CELLS TOPIC ONE

1. Outline cell theory. all living things are made of one or more cells the cell is the smallest unit of life all cells come from pre-existing cells

2. Discuss the evidence for the cell theory. a theory is a general system of ideas used to explain or interpret

observations theories provide predictive power by generating hypotheses a hypothesis is a specific prediction than can be tested through

observation or experiment each aspect of cell theory is based on evidence obtained from

observations and experiments all living things are made of one or more cells

microscopes allow us to observe that all living things are either unicellular or multicellular

exceptions: 1. skeletal muscle, some fungal hyphae, and some algae have

multinucleate cytoplasm, lacking normal cell separations 2. connective tissue, such as bone, blood and cartilage, is composed

of both cellular and extracellular structures, especially extracellular proteins and fluids; however, these extracellular structures are products of cellular activities the cell is the smallest unit of life:

nothing smaller than a cell can survive independently subcellular structures cannot survive independently (nuclei, ER,

golgi, chloroplasts, mitochondria) the lower limit on cell size is about 200nm, large enough for DNA,

ribosomes, and membranes all cells come from pre-existing cells:

this seems to imply that life has always existed, which is incompatible with geological evidence about the age of Earth

therefore, an exception is made for the origin of life, when cells must have arisen from non-living substances

since the conditions of early Earth were anaerobic, they allowed for cells to form from non-living substances

the conditions of present Earth are aerobic, precluding the formation of cells from non-living substances 3. State that unicellular organisms carry out all the functions of life

metabolism: chemical reactions inside the cell, including cell respiration to release energy

sensitivity: perceiving and responding to changes in the environment

homeostasis: keeping conditions inside the organisms within tolerable limits

growth: an irreversible increase in size reproduction: producing offspring either sexually or asexually nutrition: obtaining food, to provide energy and the materials

needed for growth 4. Compare the relative sizes of molecules, cell membrane thickness, viruses, bacteria, organelles and cells, using appropriate SI units

molecules: ~ 1 nm cell membrane thickness: ~ 10 nm viruses: ~ 100 nm bacteria: ~ 1 µm organelles: up to 10 µm eukaryotic cells: up to 100 µm

5. Calculate linear magnification of drawings and the actual size of specimens in images of known magnification magnification = size of image / actual size of specimen drawings of microscopic structures must include at least one of:

scale bars: |-----------| = 1 µm magnification: x 250

6. Explain the importance of the surface area to volume ratio as a factor limiting cell size surface area

(SA) = f(x2) rate of exchange = f(SA)

volume (V) = f(x3) metabolism = f(V) metabolism includes heat production/waste production/resource

consumption of a cell therefore

as the dimensions of a cell increase, V increases proportionally faster than SA

thus, SA/V ratio decreases with cell size setting an upper limit on cell size because lower relative SA reduces rate of exchange while higher relative V increases metabolic demands thus, rate of exchange can’t meet needs of metabolic demands

7. State that multicellular organisms show emergent properties.

emergent properties arise from the interaction of component parts the whole is greater than the sum of its parts life itself can be viewed as an emergent property

8. Explain that cells in multicellular organisms differentiate to carry out specialized functions by expressing some of their genes but not others. unicellular organisms

must solve all of life’s challenges within the confines of a single cell multicellular organisms

can differentiate into a variety of interdependent cell types each specialized to carry out a subset of functions thereby achieving a greater efficiency through division of labor among a multicellular cooperative

cellular differentiation achieved through differential gene expression all cells in an organism have identical DNA = genome different cell types make different proteins usually as a result of transcriptional regulation each cell type expresses a closely regulated subset of its genome “turning on” some genes and “turning off” others

9. State that stem cells retain the capacity to divide and have the ability to differentiate along different pathways. 10. Outline one therapeutic use of stem cell.

bone marrow transplants use hematopoietic stem cells (HS cells) HS cells are found in bone marrow and divide continually,

producing a variety of red and white blood cells just 100 HS cells can completely replace the blood system of mice

when all cells in the marrow have been destroyed by radiation HS cells are used in the treatment of numerous blood disorders 1. acute leukemia 2. SCID (severe combined immune deficiency) 3. multiple myeloma 4. lymphoma in lymphoma: 1. cells are removed from the bone marrow of the patient 2. high doses of chemotherapy drugs are taken by the patient to kill

dividing cells in the body 3. both cancerous and normal are killed 4. HS cells from the bone marrow are then transplanted back into the

patient 5. these HS cells can then fully restore healthy production of blood

cells in the bone marrow ethical issues: use of embryonic stem cells involves the death of

early-stage embryos ethical issues: therapeutic cloning could reduce suffering for

patients with a wide variety of conditions

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

2. Annotate the diagram from 2.2.1 with the function of each named structure: cell wall:

always present composed of peptidoglycan provides physical protection maintains cell shape prevents bursting in hypotonic environment

plasma membrane: thin layer mainly composed of phospholipids pushed up against

the inside of the cell wall provides selectively permeable barrier between homeostatically

controlled interior and fluctuating exterior environments controls entry and exit of substances can also pump substances in or out by active transport can produce ATP by cell respiration

pili: protein filaments protruding from the cell wall can be pulled in or push out by a ratchet mechanism used for cell to cell adhesion used when bacteria stick together to form aggregations of cells used when two cells are exchanging DNA during conjugation

flagella: structures protruding from the cell wall with a corkscrew shape base is embedded in the cell wall using energy, they can be rotated, to propel the cell from on area

to another unlike eukaryotic flagella, they are solid and inflexible, working like

a propeller cytoplasm:

fluid filling the space inside the plasma membrane water with many dissolved substances contains many enzymes contains ribosomes does not contain any membrane-bound organelles carries out the chemical reactions of metabolism

ribosomes: small granular structures (70S) smaller than eukaryotic ribosomes which are 80S sites of protein synthesis

nucleoid: region cytoplasm containing the genetic material (usually one

molecule of DNA) DNA is circular and naked (not associated with protein) total amount of DNA is much smaller than in eukaryotes the nucleoid is stained less densely than the rest of the cytoplasm

because there are fewer ribosomes in it and less protein 3. Identify structures from 2.2.1 in electron micrographs of E. coli.

4. State that prokaryotic cells divide by binary fission.

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

2. Annotate the diagram from 2.3.1 with the functions of each named structure. Free ribosomes:

sites of protein synthesis for use within the cytoplasm ribosomes are constructed in the nuclear region called the

nucleolus Rough endoplasmic reticulum:

flattened membrane sacs (cisternae) ribosomes attached to outside of cisternae proteins synthesized by ribosomes enter cisternae proteins collected within cisternae are packaged in vesicles vesicles transport proteins to Golgi apparatus

Lysosomes: spherical vesicles formed by Golgi apparatus contain hydrolytic/digestive enzymes enzymes for breaking down ingested food, damaged organelles, or

entire cells Golgi apparatus:

consists of flattened membrane sacs called cisternae unlike ER, cisternae are curved, shorter, and lack ribosomes proteins received from arriving vesicles are processed carbohydrates added to proteins to form glycoproteins vesicles of glycoproteins exit Golgi for exocytosis or intracellular

use Mitochondria:

double membrane bound inner membrane invaginated to form cristae site of aerobic respiration, producing ATP

Nucleus: double membrane bound, containing pores for transport of

proteins and ribosomes contains chromosomes, made of DNA + protein uncoiled chromosomes = chromatin site of DNA replication and transcription into RNA

3. Identify structures from 2.3.1 in electron cirographs of liver cells.

4. Compare prokaryotic and eukaryotic cells. Prokaryotic

naked DNA DNA in cytoplasm (no nuclear membrane) No membrane-bound organelles (no mitochondria, ER, golgi) ribosome size = 70S Only bacteria Size: 1 - 10 µm Evolved at least 3.5 billion years ago

Eukaryotic DNA associated with proteins True nucleus (enclosed by nuclear membrane) Many membrane-bound organelles (mitochondria, ER, golgi) to

compartmentalize functions ribosome size = 80S All cells other than bacteria Size: 2 - 1000 µm Evolved 1.5 - 2 billion years ago

5. State three differences between plant and animal cells. Plant cells

cellulose cell walls chloroplasts large central vacuole

Animal cells no cell walls no chloroplasts lacking or small vacuoles

6. Outline two roles of extracellular components. Plant cell wall

composition: cellulose microfibrils functions: 1. provides physical protection 2. prevents excessive water uptake precluding bursting in hypotonic

environment 3. produces turgor pressure which holds whole plant up against the

force of gravity Animal extracellular matrix

animal cells secrete glycoproteins that form the extracellular matrix

functions: support, adhesion, movement . Draw and label a diagram to show the structure of membranes.

Phospholipid bilayer Cholesterol Glycoproteins Integral proteins embedded in th phospholipid of the membrane Peripheral proteins attached to the phospholipid surface

2. Explain how the hydrophobic and hydrophilic properties of phospholipids help to maintain the structure of cell membranes.

Hydrophobic fatty acid tails repel water and form the middle layer of the membrane.

Hydrophilic phosphate heads attract water and form the outer layers of the membrane.

3. List the functions of membrane proteins including: Hormone binding sites Immobilized enzymes Cell adhesion Cel-to-cell communication Channels for passive transport Pumps for active transport.

4. Define: Diffusion = the passive movement of particles from a region of

higher concentration to a region of lower concentration. Osmosis = the passive movement of water molecules, across a

partially permeable membrane, from a region of lower solute concentration to a region of higher solute concentration. 5. Explain passive transport across membranes in terms of simple diffusion and facilitated diffusion. Concentration gradient: Molecules can diffuse across membranes from areas of higher to lower concentration by:

Simple diffusion: traveling directly through the membrane if they are small and uncharged, thus avoiding repulsion by the hydrophobic, non-polar tails of phospholipids in the middle of the membrane.

Facilitated diffusion: traveling through special transport proteins, if they match the shape and charge requirements to fit through the channels provided by the transport proteins.

6. Explain the role of protein pumps and ATP in active transport across membranes. Against the concentration gradient: Moves substance from an area where it is in lower concentration to an area where it is in higher concentration. Protein pumps:

Integral protein pumps embedded within membranes. Specific to molecule transported.

Requires energy: Usually provided by ATP. Often by phosphorylating the protein pump as ATP is hydrolyzed.

7. Explain how vesicles are used to transport materials within a cell between the rough endoplasmic reticulum, Golgi apparatus, and plasma membrane.

Protein synthesis: rER produces proteins which travel through the lumen of the ER

Transport in vesicles: Membranes produced by the rER flows in the form of transport vesicles to the Golgi, carrying proteins within the vesicles

Modification: Golgi apparatus modifies proteins produced in rER Transport to membrane: Golgi pinches off vesicles that contain

modified proteins and travel to plasma membrane Exocytosis: Vesicles then fuse with plasma membrane, releasing

their contents by

8. Describe how the fluidity of the membrane allows it to change shape, break and reform during endocytosis and exocytosis.

Lipids move laterally in a membrane, but flip-flopping across the membrane is rare.

Unsaturated hydrocarbon tail of phospholipids have kinks that keep the molecules from packing together, enhancing membrane fluidity.

Cholesterol reduces membrane fluidity by reducing phospholipid movement at moderate temperatures but it also hinders solidification at low temperatures. 2.5 Cell Division1. Outline the stages in the cell cycle, including interphase (G1, S, G2), mitosis and cytokinesis. interphase

G1: growth, protein synthesis, increase in the number of mitochondria and/or chloroplasts

S: DNA replication G2: growth, protein synthesis, preparation for mitosis/cytokinesis

mitosis = nuclear division prophase metaphase anaphase telophase

cytokinesis = cellular division

2. State that tumors (cancers) are the result of uncontrolled cell division and that these can occur in any organ or tissue. 3. State that interphase is an active period in the life of a cell when many metabolic reactions occur, including protein synthesis, DNA replication and an increase in the number of mitochondria and/or chloroplasts. 4. Describe the events that occur in the four phases of mitosis: Prophase:

Chromosomes condense by supercoiling, becoming visible Centrioles move to opposite poles Nucleolus disappears Nuclear membrane disappears Microtubular spindle apparatus forms at each pole

Metaphase: Spindle microtubules attach to chromosome centromeres Chromosomes move to the equator

Anaphase: Centromeres split as spindle microtubules pull chromatids to

opposite poles (after centromeres split, sister chromatids are known as sister chromosomes)

Sister chromosomes move to opposite poles as microtubules shorten Telophase:

Sister chromosomes have arrived at poles Spindle disappears Centrioles replicate Nuclear membrane becomes visible Nucleolus becomes visible Chromosomes decondense, becoming chromatin

5. Explain how mitosis produces two genetically identical nuclei. DNA replication during S phase of interphase produces two

identical copies of DNA Identical sets of DNA are attached to each other as sister

chromatids of each of the cell’s chromosomes Mitosis segregates the two chromatids of each chromosome to

opposite poles, forming two identical nuclei, each with one complete copy of the original DNA

Cytokinesis separates the two daughter nuclei into two identical daughter cells 6. State that growth, embryonic development, tissue repair and asexual reproduction involve mitosis.

Previous IB Exam Essay Questions: Unit 1

1. Discuss possible exceptions to cell theory. 4 marks skeletal muscle fibers are larger/have many nuclei/are not typical

cells fungal hyphae are (sometimes) not divided up into individual cells unicellular organisms can be considered acellular because they are larger than a typical cell/carry out all functions of

life some tissues/organs contain large amounts of extracellular

material e.g. vitreous humor of eye/ mineral deposits in bone/ xylem in

trees/other example statement of cell theory/all living things/most tissues are

composed entirely of true cells 2. Explain how the surface are to volume ratio influences cell sizes. 3 marks

small cells have larger ratio (than larger cells)/ratio decreases as size increases

surface area/membrane must be large enough to absorb nutrients/oxygen/substances needed

surface area/membrane must be large enough to excrete/pass out waste products

need for materials is determined by (cell) volume cell size is limited (by SA/Volume ratio)/cells divide when they

reach a certain size reference to diffusion across/through membrane/surface area

3. Outline differentiation of cells in a multicellular organism. 4 marks differentiation is development in different/specific ways cells carry out specialized functions/become specialized example of a differentiated cell in a multicelluar organism cells have all genes/could develop in any way some genes are switched on/expressed but not others position/hormones/cell-to-cell signals/chemicals determine how a

cell develops a group of differentiated cells is a tissue

4. Draw a diagram of a prokaryotic cell 6 marks cell wall shown clearly and labelled cell surface membrane shown thinner than and adjacent to cell

wall and labelled cytoplasm shown with no nucleus present and labelled ribosomes shown free in the cytoplasm and labelled loop of DNA shown in the cytoplasm/nucleoid and labelled as DNA plasmid shown as a small loop and labelled slime capsule shown as a layer outside the cell wall and labelled mesosome shown as a membrane invagination and labelled flagellum shown and labelled (reject if shown with microtubules)

5. Draw a diagram to show the organelles which are found in the cytoplasm of plant cells. 6 marks Award 1 mark for each of the following structures accurately drawn and labelled

rough endoplasmic reticulum (free ribosomes) Golgi apparatus mitochondrion chloroplast vacuole nucleus lysosome smooth endoplasmic reticulum

6. State one function of each of the following organelles: lysosome, Golgi apparatus, rough endoplasmic reticulum, nucleus, mitochondrion. 5 marks

lysosome: hydrolysis/digestion/break down of materials (macromolecules)

Golgi apparatus: synthesis/sorting/transporting/secretion of cell products

rough endoplasmic reticulum: site of synthesis of proteins (to be secreted)/ intracellular transport of polypeptides to Golgi apparatus

nucleus: controls cells activities/mitosis/replication of DNA/transcription of DNA (to RNA)/directs protein synthesis

mitochondrion: (aerobic) respiration/generates ATP 7. Draw a diagram of the ultra-structure of an animal cell as seen in an electron micrograph. 6 marks

Award 1 mrak for each of the following structure clearly drawn and labelled correctly. Award marks for labelled eukaryotic structures, then deduct 1 mark per labelled prokaryotic structure shown, e.g. mesosome, cell wall.

nuclear membrane/nucleus (with nuclear membrane shown double with pores)

ribosomes (free or attached to ER) endoplasmic reticulum/ ER plasma/cell membrane (reject if shown as a double line) mitochondria (shown with inner and outer membrane) Golgi (apparatus) lysosomes

8. Distinguish between the structure of plant and animal cells. 6 marks Award 1 mark per difference plant cells

have cell walls, animals do not have plastids/ chloroplasts, animals do not have a large central vacuole, animals do not store starch, animal cells store glycogen have plasmodesmata, animal cells do not

animal cells have centrioles, plant cells do not have cholesterol in the cell membrane, plant cells do not plant cells are generally have a fixed shape/ more regular whereas

animal cells are more rounded 9. Using a table, compare the structures of prokaryotic and eukaryotic cells. 5 marks prokaryotic cells eukaryotic cells

DNA naked/loop of DNA associated with protein/histones/nucleosomes/DNA in chromosomes

location of DNA in cytoplasm/nuceloid/no nucleus within a nucleus/nuclear membrane

membrane bound organelles none present ribosomes 70S 80S plasma membrane same structure within both groups cell wall peptidoglycan/not cellulose/not chitin cellusose/chitin/not

peptidoglycan respiratory structures mesosomes/no mitochondria mitochondria

10. Draw a diagram to show the structure of a cell membrane 5 marks phospholipids labelled with hydrophillic (heads) and hydrophobic

(tails) phospholipid bilayer clearly shown and labelled proteins shown in the bilayer and labelled transmembrane and peripheral/extrinsic proteins shown and

labelled glycoproteins shown and labelled cholesterol shown and labelled glycolipids shown and labelled thickness shown as 10 nm/ + or - 2 nm

11. Explain how the structure and properties of phospholipids help to maintain the structure of cell membranes. 9 marks phospholipid structure

hydrophobic tail/hydrophilic head head made from glycerol and phosphate tail made from two fatty acids saturated/ unsaturated fatty acid (in tail)

arrangement in membrane phospholipids form a bilayer heads face outside the membrane/ tails face inside the membrane/

hydrophic interior/ hydrophilic exterior of membrane A suitable annotated diagram may incorporate all or many of the above points. Award 5 marks maximum for a suitable diagram that is labelled correctly.

phospholipids held together by hydrophobic interactions phospholipid layers are stabilized by interaction of hydrophilic

heads and surrounding water phospholipids allow for membrane fluidity/ flexibility fluidity/ flexibility helps membranes to be (functionally) stable phospholipids with short fatty acids/ unsaturated fatty acids are

more fluid fluidity is important in breaking and remaking membranes (e.g.

endocytosis/ exocytosis) phospholipids can move about/ move horizontally/ "flip flop" to

increase fluidity hydrophilic/ hydrophobic layers restrict entry/ exit of substances

12. Explain the role of vesicles in transportation of materials within cells. 8 marks

vesicles are membrane bound packages/droplets formed by pinching off/budding off a piece from a membrane can carry proteins rough ER synthesizes proteins proteins enter/accumulate inside the ER transported to Golgi apparatus for processing targeted to/transported to specific cellular organelles fuse with membrane of organelle so contents of vesicle join the

organelle transported to the plasma membrane fuses with plsma membrane releases/secretes contents exocytosis

13. Describe the process of active transport. 4 marks uses/ requires energy/ ATP goes against concentration gradient/ lower to higher concentration requires a protein in the cell membrane/ pump/ carrier protein

(reject channel) hydrolysis of ATP/ ATP --> ADP + phosphate involves a conformational change in the pump/ protein/ diagram

to show this 14. Outline the ways in which substances move passively across membranes. 5 marks

diffusion (is a method of passive transport across the membrane) pore/ channel proteins for facilitated diffusion/ to allow

hydrophilic particles across movement from high to low concentration/ down the

concentration gradient membrane must be permeable to the substance diffusing oxygen/ other named example of a substance than can diffuse

through membranes osmosis is movement of/ diffusion of water through a membrane from a region of lower to a region of higher solut concentration/

higher to lower water potential membranes are (nearly) always freely permeable to water

15. Explain the reasons for cell division in living organims. 8 marks to increase the number of cells in an organism to allow differentiation/ cell specialization for greater efficiency to replace damaged/ lost cells example binary fission asexual reproduction of unicellular organisms gamete/ spore formation cells only arise from pre-existing cells refer to Virchow cells cannot grow beyond a certain size surface area to volume ratio becomes too small transport across the membrane too slow example nucleus cannot control the cell control of cell division sometimes lost tumor formation

16. Outline the processes that occur in a cell during interphase, including those needed to prepare for mitosis. 4 marks

DNA replication DNA transcription enzyme/ protein synthesis biochemical reactions/ example of a biochemical reaction cell respiration growth organelles replicated