Plant Ecology Questions and Answers

Answer: B

Greenhouse gases act by trapping heat in the earth's atmosphere.

Sunlight, mostly visible and near-infrared, passes through the atmosphere and warms the surface, which re-radiates the energy as longer-wavelength infrared. Carbon dioxide, methane, water vapour and nitrous oxide absorb that infrared and re-emit much of it back towards the surface, so the lower atmosphere stays warmer than it otherwise would.

Ozone destruction is caused by chlorofluorocarbons and is a different problem. Greenhouse gases do not let in more visible light, and they do not reduce the energy reaching the surface; they slow its escape.

Answer: C

Energy flows Sun \(\rightarrow\) Producers \(\rightarrow\) Primary consumers \(\rightarrow\) Secondary consumers.

Energy enters an ecosystem as sunlight, is captured by producers (green plants and algae) in photosynthesis, passes to primary consumers (herbivores) that eat the producers, and then to secondary consumers (carnivores) that eat the herbivores. At each step much of it is lost as heat, so the flow is one-way.

The option without the Sun omits the source of the energy. Putting secondary consumers before primary consumers breaks the food chain, and the last option runs the flow backwards.

Answer: B

Plants adapted to acidic soil are oxylophytes.

The name comes from the Greek oxys, sharp or acid. Oxylophytes grow on acid soils such as peat bogs and heaths, where they tolerate low pH and the soluble aluminium and manganese that come with it.

Halophytes grow in saline soil, lithophytes grow on the surface of rocks, and chasmophytes root in the crevices of rocks. These terms describe the salt content or the physical substrate, not the acidity of the soil.

Answer: C

Insectivorous plants are adapted to a low-nutrient environment.

Plants such as the pitcher plant, sundew, Venus flytrap and bladderwort grow in bogs, swamps and poor soils that are deficient in nitrogen. They photosynthesise normally but trap and digest insects to obtain the nitrogen and other minerals the soil does not supply.

Their adaptation is to nutrient poverty, not to dryness or cold, and in high-nutrient soils they would have no advantage.

Their leaves are modified into traps, such as pitchers, sticky glandular hairs, snapping lobes or bladders, and secrete enzymes that digest the proteins of the captured prey.

Answer: D

Insectivorous plants are found in nitrogen deficient places.

Plants such as the pitcher plant (Nepenthes), sundew (Drosera), bladderwort (Utricularia) and Venus flytrap grow in bogs, marshes and poor, acidic soils that lack nitrogen. They photosynthesise normally, but trap and digest insects to obtain the nitrogen (and some other nutrients) that the soil cannot supply.

They are not short of carbon, which they fix from the air, or of oxygen; and although such soils may also be poor in phosphorus, nitrogen deficiency is the classic textbook reason for insectivory.

Answer: B

Halophytes grow on saline soil.

Halophytes are salt-tolerant plants, such as mangroves and Salicornia, adapted to soils and waters with high salt concentrations. They cope through mechanisms like salt excretion from glands, succulence and compartmentalising salt in vacuoles.

Plants adapted to waterlogged soil are hydrophytes (or helophytes), and those of dry sandy soil are xerophytes or psammophytes; acidic soils have their own acid-tolerant flora.

Answer: A

Lake succession runs Oligotrophic-Mesotrophic-Eutrophic.

A young lake is usually deep, clear and poor in nutrients (oligotrophic). Over time it gains nutrients and sediment from its catchment, productivity rises through a mesotrophic stage, and it becomes shallow, nutrient-rich and highly productive (eutrophic), often with oxygen-poor bottom water. It may eventually fill in to marsh and land.

The other orders either reverse the trend, as in eutrophic to oligotrophic, or skip the intermediate stage, which does not fit the gradual enrichment that drives the sequence.

Answer: B

Heliophytes are plants growing under direct sunlight.

The name comes from Greek helios, sun. Heliophytes, or sun plants, are adapted to high light intensity, with features such as thick leaves, a high light-saturation point and high photosynthetic capacity.

Plants growing in shade are sciophytes. Plants of waterlogged soils are hydrophytes or helophytes (marsh plants), and plants of saline conditions are halophytes.