Competition and population sizeIB MYP Biology: Subtopic test

1. 1
   A forestry team in Poland planted young oak seedlings in two plots of the same woodland clearing. In plot 1 the seedlings were planted 10 cm apart. In plot 2 they were planted 1 m apart. Both plots have the same soil and receive the same rainfall.

   (a)

   Which pair of resources are the oak seedlings in plot 1 mainly competing for?

   [1 mark]

   • AMates and territory
   • BPrey and shelter
   • CLight and water
   • DSunlight and mates

   (b)

   Which outcome is most likely for the seedlings in plot 1 after several years?

   [1 mark]

   • AAll seedlings grow taller and thicker than those in plot 2
   • BSome seedlings are shaded and grow slowly or die
   • CAll seedlings receive more light than those in plot 2
   • DEach seedling receives more water than those in plot 2

   (c)

   Explain why the seedlings in plot 1 are likely to grow more slowly than those in plot 2.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   On a beach in Namibia, a colony of Cape fur seals gathers every year to breed. Each adult male defends a small patch of beach and tries to keep other males away from the females on it. The colony grows larger each year, but the amount of fish in the nearby sea stays about the same.

   (a)

   The males compete with each other for territory. What is this type of competition called?

   [1 mark]

   • AIntraspecific competition
   • BInterspecific competition
   • CPredation
   • DMutualism

   (b)

   On the breeding beach, which resource are the males mainly competing for?

   [1 mark]

   • ALight
   • BCarbon dioxide
   • CMineral ions
   • DMates

   (c)

   Explain why competition for food between the seals is likely to increase as the colony grows.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student grew yeast in a sealed flask containing a fixed volume of sugar solution kept at 30 °C. Every three hours she counted the yeast cells in a small sample. The count was 2000 cells per mm³ at 0 hours and 2400 at 3 hours. It rose to 38 000 at 9 hours and 52 000 at 15 hours, stayed at about 52 000 until 30 hours, and then fell to 20 000 by 48 hours.

   (a)

   Name the phase of population growth shown between 0 and 3 hours, between 3 and 9 hours, and between 15 and 30 hours.

   [3 marks]

   (b)

   Explain why the number of yeast cells stopped rising after 15 hours and then fell.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A school garden club in Kenya wants to grow maize to raise money for new equipment. Local farmers plant maize at very different spacings: some plant seeds close together to fit in as many plants as possible, while others leave wide gaps between plants. The club decides to test the idea using fast-growing cress seedlings first.

   (a)

   Outline an investigation using cress seedlings to test how planting density affects growth.

   [6 marks]

   (b)

   Evaluate whether the farmers should always plant maize as densely as possible.

   [6 marks]

   Total for question 4: 12 marks

End of questions