AP Biology : Understanding Other Plant Functions

Study concepts, example questions & explanations for AP Biology

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Example Questions

Example Question #5 : Plant Functions

Which of the following techniques could be used to determine if a species of plant requires potassium?

Possible Answers:

Analyze root contents for potassium

Measure the amount of potassium in a sample of plants

Grow a sample of plants in a potassium-rich environment and another sample in a potassium-deprived environment

Use autoradiography to find potassium in leaf tissues

Measure how fast radioactive potassium enters the plant

Correct answer:

Grow a sample of plants in a potassium-rich environment and another sample in a potassium-deprived environment

Explanation:

In hypothesis-based scientific inquiry, the experiment must have an experimental group and a control group. In this case, growing plants with potassium would be the experimental group and growing plants without potassium would be the control group. Maintaining all other experimental variables, this method would allow the researcher to determine whether the plant species requires potassium. If the plants in the potassium-deprived environment die, but the plants in the potassium-rich environment survive, we can conclude that potassium is necessary for this species to survive.

The presence of potassium in the plant, leaves, or roots does not indicate it is a required nutrient. This simply indicates that the plant is capable of absorbing potassium, but does not show a dependency on potassium. Also, the movement of potassium into the plant does not indicate it is a required nutrient.

Example Question #1 : Understanding Other Plant Functions

Which of the following nutrients is most likely to be abundant in soil? 

Possible Answers:

Oxygen

Phosphorus

Carbon

Iron

Hydrogen

Correct answer:

Iron

Explanation:

There are many necessary nutrients involved in plant development. The nutrients are used in different quantities and are grouped accordingly in two categories: micronutrients and macronutrients. Micronutrients, such as iron, are important to healthy plant growth but are used in small quantities. Macronutrients, such as oxygen, carbon, hydrogen, and phosphorus, are also used for healthy plant growth but are used in the greatest quantities.

As a result, the macronutrients are more likely to become depleted in the soil as the plant absorbs them, while the micronutrients remain abundant. Iron, as a micronutrient, is more likely to be abundant in soil than any of the macronutrients.

Example Question #2 : Understanding Plant Hormones

Perishable fruit is often picked before it is ripe. This hard, unripe fruit is easier to transport as it is less likely to bruise or spoil while in transit. Once fruit reaches its destination, it can be sprayed with a plant hormone that will promote its rapid ripening. What hormone is most likely used for this function?

Possible Answers:

Abscisic acid (ABA)

Ethylene

Gibberellins

Cytokinins

Correct answer:

Ethylene

Explanation:

Ethylene gas promotes fruit ripening; in a classic example of a positive feedback loop, ripe fruit causes the production of more ethylene gas, which promotes more fruit ripening (this is the origin of the phrase "one bad apple spoils the bunch!")

Cytokinins stimulate cell division and cytokinesis, and they can delay senescence (deterioration due to age, as in the case of cells). Gibberellins promote cell growth, and also promote stem and leaf elongation. Abscisic acid (ABA) promotes seed dormancy, inhibits plant growth, and closes plant stomata during water shortages. 

Example Question #3 : Understanding Plant Hormones

Which of the following is not true of auxins, a class of plant hormones?

Possible Answers:

They are responsible for phototropism—plants' tendency to grow toward light sources

They enhance apical dominance, which promotes plants' upward growth, as opposed to lateral growth

They promote fruit ripening, which triggers the production of more auxins

Indoleacetic acid (IAA) is a natural auxin

Correct answer:

They promote fruit ripening, which triggers the production of more auxins

Explanation:

Auxins play a number of crucial roles in plant growth, behavior, and development. They were the first major class of plant hormone to be discovered and are present in all parts of a plant in varying concentrations. Some of their more notable functions include causing phototropism, enhancing apical dominance, and softening the cell wall to stimulate cell elongation and growth. Indoleacetic acid (IAA) is a naturally occurring auxin, though some synthetic auxins are used as weed killers.

Ethylene gas is a plant hormone that promotes fruit ripening in a positive feedback loop. Ripe fruit produces more ethylene gas, which promotes more fruit ripening, and so on. It is not a kind of auxin.

Example Question #2 : Understanding Other Plant Functions

What is the function of lateral meristems?

Possible Answers:

Provide secondary growth in woody plants

Maintain water homeostasis

Stimulate root hair growth

Provide nutrients to apical meristems

Correct answer:

Provide secondary growth in woody plants

Explanation:

In addition to growing in height, woody plants also grow in thickness. This is the function of lateral meristems. Lateral meristems are comprised of the vascular cambrium, and by cork cambrium that form vascular cylinders. The vascular cambrium adds layers of secondary xylem and phloem (wood), whereas the cork cambrium replaces the outer epidermis with a thicker and tougher layer called periderm.

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