AS & A Level Biology - 9700 Paper 5 2016 Winter Zone 3

(a) The opening and closing of stomata involves the movement of potassium ions into and out of guard cells in response to environmental factors, for example light and water stress.

This movement of potassium ions is influenced by the concentration of calcium ions in the cytoplasm of guard cells. When plants are water stressed, abscisic acid (ABA) release causes the concentration of calcium ions in the cytoplasm to increase. The increase in calcium ions causes a series of changes resulting in the loss of potassium ions, so the stomata close in light.

A student investigated the effect of calcium chloride in overcoming the effect of light on stomata.

The student was provided with:
• 500 cm³ of 1.0 mmol dm^–3 buffered calcium chloride (CaCl₂) solution
• freshly picked leaves from a plant that had been kept in light for 2 hours so that all the stomata were open.

The student soaked three epidermal strips of leaves in each of a range of calcium chloride solutions for 3 hours and recorded the number of closed stomata. An epidermal strip is made by peeling the epidermis from a leaf as a single layer.

(i) Identify the independent and dependent variables in this investigation.

independent variable ...........................................................
dependent variable ...........................................................

(a) (ii) The student used the 1.0 mmol dm^–3 CaCl₂ solution provided to prepare 50 cm³ of four other concentrations by reducing the concentration by half each time.

State the method that the student used to make these four concentrations.

(b) (i) Suggest a hypothesis that the student could test about the effect of CaCl₂ on the opening and closing of stomata.

(b) (ii) Describe a method the student could use to investigate the effect of different concentrations of CaCl₂ solution on the closing of stomata.

Your method should be detailed enough for another person to follow and should not include the details of how to dilute the 1.0 mmol dm^–3 solution of CaCl₂.

(c) (i) State two ways in which the method of measuring the diameter of the stomata has been standardised.

1. ...........................................................
2. ...........................................................
Fig. 1.1 shows stomata at different stages of opening.


(c) (ii) Fig. 1.2 shows the eyepiece graticule and stage micrometer used by the student.

The diameter of a stomatal aperture was 3 eyepiece units.

Calculate the actual size of the aperture. .......................................................... µm


(d) (i) State one piece of evidence in Fig. 1.3 that supports the student’s hypothesis that:
The stomata on the upper epidermis of a leaf and the stomata on the lower epidermis respond differently to ABA.



(d) (ii) The confidence limit of each of the mean values plotted on Fig. 1.3 is 95%. State what this tells you about each mean value.



(d) (iii) State a statistical test that could be used to find out if the difference in the stomatal aperture at different concentrations of ABA is significant.
Give a reason for your choice.

test ...........................................................
reason ...........................................................

(e) The experimental procedure carried out by the student was considered to have given data that could be trusted to support the hypothesis:
The stomata on the upper epidermis of a leaf and the stomata on the lower epidermis respond differently to ABA.

Describe the aspects of the experimental procedure which ensure that the data can be trusted.

(a) The opening and closing of stomata involves the movement of potassium ions into and out of guard cells in response to environmental factors, for example light and water stress.

This movement of potassium ions is influenced by the concentration of calcium ions in the cytoplasm of guard cells. When plants are water stressed, abscisic acid (ABA) release causes the concentration of calcium ions in the cytoplasm to increase. The increase in calcium ions causes a series of changes resulting in the loss of potassium ions, so the stomata close in light.

A student investigated the effect of calcium chloride in overcoming the effect of light on stomata.

The student was provided with:
• 500 cm³ of 1.0 mmol dm^–3 buffered calcium chloride (CaCl₂) solution
• freshly picked leaves from a plant that had been kept in light for 2 hours so that all the stomata were open.

The student soaked three epidermal strips of leaves in each of a range of calcium chloride solutions for 3 hours and recorded the number of closed stomata. An epidermal strip is made by peeling the epidermis from a leaf as a single layer.

(i) Identify the independent and dependent variables in this investigation.

independent variable ...........................................................
dependent variable ...........................................................

(a) (ii) The student used the 1.0 mmol dm^–3 CaCl₂ solution provided to prepare 50 cm³ of four other concentrations by reducing the concentration by half each time.

State the method that the student used to make these four concentrations.

(b) (i) Suggest a hypothesis that the student could test about the effect of CaCl₂ on the opening and closing of stomata.

(b) (ii) Describe a method the student could use to investigate the effect of different concentrations of CaCl₂ solution on the closing of stomata.

Your method should be detailed enough for another person to follow and should not include the details of how to dilute the 1.0 mmol dm^–3 solution of CaCl₂.

(c) (i) State two ways in which the method of measuring the diameter of the stomata has been standardised.

1. ...........................................................
2. ...........................................................
Fig. 1.1 shows stomata at different stages of opening.


(c) (ii) Fig. 1.2 shows the eyepiece graticule and stage micrometer used by the student.

The diameter of a stomatal aperture was 3 eyepiece units.

Calculate the actual size of the aperture. .......................................................... µm


(d) (i) State one piece of evidence in Fig. 1.3 that supports the student’s hypothesis that:
The stomata on the upper epidermis of a leaf and the stomata on the lower epidermis respond differently to ABA.



(d) (ii) The confidence limit of each of the mean values plotted on Fig. 1.3 is 95%. State what this tells you about each mean value.



(d) (iii) State a statistical test that could be used to find out if the difference in the stomatal aperture at different concentrations of ABA is significant.
Give a reason for your choice.

test ...........................................................
reason ...........................................................

(e) The experimental procedure carried out by the student was considered to have given data that could be trusted to support the hypothesis:
The stomata on the upper epidermis of a leaf and the stomata on the lower epidermis respond differently to ABA.

Describe the aspects of the experimental procedure which ensure that the data can be trusted.

A common weed in barley fields is couch grass. A laboratory investigation was carried out to study the effect of couch grass on the yield of barley.
Barley was grown in standard sized pots in a glasshouse. The number of barley plants per pot was constant. The supply of water and mineral salts, the light and the temperature were controlled automatically. Six replicates of each of four different experiments were carried out.
experiment 1: Couch grass and barley were sown together at the same time.
experiment 2: Couch grass was sown 14 days before the barley.
experiment 3: Barley sown 14 days before the couch grass.
experiment 4: Barley grown alone.
The yield of barley from each of the different experiments was measured.
The results showed that the yield of barley from experiments 1, 3 and 4 were the same. The results from experiment 2 showed a significant decrease in the yield of barley in comparison to the others.
(a) One hypothesis to explain the results of these experiments is:
Older couch grass roots produce a substance that inhibits the growth of younger barley roots.
(i) Outline how this hypothesis could be tested.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................[4]

(ii) Suggest one other hypothesis that could explain the results of experiment 2.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................[1]

(iii) Suggest a null hypothesis that could be used in a statistical test to compare the yield of barley with the control.
....................................................................................................................................
....................................................................................................................................[1]

(b) In a second investigation the biodiversity in two fields of barley was studied.
Barley was planted at the same density in each field and left to grow until it reached maturity. In one of the fields pesticides (herbicides and insecticides) were used to manage pests. In the other field pesticides were not used.
When the barley was mature, a standard sampling method was used to estimate the number of each different type of organism found in each field. These numbers were used to calculate the species diversity of each field using the formula for Simpson’s Index of Diversity ($D$).
$$D = 1 - \sum \left( \frac{n}{N} \right)^2$$
$n$ = number of individuals of each type present in the sample
$N$ = the total number of all individuals of all types
$\Sigma$ = the sum of
Table 2.1 shows the results of this investigation and some of the calculations for Simpson’s Index of Diversity.
[Table_1]
(i) Complete Table 2.1 and use the data to calculate $D$ for both fields of barley.
In fields using pesticides $D$ = .................................................................
In fields without pesticides $D$ = ........................................................[3]

(ii) State what the results of this investigation show about the effect of pesticides on the plants and animals studied.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................[2]

A common weed in barley fields is couch grass. A laboratory investigation was carried out to study the effect of couch grass on the yield of barley.
Barley was grown in standard sized pots in a glasshouse. The number of barley plants per pot was constant. The supply of water and mineral salts, the light and the temperature were controlled automatically. Six replicates of each of four different experiments were carried out.
experiment 1: Couch grass and barley were sown together at the same time.
experiment 2: Couch grass was sown 14 days before the barley.
experiment 3: Barley sown 14 days before the couch grass.
experiment 4: Barley grown alone.
The yield of barley from each of the different experiments was measured.
The results showed that the yield of barley from experiments 1, 3 and 4 were the same. The results from experiment 2 showed a significant decrease in the yield of barley in comparison to the others.
(a) One hypothesis to explain the results of these experiments is:
Older couch grass roots produce a substance that inhibits the growth of younger barley roots.
(i) Outline how this hypothesis could be tested.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................[4]

(ii) Suggest one other hypothesis that could explain the results of experiment 2.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................[1]

(iii) Suggest a null hypothesis that could be used in a statistical test to compare the yield of barley with the control.
....................................................................................................................................
....................................................................................................................................[1]

(b) In a second investigation the biodiversity in two fields of barley was studied.
Barley was planted at the same density in each field and left to grow until it reached maturity. In one of the fields pesticides (herbicides and insecticides) were used to manage pests. In the other field pesticides were not used.
When the barley was mature, a standard sampling method was used to estimate the number of each different type of organism found in each field. These numbers were used to calculate the species diversity of each field using the formula for Simpson’s Index of Diversity ($D$).
$$D = 1 - \sum \left( \frac{n}{N} \right)^2$$
$n$ = number of individuals of each type present in the sample
$N$ = the total number of all individuals of all types
$\Sigma$ = the sum of
Table 2.1 shows the results of this investigation and some of the calculations for Simpson’s Index of Diversity.
[Table_1]
(i) Complete Table 2.1 and use the data to calculate $D$ for both fields of barley.
In fields using pesticides $D$ = .................................................................
In fields without pesticides $D$ = ........................................................[3]

(ii) State what the results of this investigation show about the effect of pesticides on the plants and animals studied.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................[2]