Sense Organ SS3 Biology Lesson Note

SPECIFIC OBJECTIVES: At the end of the lesson, pupils should be able to

1. Describe the mechanism of smelling with the help of olfactory chemoreceptor
2. Identify the primary sense organs.
3. Discuss the adaptation for survival of a dog

INSTRUCTIONAL TECHNIQUES: 

• Identification, 
• explanation, 
• questions and answers, 
• demonstration, 
• videos from source

INSTRUCTIONAL MATERIALS: Videos, loudspeaker, textbook, pictures

NOTE

SENSE ORGANS

Sense organs are specialised structures in the human body that enable the perception of various stimuli from the external environment. These organs play a crucial role in gathering information about the surroundings and transmitting signals to the nervous system, allowing individuals to interpret and respond to their environment.

The primary sense organs include:

1. Eyes (Vision): Detects light and colour, allowing the sense of vision.

• Location: Orbit of the skull.

2. Ears (Hearing and Balance): Detects sound waves for hearing and contributes to balance and spatial orientation.

• Location: Sides of the head.

3. Nose (Smell): Detects airborne molecules, providing the sense of smell.

• Location: Nasal cavity.

4. Tongue (Taste): Contains taste buds that detect different flavours, providing a sense of taste.

• Location: In the mouth.

5. Skin (Touch, Temperature, Pressure): Detects various stimuli such as pressure, temperature, and touch.

• Location: Distributed throughout the body.

Mechanism of smelling with the help of olfactory chemoreceptor

The mechanism of smelling involves the activation of olfactory chemoreceptors, specialised sensory cells located in the olfactory epithelium within the nasal cavity. Below is a simplified explanation of how the olfactory system works:

1. Detection of Odorants: When we inhale, airborne molecules (odorants) enter the nasal cavity.
2. Olfactory Epithelium: The olfactory epithelium, located on the roof of the nasal cavity, contains specialized sensory cells called olfactory receptor neurons.
3. Olfactory Receptor Neurons: Each olfactory receptor neuron has hair-like structures called cilia, which extend into the mucus lining the nasal cavity.
4. Binding of Odour Molecules: Odorants dissolved in the mucus bind to receptor proteins on the cilia of olfactory receptor neurons.
5. Generation of Action Potential: The binding of odour molecules to the receptor proteins triggers a series of biochemical reactions within the olfactory receptor neuron, leading to the generation of an action potential.
6. Transmission to Olfactory Bulb: The action potentials travel along the axons of the olfactory receptor neurons, which bundle together to form the olfactory nerve. The olfactory nerve transmits these signals to the olfactory bulb, located at the base of the brain.
7. Processing in the Olfactory Bulb: The olfactory bulb processes the incoming signals, helping to identify the specific qualities of the odour.
8. Transmission to the Brain: Information about the odour is then transmitted to higher brain regions, including the olfactory cortex and limbic system, which are associated with memory and emotion.
9. Perception of Smell: Finally, the brain interprets the signals and creates the perception of smell, allowing us to recognize and respond to various odours.

Adaptation for survival

Adaptation for survival is a crucial aspect of the evolutionary process, and behaviours like sniffing in animals, such as dogs during hunting, are excellent examples. Here’s how this adaptation contributes to survival:

1. Enhanced Detection of Odours: Dogs have an acute sense of smell, and sniffing allows them to detect and analyze a wide range of odours in their environment. This heightened olfactory ability is a result of evolutionary adaptations in their nasal anatomy and a large number of olfactory receptors.
2. Tracking and Hunting: Sniffing helps dogs track and locate prey. The ability to follow scent trails enables them to locate food sources efficiently, making them effective hunters.
3. Identification of Surroundings: Dogs use sniffing not only for hunting but also to gather information about their surroundings. They can detect the presence of other animals, identify territories, and assess potential threats or resources.
4. Communication: Dogs use scent marking and sniffing as a means of communication with other animals. This is important for establishing social hierarchies, identifying individuals, and conveying information about their presence.
5. Survival Instinct: The ability to use their sense of smell for survival is deeply ingrained in dogs’ instincts. It helps them navigate and make decisions in their environment, contributing to their overall survival and success as a species.
6. Avoidance of Danger: Dogs can sniff out potential dangers, including predators or hazardous substances. This ability aids in avoiding threats and navigating through environments safely.

EVALUATION: 

1. What are sense organs

1. Describe the mechanism of smelling with the help of olfactory chemoreceptor
2. Describe the adaptation for survival in dogs

CLASSWORK: As in evaluation

CONCLUSION: The teacher commends the students positively