IGCSE Biology Paper-3: Specimen Questions with Answers 236 - 238 of 358

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Passage

Fig. shows a species of bacterium, Lactobacillus bulgaricus.

Bacteria from Other Groups

Question 236 (2 of 5 Based on Passage)

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Short Answer▾

List two features that distinguish bacteria from other groups of organisms.

Explanation

Bacteria and Archaea

Question 237 (3 of 5 Based on Passage)

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Bacteria, such as L. bulgaricus, can reproduce rapidly.

Name the process of reproduction in bacteria.

Explanation

Binary fission is a type of asexual reproduction typically observed in prokaryotes and few single-celled eukaryotes. In this method of asexual reproduction, there is a separation of the parent cell into two new daughter cells. This process happens with the division and duplication of the parent՚s genetic matter into two parts, here, each daughter cell receives one copy of its parent DNA. It is a primary method of reproduction in prokaryotic organisms. Binary Fission occurs without any spindle apparatus formation in the cell.

Question 238 (4 of 5 Based on Passage)

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L. bulgaricus are added to milk to make yoghurt.

Fig. A. shows the changes in a population of L. bulgaricus during fermentation to make yoghurt.

Number of Living Bacterial Cells

Name the stages shown on Fig. A. Write your answers in the boxes on Fig. A.

Explanation

Number of Living Bacterial Cells

The bacterial growth curve represents the number of live cells in a bacterial population over a period.

  • There are four distinct phases of the growth curve: lag, exponential (log) , stationary, and death.
  • The initial phase is the lag phase where bacteria are metabolically active but not dividing.
  • The exponential or log phase is a time of exponential growth.
  • In the stationary phase, growth reaches a plateau as the number of dying cells equals the number of dividing cells.
  • The death phase is characterized by an exponential decrease in the number of living cells.

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