Bio 102 Quiz #6

Plant hormones are chemical signals that play a crucial role in regulating various processes such as growth and development in plants. They are not required to be produced in large quantities to be effective, as even small amounts can have significant effects. These hormones act on specific target cells and tissues, rather than all cells they encounter. Additionally, different plant hormones often interact and work together in a coordinated manner, rather than independently. Plant hormones are not rare; they are naturally produced by plants in response to various internal and external stimuli, including stress.

Thigmotropism is the correct answer because it refers to the plant's response to touch or mechanical stimulation. When a plant comes into contact with an object, it can change its growth pattern to either curl around the object or avoid it. This response allows the plant to adapt to its environment and protect itself from potential harm.

Placing a green tomato in a sealed plastic bag with an overripe banana would be a good way to ripen it. This is because bananas release ethylene gas, which is a natural plant hormone that promotes ripening. By sealing the tomato with the banana in a bag, the ethylene gas is trapped and concentrated around the tomato, accelerating the ripening process.

Plants grow towards the light through the action of hormones. Specifically, the hormone auxin plays a crucial role in this process. When light is received by the plant, auxin accumulates on the shaded side of the stem, causing the cells on that side to elongate. This differential growth causes the plant to bend towards the light source. This phenomenon is known as phototropism and allows plants to optimize their exposure to sunlight for photosynthesis.

Auxins are plant hormones that play a crucial role in plant growth and development. One of the main effects of auxins is to promote cell division and elongation. Auxins stimulate the growth of plant cells by increasing their rate of division, leading to the formation of new cells. Additionally, auxins also promote cell elongation, which results in the elongation and expansion of plant tissues. This overall effect of auxins on plant growth leads to increased growth and development of the plant.

When a plant is not pollinated, it produces fruit that lacks seeds. This is because the formation of seeds in a fruit is a result of successful pollination and fertilization. Without pollination, the plant does not receive the necessary pollen to fertilize the ovules and develop seeds. Therefore, the fruit that forms on an unpollinated plant will be seedless.

If the auxin produced by an apical meristem is transported in equal amounts down all sides of a twig, it will likely elongate evenly. Auxin is a plant hormone that promotes cell elongation and growth. When it is distributed evenly on all sides of a twig, it will stimulate growth in a balanced manner, causing the twig to elongate uniformly. This is in contrast to when auxin is concentrated on one side of a plant, which can cause uneven growth and bending towards the side with higher auxin levels.

The holes in the plastic bags facilitate the diffusion of ethylene away from the fruit. Ethylene is a natural plant hormone that promotes ripening and can cause fruits to overripen quickly. By allowing ethylene to escape through the holes in the bag, the fruits are less likely to overripen and can stay fresh for longer periods of time.

Auxin is a plant hormone that promotes cell elongation. When grass shoots are in the shadow, there is a reduction in auxin levels on the shadowed side. This reduction in auxin levels prevents cell elongation on the shadowed side, causing the grass shoots to bend toward the light. Therefore, an increase in auxin levels promotes cell elongation and is the reason for the grass shoots bending toward the light.

Cytokinins are a class of hormones produced in the roots of plants that promote cell division and growth. They play a crucial role in regulating plant development and are responsible for delaying the aging of flowers and leaves. Cytokinins stimulate the production of enzymes that promote cell division, leading to increased growth and development in plants. Additionally, they help in the maintenance of the meristem, which is responsible for the continuous growth of plants. Thus, cytokinins are the correct answer for this question.

Shoot branching is controlled mainly by the interaction of auxins and cytokinins. Auxins are plant hormones that promote the growth of the main shoot and inhibit the growth of lateral shoots. Cytokinins, on the other hand, promote the growth of lateral shoots. The balance between these two hormones determines the degree of shoot branching. When auxin levels are high and cytokinin levels are low, the main shoot grows vigorously and inhibits the growth of lateral shoots. Conversely, when cytokinin levels are high and auxin levels are low, lateral shoots are promoted, resulting in increased shoot branching.

Abscisic acid is a plant hormone that generally acts as a growth inhibitor. It regulates various physiological processes in plants, including seed dormancy, stomatal closure, and inhibition of shoot growth. It plays a crucial role in plant responses to environmental stresses such as drought, cold, and salinity. Abscisic acid inhibits cell division and elongation, leading to the suppression of plant growth. Therefore, it is the correct answer to the question.

After a hard rain in the desert, the seeds of desert plants are stimulated to germinate due to the removal of abscisic acid. Abscisic acid is a hormone that inhibits seed germination and growth. When there is a sufficient amount of water available after a rain, it washes away the abscisic acid from the seed, thereby removing its inhibitory effect and allowing germination to occur.

Plant hormones are produced in very small concentrations because they act as chemical messengers in plants, regulating various growth and developmental processes. Even though they are present in small amounts, they have significant effects on plant growth, development, and responses to environmental stimuli. Plant hormones are involved in various physiological processes such as cell division, elongation, differentiation, and flowering. They also regulate responses to light, gravity, and stress. Therefore, the statement that plant hormones are produced in very small concentrations is true.

Gibberellins are plant hormones that promote stem elongation, which is known as "bolting" in plants. When plants bolt, their stems rapidly elongate, often in response to environmental stimuli such as changes in temperature or light conditions. Gibberellins stimulate cell division and elongation, leading to the rapid growth of the stem. This hormone is commonly used in agriculture to promote the growth of certain crops, such as lettuce and cabbage, where elongated stems are desired.

Abscisic acid is a hormone that inhibits seed germination and promotes seed dormancy. It prevents seeds from germinating immediately after being released in the fall, allowing them to survive through unfavorable conditions such as winter. This hormone helps in regulating seed dormancy and controlling the timing of seed germination, ensuring that seeds only germinate when conditions are favorable for their growth and survival.

Starch granules in plant cells are thought to contribute to gravitropism. Gravitropism is the response of plants to gravity, causing them to grow in a particular direction. Starch granules are dense storage granules that can settle under the influence of gravity, providing a reference point for the plant to sense the direction of gravity. This helps the plant to orient its growth and maintain an upright position. Lipids, cellulose, proteins, and chlorophyll do not have the same ability to settle and therefore are not directly involved in gravitropism.

Gravitropism is the growth response that causes the shoots of a plant grown in the dark to grow upward. Gravitropism is the plant's ability to sense and respond to gravity, causing the shoots to grow against gravity and towards the light source. This response helps the plant to maximize its exposure to light and ensure proper photosynthesis for its survival. Phototropism, on the other hand, causes the shoots to grow towards the light source, but this response requires light for activation, so it is not applicable in the given scenario. Thigmotropism, photoperiodism, and heterotropism are not relevant to the upward growth of shoots in the dark.

Cytokinins are plant hormones that promote cell division and growth in plants. When the terminal buds of a chrysanthemum plant are pinched off, it stimulates the production and distribution of cytokinins, which in turn promotes the growth of side branches. Therefore, cytokinins are mainly responsible for the growth of side branches in this scenario.

Gibberellins are plant hormones that promote stem elongation and cell division. If applied to a bush bean, gibberellins could cause the internodes to elongate and the plant to grow taller, resulting in a vine habit rather than a bush habit.

Increasing the amount of soybeans in the human diet has been associated with a health benefit of decreased LDL levels. LDL, or low-density lipoprotein, is often referred to as "bad" cholesterol because high levels of LDL can lead to plaque buildup in the arteries and increase the risk of heart disease. Soybeans contain compounds called isoflavones, which have been shown to have cholesterol-lowering effects. These isoflavones can help to decrease the levels of LDL cholesterol in the body, promoting heart health.

Gibberellin is a hormone that can induce seeds to break dormancy. It promotes seed germination by stimulating the production of enzymes that break down stored nutrients in the seed, allowing it to grow and develop. This hormone also helps in promoting stem elongation and flowering in plants. Therefore, gibberellin is the correct answer as it is known for its role in breaking seed dormancy.

Plants use animals as a defense against herbivores by attracting wasps that kill herbivorous caterpillars. This is a form of biological control where the plants release chemical signals that attract parasitic wasps. These wasps lay their eggs inside the caterpillars, leading to their death. This strategy helps to reduce herbivory and protect the plants from damage.

Synthetic auxins are used commercially as a broadleaf weed killer. This means that they are specifically designed to target and kill broadleaf weeds, while leaving other plants unaffected. This is a common use for synthetic auxins in agriculture and gardening, as broadleaf weeds can be detrimental to crop growth and yield. By selectively targeting these weeds, synthetic auxins help to promote the growth and health of desired plants.

Ethylene gas can also be produced through the combustion of kerosene. When kerosene is burned, it releases various gases and compounds, including ethylene. This process occurs due to the high temperatures reached during combustion, which break down the hydrocarbon molecules in kerosene and produce ethylene gas as a by-product.