Flowering plants have four major part types: roots, stems, leaves
and flowers. These parts each have different responsibilities.
Roots are responsible for anchoring the plant to the ground and extracting
water and minerals from the soil. There are three types of roots: taproots,
fibrous roots and adventitious roots. Taproots are large and fleshy in appearance
and grow deep into the ground to search for food. They can also store food,
which is particularly necessary for perennial plants during periods of dormancy.
Taproots are mostly found in plants with two seed-leaves (dicots). Fibrous
roots lie close to the surface of the soil and collect precipitation before
it sinks deep into the ground. This type is mostly found in plants with
one seed-leaf (monocots). Adventitious roots develop to help the plant climb,
for example ivies, and help develop modified underground stems, such as
bulbs. They are common in both dicots and monocots.
Stems are responsible for supporting leaves and flowers physically, holding
the leaves and flowers in the best position for food gathering and reproduction
and storing nutrients for future use. Stems may be simple, branched, upright
or creeping and can form underground food storage organ.
Leaves are responsible for absorbing the sun’s rays, the majority
of the photosynthetic production, taking in carbon dioxide and releasing
oxygen and water vapor (breathing), and removing waste products from the
plant. Usually, the largest leaves grow closest to the ground so they don't
block the leaves below them from the sun. To maximize the amount of surface
area exposed to the sun, leaves are arranged in many different ways: alternate,
opposite and whorled. An alternate leaf arrangement involves one leaf per
node (point of attachment to the stem). An opposite leaf arrangement involves
two leaves per node, while a whorled leaf arrangement involves three or
more leaves per node.
Flowers are responsible for one important function: reproduction. There
are many different kinds of flowers in the plant kingdom. They are composed
of modified shoots and leaves that vary in shape, size, number, etc.
Temperature influences a wide variety of plant functions, so it is not
surprising that soil temperature affects root growth in many ways and that
expansion of crop root systems in temperate regions is limited by cool soil
temperatures. Root system expansion is a function of three temperature dependent
processes: growth, development, and orientation. Temperature affects root
growth through its influence on root weight, root length, and root diameter.
Root development is affected by temperature's effect on root initiation
and root turnover. Lastly, temperature controls root orientation through
its impact on the direction of root growth and the gravitropic response.
Warm seasons vegetables do best when temperatures average 65 to 95 degrees.
They thrive in warm summers and should be planted after the danger of frost
is over in the spring. Favorite warm season vegetables include beans, cucumbers,
eggplant, peppers, summer squashes and tomatoes.
Plant cool season vegetables several weeks before the last spring frost
is expected in your location. They grow best when daily temperatures reach
only 55 to 75 degrees. The most popular cool season vegetables are beets,
broccoli, cabbage, carrots, green onions, peas, radishes and spinach.
Most science students do not have the opportunity to observe the development
of a plant’s root system. They observe stems, leaves, and flower development,
but the root system is usually hidden beneath the surface of the soil. Materials
and procedures are available that enable a student to make root development
observations. This mini-research unit will describe how a teacher can uncover
this world down under for his/her students.