Curriculum

GROWING UP!

The warmth of the spring sun seeping into the earth is a crucial signal to a seed to begin its journey out of the earth and into the air. Once the stem has emerged from the soil, the plant begins the amazing process of turning energy into food for growth. This is called photosynthesis, which literally means “to put together with light.” Photosynthesis occurs in two distinct stages: the light reaction, in which plants turn sunlight into chemical forms of energy called ATP and NADHP; and the dark reaction, during which this chemical energy is turned into sugars. The light reaction of photosynthesis occurs in the plant leaves and stems, specifically in small cellular structures called chloroplasts. Found inside the chloroplasts is a compound called chlorophyll, which has the ability to grasp the sun’s energy and harness it for the plant’s use. An interesting feature of the chlorophyll compound is that it is always green—therefore, whenever we see green parts of a plant we know chlorophyll is present and photosynthesis can occur. Once sunlight is absorbed by the chloroplasts, it mixes with water and carbon dioxide to form oxygen and chemical energy. As the oxygen is released through the pores of the leaves back into the air, the plant uses the chemical energy to initiate the dark reaction of photosynthesis. In this process, ATP and NADHP are combined with carbon dioxide inside the plant in order to create sugars. These sugars then travel throughout the plant as food.

CHEMICAL REACTION OF PHOTOSYNTHESIS
6 CO2 + 6 H2O → C6H12O6 + 6 O2

 


Carbon dioxide + Water + Light energy → Glucose + Oxygen

 

As shown in the formula for photosynthesis (above), plants breathe in carbon dioxide and release oxygen as a byproduct. This is the opposite of human respiration, in which we breathe in oxygen and release carbon dioxide. Thus we can see that humans and plants are in symbiosis; we need each other to make available the elements necessary for survival.

WHAT IS A STEM

A stem can be considered the pump of the plant, transporting food from the roots to the leaves and glucose from the leaves to the rest of the plant. The stem also provides structural support for the plant, whether it is standing upright or spread along the ground. This helps the leaves to receive as much sunlight as possible for photosynthesis.

Water is another element that plays a vital role in every stage of a plant’s development, beginning with the germination of the seed. Every seed is dormant until exposure to water and sunlight causes the seed to split open, allowing the primary root to begin its descent into earth. The plant roots can then absorb water from the soil through the tiny hairs covering the root’s surface. Although it is nice to think of roots “sipping” up water from the soil, the process by which water enters into the plant root is through a process called osmosis. During osmosis, water simply moves into the root hairs because they have a lower concentration of water than the soil in which they are located.

OSMOSIS

Osmosis is the process by which water moves across a permeable membrane from an area of high water concentration to an area of low water concentration.

Located inside every plant are special cells called xylem, which transport water and dissolved nutrients throughout the entire plant. Some of this water is released through openings on the leaf, called stomata. It is actually this emitting of moisture from the leaves that causes lower water pressure at upper ends of the plant in relation to the water pressure at the roots and stem. This results in a low-to-high-pressure gradient that enables water to be “sucked up” via the xylem from the roots into the stem, leaves, and flowers of the plant.

A third requirement for successful plant growth in your garden is nutrient availability. Nutrients like potassium, nitrogen, phosphorous, calcium, sulfur, and magnesium are absorbed from soil via the root hairs, although oxygen and nitrogen are also taken in from the air via the leaves. These nutrients then travel through the plant to where they are used by the plant’s cells. If your garden’s soil tests came back low in any of the main nutrients, you should probably supplement with an organic fertilizer or homemade compost in order to maximize fruit and vegetable growth. (Sources: Davis 2008, Gershuny 1993)

WHAT IS THE ROLE OF A ROOT

Roots have three important jobs: absorbing water and nutrients from the soil, anchoring the plant in the soil (delicate young plants would blow away in the wind), and storing extra food for the future.

Check out Organic Gardening’s Nutrient Deficiency Problem Solver as you read your soil test results or try to troubleshoot the signs of nutrient-deficient plants. Compost is an excellent way to add macronutrients and micronutrients to your soil. You can also add fertilizers to your soil, but be sure that you understand the difference between organic and chemical fertilizers so you can pick something that’s safe for the environment. Or, try making your own organic fertilizer!

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