Biol 002 Exam 1 Follow Up Questions

Homeostasis

ability of an organism to maintain internal conditions and keep them stable

-internal conditions include blood sugar level, and body temperature

-mechanisms that maintain homeostasis share the same characteristics (sense, communicate, interpret, and integrate or carry out the response)

why is homeostasis essential for all organisms

it is essential for normal cell function (balance between salt and water levels)

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 although they might carry out specific functions the internal temperature range will be different

what does it mean that hypotheses must be testable?

it must be measurable or observable, there must be a baseline for comparison that addresses alternative explanations for results

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

to ensure that the results were accurate and would repeat

explain why an experiment CANNOT definitely prove that a hypothesis is true

because there are many variables etc

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

the larger the sample size, the more likely the results reflect the actual population

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?

Need to know the height of the plants

If 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 that was created was incorrect/not supported by the experiment performed

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

"Published to ensure that the research is of high quality, contributes to the field of research and is accurately presented"

Why can't some questions be answered scientifically? Come up with a hypothesis that CANNOT be assessed scientifically

Some questions can't be answered scientifically because they lie outside the realm of science. Things like existence of other minds, basic beliefs, religion, and ethical facts

If observations can't be made something can not be answered scientifically

Hypothesis:

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 there is always the possibility that there was a third or another variable that was affecting what was being tested on

Make an observation and/or consider a question you have about the world and form a hypothesis. Can your hypothesis be assessed scientifically? Why or why not? If not, can you think of a way to rephrase your hypothesis so that it can? 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?

hypoth:

Sleeping for 9 hours every night will improve memory.

-it can be assessed scientifically

prediction:

sleeping 9 hours a night will improve memory

-have people sleep 9 hours every night and take a memory test, control is people who sleep 6 hours every night

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.

-first, my body would sense that my blood sugar levels are high (changes to internal and external temps), then communicate this to other organisms in my body (pancreas)

-my pancreas would receive and interpret this and respond by secreting more insulin throughout my body to maintain glucose levels

Similarities between plants and animals with homeostasis

plants and animals both are multicellular organisms that will allow communications between cells throughout an individual

difference between plants and animals with homeostasis

Plants:

- cannot move to better conditions to escape threats

-plants have a very flexible growth pattern, there is not a fixed amount of leaves and branches

-no central control system (brain

Animals:

- are able to move to better conditions and remove themselves from threats

- have a fixed body plan (2 arms, 2 legs)

- have a central nervous system

stomata

are the pores of the leaf that contain the mouth

- are located on the outermost cellular layer of leaves, stems, and other plant parts.

- this mouth allows carbon dioxide and water in, oxygen goes out

- water can be taken out by evaporation

why is it important for stomata to open and close

with out the constant flow of carbon dioxide and water in and oxygen out, plants would not be able to create carbohydrates

- open stomata facilitates photosynthesis

Describe the function of vascular tissue.

- tubing system that goes throughout a plant

- allows transport of water, nutrients, signaling

molecules, and other types of molecules

- water is taken through the roots, stems, and leaves

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.

during photosynthesis, plants take in carbon dioxide (CO2) and water (H2O) from the air and soil

- water is oxidized (H2O --> O2 and CO2 --> glucose)

- plant then releases O2 back into the air and stores energy within the glucose molecules

(The glucose is used in respiration, or converted into starch and stored. Oxygen is produced as a by-product)

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

indeterminate growth is beneficial for plants because it is the type of growth that allows stationary organisms to respond to the environment in order to maintain homeostasis

-this doesn't apply to animals because they are not stationary

• 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 talle

if you put a nail into a tree trunk, the height of the nail above the ground won't change even as the tree gets taller because of lengthwise growth

- lengthwise growth only occurs at the tips and shoots of the root

Describe the role of hormones in homeostasis.

are also responsible for sending chemical messages that will change cell functions which is what homeostasis is (responsible for key homeostatic processes)

-respond to diseases, changing in environment, etc

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.

-florigen (or flowering hormone) is the hypothesized hormone-like molecules responsible for controlling and/or triggering flowering in plants

-florigen is produced in the leaves, amd acts in the shoot apical meristem of buds and growing tips

(the shoot system is the leaves and stem, the apical bud is the tip of the item)

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

a hormone usually only affects a limited number of cells

- ensures particular response will only be triggered when a specific hormone is released

- a hormone has target cells (which have receptor proteins that can interact with this hormone)

- these target cells responds to the hormone because it bears receptors for the hormone

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

-overall responses depend on the combination of hormone signals...

1. on the same same cell, depending on the concentration

2. on the same cell, depending on the concentration of that hormone

3. because different cell types have different receptor proteins for a particular hormone (i.e. shoot and root cells respond differently to the hormone auxin)

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

little energy means a big response quicklyex.- interaction of one molecule hormone A causes MANY copies of molecule R to be produced

key characteristics of hormones.

-allows messages to be carried throughout an entire organism

- chemical messages that are important for long distance communication

- hormones can regulate the behavior of target cells

- they are secreted only when needed

- their function is to stimulate or inhibit the target organs

permanent defenses

defenses that are always present

- i.e. rose bush thorns, capacia in peppers (jalpeño) causes irritation when animals eat it, deadly nightshade (poison berry)

pro- always present and often require immediate protection for the plant

con- can require a lot of enerfy

induced defenses

responses (defenses) that are triggered or activated when a plant is attacked

con- can take a while to initiate the defense

- 2 categories

1. local (at site of infection)

2. systematic (occurs in multiple places)

systemic acquired resistance (SAR)

-increased resistance of whole plant to infection by specific pathogen

- "whole plant" resistance response that occurs following an earlier localized exposure to a pathogen

- it "pops" up only when a specific pathogen harms the plant, it's not always there (induced defense)

• 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.

there needs to be a control group, if the hypothesis states that a plant develops resistance in area B if area A is infected, it is important to do the opposite (to see if that is also true)

• 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.

- it was important because the fact that there were less lesions in the upper leaf prior to infection of the lower we could infer that the hormone sent signals and offered protection

-we could say that it was not important because we do not know if it was a hormone at all, because we have yet to test if the same reaction would occur if you infected the upper leaf first, and the the lower leaf

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?).

allowed for a comparison of molecules (signals) produced by wet and dry roots of the same plant

- half watered and half unwatered can determine if ABA is released on one side but not on the other; the point is to see if the stomata is closed before the plant dries out (watered half so the plant wouldn't dry out before they could measure whether the stomata closed and the levels of ABA increased)

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

-Dry roots produced more ABA, and more ABA was found in leaves, but they did not directly measure transport of ABA from roots to leaves

-correlation does not equal causation

Why is apical dominance beneficial for plants?

it promotes upward growth, more towards the light where it can better undergo 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 include intact untreated plants?

-the untreated intact plant was important because we needed a comparison for regular apical bud dominance (with tip), and how it would grow upward and inhibit lateral bud growth

-decapitated plants would provide a comparison for lateral bud growth and the effect of having no tip

- decapitated plants with plain agar blocks would provide knowledge to see if the agar had any affect on its own of lateral bud growth

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.

we were only testing to see if there were molecules in the tips that would inhibit lateral bud growth

Systematic aquired resistance (SAR)

hormone: salicylic acid

-increased resistance of whole plant to that specific pathogen (induced defense)

conclusion of TMV plant infection

- Resistance to TMV infection in one part of a plant develops following infection of a different part of the plant with TMV

Apical Dominance

hormone: auxin (promotes or inhibits lateral bud growth)

-apical dominance: presence of apical bud inhibits lateral bud growth

conclusion from auxin lateral bud growth study:

-A substance present in tips of growing shoots inhibits growth of lateral buds.

Drought Stress

hormone: abscisic acid

- seed and bud dormancy and closing stomata (stops plants from growing and flowering)

conclusion from ABA dry root study:

- Dry roots produced more ABA, and more ABA was found in leaves, but they did not directly measure transport of ABA from roots to leaves

These data suggest that Asiatic dayflowers respond to drought stress prior to a decrease in the water content of leaves

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

they have primary responses including altering growth (either more or less in a particular direction) and initiating or stopping developmental processes

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 fixed growth process unlike animals

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

photoperiodism- developmental responses due to change in lengths of day and light (darkness and daylight), also deals with flowering

phototropism- growth ONLY towards light, this is cell elongation towards and because of smth

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) plants only flowers when the amount of consecutive darkness is more than the critical period

-long day (short night) plants only flowers when the amount of consecutive darkness is less than the critical period

• 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?

what we know: plants of the same type planted at different times but still in the same location will STILL flower at the same time (very fixed flowering time)

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 because if long night plants are interrupted with light it will affect the flowering process

- light is detected as an interruption to darkness by both short-day (long-night) and long-day (short-night) plants

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 could you perform to determine how the plant should be categorized.

we cannot tell what type of plant it is because we need to know the critical period, and whether a plant needs more or less hours than the critical period

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

i can infer that it is a short night plant because it didn't flower with either long night or day neutral but we cannot conclude anything because we do not know the critical period

• 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.

we can eliminate long night because the flash of red light in the 12 hours of darkness would break up the darkness meaning its not continuous so we can infer its either neutral day or short night

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.

the long night plant would need more than 10 consecutive hours of darkness, so --> 14 hrs of darkness and 8 hours of light

the short night plant would need less than 10 consecutive hours of darkness so --> 8 hours of darkness and 6 hours of light

• Describe the role of phytochromes in photoperiodism.

phytochromes are a type of photoreceptor (molecule that absorbs and responds to specific wave lenghts of light) that allows plants to sense both red and far red light

-can allow a plant to sense a light and respond accordingly

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.

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

• Identify at least two ways photoperiodism and phototropism are similar. What makes them different?

photoperiodism- growth of plant due to the amt of day light and darkness

phototropism- growth towards light

they are both responding to some sort of stimuli which effects developmental process

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

plants don't bend, one side grows longer towards the light due to uneven levels of cell growth

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. but it is not a permanent change happening from periods of darkness

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?

we didn't want the seedlings exposed to light while the tips were being infused into the agar block to prevent any growth happening before the tip was placed back on. we needed a comparison for group that was tips on agar block WITH light. and we need to know if plain agar blocks will have any affect on its own.

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 is transported from the lighter side of seedling tips to the darker side, which results in more auxin moving down the darker side. Cells on the darker side get longer in response to auxin signaling, causing growth towards light.

other explanations:

-Light inactivates auxin on the lighter side without changing the total amount of auxin that's present.

-Growth inhibitor(s) accumulates on the lighter side of seedling tips and moves 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.

Shoots: negative gravitropism, needs to respond to gravity to obtain sunlight (photosynthesis)

Roots: positive gravitropism, they need to grow down to obtain water and nutrients

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

because light can't reach roots

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.

-having high auxin levels in lower part of the root would inhibit cell growth in the lower part and cause the upper part of the root to grow downward (Movement of statoliths to the bottoms of root tip cells in response to gravity causes auxin to be transported to cells at the bottom of the root, promoting downwards growth.)

-having high auxin levels in the lower part of the shoot would promote cell growth making the bottom part grow upwards

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 negative phototropism. 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