(a) Name the types of lymphoid organs lymph nodes and thymus are. Explain the role played by them in causing immune response.

(b) Differentiate between innate immunity and acquired immunity.

OR

a) How does Bacillus thuringiensis act as a bio-control agent for protecting Brassica and fruit trees? Explain.

b) 1. List the components of biogas.

2. What makes methanogens a suitable source for biogas production?

a) The lymphatic system is a vascular network of tubules and ducts that collect filter and return lymph to blood circulation. Lymph is a fluid that is separated from blood plasma. Lymph composed of water, proteins, salts, lipids, white blood cells, and other substances it again secreted back to blood.

The principal functions of the lymphatic system are secretion of interstitial fluid to the blood, to absorb lipids from the digestive system to the blood, and to filter pathogens, damaged cells, cellular debris, and malignant cells. The major components of the lymphatic system include lymph, lymphatic vessels, and lymphatic organs mainly tissues. Lymphatic vessels absorb fluid that spreads from blood vessel capillaries into surrounding tissues. This fluid is drained into lymph nodes to be filtered and finally re-enters blood circulation through veins in the heart.

The lymph nodes swell in response to infection, due to a build-up of lymph fluid, bacteria, or other organisms and immune system cells. A person with a throat infection may feel that their glands are swollen. Swollen glands can be felt in jaw, in the armpits, or the groin area. These are not glands but lymph nodes.

The tonsils produce lymphocytes, a type of white blood cell, and antibodies. In inflammation condition the tissue affected by tonsillitis. The area they have situated in the thoracic region enables them to protect against inhaled and swallowed foreign bodies.

The spleen is not connected to the lymphatic system as lymph nodes, but it is lymphoid tissue. This means it plays a role in the production of white blood cells that form part of the immune system. Its other role is to filter the blood to remove microbes and old and damaged red blood cells and platelets.

The thymus gland is a lymphatic organ and an endocrine gland that is found just behind the sternum upper portion of the heart. It secretes hormones and is crucial in the production, maturation, and differentiation of immune T cells. It is active in developing the immune system in the different development stage.

B)

OR

a. Biocontrol is the use of biological methods for controlling plant diseases and pests. Chemicals, insecticides and pesticides are very harmful to humans and also these pollute the environment. The use of biocontrol reduces the dependence on toxic chemicals and pesticides. Biocontrol agents are which are useful in controlling plant diseases and pests are the ladybird and dragonflies are useful to get rid of aphids and mosquitoes. Bacteria Bacillus thuringiensis (Bt) is used to clear butterfly caterpillars where dried spores of Bacillus thuringiensis are mixed with water and sprayed onto weak plants which are eaten by the insect larvae and in the gut of the larvae, the toxin is released and the larvae get killed.

b. H₂S, H₂, CO₂, CH₄

c. Its anaerobic, the cell membrane component, ability to produce large volume of methane gas with other gas such as CO₂ and H_2.