Biology Coursework Enzymes

Human senses

1 Reaction time
The distance a vertical ruler falls before being gripped is converted to a time interval

1.01 Reaction time
1.02 Discussion
1.03 Discussion - answers
1.04 Reaction time - preparation
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2a The blind spot (1)
A dot seems to disappear when its image falls on the blind spot
2b The blind spot (2)
A gap in a line is 'filled in' when its image falls on the blind spot

2.01 The blind spot (a) & (b)
2.02 Discussion - answers
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3 Inversion of the image
When a pin is viewed via a pinhole in front of the pin, its image appears to be inverted

3.01 Inversion of the image
3.02 Discussion & preparation
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4a The iris diaphragm (1)
The iris is observed to reduce the size of the pupil when the eye is exposed to light
4b The iris diaphragm (2)
(Broca's pupillometer) A pattern of pinholes appears to change when one eye is exposed to light

4.01 Iris diaphragm (1) & (2)
4.02 Discussion - answers & preparation
4.03 Ray diagram for pupillometer
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5 Retinal capillaries
By moving a pinhole about in front of the eye, an image of retinal capillaries appears

5.01 Retinal capillaries
5.02 Discussion - answers & preparation
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6a Binocular vision: eye dominance
A pencil lined up with a window frame appears to 'jump' when the dominant eye is closed
6b Binocular vision: double vision
Slight pressure on one eyeball causes a single object to appear as a double image

6.01 Binocular vision (a) and (b)
6.02 Discussion - answers
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7 Judgement of distance
The space sequence of coloured pinheads is judged using either one or both eyes

7.01 Judgement of distance
7.02 Discussion & preparation
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8 Eye and hand co-ordination
A star pattern is traced while looking in a mirror

8.01 Eye and hand co-ordination
8.02 Discussion
8.03 Discussion - answers
8.04 Eye and hand co-ordination - preparation
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9 Perception
Two shapes are observed, and demonstrate that the brain makes an interpretation of the image

9.01 Perception

10 Sensitivity of the skin to touch
Different areas of skin are tested with light touch to see if there are differences in reponse

10.01 Sensitivity of the skin to touch
10.02 Discussion
10.03 Discussion - answers
10.04 Sensitivity to touch - preparation
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11 Recognition of separate stimuli
(Spatial discrimination) Different areas of skin are tested with a 'hairpin' to see if they can discriminate a double touch from a single touch

11.01 Recognition of separate stimuli
11.02 Discussion
11.03 Discussion - answers
11.04 Recognition of stimuli - preparation
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12 Sensitivity to temperature
One finger is placed in hot water and another in cold water. Both are then placed in warm water and the sensations compared

12.01 Sensitivity to temperature
12.02 Discussion and preparation
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13 Location of stimuli
A marble is rolled between crossed fingers to give the sensation of two marbles

13.01 Location of stimuli
13.02 Discussion - answers & preparation
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Transport in plants

1 Uptake and evaporation in leaves
The uptake of water by single leaves is measured after coating either, neither or both surfaces with Vaseline

1.01 Uptake and evaporation in leaves
1.02 Discussion
1.03 Discussion - answers
1.04 Uptake and evaporation in leaves - preparation
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2 Uptake of water by shoots
The uptake of water by a shoot is measured, using a potometer

2.01 Uptake of water by shoots
2.02 Discussion
2.03 Discussion - answers
2.04 Uptake of water by shoots - preparation
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3 Rates of transpiration
The potometer is used in different conditions to compare rates of uptake by the shoot

3.01 Rates of transpiration
3.02 Discussion
3.03 Discussion - answers
3.04 Rates of transpiration - preparation
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4 Rate of transpiration and water uptake
By weighing the shoot and potometer, the uptake and loss of water are compared

4.01 Rate of transpiration and water uptake
4.02 Discussion
4.03 Discussion - answers
4.04 Rate of transpiration and water uptake - preparation
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5 Uptake of water by an uprooted plant
The potometer is modified to accept a whole plant rather than a cut shoot

5.01 Uptake of water by an uprooted plant
5.02 Discussion
5.03 Discussion - answers
5.04 Uptake of water by an uprooted plant - preparation
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6 Conditions affecting evaporation
A simple atmometer is used to investigate the effects of different atmospheric conditions on the rate of evaporation

6.01 Conditions affecting evaporation
6.02 Discussion
6.03 Discussion - answers
6.04 Conditions affecting evaporation - preparation
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7 Water tension in the stem
The lower end of the potometer is placed in mercury, which is pulled up the capillary by the transpiration force

7.01 Water tension in the stem
7.02 Water tension in the stem - preparation
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8 Pathways for gases in a leaf
A leaf is immersed in hot water to expand and force out any air inside it

8.01 Pathways for gases in a leaf
8.02 Pathways for gases in a leaf - preparation
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9 Evaporation from the leaf surface
Evaporation from the upper and lower leaf surface is compared and correlated with the distribution of stomata

9.01 Evaporation from the leaf surface
9.02 Discussion
9.03 Discussion - answers
9.04 Evaporation from the leaf surface - preparation
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10 To collect and identify the product of transpiration
The shoot of a plant is enclosed in a plastic bag. The liquid which condenses is identified

10.01 To collect and identify the product of transpiration
10.02 To collect and identify the product of transpiration - preparation
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11 To trace the path of water through a shoot
Shoots are placed in a dye in order to investigate the route it takes through the stem and leaves

11.01 To trace the pathway of water through a shoot
11.02 To trace the pathway of water through a shoot - preparation
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12 Conducting pathways through the shoot
A syringe is used to force air through a shoot held under water, Air bubbles show the continuity of the vessels

12.01 Conducting pathways in the shoot
12.02 Discussion
12.03 Discussion - answers
12.04 Conducting pathways in the shoot - preparation
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13 Measuring the transpiration rate of a potted plant
Two potted plants, one in sunlight and one in shadow are weighed at intervals

13.01 Measuring the transpiration rate of a potted plant
13.02 Measuring the transpiration rate of a potted plant - preparation
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14 Measuring the transpiration rate of an uprooted plant
Two flasks of water are weighed at intervals. One of them contains a plant

14.01 Measuring the transpiration rate of an uprooted plant
14.02 Measuring the transpiration rate of an uprooted plant - preparation
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Germination and tropisms

Introduction

Introduction
Resources list
Germination times - peas and wheat
Germination times - sunflower and maize
Germination times - French bean
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1 The need for oxygen
Cress seeds are sown on moist cotton wool in 2 flasks one of which contains pyrogallic acid and sodium hydroxide

1.01 Need for oxygen
1.02 Discussion
1.03 Discussion - answers
1.04 Need for oxygen - preparation
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2 Effect of temperature
Maize fruits are germinated in moist blotting paper at different temperatures

2.01 Effect of temperature
2.02 Discussion
2.03 Discussion - answers
2.04 Effect of temperature - preparation
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3 The need for water
Seeds are left in moist, dry and waterlogged conditions for a week

3.01 Need for water
3.02 Discussion answers and preparation
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4 The role of cotyledons
Runner bean embryos attached to varying amounts of cotyledon are germinated on moist blotting paper in jars

4.01 Role of cotyledons
4.02 Discussion
4.03 Discussion - answers
4.04 Role of cotyledons - preparation
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5 Use of food reserves in germination
Coleoptiles and endosperm of cereal seedlings and grains are tested for starch and sugar

5.01 Use of food reserves
5.02 Discussion
5.03 Discussion - answers
5.04 Use of food reserves - preparation
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6 Geotropism in radicles
Pea seedlings are pinned to a clinostat, or a stationary base, with their radicles horizontal

6.01 Geotropism in radicles
6.02 Discussion
6.03 Discussion - answers
6.04 Geotropism in radicles - preparation
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7 The region of growth and response in radicles
Radicles are marked with equidistant lines and left horizontally or vertically for two days

7.01 Region of growth and response in radicles
7.02 Discussion
7.03 Discussion - answers
7.04 Region of growth and response in radicles - preparation
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8 Region of detection and response to one-sided gravity in radicles
Different lengths of root tip are excised to see if the radicles still grow and respond to gravity

8.01 Detection of unilateral gravity
8.02 Discussion
8.03 Discussion - answers

Class practical or demonstration

Hydrogen peroxide (H2O2) is a by-product of respiration and is made in all living cells. Hydrogen peroxide is harmful and must be removed as soon as it is produced in the cell. Cells make the enzyme catalase to remove hydrogen peroxide.

This investigation looks at the rate of oxygen production by the catalase in pureedpotato as the concentration of hydrogen peroxide varies. The oxygen produced in 30 seconds is collected over water. Then the rate of reaction is calculated.

Lesson organisation

You could run this investigation as a demonstration at two different concentrations, or with groups of students each working with a different concentration of hydrogen peroxide. Individual students may then have time to gather repeat data. Groups of three could work to collect results for 5 different concentrations and rotate the roles of apparatus manipulator, result reader and scribe. Collating and comparing class results allows students to look for anomalous and inconsistent data.

Apparatus and Chemicals

For each group of students:

Pneumatic trough/ plastic bowl/ access to suitable sink of water

Conical flask, 100 cm3, 2

Syringe (2 cm3) to fit the second hole of the rubber bung, 1

Measuring cylinder, 100 cm3, 1

Measuring cylinder, 50 cm3, 1

Clamp stand, boss and clamp, 2

Stopclock/ stopwatch

For the class – set up by technician/ teacher:

Hydrogen peroxide, range of concentrations, 10 vol, 15 vol, 20 vol, 25 vol, and 30 vol, 2 cm3 per group of each concentration (Note 1)

Pureed potato, fresh, in beaker with syringe to measure at least 20 cm3, 20 cm3 per group per concentration of peroxide investigated (Note 2)

Rubber bung, 2-holed, to fit 100 cm3 conical flasks – delivery tube in one hole (connected to 50 cm rubber tubing)

Health & Safety and Technical notes

Wear eye protection and cover clothing when handling hydrogen peroxide.
Wash splashes of pureed potato or peroxide off the skin immediately.
Be aware of pressure building up if reaction vessels become blocked.
Take care inserting the bung in the conical flask – it needs to be a tight fit, so push and twist the bung in with care.

1 Hydrogen peroxide: (See CLEAPSS Hazcard) Solutions less than 18 vol are LOW HAZARD. Solutions at concentrations of 18-28 vol are IRRITANT. Take care when removing the cap of the reagent bottle, as gas pressure may have built up inside. Dilute immediately before use and put in a clean brown bottle, because dilution also dilutes the decomposition inhibitor. Keep in brown bottles because hydrogen peroxide degrades faster in the light. Discard all unused solution. Do not return solution to stock bottles, because contaminants may cause decomposition and the stock bottle may explode after a time.

2 Pureed potato may irritate some people’s skin. Make fresh for each lesson, because catalase activity reduces noticeably over 2/3 hours. You might need to add water to make it less viscous and easier to use. Discs of potato react too slowly.

3 If the bubbles from the rubber tubing are too big, insert a glass pipette or glass tubing into the end of the rubber tube.

Procedure

SAFETY: Wear eye protection and protect clothing from hydrogen peroxide. Rinse splashes of peroxide and pureed potato off the skin as quickly as possible.

Preparation

a Make just enough diluted hydrogen peroxide just before the lesson. Set out in brown bottles (Note 1).

b Make pureed potato fresh for each lesson (Note 2).

c Make up 2-holed bungs as described in apparatus list and in diagram.

Investigation

d Use the large syringe to measure 20 cm3 pureed potato into the conical flask.

e Put the bung securely in the flask – twist and push carefully.

f Half-fill the trough, bowl or sink with water.

g Fill the 50 cm3 measuring cylinder with water. Invert it over the trough of water, with the open end under the surface of the water in the bowl, and with the end of the rubber tubing in the measuring cylinder. Clamp in place.

h Measure 2 cm3 of hydrogen peroxide into the 2 cm3 syringe. Put the syringe in place in the bung of the flask, but do not push the plunger straight away.

i Check the rubber tube is safely in the measuring cylinder. Push the plunger on the syringe and immediately start the stopclock.

j After 30 seconds, note the volume of oxygen in the measuring cylinder in a suitable table of results. (Note 3.)

k Empty and rinse the conical flask. Measure another 20 cm3 pureed potato into it. Reassemble the apparatus, refill the measuring cylinder, and repeat from g to j with another concentration of hydrogen peroxide. Use a 100 cm3 measuring cylinder for concentrations of hydrogen peroxide over 20 vol.

l Calculate the rate of oxygen production in cm3/s.

m Plot a graph of rate of oxygen production against concentration of hydrogen peroxide.

Teaching notes

Note the units for measuring the concentration of hydrogen peroxide – these are not SI units. 10 vol hydrogen peroxide will produce 10 cm3 of oxygen from every cm3 that decomposes.(Note 1.)

In this procedure, 2 cm3 of 10 vol hydrogen peroxide will release 20 cm3 of oxygen if the reaction goes to completion. 2 cm3 of liquid are added to the flask each time. So if the apparatus is free of leaks, 22 cm3 of water should be displaced in the measuring cylinder with 10 vol hydrogen peroxide. Oxygen is soluble in water, but dissolves only slowly in water at normal room temperatures.

Use this information as a check on the practical set-up. Values below 22 cm3 show that oxygen has escaped, or the hydrogen peroxide has not fully reacted, or the hydrogen peroxide concentration is not as expected. Ask students to explain how values over 22 cm3 could happen.

An error of ± 0.05 cm3 in measuring out 30 vol hydrogen peroxide could make an error of ± 1.5 cm3 in oxygen production.

Liver also contains catalase, but handling offal is more controversial with students and introduces a greater hygiene risk. Also, the reaction is so vigorous that bubbles of mixture can carry pieces of liver into the delivery tube.

If collecting the gas over water is complicated, and you have access to a 100 cm3 gas syringe, you could collect the gas in that instead. Be sure to clamp the gas syringe securely but carefully.

The reaction is exothermic. Students may notice the heat if they put their hands on the conical flask. How will this affect the results?

Health and safety checked, September 2008

Downloads

Download the student sheet  Investigating an enzyme-controlled reaction: catalase and hydrogen peroxide concentration (67 KB) with questions and answers

Web links

http://www.saps.org.uk/secondary/teaching-resources/293-student-sheet-24-microscale-investigations-with-catalase Microscale investigations with catalase – which has been transcribed onto this site at Investigating catalase activity in different plant tissues.

(Website accessed October 2011)

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