Biology exam 1 class questions

Scientists hypothesize that a hormone, currently called florigen, is produced in flowering plants and is important for the development of flowers in response to changes in relative length of day (sunlight) vs. night (darkness). In general terms, describe the steps required for florigen (or any hormone) to promote flower development. What feature must all cells that respond to florigen share? List two ways that florigen could alter the behavior of target cells.o

-Florigen (or flowering hormone) is the hypothesized hormone-like molecule responsible for controlling and/or triggering flowering in plants.-Florigen is produced in the leaves, and acts in the shoot apical meristem of buds and growing tips. It is known to be graft-transmissible, and even functions between species.1) signal (stimulus) sensed by specific cells2) causes specific hormone(s) to be produced and released3) hormone travels throughout plant (via vascular tissue fluid). Increase or decrease of molecule present changing activity of molecule changing how it goes

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 flowe

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 increased on the dark side of the plant to promote the seeding's growth toward light. ***

A short-day (long-night) plant and a long-day (short-night) plant both have critical periods of 10 hours. Describe conditions (light/dark cycles) under which ONLY the short-day plant would flower and conditions under which ONLY the long-day plant would flower. Are there conditions under which BOTH would flower? Assume that you are limited to one "chunk" of light and one "chunk" of darkness per 24 hr. cycle.

Both cannot flower at the same time because we are unable to interrupt the hours of darkness and light. For the long day and short night plant, I can give the plant 15 hours of day and 9 hours of darkness. For the short day and long night plant, I can give the plant 15 hours of darkness and 9 hours of light.

Explain why you CANNOT conclude from the results that ABA produced by dry roots is transported to leaves where it causes stomata to close.

Experiment does NOT provide direct evidence that ABA causes stomata to close. Because correlation does not equal causation. They did not directly record the transport of ABA from roots to leaves

Review the experiments carried out by Went that assessed the effects of placing agar blocks, treated in various ways, on the growth of tipless seedlings. Why was it important that the seedlings used were germinated in the dark and kept in the dark for the whole experiment? ... 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

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

Shoots show negative gravitropism because they respond to gravity to obtain sunlight while roots show positive gravitropism because they need to grow downward to get water and nutrients.

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. because correlations are relationships between two variables, nit all factors are accounted for.

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

Florigen could be triggered by phytochromes that make a hormone get distributed in the plant and cause it to flower.

Review the experiment we discussed that assessed the effects of dry roots on ABA levels and stomata closure. Using a similar experiment, how could you test 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.

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.

Explain why it was important to measure 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?).

It prevented the plant from drying out

Come up with at least two observations that would support the hypothesis that 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.

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.

Movement of statoliths to the bottom of root tip cells in response to gravity causes auxin to be transported to cells at the bottom of the root, promoting downward growth. It's reasonable to predict that higher amounts of auxin inhibit root cell growth

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

you cannot consecutively prove that a hypothesis is true because it is generally impossible to examine all possible outcomes and account for all relevant variables

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)

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)

You're studying a species of flowering plant found in many different regions of the world. You collect information on the time of year the plant flowers in Burlington, VT and Sydney, Australia (where winter begins in June). What data would support the hypothesis that it is a short-day (long-night) plant? A long-day (shortnight) plant? A day-neutral plant?

Plants of the same type that are planted at different times in the same location often flower at the same timeShort day (long night) - only flower when consecutive darkness hours for longer than critical periodLong day (short night) - only flower when consecutive darkness hours are shorter than critical periodDay-neutral - flower at any pointMoving plants to a different region can change when they flower

A short-day (long-night) plant and a long-day (short-night) plant both have critical periods of 10 hours. Describe conditions (light/dark cycles) under which ONLY the short-day plant would flower and conditions under which ONLY the long-day plant would flower. Are there conditions under which BOTH would flower? Assume that you are limited to one "chunk" of light and one "chunk" of darkness per 24 hr. cycle.

Short-day (long-night plants) need a minimum of 10 hours of consecutive darkness to flower, while long-day (short-night) plants need a maximum of 10 hours consecutive darknessOnly the short-day (long-night) flowers: 8 hours light, 12 hours of darkOnly the long-day (short-night) flowers: 12 hours light, 8 hours of darkBoth flowers: 10 hours of light and 10 hours of dark

Review the experiment related to apical dominance we discussed in a previous class that tested the hypothesis that a "growth substance" produced by the tip of a plant inhibits lateral bud growth. How is it similar to the experiment we discussed last class assessing phototropism (the one where agar blocks treated in different ways were placed in different positions on decapitated seedlings)? How are the analyses different? For each experiment, what did they measure? Can you conclude from either experiment that auxin is responsible for the observed results? Why or why not?

Similar experiment because both assessed hormones in the tips of seedlings that affect growth (apical dominance: assessed lateral growth. The other experiment assessed growth towards light)Analysis different: phototropism has multiple valid hypotheses while the apical dominance accepted the hypothesis. Apical dominance measured: lateral bud length. Phototropism measured: auxin levels cannot conclude that auxin is is responsible because many molecules were collected from the tip onto the agar block

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

The current hypothesis for root gravitropism is that roots must grow down to obtain water and nutrients from soil Support observation: roots of seeds grow downward regardless of seed orientation Refute observation: removing the tip prevents downward growth (not just gravitropism but tip also important)

Evidence suggests that roots of some plant species have a phototropic response (i.e. grow directionally in response to light). Do you predict that the roots show positive or negative phototropism? Is it reasonable to predict that the current hypothesis for shoot phototropism, which says that auxin is redistributed to the darker side of a shoot, could also be proposed for roots? Explain your answer.

The roots show positive phototropism. Roots need to grow down into the soil to obtain water, so roots should display positive 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

A researcher plants individual seeds of a certain plant species in pots and divides the pots into two groups. One group is subjected to photoperiods of 12 hours of light and 12 hours of dark. The other group is subjected to the same photoperiods, but the 12 hours of dark is interrupted each day with a flash of red light. All other conditions for the two groups are identical. Both groups flower at the same time. Based on these results, can you conclusively classify the plant species as short-day (long-night), long-day (short-night), or day-neutral? If so, how would you classify it? If not, can you eliminate any of the three possibilities? Explain your answers.

The species are day neutral since the critical period is not given. If the plants were short day long night plants, they would have been screwed up by the flash of light which would prevented them from flowering. However since they are the same species and a neutral plant it does not matter if it gets darkness or light, it will flower either way.

You performed an experiment to test the effectiveness of a new type of fertilizer. Plants treated with the fertilizer grew and average of 2.7 inches taller compared to plants that were not given fertilizer. What do you need to do in order to properly interpret your results and draw conclusions?

compare the data by making a chart or table so that the patterns are more easily recognizable

Orchids are short-day (long-night) plants with a critical period of 9 hours. A florist is growing orchids in a greenhouse using a light cycle that promotes flowering. One night around midnight, the florist, who lives next door to their shop, hears a noise in the greenhouse. The florist rushes over and turns on the light to check things out. The noise turns out to be a stack of pots that fell off a shelf. The florist picks up the pots, turns off the light and goes back to bed. Should the florist be concerned that the orchids might not flower? Why or why not?

Yes. Short-day flowers are very sensitive to light and their "cycle" will now change so they didn't receive enough darkness to bloom

A researcher plants individual seeds of a certain plant species in pots and divides the pots into two groups. One group is subjected to photoperiods of 12 hours of light and 12 hours of dark. The other group is subjected to the same photoperiods, but the 12 hours of dark is interrupted each day with a flash of red light. All other conditions for the two groups are identical. Both groups flower at the same time. Based on these results, can you conclusively classify the plant species as short-day (long-night), long-day (short-night), or day-neutral? If so, how would you classify it? If not, can you eliminate any of the three possibilities? Explain your answers.

You can conclude this is a long-day (short-night) because the consecutive hours dark now short enough to flower

A plant whose flowering is controlled by the photoperiod does NOT flower when it is exposed to photoperiods of 8 hours of light and 16 hours of darkness. You expose the plant to photoperiods of 12 hours of light and 12 hours of darkness and observe that it does NOT flower. From these observations, can you determine whether the plant is a short-day (long-night) plant or a long-day (short-night) plant? Explain your answer.

You can determine the plant is a long-day (short-night) because it needs more hours of sunlight to flower

why is apical dominance beneficial for plants?

apical dominance is beneficial for plants because it helps them grow to better the photosynthesis process

Explain why maintaining homeostasis is essential for all organisms.

because the range of internal conditions is necessary for growth and function. many enzymes can only function in a certain pH range. The plant's pH must match the enzyme's to work

Review the analyses we discussed the role of auxin in apical dominance. In their experiment, the researchers included two control groups- untreated intact plants and decapitated plants with plain agar blocks. Explain why BOTH groups were important. why did they include treated plants?

both were important for comparing lateral bud growth under normal conditions, when tips are removed, and how the agar affected lateral bud growth

Come up with at least two reasons learning what others have found related to a question is valuable/important prior to developing a specific hypothesis and designing an experiment to assess it.

building off others allows people to have a clearer picture in making a testable hypotheses and steps to test. having knowledge will allow you to better account for lurking variables

An experiment is designed to test the hypothesis that taking chilling cookie dough in the refrigerator overnight prior to baking increases the thickness (height) of cookies and reduces the diameter (spread). Come up with an appropriate control condition for the experiment.

having cookie dough at room temp

Write your own description/explanation of homeostasis.

homeostasis is an organism's ability to regulate and maintain consistent internal and external conditions

Describe the role of hormones in homeostasis.

hormones are chemical messengers important for long distance communication. They work to tell the body to adjust to adapt to stimuli

In addition to salicylic acid, evidence suggests that other hormones are involved in SAR. Come up with at least one observation that would support the role of a particular hormone in SAR in response to TMV infection, and at least one observation that would suggest the hormone was not important for SAR in response to TMV infection.

important because protection from subsequent inflections. less damage from toxicant from more interacts 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.

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.

increase in blood sugar sense that candy bar was consumed communicate to pancreas to secrete insulin insulin travels through body insulin is detected blood sugar decreases

Define/describe systemic acquired resistance (SAR) and explain why SAR is categorized as an induced defense mechanism.

increased resistance of whole plant to inflection. must be in center with pathogen to activate

Why is indeterminate growth beneficial for plants? Explain why indeterminate growth is less important for animals.

it allows stationary organisms to respond to stimuli throughout the lifespan. animals cannot readily grow at any point as a means of adapting to environmental change

Explain why it is not possible to conclude from the experiment we discussed that there are specific molecules produced in the tips of plants that are capable of both promoting apical bud growth and inhibiting lateral bud growth

it was not tested. no molecules were taken into consideration for the experiment

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

light doesn't reach the roots

Make an observation and/or consider a question you have about the world and write an appropriate a hypothesis (i.e. phrased as a statement; testable). Generate a prediction and try to design an experiment (or at least an idea of what you'd do) to test it. What data would support your hypothesis? Refute it?

natural sun lighting causes less headaches than artificial lighting. have a group for sun and a group for artificial lighting. have them eat a snack and read for 1 hour in the room. artificial lighting will cause more headaches. compare people's symptoms immediately when they leave the room

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

no. hypotheses are educated guesses so the outcome may be different from what is expected

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

obtain light and co2 from leaves co2 turns to o2

List THREE things that affect the response in a target cell when a particular hormone interacts with its receptor.

other hormone signals, concentration, number of receptors

Explain the difference between permanent defenses and induced defenses in plants. Come up with at least one benefit and one "down side" to each type of defense mechanism. What would be a benefit of local vs. systemic induced defenses? Of systemic vs. local induced defenses?

permanent: present at all times induced: triggered when a plant is influenced or attacked present benefit: always ready for potential threat con: not specific towards certain stimuli Local benefit: all resources being put to one part of plant con: do not protect the entire plant systemic: protects the whole plant if effective con: may not have enough resources to be effective

Describe the role of phytochromes in photoperiodism.

phytochromes are photoreceptors that allow a plant to sense light and respond accordingly.

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.

plants only grow longer at the tips of shoots and roots. The trunk does not grow, so the nail stays at the same height

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

record auront levels separately in roots and shoots and compare to growth. use the agar blocks to measure auxin concentration and compare to apical bud growth.

You discover a new molecule that you hypothesize acts as a hormone. Come up with THREE observations that would support your hypothesis. Hint: Think about the key characteristics of hormones.

released in response to stimuli travel throughout entire body/plant causes changes in target cells

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

short-day (long night) - only flower when the consecutive hours of darkness are more than the critical periodLong-day (short-night) - only flower when the consecutive hours of darkness are less than the critical period

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 respond to stimuli, externally and internally with the same four steps. both rely on hormones. both have a range of normality. differencesL plants cannot move, animals can. animals have fixed growth, plants do not

Explain why sample size is important to consider when evaluating/designing experiments.

smaller sample sizes are more prone to variation and confounding variables

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

so that the response can happen more immediately

Review the analysis we discussed that assessed the effects of TMV infection in one part of a plant on resistance to TMV in other parts of the plant. Explain why it was important to have some plants where the lower leaves were infected first and the upper leaves second, and some where the upper leaves were infected first and the lower leaves second.

so that we know the order does not have an impact on the plant's infection

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?

some questions can not be tested. ex: aliens are the primary inhabitants on the moon. there is life on the moon can be tested by satellite

Why is it important that a certain type of hormone receptor interacts with only ONE type of hormone? What's the benefit of a particular type of hormone being able to interact with receptors present on different cell types?

the same hormone can have different affects on different receptor sites. one receptor must interact with one hormone to produce the correct response. different responses for different types of cells

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

the stomata is also known as leaf pores. they allow co2 in and H2O and O2 out. when the stomata is deflated, it is closed. when it is inflated, it is open. It is important because it allows plants to regulate the flow or concentrations of various substances in and out of the cells

Some species of single-celled organisms live in hot springs where the temperatures are close to boiling. Other single-celled organisms live in ice. Do you think that the internal temperature ranges each of these species must maintain to survive are the same? Why or why not?

they are different. the external conditions between the two vary greatly. so it is expected that the internal range of temp is quite different from each other

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

to gather more support. variations in the experiment can reveal more information that can support or disprove the hypothesis. Different experiment processes can reveal lurking variables

Describe the function of vascular tissue.

vascular tissues is a plant transportation system. it transports nutrients, water, signaling molecules, and other molecules.

What does it mean that hypotheses must be "testable"? Come up with a testable hypothesis to address the question: What causes plants to grow towards light?

you must be able to design an experiment that can gather data to support or disprove a hypothesis. A higher concentration of auxin causes plants to grow towards light. You can test hormone levels in plants and compare growth patterns