Question

Write a note on the following:
(i) Gregor Johann Mendel
(ii) Reflex arc

Hint:

Mendel's laws help predict how traits are passed from one generation to the next, while reflex arcs allow for immediate and protective responses to environmental stimuli.

Answer 1

(i) Gregor Johann Mendel:
Gregor Johann Mendel (1822–1884) was an Austrian scientist and the father of modern genetics. He is best known for his work on the inheritance of traits in pea plants, which laid the foundation for the study of heredity. Mendel's work was largely ignored during his lifetime, but later it became a critical part of the development of genetics.
1. Mendel's Experiments:
- Mendel conducted experiments on pea plants, focusing on seven different traits, including seed shape, seed color, flower color, and plant height.
- He carefully cross-pollinated pea plants with different characteristics and studied the inheritance patterns of these traits in subsequent generations.
2. Mendel's Laws of Heredity:
Mendel discovered two fundamental laws of inheritance:
- Law of Segregation: Each organism has two alleles for a trait, and these alleles separate (segregate) during the formation of gametes.
- Law of Independent Assortment: The alleles for different traits assort independently of each other during the formation of gametes.
3. Impact of Mendel's Work:
Mendel's principles laid the groundwork for the field of genetics, though they were rediscovered only decades after his death. His work showed that traits are inherited in a predictable pattern, based on the combination of alleles.
(ii) Reflex Arc:
A reflex arc is the simplest neural pathway involved in a reflex action, a rapid and automatic response to a stimulus. It is a fundamental part of the nervous system that allows an organism to respond quickly to certain stimuli, often without conscious thought.
1. Components of the Reflex Arc:
A reflex arc typically involves five components:
- Receptor: The sensory receptor detects the stimulus, such as heat or pressure.
- Sensory Neuron: The sensory neuron transmits the impulse from the receptor to the spinal cord.
- Integration Center: The spinal cord or brain processes the sensory information and sends signals to the motor neurons.
- Motor Neuron: The motor neuron carries the impulse from the spinal cord to the effector organ (e.g., a muscle or gland).
- Effector: The effector is the organ that carries out the response, such as a muscle contracting.
2. Example of a Reflex Arc:
A classic example of a reflex arc is the knee-jerk reflex. When the knee is tapped with a reflex hammer, the sensory neurons detect the stimulus and send the signal to the spinal cord. The spinal cord processes the information and sends an immediate response through motor neurons to the quadriceps muscle, causing it to contract and the leg to jerk forward. This is an involuntary action that does not require conscious thought.
3. Importance of Reflex Arcs:
Reflex arcs are essential for survival as they allow for quick responses to potential threats, such as pulling a hand away from a hot surface, thus preventing injury.
Conclusion:
- Mendel's discoveries about inheritance provided the foundation for the field of genetics, transforming our understanding of heredity.
- Reflex arcs are critical for quick, involuntary responses that protect the body from harm and help maintain bodily functions without conscious control.