question_answer

(i) Following are the various diseases that infect humans. Name the causative agent and the symptoms of each alongwith their mode of infection.

(a) Pneumonia

(b) Amoebiasis

(c) Filariasis

(d) Dengue

(ii) How do macrophages respond to the infections in human body?

Or

(i) Define the term 'mutation'. List few steps by which mutation breeding is carried out in an agricultural crop.

(ii) Differentiate between outcrossing and cross-breeding.

Answer:

(i) (a) Pneumonia
· Causative agent Streptococcus pneumoniae
· Mode of Infection Droplets from infected person and sharing contaminated articles.
· Symptoms Fluid-filled alveoli of lungs, resulting in severe difficulty in breathing, cough, headache and chills.
(b) Amoebiasis
· Causative agent Entamoeba histolytica
· Mode of infection Houseflies (mechanical carrier) transfer the parasite from the faeces of infected person to food and water which then cause infection.
· Symptoms Abdominal pain, stools with excess mucus and blood clots.
(c) Filariasis
· Causative agent Wuchereria bancrofti
· Mode of infection through the vector, female Culex mosquito.
· Symptoms Inflammation and swelling of organs in which they live, e.g. lymph vessels of lower limbs (elephantiasis) and genital organs.
(d) Dengue
· Causative agent Flavivirus
· Mode of infection. The vector is Aedes aegypti only.
· Symptoms Hemorrhagic fever in which blood platelet count decreases, characteristic skin rash, muscles and joint pain.
(ii) Macrophages are among first cells that respond to infections and provide immunity. They engulf microbes and display them as antigens to lymphocytes. They also secrete pyrogens to alert B-cells and T-cells and cause fever to slow down microbial activity.
Or
(a) Mutation is the process by which genetic variation is achieved through the changes in base sequences within the genes.
(i) Mutation breeding involves changing the genotype of plants for crop improvement.
Steps involved in mutation breeding are
(a) Inducing mutations in plants by chemicals or radiations.
(b) Screening the plants with desired variations.
(c) Selecting the desirable plant for multiplication and further breeding.
(ii) Differences between outcrossing and cross-breeding are as follows
Outcrossing	Cross-breeding
It is the practice of mating of animals within the same breed but having no common ancestors on either side of their pedigree upto 4-6 generations.	It refers to the mating of superior males of one breed with the superior female of another breed.
A single outcross helps to overcome inbreeding depression.	It is done to combine the desirable qualities of the two breeds into one individual.