The inability of a normal eye to see objects clearly when they are placed closer than 25 cm is due to the physiological limitation known as the near point. The near point is the closest point to the eye at which an object can be brought into focus, and it is generally around 25 cm for a normal, emmetropic (non-presbyopic) eye.

The primary reason for this limitation is the inability of the eye’s lens to adjust its focal length sufficiently to bring close objects into sharp focus. The lens of the eye can change its shape through a process called accommodation, controlled by the ciliary muscles. When the ciliary muscles contract, the lens becomes more convex, increasing its refractive power for focusing on nearby objects.

However, there is a limit to the extent of accommodation. As an object is brought closer to the eye, the ciliary muscles contract to increase the curvature of the lens, but there comes a point where the lens cannot adjust any further. Beyond this point, the light rays from a close object converge too much, and the image is formed behind the retina instead of directly on it. As a result, the image appears blurred.

The near point represents the minimum distance at which the lens can focus light properly on the retina. Beyond the near point, the eye requires additional optical assistance (such as reading glasses) to converge light properly and form a clear image on the retina.

If we say in overall, the inability of a normal eye to see objects clearly when placed closer than 25 cm is due to the limited accommodation range of the eye’s lens, which prevents it from adjusting sufficiently to focus on objects at very close distances.

(i) The hormone that is commonly secreted into the blood when an individual is under stress is cortisol. Cortisol is a steroid hormone that belongs to the glucocorticoid class and is produced by the adrenal glands.

(ii) Cortisol plays a crucial role in helping the body cope with emergency or stressful situations through the following mechanisms:

1. Energy Release: Cortisol promotes the breakdown of glycogen (stored in the liver) into glucose. This process, known as glycogenolysis, increases the availability of glucose in the bloodstream. This elevated glucose level provides a quick and readily available source of energy for the body’s cells, especially in situations where increased energy is needed, such as during the “fight or flight” response to stress.

2. Protein and Fat Metabolism: Cortisol stimulates the breakdown of proteins into amino acids and fats into fatty acids. The resulting amino acids can be used for energy production, and fatty acids can be utilized for additional energy needs.

3. Anti-inflammatory Action: Cortisol has anti-inflammatory properties. In stressful situations, the body may experience inflammation as part of the stress response. Cortisol helps to suppress the immune system’s inflammatory response, reducing the potential for excessive inflammation.

4. Suppression of Non-Essential Functions: Cortisol helps to redirect the body’s resources towards functions that are essential for immediate survival. It can suppress non-essential functions, such as the reproductive and immune systems, temporarily prioritizing resources for dealing with the stressor at hand.

5. Maintenance of Blood Pressure: Cortisol supports blood vessel constriction, which helps to maintain blood pressure during stressful situations. This is important for ensuring an adequate blood supply to vital organs and tissues.

While cortisol is beneficial in the short term for coping with acute stress, chronic or prolonged elevation of cortisol levels due to ongoing stress can have negative effects on health. It is important for the body’s stress response to return to baseline levels once the stressor has been resolved to maintain overall well-being. Chronic stress and prolonged elevation of cortisol can contribute to various health issues, including metabolic disorders, immune system suppression, and cardiovascular problems.

The phenomena described in each scenario can be explained by different principles in biology. Here are the explanations for each:

i) Camouflage/Mimicry: (Natural selection): The green beetles are not eaten by crows because they blend in with the green bushes, making them difficult for the crows to spot. This is an example of natural selection favoring traits that provide better camouflage or mimicry.

ii) Ecological Succession: (Genetic drift): The increase in the number of blue beetles in green bushes is a consequence of the red beetles being trampled by a herd of elephants. This event leads to a change in the ecological conditions, allowing the blue beetles to thrive in the absence of competition from the red beetles.

iii) Mendelian Inheritance (Law of Dominance) : The absence of ‘medium height plants’ in the F1 generation upon crossing pure tall and dwarf pea plants is explained by Mendel’s law of dominance. In this case, the tall trait is dominant, and the dwarf trait is recessive, resulting in only tall plants in the first generation.

iv) Lamarckian Inheritance: (Acquired characters are not inherited): The persistence of tails in mice even after surgical removal for several generations suggests a Lamarckian inheritance, where acquired traits are passed on to offspring. However, it’s important to note that Lamarckian inheritance is not a widely accepted concept in modern biology.

v) Gene Flow: The migration of beetles and the incorporation of genes from the migrant beetle into the local population exemplify the phenomenon of gene flow. This process contributes to genetic diversity within a population by introducing new alleles from individuals of another population.

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