Exam 1 Follow Up Questions- BIOL 1450

Write your own description of homeostasis

The ability for an organism to maintain its internal conditions in a range that is survivable and healthy

- required for proper functioning of ALL organisms

-dynamic process - internal conditions are NOT held constant

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)

-Changing conditions within a specific range is vital to survival

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 - the environments in which they live have made it so that their range for temperatures are both very different. They have both individually adapted to each end of the temperature spectrum

Homeostasis exists in a specific range - one species that lives at a freezing temperature would not have the range to live in boiling temperature

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.

- 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

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.

Similarities:

-Multicellular organisms need mechanisms to communicate between cells (hormones)

- Maintaining homeostasis is vitally important to survival

Differences:

-Plants are stationary while animals can move

-Plants have flexible growth patterns

-Animals have fixed body plan

-Plants have central control system while animals don't

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

- Stomata (leaf pores) allow carbon dioxide in and oxygen and water out

- These are vital for plants survival - they allow the plants to survive in drought conditions better

Describe the function of vascular tissue.

It's the tubing system that goes throughout a plant and transports water, nutrients and signaling molecules

Similar to our blood but it's not being pumped, rather pulled through capillary action from roots

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.

Water - transported by vascular tissue

Light Energy

CO2 - stomata (leaf pores) allow carbon dioxide in

Why is indeterminate growth beneficial for plants? Explain why indeterminate growth is less 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

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.

This is due to lengthwise growth - this type of growth occurs only at the tips and roots of a plant

When the tree gets taller it's not the entire tree growing up, only the top

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)

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.

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)

Why is it important that a certain type of hormone receptor interacts with one type of hormone?

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

List THREE ways a particular type of hormone can cause different responses in target cells.

- Different types of cells can have different receptors for the same hormone

- A particular hormone can cause different responses in different cells

-In the same cell, depending on presence of other hormones and the concentration of that hormone

-Difference cell types have different receptor proteins for a particular hormone

-Overall response depends on a combination of hormone signals - not just one

Explain why it's important that only a small amount of hormone is required to produce a significant response in target cells.

This is because it costs a lot to produce a hormone; the less that is needed, the better.

Most plant processes are controlled by hormone signals - it's important for the process to be efficient

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

It is specific - only exists in certain plants

A response is exhibited in the cells when this molecule is present

Certain conditions make this molecule present

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?

-Permanent defenses are always present, like thorns on a plant, and induced defenses are triggered when a plant is infected or attacked

-Downside of permanent defenses: capsaicin in peppers is meant to deter animals, but humans enjoy the spice

-Downside of induced defenses: it can reduce number of leaves in the process of trying to protect itself

-Benefits of local vs systemic induced defenses are that the infection can be immediately handled (leaf falling off ie) which can prevent spread of pathogens. There's not always the need for systemic induced - may in some cases do more harm than good

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

-SAR - increased resistance of whole plant to that specific pathogen

- It's categorized as induced because it was seen that in tobacco plants, the area around the site of infection is resistant to subsequent infections due to the fact that once the plant sense the first infected leaf, resistance to tMV infection spreads to different parts of plant

-It only happens when the infection starts - the plant does not have properties that permanently defend it against the infection

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.

-This was important so that the researchers could determine whether the response was local or systemic

- It was not local because the response was felt throughout the entire plant in the second infection

-They wanted to also look at a possible direction the response molecules were moving in the plant

-Doing the lower leaves on one trial and the upper on another allows them to see if the response operates the same way in both runs

Review the experiment we discussed that assessed the effects of dry roots on ABA levels and stomata closure. Why was it necessary for one half of each experimental plant's roots to receive water, and the other half of each plant's roots to be dry?

- ABA - abscisic acid

- Some evidence has been shown that plants with dry roots close stomata before leaf water content changes - applying ABA to leaves causes stomata to close

-Levels of ABA increase in leaves when leaf water content decreases

-This is important so that the researchers could see if the plant closed its stomata in response to some dry soil - not all of it needs to be dry for the plant to respond

-Wanted to look at ABA levels in the roots

Do the data indicate that watering half a plant's roots results in similar leaf water levels compared to watering all of a plant's roots? Why is this an important question to address in this study?

Yes - because the drought stressed plants were able to sense it before the leaf water content went town, and so they close their stomata

-This made it so that the control and the experiment plant leaves had the same leaf water content, even though different things were happening

-ABA is working the way that was hypothesized

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?)

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

Do the results support the hypothesis that plants exposed to drought close their stomata before the leaf water content changes? What specific data support/don't support this hypothesis?

Yes - there were higher levels of ABA in the drought side than the watered side of the experimental plants

ABA produced by dry roots is transported to leaves where it causes stomata to close (based on additional analyses)

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

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

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

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.

More ABA in dry roots = more closed stomata

There was a similar water content level in control and experimental leaves

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.

Why is apical dominance beneficial for plants?

Favors upwards growth over outwards growth

Important for increasing access to sunlight required for photosynthesis

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: provides comparison for lateral bud growth under normal conditions

Decapitated with plain agar: can assess alternative hypothesis that agar blocks affect later bud growth

Explain why it is not possible to conclude from the experiment we discussed that one or more specific molecules produced in the tips of plants 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

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.

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

For the three plant processes and hormones we discussed, list the stimulus, the hormone, and the response.

SAR - hormone = salicylic acid

-Stimulus: infection in plant

-Response: plant produces lesions and drops infected area. Further infections are less likely to occur

Apical dominance - hormone = auxin

-Stimulus: apical buds being cut

-Response: lateral buds grow more - plant is bushier

Drought stress - hormone = abscisic acid (ABA)

-Stimulus: dry soil

-Response: ABA causes stomata of leaves in dry soil to close before the leaf water content goes down

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.

For all 3 the researchers weren't specifically looking at molecules moving through the plants; they were just observing differences that may have been caused by these hypothesized hormones

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)

What are the main ways in which plants respond to external stimuli?

Primary response is altering growth and developmental processes

Photoperiodism and tropisms are the main way they respond to stimuli

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 have indeterminate growth - they change throughout their lives dramatically based on many factors

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

Photoperiodisms are developmental responses due to changes in relative lengths of day and night while tropisms are growth responses that promote growth towards or away from a specific stimulus

They are similar because they both aid in the plants growth and development overall

In your own words, describe the difference between short-day (long-night) and long-day (short-night) plants. Use the term "critical period" in your description.

Long-night plants: the critical period is the minimum number of hours of darkness that a plant needs to flower

- If it goes under this amount of darkness, the plant will NOT flower

- If it goes over this amount of darkness, the plant WILL flower

Short-night plants: the critical period is the maximum number of hours of darkness that a plant requires to flower

-If there are more hours of darkness than the critical period the plant will NOT flower

-If there are less numbers of hours of darkness the plant WILL flower

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?

Long-night: this plant would flower in the fall/winter of Burlington VT

Short-night: this plant would flower in same time period but in Australia

Day-neutral: this one wouldn't matter

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?

Yes - long-night plants need a certain amount of darkness to flower. Turning on the light at midnight likely means that the plant won't have 9 straight hours or more of darkness, which is what it needs. This means it might not flower.

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.

Because it's unclear whether or not these hours of darkness are consecutive

We can't tell because there's no description of what this plants critical period is. If it's more than 18 hours it would be short-night, if it's less than it's long-night.

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.

Short-night - it may need even less light to 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 block of light and one block of darkness per 24 hr cycle

Long-night: this plant would flower only when it received 10 hours or more of darkness

Short-night: this plant would flower only when it received 10 hours or less of darkness

Both would flower with exactly 10 hours of darkness, as it is the minimum for long-night and the maximum for short-night

Describe the role of phytochromes in photoperiodism.

This is a type of photoreceptor that allows plants to sense red and far-red light

Some plants flower when they sense far-red or red light, while some don't

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?

Identify at least two ways photoperiodism and phototropism are 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.

It's not technically "bending"- one side of the plant is experiencing elongation of its cells while the other does not. This results in the ability for the plant to "bend" towards the stimulus or away. These are just directional responses in plants

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

This is not a directional response - non-directional responses to stimuli that occur more rapidly than tropisms and are usually associated with plants

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.

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

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.

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

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 down toward stimulus

Negative Shoot Gravitropism - shoots grow up away from stimulus

Which of the observations below, if either, would support the current hypothesis for root gravitropism?

- Levels of auxin are the same in the upper and lower portion of a root when it's tipped on its slide. YES

- Plants whose roots lack statoliths do not show a gravitropic response. NO

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.