03. Movement of substances across Plasma Membrane

Written Practical (Pg 28-29)

Question 1
a(i) Observation 1 :The change in length of potato strips in 0.1 M concentration of sucrose solution is +0.25 cm.

Observation 2:The change in length of potato strips in 0.4 M concentration of sucrose solution is – 0.30 cm.

(ii) Inference 1:There is an increase in length of potato strip in 0.1M sucrose solution because this solution is hypotonic to the cell sap of the potato cells. Water diffuses into the cell sap of the potato cells by osmosis.

Inference 2:There is a decrease in length of potato strip in 0.4M sucrose solution because this solution is hypertonic to the cell sap of the potato cells. Water diffuses out of the cell sap of the potato cells by osmosis.

b) As the concentration of the sucrose solution increases, the length of potato strips decreases. The concentration of the sucrose that did not cause any change in length of the potato is isotonic to the cell sap of the potato.

c) (i) & (ii)

Concentration of sucrose solution (M)	Length of potato strips (cm)						Change in length of potato strips (cm)
	Initial			Final
	1	2	Mean	1	2	Mean
0.1	5.00	5.00	5.00	5.30	5.20	5.25	+0.25
0.2	5.00	5.00	5.00	5.10	5.10	5.10	+0.10
0.3	5.00	5.00	5.00	4.90	4.90	4.90	-0.10
0.4	5.00	5.00	5.00	4.60	4.80	4.70	-0.30

d) (i) Concentration of the sucrose solution

(ii) Length of the potato strip

(iii) Temperature// Soaking time //Type of potato//Size and shape of potato

(e) (i) Use different concentration of sucrose solution

(ii) Measure and record the initial and final length of potato strips using a ruler.

(iii) Fix the surrounding temperature to be constant // Fix the soaking time to be 30 minutes for all the experiments.

f)

g) 0.25 M. There is no change in the length of the potato strips at this concentration. This means the rate of movement of water molecules in and out of the potato cells is the same.

(h) (i) Osmosis

(ii) The cell sap of the potato (0.25M) is hypertonic to the 0.2 M sucrose solution. Water molecules from the 0.2M sucrose solution move into the vacuoles of the potato cells, causing the vacuoles to exert pressures on the cytoplasm. The cells swell and lengthens the potato strips.

i) Osmosis is movement of water molecules in or out of the potato strips which causes the change in length of potato strips which is affected by the concentration of the sucrose solution in which the potato strips are immersed.

Question 2

Aim:	To study the effects of isotonic, hypotonic and hypertonic solutions on animal cell.
Problem Statement:	What is the effect of isotonic, hypotonic and hypertonic solutions on an animal cell?
Hypothesis:	An animal cell will swell and may burst when put into a hypotonic solution. An animal cell will shrink when put into a hypertonic solution. There is no change in the size and shape of the animal cell when put into an isotonic solution.
Variables:	Manipulated: Concentration of solutions Responding: Conditions of cells Fixed: Time, temperature, type of cells
Materials & Apparatus:	Materials: chicken blood (sodium citrate added to prevent it from clotting), 0.17 M sodium chloride solution, 0.50 M sodium chloride solution and distilled water. Apparatus: slides, cover slips and light microscope
Technique:	Observe and draw the blood cells as seen under a light microscope.
Procedure:	1. Label four slides as A, B, C and D. 2. Put a drop of blood on slide A and cover with a cover slip. Observe under a light microscope. 3. Put a drop of distilled water on slide B and cover with a cover slip. Put a drop of blood at the edge of the cover slip. 4. Observe the slide under a microscope when the blood is drawn into the water. 5. Observe and draw the blood cells as seen under a light microscope. 6. Repeat steps 3, 4 and 5 by using 0.17M and 0.5M sodium chloride solutions on slides C and D respectively. 7. Dispose all specimens carefully after use.
Results :	Specimen A B C D Drawing of the cell Shape /condition of cell
Conclusion:	Hypothesis is accepted. An animal cell will swell and may burst when put into a hypotonic solution. An animal cell will shrink when put into a hypertonic solution. There is no change in the size and shape of the animal cell when put into an isotonic solution.

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