Plant Biology Questions

Bring on the tough stuff

1. If you pushed a small thumbtack into a tree’s trunk, what would happen to that thumbtack in twenty years? Would it get higher, lower, become embedded in the tree or fall out?

2. Why doesn’t cutting grass with a lawnmower kill the grass? Doesn’t it damage the shoot apical meristem?

3. If you pick up a bottle of plant food or fertilizer, it usually has three numbers in a ratio on it. What might these numbers refer to?

4. In some ecosystems, many of the leaves look the same, even though they are on different plants. For example, in the desert most of the plants have prickly leaves, and on mountaintops the plants have needles or small whitish leaves. Why do all the leaves look the same in the same habitat?

5. Why are flowers so important for angiosperm reproduction?

6. Abscisic acid (ABA) inhibits seed germination. Why would it be advantageous for prolonged cold temperatures to break down ABA and cause seeds to germinate?

Plant Biology Answers

1. Thumbtacks are small, so we will assume it only pushed into the outer layers of bark. Over twenty years, the tree will shed its outermost bark layers, and the tree will continue growing outward. Most likely, the thumbtack will fall off with the bark.

2. Grasses are monocots, and therefore have intercalary meristems. Even though the lawnmower takes off the top of the grass stems and leaf blades, the intercalary meristems further down the stem can produce new cells quickly. This allows the grass to re-grow stems and leaves, and gives you summer job security if you want it.

3. The ratio on fertilizer bottles is the relative amount of the primary macronutrients: nitrogen (N), phosphorus (P), and potassium (K). You will be looking at the N-P-K ratio. Other nutrients included in the fertilizer are often listed somewhere else on the bottle, but N, P and K are the most important. If the ratio is even, such as 10-10-10, there are equal amounts of each primary macronutrient.

4. Many leaves are modified to provide an advantage to the plant in a particular environment. In the desert, needle-shaped leaves don’t lose as much water as flat, broad leaves because they have less surface area. On mountaintops, leaves are often lighter in color to reflect the intense sunlight; they are also smaller to minimize water loss from the winds present on mountains. Rainforest plants usually have broad leaves to maximize the sunlight they receive, since they are experiencing intense competition for light with all the other plants around. If organisms have features that make them look the same but they aren’t closely related, it is called convergent evolution because the organisms converge on one adaptive form through evolution.

5. Flowers attract pollinators, which is a huge development for angiosperms. Plants that are wind-pollinated have to make a lot of pollen so that eventually some pollen grains will end up on different individuals of the same species. Animal-pollinated plants can make less pollen because they have a personal courier delivering pollen to other plants of the same species. The bright colors of flower petals advertise to bees, butterflies, hummingbirds and other pollinators that the plant is offering a nice sugary snack, and animals often end up doing the pollination inadvertently because they have to brush against the anthers on their way to the nectary.

6. ABA prevents seed germination, which is good when conditions aren’t right for plants to grow. For example, the beginning of winter in the northern United States is not a good time for plants since freezing temperatures can harm plants. However, over time cold destroys ABA. This happens slowly enough that after three or four months, when ABA levels are low enough that the seed starts to germinate, spring is just around the corner and it’s safe to be a growing plant again.