A Cell Mitochondrion Nucleus Selectively permeable cell membrane Cytoplasm

Selective Membrane

Why do cells need to transport materials across the cell membrane? Cells need to obtain various substances in order to carry out life processesCells need to obtain various substances in order to carry out life processes What are some of the substances that they need to obtain?What are some of the substances that they need to obtain? e.g. nutrients, oxygen, water, etc.e.g. nutrients, oxygen, water, etc.

Why do cells need to transport materials across the cell membrane? Cells also need to get rid of substances that are useless and harmful to themCells also need to get rid of substances that are useless and harmful to them What are some of the substances that must be removed?What are some of the substances that must be removed? e.g. carbon dioxide, metabolic wastes, etc.e.g. carbon dioxide, metabolic wastes, etc.

Transportation of Materials There are 3 different processes for transporting materials in and out of a cell: There are 3 different processes for transporting materials in and out of a cell: DiffusionDiffusion OsmosisOsmosis Active TransportActive Transport

DIFFUSION

Hi. I am Moley. I am a gas molecule. I am constantly moving around. This is because I possess kinetic energy.

Here I am with my brothers and sisters. Notice that we are all cramped to one side of the area. In other words, there is a HIGH CONCENTRATION of molecules on the left side of the area. Area of High Concentration

Well, since we are moving all the time, we will eventually spread out to cover the rest of the area. That is, we will move along the concentration gradient, from an area of HIGH CONCENTRATION to an area of LOW CONCENTRAION!

Area of Low Concentration CONCENTRATION GRADIENT

EQUILIBRIUM – Particles are evenly distributed

Diffusion Diffusion is the net movement of the particles of a substance from a region of higher concentration to a region of lower concentrationDiffusion is the net movement of the particles of a substance from a region of higher concentration to a region of lower concentration It is a passive process and no external energy is requiredIt is a passive process and no external energy is required It can occur in a liquid or gaseous mediumIt can occur in a liquid or gaseous medium

We can also pass through a selectively permeable membrane because we are so small!!! Area of High Concentration

Area of Low Concentration CONCENTRATION GRADIENT

Area of High Concentration Area of Low Concentration CONCENTRATION GRADIENT

EQUILIBRIUM – Particles are evenly distributed

Diffusion A small amount of ink is added to a beaker of water. What do you think will happen?

Diffusion Can you explain the - Can you explain the color change? color change? - Do you think the ink particles will continue particles will continue to move even after they to move even after they have spread out evenly have spread out evenly in the water? in the water? - Will the result be the same if this is carried out same if this is carried out in hot water? in hot water?

Factors Affecting the Rate of Diffusion Molecular size – will small or large particles diffuse faster?Molecular size – will small or large particles diffuse faster? Concentration gradient – will diffusion occur more rapidly if there is a large or small difference in concentration between two regions?Concentration gradient – will diffusion occur more rapidly if there is a large or small difference in concentration between two regions? Distance of diffusion – will diffusion be faster or slower if the distance of diffusion is long?Distance of diffusion – will diffusion be faster or slower if the distance of diffusion is long?

Factors Affecting the Rate of Diffusion Medium – is diffusion faster in a gaseous or liquid medium?Medium – is diffusion faster in a gaseous or liquid medium? Surface area – will diffusion occur faster in a large or small surface area?Surface area – will diffusion occur faster in a large or small surface area?

Factors Affecting the Rate of Diffusion

Medium – is diffusion faster in gaseous or liquid medium?Medium – is diffusion faster in gaseous or liquid medium? Surface area – will diffusion occur faster in a large or small surface area?Surface area – will diffusion occur faster in a large or small surface area? Temperature – will diffusion be faster under high or low temperature?Temperature – will diffusion be faster under high or low temperature?

Examples of Diffusion Exchange of gases (i.e. oxygen and carbon dioxide) in the air sacs of lungsExchange of gases (i.e. oxygen and carbon dioxide) in the air sacs of lungs Absorption of digested food in the gutAbsorption of digested food in the gut The detection of smell e.g. perfumeThe detection of smell e.g. perfume The movement of carbon dioxide through the stomata during photosynthesisThe movement of carbon dioxide through the stomata during photosynthesis

OSMOSIS

Osmosis Osmosis is the net movement (i.e. diffusion) of water molecules from a less concentrated solution (with a higher water potential) to a more concentrated solution (with a lower water potential) through a selectively permeable membraneOsmosis is the net movement (i.e. diffusion) of water molecules from a less concentrated solution (with a higher water potential) to a more concentrated solution (with a lower water potential) through a selectively permeable membrane

This is a water molecule This is a sucrose molecule Region A – Dilute sucrose solution Region B – Concentrated sucrose solution

This is a water molecule This is a sucrose molecule Region A – Dilute sucrose solution Region B – Concentrated sucrose solution

INVESTIGATION #1 Illustration of osmosis using a dialysis tubing

Introduction to Investigation In this experiment, osmosis will be demonstrated by using a dialysis tubing, which acts as a selectively permeable membraneIn this experiment, osmosis will be demonstrated by using a dialysis tubing, which acts as a selectively permeable membrane

Procedure Please refer to pages 83 and 84 in your ARISTO text bookPlease refer to pages 83 and 84 in your ARISTO text book

Results Table Time Distance from initial mark After 5 minutes After 10 minutes After 15 minutes After 20 minutes

Plot the data on a graph Distance risen by the sucrose solution Time (Mins.) What will the graph look like?

Can you predict the results in the following situations? TreatmentInside tubingIn beakerChange in level 1Sucrose solution Distilled water Rises 2Distilled waterSucrose solution ? 3Concentrated sucrose solution Distilled water ? 4 ?

Variations to the Experiment Instead of dialysis tubing, we can also use living tissues, such as potatoes, to illustrate the process of osmosisInstead of dialysis tubing, we can also use living tissues, such as potatoes, to illustrate the process of osmosis

Variations to the Experiment What do you think is the result of this experiment?

Water Potential Water potential is represented by the Greek letter “psi”Water potential is represented by the Greek letter “psi” A measure of the free energy of water or the energy for water molecules in a solution to move aboutA measure of the free energy of water or the energy for water molecules in a solution to move about Water potential is dependent on the proportion of free water molecules in a solution (free water molecules = water molecules that are not engaged with other molecules)Water potential is dependent on the proportion of free water molecules in a solution (free water molecules = water molecules that are not engaged with other molecules)

Water Potential The water potential of pure water is defined as zeroThe water potential of pure water is defined as zero If solutes are dissolved in water, the proportion of free water molecules will decrease. The water potential will also decrease to less than zeroIf solutes are dissolved in water, the proportion of free water molecules will decrease. The water potential will also decrease to less than zero

Water Potential A concentrated solution has a lower water potential than a dilute solutionA concentrated solution has a lower water potential than a dilute solution The net movement of water molecules is always from a region of HIGHER water potential to a region of LOWER water potentialThe net movement of water molecules is always from a region of HIGHER water potential to a region of LOWER water potential

Tonicity Osmotic movements across cell membranes are affected by the tonicity: the relative concentrations of solutes in 2 fluids, e.g. the cytoplasm of a cell and the fluid outside the cellOsmotic movements across cell membranes are affected by the tonicity: the relative concentrations of solutes in 2 fluids, e.g. the cytoplasm of a cell and the fluid outside the cell

Tonicity We are going to use a red blood cell as an example. On a piece of paper, draw three beakers. In each of the beaker, add a RBC. We will discuss what happen to the RBC when it is put into 3 different types of solutions of different concentrations of sodium chloride (i.e. salt)We are going to use a red blood cell as an example. On a piece of paper, draw three beakers. In each of the beaker, add a RBC. We will discuss what happen to the RBC when it is put into 3 different types of solutions of different concentrations of sodium chloride (i.e. salt)

Isotonic CELL Salty Water The water potential inside the cell is the same as that outside the cell. There is no net movement of water into or out of the cell

Hypertonic CELL Very Salty Water There is less water molecules outside the cell, and therefore the solution outside has a lower water potential than that of the cell What will happen to the cell?

Hypotonic CELL Pure Water There is more water molecules outside the cell, and therefore the solution outside has a higher water potential than that of the cell. What will happen to the cell?

Effects of Osmosis on Plant Cells Plant cells placed in a hypertonic solution will undergo plasmolysis, a condition where the plasma membrane pulls away from the cell wall as the cell shrinks. The cell wall is rigid and does not shrink. Turgid Cells Flaccid Cells

Effects of Osmosis on Animal Cells

Shrinking RBC Swelling RBC

Active Transport

Some solutes have a higher concentration inside the cell than outside so they have to cross the membrane against the concentration gradient. These solutes need to enter the cell by means of active transportSome solutes have a higher concentration inside the cell than outside so they have to cross the membrane against the concentration gradient. These solutes need to enter the cell by means of active transport Why is this called ACTIVE transport?Why is this called ACTIVE transport?

Cell membrane Low concentration outside the cell High concentration inside the cell Active Transport

Cell membrane Active Transport

Cell membrane Active Transport

Cell membrane Active Transport

Cell membrane Active Transport

Cell membrane Active Transport

Cell membrane Active Transport

Cell membrane Active Transport

Cell membrane Active Transport

Cell membrane Active Transport

Cell membrane Active Transport

Cell membrane Active Transport

Cell membrane Active Transport

Cell membrane What is this??? Active Transport

Active transport requires special protein carriers. These carriers are embedded within the cell membraneActive transport requires special protein carriers. These carriers are embedded within the cell membrane Active transport also requires energy obtained from respirationActive transport also requires energy obtained from respiration The energy is used to change the shape of the protein carriers so that the molecules can attach to the carriers for transportationThe energy is used to change the shape of the protein carriers so that the molecules can attach to the carriers for transportation

Active Transport The process of active transport is useful when there is no concentration gradient or when diffusion is too slow for the transportation of substancesThe process of active transport is useful when there is no concentration gradient or when diffusion is too slow for the transportation of substances

Examples of Active Transport Nutrients are actively transported into the small intestineNutrients are actively transported into the small intestine Substances that are useful to the body are actively reabsorbed into the blood vessels surrounding the kidney tubulesSubstances that are useful to the body are actively reabsorbed into the blood vessels surrounding the kidney tubules Root hairs actively absorb mineral salts from the soilRoot hairs actively absorb mineral salts from the soil

Comparison of Passive and Active Transport