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.