2019 WAEC Biology Theory a. Explain briefly the importance of the following factors and organisms in the nitrogen cycle…

Explanation

a. Importance  of the following in the Nitrogen Cycle
   (i) Lightning
    - When lightning occurs, nitrogen reacts with oxygen in air to form nitrous oxide/oxides  of nitrogen;
    - which is further oxidised to form nitrogen (IV) oxide /nitrogen dioxide;
    - which dissolves in rain water to form nitric and nitrous acids;
    - (that fall to the ground) when it reaches the soil combines with bases/mineral salts to form nitrates;
    - which the plants absorbs.

   (ii) Nitrosomonas
    - Is a nitrifying bacterium in the soil;
    - that converts ammonia to nitrites in the soil.

   (iii) Azotobacter
    - Is a nitrogen-fixing bacterium in the soil;
    - that converts nitrogen in the soil;
    - into ammonium compounds/amino compounds and protein in the soil;
    - converts  nitrites to nitrates in the soil.

b. Excretory organs
    Insects –  malpighian tubules;
    Earthworm –  nephridium

c. Explanation of diseases
    (i) Hepatitis
    - Is the inflammation/destruction of liver cells;
    - hepatitis can arise from bacteria/virus/an autoimmune disease;
    - or from excess consumption of alcohol.

    The symptoms include fatigue;
    - loss of appetite/anorexia;
    - muscle aches/pains;
    - flu;
    - fever;
    - nausea;
    - jaundice;
    - and  dark coloured urine/stool.

    (ii) Kidney stones
    - Are small solids/crystals of concentrated minerals/uric acid found in the urine;
    - they are formed if there is an excessive loss of water/insufficient water intake;
    - so that the solubility of minerals/calcium phosphate/calcium oxalate in the urine is reduced;
    - high levels of uric acids/amino acids can lead to kidney stones;
    - bacteria may be trapped in the kidney tubules as the kidney stones get bigger;
    - symptoms are sharp pain at the flank of back;
    - frequent urination;
    - nausea;
    - sweating;
    - kidney stones can be treated by medications;
    - change in diet of food rich in calcium;
    - surgery;
    - drinking plenty of water.

d. (i)  Effects of lack of sense receptors in the skin
    - Humans will not be able to sense/feel/perceive external stimuli in the environment;
    - pain;
    - touch;
    - a change in temperature;
    - pressure;
    - danger which could lead to death.

   (ii) Layers of the epidermis
    - cornified layer/stratum corneum;
    - granular layer/stratum granulosum;
    - malpighian layer/stratum Malpighi.

e. (i)  Metamorphosis
    Is the development of some/certain organisms from the egg; to an adult stage; involving three to four stages.

   (ii) Type of metamorphosis of listed insects