BiologyNEB 2076 (old course)
Answer in short on any seven. a) Name the place where actual exchange of gases takes place inside the lung. b) What is double circulation? c) Which hormone controls osmoregulation? d) Define nerve…
7Answer in short on any seven.
- a) Name the place where actual exchange of gases takes place inside the lung.
- b) What is double circulation?
- c) Which hormone controls osmoregulation?
- d) Define nerve impulse.
- e) What is vaccine? Name their types.
- f) Give limitations of organ transplantation.
- g) What is a fingerprint?
- h) What are pullets?
- i) Why do drug addicts suffer from AIDS?
- j) Hepatitis is more dangerous than AIDS, why?
Answer
a) Place of actual gas exchange in the lung
The respiratory (alveolar) membrane – the thin walls of the alveoli and surrounding capillaries – is where oxygen diffuses into the blood and carbon dioxide diffuses out of the blood.
b) Double circulation
Double circulation refers to the two separate circulatory loops in mammals:
- Pulmonary circuit – carries de‑oxygenated blood from the right ventricle to the lungs and returns oxygen‑rich blood to the left atrium.
- Systemic circuit – carries oxygenated blood from the left ventricle to all body tissues and returns de‑oxygenated blood to the right atrium.
This arrangement ensures that oxygenated and de‑oxygenated blood do not mix and that high‑pressure systemic flow is maintained.
c) Hormone that controls osmoregulation
Antidiuretic hormone (ADH), also called vasopressin, secreted by the posterior pituitary, regulates water balance by increasing water re‑absorption in the collecting ducts of the kidneys, thereby maintaining plasma osmolarity.
d) Definition of nerve impulse
A nerve impulse (or action potential) is a rapid, self‑propagating electrical disturbance along a neuron's axon, produced by the sequential opening and closing of voltage‑gated Na⁺ and K⁺ channels, resulting in a brief reversal of the membrane potential.
e) Vaccine and its types
Vaccine – a biological preparation containing antigens (live attenuated, killed, subunit, toxoid, or recombinant) that stimulates the immune system to develop protective immunity without causing disease.
| Type of vaccine | Principle | Example |
|---|---|---|
| Live attenuated | Pathogen weakened so it cannot cause disease but still replicates | BCG, MMR |
| Inactivated (killed) | Pathogen killed by heat/chemicals; cannot replicate | Polio (Salk), Hepatitis A |
| Subunit / toxoid | Only specific antigenic parts (proteins, polysaccharides) or inactivated toxins | Hepatitis B (HBsAg), DPT (toxoid) |
| Recombinant DNA | Genes encoding antigen expressed in host cells; purified protein used | HPV, Hepatitis B |
| Conjugate | Polysaccharide antigen linked to protein carrier to enhance immunity | Hib, Pneumococcal |
f) Limitations of organ transplantation
- Donor shortage – scarcity of suitable organs leads to long waiting lists.
- Immunological rejection – recipient’s immune system may attack the graft; requires lifelong immunosuppression.
- Risk of infection – immunosuppressive drugs increase susceptibility to opportunistic infections.
- Technical complications – vascular thrombosis, anastomotic leaks, or graft dysfunction.
- Cost and infrastructure – high surgical and postoperative care expenses; limited facilities in many regions.
- Ethical and legal issues – consent, organ trafficking, and allocation fairness.
g) Fingerprint
A fingerprint is the unique pattern of ridges, furrows, and pores on the skin of the fingertip. The pattern is formed during fetal development and remains unchanged throughout life, making it a reliable means of personal identification in forensic and biometric applications.
(Any two of the remaining items – h, i, j – may be omitted as only seven answers are required.)
Discussion
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