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The current 2025 Syllabus for Biology Pre-IB T1
The Cell Theory
1. All living things are composed of cells
2. Cells are the smallest units of life
3. All cells come from pre-existing cells
What do all cells contain?
cytoplasm, a plasma membrane, genetic material, cell activities through chemical reactions and their own energy release system
What are the relative size of cells?
In order: Molecules, membranes, viruses, bacteria, organelles, eukaryotes
1nm, 10 nm, 100 nm, 1 um, 10 um, 10 - 100 um
Atypical Examples of Cell Theory
Red blood cells (no nucleus), Phloem sieve tube elements (no nucleus), Aseptate fungal hyphae (multinicleate in a filamentous structure), skeletal muscle cells (multinucleate).
The Functions of Life
•Metabolism: chemical reactions inside the cell, e.g. cell respiration to release E.
•Response: react to stimuli.
•Homeostasis: keep conditions inside the organisms within set limits.
•Growth: irreversible increase in size.
•Reproduction: produce offspring sexually or asexually.
•Excretion: getting rid of waste products of metabolism.
•Nutrition: obtaining food needed for E and growth.
Unicellular vs. Multicellular
Uni- 1 cell, responsible for ALL functions of life. e.g bacteria, paramecium
Multi- 2+ cells, differentiated to make different tissues to perform specialised functions
Prokaryotes
lack membrane-bound organelles (structures that perform a specific function)
What cell parts are in a Prokaryote?
Flagellum
Ribosomes
Pilli
Cell Wall
Cytoplasm
Nucleoid
Plasma Membrane
Eukaryotic cell
membrane-bound organelles
multicellular
Compare Eukaryote and Prokaryote cells
Prokaryote-
'smaller-10microns
'cell wall
'naked DNA (no protein)
'DNA free in cytoplasm
'Circular/closed loop DNA/chromosones
'some have plasmids
'1 chromosone
'no introns or extrons
'70S ribosomes
'no membrane bound organelles
'no mitochondria
Eukaryote-
'Larger, 100microns
'DNA w/ proteins/histones
'DNA in membrane bound nucleus
'Linear chromosones
'no plasmids
'multiple chromosones
'introns + extrons
'80S ribosomes
'membrane bound organelles
Compare a plant and animal cell
Plant:
Cell wall - made of cellulose for strength and support of the cell.
Chloroplasts - surrounded by two membranes and allow photosynthesis
Large vacuole - storage organelle
Store carbohydrates as starch.
Do not contain centrioles
Fixed, angular shape
No cholesterol in the cell membrane
Animal Cell:
No cell wall
No chloroplasts
Small vacuole
Store carbohydrates as glycogen
Contain centrioles
Flexible, round shape
Have cholesterol in the cell membrane
Identify the functions of life on a prokaryote cell
Excretion-plasma membrane
Reproduction - nucleus
Response- cillia
Metabolism- cytoplasm
Nutrition- vacuoles
Growth- Assimilation
Homeostasis - contractile vacuoldx
Light Microscope
enables examination of small objects not visible to the naked eye. It uses light rays and lenses to enlarge images. It has low resolution. Specimens may be alive or dead. They are relatively cheap.
Electron Microscope
uses electron beams to capture an image and enlarge it. Allows for high resolution 3D images. Much greater magnification power than a light microscope. Only dried and dead organisms are seen. Expensive.
Magnification
The size of an enlarged image
Resolution
The clarity of an image
The features of a microscope
Eyepiece
Coarse adjustment knob
Fine adjustment knob
High and low power objective lenses
Stage
Light
Magnification Formula
Magnification = measured length / scale bar label
Actual Size Formula
actual size = measured length / magnification
Measured Length Formula
Measured length formula = image size / magnification
Stem Cells
undifferentiated cells by expressing genes and not others
Can be used to treat leukemia, lymphoma and diabetes, and repair tissue/heal wounds
They are capable of differentiating into various cell types.
Plant stem cells are found in meristems
Animal stem cells are found in embryos, umbilical cord cells, and some adult cells (e.g. bone marrow)
Phospholipid Bilayer
Plasma membrane layers composed of phospholipid molecules arranged with polar heads facing the outside and nonpolar tails facing the inside.
Phosphate hydrophilic head
Fatty acid hydrocarbon lipid tails
Hydrophobic fatty acid tails
Saturated Fatty acids- straight chains - packing to form bilayers - reduces fluidity and permeability - however stronger and high melting point - thicker and high density
Unsaturated fatty acids - one or more kinks so packs together loosely - flexible - lower melting points
Ideal ratio of these depends on the temperature the cell experiences
The Fluid Mosaic Model
model that describes the arrangement and movement of the molecules that make up a cell membrane
highlights the structure of the membrane is flexibile, adaptable, and in motion
Integral proteins
permamently embedded inside the membrane.
Enzymes - sites for chemical reactions
Pumps - for active transport of molecules
if the integral protein goes all the way through the membrane, it is 'polytopic'
one surface penetrating is monotopic
Peripheral proteins
temporarily attatched/embedded to the outer layer of the membrane. Acts as receptors and 'recognises' other cells.
Monotopic
Cholesterol
makes the phospholipids pack more tightly and regulates the fluidity and flexibility of the membrane. It stabilises membranes at higher temperatures and preventing stiffening at lower temperatures.
Glycolipids and Glycoproteins
1 is carbohydrates (monodaccharide) linked to lipids (1 or 2 hydrocarbon chains) that fit into the hydrophobic core of a membrane
2 is conjugated proteins with carbohydrate as the non polypeptide component.
Protein part is embedded in the membrane. Carbohydrate part projecting out the exterior environment of the cell.
ROLE: cell to cell communication and cell recognition, and can allow adjacent cells to bind together forming a tissue.
Draw the fluid mosaic model of a membrane
It should contain:
-ion channel protein (with pore)
-peripheral protein
-cholesterol
-integral protein (polytopic)
-phospholipid bilayer
-glycoprotein and glycolipid
The methods of moving particles across membranes
1.Simple diffusion (PT)
2.Facilitated diffusion (PT)
3.Osmosis (PT)
4.Active transport (AT)
5.Endocytosis and exocytosis (AT)
Three solutions
1.Diluted solution (little solute, can dissolve more solute)
2.Concentrated solution (lot of solute, can dissolve little more)
3. Saturated solution (max solute, cannot dissolve any more, excess solute at the bottom)
{usually dissolved in an aqueous solution)
Diffusion
The passive net movement of molecules from regions of high concentration to low concentration
(higher concentration gradient = increased diffusion rate as molecules have more energy)
Osmosis
-The passive net movement of water molecules from regions of low solute concentration to high solute concentration, through a partially/selectively permeable membrane
-movement down a concentration gradient (but specifically the water molecules)
Facilitated Diffusion
The passive movement of specific molecules across cell membranes, faciliated by carrier proteins through a selectively permeable membrane (down the concentration gradient)
Comparison of diffusion and osmosis
Similarities - passive and down a concentration gradient
Differences - Diffusion is of solutes + membrane not needed
Osmosis considers water molecules only + partially/permeable membrane essential
Importance of osmotic control
to prevent damage to cells and tissues
hypertonic
osmosis- more water outside the cell
animal - shrivelled (crenated) - plasma membrane that develops indentations due to being bathed in a hypertonic solution
plant - plasmolysed - cell is flaccid/floppy - plasma membrane pulls away from cell wall
dehydration
isotonic
normal water balance inside and outside the cell (osmosis)
hypotonic
more water inside the cell than outside
animal - lysed (the cell membrane pops)
plant - turgid
turgor pressure - high pressure inside cell due to water entering (osmosis). This provides support and strength to a plant
Water potential
Measure of potential energy of water per unit of volume of water, relative to the potential energy of pure water at standard conditions.
In a hypertonic solution (lots of particles dissolved):
*osmolarity high
*water potential low
*solute concentration high
In a hypotonic solution (few particles dissolved):
*osmolarity low
*water potential high
*solute concentration low
passive transport
does not require energy. Down a concrentration gradient (high to low)
active transport
requires energy in the form of ATP. Against a concentration gradient using membrane protein pumps. Key for homeostasis in organisms.
Transmembrane (polytopic) proteins
recognises a particular molecule (thats large and polar and cant get across via diffusion) and helps it move across the membrane. The direction it moves is dependent on the concentration gradient.
Potassium channels
Voltage gated. Enable the facilitated diffusion of potassium out of the axon.
Sodium potassium pumps
active transport mechanisms that pump Na+ ions out of neurons and K+ ions in
ATP (adenosine triphosphate)
The wonder molecule. Used to power most cellular processes, such as active transport and DNA replication.
Exocytosis
the export of macromolecules from the cell. ATP is required. Active transport.
Endocytosis
The import of macromolecules (enter cell process).
ATP is required to make a vesicle this way.
Phagocytosis
the ingestion of solid molecules (when referring to endocytosis)
Pinocytosis
The ingestion of liquids and solutes (when referring to endocytosis)
Draw a diagram of endo and exo cytosis :)
Lable the vesicle forming/leaving.
Pasteur's experiment
Louis Pasteur designed an experiment to test whether sterile nutrient broth could spontaneously generate microbial life.
Method:
•Two experiments were setup
•In both, Pasteur added nutrient broth to flasks and bent the necks of the flasks into S shapes
•Each flask was then heated to boil the broth in order than all existing microbes were killed.
•After the broth had been sterilized, Pasteur broke off the swan necks from the flasks in Experiment 1, exposing the nutrient broth within them to air from above.
•The flasks in Experiment 2 were left alone.
Results:
•The broth in experiment 1 turned cloudy whilst the broth in experiment 2 remained clear.
•This indicates that microbe growth only occurred in experiment 1.
Conclusion: Pasteur rejected the hypothesis of spontaneous generation as for growth of microbes to occur a source of contamination was needed.
Conditions of Early Earth
4.6bya formed and was pre-biotic
-lightening: triggers chemical processes
-high temperature
-no ozone layer due to lack of O2 - high UV
-Early Earth's atmosphere: trace oxygen, high methane (from volcano + meteorite), high carbon dioxide (water vapour, ammonia).
RNA
The first genetic material
-hypothesised to be because it can: store genetic information, self-replicate and catalyse reactions
Ribozymes (RNA molecules) in the ribosome catalyse the formation of peptite bonds during protein synthesis
Miller and Urey experiment
recreated the conditions of pre-biotic Earth in a closed system.
•These conditions included a reducing atmosphere (low oxygen), high radiation levels, high temperatures and electrical storms
•Water was boiled to form vapour and then was mixed with methane, ammonia and hydrogen
•The mixture of gases was exposed to an electrical discharge (sparks) to simulate lightning
•After one day, the water turned pink, then dark red
•The mixture was then allowed to cool and after one week was found to contain some simple amino acids and complex oily hydrocarbons.
•Based on these findings, it was concluded that under the hypothesised conditions of pre-biotic Earth, organic molecules could be formed
Hydrothermal vents
deep-sea thermal vents
•Fissures in a planet's surface from which geothermally heated water issues. Vents are commonly found near in volcanically active areas)
•Along with heat energy the Vents issue a ready supply of reduced inorganic chemicals
•Vents provide the right conditions and chemicals to allow organic polymers to arise.
DNA and RNA
•DNA though very stable and effective at storing information is not able to self-replicate - enzymes are required
•However RNA can both store information and self-replicate - it can catalyse the formation of copies of itself.
•In ribosomes RNA is found in the catalytic site and plays a role in peptide bond formation
Formation of membranes to package the organic molecules
phospholipids natural assemble into bilayers, if conditions are correct.
Formation of the bilayer creates an isolated internal environment.
The formation of an internal environment means that optimal conditions, e.g. for replication or catalysis can be maintained.
Strengths and limitations of Miller and Urey's experiment
Strengths:
-modelled prebiotic earth and its atmosphere
-demonstrates that molecules such as amino acids can be generated spontaneuosly under certain conditions
-Design of the experiment allows it to be replicated by other scientists
Limitations:
-Remains debate on the actual atmosphere of prebiotic Earth
-Experiment did not produce all of the organic molecules required for life
-Simulation could not accound for all conditions on prebiotic Earth
Endosymbiotic Theory
explains the existence of several organelles of eukaryotes. The theory states that the organelles originated as symbioses between separate single-celled organisms
(e.g. mitochondria and chloroplasts w/double membrane, circular DNA, ribosomes, multiply by binary fission. They both evolved via endosymbiosis)
Endosymbiotic Theory exemplar
The evidence supporting the endosymbiotic theory for mitochondria and chloroplasts:
•They have their own DNA (which is naked and circular)
•They have ribosomes that are similar to prokaryotes (70S)
•2 membranes (one was the prokaryotic cell, the other is the vesicle from the larger cell
•They are roughly the same size as bacteria and are susceptible to the antibiotic chloramphenicol
•They transcribe their DNA and use the mRNA to synthesize some of their own proteins.
•They can only be produced by division of pre-existing mitochondria and chloroplasts.
Why is SA:V ratio of a cell important
1. Diffusion pathways are shorter, therefore efficient
2. Concentration gradients are easier to generate
*A LARGE SA:V RATIO IS NOT ALWAYS ADVANTAGE!!
e.g. warm blooded animals lose heat quickly due to large SA:V. They eat constantly.
e.g. Some desert plants minimise SA:V to conserve water with their flat leaves.
Cell Division
to maximise their SA:V ratio.
The Cell Cycle
Series of events that cells go through as they grow and divide
Interphase
(G1)
(S)
(G2)
Mitosis
(Prophase, metaphase, anaphase, telophase)
Interphase (Growth 1)
-Cell grows
-Number of organelles increases (e.g. mitochondria)
-DNA transcribed
-Protein is synthesised
Interphase (Synthesis)
-DNA is transcribed
-DNA is replicated
Interphase (Growth 2)
-Cell prepares for division
-Further growth
-Organelles increase in number
-DNA condenses to form visible chromosones (chromatins to chromosomes)
-Microtubules begin to form
Mitosis
The division of the eukaryote nucleus, making sure that each new daughter cell gets a full set of chromosones and is therefore genetically identical to the parent cell.
Order: prophase, metaphase, anaphase, telophase
Cell Terminology for mitosis
plasma membrane, spindle microtubules, sister chromatids, centromere, centriole, telomere
Prophase
1 in mitosis.
-DNA supercoils. Chromatin condenses and becomes sister chromatins, visible under a light microscope.
-Centrosomes move to opposite poles of cell and spindle fibers form between them
-Nuclear membrane is broken down and disappears
Metaphase
2 in mitosis.
-Spindle fibers from each of the 2 centrosomes attatch to the centrometre of each pair of sister chromatids
-Contraction of the microtuble spindle fibers cause the sister chromatids to line up along the center of the cell
Anaphase
3 in mitosis.
-continued contraction of the microtuble spindle fibres cause seperation of sister chromatids
-chromatids are now chromosones
-chromosones move to opposite poles of cell
Telophase
4 in mitosis.
-Chromosones uncoil and de-condense to chromatin (no longer visible under light microscope)
-Chromosones arrive at poles
-Microtubule spindle fibres disappear
-New nuclear membranes reform around each set of chromosones
-Cytokinesis begins
Cytokinesis
division of the cytoplasm to form two separate daughter cells
In animal cells:
•A ring of contractile protein (microfilaments) immediately inside the plasma membrane at the equator pulls the plasma membrane inwards.
•These proteins are actin and myosin (similar to skeletal muscle).
•The inward pull on the plasma membrane produces the characteristic cleavage furrow.
•When the cleavage furrow reaches the centre of the cells it is pinched apart to form two daughter cells.
In plant cells:
•During telophase, membrane-enclosed vesicles derived from the Golgi apparatus migrate to the equator of the cell. Vesicles fuse to form tubular structures.
•The tubular structures merge (with the addition of more vesicles) to form two layers of plasma membrane (i.e. the cell plate)
•The cell plate continues to develop until it connects with the existing cell's plasma membrane.
•This completes the division of the cytoplasm and the formation of two daughter cells.
•Vesicles deposit, by exocytosis, pectins and other substances in the lumen between the daughter cells to form the middle lamella ('gluing' the cells together)
•Both daughter cell secrete cellulose to form their new adjoining cell walls.
The mitotic index
the ratio between the number of cells in mitosis in a tissue and the total number of observed cells.
Mitotic index =
number of cells in mitosis / total number of cells
Binary fission
Asexual reproduction (for primarily prokaryote cells), where a cell divides into two identical daughter cells after replicating its genetic material.
-DNA replicates semi conservatively (plasmid duplicates)
-2 DNA loops attach to the membrane
-membrane elongates and pinches off (cytokinesis) forming 2 seperate cells
Difference between Binary fission and mitosis
Binary fission does not duplicate its looped DNA, as prokaryotes do not use all the DNA at the same time, therefore unaffected.
Mitosis does duplicate DNA, as eukaryotes depend on having their complete set of DNA.
Tumor formation
uncontrolled cell division
-if genes mutate, cell cycle is no longer controlled. Cell will divide abnormally.
Benign Tumor
Do not invade any body tissue. Often inactive and harmless.
Malignant Tumor
Detached and carried in the bloodstream to other parts of the body.
Result in secondary tumours or metastasis.
Known as cancer.
Carcinogen
Can cause mutations in a gene which tells the cell to stop dividing
(e.g. tobacco smoke, UV exposure, radiation, infectin ect.)
Primary and Secondary Tumors
•When a malignant tumour metastasises, the original tumour is called the primary tumour, and the tumour that has spread from the primary tumour is called the secondary tumour.
•Secondary tumours are often more difficult to treat than primary tumours because they have the ability to spread to other parts of the body and may therefore be more widespread and harder to locate and completely eliminate.
•secondary tumours indicate a more advanced stage of cancer, more likely to affect vital organs or functions.
