Question 1
Which statement describes a population?
- All the organisms in an ecosystem
- A group of organisms of one species, living in the same area, at the same time
- All the species in a habitat
- A group of different species living together
Show mark scheme for question 1
Answer: B (1)
Question 2
A woodland contains oak trees, foxes, rabbits, fungi and soil, light and water. (a) State what is meant by the term community. [1] (b) State what is meant by the term ecosystem. [1] (c) Name one population in the woodland. [1]
Show mark scheme for question 2
- (a) all of the populations of different species in an ecosystem (1)
- (b) a unit containing the community of organisms and their environment, interacting together (1)
- (c) all the foxes / all the rabbits / all the oak trees (1) reject an answer naming more than one species
Question 3
State four factors that affect the rate of population growth of an organism.
Show mark scheme for question 3
- food supply (1)
- competition (1)
- predation (1)
- disease (1)
Question 4
A small number of bacteria were added to a flask of nutrient broth. The number of bacteria was counted every 2 hours. (a) Name the phase of growth between 4 and 6 hours. [1] (b) Name the phase of growth between 8 and 12 hours. [1] (c) Describe what happens to the number of bacteria between 12 and 14 hours. [1] (d) Calculate the increase in the number of bacteria between 2 and 6 hours. [1]
| time / hours | number of bacteria / millions per cm³ |
|---|---|
| 0 | 2 |
| 2 | 3 |
| 4 | 12 |
| 6 | 60 |
| 8 | 100 |
| 10 | 100 |
| 12 | 100 |
| 14 | 40 |
Show mark scheme for question 4
- (a) exponential / log (phase) (1)
- (b) stationary (phase) (1)
- (c) falls / decreases (from 100 to 40 million per cm³) (1)
- (d) 60 − 3 = 57 million per cm³ (1) allow 57 000 000 per cm³
Question 5
Supplement (what this means)
Supplement: only for the Extended papers (2 and 4). Core students can skip it. What the labels meanExplain why the number of bacteria in the flask in the previous question became constant between 8 and 12 hours.
Show mark scheme for question 5
- (nutrients / food become) limiting factor(s) (1)
- nutrients / food running out / lack of space / toxic waste products build up (1)
- more competition (for nutrients) (1)
- rate of reproduction / birth rate equals death rate (1)
- so there is no overall change in numbers (1)
- Max 4
Question 6
Supplement (what this means)
Supplement: only for the Extended papers (2 and 4). Core students can skip it. What the labels meanExplain why a population of yeast cells grows slowly at first, then very quickly, in a closed container with a limited supply of sugar.
Show mark scheme for question 6
- at the start there are few cells to reproduce / cells adjusting (1)
- so the birth rate is low and growth is slow (lag phase) (1)
- sugar and space are plentiful, so there is little competition (1)
- cells reproduce faster than they die, and each new cell can reproduce (1)
- so numbers increase rapidly (exponential phase) (1)
- limiting factors are not yet acting (1)
- Max 5