IB Biology 2013Cell theory notes

2.1 Cell theory (SL)

2.1.1 Outline the cell theory (2)

1. All living organisms are made of cells2. Cells are the smallest units of life3. All cells come from other pre-existing cells

2.1.2 Discuss the evidence for the cell theory (3)

Evidence: Robert Hooke (1662) devised a compound microscope and used it to observe the structure of cork. First to use the term cells Anthony van Leeuwenhoek (1680) made high focus lenses so magnifications of x240 were achieved. Observed blood cells, sperms, protozoa and even bacteria. Robert Brown (1831) observed and named the nucleus. Theodor Schwann (1839) established cells as the natural unit of living things Rudolf Virchow (1856) established that cells only arise by division of other cells Louis Pasteur established that life does not spontaneously generate.

2.1.3 State that unicellular organisms carry out all the functions of life (1)

Unicellular organisms carry out all the functions of life Movement, Respiration, Sensing, Homeostatis, Growth, Reproduction, Excretion, Nutrients

2.1.4 Compare the relative sizes of molecules, cell membrane thickness, viruses, bacteria, organelles and cells (3)

Molecules 1nm thickness of membranes 10nm viruses 100nm, bacteria 1m organelles up to 10 m Most cells up to 100 m

2.1.5 Calculate the linear magnification of drawings and the actual size of specimens in images of known magnification (2)

Magnification = size of image/size of specimen

2.1.6 Explain the importance of the surface area to volume ratio as a factor limiting cell size (3)Importance of surface area to volume ratio:

Heat production/waste production/resource consumption is function of volume Rate of exchange of materials and energy is function of surface area Volume increases faster than surface area Increase of size means decrease in SA:V ratio The smaller the cell is, the more quickly and easily materials can be exchanged between cytoplasm and environment When maximum size is reached, cell growth stops.

2.1.7 State that multicellular organisms show emergent properties (1)

Multi-cellular organisms show emergent properties, arising from the interaction of component parts the whole is greater than the sum of its parts.

2.1.8 Explain that cells in multicellular organisms differentiate to carry out specialized functions by expression some of their genes but not others (3)

Cells in multicellular organisms can differentiate to carry out specialized functions by expressing some genes but not others Genes that are expressed with determine function and characteristics of cell;

Totipotent: Can divide into all other cellsPluripotent: Can divide into any other cell except for embryonic membrane cellsMultipotent: Can divide into many other cellsUnipotent: Can only divide into one kind of cellNullipotent: Cannot divide (e.g. blood cells)

2.1.9 State that stem cells retain the capacity to divide and have the ability to differentiate along different pathways (1)

Stem cells retain the capacity to divide Stem cells are derived from blastocysts/human embryos/left over from IVF/placenta and umbilical cord/some adult tissues

2.1.10 Outline one therapeutic use of stem cells (2) Technologies rely on replacing diseased/dysfunctional cells with healthy/functioning ones Need to identify desired type of stem cell and grow in culture/special controlled conditions Develop means of implanting/integrating cells into a patients own tissues so they function with the bodys natural cells Danger of rejection of cells therefore need to suppress immune system Must make sure new cells do not become overgrown/develop into cancerous tissues Retinal cells replace dead cells in retina to cure presently incurable diseases such as glaucoma and macular degeneration Graft new skin cells to treat serious burn victims Help repair catastrophic spinal injuries/help victims of paralysis regain movement by replacing nerve tissueE.g. In 2005, stem cells were used to restore insulation tissue of neurons in lab rats Resulted in subsequent improvements in their mobility

2.2 Prokaryotic cells2.2.1 Draw and label a diagram of the ultra-structure of Escherichia coli (E. coli) as an example of a prokaryote (1)

2.2.2 Annotate the diagram from 2.2.1 with the functions of each named structure (2)StructureFunction

Cell wallA rigid outer layer made of peptidoglycan that maintains shape and protects the cell from damage or bursting if internal pressure is high

Cell membraneSemi-permeable barrier that controls the entry and exit of substances

CytoplasmFluid component which contains the enzymes needed for all metabolic reactions

NucleoidRegion of the cytoplasm which contains the genophore (the prokaryotic DNA)

PlasmidAdditional DNA molecule that can exist and replicate independently of the genophore - it can be transmitted between bacterial species

RibosomeComplexes of RNA and protein that are responsible for polypeptide synthesis (prokaryotic ribosomes are smaller than eukaryotes - 70S)

FlagellaLong, slender projection containing a motor protein which spins the flagella like a propellor, enabling movement

PiliHair-like extensions found on bacteria which can serve one of two roles

2.2.3 Identify structures from 2.2.1 in electron micrographs of E. coli (2)

2.2.4 State that prokaryotic cells divide by binary fission (1) Prokaryotic cells divide by binary fission A form of asexual reproduction; not the same as mitosis Circular DNA is copied in response to a replication signal Two DNA loops attach to membrane, then membrane elongates and pinches off, forming 2 separate cells

2.3 Eukaryotic cells2.3.1 Draw and label a diagram of the ultra-structure of a liver cell as an example of an animal cell (1)

2.3.2 Annotate the diagram from 2.3.1 with the functions of each named structure (2)StructureFunction

RibosomesComplexes of RNA and protein that are responsible for polypeptide synthesis (80S)

Rough ERHas ribosomes on surface, used in membrane production, helps to synthesize proteins and transport of proteins destined for secretion

Cell membraneSemi-permeable barrier that controls the entry and exit of substancesContains glycoproteins (immune system), imbedded and integrated proteins; phospholipid bilayer with hydrophobic tails.

CytosolFluid portion of cytoplasm (no organelles)

NucleusContains DNA; control centre of cell (for transcription and DNA replication)

NucleolusSite of production and assembly of ribosome components

MitochondriaSite of aerobic respiration; produces ATP from organic compounds

Golgi ApparatusAssembly of vesicles and folded membranes involved in the sorting, storing and modification of secretory products

LysosomeSite of hydrolysis/digestion/breakdown of macromolecules (digestive sacs)

Peroxisome:Catalyses breakdown of toxic substances

CentriolesMicrotubule organizing centres involved in mitosis/meiosis and cytokinesis

Smooth ERInvolved in synthesis and transport of lipids and steroids; metabolism of carbohydrates

2.3.3 Identify structures from 2.3.1 in electron micrographs of liver cells (2)

2.3.4 Compare prokaryotic and eukaryotic cells (3)

Similarities: Both have cell membrane Both contain ribosomes Both have DNA and cytoplasm

2.3.5 State three differences between plant and animal cells (1)

2.3.6 Outline two roles of extracellular components (2)Plants: Cell wall made from cellulose (-pleated sheets) secreted from the cell Provides support and mechanical strength for the cell (maintains cell shape) Prevents excessive water uptake by maintaining a stable, turgid state Serves as a barrier against infection by pathogens

Animals: Extracellular matrix (ECM) is made from secreted glycoproteins Provides support and anchorage for cells Segregates tissues from one another Regulates intercellular communication by intercepting growth factors2.4 Membranes2.4.1 Draw and label a diagram to show the structure of membranes (1)

2.4.2 Explain how the hydrophobic and hydrophilic properties of phospholipids help to maintain the structure of cell membranes (3)Structure of Phospholipids Consist of a polar head (hydrophilic) made from glycerol and phosphate Consist of two non-polar fatty acid tails (hydrophobic)

Arrangement in Membrane Phospholipids spontaneously arrange in a bilayer Hydrophobic tail regions face inwards and are shielded from the surrounding polar fluid while the two hydrophilic head regions associate with the cytosolic and extracellular environments respectively

Structural Properties of Phospholipid Bilayer Phospholipids are held together in a bilayer by hydrophobic interactions (weak associations) Hydrophilic / hydrophobic layers restrict entry and exit of substances Phospholipids allow for membrane fluidity / flexibility (important for functionality) Phospholipids with short or unsaturated fatty acids are more fluid Phospholipids can move horizontally or occasionally laterally to increase fluidity Fluidity allows for the breaking / remaking of membranes (exocytosis / endocytosis) Stability can be increased by the presence of cholesterol molecules

2.4.3 List the functions of membrane proteins (1)

Transport:Protein channels (facilitated) and protein pumps (active)Receptors:Peptide-based hormones (insulin, glucagon, etc.)Anchorage:Cytoskeleton attachments and extracellular matrixCell recognition:MHC proteins and antigensIntercellular joinings:Tight junctions and plasmodesmataEnzymatic activity:Metabolic pathways (e.g. electron transport chain)

2.4.4 Define diffusion and osmosis (1)Diffusion: The passive movement of particles from a region of high concentration to a region of low 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.

2.4.5 Explain passive transport across membranes by simple diffusion and facilitated diffusion (3) The plasma membrane is semi-permeable and selective in what can cross Substances that move along the concentration gradient (high to low) undergo passive transport and do not require the expenditure of energy (ATP)

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

Facilitated diffusion: Larger, polar substances (ions, macromolecules) cannot freely diffuse and require the assistance of transport proteins (carrier proteins and channel proteins) to facilitate their movement (facilitated diffusion)

2.4.6 Explain the role of protein pumps and ATP in active transport across membranes (3)The passive movement implies that there is no expenditure of energy in moving the molecules from one side of the membrane to the other:However the molecules themselves possess kinetic energy which accounts for why they are in movement.The membrane therefore 'allows' the molecules to pass through without needing to add any additional energy to the kinetic energy already possessed by the particles.Particles will in fact pass in both directions but overall the emerging pattern is that molecules move from a region of their high concentration to a region of their low concentration. Some molecules are so small that they pass through the membrane with little resistance This includes Oxygen and Carbon Dioxide Lipid molecules (even though very large) pass through membranes with very little resistance also.

Larger molecules (red) move passively through the membrane via channel proteins These proteins(grey) have large globular structures and complex 3d-shapes The shapes provide a channel through the middle of the protein, the 'pore' The channel 'shields' the diffusing molecule from the non-charged/ hydrophobic/ non-polar regions of the membrane.

2.4.7 Explain how vesicles are used to transport materials within a cell between the rough ER, Golgi apparatus and plasma membrane (3)

2.4.8 Describe how the fluidity of the membrane allows it to change shape, break and re-form during endocytosis and exocytosis (2)

2.5 Cell division2.5.1 Outline the stages in the cell cycle, including interphase (G1, S, G2), mitosis and cytokinesis (2)Interphase: Longest part of the cell cycle Chromosomes cease to be visible as thread-like structures at interphase, becoming dispersed as chromatin. Become actively involved in protein synthesis Synthesis of new organelles takes place in the cytoplasm Each chromosome replicates forms chromatids Mitosis: Cell division chromosomes, present as chromatids, separated and distributed into two daughter nuclei Mitosis is a continuous process with no breaks between the phases.

Cytokinesis: Division of the cytoplasm Following telophase, cell organelles become distributed between cells and plasma membrane tucks in, pinching the cytoplasm in half to form two new, identical cells2.5.2 State that tumours (cancers) are the result of uncontrolled cell division and that they can occur in an organ or tissue (1) Tumour cells (cancers) are the result of uncontrolled cell division and can occur in organs or tissues

2.5.3 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 (1) Interphase in an active period in the life of a cell when many metabolic reactions occur- Protein synthesis- DNA replication- increase in no. of mitochondria and/or chloroplasts

2.5.4 Describe the events that occur in the four phases of mitosis (prophase, metaphase, anaphase and telophase) (2) Prophase: chromosomes supercoil; nucleolus disappears and membrane breaks down

Metaphase: centrioles move to opposite sides of the cell; microtubules attach to the centromeres and arrange them at equator

Anaphase: spindles shorten, chromatids pulled to opposite poles to form chromosomes

Telophase: nuclear membrane reforms, chromosomes uncoil

2.5.5 Explain how mitosis produces two genetically identical nuclei (3) Daughter cells produced by mitosis have identical sets of chromosomes to each other and to the parent cell Exact copy of each chromosome is made via replication Chromatids remain attached by centromeres during mitosis, Centromeres divide during anaphase and chromatids of each pair are pulled apart to opposite poles; thus, one copy of each chromosome moves to each pole Two cells are formed via division of the cytoplasm at the exact midpoint

2.5.6 State that growth, embryonic development, tissue repair and asexual reproduction involve mitosis (1) Growth in, embryonic development, tissue repair and asexual reproduction involve mitosis.