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2. Cells

Notes for IB Biology

Ruru (Juan Ru) Hoong

on 23 June 2014

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Transcript of 2. Cells

Rod-shaped organelles (same size as bacteria)
Own DNA/ chromosome to allow some autonomy
Double membrane
Smooth outer membrane
Folded inner layer, cristae
Semi-fluid matrix
Production of usable cellular energy, ATP
2. Cells
2.1 Cell Theory
2.2 Prokaryotic Cells
2.3 Eukaryotic Cells
2.4 Membranes
2.1.1 Outline Cell Theory
All living organisms are composed of one or more cells
Cells are the smallest units of life (individual cells can perform all the functions of life)
All cells come from pre-existing cells
2.1.2 Discuss Evidence for Cell Theory
Louis Pasteur sterilized chicken broth by boiling - living organisms would not 'spontaneously reappear; only after exposure to pre-existing cells was life able to reestablish itself in sterilized chicken broth
Have not been able to find living entity not made of at least one cell
Robert Hooke studied cork with a microscope he built himself, made of cells. Schleiden said that plants are made of 'individual separate beings' called cells. Leeuwenhoek observed 'animalcules'
2.1.3 State that unicellular organisms carry out all the functions of life.






molecules passed on to offspring (asexual/sexual)
Sensitivity/ response
ability to detect and respond to stimuli
: Increase in cell size/ number
internal environment
: source of compounds with many chemical bonds which can be broken down to provide organisms with energy and nutrients to maintain life.
2.1.4 Compare relative sizes
1000 mm = 1m
1000 µm = 1 mm
1000 nm = 1 µm
2.5 Calculate the linear magnification of drawings and the actual size of specimens in images of known magnification.
Magnification =
2.1.6 Explain the importance of the surface area to volume ratio as a factor limiting cell size
Cells are very small, no matter how large an organism is, because surface area to volume ratio limits cell size.
2.1.7 State that multicellular organisms show emergent properties
Differentiation allows for emergent properties
Different cell types interact with each other to allow more complex functions to take place
eg. nerve cells interact with muscle cells to allow movement to take place
2.1.8 Explain that cells in multicellular organisms differentiate to carry out specialized functions, by expressing some genes but not others.
Every cell contains all the DNA and genes of the organism
Genes encode for proteins that affect the cell’s structure and function so that the cell can specialize
Differentiation process is a result of expressing certain genes
2.1.9 State that stem
cells retain the capacity to divide
and have the ability to differentiate
along different pathways.
Pluripotent/ embryonic stem cells
eg. Blastocyst
Retain the ability to form any type of cell
Multipotent cells
eg. Bone marrow - blood cells
Allow for continual production of a particular type of tissue
2.1.10 Outline one therapeutic use of stem cells
Treats certain types of leukemia, cancer which causes overproduction in WBCs
Chemotherapy to destroy patient's own bone marrow cells, matched stem cells transferred through needle in pelvis
20µm- 100µm
1µm- 10µm
0.5µm- 1µm
5nm - 10nm
1nm - 2nm
Image size
Actual size
Volume of cell: level of metabolic activity
Heat and waste production
Rate of resource consumption
Rate of chemical reactions
Surface area of cell: membrane controls movement of materials
Rate of exchange with outside environment (nutrients, etc.)
As cell size increases, volume increases in a greater proportion than surface area.
Larger cells less S.A to obtain materials and dispose of waste
Cannot keep up with cell's living requirements
To overcome this...
Microvilli and folds for increased surface area for diffusion and absorption
Cells elongate and flatten
Divide and become multicellular organisms
Grow in complexity as well as size
Cells differentiate and can take on specific functions that improve efficiency
Gene expression regulated during TRANSCRIPTION.
Differentiation allows for specialization and hence greater efficiency.
eg. Gene that codes for keratin active in hair and nails.
Stem cells differ from normal cells:
Large nucleus relative to volume of cytoplasm
Divide repeatedly: large # of new cells
Other person's bone marrow cells
Umbilical cord of a newborn baby (multipotent; any type of blood cell)
Embryonic stem cells discarded from IVF clinics (ethical issues)
2.2.1 Draw and label a
diagram of the ultrastructure of
Escherichia coli
- example of a prokaryote.
2.2.2 Functions
of each structure.
2.2.3 Identify structures in electron micrographs of E. coli.
2.2.4 State
that prokaryotic cells
divide by binary fission.
DNA is copied, cell elongates
2 daughter chromosomes are attached to different regions of the plasma membrane; partitioning of DNA by microtubule-like fibres made of protein
Divides into two genetically identical cells (asexual reproduction)
2.5 Cell Division
2.3.1 Draw and label a diagram
of the ultrastructure of a liver cell, as an example of an animal cell.
2.3.5 State the differences between plant & animal cells.
Cell wall of cellulose present (fixed, angular)
Large, central vacuole
Store carbohydrates as starch
Do not contain centrioles
2.3.6 Outline roles of extra cellular components
Extracellular Matrix (ECM)
Form supporting network for cell membrane
Allows adjacent cells to attach to one another and intersect
Cell migration and movement due to interactions
Cell Wall (in both plant and fungi cells)
Provides support
Maintains cell shape
Prevents excessive water uptake
2.4.3 List the functions of membrane proteins
Integral Proteins: both hydrophobic and hydrophilic regions in the same protein
Peripheral proteins: bound to surface
2.4.4 Define
diffusion and osmosis.
Diffusion: the passive movement of molecules from a region of higher concentration to a region of lower concentration down a concentration gradient, without the need of energy.
2.4.5 Explain passive
transport across membranes by
simple and facilitated diffusion.
Membranes are semi-permeable; small molecules can move in and out via passive transport.
2.4.6 Explain the role of
protein pumps and ATP in active transport across membranes.
Active transport: the movement of substances across a partially permeable membrane, against a concentration gradient, using energy from ATP.
Allows cell to maintain interior concentrations of molecules that are different from exterior concentrations (eg. animal cells with high K, low Na)
2.4.8 Describe how the fluidity
of the membrane allows it to change shape, break and reform during endocytosis and exocytosis.
The phospholipid molecules are not solid and closely packed together largely due to 'loose' connections between tails
Can move, but stable in aqueous environment
Fluidity of the membrane is important for fusion and secretion
2.3.2 Functions of structure.
2.3.3 Identify
structures in electron micrographs of liver cells.
2.3.4 Compare prokaryotic & eukaryotic cells.
Composed of peptidoglycan
Maintains shape of cell
Protects cell from bursting
Controls movement of materials in and out of cell
Plays a role in binary fission
Semi-permeable, lets substances in by active and passive transport
In-folding: photosynthetic membrane/ nitrogen fixing
Contains all the enzymes for chemical reactions and genetic material
Region involved with cell control and reproduction
Contains hereditary material that is passed on to daughter cells
Sites of protein synthesis
Large numbers, but very small (70S)
Increased protection/ chances of survival
Adherence to structures (eg. teeth, skin food)
Made of complex sugar/ polysaccharide
Small circular DNA molecules
Independent replication allows adaptation (eg antibiotic resistance)
Can be passed from one cell to another
Sexual reproduction (joining bacterial cells in preparation for exchange of genetic material)
Hair-like growth outside cell wall
Enables cell motility (locomotion)
Large than pili: projects from cell wall
no nucleus, organelles, little compartmentalization
Occurs inside the plasma membrane and contains organelles
Fluid portion of cytoplasm called cytosol
Medium for metabolic reactions
Smooth E.R
Extensive network of tubules and channels
Transportation of materials throughout internal region of cell
Rough E.R
No ribosomes on surface
Production of membrane phospholipids and cellular lipids
Production of sex hormones
Detoxification of drugs in liver
Storage of calcium ions needed for contraction in muscle cells
Transportation of lipid-based compounds
Aid liver in releasing glucose into bloodstream
Ribosomes on the exterior of channels
Protein development and transport
Synthesizes proteins for membranes, enzymes, messengers, etc.
Protein synthesis
Made of RNA and protein and has no membranes
Large (80S); free or attached to RER
Collection, packaging, modification and distribution of materials within cell
Esp. in glandular cells, like pancreas
Flattened sacs called cisternae
Isolated region where DNA resides (genetic material)
Double membrane nuclear envelope
Nuclear pores for communication with cytoplasm
Chromosomes composed of chromatin
Strands of DNA and protein histones
Nucleolus manufactures ribosomes
Controls movement of materials in and out of cell
Semi-permeable, lets substances in by active and passive transport
Pair of centrioles at 90 degrees to one another
Assembles microtubules
Provide structure and allow movement
Cell division
Higher plant cells have no centrioles
Intracellular digestive centers from Golgi apparatus
Contain hydrolytic enzymes that catalyze breakdown of proteins and lipids
Fuse with old damaged organelles/ phagocytosis
Composed of cellulose in plants (lignin and pectin as well)
Give plant cells further support and rigid structure
Turgidity: strength and support to hold leaves in optimal position for sunlight
Composed of chitin in fungi
Storage organelles that usually form from Golgi apparatus
Store substances (potential food, metabolic waste, or water)
Provide rigidity in plants
Allow high surface area to volume ratio
Double membrane, own DNA in the form of ring
Absorption of light for photosynthesis; produces glucose (where food is made)
Has ribosomes and able to reproduce independently of cell
Both have cytoplasm
Both have DNA
Both have plasma membrane
Both have ribosomes
Both carry out functions of life
DNA in ring/strands, free in cytoplasm
No mitochondria or endoplasmic reticulum
Ribosomes are not dense; small: 70S
Always present cell wall of peptide
No chloroplasts
DNA as chromatin, nucleus present
Mitochondria & endoplasmic reticulum
Ribosomes are dense; large: 80S
Only plant cells have cellulose cell wall
Chloroplasts present in plant cells
Cell wall absent
Chloroplasts absent
Small vacuoles/ not present
Store carbohydrates as glycogen
Contain centrioles in centrosome
2.4.1 Draw and label a diagram to show the structure of a membrane
Membrane is a fluid mosaic model
Always changing shape/ dynamic; moves freely
Proteins distributed unevenly in mosaic pattern
Based on chemical and experimental calculations
2.3.2 Explain how the hydrophobic and hydrophilic properties of phospholipids help to maintain the structure of the cell membranes.
The phosphorylated head is hydrophilic (highly polar and water soluble)
The fatty acid tails are hydrophobic (non-polar and insoluble in water)
Outer surroundings and cytoplasm are both aqueous
Phospholipid bilayer constructed in a way such that tails face inward, and avoid water heads face outwards and align
Ions and polar molecules cannot pass through the hydrophobic tails
Helps maintain internal concentration and exclude other substances
However membrane is still flexible
*Cholesterol: determine the fluidity of the membrane; makes it more rigid and less permeable and allows effective membrane function (fluidity varies with temperature)
Cell-to-cell communication: glycoprotein to identify label of other cells
Cell-to-cell adhesion: gap junctions and tight junctions
Hormone binding sites: recognizes specific hormones
Enzymatic action to carry out metabolic reactions
Channels for facilitated diffusion
Pumps for active transport
2.4.7 Explain how vesicles are used to transport materials within a cell between the rER, Golgi apparatus, and plasma membrane.
Endocytosis (uptake):
Phagocytosis (taking in of particles, like bacteria)
Pinocytosis (taking in of substances in solution)
Osmosis: the movement/ diffusion of water molecules from a region with higher water potential (dilute) to a region of lower water potential (concentrated) down a water potential gradient, through a partially permeable membrane.
Simple Diffusion: small molecules and gases move between phospholipid molecules/bilayer. These are hydrophobic (lipid soluble), as the membrane is hydrophobic inside.

Facilitated Diffusion: Large/charged/hydrophilic molecules pass through channels in integral proteins. Some are permanently open, others open and close without energy.
Plasma membrane pinches off to form an enclosed vesicle
Vesicle enters cytoplasm of cell
Ends of membrane reattach due to hydrophobic and hydrophilic properties of the phospholipids and presence of water
Exocytosis (export):
Digestive enzymes
Bacterial remains
Ribosomes produce proteins, passes through rER
Vesicles brings protein from rER to cis side of Golgi apparatus
Protein modified in Golgi apparatus and exits trans side
Moved along microtubules to plasma membrane
Fuses with plasma membrane, releasing contents outside
2.5.1 Outline the stages in the cell cycle, including interphase, mitosis, & cytokinesis.
2.5.2 State that tumours (cancers) are the result of uncontrolled cell division and that these can occur in any organ or tissue.
Cell division continues unchecked and tumors form
Benign (restricted to that tissue)
Malignant (abnormal cells migrate and can cause cancer)
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.
G1: growth of cell, increase in number of organelles, protein synthesis

S: DNA replication, chromosomes are duplicated

G2: Growth further occurs, increase in number of organelles, protein synthesis, DNA starts
to condense to form visible chromosomes

2.5.4 Describe the events that occur in the four phases of mitosis (prophase, metaphase, anaphase and telophase).
2.5.5 Explain how mitosis produces two genetically identical nuclei.
DNA in chromosomes is replicated so that after cell division there will be two daughter cells with nuclei that have exactly the same number of chromosomes
2.5.6 State that growth,
embryonic development, tissue repair
and asexual reproduction involve mitosis.
Growth and development of embryos
Repair of worn/ damaged cells (tissue repair)
Asexual reproduction
Caused by damage to genes
Mistake in DNA replication
Environmental factors (radiation, etc.)
Genetic predisposition
interphase (90%)
Mitosis: Replicated chromosomes separate and the cell divides
Four phases: Prophase, metaphase, anaphase, telophase
Cytokinesis: Division of cytoplasm
Animal: cell membrane pinches; cleavage furrows
Plants: Cell plate forms midway and moves outwards toward sides of cell
1. The chromatin fibres become more densely coiled into chromosomes
2. The nuclear membrane disintegrates and nucleoli disappear
3. Centrosome splits and starts moving to poles due to lengthening microtubules
4. Mitotic spindle begins to form and is completed
5. Spindle attaches to centomere at kinetochrome
1. Chromosome aligns at equator of cell/ metaphase plate
2. Movement of chromosomes due to action of spindle
3. Centrosomes/ Centrioles at opposite poles
1. Shortest phase of mitosis: sister chromatids split longitudinally
2. Shortening microtubules and spindle fibers pull sister chromatid to opposite poles
3. Centromeres move first; each side with complete identical set of chromosomes
1. A nuclear membrane forms around each set of chromosomes & nucleoli appear
2. Chromosomes uncoil and become chromatin again
3. Spindle apparatus disappears; cell elongates
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