (ex. sprouting/blossoming) Tropisms = GROWTH responses that promote growth toward/away from a specific stimulus (ex. toward light, gravity, etc.

In what basic way(s) are photoperiodism and phototropism similar? What makes them different?

Photoperiodism = developmental response due to changes in relative lengths of day & night (ex. sprouting/blossoming) Phototropism = growth due to light -Both responding to stimuli (photoperiodism = length of darkness; phototropism = light)

In broad terms, explain the difference between photoperiodism and tropisms. In what ways are they similar?

Photoperiodism = response to DEVELOPMENT via lengths of day and night Tropism = responses to GROWTH

Describe the role of phytochromes in photoperiodism

Phytochromes - a type of photoreceptor (molecule that absorbs and responds to specific wavelengths of light) The amounts of inactive vs. active phytochrome allow plants to measure the photoperiod. (Night = high INACTIVE phytochrome; Day = high ACTIVE phytochrome)

Explain why maintaining homeostasis is essential for all organisms.

Plants AND animals are multicellular organisms - require mechanisms that allow communication between cells throughout an individual (e.g. hormones)

Explain why it is NOT appropriate to state that tropisms involve plants bending towards or away from a stimulus.

Plants do not "bend"; they have uneven levels of cell growth (more on one side, so that's why it looks like it's bending)

Explain how the current hypothesis, that auxin levels increase in cells in the lower part of a root or shoot, can explain both positive root gravitropism AND negative shoot gravitropism.

Positive Root Gravitropism - roots grow upward (need to keep growing/spreading throughout the soil) Negative Shoot Gravitropism - shoots grow down

induced defenses in plants...

defenses triggered when a plant is infected or attacked by a particular pathogen/herbivore (specific) - two categories -local = only acts at site of infection -systemic = response occurs in multiple parts of a plant *SYSTEMIC AQUIRED RESISTANCE (SAR) with tobacco mosaic virus

Why is it important that a certain type of hormone receptor interacts with only ONE (or a few related) hormones? What is the benefit of a particular type of hormone being able to interact with multiple types of receptors?

Receptor proteins are specific - ONLY interact with ONE type of hormone (this increases efficiency/ensures that the reaction is completed)

You performed an experiment to test the effectiveness of a new type of fertilizer. Plants treated with the fertilizer grew, on average, 25% taller compared to plants that were not given fertilizer. What do you need to do in order to interpret your results and draw conclusions?

Repeat the study, and if you get the same results over and over again, it means that the findings are probably valid. Also, submit them for peer review.

Review your notes and the lecture slides from our overview of plant structure and growth.

Roots = take up water & nutrients from the soil Leaves = absorb light energy Stomata = leaf pores/allow CO2 in, and O2 out Vascular Tissue = tubing system that goes throughout a plant; allows transport of water, nutrients, signaling molecules and other types of molecules Indeterminate Growth = open-ended growth that can be lifelong (plant shoots and roots) Determinate Growth = growth that stops when adult state is reached (ex. humans) Length-wise Growth = occurs only at tips of shoots and roots

In your own words, explain why it is important for plants' roots AND shoots to sense and respond to gravity.

Roots need to grow further into the soil to obtain more nutrients Shoots need to grow upward to be closer to the sun/obtain more sunlight this movement is sensed and relayed to cells that secrete the growth-regulating plant hormone auxin on the new undersides of root and shoot. The hormone has opposite effects in the two locations, triggering growth suppression on the underside of roots and growth enhancement on the underside of shoots. As a result, roots veer earthward; shoots veer skyward.

Gravitropism in Roots and Shoots

Roots: - auxin inhibits cell growth - lower cells don't grow - overall growth of root is downwards -POSITIVE GRAVITROPISM Shoots: - auxin promotes cell growth - lower cells grow MORE - overall growth of shoot is upwards -NEGATIVE GRAVITROPISM

Based on what we've discussed and what you know about animals (e.g. humans) start to make lists of ways in which plant and animal homeostatic mechanisms are similar, and ways in which they differ. Revise and add to your lists as we continue our discussions of plant and animal homeostasis.

Similar: -Both involve oxygen and water Different: -Humans can pick up & move when they are threatened, but plants can't -Plants have indeterminate growth (unlimited), but humans have determinate (fixed)

Propose ONE observation that could support the current hypothesis for root gravitropism and ONE observation that would refute the hypothesis.

Support = Refute =

For the three plant processes and hormones we discussed, list the stimulus, the hormone, and the response. Review the three experiments we went through and, for each one, explain why the results do NOT allow you to draw the conclusion that the hormone acts as a signaling molecule. Which experiment(s), if any, provide direct support for the role of a particular hormone? Explain your answer.

Systemic Acquired Resistance = Salicylic Acid *Tobacco Mosaic Virus Abscisic Acid = Drought Stress *ABA = involved in seed dormancy; closing stomata decreases water loss by evaporation (applying ABA to leaves closes stomata = levels of ABA increase in leaves when leaf water content goes down) Auxin = Apical Dominance

Why is it important to test hypotheses multiple times in the same way and in multiple ways?

Testing something multiple times ensures it's validity; if the hypothesis is proven once, it may have been due to a "fluke" in the experiment, so more testing is needed to produce a more reliable result

Why can't some questions be answered scientifically? Come up with a hypothesis that CANNOT be assessed scientifically. Is there a hypothesis you can design based on the same question that could be assessed scientifically?

The goal of science is to explain/describe the natural world, and questioning "morals/aesthetics/beliefs/the supernatural" cannot be described or evaluated through an experiment

What does it mean that hypotheses must be "testable"? Come up with a testable hypothesis to address the question: What causes wind to blow in a specific direction?

The issue has to be MEASURABLE; a hypothesis has to be able to be supported or refuted

Hormones! what they do!

The overall response of a cell to hormone signals depends on the combination of signals it receives. The presence of hormones that have opposite effects on the same process, allows the process to be more finely tuned (i.e. the overall response is a balance between the two signals). A hormone that causes the opposite response would NOT be an appropriate "back up." Each hormone can contribute to the response of the plant, but the presence of one hormone is not required for cells to respond to the other hormone. A small amount of a single hormone alone can cause a significant response in a cell.

Every experiment has limits. Identify one limit in the study we discussed. How could you modify the experiment to address that particular limit?

The sample size of the chocolate experiment was 116, which is somewhat small. Therefore, the researchers should have recruited a larger group or participants.

Explain why it is NOT possible to conclude from Thimann and Skoog's experiments that there are specific molecule(s) produced in the tips of plants that are capable of both promoting apical bud growth and inhibiting lateral bud growth.

There has been some conflicting research that auxin does NOT inhibit lateral bud growth in some plant species -Also it does NOT enter the cells of lateral buds (so, there may be a second messenger/different horn that's involved in inhibition of lateral bud growth by auxin

Explain why an experiment CANNOT definitely prove that a hypothesis is true.

There may be some other variables that the researcher is unaware of that could affect the hypothesis.

Explain why it was important that Zhang et al. measured the levels of ABA in the roots on both sides (dry and wet) of experimental plants (i.e. why couldn't they simply have compared the ABA levels in the roots on the dry side of experimental plants to the control plants' roots?).

This compares whether there was a difference between dry/wet roots within ONE plant, rather than across/between two different plant groups.

Review the analyses performed by Thimann and Skoog that assessed the role of auxin in apical dominance. Why was it important to determine the length of time it took for all of the growth substance to be transferred from an agar block to a plant before performing their experiment?

To ensure that the plant actually absorbed the growth substance (auxin) from the block, rather than the block just "sitting there" on the plant.

What is the role of peer review in the scientific process?

To establish validity of results & to eliminate any potential biases of the original investigator from the results

In their experiment, Thimann and Skoog used two control groups - untreated intact plants and decapitated plants with plain agar blocks. Explain why BOTH control groups were important.

Untreated intact plants showed "normal" levels of auxin hormones since there was no blocks to interfere with Decapitated plants with plain agar blocks are not being treated with any plant substances which have growth-promoting factors in them These groups both establish baselines for normal/uninhibited growth for comparison

Explain how plants obtain the water, light energy, and carbon dioxide required for photosynthesis, the process by which plants generate food (sugars) using the energy of light.

Water - transported by vascular tissue Light Energy CO2 - stomata (leaf pores) allow carbon dioxide in

How could you assess the hypothesis that different amounts (concentrations) of auxin have different effects on apical bud growth? How could you assess the hypothesis that auxin has different effects on roots compared to shoots?

You could measure the length of apical bud growth with differing concentrations of auxin on plants. Ex. One plant has 1 mg of auxin, another has 5 mg, another has 10 mg; then measure the lengths of apical buds after one week of steady dosages

Why is it important that only a small amount of hormone is required to produce a significant response in target cells?

You wouldn't want to use an unnecessary amount of hormones on one interaction when you really needed only a few (efficiency)

Why is apical dominance beneficial for plants?

apical dominance: presence of apical bud inhibits lateral bud growth -helps the plant grow toward the sun!!

The length of a critical period does NOT...

determine whether a plant is a short-day or long-day plant Response is to min/max # of hours of consecutive darkness

Explain why, if you put a nail in the trunk of a tree, the height of the nail above the ground won't change even as the tree gets taller.

length-wise growth occurs only at tips of shoots and roots (so, the growth is occurring below the surface, and is pushing the tree UPWARDS)

For a long-day (short-night) plant, the _____ is important for determining if flowering will occur.

maximum number of hours of darkness Long-day (short-night) plants require LESS than a certain number of consecutive hours of darkness. Therefore, the critical period is the maximum number of hours.

For a short-day (long-night) plant, the _____ is important for determining if flowering will occur.

minimum consecutive hours of darkness Short-day (long-night)) plants require MORE than a certain number of consecutive hours of darkness. Therefore, the critical period is the minimum number of hours.

Evidence suggests that roots of at least some plant species have a phototropic response (i.e. grow directionally in response to light), and that directional growth is due to a redistribution of auxin. Based on what you know about plants and the role of auxin in root gravitropism, it is reasonable to predict that roots show _______ phototropism and auxin is redistributed to the ___________ side of roots.

negative; darker In gravitropism, redistribution of auxin to the lower portion of a root inhibits growth of the root cells in the lower portion. This causes the root to grow so it curves downwards. Roots need to grow down into the soil to obtain water, so roots should display negative phototropism and grow away from light. Since auxin inhibits growth of root cells, auxin should be redistributed to the darker side of roots to cause them to grow away from light.

For many plant species, the current hypothesis is that auxin redistribution to the lower portion of a plant is important for gravitropism of both roots and shoots. The fact that movement of auxin to the lower part of a shoot results in negative gravitropism, while accumulation of auxin at the bottom of a root leads to positive gravitropism illustrates the fact that: different concentrations of a hormone can cause different responses in the same cell. one particular hormone can cause different responses in different types of cells. a small amount of a hormone results in a significant response in a cell.

one particular hormone can cause different responses in different types of cells. Root cells and shoot cells respond differently to auxin. Auxin inhibits root cell growth, promoting downwards growth of roots (positive gravitropism). Auxin promotes shoot cell elongation, causing upwards growth of shoots (negative gravitropism).

length-wise growth in plants occurs...

only at tips of shoots and roots!

MB: In addition to auxin, the hormone cytokinin has been shown to play a role in apical dominance in many plant species. Unlike auxin, cytokinin promotes lateral bud growth. This information illustrates the fact that

plant processes are most often controlled by multiple hormones!

Describe the function of stomata and explain why an ability to regulate opening and closing of stomata is important for plants

stomata (leaf pores) allow carbon dioxide in and oxygen and water out -stomata help a plant during a drought!

Far-red light can reverse the effects of red light, therefore...

these plants MUST be able to sense far-red light.

Describe the function of vascular tissue.

vascular tissue: - tubing system that goes throughout a plant - allows transport of water, nutrients, signaling molecules, and other types of molecules