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.

NOTES: Movement of Substances across the Plasma Membrane

•Living cells carry out the following life processes:

–absorb water and nutrients (minerals, ions,glucose, amino acids) from the surroundings.

–Excrete waste products (urea, uric acid)

–Exchange respiratory gases during resp.

•These processes are important to a cell because they help the cell to:

–maintain the optimum pH value and concentration gradient of ions that are suitable for the activities of the cell (muscle and nerve activities)

–obtain nutrients for metabolism

–eliminate toxic waste products from the cell

–secrete useful substances (hormones,enzymes)

•The movement of substances in and out of the cell occurs across the plasma membrane.

•The plasma membrane regulates the exchange of substances between the content of the cell and the external environment.

The structure of the plasma membrane

•Plasma membrane, according to the fluid mosaic model (S. Singer and G. Nicolson, 1972) are composed mainly of phospholipids and proteins.

•Each phospolipid molecule consist of two parts:

–a polar head that gives it a hydrophilic property (attracted to water)

–a pair of non-polar fatty acid tails  that give it a hydrophobic property (repelled by water)

•At the plasma membrane, phospholipids are arranged in a double layer, called phospholipid bilayer.

•

•According to this model,

–the phospholipid, proteins and other components of the membrane are not rigid or static, but form a dynamic and fluid structure.

Phospholipid Bilayer

–The protein molecules float about freely in the phospholipid bilayer.

•The protein and phospholipids are free to move sideway within the membrane, and this causes the membrane to have a fluid characteristic.

•The various proteins built into the plasma membrane form a mosaic pattern

Fig. A model of the plasma membrane (fluid- mosaic  structure)

Fluid Mosaic Model

•Cell-cell recognition proteins 

- identify type of cell and identify a cell as “self” versus foreign

–Most are glycoproteins

•-Carbohydrate chains vary between species, individuals, and even between cell types in a given individual.

•-Glycolipids also play a role in cell recognition

Fluid Mosaic Model of the PM

•A membrane is a mosaic

–-Proteins and other molecules are embedded in a framework of phospholipids

•

•A membrane is fluid

–-Most protein and phospholipid molecules can move laterally

The permeability of the Plasma Membrane

•-The plasma membrane is selectively permeable/ semi- permeable/partially permeable.

•-This means that certain substances can move across the membrane freely while  others cannot.

•The selective permeability of the plasma membrane depends on the:

–- the size of molecules or ions, or

–- the polarity of the molecules.

•The phospholipid bilayer is permeable to:

–-non-polar molecules (lipid-soluble)

–-small, uncharged molecules

•The phospholipid bilayer is not permeable to:

–-charged ions

–-polar molecules (lipid-insoluble)

•Due to hydrophobic core of the bilayer. The plasma membrane is only permeable to:

–- small hydrophobic solutes such as fatty acids, glycerol, steroids and all the fat soluble vitamins (A,D,E,K).

–- non- polar molecules such as oxygen and carbon dioxide

–- water as it is small enough to slide between the phospholipid bilayer or move through the pores.

•- Pore proteins allow small water-soluble molecules and ions to pass through the membrane.

•- Charged and large molecules such as glucose, amino acids, water soluble vitamins and polysaccharides cannot pass across the plasma membrane and therefore they are transported by either facilitated diffusion or active transport (aided by carrier proteins)

•There are two ways of transporting substances or solutes across the plasma membrane:

–-Passive transport (without the involvement of chemical energy)

–- Active transport (use energy and carrier proteins)

Diffusion

•-Movement of molecules from an area of high concentration to an area of low concentration.

•

•-Movement from one side of a membrane to another, un-facilitated

•A. Passive Transport

•i) Simple Diffusion

•lipid-soluble molecules, gases and water.

•not control by cell.

•movement of the molecules from a region of higher concentration to a region of lower concentration.

•Factors affecting the rate of diffusion are temperature, size of molecules/ions, diffusion gradient, surface area and diffusion medium.

•example: diffusion of oxygen and carbon dioxide at the alveolus

Osmosis

•Osmosis – diffusion of water across a selectively permeable membrane

•- Water moves from an area of high water concentration (dilute solution) to an area of low water concentration(concentrated solution).

– Is energy required ?

•Type of Solution

•-Hypotonic

•-Isotonic

•-Hypertonic

•1) Hypotonic

•Solute concentration in the external solution is lesser than solute concentration inside the cell.

•Water concentration outside the cell is higher than the water concentration inside the cell.

•2) Isotonic

•Solute concentration in the external solution is equal to the solute concentration inside the cell.

•Water concentration inside and outside of the cell is the same.

•3) Hypertonic

•Solute concentration in the external solution is greater than solute concentration inside the cell.

•Water concentration outside the cell is lower than the water concentration inside the cell.

Osmosis and Animal Cells

Osmosis and Plant Cells

Osmosis Summary

•When a cell is placed in a Hypotonic solution:

–-Cell gains water through osmosis

–-Animal cell lyses; plant cell becomes turgid (firm)

–

–

•When a cell is placed a Hypertonic solution:

–-Cell loses water through osmosis

–-Animal cell shrivels; plant cell plasmolyzes

•Facilitated Diffusion:

•very specific: glucose, nucleic acids, amino acids and mineral ions.

•control by cell.

•transport of molecules (only certain molecules) across the outer membrane of living cell aided by a  carrier protein within the cell membrane.

•normally take place from a region with higher concentration of molecules to a region of lower concentration.

•example: absorption of digested food in the villus

•Process of Active Transport

•very specific: minerals ions and amino acids.

•control by cell.

•This process needs carrier proteins and energy (due to against concentration gradient) from a region of lower concentration to a region of higher concentration).

•Cell must expend energy that derived from ATP (adenosine triphosphate)

•example: human nerve cells (sodium ions are constantly transport out of the cell) / ions intake by root hairs of a plant

Active Transport

•Active transport proteins move substances across the PM against their concentration gradient.

–Requires energy (ATP)

–Active transport proteins are highly selective

–Active transport is needed for proper functioning of nerves and muscles

•Application

•Food is soaked in a concentrated salt solution to prevent bacteria and fungus to survive.

•Chemical fertiliser (dissolved ions) increases solute concentration (decrease water molecules) in soil. Therefore, water leaves from the cell sap of the plant which result the plant wither.

CHAPTER 3 : MOVEMENT OF SUBSTANCES ACROSS PLASMA MEMBRANE

Activity 3.1

1.     Q :What are the substances required by cells?

        A : Oxygen, amino acids, glucose, minerals ( Na⁺, K⁺ ), water, vitamins. 

2.     Q : What are the substances that need to be eliminated from cells?

        A :  Carbon dioxide, urea.

3.     Q : Explain the necessity for the movement of  substances across the plasma  membrane.

        A : (i)      To maintain the concentration of substances inside and outside the cell

              (ii)     To maintain constant internal environment ( homeostasis ), to ensure that the cells can function effectively.

Activity 3.2

2.             Discuss he following questions with you groups members:

a)   Q: How does diffusion occur?

A:  The movement of substances or molecules from a region of higher   concentration to a region of lower concentration.

b)  Q:What is the differences between simple diffusion and osmosis?A:In osmosis the movement of substances are across the plasma membrane , while in simple diffusion , plasma membrane is non required.

c)   Q:What are the substances that can be transported across the plasma membrane by facilitated diffusion?

A:Water –soluble molecules /not soluble in lipids  such as nucleic acids, ions, amino acids and glucose        .

d) Q:Explain how active transport occurs?

    Answers 

i)  The concentration of sodium ion is higher on the outside of the cell.

ii)         The sodium ion approach the carrier protein to bind to one of the    binding sites and the other binding site attach to ATP.

iii)                   Energy from ATP is used by carrier protein and cause it to change its shape and allows sodium ions to bind to the active site..

iv)                   This causes the carrier protein to release the sodium ions outside the cell.

Activity 3.3

2. (a)       Q : How a gaseous exchange occurs in the alveoli and blood capillaries?

A : The concentration of oxygen in alveoli is higher than in the blood capillaries.   Therefore, oxygen diffuses across the surface of the alveolus and blood capillaries into the blood.

(b)  Q : How food is absorbed in the villi of the small intestine ? 

  

Types of transport	Substances	Explaination
Simple diffusion	Water-soluble and lipids-soluble molecules	Move into the villi through the plasma membrane
Facilitated diffusion	Glucose, amino acids	Glucose, amino acids are transported via facilitated diffusion
Active transport	Ions ( Na+, K+ )	The ions are transported via active transport

    ( c )      

Water	Ions
-       uptake by roots -       the soil has a higher water concentration compared to the cell sap of the root hair -       therefore, water diffuses into the vacuoles of root hair by osmosis	-       uptake of mineral salts by root hair -       the concentration of ions and mineral salts in the cell sap is higher compared to the soil -       these substances are transported into the cells via active transport.

ASSESMENT ( CHAPTER 3 )

OBJECTIVE QUESTIONS

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

Assessment Chapter 3

1.     Figure 2 shows the fluid-mosaic model of plasma membranes.

a)         Name the structure labeled W, X, Y and Z in figure 2.

        W:  Carrier protein  X:  Pore protein      Y:  Non-polar tail   Z: Polar head

b)   What are the characteristics of plasma membranes based on the model in     Figure 2?

Plasma membrane made up of phospholipid bilayer and proteins that are not rigid or static but form dynamic and flexible structure.  Membrane has fluid characteristic  with the protein and phospholipid molecules free to move within the membrane. It acts as a barrier to isolates the two sides of membrane. The plasma membrane is selectively permeable.

c)   State one molecule that can pass through structure X.

      Calcium ion/water molecule/small soluble water molecule

d)  Explain how molecules pass through structure W.

W is carrier protein which are specific as it  can only combine with certain molecules . The carrier protein functions by binding to the molecules. It changes shape to allow the molecules to pass through to the other side of plasma membrane.

1.   Figure 3 shows the process of osmosis.

The beaker is separated into 2 compartments by a semi-permeable membrane that is only permeable to water molecules.

    Compartment A contains sucrose and water molecules while compartment B contains only water molecules.

    (a)   Name the process that take place in the beaker.

           The process is osmosis.

    (b)   Explain the process that occurs in the beaker.

        There is a concentration gradient occurs between the two compartments. Therefore, water molecules from Compartment B which has higher water concentration diffuse through a semi-permeable membrane to Compartment A which has lower water concentration 

(c ) Predict what would happen to:

(i)    the concentration of solution in Compartment A, and

The concentration of solution becomes lower after the system has reached a dynamic equilibrium

(ii)   the level of solutions in both compartments

The level of solution in Compartment A is higher than in Compartment B

after the system has reached a dynamic equilibrium.

SECTION C

1.     Explain what you understand about the term ‘semi-permeable’.

This means that some substances can move across the membrane freely while others cannot.

        2.     Explain how facilitated transport is different from active transport.

FACILITATED DIFFUSION

-       going down concentration gradient

-       facilitated by carrier proteins

-       movement of glucose and amino acids in the villi

   ACTIVE TRANSPORT

-       against the concentration gradient

-       occurs in living cells

-       cellular energy

( ATP ) is required

-       the process results in the accumulation of or elimination of substances from the cell

-        movement of mineral salts and ions

    3.     Explain :

  (i)    How gaseous exchange occurs in alveoli and blood capillaries.

- The concentration of oxygen in alveoli is higher than in the blood capillaries.   Therefore, oxygen diffuses across the surface of the alveolus and blood capillaries into the blood.

(ii)   the uptake of ions by the root hairs of a plant.

-       uptake of mineral salts by root hair -       the concentration of ions and mineral salts in the cell sap is higher compared to the soil these substances are transported into the cells via active transport.