1.3 Variation in population size

Question 1

Define population size

Answer 1

The number of individuals in a population

Question 2

Population growth curves:

Phase 1 = ? (2)
Phase 2 = ? (3)
Phase 3 = ? (4)

Answer 2

Phase 1 = period of slow growth

• Initially small number of individuals reproduce
• Steepness of gradient slowly increases

Phase 2 = period of rapid growth

• Ever-increasing number of individuals continue to reproduce
• Population size doubles during each time individual
• Steepness of gradient rapidly increases

Phase 3 = period of decline

• Until population stable - due to limiting factors
• Gradient levels out - cyclic fluctuations due to variations in factors

Question 3

Population size:

Why does no population continue to grow indefinitely?
Each population has?

Answer 3

limiting factors eventually slow growth

a maximum size that can be sustained over a relatively long period

Question 4

Define abiotic factor

Answer 4

An ecological factor that makes up part of the non-living/non-biological environment of an organism.

Question 5

Define biotic factor

Answer 5

An ecological factor that makes up part of the living/biological environment of an organism.

Question 6

Temperature:

Affects?
Each enzyme (and therefore species) has?
Further organism deviates from optimum…
Due to?

Answer 6

Enzyme activity
Different optimum.
…Slower population growth/smaller population.
Enzyme denaturation

Question 7

Light:

Affects?
Increase in light intensity = ?
Decrease in light intensity = ?

Answer 7

Affects rate of photosynthesis
Increase in light intensity = more rapid population growth/larger population.
Decrease in light intensity = slower population growth/smaller population.

Question 8

pH:

Affects?
Each enzyme (and therefore species) has?
Further organism deviates from optimum…
Due to?

Answer 8

Enzyme activity
Different optimum.
…Slower population growth/smaller population.
Enzyme denaturation

Question 9

Water and humidity:

Humidity affects? (2)
More water/humidity =
Less water/humidity =

Answer 9

transpiration/evaporation
more rapid population growth/larger population.
slower population growth/smaller population.

Question 10

EXAM QUESTION

The population number of both species of lizard varied at different times of the year. Suggest two reasons why. (2)

Answer 10

1. Breeding (of lizards);
2. Food source/prey;
3. Predator;
4. Variation in malarial infection;
5. Temperature variation;
6. Availability of water eg
   drought/’rainy season’

Question 11

EXAM QUESTION

Other than temperature, suggest one abiotic factor that is likely to affect the position of the tree line on the mountain (1)

Answer 11

Accept an abiotic factor that may
limit photosynthesis/growth;
E.g. Water
Named soil factor
 Light
Carbon dioxide
Incline/aspect
Wind/wind speed