Bab 3 Biology

7/28/2019 Bab 3 Biology

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3.1 MOVEMENT OF SUBSTANCES

ACROSS THE PLASMA MEMBRANE

3.1 THE MOVEMENT OF SUBSTANCES ACROSS

THE PLASMA

3.1.1 Substances Required by Cells and

Substances Eliminated from Cells

3.1.2 The Necessity for Movement of Substances

Across the Plasma Membrane3.1.3 The Structure of The Plasma Membrane

3.1.4 Permeability of The Plasma Membrane


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3.1.1 Substances Required by Cells

and Substances Eliminated from Cells

1. All living cells carry out metabolism to stay alive.

2. Metabolism refers to all the chemical activities takingplace in the cell.

3. Metabolism consist of two processes:

a. Anabolism, which is building up of molecules.Examples are the syntheses of proteins and

ATPs, which a cell needs.

b. Catabolism, which is the breaking down of large

molecules to smaller; simpler molecules. Anexample is the oxidation of glucose in the cellrespiration.


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4. A cell takes in raw substances for

anabolism from its external environment.

5. Wastes from catabolism and excess

substances are removed from the cell.

6. Also, water and various salts are either

brought into, or are taken out of the cell.

7. Table 3.1 and Table 3.2 show some

substances that leave the cell and some

that enter the cell respectively.


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Table 3.1

Substances that leave the cell

SUBSTANCE REASON OF REMOVAL

Carbon dioxide

(animal cell)

A waste product of respiration

Oxygen (plant cell) A waste product ofphotosynthesis

Secretions

Are cellular products for use in

order parts of the bodyNitrogenous waste

Are waste products from

breakdown of excess proteins

Excess water Osmoregulation


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Table 3.2

Substance that enter the cell

SUBSTANCE REASON OF REMOVAL

Oxygen

(animal cell)

For cell respiration

Carbon dioxide(plant cell)

As a raw materials for proteinsynthesis

Glucose For cell repsiration

Amino Acids As aw materials for proteinsynthesis

Ionic Salts

For cell metabolism and

osmoregulation


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1. All movements of substances go through thecell membrane, which is also known as theplasma membrane

2. The necessities for the movement of

substances across a plasma membrane are:a) Cells need nutrients and oxygen. These pass

through the plasma membrane from the externalenvironment.

b) Cells produce waste products which exit throughthe plasma membrane.

c) The plasma membrane can control the types andthe amounts of substances needed by the cell atany time.

3.1.2 The Necessity for Movement of

Substance Across The Plasma Membrane


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plasma

membrane

cytoplasm

cell

nucleus

Movement of

substances into

the cell

Movement of

substances out

the cell

External Environment

THE NECESSITY FOR MOVEMENT OF SUBSTANCES ACROSS

THE PLASMA MEMBRANE

Figure 3.1 Movement of substances in and out of a cell


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A MODEL OF PLASMA

MEMBRANE


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To understand the concept of the plasma

membrane, we shall look ata) Basic unit of the plasma membrane

b) Formation of the plasma membrane

c) Other molecules present in the plasmamembrane.


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The Structure of Plasma

Membrane


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The basic unit of the plasma membrane

is the phospholipid molecule.

The phospholipid molecule consists of:

a. A polar phosphate molecule head which is

hydrophilic and

b. Two non-polar fatty acid tails which are

hydrophobic.


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Permeability of The Plasma

Membrane


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Permeability of The Plasma Membrane

Permeable means allowing something to

pass through

The proteins and the phospholipids of the

plasma membrane affect the permeability

of the plasma membrane.

The phospholipid bilayer is permeable to:

Small non-polar (hydrophobic)

Small uncharged molecules

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