IGCSE Biology Paper-3: Specimen Questions with Answers 239 - 240 of 358

Passage

Fig. shows a species of bacterium, Lactobacillus bulgaricus.

Bacteria from Other Groups

Question 239 (5 of 5 Based on Passage)

Write in Short

Short Answer▾

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.

Question 240

Write in Short

Short Answer▾

Mitosis and meiosis are types of nuclear division.

(i) Table 3.1 shows some features of mitosis and meiosis.

Place ticks (Π) in the boxes to show which features occur in which type of nuclear division.

Table 3.1

Some Features of Mitosis and Meiosis
featuremitosismeiosis
produces gametes
produces genetically different cells
produces genetically identical cells
produces new cells during growth and repair to damaged tissues
used in asexual reproduction
replaces cells

Explanation

Mitosis and Meiosis Are Types of Nuclear Division
featuremitosismeiosis
produces gametes
produces genetically different cells
produces genetically identical cells
produces new cells during growth and repair to damaged tissues
used in asexual reproduction
replaces cells

Mitosis and meiosis both involve cells dividing to make new cells. This makes them both vital processes for the existence of living things that reproduce sexually. Meiosis makes the cells needed for sexual reproduction to occur, and mitosis replicates non-sex cells needed for growth and development. Together, they provide the cellular basis for healthy growth and sexual reproduction.