BIOLOGY 4 Marks Question

→ No population of any species in nature has at its disposal unlimited resources to permit exponential growth.
→ This leads to competition between individuals for limited resources. Eventually, the 'fittest' individual will survive and reproduce.
→ The government of many countries have also realised this fact and introduced various restraints with a view to limit human population growth.
→ In nature, a given habitat has enough resources to support a maximum possible number, beyond which no further growth is possible. Let us call this limit as nature's carrying capacity (K) for that species in that habitat.
→ A population growing in a habitat with limited resources show initially a lag phase, followed by phases of acceleration and deceleration and finally an asymptote, when the population density reaches the carrying capacity.
→ A plot of N in relation to time (t) results in a sigmoid curve.
→ This type of population growth is called Verhulst-Pearl Logistic Growth (Figure 11.3) and is described by the following equation:



Where N = Population density at time t
r = Intrinsic rate of natural increase
K = Carrying capacity
→ Since resources for growth for most animal populations are finite and become limiting sooner or later, the logistic growth model is considered a more realistic one.

→ Early detection of cancers is essential as it allows the disease to be treated successfully in many cases.
→ Cancer detection is based on biopsy and histopathological studies of the tissue and blood and bone marrow tests for increased cell counts in the case of leukemias.
(a) Biopsy
→ In biopsy. a piece of the suspected tissue cut into thin sections is stained and examined under microscope (histopathological studies) by a pathologist.
(b) Radiation Diagnosis
→ Techniques like radiography (use of X-rays), CT (computed tomography) and MRI (magnetic resonance imaging) are very useful to detect cancers of the internal organs.
→ Computed tomography uses X-rays to generate a three-dimensional image of the internals of an object.
→ MRI uses strong magnetic fields and non-ionising radiations to accurately detect pathological and physiological changes in the living tissue.
(c) Pathological Diagnosis
→ Antibodies against cancer-specific antigens are also used for detection of certain cancers.
(d) Molecular Diagnosis
→ Techniques of molecular biology can be applied to detect genes in individuals with inherited susceptibility to certain cancers.
→ Identification of such genes, which predispose an individual to certain cancers, may be very helpful in prevention of cancers.
→ Such individuals may be advised to avoid exposure to particular carcinogens to which they are susceptible (e.g., tobacco smoke in case of lung cancer).

→ The oviducts (fallopian tubes), uterus and vagina constitute the female accessory ducts.
→ Structure of Oviducts :
→ Each fallopian tube is about 10-12 cm long.
→ It extends from the periphery of each ovary to the uterus.
→ The part closer to the ovary is the funnel-shaped infundibulum.
→ The edges of the infundibulum possess finger-like projections called fimbriae, which help in collection of the ovum after ovulation.
→ The infundibulum leads to a wider part of the oviduct called ampulla.
→ The last part of the oviduct, isthmus has a narrow lumen and it joins the uterus.
→ Structure of Uterus :
→ The uterus is single and it is also called womb.
→ The shape of the uterus is like an inverted pear.
→ It is supported by ligaments attached to the pelvic wall.
→ The wall of the uterus has three layers of tissue.
(i) The external thin membranous perimetrium.
(ii) middle thick layer of smooth muscle, myometrium.
(iii) inner glandular layer called endometrium that line the uterine cavity.
→ The endometrium undergoes cyclical changes during menstrual cycle while the myometrium exhibits strong contraction
during delivery of the baby.
→ The uterus opens into vagina through a narrow cervix.
→ The cavity of the cervix is called cervical canal which along with vagina forms the birth canal.