Herb Plant Structures and Adaptations

Plant_Diagram_2.pngA plant is a collection of different internal (inside) and external (outside) structures that help it to survive and reproduce. Heritable structures or behaviors that help an organism to survive and reproduce are classified as adaptations. Not all structures or behaviors are adaptations, and if an organism is moved into a new environment or the environment changes, a structure or behavior might no longer be adaptive.

Flower: Flowers function to attract insects and other organisms, which help the plant to reproduce by transporting pollen (sperm) to other plants. Both the color Bee_on_Thyme.jpgand the odor (smell) produced by the flower attract pollinators. Rosemary, Thyme, Dill, Lavender, and Chives all produce flowers that attract bees, butterflies, and other insects. Rosemary produces blue flowers, while thyme, lavender and chives produce purple flowers; both colors work well at drawing in bees and butterflies.

Leaf (Leaves): Oregano_2.pngThe main function of a leaf is to perform photosynthesis, which generates food (sugar) for the plant using water, sunlight, and carbon dioxide. Chloroplasts, organelles found inside leaf cells, perform photosynthesis and thus help the plant to survive by generating energy for the plant.

Not all leaves look alike, and their structure is different (varies) in different climates. In dry climates, the leaves are often waxy or leathery and thick; this prevents the plant from loosing water on hot days. Rosemary, oregano, and thyme are all examples of herbs with these types of leaves. Some herbs, like Sage and Oregano, also have fuzzy leaves, which help trap water or moisture from the air.

Leaves also contain many organic compounds, which give each a unique flavor and odor. Humans value herbs for these traits, using their leaves and flowers to flavor food, create perfumes, and treat illnesses. In the wild, the organic compounds help the plants to survive. Some of the chemicals in the leaves act like insecticides and repel insects that might try to eat the plant's leaves. In fact, some commercial insecticides use compounds from herb plants. Other chemicals act as an antibiotic and kill bacteria that might also try to harm the plant.
Organic Compounds
dolichodial, menthol, and pulegone
thymol and carvacrol
thymol, carvacrol
Disulfide and trisulfides
apiol and myristicin

Online Resources:

Xylem.jpgStem: The stem is similar to the skeleton of a human, helping the plant to stand upright and support all its different parts. Located inside the plant's stems are tube-like structures called the xylem (pronounced zy-lem) and phloem (pronounced flow-em). The xylem transports water and other nutrients from the roots to the all parts of the plant. The phloem transports sugar molecules. The xylem and phloem are like the circulatory system in humans; however, plants do not have a heart. Without the xylem, a plant could not transport much of the water and oxygen needed for photosynthesis to the rest of the plant. Without the phloem, plants could not transport the sugar made by photosynthesis to other parts of the plant. This is why cracking the stem of a plant will often cause the part above the break point to die.

How does water travel up the xylem without a pump like a heart? The process is similar to sticking the end of a paper into water. Slowly, the water will rise up the paper. This is a result of two processes: water cohesion, the attraction between water molecules, and adhesion, the attraction of water to the wall of the xylem. During transpiration water is lost through openings (stomata) on the leaves of the plant. As the water leaves the plant, more water is forced up from the roots.

Like some leaves, the stems of plants can be covered in hair-like structures that help trap moisture; for example, in sage and oregano.

Roots: The roots of the plant serve two functions. First, they act like the foundation of a building, and prevent the plant from moving or being knocked over. Second, they absorb or take in nutrients from the ground, including water and oxygen. Plants also require many other minerals like phosphorus and nitrogen that are also absorbed by the roots. Although plants need water, adding too much water can block the absorption or uptake of oxygen and suffocate the plant.

Tropisms: Phototropism.jpgLike animals, plants respond to external (outside) stimuli (signals). Because plants depend on light to generate food, most plants will grow towards an area with greater light. This response is defined as phototropism, and it allows plants to seek out better sources of light. Plants with more access to light are more likely to survive.

Plants also respond to gravity, and their root and stem cells "know" what is up and what is down. Positive geotropism is plant growth in the same direction as gravity, which occurs with the plant's roots. Negative geotropism is plant grow in the direction opposite of gravity, which occurs with the plants stem. If plants were unable to differentiate between up and down, the leaves might grow underground or the roots above ground causing the plant to die.

Online Resources:
  • Plants in Motion: Click here and watch videos showing phototropism and geotropism

Photomorphogenesis: As you've now observed, plants grown in the dark will at first grow differently than those grown in the dark. Plants grown in the dark grow taller stems, shorter roots, fewer leaves, and produce less chlorophyll, which gives the plant its green color and iused by chloroplast to perform photosynthesis. Why does the plant do this? First, the plant is trying desperately to locate light, which it needs to generate food. By growing the stem faster and longer, it increases the chance of finding light. Second, by slowing the growth of leaves and roots, the plant is not wasting its limited resources on building structures it presently does not need. Simply, the plant is dedicating all of its limited resources into finding light. Thus, the plants growth or development is dependent on light, and this process is called photomorphogenesis.

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Seeds: Parsley_Seeds.jpgPlant seeds can also display adaptations. For example, parsley seeds are coated in chemicals called furamocoumarins that kills neighboring weeds. This helps eliminate competition for resources. Other structures inside the leaves store food, which allows the seed to germinate withouth any light.