Ecology

Question 1

How should the student decide where to place the quadrat?

Give the reason for your answer

Answer 1

(grid and) coordinates

to achieve randomness

Question 2

Using the mean from this investigation to calculate the number of daisy
plants on the lawn may not be accurate.
Give two reasons why

Answer 2

too few quadrats or quadrat too small
allow sample size too small

sample may not be representative of the lawn

Question 3

The horn of the Siberian rhinoceros is estimated to have been 150 cm long.
Suggest one advantage of this adaptation to the Siberian rhinoceros.

Answer 3

• fighting / competing for mates / food / territory
• to kill predators / prey

Question 4

Give one reason why only the bones of the body of the Siberian
rhinoceros became fossils.

Answer 4

(bones or hard tissues) did not decay

Question 5

Suggest how scientists can estimate when the Siberian rhinoceros was
alive.

Answer 5

• compare to other fossils of known age
  allow compare with the fossil record
• by the age of the rocks (where fossil was found)

Question 6

Suggest two factors that may have caused the extinction of the Siberian
rhinoceros.

Answer 6

• drought
• ice age / global warming
• volcanic activity
  allow earthquakes / tsunami
• asteroid / meteor collision
• (new) predators
  allow hunters / poachers / eaten
• (new) disease
  allow named pathogen
• competition for food
  allow lack of food
• competition for mates
  allow isolation or lack of mates
• lack of habitat or habitat change

Question 7

The jerboa is adapted for survival in the desert.
The jerboa spends the daytime in its underground burrow.
The jerboa only leaves its burrow to look for food during the night.
(d) Describe how these adaptations help the jerboa to survive in the desert.

Answer 7

• cooler underground / at night
  or
  the jerboa can keep cool
• loses less water
  or
  sweats less
• less likely to be seen (by predators / prey)

Question 8

Explain how temperature tolerance can help the dromedary to survive in
the desert.

Answer 8

less sweating so less water loss
(as) no / little water available in deser

Question 9

The student wanted to get a more valid estimate of the percentage cover of
buttercup plants in the field.
Suggest two improvements to the method to make the results more valid.

Answer 9

• place (many) more quadrats
  allow repeat
  allow combine results with results of
  other students
• divide quadrats into more / smaller squares
• estimate actual percentage cover in quadrat (instead of
  counting squares)
• only count squares with at least 50% cove

Question 10

Give three environmental factors that would affect the growth of buttercup
plants in a field.

Answer 10

• light
• water
  allow rain / moisture
• minerals / ions / salts
  allow named example such as nitrate /
  phosphate
  allow fertiliser
• pH
• temperature
• herbivores
  allow named example
• trampling / cultivation

Question 11

• describe how microorganisms in the layers of soil help to recycle chemicals in the
  dead plants
• how the chemicals are used again by living plants.

Answer 11

• digestion or large molecules to small molecules
• enzymes or named example
• respiration
• production of carbon dioxide
• release of mineral ions or named example such as nitrate /
  phosphate / magnesium
  in plants
• carbon dioxide (from air) taken in by leaves
• by diffusion
• via stomata
• carbon dioxide used in photosynthesis
• making glucose / sugar / starch / cellulose or making other correctly
  named example
• (named) ions taken in by roots
• by active transport
• nitrate ions for making amino acids / proteins / DNA / chlorophyll
• phosphate for making DNA

Question 12

Name two types of microorganism that cause decay.

Answer 12

bacteria
fungi

Question 13

Name the product that causes the pH to decrease

Answer 13

fatty acid(s)

Question 14

Which type of milk stays fresh the longest at 10 °C?

Answer 14

almond (milk)

Question 15

The time taken for cows’ milk to reach pH 5 at 10 °C is less than the time
taken for cows’ milk to reach pH 5 at 5 °C Suggest one reason why

Answer 15

• bacteria / microbes / microorganisms / fungi dividing faster
  (when warmer)
  allow converse if clearly describing 5 °C
  allow number of bacteria / microbes /
  microorganisms / fungi increasing
  (when warmer)
  allow more bacteria microbes /
  microorganisms / fungi
• reactions (in the bacteria) are happening faster (to decay milk)
• (because there is) more (kinetic) energy
  allow particles move faster
  allow more collisions between particles
• enzyme activity is higher (at 10 °C than at 5 °C)

Question 16

Suggest two reasons why the different types of milk took different lengths
of time to reach pH 5.

Answer 16

• different concentration / type of fat / lipid
  allow different amounts of fat / lipid
• different concentration / type of proteins / carbohydrate / sugar
  allow different amounts of proteins /
  carbohydrate / sugar
• different (amount / type of) bacteria present
• may have been pasteurised by a different process
  allow may have been treated in different
  ways (before the investigation)
• different starting pH
  ignore different oxygen concentration

Question 17

Which two types of organism cause decay?

Answer 17

bacteria

fungi

Question 18

Give one environmental factor needed for decay

Answer 18

water

Question 19

Gas X is the main fuel gas found in the biogas.
What is gas X?

Answer 19

methane

Question 20

The dead plant material in the compost heap and biogas generator does
not decay completely.
Explain why a farmer might spread the remaining dead plant material onto
his fields.

Answer 20

so plants / crops grow faster / better

(decays further and) releases / contains mineral ions / named
example

Question 21

Suggest why a large surface area to volume ratio is an advantage to an
earthworm.

Answer 21

(earthworm) can absorb more oxygen (in a given time)

increases / more gas exchange

Question 22

Which type of enzyme would digest fats

Answer 22

lipase

Question 23

Dead plants decay faster in soil containing earthworms compared with soil
containing no earthworms.
Explain why

Answer 23

more oxygen (in soil with earthworms)
allow earthworms bring oxygen to soil

(for) more (aerobic) respiration
do not accept anaerobic respiration

(of) bacteria / fungi / microorganisms / microbes / decomposer

Question 24

Explain why the students used water on one side of the lawn instead of
weed killer

Answer 24

as a control / comparison

Question 25

Suggest one improvement the students could have made to the method to
make the results more valid.

Answer 25

use more quadrats
original may not be representative or reference to weeds being
distributed unevenly

Question 26

Light intensity affects the number of dandelion plants that grow in an area.’
(c) Plan an investigation to test this hypothesis.

Answer 26

• placing of quadrat
• large number of quadrats used
• how randomness achieved − e.g. table of random numbers or
  random number button on calculator or along transect
  AQA Biology GCSE - Organisation of an Ecosystem
  PhysicsAndMathsTutor.com
  Page 12 of 19
• quadrats placed at coordinates or regular intervals along
  transect
• in each of two areas of different light intensities or transect
  running through areas of different light intensity
• for each quadrat count number of dandelions
• for each quadrat measure light intensity
• compare data from different light intensity

Question 27

Give two other environmental factors that affect the growth of dandelion
plants.

Answer 27

any two from:
* temperature
allow heat
* water
allow moisture / rain
* (soil) pH
allow acidity
* minerals / ions
allow e.g. magnesium ions or nitrate
allow salts / nutrients
* winds
* herbivores

Question 28

Give one reason why the students sterilised the flask before adding the
milk.

Answer 28

to kill microorganisms on / in the flas

Question 29

Describe how the students could sterilise the flask in a school laboratory.

Answer 29

heating
1
to over 100 °C

Question 30

Why did the students put a cap on top of the flask?

Answer 30

to prevent microorganisms entering from the air

Question 31

Describe two features of the sprinkler bed that encourage aerobic
respiration.

Answer 31

• sprinkled through air
• air spaces between stones
• thin layer over stones (for efficient diffusion)
• slow flow (for efficient diffusion)

Question 32

Figure 2 shows that the bacteria change organic matter into carbon
dioxide and inorganic mineral ions.
Describe how the bacteria do this.

Answer 32

• (external) enzymes released
• role of enzymes – e.g. amylase / protease / lipase
• substrates & products – e.g. starch ⟶ sugar / protein ⟶ amino acids
  / fat ⟶ fatty acids
  absorption:
• by diffusion / active transport
  deamination:
• amino acids ⟶ ammonia / ammonium ions
  release of other ions:
• e.g. phosphate / nitrate / magnesium
  respiration:
• produces carbon dioxide (+ water)
  or
  equation is given
• release of energy allows other processes to take place e.g. active
  transport

Question 33

An airtight compost heap causes anaerobic decay.
Explain why the gardener might be against producing compost using this
method

Answer 33

methane is produced

which is a greenhouse gas / causes global warming

Question 34

Explain how the carbon is recycled into the growth of new leaves.

Answer 34

• (carbon compounds in) dead leaves are broken down by
  microorganisms / decomposers / bacteria / fungi
• photosynthesis uses carbon dioxide
  explanations:
• (microorganisms) respire
• (and) release the carbon from the leaves as carbon dioxide
• plants take in the carbon dioxide released to use in photosynthesis to
  produce
  glucose
  use of carbon in growth:
• glucose produced in photosynthesis is used to make amino acids /
  proteins / cellulose
• (which are) required for the growth of new leaves

Question 35

Give three possible reasons that may have caused strawberry A to
decay.

Answer 35

• (at) higher temperature / hotter
• (had) more oxygen
• (had) more water / moisture
• (contained) more microorganisms (that cause decay)

Question 36

The biomass of mackerel is much less than the combined biomass of krill
and squid.
One reason for this is that the mackerel cannot digest all parts of the krill
and squid.
Give two other reasons.

Answer 36

non-eaten parts (of squid / krill)

• respiration or respiring (in mackerel)

makes / creates energy
* excretion (by mackerel)

Question 37

Explain how making dog food from insects could improve human food
security in the future.

Answer 37

less land required

(so) more space for crops (for humans)
allow more meat (from cows etc) for
humans

less methane (from animals) therefore less global warming