Chapter 12: Plants

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.