UNIT
2: LESSON 2
CORN EATS LUNCH
SUBJECT: Science
OBJECTIVE: Students will be able to label a diagram of
a corn root and describe the process of nutrient exchange (eating lunch)
in a corn plant.
EVALUATION: Students can to identify the parts of a corn root
and describe in simple terms how it eats lunch.
BACKGROUND FOR TEACHERS:
Corn obtains nutrients and moisture from the soil through its roots.
The hard, tough root cap, located on the tip, protects the growing
root. In the area immediately behind the root cap, cells are rapidly
dividing to form new cells. This is called the region of elongation.
The combination of cell division and elongation creates great pressures
that push the root through the soil.
Roots get energy to grow from sugars that are made during photosynthesis
(see Unit 1, Lesson 1) which occurs
in the leaves. As the roots grow, they use oxygen from the surrounding
pore spaces (see Unit 2, Lesson 3) to breathe.
The carbon dioxide given off in respiration reacts with soil water to
form weak carbonic acid.
Roots absorb nutrients and water primarily through tiny projections
called root hairs. This is called the region of absorption. Soil water
places the root hairs in chemical contact with nutrients that are on
the surface of clay and organic matter particles. The weak carbonic
acid clinging to the root hairs provides hydrogen ions to the soil water.
The hydrogen ions are then exchanged with chemical nutrients held on
the surfaces of soil particles. These nutrients are then absorbed by
root hairs.
Soil water is distributed through the corn plant by osmosis, a method
of diffusion by which a solvent (water) and solute (nutrients) pass
through membranes of living cells. This is how the water, nutrients
and chemicals slowly progress from the root to the tip of the plant.
The growth of a corn plant is affected by the fertility of the soil.
Most plants need about 10-12 chemical elements. Three major elements
include nitrogen, phosphorus and potassium. Secondary elements include
calcium, magnesium, and sulfur. Trace, or minor, elements include zinc,
iron, boron, manganese, copper, and aluminum.
Nitrogen stimulates the growth of leaves and stems, and produces the
rich green color which is characteristic of a healthy plant. The plant's
use of potassium, phosphorus and other nutrients is also stimulated
by the presence of nitrogen.
Phosphorus is present in all living tissue. It is particularly concentrated
in the younger parts of the plant and in the flowers and the seed. Phosphorus
is necessary for such life processes as photosynthesis, the synthesis
and breakdown of carbohydrates, and the transfer of energy within the
plant.
Potassium is necessary for basic plant physiological functions and
also assists different plants in a number of specialized ways. It enhances
the size, flavor and color of some fruits and vegetables. It increases
the resistance of some plants to particular diseases. It improves the
rigidity of stalks and stems.
Nitrogen, phosphorus and potassium are so commonly used in commercial
fertilizers that their percentage is always noted on the fertilizer
bag in the same order. For example, a 10-20-10 fertilizer is one that
contains 10 percent nitrogen (N), 20 percent phosphorus (P), and 10
percent potassium (K).
Since very few soils contain the right balance of all the elements
needed for any one plant, some kind of fertilizer is usually needed.
A soil may be high in nitrogen and potassium but low in phosphorus.
Since crop yields are limited by the element most deficient, the elements
that are deficient should be added.
STUDENT ACTIVITIES:
1. Ask students to read the story Ann Learns
to Plow, and ask them to imagine, as she does, how corn eats."Once
she'd seen a root under a microscope.She'd heard her dad talk about
feeding phosphorus and potassium to the corn.Thinking of corn plants
eating supper made her laugh."
2. Explain "nutrient exchange" with this simple analogy: The root hairs
use hydrogen from their root surface like money to "buy" a nutrient
from the soil. The soil takes the hydrogen, and the roots keep the nutrient.
Ask students to role-play the process. One student can be a "root"
holding a hydrogen ion, another student is the "soil particle" (see
Lesson 3 to learn more about soil particles) holding a phosphorus or
potassium nutrient. The "root" gives the hydrogen to the "soil" and
in exchange, the "soil" hands over the nutrient, which the "root" then
"eats" (absorbs).
3. To demonstrate the ability of plants to absorb the nutrients ("eat"),
and move them to the leaves, ear and other important parts of the plant
where they're used to manufacture food (See Unit
1, Lesson 1), use the following activity:
-
Cut a celery stalk at the end where the stalks meet.
-
Stand the stalk in a jar of water and add red ink or food color
to the water.
-
At the next class period, remove the stalk and cut it into cross
sections at various places. Have the students observe the red areas.
Explain that the water has been rising in the plant, carrying nutrients
with it.
4. To better understand roots, and their importance to the plants,
ask students to complete the following worksheets. Younger students
can match the names of the parts of the corn root to the picture; older
students can fill in blanks in the worksheet. (Worksheet 1 for younger
students, Worksheets 2 & 3 for older students.)
5. To allow students to see root hairs, germinate a package of radish
seeds between two moist cloths. They germinate and grow very quickly!
Or use a microscope to examine roots of corn, grass, or any other available
plants.
