BIOL 002 Exam 1
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?
A scientific hypothesis must be testable, meaning measurable or observable. Science cannot answer questions of morality, beliefs or aesthetics. Testable hypothesis: Plants grow towards light because they require sunlight for "food" (to continue photosynthesis).
An experiment is designed to test the hypothesis that 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.
A control condition is one that experimental conditions are compared to. So for this experiment, a control condition would be cookies that did not chill in the fridge overnight before being baked.
Explain why sample size is important to consider when evaluating/designing experiments.
Bigger sample size means the results are more likely to be accurately representative of the "truth" in the population.
You performed an experiment to test the effectiveness of a new type of fertilizer. Plants treated with the fertilizer grew an 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?
Analyze the data using statistical analyses. Look at the p-value given from the statistical analysis. If the p-value is low, then there is a low possibility that your data shows results due to random chance. If the p-value is high, there is a high possibility that results were due to random chance. So, using the p-value to interpret the results, you can draw conclusions accordingly.
Why is apical dominance beneficial for plants?
Apical dominance means that the presence of apical buds inhibits the growth of lateral buds. It is beneficial for plants because buds are able to grow closer to the sun, increasing access to sunlight required for photosynthesis.
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 (i.e. photoperiod) that promotes flowering. One night at midnight, the florist, who lives next 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?
As we discussed in the analysis in class, short day plants may not flower if they receive interrupted darkness. So, turning on the lights at midnight, and then the sun rising a few hours later most likely did not allow for the orchids to receive their 9 uninterrupted hours needed for flowering (critical period).
Why does it make sense that plants rely on gravity rather than light to ensure that roots grow downwards and shoots grow upwards?
Auxin in bottom of roots due to gravity inhibits growth of bottom of root, so top of root grows and turns root growth downward to collect water and nutrients from soil Auxin in the Shoots is at the bottom of the shoot due to gravity and auxin promotes shoot growth, so shoots grow upwards. Plants also grow away from the roots, so the plant knows where "up" is due to gravity
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 in shoot cells promotes cell growth. So, the plant transports more auxin to the darker side, leaving less auxin than the side facing the light. When more auxin is abundant on the darker side, the cells grow, allowing the plant to bend towards the light. Other hypotheses are 1. that sunlight inactivates auxin on the side of the plant closer to the light, so auxin only causes growth on the darker side 2. Growth inhibitors accumulate on the lighter side of seedling tips and move down, inhibiting growth on the lighter side. Auxin distribution is unaffected.
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?).
Because by comparing both sides of the experimental plant roots, there are fewer differences between the roots because it is the same plant. Therefore there are the fewest other factors that could impact results.
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.
Both plants and animals: require homeostatic mechanisms to send messages between cells - Maintaining internal conditions Plant Homeostasis: - plants cannot move, so they need mechanisms to keep them safe from predators - Plants have mechanisms that allow them to grow in flexible patterns to approach sunlight or nutrients - Indeterminate growth - Receptors, cells hormones used are different (Ex: plants have auxin) - Plants dont have central nervous system Animal Homeostasis: - Animals can move, so they need mechanisms that allow them to flee from harm - Determinate growth - Receptors, cells hormones used are different (Ex: animals have insulin) - Animals have central nervous system -- Our central nervous system senses our touching/ surroundings and sends signals to brain and parts of body
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 assessing phototropism 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?
Both used agar blocks with a growth molecule on top of decapitated plants to observe growth patterns Apical dominance: tip cut off lead to lateral bud growth, agar block with tip molecules allowed the decapitated plant to grow tall. Meaning apical bud growth requires a certain growth molecule in the tip. Phototropism: if the agar block exposed to light is right above the decapitated plant, plant will grow straight up, but if the block exposed to light is placed on top to the side, the plant will grow bent. We cannot conclude with certainty that auxin is responsible for the observed results because we do not have measurements of auxin content in each plant. These experiments more so tested the impacts of a hypothetical tip molecule or light exposure. We believe that light exposure leads to movement of auxin in the plant but we cannot make a causal conclusion.
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 mean causation because correlation simply states that two things are true, but does not guarantee that both things are caused for the same reason. (example from class: a study noted that more chocolate consumed in a specific country was correlated to an increase in number of nobel prize winners. If causation was claimed, then that means we just need to eat more chocolate to win the nobel prize. Soooo correlation is not causation)
Propose ONE observation that could support the current hypothesis for root gravitropism and ONE observation that would refute the hypothesis.
Current hypothesis: statoliths settle at the bottom of root tip and shoot cells in response to gravity, causing auxin to be transported to cells at bottom of root/shoot. For roots, auxin inhibits cell growth at the bottom of the root, so the plant is forced to grow downwards. Observation that supports: auxin levels are more concentrated at the bottom of root tip and the tip grows downwards Observation that refutes: auxin levels are more concentrated at the bottom of root tip and the tip grows out sideways or upwards
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.
First, the hormone must locate a receptor protein on a target cell (target cells have the corresponding receptor proteins) of the plant. All cells that respond to florigen must share this receptor protein that can interact with the specific hormone. Once attached to the specific receptor protein, hormones such as florigen can impact the target cell in several ways. It can increase or decrease production of certain molecules, activate or inactivate molecules already present or alter growth of the target cell.
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 under these light conditions either. 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.
From this information, you can determine that the plant is a long day (short night) plant. This is known because it does not flower during a long night (16 hour darkness) and does not flower when there is an evenly split light and darkness (12 hour darkness), so the plant must require even less than 12 hours of darkness to flower.
In your own words, explain why it is important for plants' roots AND shoots to sense and respond to gravity.
Gravitropism (directional growth in response to gravity) is essential for roots because roots have to stretch downwards (positive gravitropism) to collect water and nutrients from the soil. For shoots, they must stretch upwards (negative gravitropism) in order to reach the sunlight. Gravity pulls auxin to the bottom of roots and shoots which inhibits root growth (causing downward direction) and promotes upward shoot growth.
Write your own description of homeostasis.
Homeostasis is the ability of an organism to maintain a specific range of internal conditions and is necessary for proper functioning of all organisms
Describe the role of hormones in homeostasis.
Hormones allow signals (messages) to be communicated throughout an entire plant 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 4. Hormone signal detected by certain cells - causes cells to change their function 5. Changes in cell functions determine overall response of the plant
Apical dominance experiment
Hypothesis: Tips of growing plant stems produce a growth substance that inhibits lateral bud growth. Results: - Lateral buds of decapitated plants with plain agar blocks grew significantly more than lateral buds of intact untreated plants - Lateral buds of decapitated plants with agar blocks containing tip moleculesshowed similar growth vs. intact untreated plants' lateral buds (very little) Conclusion: A substance present in tips of growing shoots inhibits growth of lateral buds.
If the results of an experiment do not support the hypothesis, does that mean that there was something wrong with the experiment?
If the results do not support the hypothesis, that still provides valuable information. It is important to know when a hypothesis is refuted. Nothing was necessarily wrong with the experiment.
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.
If you put a tracer hormone in to go through the vascular tissue, that would be the most conclusive evidence Experiment with a blocker between the roots and the stomata. Dry roots but open stomata would show that the blocker stopped ABA from signaling the stomata to close.
List THREE ways a particular type of hormone can cause different responses in target cells.
In different cells because they can have different receptor proteins that correspond to the same hormone (Example: hormone A causes a certain change in root cells and hormone A causes a different change in shoot cells) In the same cell, depending on the presence of other hormones, hormone A could have different responses In the same cell, depending on the concentration of the hormone
Why is indeterminate growth beneficial for plants? Explain why indeterminate growth is less important for animals.
Indeterminate growth benefits plants because they cannot move and therefore must be able to adapt by growing throughout their whole lives. Plants continue to form plant shoots and roots and may continue growing towards sunlight throughout their entire lives. Indeterminate growth is less important for animals because they are not stationary. Growth stops around adulthood because animals can physically leave an environment if they choose to and can move to resources.
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 block of light and one block of darkness per 24 hr. Cycle.
Short day (long night) plant: if it receives more than 10 hours of darkness, it will flower Long day (short night) plant: if it receives less than 10 hours of darkness, it will flower There is not a condition under which both would flower because they both have a critical period of 10 hours
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 bowl of sweet strawberries.
Internal mechanisms would SENSE the internal stimuli of the sweet strawberries, then the next mechanisms would COMMUNICATE messages ("there is more sugar!") throughout the body, then the next mechanism would INTERPRET and INTEGRATE messages together to determine the appropriate response. Finally, other homeostatic mechanisms would execute the RESPONSE if it is deemed necessary.
Explain why it's important that only a small amount of hormone is required to produce a significant response in target cells.
It is beneficial for only a small amount of hormone to be required for a significant response in target cells, because then less hormone has to be produced for the response to occur.
Why is it important that a certain type of hormone receptor only interacts with one type of hormone?
It is important that a certain type of hormone receptor only interacts with one type of hormone because it ensures that a particular hormone will always cause the same specific response in the organism.
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.
It is important to run the experiment with some plants that had their lower leaves infected first and upper leaves second AND some plants where the upper leaves were infected first and the lower leaves second because it eliminates the possibility that the results were only due to the placement of the initial infection on the plant. Ruling out alternative hypothesis
Review the experiments we discussed 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? Why was it important to include 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?
It was important that the seedlings used were kept in the dark for the entire experiment so that there was no light that could have impacted directional growth. Isolating the variable To be sure that the plant did not grow in a certain direction without sunlight impacting growth To be sure that the plain agar blocks themselves did not impact directional growth
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.
Leaves absorb the light energy, stomata take in the carbon dioxide and the roots take up the water needed for photosynthesis.
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.
Lengthwise growth of a tree only occurs from the shoots (top of plant) and the roots (underground). So the plant is expanding from the top and bottom, but if you put a nail in it wouldn't move.
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 (short-night) plant? A day-neutral plant?
Let's say its January. In Burlington, short day plants would be flowering because they require less daylight to flower, which is currently available. In Sydney, short day plants would not be flowering because they also require less daylight to flower, but it would currently be summer and there would be more daylight. Hypotheses for Burlington in January Short day: if the plant flowers Long day: if the plant does not flower Neutral day: if the length of day does not impact flowering
Explain why maintaining homeostasis is essential for all organisms.
Maintaining homeostasis is essential for all organisms because being in homeostasis means that the parts of an organism are functional and working in order. Homeostasis is dynamic and not constantly "perfect" because internal and external conditions vary.
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?
No, because these organisms are living with very different external conditions (temperature), so homeostasis of internal body temperature will be different. Depending on environmental (external) conditions, our survival may require different internal conditions.
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.
One hormone in multiple processes: auxin is a growth promoter (in shoots, makes plants taller) phototropism! and growth inhibitor (in roots, makes roots grow slowly and with gravity grow down) gravitropism! Multiple hormones in one process: Salicylic acid and jasmonate (and maybe other hormones) are both released in response to the TMV virus
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 defenses: defenses that are always present Examples: Capsaicin in hot peppers, Thorns on a rose bush Benefit: plant less likely to be eaten by predators Draw back: capsaicin or thorns don't harm all predators Induced defenses: defenses triggered when a plant is infected or attacked Benefit: result from a specific stimulus, will be a hardier and specific defense Draw back: delayed defense, takes time Two categories: local and systemic - Local induced defenses: only act at the site of the infection Example: cells near the infection die to protect the rest of the plant Beneficial because uses less energy and resources to "heal" smaller portion of body - Systemic induced defenses: response occurs in multiple parts of the plant Example: increased resistance of the whole plant to that specific pathogen Beneficial because increases protection of more parts of plant from disease Draw back: if first virus kills whole plant, there's no need to acquire resistance, ur dead.
In broad terms, explain the difference between photoperiodism and tropisms. In what ways are they similar?
Photoperiodism: developmental responses due to changes in relative length of day (light) and night (darkness) Tropisms: growth responses that promote growth towards or away from a specific stimulus They are both in response to a stimulus, but different ones.
The leaves of certain plant species fold up at night and then reopen at dawn. Explain why this is NOT an example of phototropism.
Phototropism takes place throughout a plant's development (not overnight). Phototropism is a more permanent growth response and does not fluctuate day to day
Describe the role of phytochromes in photoperiodism.
Phytochromes are photoreceptors meaning they are molecules that absorb and respond to specific wavelengths of light. Specifically, photochromes allow plants to sense red and far-red light. The amounts of active vs inactive phytochrome allow plants to measure photoperiod.
Describe the main ways in which plants respond to external stimuli.
Plants' primary response to external stimuli is altering growth processes and developmental processes.
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 downwards because there is a higher concentration of auxin at the lower part inhibits cell growth. Because of this, the top part of the root grows, forcing the whole root downwards Negative shoot gravitropism - increased levels of auxin promotes shoot cell elongation in shoot cells, so the plant grows upwards
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?
Question: Do chicks who hatch in the wild have better health than chickens who hatch in an incubator? Hypothesis: Chicks (chickens) who hatch in the wild have better health than chickens who hatch in an incubator. Prediction: Chicks develop fewer diseases when they hatch in the wild versus chicks who develop and hatch in an incubator because the incubator possesses some health risks. Experiment: Take two eggs from a chicken and have one hatch "in the wild" (with a parent, the natural way) and the other hatch in an incubator. Run the same experiment with 50 different parent chickens and monitor the chicks' health over lifetime. Supporting evidence: chickens who hatched in the natural way, develop fewer health issues over their lives than incubated chickens Refuting evidence: chickens who hatched in the natural way develop more health issues compared to incubated chickens
Why is it important to test hypotheses multiple times in the same way and in multiple ways?
Repeating the same test multiple times in the same way lessens the likelihood that another variable was impacting the results if you run multiple of the same experiments and they all yield the same results Testing a hypothesis in multiple ways eliminates the possibility that certain results only occurred due to the method of experimenting
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.
Roots grow downwards, away from the light source, so that would be negative phototropism The current hypothesis which states that auxin is redistributed to the darker side of the shoot wouldn't be relevant for the root cells because all roots are in the dark (underground), so there is no lighter or darker side.
Explain the difference between short-day (long-night) and long-day (short-night) plants. Use the term "critical period" in your explanation.
Short day plants only flower when length of day is less than a certain number of hours. Long-day plants only flower when the length of daylight is more than a certain number of hours. This certain number of consecutive darkness hours that determines flowering for a particular species is called the critical period. The critical period for short day (long night) plants is the MINIMUM number of consecutive hours of darkness in order to flower and the critical period for Long day (short night) plants is the MAXIMUM number of consecutive hours of darkness in order to flower.
Identify at least two ways photoperiodism and phototropism are similar. What makes them different?
Similarities: both responses due to light, both involving plant growth Photoperiodism: flowering (reproduction) response due to number of consecutive darkness hours Phototropism: directional growth in response to light
basics of systemic acquired resistance (SAR) experiment
Stimulus: bacteria, pathogen, virus (tobacco mosaic Virus) Hormone: salicylic acid Response: whole plant becomes resistant to the particular pathogen
DROUGHT STRESS For the three plant processes and hormones we discussed, list the stimulus, the hormone, and the response.
Stimulus: drought (lack of water) Hormone: abscisic acid (ABA) Response: ABA is produced in dry roots and is transported to leaves and causes stomata to close, so plant maintains water
basics of Drought Stress experiment
Stimulus: lack of water Hormone: Abscisic acid ABA (in dry roots) Response: Close stomata
SYSTEMIC ACQUIRED RESISTANCE For the three plant processes and hormones we discussed, list the stimulus, the hormone, and the response.
Stimulus: pathogen/ virus Hormone: salicylic acid Response: plant increases resistance to virus throughout whole plant (not just infected area), so the infection doesn't spread
APICAL DOMINANCE For the three plant processes and hormones we discussed, list the stimulus, the hormone, and the response.
Stimulus: presence of apical bud Hormone: auxin Response: auxin (and potentially other hormones) promote apical bud growth and limit lateral bud growth, so the plant grows higher up towards the sun
Describe the function of stomata and explain why the ability to regulate opening and closing of stomata is important for plants.
Stomata are the pores on leaves that open and close, allowing carbon dioxide in and oxygen and water out. The ability to regulate this opening and closing is important because depending on the climate, the plant may want to close or open its stomata more (ex: a really hot climate where the plant would want to keep stomata closed to store more water)
Red light vs far red light
red light is sensed as an interruption in darkness far red light is not sensed as an interruption of darkness far red light can reverse the effect of red light red light = phytochrome active form far red light = phytochrome inactive form
Review the three experiments we discussed and, for each one, explain why the results do NOT allow you to draw the conclusion that the hormone acts as a signaling molecule.
Systemic Acquired Resistance: This experiment did not assess levels of molecules that may be acting as signals, but we can hypothesize that the hormone travels from infected leaves to uninfected leaves Drought Stress: Although dry roots produced more ABA and more ABA was found in leaves, the experiment did not measure the transport of ABA from roots to leaves Apical dominance: We cannot guarantee that auxin is the only signaling molecule, there may be other messenger hormones
Define/describe systemic acquired resistance (SAR) and explain why SAR is categorized as an induced defense mechanism.
Systemic acquired resistance (SAR) is a type of systemic induced plant defense where the whole plant increases resistance to a specific pathogen. SAR is an induced defense mechanism because it occurs in response to a pathogenic bacteria infecting one part of the plant.
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.
The molecule interacts with target cells with a specific corresponding receptor protein The molecule is released in response to a stimulus (not constantly around) The molecule is released everywhere, but only affects cells with the specific receptors
Explain why it is NOT appropriate to state that tropisms involve plants bending towards or away from a stimulus.
The plants are not "bending" as humans bend their knees, the plants are growing in a curved direction towards the stimulus (sunlight). Growth response are relatively permanent
Explain why it is not possible to conclude from the experiment we discussed one or more specific molecules produced in the tips of plants are capable of both promoting apical bud growth and inhibiting lateral bud growth.
While we can conclude that there is a substance present in growing shoots that inhibits growth of lateral buds, we do not know exactly what tip molecule or molecules are impacting lateral growth. If we do not have all of the data/information, we cannot make a cause conclusion.
Explain why an experiment cannot definitely prove that a hypothesis is true.
There are always potential uncontrolled conditions and human error in experiments also the hypothesis can be incorrect
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? Just come up with ideas, don't worry about the technical details.
To test the hypothesis that different concentrations of auxin have different effects on apical bud growth you could soak agar blocks in auxin for different increments of time so they have different concentrations of auxin. Then, test each block with the bean sprout and take note of bud growth To assess the hypothesis that auxin has different effects on roots and shoots, you could hypothetically separate the roots and shoots and expose them each to auxin separately. Without letting the two portions of the plant communicate. You could analyze the different impacts of auxin on each.
Review the analyses we discussed that assessed 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 control groups were important. Why did they also include intact untreated plants?
Untreated intact plants are an important control in this experiment because it provides a comparison for lateral bud growth under normal conditions. It rules out any initial factors that could be impacting lateral bud growth before the experiment begins. Decapitated plants with plain agar blocks are an important control because it allows scientists to assess an alternative hypothesis that agar blocks alone impact 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.
Utilizing prior studies and evidence is useful when designing a hypothesis because it can inform our hypothesis by ruling out what we already know Prior related experiments can help us fine tune our own experiment because we can note what methods did and did not work for previous researchers
Describe the function of vascular tissue.
Vascular tissue is the tubing system that goes throughout a plant which allows transport of water, nutrients, signaling molecules, and other types of molecules
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).
Water a plant (keep track of amount of water) and measure how much ABA is in the roots. If the hypothesis we discussed in the other experiment is supported, we would anticipate that less water results in more ABA in the roots. If the hypothesis is refuted, we would see more water resulting in more ABA. this question is weird
Explain why you CANNOT conclude from the results that ABA produced by dry roots is transported to leaves where it causes stomata to close.
We do not have proof of causation, we only know that ABA produced dry roots is associated with leaves closing stomata. We do not have proof of how those two occurrences connect. We don't have a measurement system that can track ABA movement in the vascular tissue
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.
When flowering is or is not happening, measure amount of the molecule Do an experiment similar to the phototropism one with the agar blocks and observe apical bud growth and flowering with the isolated molecule in the agar block. Give some plants agar blocks with the molecule and some without and observe flowering.
Flowering in a particular species of plant is known to be controlled by changes in the photoperiod; it flowers when exposed to photoperiods of 6 hours of light and 18 hours of dark. Explain why you cannot tell from this information whether it is a short-day (long-night) or a long-day (short-night) plant. Come up with an experiment you could perform to determine how the plant should be categorized.
You cannot tell from this information whether it is a short day (long-night) plant or a long day (short night) plant because we do not know the critical period. the critical period is key to knowing whether the plant is long or short night. to determine whether this plant is long night or short night, test the same species plant in different photoperiods and evaluate.
what do scientists believe is the growth substance in the plant experiments we discussed
auxin
how does a higher concentration of auxin impact ROOT cell growth
inhibits cell growth
phototropism vs photoperiodism
phototropism is a growth response towards or away from the stimulus (sunlight) photoperiodism is a plant's growth response to the number of consecutive hours of darkness it receives (for our purposes, flowering vs not flowering)
Explain why a much greater variation in form (e.g. branching pattern, number of branches) is observed between the exact same species of plants grown under the exact same conditions compared to a group of animals that are all the same species and exposed to identical conditions.
plants grow indeterminately animals grow determinately Animals of the same species will develop similarly because animals are not stationary like plants, so animals are able to move to resources or away from predators. Plants must compete with other stationary plants for sunlight (up above) and water (down below with the roots), so they grow in intricate ways to access what they need.
positive vs negative phototropism
positive: growth towards light negative: growth away from light
positive vs negative gravitropism
positive: growth with gravity (down) negative: growth against gravity (up)
how does a higher concentration of auxin impact SHOOT cell growth
promotes cell elongation
basics of photoperiodism experiment
stimulus: Length of darkness hormone: Florigen (hypothetical) response: Flowering
basics of phototropism experiment
stimulus: Light hormone: auxin response: Directional growth (towards light)
basics of gravitropism experiment
stimulus: gravity hormone: auxin (roots and shoots different effects) response: directional growth (with or against gravity)
basics of Apical dominance experiment
stimulus: presence of the apical bud hormone: auxin response: apical bud growth (inhibited lateral bud growth)
a long day (short night) plant and a short day (long night) plant both flower when exposed to the same photoperiod. Based on this observation, what can you say about the plants' critical periods.
the plants must have different critical periods
what is apical dominance
the presence of an apical bud inhibits lateral bud growth important because plants need to grow upwards to compete for sunlight
