Amoeba feeding

Amoeba in motion

Answer to Written Practical Question

Bread is made from a mixture of flour, yeast, sugar and water. The dough is kneaded and left to rise before baking. The time taken for the dough to double its size depends on the amount of yeast used.

Plan a laboratory experiment to study the relationship between the amount of yeast used and the time taken for the dough to double its size. The planning of the experiment should include the following aspects:

· Aim of investigation

· Problem statement

· Hypothesis

· Variables

· List of apparatus and materials

· Technique used

· Experimental procedures or methods

· Presentation of data

· Conclusion

ANSWERS

Aim of investigation

To study the relationship between the amount of yeast used and the time taken for the dough to double its size.

Problem statement

What is the effect of the amount of amount of yeast used on the time taken for the dough to double its size?

//How does the amount of yeast used affect the time taken for the dough to double its size?

Hypothesis

The more the amount of yeast used, the faster the time taken for the dough to double its size.

Variables

Manipulated variables: Amount of yeast used

Responding variables: Time taken for the dough to double its size

Fixed variables: Amount of flour// sugar// water (write only one)

Materials

3 g of yeast, 15 g of sugar, 150 g of flour, 150 g of water

Apparatus:

Weighing machine, beakers, mixing bowls, stopwatch

Technique used

Measure and record the time taken for the dough to double its size using a stopwatch.

Procedure

1. Mix 50 g of flour and 5 g of sugar thoroughly in a mixing bowl. Labeled as P. Repeat for mixing bowls Q and R.

2. Mix 0.5 g, 1.0 g and 1.5 g of yeast to mixing bowls P, Q and R respectively.

3. Add 50 ml of water to each mixing bowl and knead for 5 minutes.

4. Place each of the kneaded dough in a beaker and press down the dough. Note the initial level of the dough.

5. Each beaker is covered with a clean cloth and placed in a warm spot.

6. Start the stopwatch and record the time taken for the dough to double its size.

7. The time taken for the dough to double its size for P, Q and R is recorded in a table.

Presentation of data

Mixing bowl	Amount of yeast (g)	The time taken for the dough to double its size (minutes)
P	0.5
Q	1.0
R	1.5

Conclusion

The hypothesis is accepted. The more the amount of yeast used, the faster the time taken for the dough to double its size.

Non organelle

b) Non organelle	Characteristics	Functions
1. Plasma/cell membrane	-made of protein & phospholipids -semi permeable	-it regulates the movement of substances in and out of the cytoplasm
2. Cell wall (Plant cell)	-made of cellulose. -permeable to all fluids	-gives shape to plant -provides mechanical support for the plant cell
3. Cytoplasm	-jelly-like matrix -medium which organelles are suspended. -contains organic and inorganic substances	-medium for biochemical reactions in the cell.

CHAPTER 2 : CELL STRUCTURE AND CELL ORGANISATION

2.1 UNDERSTANDING CELL STRUCTURE AND FUNCTION

Cell Structure : Organelle

1. What is organelle?

Organelle is a minute structure in the cytoplasm that has a specific function.

a) Organelle	Characteristics	Function
1. Nucleus	-the largest organelle -has chromatin thread	-control all activities of the cell -contain DNA which determine the characteristics and cell functions.
2. Vacoule (plant cell)	-fluid filled sac enclosed by membrane called tonoplast. -the fluid is called cell sap.	-vacoule in plants store chemicals such as water, amino acid, sugar, mineral, waste product. -vacoule regulates water balance in plant cell and paramecium -supports herbaceous plants
3. Mitochondrion	-cylindrical shape -made up of two membrane units	-the site of energy production through cellular respiration. Glucose + O2 +Energy + H2O + CO2 -energy released is used for cellular activities
4. Lysosomes (animal cell)	-contain hydrolytic enzyme. -membrane-bound sac	-release enzyme to digest material in food vacuoles in organisms like Paramecium -break down complex organic molecules(eg protein, lipid, polysaccharides & nucleic acid). -digest bacteria, dead or damaged organelles to enable a cell to renew itself
5. Chloroplast (plant cell)	-lens-shaped -contains chlorophyll.	-traps sunlight (energy) during photosynthesis
6. Centriole (animal cell)	-small cylindrical structure	-form spindle fibres during cell division in animal cells
7. Ribosome	-small spherical organelles -either attached to RER or free	-the site of protein synthesis -use information from nucleus to make these proteins.
8. Endoplasmic reticulum (ER) i) RER ii) SER	-The membranes of ER are continuous with the nuclear membrane -has ribosomes attached to its surface -does not have ribosomes attached to its surface	i) RER – Transports protein (made by ribosomes) to Golgi apparatus. -Protein are packaged in vesicles which are called transport vesicle. ii) Synthesis of lipids (phospholipids and steroids) -Detoxification of drugs & poisons
9. Golgi body/ apparatus	-stacks of flattened membranous sacs. -new membrane is continuously added to one end of Golgi apparatus and buds off as secretoryvesicles at the other end.	-processing, packaging and transport center of synthesized proteins (such as enzyme/hormone/antibody, phospholipids and carbohydrate & glycoproteins (such as mucus). -all these modified substances, enclosed in a secretory vesicle and bud off from the Golgi body to the cell membrane/other parts of the cell.

2010 Biology Paper 3- Question 2

Organisms in an environment compete with each other for the same basic needs in their survival. Competition between individuals of different species is called interspecific competition and competition between individuals of the same species is called intraspecific competition. The effect of the competition is shown in their growth such as the height, size and dry mass.

Based on the above information, plan a laboratory experiment to study the effect of interspecific competition between maize and paddy plants on their growth.

The planning of your experiment must include the following aspects:

• Problem statement
• Hypothesis
• Variables
• List of apparatus and materials
• Experimental procedure
• Presentation of data

Sample answer

Problem statement (3 marks)	What is the effect of interspecific competition between maize and paddy plants on their growth?
Hypothesis (3 marks)	Maize plant grow taller than paddy plant// The growth of maize plant is less when it is grown with paddy plant than when it is grown alone.
Variables (3 marks)	Manipulated variable : Type of plant// Maize and paddy plants (only one) Responding variable : Growth of plant//dry mass//height//size (only one) Constant variable : Distance between each seedling//amount of water//intensity of sunlight//nutrient//temperature//duration (only one)
List of apparatus and materials (3 marks)	Apparatus : Tray, oven, balance and ruler Material : Paddy, maize, soil, water
Experimental procedure (3 marks)	1. 3 trays : X is planted with paddy, Y planted with maize and Z with maize and paddy. 2. The seedling trays are filled with equal amount of garden soil. 3. Initial dry mass/any other growth parameter of the seedlings are measured. 4. 5-30 paddy/maize seedlings are planted at 5 cm apart. 5. The seedlings are watered everyday. 6. The trays are weeded. (precaution) 7. After 7-30 days, 5-10 paddy seedlings are removed from tray X and the roots are cleaned (precaution) and then heated/dried in an oven at 105oC. 8. The average dry mass of seedlings is measured using a balance and recorded. 9. Steps 7-8 are repeated with maize seedlings in tray Y and maize and paddy seedlings in tray Z. 10.All data are recorded in a table.
Presentation of data (2 marks)	Types of plants(Tray) Initial dry mass (g) Final dry mass (g) Difference in dry mass (g) Paddy (X) Maize (Y) Paddy (Z) Maize (Z)

2010 Biology Paper 3 - Question 1(Continuation)

1(e(i) Construct a table and record all the data collected in the experiment. Your table should have the following titles:

• Type of activity
• Initial and final readings of the lengths of air column
• Percentage of carbon dioxide in the air sample

Type of activity	Initial readings of the lengths of air column (cm)	Final readings of the lengths of air column (cm)	Percentage of carbon dioxide in the air sample (%)
Resting 0 minute	10.0	9.9	1
1 minute running on the spot	10.0	9.8	2
2 minute running on the spot	10.0	9.7	3
3 minute running on the spot	10.0	9.6	4

(e) (ii) Use the graph paper provided on page 9 to answer this question. Using the data in l(e)(i), draw a line graph of the percentage of carbon dioxide against the time of activity.

Uniform scales on both axes : 1 mark

4 points plotted correctly : 1 mark

Join all 4 points correctly : 1 mark

f) Based on the line graph in l(e)(ii), explain the relationship between the time of activity and the percentage of carbon dioxide in the air sample.

When the time of activity increases, the percentage of CO2 released increases because more energy is required, so respiration takes place at a faster rate.

g) This experiment is repeated on the same student but the exhaled air is collected 10 minutes after each activity. Predict the percentage of carbon dioxide released. Explain your prediction.

1% //decrease because respiration went back to normal rate, ie same as resting. Less energy is produced/needed.

h) State the operational definition for exhaled air.

Exhaled air contains CO2/is the air column which is absorbed by potassium hydroxide in the J-tube. The length of air column is influenced by time of activity.

(i) The following list is part of the materials and apparatus used in this experiment.

Complete Table 4 based on the list given above.

Material	Apparatus
Exhaled air sample Water Potassium hydroxide solution	Beaker Boiling tube Rubber tube J-Tube

2010 Biology Paper 3 - Question 1

Q1. An experiment was carried out to investigate the effect of different duration of activity on the percentage of carbon dioxide in exhaled air.

In this experiment, a student rests for 0 minute and his exhaled air is collected to analyse the carbon dioxide content in the air sample.

The experiment is repeated with the same student after running on the spot for 1 minute, 2 minutes and 3 minutes.

The exhaled air is collected immediately after each activity. In this experiment, a J-tube is used to analyse the carbon dioxide content in the exhaled air. Potassium hydroxide solution is used to absorb carbon dioxide in exhaled air.

Sample answers

(a) Record the lengths of air column in the four boxes provided in Table 2.

Activity	Length of air column (cm)
Resting 0 minute	9.9
1 minute running on the spot	9.8
2 minute running on the spot	9.7
3 minute running on the spot	9.6

(b) (i) State two different observations made from Table 2.

Observation 1: The length of air column during resting time is 9.9 cm

Observation 2: The length of air column after running on the spot for 3 min is 9.6 cm

(ii) State the inferences which correspond to the observation in 1(b) (i).

Inference from observation 1: During resting, the least CO2 is released and absorbed by potassium hydroxide solution

Inference from observation 2: During running on the spot for 3 min, the most CO2 is released and absorbed by potassium hydroxide solution

c) Complete Table 3 based on this experiment.

Variable	Method to handle the variable
Manipulated variable Time of activity // Type of Activity	Use different time of activity, ie 0 minute, 1 minute, 2 minutes and 3 minutes // Resting and running on the spot
Responding variable Length of air column	Measure and record the length of air column using a metre rule.
Constant variable Same student Initial length of air column	Fix the same student to carry out all the activities Fix the length of air column to be 10 cm.

(d) State the hypothesis for this experiment.

As the time of activity increases, the length of air column decreases/CO2 released increases

To be continued......