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Chapter 12: Plants
The AP exam focuses on how plants interact with their environment.
Many of the suggested laboratory exercises for the course involve the influence of the environment on plants.
Basic characteristics of plants are what you need to observe, identify, and discuss these interactions.
Plants have four major organs.
The surface area is increased by the absorption of water and nutrients.
Plants supply the fungi with sugars.
Mycorrhizae has been associated with most plants.
Plants have thorns that protect their stems.
The cells are usually arranged in one or more layers at the upper surface, but can also be found at the leaves of plants adapted to dry habitats.
The CO2 and O2 can be exchanged.
The structure of the leaf is adapted to the growth habit of the plant, balancing the needs of photosynthesis with the costs of transpiration.
The leaves are targets for herbivores.
Plants grow in hot or dry environments.
They open to allow gas exchange, but close when excessive transpiration from high temperatures or low humidity threatens the survival of the leaf or plant.
The transpiration is caused by air movement over the surface of the leaf.
They can affect air movement and reduce transpiration.
Their presence may discourage egg laying by insects.
The leaf surfaces are toxic due to inhospitable glandular trichomes.
Eggs and pollen are produced here.
Wind or insects can transfer pollen between flowers.
The AP exam doesn't require you to know the reproductive cycles of plants.
The leaves take in CO2 and release O2.
In all parts of the plant, cellular respiration is taking place, consuming O2, releasing CO2, and generating ATP.
The opening of the stoma is controlled by two guard cells.
When the environment is suitable, guard cells open and allow CO2 to diffuse into the leaf.
CO2 diffuses into the water lining the cells after entering the spaces in the mesophyll tissue.
CO2 diffuses into the cells once in the water.
CO2 enters the palisade mesophyll.
These cells are tightly fitted against the top surface of the leaf to maximize the amount of photosynthesizing surface area exposed to sunlight.
Roots need to carry out respiration to get energy from stored carbohydrates.
They need a supply of O2 from the soil.
There is little risk of water loss from transpiration in aquatic plants.
Both CO2 and O2 enter the leaves through the stomata and pass into the air spaces of the mesophyll.
Both CO2 and O2 are transported throughout the plant through the air spaces.
The CO2 from the submerged plant parts is returned through the air spaces to the leaves.
Air spaces help keep the plants upright.
The guard cells' cell walls are not uniformly thick.
The rest of the cell wall is thinner than the cell wall that borders the stoma.
The guard cell is surrounded by the radially arranged cellulose microfibrils.
The guard cell expands when water diffuses into it.
Most of the expansion is realized by the bulging out of the thinner wall, the wall away from the stoma, because of the nonuniform and radially constructed cell wall.
The effect is to create two guard cells that create an opening between them.
When water diffuses out of the guard cells, the shape of the kidneys collapses.
The opening and closing of the stomata is controlled by the movement of water into and out of the guard cells.
The electrical gradient has been established.
The opening of the stomata is initiated by the active pumping of H+ out of the guard cells.
This establishes an electrical field.
The H+ pump is activated by sunlight.
The osmotic gradient has been established.
The guard cells have a K+) that is driven into them by the electrical gradient.
The electrical imbalance causes the Chloride ion to follow.
The influx of ion creates a solute gradient.
Water enters the guard cells.
Water enters the cell, guard cells expand, and the stomata opens as a result of the osmotic gradient.
Water exits the guard cells.
There is a decrease in concentrations of K+, Cl-, and sugars when the stomata is closed.
Abscisic acid is a plant hormone.
The cells in the tissue are arranged in long columns and have thick walls.
xylem cells have a secondary cell wall that gives them more strength than the primary cell wall.
Water can be passed between xylem cells with little or no interference.
The cells that form fluid-conducting columns are the majority of the tissue.
The end walls of phloem cells allow for movement of organic materials between cells.
The walls of the xylem cells have hydrogen bonds with any adjacent polar substance because water is a polar covalent molecule.
Water cohesion is caused by hydrogen bonding between adjacent water molecules.
The water in the xylem cells behaves like a single molecule.
The water moves by bulk flow through the xylem when it is transmitted down the plant.
Since transpiration is caused by the heating action of the sun, it is the driving force for the ascent of water and dissolved minerals through plants.
Chemical reactions can no longer occur if water is unavailable.
During the later stages of fruit development, ethylene gas fills the intercellular air spaces within the fruit and stimulates its ripening by the breakdown of cell walls.
Fruit ripening is an example of a positive feedback mechanism.
The ripening process is accelerated when more and more ethylene is produced.
Plants can't move in response to environmental stimuli because they are anchored by their roots.
They change their growth pattern, modify their structures, or make other changes in response to abiotic and biotic stimuli.
Auxin moves down the shoot by active transport and increases the absorption of water.
The movement of H+ into the cell wall is stimulated by Auxin.
The decrease in pH causes the break down of connections between fibers.
The movement of water into the cell is promoted by this.
The stem grows straight when all sides of the apical meristem are illuminated.
On the shady side is where Auxin ends up.
The stem bends toward the light when the shady side grows more than the sunny side.
The action of auxin depends on its relative concentration and the target organ.
The lower side of the cell grows faster than the upper side, and the stem bends upward as it grows.
The assumption is that the auxin concentrates on the lower side of the root.
Maybe the concentration of auxin is different in roots than it is in shoots.
There is a need for more research to provide a more complete explanation.
When vines and other climbing plants come in contact with something, they wrap around it.
The mechanism for this kind of growth is not well understood.
The winter presents unfavorable conditions of cold temperatures, low light intensity, and a lack of water in the form of snow.
Plants respond to these conditions by shutting down their photosynthesis.
Valuable resources are withdrawn before leaves are released.
The fall colors of leaves are a result of the breakdown of pigments.
The approach of winter is determined by the changes in the length of daylight.
A seed has food and an embryo in it.
The inactive condition is maintained by the absence of water.
A tough seed coat protects the embryo.
When seeds drink water, they start cellular respiration.
Water may be needed to suck up the chemicals that affect germination.
Aerobic cellular respiration requires oxygen.
It is possible that temperature may also be a factor.
A minimum temperature is needed for the function of the enzyme, but a higher temperature is needed to signal that winter is over.
Other seeds need a specific temperature regime in order to respond to a warm temperature.
Fire is a common source of fire for species that grow in habitats where fires are common.
After a wildfire, seeds that are exposed to sunlight do not need to compete with established vegetation for water.
The burned vegetation has become available in the soil.
A photoperiod, or specific length of daylight, may be required for some seeds to grow.
Water absorption can begin if the seed coat is scarred or damaged.
If seeds are roughed up by animals, such scarification can occur.
gibberellins, produced by the embryo, bind to DNA and release transcription factors.
The genes that are activated by these transcription factors are needed for germination.
A-amylase contributes to the breakdown of carbohydrates in food.
The clock can be reset to maintain accuracy.
The mechanism for maintaining the rhythm is not fully understood.
There are two different forms of the same substance.
WhenPr is exposed to red light, it is converted to Pfr, and when Pfr is exposed to far-red light, it is converted back toPr.
The cytoplasm is where it is synthesised.
Exposure to the red light in sunlight convertsPr to Pfr.
Some of the Pfr is converted back into Pr because of the red light in the sun.
Because there is no sunlight, the conversion fromPr to Pfr and Pfr toPr breaks down faster.
The cell makesPr at night.
Night length affects the clock.
Daylight can be interrupted with a brief dark period.
The clock can be reset by flashes of red or far-red light during the night.
If a plant is exposed to a flash of red light during the night, it will convert back to Pfr and a shorter night period will be measured.
The effect of the red light is reversed if a flash of red light follows the red light.
The perception of night length is affected by the last flash of red and farred light.
Red light shortens the night and far-red light restores it.
Changes in the photoperiod can cause many flowering plants to start flowering.
The temperature or water can cause flowering.
It has been difficult to identify florigen in plants.
New research has shown that the production of florigen is complex with multiple genes and multiple pigments.
ConSTANS is involved in measuring day length.
The genes that produce an FT mRNA are the FT genes.
FT travels through phloem tissue to the shoot apex to initiate flower development.
The florigen is believed to be called FT.
The sharp edges of leaves are used to discourage herbivory.
When touched, some trichomes release sticky or noxious chemicals.
The bark of trunks and roots are examples of physical barriers.
Plants have a lot of toxic metabolites to discourage browsing.
For example, the nicotine in tobacco, the capsicum in hot peppers, and the mustard oils in broccoli are toxic to many insects.
Toxic products can be released when secondary metabolites are eaten in the gastrointestinal tract of animals.
Some plants recruit animals or other plants to help protect them from insects.
The plant releases volatile chemicals in response to the chewing insect.
The wasp lays its eggs on the insects and the eggs hatch.
In the above examples, volatile substances produced by one plant to attract predatory insects also serve as a signal to other plants that herbivores are nearby.
The opportunity to mount an early defense is given by this.
Ant protection is provided to certain acacia trees.
The hollow thorns of the acacias give sustenance.
In return, the ants provide security, attacking any browser that touches the plant and even trimming other plants that may shade the plant.
Chemicals that are present in the plant are used in the chemical defense.
The saliva of a chewing insect causes the hormone systemin to be produced in some plants.
Systemin is a hormone that is distributed throughout the plant.
The bicyle of the browsing insect is damaged by the binding of theidases to it.
In the hypersensitive response, a plant recognizes an invading pathogen and, in response, kills plant cells at and around the invasion site.
The dead tissues prevent the pathogen from spreading to other parts of the plant.
A review of the material presented in this chapter is provided by the questions that follow.
They can be used to evaluate how well you understand the concepts.
AP multiple-choice questions are often more general, covering a broad range of concepts.
The two practice exams in this book are for these types of questions.
Four possible answers or sentence completions are followed by each of the following questions or statements.
The one best answer or sentence is what you choose.
A flowering plant was exposed to a sequence of red and far-red light in the middle of the night.
Pfr is the active form of phytochrome.
At the end of the sequence, there would be high levels of Pfr.
At the end of the sequence, there would be low levels ofPr.
In short-day plants, flowering would start.
The leaf has low CO2 levels.
The guard cells are not being used.
The environment is very hot.
It is dark.
Shoots move toward light.
Auxin diffuses down the stem when it is produced at the shoot tip.
There is Auxin on the shady side of the shoot.
Active transport moves auxin down a stem.
The questions that follow are typical of an entire AP exam question or just that part of a question that is related to this chapter.
There are two types of questions on the AP exam.
It takes about 20 minutes to answer a long free-response question.
Sometimes they offer you a choice of questions to answer.
6 minutes is the time it takes to answer a short free-response question.
diagrams can be used to supplement your answers, but a diagram alone is not adequate.
"A rotten apple spoils the barrel" is a phrase that originated from the observation that a ripened fruit placed in a container of many unripened fruits will lead to their quick ripening.
In two or three sentences, explain how one ripe fruit can cause other fruit to grow.
In one or two sentences, describe an environment in which daytimelength wouldn't be useful for flowering.
The movement of water through xylem is dependent on transpiration.
osmotic pressure can't occur in xylem because it consists of dead cells.
phloem cells do not transport water.
It is not known if chlorophyll is involved in flowering.
The last light that the plants were exposed to made the final conversion.
Since red light was last used, all of thePr is converted to Pfr, a shorter night period is measured, and the clock is reset.
Short-day plants are unaffected by flowering in long-day plants.
When the stomata is open, the levels of CO2 in leaves are low.
CO2 levels increase as a result of respiration when the environment is hot and dry.
Guard cells close when water moves out of the cells, relaxing the guard cells and allowing the stoma to close.
There is a gas in the plant that promotes ripening.
Fruit is picked green and artificially ripened before it is delivered to markets.
Although auxin is produced at the apical meristem, it does not move down the stem by diffusion, as indicated in choice D.
Most plant roots have a mutualistic relationship with mycorrhizae.
In areas where gas exchange occurs, the cuticle and stomata don't increase surface area.
The density of phloem cells does not affect transpiration.
Many plants in hot climates have smaller leaves.
Plants with leaves that are vertically oriented reduce the amount of surface area exposed to the sun.
Air bubbles prevent the transport of water because they interrupt the continuity of water columns.
The tension in xylem is caused by the pulling force generated by the sun through transpiration.
There is a hormone that makes fruit ripening quicker.
If the fruit and gas are restricted to a closed container, it affects the fruit from where it came from, as well as nearby fruit.
There are no significant differences in day and night lengths.
Day and night lengths are not useful for identifying the beginning of a season.
Water enters roots through root hairs, hair-like extensions of cells.
Mycorrhizae, a mutualistic relationship between the plant roots and fungi, increases surface area and aids in the absorption of water and minerals.
Water can be moved from one cell to the next through the cell walls or through the root.
Water moves through a tube through the dead cells of the xylem to the leaves and other plant parts.
The leaves have water in them.
The movement of water is explained by the theory.
The water is pulled up a column by the transpiration of water.
The stability of the water column is maintained by the water molecule's attachment to the sides of xylem cells.
The sun is the driving force for this mechanism.
The mechanisms described in this chapter could be chosen by you.
The question doesn't limit you to any specific mechanism.
You may be asked to choose from a list of mechanisms.
Thechoices would likely be among different kinds of organisms, not just plants, in an actual multi-part question on the exam.
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