4 methods by which substances (eg. oxygen, carbon dioxide, water, amino acids, fatty acids, sugars,...

DIFFUSION 4 methods by which substances (eg. Oxygen, Carbon Dioxide, Water, Amino acids, Fatty acids,

Sugars, Vitamins, Mineral ions, hormones etc) move across cell membranes DIFFUSION FACILITATED DIFFUSION OSMOSIS ACTIVE TRANSPORT

The cell membrane is selectively permeable some particles are small enough to fit through pores in the membrane some are helped through large molecules restricted molecules such as water, carbon dioxide, oxygen can pass through

easily glucose and ions can move through channels with the assistance of

transport proteins

Diffusion

Movement of particles from a region of HIGH CONCENTRATION to a region of LOW CONCENTRATION

Aims to achieve equilibrium (will continue to occur whilst there is a CONCENTRATION GRADIENT)

DOES NOT require energy

In cells, it is driven by concentration differences across the membrane

Diffusion rate can be increased by increase in particle concentration (i.e. Concentration gradient made steeper) smaller solute size high temperatures

Faci l itated Diffusion

Molecule aided across a membrane by attachment to a specific carrier molecule

Speeds up the rate of diffusion of particular molecules

Substances moved by facilitated diffusion usually cannot diffuse by dissolving in the lipid bilayer

Large polar and non-

polar molecules need carrier proteins to move through the membrane

(eg. Glucose)

Active Transport

Net movement of molecules against a concentration gradient from region of LOW concentration to a region of HIGH concentration

ENERGY REQUIRING (ENDERGONIC)

Allows cells to maintain stable internal conditions despite outside conditions

Can select which molecules move into or out of the cell via specific carrier molecules in the membrane

ATP transfers a phosphate molecule to a carrier protein (ATP ADP + Pi) ------ENERGY REQUIRED - carrier protein changes shape - allows substance bound to it to move

across the membrane

EXAMPLES

Sodium – Potassium Pump-Uses energy to exchange Na+ for K+- This then drives other active transport mechanisms

Proton Pumps-Uses energy to move H+ ions from inside to outside the cell- The potential (charge) difference is then used to drive other reactions

Osmosis

The net movement of WATER molecules from a low concentration solution (high water content) to a high concentration solution (low water content) through a semi-permeable membrane

DOES NOT require energy Cells with maximum water = TURGID Cells with low water content = FLACCID PLASMOLYSIS is the process of water being lost from plant cells

VIDEO – OSMOSIS THE BASICS

https://www.youtube.com/watch?v=IaZ8MtF3C6M



MOVEMENT ACROSS THE PLASMA MEMBRANE

PROCESS DEFINITION PART OF THE CELL INVOLVED

PASSIVE/ ACTIVE

EG. OF MATERIAL MOVED

DIFFUSION Movement of particles from a region of HIGH concentration to a region of LOW concentration

Cell Membrane, various organelles

Passive Carbon dioxide, Oxygen, Ethanol, Glycerol

FACILITATED DIFFUSION

Same as diffusion but aided by attachment to a specific carrier molecule (IONOPHORE) to pass across a membrane. May involve transport proteins or channel proteins

Cell membrane (Carrier proteins, Channel proteins)

Passive or Active

Simple sugars, amino acids, nucleotides, charged ions

OSMOSIS Net movement of WATER molecules from a region of HIGH concentration to a LOW concentration through a semi-permeable membrane

Cell membrane, various organelles

Passive Water

ACTIVE TRANSPORT

Movement of particles against a concentration gradient from a region of LOW concentration to a region of HIGH concentration

Cell membrane (Carrier proteins)

Active Glucose, some ions

BULK TRANSPORTENDOCYTOSIS The movement of solids or liquids

into the cellCell membrane, vesicles

Mostly passive

Various usually large particles such as digestive enzymes, hormones, toxins

EXOCYTOSIS The movement of solids or liquids out of the cell (usually via vesicles)

Cell membrane, vesicles

Mostly passive

Various usually large particles such as digestive enzymes, hormones, toxins

PINOCYTOSIS Endocytosis involving the movement of LIQUIDS into the cell


Mostly passive

Liquids

PHAGOCYTOSIS

Endocytosis involving the movement of foreign material (mostly solids) into the cell for diigestion


Mostly passive

Solids (usually foreign matter such as bacteria

CELL MEMBRANE FUNCTION: Acts as a SELECTIVE BARRIER between the inside of the cell and external fluid Regulates the transfer of substances into and out of the cell. Supplying nutrients

and removing wastes Utilises the processes of DIFFUSION & ACTIVE TRANSPORT Width is usually 7 – 10 nm

PHOSPHOLIPID BILAYER

HYDROPHOBIC tails form a non-polar hydrophobic interior(VERY INSOLUBLE IN WATER – NON-POLAR)

HYDROPHILIC ends face the aqueous medium and are polar(VERY SOLUBLE IN WATER)

VIDEO: CRASH COURSE CELL MEMBRANES & TRANSPORT

https://www.youtube.com/watch?v=dPKvHrD1eS4




FLUID MOSAIC MODEL The hydrophobic head tends to dissolve in water and the hydrophobic tails are repelled and

force inward forming a PHOSPHOLIPID BILAYER

Phospholipids are capable of sideways movement

Specialised protein molecules are also embedded in a ‘mosaic’ pattern

Proteins and lipids can flip around in the membrane - protein molecules in the membrane have particular functions and can carry a

sugar molecule (GLYCOPROTEIN)

Glycoproteins are often receptors/marker molecules important in cell recognition

The lipid structure gives it the property of being flexible and able to repair itself

Allows it to change shape and for vesicles to be pinched off from them or fuse to it

PERMEABLE SUBSTANCES NON-PERMEABLE SUBSTANCES

Small hydrophobic molecules Ions - Oxygen, Carbon Dioxide, Nitrogen Na+, H+, K+, Mg+, Cl-, HCO3

-

Small uncharged polar molecules Larger uncharged molecules Water, Glycerol, Ethanol Amino acids,

Nucleotides, Glucose

MEMBRANE CONTENTS PHOSPHOLIPIDS:The bilayer structure means the non-polar tails act as a barrier for ions and watersoluble substances

CHOLESTEROL:Help regulate the fluidity of the membrane preventing it from becoming too rigid. Mechanical stability so membranes don’tbreak easily

PROTEINS:Transport Proteins: provide hydrophilic channels for ions & polar molecules. Specific for the molecule being transported. Some are enzymes which may catalyse reactions. Can be gated or non-gated. Gated are important for Ca+, Na+ & K+ and muscle/nerveoperation

Cell Adhesion Proteins: attach adjacent cells to one another

Hormone Binding Proteins: allow hormones to bind to themand a signal is transmitted to inside of the cell

Cell Recogniition Proteins: allows the cell to be recognised as‘self’ or ‘foreign’ and act as markers

GLYCOLIPIDS & GLYCOPROTEINS: Carbohydrate chains are often attached to the lipids and proteins of the outer membrane. These areknown as glycolipids and glycoproteins. Project out into watery fluidssurrounding the cell where they form hydrogen bonds with water. They help stabilise the membrane structure. Can act as receptor molecules

forhormones or neurotransmitters. Are the basis for cell ANTIGENS.

*may be called glycocalyx

CELL MEMBRANEand PROTEINS

Some definitions

SOLVENT: a liquid in which a substance is dissolved in (H2O is the UNIVERSAL SOLVENT)

SOLUTE: particles/molecules that are dissolved in the solvent

SOLUTION: the mixture of dissolved particles in the solvent

HYPERTONIC: A highly concentrated solution (high solute) - water molecules will diffuse OUT OF cells in a

hypertonic solution

HYPOTONIC: A low concentrated solution (low solute) - water molecules will diffuse INTO cells in hypotonic

solution

ISOTONIC: A solution with the same concentration as its surrounding - water molecules will NEITHER move into or out of

cells in an isotonic solution

(concentration inside and outside the cell are equal)

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Cellular Structure and Function

Which of the following factors does NOT affect the rate of diffusion across a membrane?

A) the number of different types of particles in a solution

B) the temperature of a solution

C) the size of the diffusing particles

D) the concentration gradient across the cell membrane

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Which of the following factors does NOT affect the rate of diffusion across a membrane?

A) the number of different types of particles in a solution

B) the temperature of a solution

C) the size of the diffusing particles

D) the concentration gradient across the cell membrane

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In a beaker separated by a membrane permeable only to water, one area has a high solute concentration and the other has a low solute concentration. What do you expect will happen in the beaker?

A) Water will move to the area of low solute concentration.

B) Water will move to the area of high solute concentration.

C) Water will move to the area of high water concentration.

D) The solute will move to the area of low solute concentration.



You take a sample of blood cells and place them in a solution. Fifteen minutes later, you observe that they appear shriveled. What is the tonicity of the solution they were placed in?

A) Hypotonic

B) Isotonic

C) Hypertonic

D) Equitonic



Which of the following characteristics distinguishes facilitated transport from simple diffusion? Passive transport ______________.A) uses membrane proteins and channels to move molecules down concentration gradients.

B) requires the input of cellular energy to transport biomolecules.

C) describes the movement of biomolecules such as proteins, carbohydrates, and fatty acids.

D) explains the movement of molecules or ions from high to low concentration.

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Which of the following characteristics distinguishes facilitated transport from simple diffusion? Passive transport ______________.A) uses membrane proteins and channels to move molecules down concentration gradients.

B) requires the input of cellular energy to transport biomolecules.

C) describes the movement of biomolecules such as proteins, carbohydrates, and fatty acids.

D) explains the movement of molecules or ions from high to low concentration.


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Which of the following statements about channel proteins is true?

A) They change shape as they move molecules across a membrane.

B) Polar compounds pass through them to avoid nonpolar regions.

C) All of them are open at all times to allow passage of materials.

D) all of these answers



Which of the following statements about channel proteins is true?

A) They change shape as they move molecules across a membrane.

B) Polar compounds pass through them to avoid nonpolar regions.

C) All of them are open at all times to allow passage of materials.







Which of the following statements about passive transport is true?

A) Membrane proteins are always needed in order for it to take place.

B) Substances move from areas of low concentration to areas of high concentration.

C) The input of ATP is required in order to facilitate transportation.

D) Substances move from areas of high concentration to areas of low concentration.



How does active transport move substances against the electrochemical gradient?

A) Sodium and potassium help push substances across membranes.

B) ATP causes red blood cells to break down membranes.

C) With the help of ATP, pumps move substances across membranes




What is the difference between phagocytosis and pinocytosis?

A) Phagocytosis takes in large food particles, while pinocytosis takes in liquid particles.

B) Phagocytosis takes in carbohydrates, while pinocytosis takes in lipids.

C) Phagocytosis takes in cations, while pinocytosis takes in anions

D) Phagocytosis takes in caveolin, while pinocytosis takes in clathrin.

4 methods by which substances (eg. oxygen, carbon dioxide, water, amino acids, fatty acids, sugars,...

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