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BFI - Plants flashcards
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Card 1
How does the structure of chlorophyll a contribute to its function in photosynthesis?
Chlorophyll a has a porphyrin ring head containing a magnesium atom, which is the site where light energy is absorbed. Its hydrocarbon tail anchors the molecule within the hydrophobic pocket of proteins in the thylakoid membranes, positioning it correctly for light capture.
Card 2
Define the relationship between the absorption spectrum and the action spectrum in photosynthesis.
The absorption spectrum illustrates the wavelengths of light absorbed by a specific pigment, such as chlorophyll a or b. The action spectrum, conversely, shows the rate of photosynthesis at different wavelengths of light, generally mirroring the combined absorption spectra of photosynthetic pigments, indicating which absorbed light is effectively used for photosynthesis.
Card 3
Explain the role of the proton gradient in ATP synthesis during the light-dependent reactions.
During the electron transport chain, protons (H+) are pumped from the stroma into the thylakoid space, creating a proton gradient where the H+ concentration is much higher inside the thylakoid space. This gradient drives protons through ATP synthase back into the stroma, and this movement powers the synthesis of ATP from ADP and inorganic phosphate.
Card 4
Distinguish between chlorophyll a and chlorophyll b based on their roles and structural differences.
Chlorophyll a is the primary pigment directly involved in capturing light energy and has a CH3 functional group. Chlorophyll b is an accessory pigment that absorbs light at different wavelengths and transfers this energy to chlorophyll a, characterized by a CHO functional group.
Card 5
Why do plants appear green?
Plants appear green because chlorophyll molecules within the thylakoid membranes of chloroplasts absorb blue and red light for photosynthesis, but they transmit or reflect green light. This reflected green light is what our eyes perceive.
Card 6
How does the Calvin Cycle utilize the products of the light-dependent reactions?
The Calvin Cycle uses the ATP and NADPH generated during the light-dependent reactions. ATP provides the energy, and NADPH provides the reducing power, both essential for converting carbon dioxide into glucose and regenerating RuBP.
Card 7
Define photolysis and explain its significance in the light-dependent reactions.
Photolysis is the process where light energy absorbed by chlorophyll in Photosystem II is used to split water molecules (H2O). This process is significant because it releases oxygen as a byproduct, provides protons (H+) that contribute to the proton gradient, and supplies electrons (e-) for the electron transport chain.
Card 8
What is the primary function of carotenoids in photosynthesis?
Carotenoids are accessory pigments that primarily absorb some blue light to protect chlorophyll from damage. They also absorb light energy and transfer it to chlorophyll a to be used in photosynthesis.
Card 9
How does carbon fixation occur in the Calvin Cycle?
Carbon fixation begins when carbon dioxide from the atmosphere enters the stroma and is attached to a five-carbon sugar molecule called RuBP. This reaction is catalyzed by the enzyme rubisco, forming an unstable six-carbon compound that quickly splits into two molecules of a three-carbon compound.
Card 10
What are the net products of the light-dependent reactions and what are their fates?
The net products of the light-dependent reactions are ATP, NADPH, and oxygen (O2). ATP and NADPH carry chemical energy and reducing power, respectively, to the Calvin Cycle to synthesize glucose. Oxygen is released as a byproduct.
Card 11
Explain how the electron transport chain contributes to ATP synthesis in photosynthesis.
As electrons from photolysis move along a series of protein carriers in the thylakoid membrane, some of their released energy is used to pump protons (H+) from the stroma into the thylakoid space. This pumping action creates a proton gradient, which is then utilized by ATP synthase to produce ATP.
Card 12
What is the role of Photosystem II in the light-dependent reactions?
Photosystem II is where light energy is initially absorbed by chlorophyll to initiate the splitting of water molecules (photolysis). This process releases electrons, protons, and oxygen, thereby providing the electrons needed to start the electron transport chain.
Card 13
How do the functional groups in chlorophyll a and chlorophyll b relate to their distinct properties?
Chlorophyll a has a methyl group (CH3) as a functional group, while chlorophyll b has an aldehyde group (CHO). These different functional groups alter their light absorption properties, allowing them to absorb light at slightly different wavelengths and thus broaden the spectrum of light usable for photosynthesis.
Card 14
What is the significance of the difference in pH between the thylakoid space and the stroma during light-dependent reactions?
The pH difference, with the thylakoid space being around 5 and the stroma around 8, signifies a substantial proton (H+) concentration gradient. This gradient, where H+ is about 1000 times more concentrated inside the thylakoid space, provides the electrochemical potential energy that drives ATP synthesis via ATP synthase.
Card 15
Where do the oxygen atoms in the glucose molecule produced during photosynthesis originate?
The oxygen atoms in the glucose molecule (C6H12O6) and the newly formed water molecules during photosynthesis originate from the carbon dioxide (CO2) incorporated during the Calvin Cycle, not from the water molecules split during the light-dependent reactions.
Card 16
What is the purpose of regenerating RuBP in the Calvin Cycle?
Regenerating RuBP (ribulose bisphosphate) is crucial because it is the initial five-carbon sugar molecule that accepts CO2 during carbon fixation. For the Calvin Cycle to continue producing glucose, RuBP must be continuously replenished using ATP and five out of every six G3P molecules produced.
Card 17
Why is rubisco an important enzyme in photosynthesis?
Rubisco (ribulose bisphosphate carboxylase) is a critical enzyme because it catalyzes the initial step of carbon fixation in the Calvin Cycle. It attaches atmospheric carbon dioxide to RuBP, forming an unstable six-carbon compound that quickly splits, thereby initiating the synthesis of glucose.
Card 18
Describe the journey of electrons in the light-dependent reactions from water to NADPH.
Electrons are released from the splitting of water molecules by light energy in Photosystem II. They then pass along an electron transport chain embedded in the thylakoid membrane, moving from Photosystem II to Photosystem I. Finally, at the outer surface of the thylakoid membrane, these electrons, along with protons, combine with NADP+ to form NADPH.
Card 19
How does the light energy absorbed by chlorophyll lead to the splitting of water?
Light energy absorbed by chlorophyll in Photosystem II excites electrons to a higher energy level. This energized state provides the necessary energy to drive the photolysis of water molecules (H2O), splitting them into H+, electrons, and oxygen.
Card 20
What is the primary difference in the energy requirements for the light-dependent and light-independent reactions?
The light-dependent reactions directly require light energy to split water and produce ATP and NADPH. In contrast, the light-independent reactions (Calvin Cycle) do not directly require light but depend on the chemical energy stored in the ATP and the reducing power of NADPH generated during the light-dependent reactions to synthesize glucose.
Card 21
Explain why the thylakoid membranes are arranged as stacked discs (grana).
The arrangement of thylakoid membranes into stacked discs, called grana, increases the surface area available for the light-dependent reactions. This maximizes the number of chlorophyll and other pigment molecules, as well as electron transport chain components and ATP synthase, allowing for efficient light capture and ATP/NADPH production.
Card 22
What is the significance of glyceraldehyde-3-phosphate (G3P) in the Calvin Cycle?
Glyceraldehyde-3-phosphate (G3P) is a crucial three-carbon compound formed during the reduction phase of the Calvin Cycle. For every six G3P molecules produced, one exits the cycle to be used for synthesizing glucose and other organic compounds, while the remaining five are used to regenerate RuBP.
Card 23
How do shorter wavelengths of visible light relate to energy content?
Shorter wavelengths of visible light correspond to higher energy content. For example, blue light, with its shorter wavelength, carries more energy than red light, which has a longer wavelength.
Card 24
Which specific part of the chlorophyll a molecule is responsible for anchoring it within the thylakoid membrane?
The hydrocarbon tail of the chlorophyll a molecule is responsible for anchoring it within the hydrophobic pocket of the proteins in the thylakoid membranes. This ensures the molecule is correctly positioned for light absorption.
Card 25
How does the accumulation of H+ in the thylakoid space lead to a proton gradient?
The accumulation of H+ in the thylakoid space occurs as electrons move along the electron transport chain, causing H+ to be pumped from the stroma into the thylakoid space. This creates a higher concentration of protons inside the thylakoid space compared to the stroma, establishing a proton gradient.
Card 26
How does the pH difference between the thylakoid space and the stroma contribute to ATP synthesis?
The thylakoid space has a pH of about 5, while the stroma has a pH of about 8, meaning H+ concentration is 1000 times higher inside the thylakoid space. This concentration gradient drives protons (H+) through ATP synthase, an enzyme complex in the thylakoid membrane, back into the stroma. This movement of protons powers the synthesis of ATP from ADP and inorganic phosphate.
Card 27
Define the physiological definition of a plant and explain why it is not sufficient for taxonomic classification.
The physiological definition of a plant focuses on metabolic processes like oxygen evolution during photosynthesis and the presence of chlorophyll a. While true for plants, this definition is not sufficient for taxonomic classification because other organisms, such as certain algae (e.g., kelp, Euglena, Ulva), also exhibit these characteristics but are not considered 'plants' in the evolutionary sense.
Card 28
What is the role of rubisco in the Calvin Cycle?
Rubisco (ribulose bisphosphate carboxylase) is an enzyme that catalyzes the first step of the Calvin Cycle, known as carbon fixation. It attaches carbon dioxide (CO2) from the atmosphere to a five-carbon sugar molecule, RuBP. The resulting six-carbon compound is unstable and quickly splits into two molecules of a three-carbon compound.
Card 29
Distinguish between the roles of the palisade mesophyll and spongy mesophyll in a leaf.
The palisade mesophyll consists of elongated, tightly packed cells located below the upper epidermis, containing a high concentration of chloroplasts. Its primary role is light absorption for photosynthesis. In contrast, the spongy mesophyll, located below the palisade mesophyll, has irregularly shaped cells with large air spaces between them, which facilitate gas exchange (CO2 and O2) within the leaf.
Card 30
Explain the significance of sporopollenin in the adaptation of land plants to terrestrial life.
Sporopollenin is a highly resistant polymer that forms the spore wall in all land plants. Its significance lies in protecting spores from desiccation (drying out) and environmental damage. This protective quality allows for the successful dispersal of spores through the air, which is crucial for reproduction in a terrestrial environment.
Card 31
How many molecules of ATP and NADPH are consumed to produce one molecule of glucose in the Calvin Cycle?
To produce one molecule of glucose (C6H12O6), the Calvin cycle must turn six times. This requires the consumption of 18 molecules of ATP (12 in the reduction step and 6 in regeneration) and 12 molecules of NADPH (in the reduction step).
Card 32
What is the primary function of stomata in a leaf, and what cells regulate their activity?
Stomata are pores, usually on the lower epidermis, that regulate gas exchange (CO2 intake and O2 release) and transpiration (water vapor release). Their opening and closing are controlled by specialized cells called guard cells.
Card 33
How does the process of ATP synthesis in the thylakoid membrane exemplify chemiosmosis?
ATP synthesis in the thylakoid membrane exemplifies chemiosmosis because it involves the movement of protons down their electrochemical gradient. The proton gradient, established by light-dependent reactions, drives H+ ions through ATP synthase, which harnesses this energy to phosphorylate ADP into ATP. This coupling of proton movement to ATP production is the essence of chemiosmosis.
Card 34
What is the key difference in mitotic cell division between Chlorophytes and Streptophytes?
Chlorophyte algal cells divide using a cleavage furrow, similar to animal cells. In contrast, Streptophyte mitotic cell division proceeds by the formation of a phragmoplast, which is a protein frame upon which the cell plate is built. This cell plate then becomes the precursor of the new cell wall.
Card 35
Why are land plants also referred to as Embryophytes?
Land plants are called Embryophytes because they possess an embryo. This embryo is the multicellular stage that develops after the zygote (formed by gamete fusion) and is retained within the female parent. This characteristic is a key distinguishing feature of land plants.
Card 36
Describe the overall net products of the light-dependent reactions of photosynthesis.
The net products of the light-dependent reactions are ATP and NADPH. ATP carries chemical energy, and NADPH carries reducing power, both of which are then supplied to the Calvin Cycle. Oxygen (O2) is released as a byproduct of these reactions.
Card 37
What is the role of the cuticle in land plants?
The cuticle is a waxy layer made of cutin that covers the epidermis of all land plants. Its primary role is to act as a waterproof layer, preventing excessive water loss from the plant's surface, which is a crucial adaptation for survival in terrestrial environments.
Card 38
How is the oxygen (O2) released during photosynthesis formed?
The oxygen (O2) evolved in photosynthesis originates solely from the photolysis of water. Water molecules are split during the light-dependent reactions, releasing electrons, protons, and oxygen as a byproduct.
Card 39
What is the definition of Viridiplantae?
Viridiplantae is a broader taxonomic group that encompasses all green algae, including Chlorophytes and Charophytes, as well as all land plants. It represents a significant lineage within the Archaeplastida.
Card 40
Explain how the Calvin Cycle uses the products of the light-dependent reactions.
The Calvin Cycle takes place in the stroma and utilizes the ATP and NADPH generated during the light-dependent reactions. ATP provides the energy, and NADPH provides the reducing power necessary to convert carbon dioxide (CO2) into glucose and other organic compounds through a series of biochemical reactions.
Card 41
What is the function of veins (vascular bundles) in a leaf?
Veins (vascular bundles) in a leaf contain xylem and phloem. Xylem is responsible for transporting water and minerals to the leaf, while phloem transports sugars, produced during photosynthesis, away from the leaf to other parts of the plant.
Card 42
Distinguish between the gametophyte and sporophyte generations in the alternation of generations.
The gametophyte is the haploid (n) generation that produces gametes (sperm and egg) through mitosis. The sporophyte, in contrast, is the diploid (2n) generation that produces spores through meiosis. These two distinct multicellular stages alternate in the life cycle of land plants.
Card 43
What is the fate of 2H+ and 2e- after they flow through the thylakoid membrane?
After flowing through the thylakoid membrane, 2H+ and 2e- are reunited at the outer surface of the thylakoid membrane. Here, they combine with NADP+ to form NADPH + H+, a molecule crucial for the reducing power needed in the Calvin Cycle.
Card 44
Which group of green algae is considered the closest relative of land plants?
Charophytes are freshwater green algae that are considered the closest living relatives of the land plants. This relationship is supported by shared characteristics, particularly in their mitotic cell division processes.
Card 45
What is carbon fixation in the context of the Calvin Cycle?
Carbon fixation is the initial step of the Calvin Cycle where atmospheric carbon dioxide (CO2) is incorporated into an organic molecule. Specifically, CO2 enters the stroma and is attached to a five-carbon sugar molecule, RuBP, a reaction catalyzed by the enzyme rubisco.
Card 46
How many molecules of G3P are produced for every six turns of the Calvin cycle, and how many are used to synthesize glucose?
For every six turns of the Calvin cycle, 12 molecules of G3P are produced. Out of these, one molecule exits the cycle to be used for synthesizing glucose and other organic compounds, while the remaining five molecules are used to regenerate RuBP.
Card 47
What are multicellular gametangia, and what are their specific female and male forms?
Multicellular gametangia are structures found in land plants that produce gametes. The female gametangium is called the archegonium, which produces a single egg. The male gametangium is called the antheridium, which produces sperm.
Card 48
Where does the Calvin Cycle take place within the chloroplast?
The Calvin Cycle takes place in the stroma of the chloroplast. This is the fluid-filled space surrounding the thylakoids, where the ATP and NADPH produced during the light-dependent reactions are utilized.
Card 49
What is the significance of the fact that the embryo is retained within the female parent in land plants?
The retention of the embryo within the female parent is a key characteristic of land plants (Embryophytes). This adaptation provides protection and nourishment to the developing young sporophyte, increasing its chances of survival in a terrestrial environment.
Card 50
What is the function of ATP synthase in the thylakoid membrane?
ATP synthase is an enzyme complex located in the thylakoid membrane. Its function is to facilitate the flow of protons (H+) from the thylakoid space, down their concentration gradient, back to the stroma. This movement of protons drives the synthesis of ATP from ADP and inorganic phosphate (Pi).
Card 51
How do Streptophytes and Chlorophytes differ in their mitotic cell division process?
Streptophytes, which include land plants and Charophytes, divide using a phragmoplast, a protein frame upon which the cell plate is built, forming the precursor to the cell wall. In contrast, Chlorophyte algal cells divide using a furrow, similar to animal cells.
Card 52
Define 'Alternation of Generations' as it applies to land plants.
Alternation of Generations is a fundamental life cycle characteristic of land plants, involving the alternation between a diploid (2n) sporophyte generation and a haploid (n) gametophyte generation. The sporophyte produces spores through meiosis, while the gametophyte produces gametes through mitosis.
Card 53
What is the function of sporopollenin in land plants, and why is it considered a key adaptation for terrestrial life?
Sporopollenin is a highly resistant polymer that forms the spore wall in all land plants. It protects spores from desiccation and environmental damage, which is crucial for their survival and dispersal through the air in a terrestrial environment.
Card 54
Distinguish between an archegonium and an antheridium.
An archegonium is the female gametangium that produces a single egg, while an antheridium is the male gametangium that produces sperm. Both are multicellular structures involved in gamete production in seedless land plants.
Card 55
How do the dominant generations differ between mosses and ferns?
Mosses typically have a dominant gametophyte generation, meaning the haploid gametophyte is the more prominent and long-lived stage of their life cycle. Ferns, on the other hand, have a dominant sporophyte generation, where the diploid sporophyte is the more conspicuous plant.
Card 56
What is the primary characteristic that distinguishes seed plants from other major groups of land plants like mosses and ferns?
Seed plants are primarily distinguished by the production of seeds. A seed contains an embryo and a food supply, protected within a seed coat, which allows for greater dispersal and survival compared to the spore-based reproduction of mosses and ferns.
Card 57
Explain the difference between gymnosperms and angiosperms.
Gymnosperms, meaning 'naked seeds,' are seed plants whose seeds are typically borne on cones and are not enclosed within an ovary. Angiosperms, in contrast, are seed plants whose seeds are enclosed within a fruit, which develops from the flower.
Card 58
How does the Columbine flower attract hummingbirds for pollination, despite potentially lacking a strong scent?
The Columbine flower attracts hummingbirds by offering nectar in a spur. Hummingbirds, which may lack a strong sense of smell, are able to access this nectar with their long beaks, making the scent less critical for their attraction.
Card 59
Why are UV patterns on flowers important for bee pollination?
UV patterns on flowers serve as 'nectar guides' that are visible to insects like bees. These patterns direct pollinators towards the nectar source, increasing the efficiency of pollination.
Card 60
Describe the unique pollination relationship between the Yucca flower and moths.
The Yucca flower, which is white and produces nectar at night, is pollinated by moths. The moth deliberately pollinates the flower and then lays an egg within the flower's ovary. The developing larva consumes only a portion of the many seeds produced, ensuring both the moth's offspring and the plant's reproduction.
Card 61
What adaptation allows the coconut fruit to be dispersed by water?
The coconut fruit has a fibrous husk (mesocarp) that provides air-filled buoyancy. This adaptation allows the coconut to float on water, facilitating its dispersal across aquatic environments.
Card 62
Define a 'simple fruit' and provide an example from the notes.
A simple fruit develops from the ovary of a single flower. An example provided is the pea fruit (Pisum), where the ovary matures directly into the fruit.
Card 63
How does an 'aggregate fruit' differ from a 'multiple fruit'?
An aggregate fruit develops from multiple carpels within a single flower, with each 'bump' on a raspberry being a fruitlet from a separate carpel. A multiple fruit, conversely, develops from the fusion of many flowers in an inflorescence, where each segment of a pineapple, for instance, originates from the carpel of one flower.
Card 64
Why is an apple considered an 'accessory fruit'?
An apple is considered an accessory fruit because its edible fleshy tissue is derived from parts other than the ovary, specifically the receptacle. The ovary itself is located below the point of insertion, making it an inferior ovary.
Card 65
Distinguish between epigeal and hypogeal germination.
In epigeal germination, the cotyledons are lifted above the ground by the elongation of the hypocotyl, as seen in common beans. In contrast, hypogeal germination involves the cotyledons remaining below the ground, with the epicotyl elongating to push the first true leaves upwards, as observed in peas and corn.
Card 66
Which part of the common bean seedling elongates to pull the cotyledons and embryonic shoot upwards during epigeal germination?
During epigeal germination in the common bean, the hypocotyl arches and elongates, pulling the cotyledons and the embryonic shoot upwards above the ground.
Card 67
What is the role of the coleoptile in hypogeal germination, as exemplified by corn?
In hypogeal germination, particularly in corn, the coleoptile is a protective sheath that emerges from the soil first. Its role is to protect the delicate first leaves as they push through the soil before they unfurl.
Card 68
How do elaiosomes contribute to seed dispersal?
Elaiosomes are food bodies attached to some seeds that attract ants. Ants carry the seed to their nest, consume the elaiosome, and then discard the seed, effectively dispersing it away from the parent plant.
Card 69
What are the characteristics of seeds or fruits adapted for wind dispersal?
Seeds or fruits adapted for wind dispersal are typically lightweight and may possess specialized structures such as wing-like appendages (e.g., maple fruits) or parachute-like structures (e.g., dandelion fruits) to aid in their aerial transport.
Card 70
Why is the embryo considered the 'young sporophyte' in land plants?
The embryo is considered the young sporophyte because it is the multicellular stage that develops directly after the zygote (formed by the fusion of gametes). This embryo is diploid (2n) and will grow into the mature sporophyte plant.
Card 71
What is the significance of the embryo being retained within the female parent in land plants?
The retention of the embryo within the female parent is a key characteristic of land plants. This provides protection and nourishment to the developing embryo, increasing its chances of survival in the terrestrial environment.
Card 72
How does the presence of stomata represent an adaptation for terrestrial life in most land plants?
Stomata are pores on the surface of most land plants that regulate gas exchange, allowing for CO2 uptake for photosynthesis and O2 release. This controlled gas exchange is a crucial adaptation for terrestrial life, balancing the need for carbon dioxide with the risk of water loss through transpiration.
Card 73
What is the primary role of the cuticle in land plants?
The primary role of the cuticle, a waxy layer covering the epidermis of all land plants, is to help prevent water loss. It acts as a boundary to the wind, keeping water in the plant, which is essential for survival in a terrestrial environment.
Card 74
How does the 'caching' mechanism of animal dispersal work?
Caching involves animals, such as squirrels, hiding seeds for later consumption. Not all cached seeds are recovered by the animal, leading to their dispersal and potential germination in new locations away from the parent plant.
Card 75
Why do some flowers, like carrion flowers (e.g., Stapelia), mimic decaying flesh?
Some flowers, like carrion flowers, mimic the appearance and scent of decaying flesh to attract flies. The flies are 'fooled' into visiting the flower, thereby acting as pollinators, even though they do not receive nectar or other typical rewards.
Card 76
How does the presence of an elaiosome on a seed facilitate its dispersal?
An elaiosome is a food body attached to some seeds that attracts ants. Ants carry the seed to their nest, consume the elaiosome, and then discard the seed, effectively dispersing it away from the parent plant.
Card 77
Distinguish between epigeal and hypogeal germination based on the fate of the cotyledons.
In epigeal germination, the cotyledons are lifted above the ground by the elongation of the hypocotyl, often becoming photosynthetic. In contrast, hypogeal germination involves the cotyledons remaining below the ground, with the epicotyl elongating to push the first true leaves upwards.
Card 78
Define a 'multiple fruit' and provide an example.
A multiple fruit develops from the fusion of many flowers within an inflorescence. Each segment of the fruit originates from the carpel of one flower. A pineapple (Ananas) is a classic example of a multiple fruit.
Card 79
Why is nitrogen fixation by bacteria essential for most plants, even though nitrogen gas is abundant in the atmosphere?
Most plants cannot directly utilize atmospheric nitrogen gas (N2). They require nitrogen in the form of nitrate (NO3-) or ammonium (NH4+). Nitrogen-fixing bacteria possess the nitrogenase enzyme, which converts N2 into usable ammonia (NH3), making this vital nutrient available to plants.
Card 80
Explain the primary difference in fungal structure between ectomycorrhizae and arbuscular mycorrhizae.
Ectomycorrhizae form a dense fungal sheath (mantle) around the root tip and grow between cortical cells. Arbuscular mycorrhizae, however, do not form a sheath but instead develop branched, tree-like structures called arbuscules within the cortical cells of the root.
Card 81
What is the role of the coleoptile in corn during hypogeal germination?
In corn, during hypogeal germination, the coleoptile is a protective sheath that emerges from the soil first. Its primary role is to protect the delicate first leaves as they push through the soil, allowing them to emerge safely.
Card 82
How does an apple fruit qualify as an 'accessory fruit'?
An apple is considered an accessory fruit because its edible fleshy tissue is derived from parts other than the ovary, specifically the receptacle. The ovary is located below the point of insertion, making it an inferior ovary.
Card 83
Describe the mutualistic exchange that occurs in the symbiotic relationship between legumes and Rhizobium bacteria.
In this mutualistic relationship, Rhizobium bacteria residing in root nodules convert atmospheric N2 into ammonium (NH4+), providing fixed nitrogen to the plant. In return, the legume plant supplies the bacteria with carbohydrates (sugars) produced during photosynthesis.
Card 84
What characteristic adaptation allows a coconut (Cocos) to be dispersed by water?
The coconut has a fibrous husk (mesocarp) that provides air-filled buoyancy. This adaptation allows the coconut to float on water, enabling its dispersal across significant distances by ocean currents.
Card 85
Distinguish between photosynthetic parasites and non-photosynthetic parasites, providing an example for each.
Photosynthetic parasites, like mistletoe, possess chlorophyll and can photosynthesize but still obtain water and minerals from their host. Non-photosynthetic parasites, such as ghost pipe, lack chlorophyll and are entirely dependent on their host for all nutritional needs, including sugars.
Card 86
Why are carnivorous plants typically found in wet environments with organic soils deficient in certain nutrients?
Carnivorous plants thrive in these environments because their specialized trapping mechanisms allow them to supplement their nutrient intake, particularly nitrogen, by consuming insects. This adaptation compensates for the nutrient-poor soil conditions where they grow.
Card 87
How does the hypocotyl contribute to epigeal germination in a common bean?
In epigeal germination of a common bean, the hypocotyl arches and elongates. This action pulls the cotyledons and the embryonic shoot upwards, lifting them above the ground after the seed coat splits.
Card 88
What is the primary function of the fungal hyphae in both ectomycorrhizae and arbuscular mycorrhizae?
In both types of mycorrhizae, the fungal hyphae extend far into the soil. Their primary function is to increase the surface area for the absorption of water and essential nutrients, particularly phosphorus and nitrogen, which the plant then utilizes.
Card 89
Explain how caching by animals can lead to seed dispersal.
Animals like squirrels hide (cache) seeds for later consumption. However, not all cached seeds are recovered by the animal. The unrecovered seeds remain in the soil, often in new locations, leading to their dispersal and potential germination.
Card 90
What defines an 'epiphyte' and how does it obtain nutrients?
An epiphyte is a plant that grows on another plant without parasitizing it. It obtains minerals from the environment, such as dust and rain, and performs its own photosynthesis for energy, without taking nutrients or water directly from the host's vascular system.
Card 91
Describe the formation of an 'aggregate fruit' and provide an example.
An aggregate fruit develops from multiple separate carpels within a single flower. Each 'bump' on the fruit is a fruitlet derived from a distinct carpel. A raspberry (Rubus) is a common example of an aggregate fruit.
Card 92
What is the significance of bacteroids within legume root nodules?
Bacteroids are differentiated forms of nitrogen-fixing bacteria found within membrane-bound vesicles inside legume root nodules. They are the active sites where atmospheric nitrogen gas (N2) is converted into usable ammonium (NH4+), facilitating nitrogen fixation.
Card 93
How do pitcher plants (Sarracenia) acquire nutrients from insects?
Pitcher plants use a pitfall trap mechanism to capture insects. Insects are lured to the pitcher, tumble inside, and are then digested. The plant derives supplementary nutrients, particularly nitrogen, from the digested prey.
Card 94
Why is the enzyme nitrogenase crucial for the process of nitrogen fixation?
Nitrogenase is the enzyme solely responsible for converting atmospheric nitrogen gas (N2) into ammonia (NH3). This conversion is critical because most plants cannot directly utilize N2, and ammonia can then be transformed into other nitrogenous compounds usable by plants.
Card 95
In the context of fruit formation, what does it mean for an apple to have an 'inferior ovary'?
An apple is referred to as having an inferior ovary because the ovary is located below the point of insertion of other floral parts. This anatomical arrangement contributes to the development of the apple as an accessory fruit, where the receptacle forms the edible flesh.
Card 96
What is the primary nutrient that mycorrhizae associations are crucial for plants to uptake, besides water?
Mycorrhizal associations are crucial for enhancing plant nutrient uptake, particularly phosphorus (P) and nitrogen (N). The fungal hyphae extend the plant's reach into the soil, allowing for more efficient absorption of these vital elements.
Card 97
How do sundews (Drosera) capture their insect prey?
Sundews capture insects using specialized sticky secretions. These secretions, present on glandular hairs covering the plant's leaves, act as a trap, adhering to insects that land on them. The plant then digests the trapped prey to supplement its nutrient supply.
Card 98
Define 'symbiosis' in the context of plant relationships and list the three main types.
Symbiosis refers to any close and long-term biological interaction between two different biological organisms. The three main types are mutualistic (both benefit), commensalistic (one benefits, other unaffected), and parasitic (one benefits at the expense of the other).
Card 99
Why do the cotyledons in epigeal germination sometimes become photosynthetic?
In epigeal germination, the cotyledons are lifted above the ground by the elongating hypocotyl. Once exposed to sunlight, they may develop chlorophyll and become photosynthetic for a period, contributing to the seedling's early energy production before true leaves fully develop.
Card 100
How does the 'pericarp' of a coconut relate to its buoyancy for water dispersal?
The pericarp of a coconut consists of three parts: the endocarp, mesocarp, and exocarp. The mesocarp, which is the fibrous husk, is specifically responsible for providing the air-filled buoyancy that allows the coconut to float and be dispersed by water.
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