Environmental Interactions

Plants get what they need to survive and reproduce from their environment.

Sunlight

Sunlight is important to the growth and development of plants. Under different lighting conditions, plants grow and develop differently. Energy from light is absorbed by plant pigments, mainly through the green pigment chlorophyll found in plants. The pigment is green because that wavelength of light color is reflected by the plant and is not used to drive photosynthesis. Blue light and red light are the two primary wavelengths of light that are used in photosynthesis. This light energy is used to break the bonds in carbon dioxide (CO₂) and water (H₂O) to produce oxygen (O₂) and carbohydrates. Carbohydrates are the sugars that plants use to produce energy.

The primary role of sunlight in plants is for use in photosynthesis. This energy is used to break the bonds of extremely stable molecules CO₂ and H₂O and then to transform them into food for respiration.

Zoom in on the poster below to learn more about the process of photosynthesis.

Some plants thrive in full sun, while other plants prefer less sunlight. The amount of light a plant can handle depends on the species, growing conditions, and its ability to make structures suited for differing light levels.

Water

Like all organisms, plants need water. Water is critical to all life, and every living organism is made up of water because it is a near-universal solvent and has a high specific heat-holding capacity. Plants use water for a variety of purposes. These purposes include:

• Stability and movement: Water helps cells keep their shape/rigidity while also allowing the plant to be flexible and capable of movement.

• Nutrient transportation: Plants use their roots to draw water up from the earth and use the water to transport nutrients/minerals to the rest of the plant.

• Photosynthesis and sugar transportation: Plants also use water during photosynthesis and to move the sugars created through photosynthesis throughout the plant.

• Temperature control: Leaves release water through their stomas (tiny pores in the leaf), and this helps the plant stay cool.

Plants use water to help them move their branches toward sunlight, to make food through photosynthesis, to move nutrients and sugars through their bodies, and to help them stay cool.

Air

Plants need air for both photosynthesis and respiration. Air is made up of many different molecules and is around 78% nitrogen (N₂), 21% oxygen (O₂), and 1% other gases. Plants use O₂ for respiration like many other organisms that need oxygen (aerobic respiration), including animals and humans. Aerobic respiration takes the energy stored in carbohydrates and then uses it to build and repair structures, reproduce, and carry out essential processes. Plants need to respirate to convert the energy stored from photosynthesis into a form that can be used by their cells. Oxygen and sugars are metabolized, producing CO₂ and H₂O. Respiration occurs in all parts of the plant, both above and below ground. This is important because soil needs to have air available in it for the roots to effectively respirate to grow new tissue. When plants grow in water, they can pull dissolved oxygen from the water. Plants also take in air from their stomas (microscopic pores on leaves and some stems). These guard cells open and close and allow air to diffuse into the plant’s leaves where CO₂ is used in the process of photosynthesis. Oxygen is also taken in through the stoma and supplied via photosynthetic reactions.

Soil

Soil is made up of both organic and inorganic matter and is host to a diverse ecosystem of living organisms. Soil holds the minerals, water, gases (air), and organic matter from decomposition that plants need to grow. Soil also contains inorganic matter, such as sand, clay, and silt, which helps it increase water-holding capacity, reinforce structure, prevent compaction, and hold vital minerals and nutrients essential for plant growth and development. Plants can survive in many different types of soils. However, rapidly changing soil conditions can have a negative impact on plant growth.

Where does the organic matter in soil come from? Matter cycles through ecosystems. Decomposition is the process by which matter is broken down from complex structures to simpler chemical components.

Animals, fungi, and bacteria break down dead organisms into nutrients and minerals that are then added back into soil. The animals and bacteria that process the dead organisms are called decomposers. Soil is the largest source of carbon on earth. When decomposers break down waste, carbon gets added to the soil. Soil health is important in the fight against climate change. When organisms die, they degrade and release CO₂. Without healthy soils full of decomposers, the newly available CO₂ gets released into the atmosphere, which contributes to climate change. By maintaining healthy soils, humans can help ensure the CO₂ becomes sequestered in the soil.

Composting speeds up the decomposition process by creating conditions ideal for these organisms to break down organic waste. As organic waste is broken down, carbon is stored in the soils in both living organisms and as humus. Humus is completely decayed organic matter and contains many nutrients because it was previously living tissue. Humus is important because organic carbon in soils helps the soil retain water and nutrients, improves structure, and provides habitat for decomposers. Earthworms help distribute this organic matter throughout the soil.

Like plants, soil organisms need water and air to survive. Wet compostable materials provide the water while dry compostable materials provide the air. Humans can promote a healthy soil ecosystem by creating and maintaining a system of dead matter and decomposers. This is called composting.

To maintain a healthy soil ecosystem, specific things can be composted and some should not because they do not break down in the soil.

Pollination

Many flowering plants depend on pollinators for their reproductive survival. Plants and animals have coevolved over thousands of years to benefit one another. Pollinators receive resources from plants in the form of pollen (powder carrying the plant’s reproductive information), nectar, or other food, while plants get their pollen moved over large distances, which populates the plant communities and promotes genetic diversity. There are many different types of pollinators from a variety of animal groups. Bees, butterflies, moths, flies, wasps, ants, and beetles are the major insect pollinators. Birds, bats, and other small mammals are larger pollinators that help to disperse seeds.

Plants cannot move from their location, so they need animals to transport their pollen to other plants where fertilization can occur. Plants use a variety of tools to attract pollinators: smell, color, and even the flower shape. Color is very important to attracting pollinators, however humans can only see part of this story. Many animals (including many pollinators) can detect ultraviolet (UV) light, and this lighting wavelength makes flowers look very different from how we see them.

Seed Dispersal

Since plants cannot move, they are confined to the general area in which they germinate (first grown out of a seed). If conditions around them are not ideal, then their offspring do not have a high chance of survival if they were to germinate in the same area as their parent. If conditions are favorable and offspring germinate near the parent, then this creates competition between parent and offspring for the same number of resources. Plants have evolved many strategies to disperse their seeds so their offspring can survive. Some of these strategies include relying on animals to transport their seeds, using natural environmental forces like wind and water, or even dispersing by force.  

Animals can transport seeds in a variety of ways. Some seeds are moved when a fruit or seed is ingested and deposited to a different site after the animal defecates. Some seeds can be transported by animals on their fur. Others can be buried by animals and forgotten about.

Many seeds have evolved to be very light weight or to have structures that allow them to drift through the wind (like dandelions). Certain types of fruit or the dried inflorescence (flowering part of the plant, including the stem the flowers grew from) can be another way the wind moves seeds. These seed pods of the inflorescence roll on the ground and scatter seeds along the way (like tumbleweed). 

Gravity is another way that seeds can be dispersed. Many seeds are round and when dropped from a great height, such as from a tree, they can roll a sufficient distance from the parent.  

Some seeds can be dispersed by force. As the seed pod or fruit dries, tension builds in the structure that encloses the seeds. When enough pressure or tension is built, the seeds are flung away from the plant (okra).