Cell ProcessesCell Processes

Middle School ScienceMiddle School Science

Moving materials in cellsMoving materials in cells

Cells need energy 24/7Cells need energy 24/7 They cannot make their own, but can They cannot make their own, but can

change energy from one form to anotherchange energy from one form to another Cells obtain energy from their Cells obtain energy from their

environment and convert it to a usable environment and convert it to a usable formform

Complex processComplex process

Moving materials in cellsMoving materials in cells

MetabolismMetabolism The sum of all activities within a cellThe sum of all activities within a cell Cannot just happenCannot just happen Need raw materialsNeed raw materials Need to eliminate wasteNeed to eliminate waste All material needs to enter and exit through All material needs to enter and exit through

the cell membranethe cell membrane

Moving materials in cellsMoving materials in cells

Materials enter and leave a cell by one of Materials enter and leave a cell by one of three methods:three methods: DiffusionDiffusion OsmosisOsmosis Active transportActive transport

DiffusionDiffusion

Cell membranes in living things need to Cell membranes in living things need to allow materials to pass throughallow materials to pass through Selectively-permeable membraneSelectively-permeable membrane Substances pass through the poresSubstances pass through the pores

Driving force behind the movement of Driving force behind the movement of many substances into or out of the cell is many substances into or out of the cell is diffusiondiffusion

DiffusionDiffusion

The process by which molecules of a The process by which molecules of a substance move from areas of higher substance move from areas of higher concentration of that substance to areas of concentration of that substance to areas of lower concentration of that substancelower concentration of that substance

DiffusionDiffusion

What causes diffusion to occur?What causes diffusion to occur? Mainly small moleculesMainly small molecules Driving force behind movementDriving force behind movement

All molecules are in motionAll molecules are in motion Solids – molecules move slowlySolids – molecules move slowly Liquids – move more quicklyLiquids – move more quickly Gases – move quicklyGases – move quickly

Molecules collide with each other, pushing away Molecules collide with each other, pushing away from one anotherfrom one another

DiffusionDiffusion

What causes diffusion to occur?What causes diffusion to occur? Driving force behind movementDriving force behind movement

Collisions will continue as molecules spread out evenlyCollisions will continue as molecules spread out evenly

DiffusionDiffusion

Why don’t the organelles and cytoplasm Why don’t the organelles and cytoplasm pass through the cell membrane?pass through the cell membrane? Cell membrane is selectively permeableCell membrane is selectively permeable

Permits only certain substances to diffusePermits only certain substances to diffuse Oxygen, water, and food molecules are permitted to Oxygen, water, and food molecules are permitted to

diffuse into the celldiffuse into the cell Carbon dioxide and other waste materials are Carbon dioxide and other waste materials are

permitted to diffuse out of the cellpermitted to diffuse out of the cell

OsmosisOsmosis

A special kind of diffusionA special kind of diffusion The diffusion of water across a selectively The diffusion of water across a selectively

permeable membrane = osmosispermeable membrane = osmosis

Water is the most important substance Water is the most important substance that passes through a cell membranethat passes through a cell membrane About 80% of the cell is waterAbout 80% of the cell is water

Diffusion and OsmosisDiffusion and Osmosis

Diffusion and osmosis are types of passive Diffusion and osmosis are types of passive transporttransport They do not require energy to be able to happen – They do not require energy to be able to happen –

they just happenthey just happen

Active TransportActive Transport

What if the cell needs materials that What if the cell needs materials that cannot diffuse through the membrane?cannot diffuse through the membrane? Active transport “carries” the materials into Active transport “carries” the materials into

or out of the cellor out of the cell Cells have several forms of active transportCells have several forms of active transport Transport proteins can “pick up” molecules Transport proteins can “pick up” molecules

and carry them into or out of the celland carry them into or out of the cell Requires energyRequires energy

Ex: calcium, potassium, and sodiumEx: calcium, potassium, and sodium

Active TransportActive Transport

What if the cell needs materials that What if the cell needs materials that cannot diffuse through the membrane?cannot diffuse through the membrane? Transport by engulfingTransport by engulfing

Another method of active transportAnother method of active transport Cell membrane surrounds, or engulfs, a particleCell membrane surrounds, or engulfs, a particle Once surrounded, the cell membrane wraps Once surrounded, the cell membrane wraps

around the particle and forms a vacuole within around the particle and forms a vacuole within the cellthe cell

Requires energyRequires energy

Cell Growth and DivisionCell Growth and Division

Limits on Cell GrowthLimits on Cell Growth Why don’t cells get bigger and bigger?Why don’t cells get bigger and bigger?

Has to do with the transportation of materials into Has to do with the transportation of materials into and out of the celland out of the cell

If a cell were to get too large, its membrane If a cell were to get too large, its membrane would not be able to handle the flow of materials would not be able to handle the flow of materials passing through itpassing through it

The amount of raw materials needed by a large cell The amount of raw materials needed by a large cell couldn’t enter fast enoughcouldn’t enter fast enough

The wastes produced couldn’t leave fast enoughThe wastes produced couldn’t leave fast enough

Cell DivisionCell Division

In order for an organism to grow, the total In order for an organism to grow, the total number of cells must increasenumber of cells must increase Cell divisionCell division

One cell divides into two new daughter cellsOne cell divides into two new daughter cells Occurs in a series of stages, or phasesOccurs in a series of stages, or phases

The process of cell division = mitosisThe process of cell division = mitosis

MitosisMitosis

Phase 1: Chromosomes are copiedPhase 1: Chromosomes are copied InterphaseInterphase

Cell is performing life functions, not dividingCell is performing life functions, not dividing Chromosomes appear as threadlike coils called Chromosomes appear as threadlike coils called

chromatinchromatin In animal cells, the two centrioles can be seen In animal cells, the two centrioles can be seen

outside the nucleusoutside the nucleus Most plant cells do not have centriolesMost plant cells do not have centrioles

MitosisMitosis

Phase 1Phase 1 Near the end, the process of cell division Near the end, the process of cell division

beginsbegins The chromosomes are duplicatedThe chromosomes are duplicated

Doubling the normal chromosome number in the Doubling the normal chromosome number in the cellcell

Each chromosome and its sister chromosome Each chromosome and its sister chromosome (copy) are attached at an area called the (copy) are attached at an area called the centromerecentromere

At this time the sister chromosomes are called At this time the sister chromosomes are called chromatidschromatids

MitosisMitosis

Phase 2: Mitosis beginsPhase 2: Mitosis begins ProphaseProphase

Mitosis beginsMitosis begins Mitosis = the process by which the nucleus of a cell Mitosis = the process by which the nucleus of a cell

divides into two nuclei and the formation of two new divides into two nuclei and the formation of two new daughter cells beginsdaughter cells begins

Threadlike chromatin shorten and form rodlike Threadlike chromatin shorten and form rodlike chromosomeschromosomes

Centrioles begin to move to opposite ends of cellCentrioles begin to move to opposite ends of cell Meshlike spindle develops, forming a bridge Meshlike spindle develops, forming a bridge

between opposite ends of the cellbetween opposite ends of the cell

MitosisMitosis

Phase 3: Chromosomes attach to the Phase 3: Chromosomes attach to the spindlespindle MetaphaseMetaphase

The chromosomes begin to attach to the spindleThe chromosomes begin to attach to the spindle Chromosomes are attached to the spindle by the Chromosomes are attached to the spindle by the

centromere, which still connects each chromatid centromere, which still connects each chromatid to its identical sister chromatidto its identical sister chromatid

MitosisMitosis

Phase 4: Chromosomes begin to Phase 4: Chromosomes begin to separateseparate AnaphaseAnaphase

The centromere splitsThe centromere splits The sister chromatids separate from each otherThe sister chromatids separate from each other Chromatids move to opposite ends of cell along Chromatids move to opposite ends of cell along

the spindlethe spindle The chromatids are again called chromosomes at The chromatids are again called chromosomes at

this pointthis point

MitosisMitosis

Phase 5: Two new nuclei formPhase 5: Two new nuclei form TelophaseTelophase

The chromosomes begin to uncoil and lose their The chromosomes begin to uncoil and lose their rodlike appearancerodlike appearance

A nuclear membrane forms around the chromatin A nuclear membrane forms around the chromatin at each end of the cellat each end of the cell

In each nucleus, a nucleolus reappearsIn each nucleus, a nucleolus reappears At this point, mitosis is complete but the cell still At this point, mitosis is complete but the cell still

has one phase to go throughhas one phase to go through

MitosisMitosis

Phase 6: Two daughter cells formPhase 6: Two daughter cells form CytokinesisCytokinesis

Final phase of cell divisionFinal phase of cell division Involves the division of the cytoplasmInvolves the division of the cytoplasm The membrane surrounding the cell begins to The membrane surrounding the cell begins to

move inward until the cytoplasm is pinched in twomove inward until the cytoplasm is pinched in two Each part contains a nucleus with identical Each part contains a nucleus with identical

chromosomeschromosomes The cell membrane (or cell wall) complete the The cell membrane (or cell wall) complete the

divisiondivision

MitosisMitosis

MitosisMitosis