IGCSE Biology Paper-4: Specimen Questions with Answers 209 - 210 of 279

Question 209

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Penicillin was discovered in 1,928 by Alexander Fleming.

Name the type of microorganism that produces the antibiotic penicillin.

Explanation

Penicillin is a member of a group of antibiotics that are widely used to treat bacterial infections. Before the introduction of antibiotics, there were no effective treatments for infections caused by bacteria, such as pneumonia, tuberculosis, gonorrhea, or rheumatic fever. Penicillin was hailed as a “miracle drug” that could save lives and effectively treat a variety of infectious diseases. Alexander Fleming, a professor of bacteriology in London, is credited with discovering penicillin in 1,928. Returning from vacation, he started cleaning up his messy lab and noticed that some petri dishes containing Staphylococcus bacteria had been contaminated with a mold, Penicillium notatum, which was preventing the normal growth of the bacteria. Fleming obtained an extract from the mold, named its active agent “penicillin, ” and determined that the extract killed many types of harmful bacteria.

Passage

Modern technology can be used to increase the yield of crops.

Question 210 (1 of 5 Based on Passage)

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The use of chemicals, such as fertilizers, herbicides, and pesticides, is one of the developments used.

(i) Name two mineral ions commonly included in fertilizers.

Explanation

Nitrogen originates from the air. The most common process in nitrogen fertilizer manufacturing is to create ammonia from a mixture of nitrogen from the air and hydrogen from natural gas. Air consists of 78 percent nitrogen, but plants cannot get the nitrogen needed directly from the air they need to take it up through their roots from the soil. The chief source of nitrogen for green plants is the soil. It is absorbed mainly in the form of nitrate ions .

  • Potassium is sourced from old sea and lake beds formed millions of years ago. Potassium fertilizers are based on naturally occurring potassium chloride. Source of to the plants is inorganic compounds like potassium sulphate, potassium nitrate, etc. Potassium is usually present in sufficient amount in clay soils, where it is firmly bound (largely as an exchangeable base) . It is prevalent cation in plants and may be involved in the maintenance of ionic balance in cells. It contains approximately percent of whole plant. In seeds, it is found in fewer amounts.
  • Phosphate is sourced from insoluble calcium phosphate rocks often referred to as “rock phosphate. ” Phosphorus is present in the soil in two general forms, organic and inorganic. Plants do not absorb organic phosphorus, either from the solid or solution phase of soil. However, organic compounds are decomposed and phosphorus is made available to plants in inorganic form. Soil solution contains phosphorus in inorganic forms as the phosphate ions and . When is low phosphate ions are present in the form of . When pH is high, phosphate ions are represented in .

  • Nitrogen (N) , phosphate (P) , and potassium (K) can also be combined to form NPK compound fertilizers, that provides the crop with the 3 major nutrients at the same time.