IB Biology SL Cells

7/17/2019 IB Biology SL Cells

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2.1.1. What is cell theory?

The main principles of cell theory are:

I.All living things/organisms are composed of one or more cells.

II.Cells are the smallest functional unit of life.

III.All cells come from pre-existing life.

2.1.2 What is the evidence for cell theory?

I. All livings when viewed under a microscope have been found to be made of cells and cell products.

II.Nothing smaller than a cell has been found tolive independently.

III.Cells cannot grow in sealed and sterile conditions, therefore they must come from pre-existing life.

2.1.3 What are the functions of life anunicellular organism must carry out?

All unimolecular organism carry out the function of life:

I.Metabolism: chemical reactions that occur within an organism.

II.Growth: Increasing in size.

III.Reproduction: Pass on hereditary molecules to offspring. Producing offspring.

IV.Response: Reacting to stimuli.

V.Homeostasis: Maintain a constant internal environment, controlling conditions inside a cell.

VI.Nutrition: Breaking down chemical bonds to provide organism with energy and necessary nutrients.

2.1.4 Relative sizes of molecules, cell membrane thickness, viruses, bacteria, organelles and cells (using appropriate SI

units).

- 1 millimetre (1 mm) = 1000 micrometres (1000 um)

- 1 micrometres (1 um) = 1000 nanometres (1000 nm)

A molecules (1 nm)< Cell membrane thickness (7.5 nm)< Virus (100 nm)< Bacteria 1-5 (um)< Organelles (<10 um)<

Eukaryotic cells (<100 um)

2.1.5 How do you calculate the actual size of a specimen from an electron microscope?

Magnification = size of a specimen (with ruler) ÷ actual size of object (according to scale bar)

Actual size = size of specimen (with ruler) ÷ magnification

2.1.6 What is the importance of thesurface area to volume ratio as a factor limiting cell size.

-Rate of metabolism of a cell is determined by mass/volume and

-The rate of material exchange in and out of the cell is determined by the surface area.

-As a cell grows, volume increasesfaster than surface area, leading to a decreased SA:Volume ratio i.e. greater volume

but less surface area.

-If the metabolic rate is greater than the rate of exchange then the cell will eventually die.

-Therefore, the cell must divide in order to achieve a viable SA:volume ration and survive.

-Cells which are specialised for gas or material exchange increase their surface area for more efficient exchange of

materials.

2.1.7 Multicellular organisms showemergent properties .

-Emergent properties come from theinteraction of componentparts.

-Multicellular organisms are capable of completing many functions that unicellular organisms could not undertake. For

example:

-Cells can group together toform tissue.

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-Organs are then formed formed fromfunctional grouping of multiple tissues.

-Organs that interact can form organ systems which are capable of carrying out specific functions.

-Organ systems carry out the life functions required by an organism.

2.1.8 Why and how do multicellular organisms differentiate?

Multicellular organisms consist of many cells. Multicellular organisms are said to show emergent properties which means

that the whole organism is more than the sum of its parts, because of the complex interactions inside the cell.

Why: To carry out specific functions by expressing some genes but not others.

How-

-All cells of an individual organism share anidentical genome, and each cell contain this entire set of genetic

information/instructions for that organism.

-The activation of genes (different instructions) within a given cell by chemical signals will cause the individual cell to

differentiate from other cells like it.

-Differentiation is the process during development whereby newly formed cells becomemore specialisedanddistinct

from one another as they mature.-Active genes are packaged in an accessible form = euchromatin

-Inactive genes are packaged in a condensed form = heterochromatin.

-Differentiated cells will have different regions of DNA packed aseuchromatinand heterochromatin, depending on

their function/specialisation.

(BioNinja)

2.1.9 Cells retain thatstem cells have the capacity todivide and have theability to differentiate along differentpathways.

Stem cells areunspecialised cells as they have:

I.Self renewal: Continuously divide and replicate.

II.Potency: Capacity to differentiate into specialised cell types.

2.1.10 Explain one therapeutic use of stem cells.

-Stem cells can come from from embryos, placenta/umbilical cord of the mother.

-Stem cells can be used to replace damaged or diseased cells with healthy, functioning ones.

Process--Use of biochemical solutions to trigger differentiation into desired cell type.

-Surgical implantation of cell into patient’s own tissue.

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-Suppression of host immune system to prevent rejection of stem cells.

-Careful monitoring of new cells to ensure they do not become cancerous.

Stem cells can be used to make nerve cells and repair damage caused by spinal injuries to enable paralysed victims to

regain movement.

2.2.1 Draw and label a diagram of the ultrastructure of E.coli (Escherichia coli) as an example of a prokaryote.

Prokaryotes are smaller and simpler than eukaryotes. Prokaryotesdo not contain a nucleus.

(BioNinja)

2.2.2 Annotate the diagram with the function of each named structure.

-Cell wall:Rigid outer layer made of peptidoglycan that canmaintain shape andprotect cells from damageor

bursting if internal pressure is high.

-Cell membrane:Semi-permeable barrierthat controls theentry and exit of substances.

-Cytoplasm: Fluid component that containenzymes needed for all metabolic reactions.

-Nucleoid: Region of cytoplasm that contains thegenophore (prokaryotes’ DNA).

-Plasmid:Additional DNA molecule that can exist and replicate independently from the genophore. Can be transmitted

between bacterial species.

-Ribosomes:Complexes of RNAand protein that are responsible forpolypeptide synthesis. Prokaryotic ribosomes

are smaller than eukaryotic ribosomes.

-Slime capsule: Thick polysaccharide layer used forprotection against desiccation (drying out) andphagocytosis.

-Flagella (singular flagellum): Longer, slender projection containing a motor protein which spins theflagella like a

propellor,enabling movement.

-Pili (singular pilus): Hair-like extensions found on bacteria which either are:

(1) Attachment pili: Shorter in length, allow bacteria to adhere to other cells.

(2) Sex pili: Longer in length, allow for the exchange of genetic material (plasmids) via process ofbacterial

conjunction.

2.2.3 Bacterial cells divide bybinary fission .

-Prokaryotes use binary fission which is a form ofasexual reproduction andcell division.

-Not the same as mitosis as the isnocondensation of genetic material andnospindle formation.

Process of binary fission:

(1) Circular DNA is copied in response to a replication signal.

(2) Two DNA loops attach to the membrane.

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(3) Membrane elongates and pinches off (cytokinesis) forming two separate cells.

(BioNinja)

2.3.1 Draw and label a diagram of the ultrastructure of a liver cell as an example of an animal cell.

(BioNinja)

2.3.2 Annotate the diagram from 2.3.1 with the functions of each named structure.

-Cell Membrane:Semi-permeable barrierthat controls theentry and exit of substances.-Cytosol:Fluid portion of the cytoplasm (does not include the organelles or other insoluble materials).

-Nucleus: Containshereditary material(DNA) and thuscontrols cell activitiesandmitosis (via DNA replication).

-Nucleolus: Site ofproduction andassembly of ribosome components.

-Ribosome:Complexes of RNAand protein that are responsible forpolypeptide synthesis. Eukaryotic ribosomes are

bigger than eukaryotic ribosomes.

-Mitochondria: Site ofaerobic respiration, which produces large quantities of ATP (chemical energy) from organic

compounds.

-Golgi Apparatus: Assembly ofvesicles andfolded membranes involved in thesorting,storingandmodificationof

secretory products.-Lysosome: Site ofhydrolysis /digestion /breakdown of macromolecules.

-Peroxisome:Catalyses breakdownof toxic substances like hydrogen peroxide and other metabolites.

-Centrioles: Microtuble organising centres involved incell division(mitosis/ meiosis and cytokinesis).

-Endoplasmic Reticulum: A system of membranes involved intransport of materialsbetween organelles:

(1) Rough ER: Studded with ribosomes and involved in the synthesis and transport of proteins destined for

secretion.

(2) Smooth ER: Involved in the synthesis and transport of lipids and steroids, as well as metabolism of

carbohydrates.

2.3.4 What are the similarities and differences of prokaryote and eukaryote cells?

Similarities:

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-Both have acell membrane.

-Both containribosomes.

-Both haveDNAandcytoplasm.

Differences:

Prokaryotes Eukaryotes

DNA Naked loop of DNA. (no histones)

DNA is circular.

Genes do not contain introns.

DNA found in cytoplasm (nucleoid).

DNA associated with histones.

DNA is linear.

Genes may contain introns.

DNA found in nucleus.

Internal Structures No membrane-bound organelles. Have membrane-bound organelles. Many

internal membranes that compartmentalise

the cytoplasm including ER, Golgi apparatus,

lysosomes.

Ribosomes Have 70S ribosomes. Have 80S ribsomes.

Reproduction Asexual (binary fission).

DNA is singular (haploid).

Asexual (mitosis).

Sexual (meiosis).

Average Size Smaller (1-5 um) Larger (10-100 um).

2.3.5 State three differences between plant and animal cells.

Plant Cell Animal Cell

Have plastids (e.g. chloroplast). Do not have plastids.

Have a cell wall (cellulose). Do not have a cell wall.

Have a large central vacuole. Have small temporary vacuoles.

Store excess glucose as starch. Store excess glucose as glycogen.

Have plasmodesmata. Do not have plasmodesmata.

Do not have centrioles. Have centrioles.

Do not have cholesterol in cell membrane. Have cholesterol in cell membrane.

Generally have a fixed, regular shape. Generally shave an amorphous shape.

2.3.6 Outline two roles ofextracellular components.

Plants- Cell wall in plants is made from cellulose secreted from cell and serves the following functions:

(1)Provides support and mechanical strength for cell (helps maintain cell shape).

(2)Prevents excessive water uptake bymaintaining a stable, turgid state.

(3)Serves as abarrier against infection by pathogens.

Animals- Extracellular matrix (ECM) is made from glycoproteins secreted from the cell and serves the following functions:

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(1)Provides supportandanchoragefor cells

(2)Segregates tissues from one another.

(3)Regulates intercellular communication by sequestering growth factor.

2.4.1 Draw and label a diagram to show the structure of membranes.

(BioNinja)

Integral proteins (channel protein and carrier protein) - embedded in the phospholipid bilayer.

Peripheral protein - on the surface of the membrane.

2.4.2 How do the hydrophilic and hydrophobic properties of phospholipids help to maintain the structure of cell

membranes?

Structure of phospholipids:

(a)Phospholipids are spontaneously arranged in abilayerand are held together byhydrophobic interactions (weak

associations).

(b)Polar hydrophilic head made from glycerol and phosphate. Two hydrophilic head regions are associated with the

cytosolic and extracellular environments respectively.

(c)Non-polar fatty acid hydrophobic tails. Hydrophobic tail regions face inwards and areshielded from surrounding

polar substances.

(d)Hydrophilic and hydrophobic layersrestrict entryandexit of substances.

(e)Phospholipids allow formembrane fluidity/flexibility, which is important for functionality.

(f)Phospholipids withshortorunsaturated fatty acids aremore fluid.

(g)Phospholipids canmove horizontally or occasionally laterally toincrease fluidity.

(h)Fluidity allows for thebreaking and remaking of membranes (exocytosis/endocytosis)

2.4.3 What are the functions of membrane proteins.

(BioNinja)

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Transport: Pumps for active transport- pumps release energy fromATP and use it tomove specific substances across

the membrane.

Receptors: Hormone binding sites- A site exposed on theoutside of the membraneallows onespecific hormone to

bind. A signal is transmitted to the inside of the cell.

Anchorage: Enzymes- Enzymes located in membranes eithercatalyse reactions inside or outside the cell,

depending on whether the active site is on the inner or outer surface.Cell Recognition: Cell to cell communication-Glycoproteins in the membrane allowcells to communicate with each

other.

Intercellular joinings: Cell adhesion-Glycoproteins in the membrane also allow cells tostick together and form tissue.

Enzymatic activity: Channels for passive transport/ metabolic pathways- Channels are passages through thecentre of

membrane proteins. Each channel allows one specific substance to pass through.

2.4.4 What is diffusion? What is osmosis?

Diffusion is thepassive movement of particlesfrom a region ofhigh concentrationto a region oflow concentration

(along the gradient) until equilibrium, resulting in therandom motion of particles.

Osmosis is thenet movement of water molecules across asemi-permeable membrane from a region oflow solute

concentrate to a region ofhigh solute concentration until equilibrium is reached.

2.4.5 Explain passive transport across membranes in terms of simple diffusion and facilitate diffusion.

(a)Plasma membrane= semi permeable and selective about what can cross.

(b)Substance that move along the concentration gradient (diffusion: high to low) undergopassive transport and do not

expend ATP.

Simple diffusion: Small, non-polar (lipophilic) molecules can freely diffuse across the membrane.

Facilitated diffusion: Large, polar substances (ions, macromolecules) cannot freely diffuse and require theassistance of

transport proteins(carrier proteins and channel proteins) tofacilitate their movement (facilitated diffusion).

2.4.6 What is the role of protein pumps and ATP inactive transport across membranes?

-Active transport is thepassage of materials AGAINSTaconcentration gradient (from low to high).

-Active transport requires the use ofprotein pumps, whichusethe energy fromATP totranslocate molecules

against the gradient.

-Hydrolysis of ATP cause aconformational change in the protein pump resulting in theforced movementof the

substance.

-Protein pumps arespecific for a given molecule, allow for movement to beregulated.

-Example of active transport mechanism is theNa⁺ /K⁺ pump which is involved in the generation ofnerve impulses.

2.4.7 How are vesicles used to transport materials within a cell between the endoplasmic reticulum, Golgi apparatus and

plasma membrane?

-Polypeptides destined for secretion contain an initial target for secretion whichdirects the ribosometo the

endoplasmic reticulum.

-Polypeptides continued to besynthesised by the ribosome into the lumber of the ER, where the signal sequence is

removed from the nascent chain.

-Polypeptide within rough ER is transferred to golgi apparatus via a vesicle, which forms the budding of the membrane.

-Polypeptide moves via vesicles from the cis face of the golgi to the trans face, and may be modified along the way.

-Polypeptide is finally transferred via a vesicle to the plasma membrane, where it is eitherimmediately released (constitutive secretion) orstored for delayed release in response to cellular signal (regulatory secretion = for a more

concentrated and more sustained effect).

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(BioNinja)

2.4.8 Describe how the fluidity of the membrane allow for it change shape. break and reform during endocytosis and

exocytosis.

Endocytosis= Re-making of the membrane

Exocytosis= Breaking of the membrane

Membrane is principally held together by therelatively weak hydrophobic associations between phospholipids.

Association allows formembrane fluidity andflexibility, as the phospholipids (and to a lesser extent proteins) can move

to some limitation. This allows for thebreaking andremakingof membranes, allowinglarger substances to access

into and out of the cell (active process).

Endocytosis: Large substances or bulky amounts of small substances canenter the cell without travelling across the

plasma membrane. An invagination of the membrane form a flask-like depression whichenvelops the material; the

invagination is then sealed forming a vesicle. Two types of endocytosis:

(1)Phagocytosis: Solid substances (food particles, foreign pathogens) are ingested; usually to be transported to the

lysosome for breakdown.

(2)Pinocytosis: Liquids/ solutions (dissolved substances) are ingested by the cell; allows quick entry for large amounts of

substances.

(BioNinja)

Exocytosis- Large substancesexit the cell without travelling across the plasma membrane.

(1)Vesicles (usually derived from the golgi apparatus) fuse with the plasma membrane.

(2)The contents of vesicles are expelled into the extracellular environment.

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(3)Membrane then flattens out.

2.5.1. Outline the stages in the cell cycle, including interphase (G1, S, G2), mitosis and citokynesis.

Interphase-

G1: Period of growth,DNA transcription and protein synthesis.

S period: Period during which all theDNA in the nucleus is replicated.G2: Period in which thecell prepares for division.

At the end of interphase the cell beginsmitosis- the process by which thenucleus divides to form two genetically

identical nuclei. Towards the end of mitosis, the cytoplasm of the cell start to divide and eventually two cells are formed,

each containing one nucleus. The process ofdividing the cytoplasm to form two cells iscytokinesis.

2.5.2 Tumours (cancers) are the result ofuncontrolled cell division and that these can occur in any organ or tissue.

Repeated uncontrolled divisions soon produce a mass of cells called a tumour. Tumours can grow to a large size and can

spread to other parts of the body.

2.5.3 Interphase is anactive period in the life of a cell when manymetabolic reactions occur , includingprotein

synthesis,DNA replicationand an increase in thenumber of mitochondriaand/orchloroplasts.

2.5.4 What are the events that occur in the four phases of mitosis?

(1)Prophase

- Early: Spindle microtubules are growing. Chromosomes are becoming shorter and fatter by supercoiling.

- Late: Each chromosome consists of two identical chromatids formed by DNA replication in interphase held

together by a centromere. Spindle microtubules extend from each pole to the equator.

(2)Metaphase: Nuclear membrane has broken down and chromosomes have moved to the equator. Spindle microtubules

from both poles are attached to each centromere on opposite sides.

(3)Anaphase: Centromeres have been divided and the chromatids have become chromosomes. Spindle microtubulespull the genetically identical chromosomes to opposite poles.

(4)Telophase

- Early: All chromosomes have reached the poles and nuclear membranes from around them. Spindle

microtubules break down.

- Late: Chromosomes uncoil and are no longer individually visible. Cell divides (cytokinesis) to form two cells with

genetically identical nuclei.

2.5.5 Explain how mitosis produces two genetically identical nuclei.

-During interphase (S phase) DNA was replicated to produce two copies of genetic material.

-Two identical DNA molecules are identified as sister chromatids and are held together by a single centromere.

-During the events of mitosis, the sister chromatids are separated and drawn to opposite poles to the cell.

-When the cell divides (cytokinesis) the two resulting nuclei will each contain one of each chromatid pair and thus be

genetically identical.

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IB Biology SL Cells