Prokaryotic vs Eukaryotic Cells

• Cells are the smallest structural and functional unit of a living organism
• Cells can be either prokaryotic or eukaryotic

Prokaryotic Cells

• Unicellular and lack membrane-bound organelles
• Measurement: 0.1 to 5.0 µm (micrometres), smaller than eukaryotic cells
• Contain four main structures: cell membrane, cytoplasm, ribosomes, genetic material
• The genetic material is found in a large loop as a bacterial chromosome, and as small circular structures, plasmids
• Other structures include cell wall, pili, fimbriae, flagella, and a capsule
• Organisms are usually unicellular
• Divided into two main groups: bacteria and archaea
• Bacteria are widespread and can either be harmful or beneficial
• Archaea live in harsh environments, subjected to extreme conditions such as hydrothermal vents and hot springs

Eukaryotic Cells

• Multicellular and contain a nucleus and membrane-bound organelles such as mitochondria and endoplasmic reticulum
• Measurement: 10 to 100 µm (micrometres) much larger than prokaryotic cells
• Each organelle has a specific function
• Organelles carry out all the biochemical processes and reactions of the cell
• Examples of organisms include: Animals, plants, fungi (multicellular) and amoeba proteus (unicellular); organisms can be either unicellular or multicellular

Prokaryotic Vs Eukaryotic Cells

• Prokaryotic cells lack a true nucleus while eukaryotic cells have a true nucleus with a nuclear membrane
• Prokaryotic cells do not have membrane-bound organelles, eukaryotic cells have numerous membrane-bound organelles
• Prokaryotic cells reproduce through binary fission, eukaryotic cells reproduce through mitosis and meiosis
• Prokaryotic cells are exemplified by bacteria such as E. Coli, eukaryotic cells are exemplified by humans, dogs, onions, and amoeba proteus
• The cell membrane of both regulates the movement of substances in and out of the cell
• Cytoplasm is present in both, where cellular processes occur

Plant Vs Animal Cells

• Plant cells have a cell wall, animal cells do not
• Plant cells have a rigid and rectangular shape, animal cells have a flexible and round/irregular shape
• Plant cells contain chloroplasts, animal cells do not
• Plant cells store energy as starch, animal cells store energy as glycogen
• Plant cells have a large, centred vacuole, animal cells have small temporary vacuoles
• Plant cells are autotrophic, making their own food via photosynthesis, animal cells are heterotrophic, consuming other organisms for food
• Both are eukaryotic cells

Light Microscope

• Uses visible light to illuminate the specimen
• Light passes through a condenser lens to focus on the specimen, then through the objective lens to magnify the image, and finally through the ocular lens to further magnify the image
• Mostly used in school laboratories
• Can view living and non-living specimens
• Relatively simple to use
• Inexpensive and widely accessible
• Allows observation of cellular structures and tissue
• Limited resolution (200 nm) which limits the observation of small structures such as organelles
• Cannot view thick specimens, they must be cut thin

Fluorescence Microscopes

• Uses fluorescent substances that bind to specific structures
• The sample is illuminated with high-intensity light to cause the fluorescent substances to emit light
• Emitted light is captured through filters to highlight specific areas
• Allows viewing of specific parts of cells using fluorescent dyes
• Can observe structures beyond the resolution limit of the light microscope
• Useful for studying specific molecules or parts of cells
• Requires special fluorescent dyes that must bind to target structures
• Only the labelled areas can be seen
• Difficult to observe other parts of the specimen that aren't labelled

Electron Microscope

• Uses an electron beam instead of light and electromagnets instead of glass lenses
• Electron interaction with the specimen forms an image on a screen
• Can reveal structures at the subcellular and atomic level
• Provides high magnification and resolution
• Can observe internal structures via TEM or surface structures via SEM
• Reveals detailed sub-cellular structures, organelles, and even atoms
• Requires vacuum for electron flow, so living tissue cannot be viewed
• Sample preparation is complex and introduces artefacts
• Expensive and requires high maintenance
• Large and requires specialised equipment

Transmission Electron Microscope (TEM) Vs Scanning Electron Microscope (SEM)

• TEM produces a 2D image showing internal structures, SEM produces a 3D image focusing on surface features
• TEM has a magnification of up to 1,500,000x, SEM has a magnification of up to 1,000,000x
• TEM has a resolution of approximately 2 nm, SEM has a resolution of approximately 10 nm
• Samples for TEM must be very thin for electrons to pass through, samples for SEM need only be coated with a conductive material and do not need to be thin
• TEM uses an electron beam to form images, SEM uses an electron beam to form images

Light Microscope VS Electron Microscope

• Light microscopes are used to make a magnified image of a specimen using light
• Electron microscopes are used to make a magnified image of a specimen using electrons
• Light microscopes have a magnification of up to 1500x, electron microscopes have a magnification of up to 1,500,000x
• Light microscopes have a resolution of 200nm, electron microscopes have a resolution of 2nm-10nm
• Light microscopes cost $100 to $500 and are cheaper, electron microscopes cost $75,000 - $10,000,000 and are expensive
• Light microscopes can use a specimen that is dead or alive, electron microscopes require a dead specimen

Rules for Drawing Diagrams

• Draw what you see, not what you think should be there
• Use a lead pencil for the diagram, titles, and labels
• It should be as simple as possible with clean cut lines showing what has been observed
• The diagram should be be done on unlined blank paper and be neatly labelled
• Must be large enough to show all parts without crowding
• The diagram should be around half a page in size and be centred
• Lines to the labelled parts should be drawn with a ruler and be parallel to each other or do not draw arrows
• Use a ruler for label lines, do not shade the drawing
• Should be titled and underlined, the title should appear immediately above the drawing
• The title should include the type of cell drawn and the magnification
• There should be a scale in the right corner, this can either be the magnification or a scale bar

Cell Organelles

• Membrane-bound internal structures, each with a specific function to ensure the efficient functioning of the cell

Nucleus

• Large, spherical/oval organelle surrounded by a double nuclear membrane with pores for communication with the cytoplasm
• Control centre of the cell; stores DNA (genetic information) that regulates cell activities and is passed to new cells during division

Nucleolus

• Dense, granular region inside the nucleus, made up of RNA and some DNA
• Produces ribosomes, which are essential for protein synthesis

Endoplasmic Reticulum (ER)

• A network of interconnected, flattened membranes continuous with the outer nuclear membrane
  • Rough ER (with ribosomes) processes proteins
  • Smooth ER (without ribosomes) synthesises lipids for membrane repair and production
• Transports proteins and lipids within the cell

Golgi Bodies

• Consists of stacked, flat membranes without ribosomes. Has a curved shape on one surface where vesicles can be seen budding off
• Processes, packages, and sorts cell products
• Adds proteins and carbohydrates, wraps products in membranes, and directs them for transport within or outside the cell

Ribosomes

• Small, dense granules made of RNA and protein, increasing surface area for protein synthesis
• Can be free in the cytoplasm or attached to the ER
• Read genetic instructions to assemble amino acids into polypeptides, forming proteins
• Newly made proteins are then transferred to the ER for folding and processing

Lysosomes

• Small organelles formed by the Golgi body, found in the cytoplasm of animal cells
• Contain digestive enzymes enclosed within a membrane
• Break down complex molecules into simpler ones for recycling
• Carry out apoptosis, where enzymes are released to destroy old or damaged cells

Mitochondria

• Rod-shaped or round organelles with a double membrane
• The inner membrane is folded to increase surface area for energy production
• Central matrix contains mitochondrial DNA and enzymes, allowing them to self-replicate
• Perform cellular respiration, combining oxygen with sugars to produce ATP, the cell's energy source
• Number of mitochondria varies based on a cell's energy needs, with more found in highly active cells

Vacuoles

• Large, permanent sacs in plant cells, enclosed by the tonoplast membrane and filled with cell sap, which contains water, minerals, sugars, and pigments
• Store nutrients and waste while maintaining turgor pressure, pushing against the cell wall to keep the cell firm and structurally supported

Chloroplasts

• Green, biconvex-shaped organelles found in plant cells, surrounded by a double membrane
• The inner membrane contains stacks of thylakoids (grana) where chlorophyll is located, and the stroma contains enzymes and starch grains
• Carry out photosynthesis by capturing sunlight to produce sugars
• The chlorophyll in thylakoids absorbs light, and the stroma contains enzymes for photosynthesis and stores the produced starch

Cell Membrane

• Thin, flexible boundary surrounding the cell and organelles
• Acts as a selective barrier, controlling the movement of substances in and out of the cell (selectively permeable)
• Membranes are used to create compartments within the cell (organelles)

Protoplasm

• The living content of a cell, consisting of the nucleus and cytoplasm
• Site of essential life processes like respiration and cellular product formation

Cell Wall

• Made of cellulose fibres, providing strength and flexibility
• It may be thickened with additional chemicals for hardness, waterproofing, or flexibility
• Provides structural support and shape to the plant cell
• It is permeable, allowing most molecules to pass through, and can resist pressure due to its flexibility

Cytoskeleton

• A network of microtubules, microfilaments, and intermediate filaments that extends throughout the cytoplasm, providing structure to the cell
• Organises and supports the placement of organelles, facilitates cell and organelle movement, and plays a role in cell division

Centrioles

• Dense, granular structures located near the nucleus in animal cells, forming part of the centrosome
• Involved in cell division, helping form the spindle fibres that align and separate chromosomes during mitosis

Fluid Mosaic Model

• Describes the cell membrane as a flexible lipid bilayer with embedded proteins that regulate material exchange

Phospholipid Bilayer

• Cell membrane is composed of 2 layers of phospholipids
  • hydrophilic heads face outward
  • hydrophobic tails face inward
• Forms the basic structure of the membrane, providing selective permeability
• Allows flexibility and fluidity, enabling the membrane to change shape and repair itself

Cholesterol

• Lipid molecules interspersed between phospholipids in animal cells, increasing membrane flexibility and stability

Phytosterol

• Lipid molecules interspersed between phospholipids in plant cells; increases membrane flexibility

Membrane Proteins

• There are proteins embedded in the lipid bilayer
  • Integral proteins span the entire lipid bilayer and participate in transport, enzymatic activity, and cell signalling
  • Peripheral proteins are only partially embedded or associated with the surface of the membrane and help in cell recognition, signalling, and maintaining the cell shape

Transport Proteins

• Proteins that form channels or carriers in the membrane, facilitating the movement of specific molecules and ions across the membrane

Receptor Proteins

• Proteins embedded in the membrane that bind to specific signalling molecules, triggering cellular responses to external signals

Recognition Proteins

• Proteins with carbohydrate chains attached, involved in cell recognition and communication
• Serve as markers that help the immune system distinguish between "self" and "non-self" cells

Adhesion Proteins

• Proteins that anchor cells to each other or to the extracellular matrix, facilitating cell-to-cell interactions and maintaining the structural integrity of tissues

Diffusion

• The net movement of any molecules from a region of high concentration to a region of low concentration until equilibrium is reached
• Equilibrium is reached when there is no net movement of molecules in either direction
• Requires no energy input
• Concentration gradient: the bigger the difference between high and low concentration, the faster diffusion occurs
• Temperature: higher temperatures speed up diffusion because molecules move faster with more energy
• Small uncharged particles such as carbon dioxide and oxygen move easily through the semi-permeable cell membrane by simple diffusion

Facilitated Diffusion

• The process by which large or charged molecules pass through the cell membrane with the help of carrier or channel proteins without requiring energy occurs when;
• Relatively large molecules such as glucose and amino acids and charged particles such as sodium and chloride ions do not easily pass through the phospholipid bilayer of the cell membrane and require assistance
• Carrier proteins and channel proteins in the cell membrane help facilitate the movement of these substances

Osmosis

• A special type of diffusion and is the net movement of solvent molecules from a region of high solvent concentration to a region of low solvent concentration through a semipermeable membrane
• Is essential for biochemical reactions, maintaining cell shape, bathing tissues, and transporting materials
• Concentrated solutions have low water concentration, while dilute solutions have high water concentration
• Moves into the cell when external water concentration is higher and moves out of the cell when external water concentration is lower
• Osmotic pressure is the pressure created by water moving across a semipermeable membrane due to osmosis
• Tonicity refers to the relative concentration of solutes in a solution compared to the inside of a cell and determines the movement of water in and out of cells through osmosis
  • Isotonic: Equal solute concentration inside and outside the cell
  • Hypotonic: Lower external solute concentration, water enters the cell
  • Hypertonic: Higher external solute concentration, water exits the cell