Session Name: Sense Receptors in Plants and Their Function 

We know that animals have different structures that help them perform different functions. These functions play a significant role in an animal’s growth and survival. Animals behave differently and have various adaptations based on their behavior. Different animals have different types of reproductive organs. 

Animals move around and interact with themselves as well as the environment. There are various ways in which animals interact with the environment. But how do they do it? 

Explanation: 

Animals gather information from their surroundings. This information can be for various purposes like smelling food, locating danger, feeling hot or cold, etc. This information is collected with the help of sensory receptors. 

A sensory receptor or a sense organ is a part that responds to a stimulus in the environment. Stimulus is defined as a change in the environment, and it can be external or internal. These sensory receptors gather information and send it to the brain. 

There are various organs in animals that help them gather information about their surroundings. These organs act as sensory receptors. 

There are five major senses on which animals rely for the majority of their functions. They include: 

• Sight 
• Sound  

• Smell 
• Taste 
• Touch 

       Fig. No.1: Five senses 

Sight: 

The sense of sight is also referred to as vision and is the ability to see. Most animals are able to interpret their surroundings by visual sensory organs, i.e., the eyes. The eyes help to detect and focus an image of our surroundings. 

Photoreceptors that are present in the eye’s retina translate light into images. Rods and cones are photoreceptors that help in image formation. The optic nerve takes this message to the brain. 

Some animals have a great sense of sight which helps them find prey, protect them from danger, etc. Examples of such animals include eagles, chameleons, owls, sharks, etc. 

Chameleons have a unique sense of sight. They can look in all directions because their eyes move independently. It means that one eye can look forward while the other looks backward. Chameleons use their unique eyes to gather important information about their surroundings. 

Fig. No.2:  Sense of sight 

Sound: 

The ability to listen to a sound is also known as auditory perception. Animals have an auditory system that helps them to hear sounds and detect vibrations. Apart from hearing, this sense is also important for balancing our body or equilibrium. 

The ears are divided into three sections:  

1. The outer ear 

2. The inner ear 

3. The middle ear  

Fig.  No.3: Internal structure of the human ear 

Sounds are mostly vibrations, so the outer ear transfers these vibrations inside the ear canal, where these vibrations are further translated by the brain into meaningful sound. 

Frogs have an amazing sense of hearing. When one frog hears another frog making a noise, the ears send the information to the brain. The brain uses this information and tells the frog it should respond. This response might be to move away from the other frog’s area or to go toward the other frog for mating. Frogs listen and respond to many other sounds that help them locate food and avoid predators. 

Some animals have heightened hearing senses than humans. For example, dogs and cats can hear higher-pitched sounds than us. 

Some animals have more developed senses that allow them to gather information in ways humans cannot. 

Bats, whales, and dolphins are able to locate prey through echolocation. These animals send out noises that echo back and allow them to ‘see’ their prey. 

Fig. No.4: Echolocation 

Smell: 

The sense of smell is also referred to as olfaction. Animals have an olfactory system by which they smell and perceive different odors and scents. The nose is an olfactory organ and can also be an aid in our sense of taste.  

When animals smell a substance, the chemicals present in it bind to the cilia in their nasal cavity. This produces a signal which is transported via the olfactory cell to the olfactory nerve fiber, then to the olfactory bulb and finally, to the brain. 

Fig. No.5: Structure of the nose receptors 

The olfactory neurons in the nose can also detect pheromones, which is a chemical substances released by animals that could affect how they interact with each other. 

Animals generally have a sharper sense of smell than humans. Animals like dogs, wolves, elephants, etc., have a great sense of smell. This allows them to find food, and mates and to detect danger easily. 

Some animals use this sense to detect the territories of other animals. 

Taste: 

Animals have tongues by which they perceive several tastes and flavors like sweet, salty, sour, and bitter. 

Animals use the sense of taste, also referred to as gustation, to detect the taste of food and other substances. The senses of smell and taste work hand in hand. If one cannot smell something, one cannot taste it either.    

The tiny bumps present on the tongue are called papillae. The taste buds lie between the papillae. Taste buds are the sensory receptors present on the tongue’s upper surface. 

Fig. 6. Structure of the taste buds. 

Different flavors are detected by different parts of the tongue: front for salty and sweet, back for bitter, and sides for sour. 

Touch: 

Skin is the largest organ because it covers the entire body. Receptors present on our skin allow us to acknowledge texture, pain, temperature, pressure, and pain. 

Touch is also referred to as tactician or somatosensation.  

The sense of touch is perceived by receptors found on the skin and hair follicles. These receptors generate an impulse which is carried first to the spinal cord and then to the brain. Pressure receptors on the skin are sensitive to changes in pressure. 

Animals rely on the sense of touch in the absence of light or when sound could attract predators. Touch also provides important information about the proximity of food, predators, and other environmental features. In some animals, touch is an important aspect of social behaviors in a group. Animals like elephants, tigers, rhinos, etc., use the sense of touch to communicate. 

Fig. 7. Sense of touch.