photosynthesis and reproduction in plants

describe double fertilization in angiosperms and explain what it achieves

1: A pollen tube releases two sperm cells into an unfertilized ovule. 2: Double fertilization occurs when one sperm cell fuses with the egg to produce a zygote, and the other sperm cell fuses with the two polar nuclei to make the endosperm. 3: After double fertilization, a seed and fruit develop.

how many molecules of ATP and NADPH are required to produce one molecule of a three-carbon sugar in the calvin cycle

6 nadph, 9 atp

explain the acid growth hypothesis of the effect of auxins on cell elongation

Acid Growth Theory states that when exposed to auxin, susceptible cells excrete protons into the wall (apoplast) at an enhanced rate, resulting in a decrease in apoplastic pH. The lowered wall pH then activates wall-loosening processes, the precise nature of which is unknown. Because exogenous acid causes a transient (1-4 h) increase in growth rate, auxin must also mediate events in addition to wall acidification for growth to continue for an extended period of time.

what is the action spectrum of light

An action spectrum is a graph of the rate of a physiological activity plotted against wavelength of light. It shows which wavelength of light is most effectively used in a specific chemical reaction. Some reactants are able to use specific wavelengths of light more effectively to complete their reactions.

how do C4 and CAM plants fix carbon compared to C3 plants

C4 plants initial steps of carbon fixation are separated structurally from the calvin cycle whereas in CAM plants, the two steps occur at separate times but within the same cell.

which are the photosynthetic pigments? compare their hydrophobicity

Chlorophyll a: This is the most abundant pigment in plants. Chlorophyll a absorbs light with wavelengths of 430nm(blue) and 662nm(red). It reflects green light strongly so it appears green to us. It contains a hydrophobic (fat soluble) phytol chain that allow it to be embedded in a lipid membrane. Chlorophyll b: This molecule has a structure similar to that of chlorophyll a. It absorbs light of 453nm and 642 nm maximally. It is not as abundant as chlorophyll a, and probably evolved later. It helps increase the range of light a plant can use for energy. Carotenoids: This is a class of accessory pigments that occur in all photosynthetic organisms. They are completely hydrophobic (fat soluble) and exist in lipid membranes. Carotenoids absorb light maximally between 460 nm and 550 nm and appear red, orange, or yellow to us.

why does the calvin cycle depend on light reactions and why do light reactions depend on calvin cycle

Chlorophyll and the other molecules responsible for the light reactions are built into the thylakoid membranes. The enzymes that catalyze the Calvin cycle are located in the stroma. Beginning with the absorption of light by chlorophyll, the light reactions convert light energy into chemical energy in the form of ATP and NADPH. The ATP provides the energy, and the NADPH supplies the electrons for the Calvin cycle, which converts carbon dioxide to sugar. The ADP and NADP+ that result from the Calvin cycle shuttle back to the light reactions, which regenerate ATP and NADPH.

what is the general function of ovules and pollen grains

During plant reproduction, pollen grains need to move from the anther of one flower to the stigma of another flower. This is called pollination. Insects can pollinate flowers, and so can the wind. Insect-pollinated flowers are different in structure from wind-pollinated flowers. Ovule, plant structure that develops into a seed when fertilized

how does ethylene help plants respond to mechanical stress

Ethylene production occurs after mechanical stimulation of plants and many studies suggest that ethylene may have a role in radial expansion aspects of thigmomorphogenesis although it is unlikely to be the primary signalling molecule that controls all touch responses.

what are the effects of ethylene on fruit ripening, senescence and leaf abscission

Ethylene, a gaseous hormone, appears to be a prime controlling agent in many aspects of plant senescence including the fading of flowers, the ripening of fruits, and the abscission of leaves. If an orchid flower goes un-pollinated it remains fresh for a long time, but very soon after it is pollinated it starts to fade. The reason for the post-pollination decline is that pollination initiates the production of ethylene, which then causes the senescence of the flower petals. The application of ethylene to many unripe fruits results in a marked rise in respiratory CO2 output called climacteric. Following this change, organic acids decline, intercellular pectin's are degraded, and fruit becomes ripe

explain the mechanism by which gibberellin stimulates seed germination. what other affects does gibberellin have

Gibberellins in the seed embryo are believed to signal starch hydrolysis through inducing the synthesis of the enzyme α-amylase in the aleurone cells. ... They stimulate cell elongation, breaking and budding, seedless fruits, and seed germination. Gibberellins also have a role in other plant processes, such as stem elongation, germination, flowering, and fruit ripening.

explain the process of imbibition

Imbibition is the process of adsorption of water by substances without forming a solution. Swelling of seeds when immersed in water is an example of imbibition. Imbibition is the temporary increase in the volume of the cell. Imbibition is a passive transport of materials that does not require energy during the process.

describe evidence that leads to charles and francis darwin to conclude that the tip of coleoptile is required of phototropism

In 1880 Charles Darwin and his son Francis found that coleoptiles only bend towards the light when their tips are exposed. ... The model proposes that auxin, a plant growth hormone, is synthesized in the coleoptile tip, which senses light or gravity and will send the auxin down the appropriate side of the shoot.

explain the functions of ATP and NADPH in the calvin cycle

In Photosynthesis, the role of ATP (together with NADPH) is to provide the energy needed for carbohydrate synthesis in the "dark" (Light-Independent) reactions. In photosynthesis, NADPH is generated (along with ATP) in the light-dependent reactions, and used in the light-independent reactions as a reducing agent in the Calvin cycle to reduce atmospheric carbon dioxide (CO2) producing monosaccharides for use by the plant for structure and energy.

what are the possible advantages of reduced gametophytes found in the seed plants

Increased cross fertilization and great dispersal of the next generation are the advantages of multicellular pollen and seeds. Spores are the way ferns and moss spread longer distances. Spores are single-celled and vulnerable .so dispersal is limited. Being tied to water, as moss & ferns are with flagellated gametes, makes self-fertilization more common so genetic recombination is at a low rate. Gymnosperm and angiosperm plants -keep the spore- until it matures as the entire male gametophyte or pollen. This groups them as Spermatophytes with multicellular pollen rather than single celled spores. Essentially the gametophyte phase is reduced to the brief period of reproduction. Male cones or male flower parts release the miniature gametophyte as the grain of pollen. Female cones or flower parts grow the female gametophyte in an ovule. In cones the ovule is sheltered by the cone's scale but is not enclosed. In flowers the ovule is inside an ovary. Spermatophytes have no flagellated gametes to restrict these plants to water for reproduction. With the mature, miniature, male gametophyte arriving as pollen the sperm nuclei are delivered to the egg nuclei to form a zygote. This allows -much- more recombination of genetic material with the mobility of pollen. Then the seed is the juvenile sporophyte that is also mobile & capable of dispersal. These plants are much less vulnerable to reproductive losses while ensuring cross-fertilization and dispersing to new locations.

What is Rubisco and what does it do?

It's an enzyme that transfers one carbon from a CO2 molecule to a five carbon molecule so it can start the Calvin-Benson Cycle. enzyme involved in the first major step of carbon fixation, a process by which atmospheric carbon dioxide is converted by plants and other photosynthetic organisms to energy-rich molecules such as glucose.

what type of chlorophyll a molecule is present in reaction centre for photosystem I and II

Photosystem II obtains electrons by oxidizing water in a process called photolysis. ... Due to the presence of chlorophyll a, as opposed to bacteriochlorophyll, photosystem II absorbs light at a shorter wavelength. The pair of chlorophyll molecules at the reaction center are often referred to as P680

Photosystems location, components, events that take place when they absorb light

Photosystems are found in the thylakoid membranes of plants, algae and cyanobacteria. They are located in the chloroplasts of plants and algae, and in the cytoplasmic membrane of photosynthetic bacteria. The Photosystem captures light with antennae pigments such as carotene, xanthophyll, Phaeophytin a, Phaeophytin b, chlorophyll a and chlorophyll b, which funnels it light and gradually concentrates it down to a "reaction center." When photosystem II absorbs light, electrons in the reaction-center chlorophyll are excited to a higher energy level and are trapped by the primary electron acceptors. Photoexcited electrons travel through the cytochrome b6f complex to photosystem I via an electron transport chain set in the thylakoid membrane.

give examples of mechanisms by which pollination is achieved

Pollinating agents are animals such as insects, birds, and bats; water; wind; and even plants themselves, when self-pollination occurs within a closed flower. Pollination often occurs within a species. When pollination occurs between species it can produce hybrid offspring in nature and in plant breeding work.

distinguish between short day, long day and day neutral plants

Short-day plants are those plants that flower when they are exposed to long periods of darkness and short periods of light. For a short-day plant to bloom, there must be less than 12 hours of daylight. The plants that bloom in the spring or later in the fall are considered short-day plants. A day-neutral plant is a plant that flowers regardless of the amount of light of daylight it receives. Corn and rice are examples day-neutral plants that will bloom whether the day is long or short. Long day plants are also called short night plants because they require darkness below a critical level.

why do plants require specific metabolic adaptions to live in arid climates

Some plants that live in hot, dry climates maintain low oxygen levels in their leaves by keeping the stomata closed to prevent water loss. To get adequate CO2 for photosynthesis, C4 plants have adapted to photorespiration by modifying the Calvin-Benson cycle. C4 plants have a special leaf anatomy, with prominent bundle sheath cells surrounding the leaf veins. Photorespiration is minimal in C4 plants compared to C3 plants, and CO2 is actively concentrated in these bundle sheath cells.

what features of seeds make them particularly advantageous for terrestrial plants

Storage tissue to sustain growth and a protective coat give seeds their superior evolutionary advantage. Several layers of hardened tissue prevent desiccation, freeing reproduction from the need for a constant supply of water. Furthermore, seeds remain in a state of dormancy induced by desiccation and the hormone abscisic acid until conditions for growth become favorable. Whether blown by the wind, floating on water, or carried away by animals, seeds are scattered in an expanding geographic range, thus avoiding competition with the parent plant.

Explain the role of the central vacuole, and orientation of cellulose fibers in the process of cell elongation in plants

Stores water, enzymes, metabolic wastes and other material. Forms as other smaller vacuoles fuss together. Can make up 90 percent of the plant cell's volume and push all other organelles into a thin layer against the cell membrane. Cell expands and the plant stands upright. orientation of cellulose fibres causes differential growth. the microfibrils do not stretch, so the cell expands mainly perpendicular to the main orientation of the microfibrils. microfibrils play a key role in regulating the plane of cell expansion. the orientation of microtubules in the cells outermost cytoplasm that determines the orientation of cellulose microfibrils, the basic structural units of the cell wall

describe the path of electrons in the linear electron flow of photosynthesis

Sunlight is absorbed by photosynthetic pigments, the most abundant of which in plants are the chlorophylls. Absorption of light excites an electron to a higher energy state, thus converting the energy of sunlight to potential chemical energy. The photosynthetic pigments are organized into photocenters in the thylakoid membrane, each of which contains hundreds of pigment molecules. The many pigment molecules in each photocenter act as antennae to absorb light and transfer the energy of their excited electrons to a chlorophyll molecule that serves as a reaction center. The reaction center chlorophyll then transfers its high-energy electron to an acceptor molecule in an electron transport chain. High-energy electrons are then transferred through a series of membrane carriers, coupled to the synthesis of ATP and NADPH.

why are the absorption spectra of the photosynthetic pigments and the action spectrum of photosynthesis different

The absorption spectrum indicates how much of each wavelength chlorophyll will absorb, whereas the action spectrum can tell us which off those wavelengths are most effective in photosynthesis

describe the evidence showing that night length is critical factor in photoperiodism

The critical factor responsible for flowering is the length of light and dark periods, which is detected by phytochromes

describe the general structure of flowers. which components of the flower develop into the seed and fruit

The female parts of a flower consist of an ovary, which contains one or more ovules, a style and the stigma. The ovary is at the base of the flower. From the ovary, extends a tubular structure called the style and on the top of the style is a surface receptive to pollen called the stigma. Ovary: female reproductive structure of flower that usually develops into the fruit. Pericarp: fruit tissues surrounding the seeds that are derived from the ovary. Ovule: egg-bearing structure of the flower that develops into a seed

which is the final electron acceptor in the linear electron flow

The final electron acceptor is NADP

what are the products of the calvin cycle

The immediate products of one turn of the Calvin cycle are 2 glyceraldehyde-3-phosphate (G3P) molecules, 3 ADP, and 2 NADP+. (ADP and NADP+ are not really "products." They are regenerated and later used again in the Light-dependent reactions). Each G3P molecule is composed of 3 carbons

describe the process of chemiosmosis in photosynthesis considering processes that generate the proton gradient and function in ATP synthase

The light reactions of photosynthesis generate ATP by the action of chemiosmosis. ... These protons then flow down their electrochemical potential gradient through an enzyme called ATP-synthase, creating ATP by the phosphorylation of ADP to ATP.

as electrons flow through the ETC between photosystems I and II, energy is released. what is this energy used for

The two photosystems absorb light energy through proteins containing pigments, such as chlorophyll. The light-dependent reactions begin in photosystem II. In PSII, energy from sunlight is used to split water, which releases two electrons, two hydrogen atoms, and one oxygen atom.

compare linear and cyclic electron flow based on path of electrons and NADP+ reduction

Under certain conditions, the photoexcited electrons take an alternative path called cyclic electron flow, which uses photosystem I (P700) but not photosystem II (P680). This process produces no NADPH and no O2, but it does make ATP. This is called cyclic photophosphorylation. The chloroplast shifts to this process when the ATP supply drops and the level of NADPH rises. Often the amount of ATP needed to drive the Calvin cycle exceeds what is produced in non-cyclic photophosphorylation. Without sufficient ATP, the Calvin cycle will slow or even stop. The chloroplast will continue cyclic photophosphorylation until the ATP supply has been replenished. ATP is produced through chemiosmosis in both cyclic and non-cyclic photophosphorylation. In the first route, electrons released from water in photosystem II (PSII) are eventually transferred to NADP+ by way of photosystem I (PSI). ... Whereas linear flow from water to NADP+ is commonly used to explain the function of the light-dependent reactions of photosynthesis, the role of cyclic flow is less clear.

which of the substrates of photosynthesis undergoes oxidation and which one undergoes reduction

Water is oxidized in photosynthesis, which means it loses electrons, and carbon dioxide is reduced, meaning it gains electrons

what is the function of water in photosynthesis

Water splits into oxygen, hydrogen ions, and electrons to replace the lost electrons of photosystem II in light-dependent reaction. Also, as hydrogen ions pass through ATP synthase, ATP is formed to use in the light-independent reaction.

what atomic events take place when isolated chlorophyll molecules absorb a photon of light

When light hits the chlorophyll molecule, it becomes excited. This energy passes through other chlorophyll molecules, and into the reaction center of Photosystem II: this is the location of the first stage of photosynthesis, and the electron transport chain.

what is the absorption spectrum of a substance

a graph plotting a pigments light absorption vs wavelength

define seed dormancy and provide examples of environmental cues for seed germination

a state in which seeds are prevented from germinating even under environmental conditions normally favorable for germination. These conditions are a complex combination of water, light, temperature, gasses, mechanical restrictions, seed coats, and hormone structures. germination depends on inhibition, the uptake of water die to low water potential of the dry seed. inhibiting water causes the seed to expand and rupture its coat and also triggers metabolic changes in the embryo that enviable it to resume growth. following hydration, enzymes begin digesting storage materials of the endosperm and cotyledon and the nutrients are transferred tot he growing regions of the embryo

what are the three stages of the calvin cycle

carbon fixaton, reduction, regernationn of the CO2 acceptor (RuBP)

which common plant species use the C4 or CAM metabolic pathways and in which part of the world are these species usually found

crassulaceae plant family (stone crop family) found in dry arid conditions

describe how cytokinins and auxin act antagonistically in the control of apical dominance

cytokinin responses are also negatively regulated by auxin. ... Consequently, the reduced levels of cytokinin increase apical dominance and inhibit axillary bud growth. MicroRNAs (miRNAs), which are post-transcriptional negative regulators in plants, are thought to play important roles in regulating shoot branching

what are the products of light reactions of photosynthesis

he end product, hygrogen is picked up by NADP(Nicotinamine Adenine Dinucleotide Phosphate) to form NADPH. The oxygen formed is released as molecular oxygen in atmosphere. The electron is used to convert ADP(Adenosine Diphosphate) to ATP(Adenosine Triphosphate). This process is called photophosphorylation since it occurs in presence of light.

what determines the colour of an object? why are leaves often green?

if a pigment is illuminated with white light, the colour we often see is the colour most reflected or transmitted by the pigment. we see green when we look at a leaf because chlorophyll absorbs violet-blue and red light while transmitting and reflecting green light.

compare common garden beans and maize in terms of their methods of breaking ground during germination

in the common garden beans, straightening of a hook in the hypocotyl pulls the cotyledons from the soil. in maize and other grasses, the shoot grows straight up through a tube of the coleoptile

how would global warming affect the prevalence and distribution of C3, C4 and CAM plants

increase their abundance and stretch over a further area

what are the two stages of photosynthesis and where in the chloroplast do they take place

light reactions and the calvin cycle and they occur in the thylakoid and stroma

what is the relationship between photorespiration, photosynthesis and arid environments

photorespiration occurs in the light and consumes O2 while producing CO2. unlike normal cellular respiration, photorespiration uses ATP rathe than generating it. and unlike photosynthesis, photorespiration produces no sugar. photorespiration decreases photosynthetic output by organic material from the calvin cycle that would otherwise be fixed

provide examples of photoautotrophs

plants, multicellular algae, unicellular protists, cyanobacteria and purple sulphur bacteria

evidence that lead francis went to conclude that auxin promotes cell growth

promote stem elongation, inhibit growth of lateral buds (maintains apical dominance). They are produced in the stem, buds, and root tips. Example: Indole Acetic Acid (IA). Auxin is a plant hormone produced in the stem tip that promotes cell elongation. Auxin moves to the darker side of the plant, causing the cells there to grow larger than corresponding cells on the lighter side of the plant. This produces a curving of the plant stem tip toward the light, a plant movement known as phototropism. Auxin also plays a role in maintaining apical dominance. Most plants have lateral (sometimes called axillary) buds located at nodes (where leaves attach to the stem). Buds are embryonic meristems maintained in a dormant state. Auxin maintains this dormancy. As long as sufficient auxin is produced by the apical meristem, the lateral buds remain dormant. If the apex of the shoot is removed (by a browsing animal or a scientist), the auxin is no longer produced. This will cause the lateral buds to break their dormancy and begin to grow. In effect, the plant becomes bushier. When a gardener trims a hedge, they are applying apical dominance.

specify the exact intracellular location of the calvin cycle

stroma (the inner space of chloroplasts)

define wavelength in relation to light. how does the wavelength correlate with the amount of energy contained in light

the distance between the crests of electromagnetic waves. their range radiation is known as the electromagnetic spectrum and is known and visible light. the amount of energy is inversely related to the wavelength of the light: the shorter the wavelength, the greater the energy of each photon of that light. thus, a photon of violet light packs nearly twice as much energy as a photon of red light

Contrast sperm delivery in seedless plants with sperm delivery in seed plants.

the flagellated sperm of seedless vascular plants must swim through a film of water, usually over a distance of no more than a few centimeters. In contrast, the sperm of seed plants do not require water because are they produced within pollen grains that can be transported long distances by wind or by animal pollinators.

Define phototropism

the orientation of a plant or other organism in response to light, either toward the source of light ( positive phototropism ) or away from it ( negative phototropism ).

what are the three possible processes that light waves undergo when light shines on an object

when light meets matter, it can be reflected, transmitted or absorbed

explain how phototropism results from a difference in cell elongation between brighter and darker side of a shoot

when shoots curve toward light, they do so because there is a higher concentration of the growth promoting chemical on the darker side of the shoot. an uneven distribution of auxin moving down from the shoot tip causes cells on the carker side to elongate faster than cells on the brighter side.