Lab #1

Title: Osmosis
Aim: To observe some effects of osmosis.
Apparatus and Materials: petri dish, NaCl (salt) solution, water, potato strips, ruler.

Diagram:
The apparatus was set up as shown below.

water
petri dish salt water
potato strip

Procedure:
1. Two potato strips were cut roughly 1cm square and 3cm long.
2. The length of each was measured.
3. The potato strips were rubbed between fingers to assess their texture.
4. Each potato strip was put into a petri dish. One was covered with clean water and the other
with a salt solution.
5. The potato strips were left in their dishes for 15 minutes.
6. The strips were removed, dried and the length of each was measured.
7. The texture of the potato strips was noted.
8. The observations were recorded.

Results:

TABLE SHOWING THE LENGTHS AND TEXTURES OF THE POTATO

Solution First texture Final texture First Final Change in

length/mm length/mm length %
Water Firm, hard Firm, hard 40 42 4

Salt Firm, hard Soft with smoother 40 36 2

solution surface.

Discussion:
 Osmosis is the movement of water molecules from a region of high water concentration
to a region of low water concentration through a semi permeable membrane.
In this experiment, the potato strips were placed in solutions of different concentrations,
to observe the effects of osmosis in the potato.
The first potato strip was placed in a solution of salt. The salt solution has a lower water
concentration and the potato cells have a higher water concentration. Therefore, water will move
from the potato cells into the salt solution until the concentrations are the same. Hence, the
length decreased. Whenever plant cells are placed in concentrated solutions, they become
flaccid. As a result, the potato became softer.
The second strip was placed in distilled water. The concentration of water was higher
outside than that of the potato cells. Therefore, water will enter the cell due to the difference in
the concentration until the concentration becomes the same. Hence, the length will increase.
Whenever plant cells are placed in less concentrated solutions, they become turgid. As a result,
the potato remained firm and hard.

Conclusion:
When potato strips were placed in a concentrated solution, its length decreased and it had a
smoother texture. When it was placed in distilled water which is less concentrated, its length
increased and it had a firm and hard texture.
Lab #2

Title: Photosynthesis
Aim: To investigate the presence of starch in a green leaf.
Apparatus and Materials: beaker, dicotyledonous leaf, petri dish, test tube, dropper, water,
iodine.

Procedure:
1. A small, fresh, green dicotyledonous leaf was picked.
2. The leaf was dipped into boiling water for about 30 seconds.
3. The leaf was placed in a test tube containing 15ml of ethanol.
4. The leaf was removed and rinsed in distilled water when it appeared colourless.
5. The leaf was placed in the petri dish and two drops of iodine solution were placed on it.
6. Observations were recorded.

Results:
TABLE SHOWING OBSERVATIONS AT EACH STAGE

Stage Observation
Boiling water Green, soft
Ethanol White, brittle, hard
Iodine Blue black, hard, brittle

Discussion:
Glucose is a product of photosynthesis. It is converted into starch and is stored. Iodine
reacts with starch to give a blue-black colour. If iodine drops on a leaf, there will be no colour
changes seen. This is because the starch is stored in the chloroplast and cannot pass through the
cell membrane and so the iodine cannot reach the starch in order to react with it.
In order to break down the cell membrane, the leaf was placed into boiling water. It was
placed in ethanol to dissolve the chlorophyll which made the leaf look black when iodine was
placed over it. The leaf was rinsed to remove any chlorophyll residue and when iodine was
placed on it, the leaf tested positive for starch. This shows that the leaf was photosynthesising.

Conclusion:
The dicotyledonous leaf tested positive for starch as it changed colour when iodine was placed
over it.
Lab #3

Title: Respiration
Aim: To investigate the effect of exercise on pulse rate.
Apparatus and Materials: Stopwatch (digital)

Procedure:
1. A student was made to sit quietly for 2 minutes to ensure complete relaxation.
2. The pulse rate was taken by placing the index and middle finger on the wrist for a minute
and recorded.
3. Step 2 repeated every other minute until a total of four counts were completed.
4. The student was made to do some vigorous exercise.
5. Immediately following; the pulse rate was taken for a minute and recorded.
6. Step 5 was repeated every other minute until the pulse rate returned to the level recorded
prior to exercising.
7. A graph of pulse rate against time elapsed was plotted.

Results:

TABLE SHOWING PULSE RATE TAKEN BEFORE AND AFTER EXERCISE

BEFORE EXERCISE AFTER EXERCISE

TIME ELAPSED / PULSE RATE / TIME ELAPSED / PULSE RATE /

MINS MINS MINS MINS
1 60 1 96

2 60 2 90

3 60 3 72

4 60 4 65

5 60 5 60
 GRAPH SHOWING PULSE RATE AGAINST TIME ELAPSED

Discussion:
In this experiment, the effect of exercise on pulse rate was investigated. The pulse rate
was taken before and after exercise. The pulse rate before exercise was 60 beats (pulses) per
minute. The pulse rate after exercise was 96 beats per minute which decreased to 90 beats per
minute to 72 beats per minute to 65 beats per minute and finally to 60 beats per minute which
was the rate before exercise (at rest). The pulse rate was affected because of respiration.
Pulse rate indicates how the heart is beating or the rate at which the heart beats. The
heart pumps blood at high pressure and so the arteries beat accordingly. This pulsating beat is
felt at the wrist which directly indicates the heartbeat itself. Respiration is the process by which
glucose is combined with oxygen to give energy. This is aerobic respiration as oxygen is used.
In order for cells to get oxygen for respiration to take place, the heart has to pump oxygenated
blood around the body until it reaches the cells.
At rest, when no exercise was done, the pulse rate was 60 beats per minute. This is
known as the normal reading since the cell used a “fixed amount” of oxygen and needed no
excess. However, when exercise was done, the pulse rate increased which means that the student
needed energy in order to exercise which means that more oxygen was needed. This means that
the heart has to pump oxygenated blood in order for the cells to receive enough oxygen for
respiration to take place so that the student would have enough energy.
However, the heart cannot pump oxygenated blood fast enough to reach the cells. The
cells then begin to respire anaerobically (without oxygen) to get enough energy to do exercise.
During anaerobic respiration, lactic acid is produced. This causes muscle fatigue. In order to
break down the lactic acid, oxygen is needed. Hence, the heat beats faster to supply oxygen to
break down the lactic acid. This is why the pulse rate increased. The lactic acid had to be
broken down quickly to reduce muscle fatigue.
Conclusion:
The effect of exercise on pulse rate was investigated. It was observed that pulse rate increases
with exercise.
Lab #4

Title: Response
Aim: To investigate the effect of light on the pupil.
Apparatus and Materials: Subjects A and B, torchlight.

Procedure:
1. Subjects A and B sat in a dark room and subject B looked directly forward.
2. The torchlight was brought by subject A near to subject B’s eye and the pupil was watched.
3. The torchlight was then removed from subject B’s eyes and the pupil was also observed.

iris iris

constricted pupil dilated pupil

DIAGRAM SHOWING A CONSTRICTED DIAGRAM SHOWING A DIALATED

PUPIL IN BRIGHT LIGHT PUPIL IN DIM LIGHT

Discussion:

In this experiment, the effect of light intensity on the pupil was investigated. There is a
sense organ which responds to changes in light intensity and colour. Light rays from objects
enter the pupil and are converted into nerve impulses which are then sent to the brain. The pupil
is the part of the eye which allows light to enter the eye. The iris is the eye colour which controls
the size of the pupil. The iris is composed of circular and radical muscles and by the alternate
contraction and relaxation of these muscles, the size of the pupil is altered. The retina is
composed of rods and cons which are photoreceptive cells. The rods function the best in low
light intensities (dim light). The rods are desensitised by bright light. Hence, it was ensured that
the light was not flashed directly in the eye of subject B.
When the light was flashed in subject B’s eye it was noticed that the pupil constricted
(became smaller). This was in response to the stimulus of bright light. This was a cranial reflex
action. A cranial reflex action is a reflex action which occurs in the head region. The stimulus
of bright light is received by the eye. The sensory nerve from the receptors in the eye sends a
message to the eye, telling the muscles to contract or relax which is a response. In this case, the
response was the pupil getting smaller. For this to happen, the radial muscles of the iris relax
and the circular muscles of the iris contracts.
When the light was moved away from subject B’s eye, it was noticed that the pupil dilated
(increased in size). This was in response to the stimulus which was dim light (decreased light
intensity). This was also a cranial reflex action. The stimulus was received by the eye. Then a
message was sent to the brain asking it what to do via the sensory nerve by the receptors in the
eye. The brain then sends a message to the muscles in the eye via the motor nerve. This brought
about the response which was the dilation of the pupil. For this to happen, the circular muscles
of the iris relax and the radial muscles contract. This action causes the iris to be pulled back;
therefore increasing the size of the pupil. The pupil constricted in bright light to decreased the
amount of light entering the eye since there was already an abundance of light. The pupil dilated
in dim light to increase the amount of light entering the eye since there was hardly any light to
enable the eye to see.

Conclusion:
It was found that in bright light, the size of the pupil decreased and in dim light, the size of the
pupil increased.
Lab #5

Title: Food Tests

Aim: To perform food tests on various substances.
Apparatus and Materials: test tube, test tube holder, test tube rack, water bath, droppers, spatula,
Benedict’s solution, NaOH solution, CuSO4 solution, iodine solution, dilute HCl, ethanol,
distilled water, solutions A, B, C, D, E.

Procedure:
1. 2cm3 of solution A was added to a test tube. A few drops of iodine solution was added.
2. Step 1 was repeated for all of the remaining solutions, B, C, D and E.
3. The observations were recorded.
4. 2cm3 of solution A was added to a test tube. 2cm 3 of Benedict’s solution was added. The
mixture was then shaken and was then gently brought to boil.
5. Step 3 was repeated for all solutions A, B, C, D, E and the observations were recorded.
6. 1cm3 of solution A was added to a test tube. 1cm 3 of dilute HCl was also added. The
mixture was then boiled for 1 minute. 1cm 3 of NaOH was then added, followed by 2cm 3 of
Benedict’s solution. The mixture was then shaken and boiled gently.
7. 2cm3 of solution A was added to a test tube. 2cm 3 of NaOH was added to solution A. the
mixture was then stirred and 2 drops of CuSO4 was added.
8. 2cm3 of solution A was added to a test tube. 2cm 3 of ethanol was then added. The mixture
was well shaken and 3cm3 of distilled water was added.
9. Steps 6 – 8 were repeated for solutions B, C, D, E and the observations were recorded.

Results:

TABLE SHOWING RESULTS FOR STARCH TEST ON SOLUTIONS A, B, C, D, E

SUBSTANCE OBSERVATION INFERENCE

A Changed from colourless to dark A great amount of starch was

brown solution present

B No change Starch absent

C No change Starch absent
D No change Starch absent
E No change Starch absent
 TABLE SHOWING RESULTS OBTAINED FOR REDUCING SUGAR TEST ON
SOLUTIONS A, B, C, D, E

SUBSTANCE OBSERVATION INFERENCE

A No change Reducing sugar absent

B No change Reducing sugar absent
C Solution changed from blue to Reducing sugar present
green and then to brick red colour

D No change Reducing sugar absent

E No change Reducing sugar absent

TABLE SHOWING RESULTS OBTAINED FOR NON-REDUCING SUGAR TEST ON

SOLUTIONS A, B, C, D, E

SUBSTANCE OBSERVATION INFERENCE

A No change Non-reducing sugar absent

B No change Non-reducing sugar absent
C No change Non-reducing sugar absent
D Red-brown precipitate formed Non-reducing sugar (probably
from the hydrolysis if sucrose sucrose) present

E No change Non-reducing sugar absent

TABLE SHOWING RESULTS OBTAINED FOR PROTEIN TEST PERFORMED ON
SOLUTIONS A, B, C, D, E

SUBSTANCE OBSERVATION INFERENCE

A No change Protein absent

B No change Protein absent
C No change Protein absent
D No change Protein absent
E Purple colour developed Protein present

TABLE SHOWING RESULTS OBTAINED FOR FAT TESTS PERFORMED ON

SOLUTIONS A, B, C, D, E

SUBSTANCE OBSERVATION INFERENCE

A No change Fats absent

B Very cloudy emulsion formed Fats present

C No change Fats absent

D No change Fats absent
E No change Fats absent