HANDS ON CHAPTER 3

Mastery Exercise

Objective Questions

1. D 2. B 3. D 4. C 5. C

6. C 7. C 8. A 9. C 10. D

11. C 12. B 13. C 14. B 15. C

Subjective Questions 

Section A

1. (a) Plot your own graph scale for y axis ----100 80 60 40 20… scale for x axis 0 0.30 0.35 0.40 0.45 0.50 0.55 Concentration of salt solution (g/100 cm3) (b) (i) 0.435 g/100 cm3 (ii) 0.55 g/100 cm3. No bursting of red blood cells occurs in this concentration because it is isotonic to the concentration of red blood cells. (c) (i) The red blood cells will shrink.  (ii) At concentration of more than 0.55 g/100 cm3, water molecules will move out from the red blood cells by osmosis to its surrounding. As a result, red blood cells will shrink due to loss of water.  2. (a) (i) Solution X is hypotonic to the cell sap of potato cell. Water molecules from solution X move into the vacuoles of the potato cells by osmosis. The enlarged vacuole will push against the cytoplasm, causing the cell to inflate. This causes the potato strip to lengthen. (ii) Solution Y is isotonic to the cell sap of potato cells. The rate of movement of water molecules in and out of the cells is the same. Therefore, there is no change in the length of the strip. (iii) Solution Z is hypertonic to the cell sap of potato cells. Water molecules move out from the vacuole of the cells. Plasmolysis takes place and the potato strip shrinks. (b) (i) Hard (ii) Soft (c) The use of excessive fertiliser will increase the osmotic concentration in the soil water, causing water molecules to move out from the root hair. The plant will wilt and may die. 

Section B

3. (a) Simple diffusion – Movement of molecules in gas or liquid from a region of high concentration to a region of lower concentration.

Facilitated diffusion – Movement of big molecules along a concentration gradient with the help of protein carriers across the plasma membrane.

Resapan berbantu – Pergerakan molekul besar merentas membran plasma mengikut kecerunan kepekatan dengan bantuan protein pembawa.

Osmosis – Movement of water molecules from a region of less concentrated solution to a region of more concentrated solution across a semi-permeable membrane.

Osmosis – Pergerakan molekul air merentas membran separa telap dari kawasan berkepekatan rendah ke kawasan berkepekatan tinggi.

Active transport – Movement of particles across the plasma membrane against the concentration gradient with the help of protein carriers and the presence of energy from ATP.

Active transport	Osmosis
(1) Needs energy.	(1)Does not need energy.
(2) Movements of molecules or ions   against a concentration gradient.	(2) Movement of water        molecules along a concentration gradient.

4. (a) • Plasma membrane is selectively permeable.

• Permits lipid-soluble molecules such as glycerol, vitamins A, D, E and K to move across.

• Small, uncharged molecules such as water move freely across.

• Large molecules such as glucose and amino acids move across the plasma membrane with the aid of carrier proteins.

• Larger molecules such as starch cannot move across the plasma membrane. 

Maximum 4

(b) • Plasma membrane consists of phospholipids bilayer and proteins.

• Phospholipid molecule consists of a polar head which is hydrophilic and a pair of non-polar fatty acid tails which is hydrophobic.

• Two types of proteins which are pore proteins and transport proteins.

• Plasma membrane is semi-permeable which allows certain substances to move in and out freely.

• Small, uncharged molecules such as oxygen and carbon dioxide move freely through the phospholipids bilayer through simple diffusion. 

• Water molecules which are attracted to the hydrophilic heads of the phospholipids move across through osmosis.

• Lipid-soluble molecules such as fatty acids and ethanol dissolve in the lipid bilayer and move across through simple diffusion.

• Large, water-soluble molecules such as glucose and amino acids require the aid of transport proteins to move them across the plasma membrane through facilitated diffusion or active transport.

• Ions such as K+ and Na+ are transported across the plasma membrane through facilitated diffusion or active transport with the help of transport proteins.

Maximum / Maksimum 10

(c) • Vegetables soak in salt solution which is hypertonic to the cell sap of vegetable cells.

• Harmful insecticides or fungicides which had been sprayed on the vegetables earlier diffuse out of the cells to the salt solution.

• Water from the cell sap in the vacuole also diffuses out the salt solution through osmosis.

• The vegetables become flaccid.

• This action cleans the vegetables of harmful insecticides but causes the vegetables to be flaccid and soft.

Maximum / Maksimum 6

Written Practical

1. (a) (i) The length of potato core in 0.1 M sucrose solution increases. The length of potato core in 0.4 M sucrose solution decreases.

(ii) 0.1 M sucrose solution is hypotonic to the cell sap of the potato cells. 0.4 M sucrose solution is hypertonic to the cell sap of potato cells.

(b) The concentration of a solution is isotonic to the cell sap of a potato cell if the solution does not change the length of the potato core.

(c) (i) & (ii)

Initial (cm)	Final (cm)	Change in length of the potato core (cm)
Mean / Min	Mean / Min
5.0	5.25	+ 0.25
5.0	5.10	+ 0.10
5.0	4.90	– 0.10
5.0	4.70	– 0.30

(d) (i) Concentration of the sucrose solution

(ii) Length of the potato core

(iii) Temperature

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

(ii) Measure and record length of potato cores using a ruler

(iii) Keep surrounding temperature constant

(f) plot your own graph

0.1 0.3 0.2 0.1 –0.1 –0.2 –0.30 0.2 0.3 0.4 0.5 Concentration of the sucrose solution (M)  Change in length of the potato core (cm)

(g) 0.24 M. There is no change in the length of the potato core 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 is hypertonic to the 0.2 M sucrose solution. Water molecules from the 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 core. 

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 / Pemboleh ubah:

Manipulated: Concentration of solutions

Responding: Conditions of cells

Fixed: Time, temperature, type of cells

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

Procedur :

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. Repeat steps 3 and 4 by using 0.17 M and 0.50 M sodium chloride solutions on slides C and D respectively.

Conclusion: Red blood cells swell and burst into fragments of cytoplasm when put into hypotonic solution. In hypertonic solution, red blood cells shrink due to water loss. There is no change in the cells when immersed in isotonic solution. Hypothesis is accepted.