CellsBiologyGCE Study Buddy

A Cell

What is a cell?A cell is a unit of lifeWhy must life be organized in cells?Life requires a structural compartment separate from the external environment in which macromolecules can perform unique functions in a relatively constant internal environmentCells onsists of living matter called protoplasmA jelly-like substance in which chemical activities are carried out Consists of 70-90% water, the rest consists of mineral salts and organic compounds (carbon compounds) such as carbohydrates, fats and proteinsIts composition varies from animal to animal and from plant to plantConsists of 2 formsSol (liquid) stateGel state (semi-solid)

Cell Theoryall organisms are made up of one or more cellsthe smallest organisms are single cellscells are the functional units of multicellular organisms all cells arise from pre-existing cells.

Cell SizeCells range in size from a few micrometers to several centimetersMost cells are small because larger cells do not function efficiently because small cells can more easily transport materials into and out of themselves.Advantageous to have a large surface-to-volume ratioas cell size increases, the volume grows more rapidly than surface areaThe larger the surface area of a cell, the faster a cell can take in substances and remove waste products.Whereas large internal volume relative to surface area makes it more difficult to traffic materials into and out of the cell

How to view cells?Use microscopes can magnify cell sizesLight Microscope (LM)Pass visible light through a specimenMagnify cellular structures with lensesMagnifies up to 1000xElectron Microscope (EM)Uses a beam of electronsHas a higher resolving power than the light microscopeAble to magnify more than 1000x2 types:Transmission Electron Microscope (TEM)Makes it possible to explore call structure.Beams of electron can only pass through thin samples so cells & tissues must be cut into ultra thin slicesScanning Electron Microscope (SEM)Electrons scan over the surfaces of the specimen.No need thin slicesCan produce 3-D images.

Animal Cell

Plant Cell

Characteristics of CellsA surrounding membrane Plasma membraneProtoplasm cell contents in thick fluidOrganelles structures for cell functionControl centre with DNA - Nucleus

Protoplasm of a cell consists of:Cell surface membrane Cytoplasm where most cell activities occur and contains enzymes and organelles. It can exist in sol or get stateNucleus which consists of nucleoplasm, nuclear envelope, one or more nucleoli and chromatin. It controls cell activities and is essential for cell division

NucleusConsists of a small spherical mass of denser protoplasm, the nucleoplasm, surrounded by a nuclear envelopeControls the normal cell activitiesResponsible for cell reproductionNeeded for the continued life of the cell and repair of worn-out partsWithin the nucleus are:Nuclear envelope: double membrane surrounding nucleusSeparates the nuclear content from the surrounding cytoplasmPerforated with thousands of nuclear pores to allow materials to move into and out of the nucleus to and from the rest of the cellNucleoli: spherical structuresMain function is the production of ribosomesChromatin: a network of long thread-like structures (DNA bound to proteins)Contain hereditary materialsControl the activities of the cellDuring cell division, chromatin threads condense and become highly coiled structures called chromosomes

Nuclear envelope

Whats in the cytoplasm?Cytoplasm: the place where most life processes occurEmbedded in the cytoplasm are important organelles:Mitochondria: small spherical or rod-shaped organellesInvolved in release of energy from food substances during cell respiration

ChloroplastsIn plant cells onlySites where plants make food, combining carbon dioxide and water, using energy from sunlight, to make sugarWhats in the cytoplasm?VacuolesIn both plant and animal cellsA fluid-filled space enclosed by a membraneAnimal cells may have many small vacuoles but are usually not permanent.May contain water and food substancesA plant cell usually has a large central vacuole which contains a liquid called cell sapCell sap contains dissolved substances such as sugars, amino acids, and mineral saltsThis large vacuole is enclosed by a membrane called tonoplast

CentriolesPlay a part in cell divisionAbsent in most plant cellsRibosomes (2 types)Free floating ribosomes in cytoplasmAttached to the Endoplasmic ReticulumRibosomes build all the cells proteinsCells active in protein synthesis are often packed with ribosomes.Endoplasmic Reticulum (ER)Composed of smooth and rough ERProduces an enormous variety of moleculesGolgi ApparatusWorks in partnership with the ERRefines, stores, and distributes the products of cells

Whats in the cytoplasm?

Vacuoles: LysosomesLysosome: a membrane-enclosed sacIn animal cellsContains digestive enzymesThe enzymes break down macromolecules

They fuse with food vacuoles to digest the foodThey break down damaged organelles

Vacuoles: Central VacuoleIn plant cellsMembrane bound storage sacsContents WaterFoodWastesMake the cell firm by swelling that helps the plant cell maintain support and rigidity

Endoplasmic ReticulumRough ER: The roughness is due to ribosomes attached to the outside of the ER membraneThe functions of the rough ER includeProduce membrane proteinsProduce digestive enzymesAfter the rough ER synthesizes a molecule it packages the molecule into transport vesiclesThe smooth ER lacks the surface ribosomes of rough ERServes many functions:Producing proteinsFatty acids for new membrane synthesisProduce steroidsProduce sex hormonesDetoxification of drugs and poisons

MitochondriaSites of cellular respiration, which involves the production of energy from food moleculesThe matrix contains enzymes which break down carbohydrates and other nutrients for energy.The breakdown of these molecules in the presence of oxygen to produce energy is called aerobic cellular respiration.Energy releases may be temporarily stored in small molecules called ATP (adenosine triphosphate) batteriesATP can be transported from one part of the cell to anotherWhen needed, ATP break down to release energy

Cell Surface MembraneAlso known as Plasma MembraneSeparates the inside of the cell from the outside environmentPartially permeable to control substances entering or leaving the cellSelective permeabilityAllowing some substances to cross more easily than othersBlock passage of some substances altogetherConsists of Phospholipid Bilayerconsists of a polar portion, called the head, and 2 long fatty acids (non-polar), the tail.

Plant Cell WallAll plants have cellulose cell walls.Made up of cellulose fibers.protect the cell from mechanical damage and help the cell maintain its rigidity under turgor pressureprevents over-expansion of the cell when water diffuses into the cell.It is a barrier to many fungi, bacteria, and other organisms that may cause plant diseases.It is fully permeable to all substances.bacterial and fungi cells also have a cell wall, but it is not made of cellulose.

Cell wall vs. Cell membraneQ. How permeable are the cell wall and cell membrane in a plant cell?

Cell WallCell MembraneAFullyFullyBFullyPartiallyCPartiallyFullyDPartiallyPartially

Animal vs. Plant cells Plant CellPresence of cellulose cell wallPresence of chloroplastA large central vacuoleCytoplasm reduced to a thin liningPresent of starch grainsAbsence of lysosomes Animal CellAbsence of cellulose cell wallAbsence of chloroplastNumerous small vacuoles (lysosomes)Cytoplasm fills the cellAbsence of starch grains

Animal vs. Plant cellsQ. Which cell structures are found in plant cells and animal cells?

Cell membrane and chloroplastsCell membrane and nucleusCell wall and chloroplastsCell wall and nucleus

*Biology - Matters*Factory Analogy of a Cell

CellFactoryCell Wall Factory WallPlasma membrane Shipping & receiving DeptsNucleusthe executive department (Manages activities, initiates production, controls activities of factory)Cytoplasmfactory floor where most of the products are assembled, finished, and shipped. Ribosomeassembly line assemble raw material to manufacture itemGolgi apparatuspackaging, shipping, distributingEndoplasmic reticulumconveyor belt move product within factory

Mitochondriongenerator produce energy for the factoryVacuolestore area - store material for later useLysosomecollection centre breakdown and recycle used partsCell membranedoor allows certain things to enter and leave factory

Biology - Matters

Specialized cells, tissues, organs, and systemsTypes of cells:Root hair cell: Long and narrow shape to increase surface area to volume ratio for efficient absorption of water and mineral salts from the soilRed blood cell (erythrocyte)Contain a red pigment called haemoglobin, enabling the cell to transport oxygen from the lungs to all parts of the bodyCircular biconcave shape to increase surface area to volume ratio so oxygen can diffuse into and out of the cell at a faster rateLacks nucleus, provide more space for haemoglobin.Xylem vessels: Transport water and mineral salts from the roots to the stem and leavesNo cross walls and protoplasm enables water to move easily through the lumenLignin strengthens the walls and prevents collapse of the vesselWhen bundled together, xylem vessels provide mechanical support to the plant

Root hair cell, Red blood cell, Xylem vesselsXylem vessel: a narrow, cylindrical tube enclosing a continuous space called the lumen. The vessel is dead because there is no protoplasm.Red blood cells: Flattened, circular biconcave shape to increase the surface area

Root hair cell

Form versus FunctionA sphere has the least surface area-to-volume ratio of any shape.Cells in multicellular organisms consist of many different types of cells that do different jobs. What does it mean for a cell to be specialized?Specific types of cells performs specific functionsAs cells mature, they may change and differentiateDifferentiation: Process where a cell becomes specialised for a specific functionDifferentiation could target any number of the following: Shape of cellComponent proteinsCell structures or organellesCell growthCell divisionThe cell becomes adapted to perform a specific function.

RecapDifferentiation is the process by which a cell becomes specialized for a specific function.

CellFunctionAdaptationsRed blood celltransport oxygenCircular, biconcave shapeAble to change into a bell shapeContains haemoglobinAbsence of nucleusXylem vesseltransport water and mineral salts from roots to stem and leaves.Absence of cross walls & protoplasmWalls strengthened by lignin

Root hair cellabsorb water and mineral salts from soilPresence of long and narrow root hair to increase SA:V ratio

Tissues, Organs, and SystemsCells of the same type may be grouped together to carry out a special function called simple tissueExamples:epithelial tissue: a sheet of cells covering both the internal and external surfaces of bodyplants have similar covering tissues called the epidermismuscle tissue: a collection of muscle cells which bring about movement in our body by their contraction and relaxationComplex tissue: tissues containing several types of cells Examples: Nervous tissue, glandular tissue etc

Tissues

OrgansDifferent tissues may be united to form an organ eg stomach, liverAn organ is a group of different tissues working together and enabling the organ to perform a particular functions

Organ SystemSeveral organs working together for a special purpose make up an organ systemExample: digestive system, respiratory systemAn organism may have a few organ systems.Plants: stem and leaves as a systemHumans have about 40 organs that are grouped into about 10 named systems.The human nervous system includes:Brain, spinal cord, nerves

SystemsAn organ system is made up of several organs working together for a special purpose.Example: Digestive systemFunction: Breakdown and absorb nutrients that are necessary for growth & maintenanceMajor organs: Mouth, oesophagus, stomach, small & large intestines

*Biology - Matters*Human Body SystemsRespiratory SystemTakes in oxygen from the surroundings. Removes carbon dioxide and water vapour into the surroundingsDigestive SystemBreaks down the food we eat into simpler substances that can be absorbed by the blood.Nervous SystemControls our actions, ensures all the parts of our body work smoothly together and enables us to respond to changes.Blood circulatory systemCarries food, oxygen and water to various parts of the body. Carries wastes away to be removed.Excretory SystemRemoves wastes from the bodyImmune SystemDefends against infections

Biology - Matters

*Biology - Matters*Human Body SystemsSkeletal systemSupports our body, gives us shape, protects our organs and enables movement.Muscular systemEnables movementReproductive systemFemale Produces eggs for reproductionMale Produces sperms for reproductionIntegumentary system (skin)Waterproof barrierRegulate temperatureLymphatic systemFilters bacteriaDestroy bacteriaEndocrine SystemSecret hormonesProduce response in the body

Biology - Matters

Plants: Vascular Tissue SystemThe xylem and phloem that functions in transport and support; is continuous throughout the plant.

****