Read the passage below. Use the information in the passage and your own knowledge to answer
the questions that follow.
Desert plants
Desert plants are adapted to survive extremes of temperature and dryness.
Some plants have structural adaptations and some plants use physiological
mechanisms. Plants that have these features are called xerophytes.
Xerophytes, such as cacti, usually have methods of storing and conserving water.
Cacti often have few or no leaves. They use chlorophyll in the outer tissue of
their stems to produce carbohydrates by photosynthesis. Spines protect the
plant from animals and shade it from the Sun. Extensive shallow root systems
spread out just beneath the surface of the soil allowing quick absorption of large
quantities of water when it rains. Because cacti store water in the centre of their
stems and roots, they are well-suited to dry climates and can survive years of
drought using the water collected from a single rainfall.
Some trees and shrubs are also adapted for life in deserts. They have very small
leaves and thorns. Phreatophytes are plants that have adapted to very dry
environments by growing extremely long roots.
Other desert plants use physiological mechanisms and have developed a lifestyle
that fits in with the seasons of greatest moisture and coolest temperatures.
These plants are annuals, plants that live for only one year.
Most annual desert plants germinate only after heavy seasonal rain and then
complete their reproductive cycle very quickly. They flower for a few weeks
in the spring. These plants are responsible for most of the annual increase in
wildflower populations in deserts. Their heat-resistant and drought-resistant
seeds then remain dormant in the soil until it rains again the following year.
Desert perennials are plants that live for several years. They survive by remaining
dormant during dry periods of the year, then springing to life when water is
available.
Some perennial plants use dormancy to survive drought by producing bulbs.
The tops of these bulbs dry out completely and leave no trace of their existence
above ground during dormant periods. They are able to store enough food to
survive for long periods in poor soils. The Desert Lily, also known as the Ajo,
has a bulb that is found at a depth of 50 cm or more. Winter rains can provide
sufficient water to stimulate the bulb to grow after years of dormancy. Bulbs
enable reproduction. Small bulbs grow on the side of a larger bulb and separate
to produce new plants.