Different organisms have different ways of responding to their environment. If you have a dog, you might have taught it how to sit, stay, or roll over. Would its ancestor, the gray wolf, do these behaviors in the wild?
And while you may be familiar with animal behaviors (of dogs at least), have you ever wondered how plants and bacteria respond to their environment? How do plants know when to flower? And can bacteria really communicate with each other?
In this article, we will discuss how organisms–specifically, animals, plants, and bacteria–respond to their environment.
Response to Environment Biology Definition
Living organisms have the ability to adjust to changes in their environment. This ability is called responsiveness. In the course of natural selection, organisms have evolved with various behavioral or physiological responses to stimuli, and these responses are integral to their survival and reproduction.
When we say behavioral responses, we’re talking about pulling your hand away when you touch a hot stove or looking for higher ground during heavy rains in anticipation of flooding. When we say physiological, we’re talking about plants flowering in response to seasonal changes or delaying seed germination in response to drought.
Natural selection is the phenomenon where individuals have varying chances of survival and reproduction because of differences in their inherited characteristics.
A stimulus (plural: stimuli) is anything that elicits behavioral or physiological responses from an organism.
Example of Response to the Environment in Biology
To make it easier to understand, we will discuss specific examples of how animals, plants, and bacteria respond to their environment.
Animal Responses to the Environment
Animals’ responses to stimuli are called behaviors. Animal behaviors can be classified as innate or learned.
Innate behaviors (also known as instinctual behaviors) are hard-wired responses that are inherited and ingrained in the organism from birth.
Learned behaviors are responses acquired through interactions with the environment and can be modified by previous experiences.
Behavioral Responses to Changing Environments
For us to better understand the difference between the two types of animal behaviors, let's discuss examples of both innate and learned animal behaviors.
A simple example of innate behavior is the reflex action, which is a quick, involuntary response to stimulus (like when you instinctively pull your hand away after touching a hot stove).
Another example of innate behavior is migration, or the seasonal movement of animals over great distances. Animals evolved with this response to changes in the availability of resources and it is a phenomenon shared by all major animal groups. Some birds, for instance, migrate south for the winter so they could find warmer climates with sufficient food supply.
Innate behaviors can also be observed in how animals communicate with each other using stimuli called signals. Signals can be visual (such as in courtship displays), aural (or using sounds), tactile (or using touch), and even chemical (or using pheromones). Animal communication can be innate or learned, or a combination of both.
The behaviors involved in courtship display are mostly instinctive. Animals inherit these behaviors to attract mates. The display acts as a signal, and if the courtship display is poorly performed or if the expected response is not given, the mating ritual would be abandoned, and the mating attempt fails. Figure 1 is an example of courtship display observed in the western grebe.
An example of learned behavior can be observed in how some species are able to recognize and be recognized by their parents. Such learned behavior usually takes the form of imprinting, where a long-term behavioral response to a specific object or individual is established.
Have you ever seen ducklings walking after their mothers?
As soon as they hatch, ducklings imprint and make a bond with the first adult they see, usually their mother. During this period in development called the sensitive period, the parents, too, would learn to recognize their young. Ducks have evolved with this behavior because it encourages newborn ducks to stay close to their mother as their mother protects them, increasing their chances of survival.
What do you think would happen if the hatchlings saw a human before they saw their mother? They would imprint on the human and would follow that human instead of their mother. Unfortunately, if bonding does not occur between the parent and the ducklings, the parent will not care for the offspring.
Another type of learned behavior is classical conditioning, a conditioned response that is associated with a new stimulus that it had not been associated with before. The new stimulus is called conditioned stimulus whereas the response to the original stimulus is called unconditioned response.
An experiment conducted by a physiologist named Ivan Pavlov demonstrates this. In his experiment, dogs were observed to salivate (an unconditioned response) when they smell food (unconditioned stimulus). The researchers introduced a conditioned stimulus: whenever the dogs were given food, a bell was rung (Fig. 2).
During this conditioning period, the dogs learned to associate the sound of the bell with food, and they responded by salivating. After the conditioning period, the dogs would salivate whenever a bell was rung even in the absence of the food which was the unconditioned stimulus .
Operant conditioning is another type of learned behavior in which the conditioned response is gradually modified by being rewarded or punished. This is the basis of popular methods of animal training. Through operant conditioning, the animal learns to associate a behavior with the punishment or reward and over time, they can be taught to perform behaviors that they would not have done otherwise in the wild.
Plants Responses to the Environment
Plants don’t move the same way that animals do. When winter is approaching, you won’t see plants uprooting themselves and traveling far away to find warmer climates. But they do have other ways to respond to changes in their environment.
Plants use hormones and other complex mechanisms to sense stimuli in the environment–such as light, gravity, and water–and transmit signals to trigger physiological changes in response.
For example, plants respond to water limitations in the environment by producing the hormone abscisic acid, which prevents seeds from germinating. By delaying germination until such time that there is adequate water for the seedling, the plant has a higher chance of survival.
Plants also respond to seasonal changes by detecting the length of the night. This response is called photoperiodism. They do this by detecting wavelengths of light using photoreceptors.
When they sense that the nights are getting shorter, they register it as a sign that spring is approaching, and some plants may respond to this seasonal change by flowering. They do so because their pollinators are most active during this period, which means that if they reproduce, their offspring would have enough time to grow and develop before braving the harsh conditions of winter.
Bacteria response to environment
Bacteria also exhibit behavioral and physiological responses to their environment. One of the ways by which bacteria respond to external stimuli is cell signaling, a process where signaling molecules secreted by one cell would bind to protein receptors on the other cell. Basically, it is how cells communicate with each other.
For example, bacterial cells release signaling molecules that can be recognized by other bacterial cells. By sensing the concentration of such signaling molecules– a mechanism known as quorum sensing–bacteria are able to monitor their own local cell density. In doing so, bacterial populations can coordinate their behaviors in activities that require many cells to work together at the same time.
Biofilm is a type of bacterial community that is stuck to a surface. The cells take in nutrients from the surface that they are on. These cells secrete signaling molecules to recruit nearby cells, leading to the colony's growth. They also secrete sugars and proteins that glue the cells to the surface and to each other, forming a slime layer.
While this may sound difficult to imagine, you probably have already encountered biofilm. The thin film on your teeth whenever you get up in the morning is an example of bacterial biofilm. If you don’t regularly brush your teeth, that biofilm can cause cavities and gum disease!
Response to Environment - Key takeaways
- In the course of natural selection, living organisms have evolved various mechanisms to respond to stimuli in their environment. These mechanisms can be physiological or behavioral.
- Animal behaviors can be classified as innate (inherited and hard-wired) or learned (influenced by the environment).
- Plants use hormones and other complex mechanisms to sense stimuli in the environment and transmit signals to trigger physiological changes in response.
- Bacteria also exhibit behavioral and physiological responses to their environment. An example of bacterial behavior is quorum sensing.
- Zedalis, Julianne, et al. Advanced Placement Biology for AP Courses Textbook. Texas Education Agency.
- Reece, Jane B., et al. Campbell Biology. Eleventh ed., Pearson Higher Education, 2016.
- Dobkin, David S., et al. “Visual Displays.” Stanford University, web.stanford.edu, 0 0 1998, https://web.stanford.edu/group/stanfordbirds/text/essays/Visual_Displays.html.
- OpenStaxCollege. “Functions of Human Life – Anatomy & Physiology.” Functions of Human Life – Anatomy & Physiology, pressbooks-dev.oer.hawaii.edu, https://pressbooks-dev.oer.hawaii.edu/anatomyandphysiology/chapter/functions-of-human-life/. Accessed 28 Aug. 2022.