Comprehensive Study Guide: Cell Biology, Microscopy, and Transport

Core Cell Biology Fundamentals

Function of Cell Organelles - Mitochondria: The organelle where aerobic respiration occurs, providing energy for the cell. - Ribosomes: The site of protein synthesis within the cell. These can be found located in the cytoplasm. - Cell Membrane: A structure that controls the movement of substances into and out of the cell. It is found in both plant and animal cells. - Nucleus: Contains the genetic material (DNA) of the cell and controls the cell’s activities. - Cytoplasm: A jelly-like substance where most chemical processes and reactions take place. - Cell Wall: A rigid outer layer made of cellulose (in plants) that provides structural support; it is not found in animal cells. - Vacuole: A large sac filled with cell sap that helps keep the plant cell rigid and maintains its shape. - Chloroplasts: Green organelles containing chlorophyll which absorbs light energy for photosynthesis to make glucose for the plant.
Chemical Equations - Aerobic Respiration: - Word Equation: $\text{Glucose} + ext{Oxygen} \rightarrow ext{Carbon Dioxide} + ext{Water} + ( ext{Energy})$ - Balanced Symbol Equation: $\text{C}<em>6 ext{H}</em>{12} ext{O}<em>6 + 6 ext{O}_2 \rightarrow 6 ext{CO}_2 + 6 ext{H}_2 ext{O}$ - Photosynthesis: - Word Equation: $\text{Carbon Dioxide} + ext{Water} \xrightarrow{ ext{Light/Chlorophyll}} ext{Glucose} + ext{Oxygen}$ - Balanced Symbol Equation: $6 ext{CO}_2 + 6 ext{H}_2 ext{O} \rightarrow ext{C}_6 ext{H}</em>{12} ext{O}_6 + 6 ext{O}_2$

Levels of Organisation

Hierarchical Structure (Smallest to Largest) 1. Organelles: Small structures within cells (e.g., mitochondria). 2. Cells: The basic building block of all living organisms. 3. Tissues: A group of cells with a similar structure and function working together. 4. Organs: A group of different tissues working together to perform a specific function. 5. Organ Systems: A group of organs working together to perform a specific function (e.g., the circulatory system). 6. Organism: A living thing formed by several organ systems working together.
Example: Circulatory System Flow Chart - Specialized Heart Muscle Cells $\rightarrow$ Heart Tissue $\rightarrow$ Heart (Organ) $\rightarrow$ Circulatory System $\rightarrow$ Human (Organism).

Microscopy Development and Technology

Historical Context - Until 1665, cells were unknown to science. The invention and subsequent improvement of the microscope allowed scientists to see into cells, which is essential for studying diseases and finding cures. - The word "micro" means extremely small, and "scope" refers to a device used to see something.
Microscope Components and Functions - Eyepiece Lens: The lens at the top that you look through; it magnifies the image. - Objective Lens: Enhances the magnification of the eyepiece lens. - Stage: The flat platform where the slide with the specimen is placed for observation. - Light Source: Provides light to see the image. - Focusing Wheel: Used to clarify/focus the image. - Condenser: A component used to focus the light onto the specimen.
Light Microscopes vs. Electron Microscopes - Light Microscope: - Uses light and lenses to magnify specimens. - Small, cheap, and easy to move. - Can be used to view living samples. - Can produce color images. - Maximum magnification: $\times 1500$ . - Electron Microscope: - Uses a beam of electrons instead of light. - More useful for scientific research because of higher resolution. - Can only view dead/non-living samples. - Maximum magnification: $\times 1,000,000$ . - Higher resolution allows for the viewing of sub-cellular structures like bacteria or the internal details of organelles.
Key Definitions in Microscopy - Magnification: The number of times larger an image is compared to the real object. - Resolution: The clarity or detail of an image; the ability to distinguish between two different objects that are close together.

Mathematical Calculations and Unit Conversions

Measurement Units and Rules - $1\,\text{cm} = 10\,\text{mm}$ - $1\,\text{mm} = 1000\,\mu ext{m}$ (micrometre) - $1\,\mu ext{m} = 1000\,\text{nm}$ (nanometre) - Rule for conversion: - Multiply by $1000$ to convert from a larger unit to a smaller unit (e.g., $\text{mm}$ to $\mu ext{m}$ ). - Divide by $1000$ to convert from a smaller unit to a larger unit (e.g., $\mu ext{m}$ to $\text{mm}$ ).
Magnification Formula - $\text{Magnification} = \frac{\text{size of image}}{\text{size of real object}}$ - $\text{Size of Real Object} = \frac{\text{size of image}}{\text{magnification}}$ - $\text{Size of Image} = \text{magnification} \times \text{size of real object}$ - Note: Units must be consistent (equal) before performing divisions.
Standard Form - A method for writing very large or very small numbers simply using powers of 10. - Positive powers move the decimal to the right; negative powers move the decimal to the left. - Examples: - $1,500,000 = 1.5 \times 10^{6}$ - $0.0000054 = 5.4 \times 10^{-6}$ - Average bacterial cell ( $0.000002\,\text{m}$ ) is written as $2 \times 10^{-6}\,\text{m}$ .

Eukaryotic and Prokaryotic Cells

Eukaryotic Cells - Definition: Complex cells containing a nucleus that encloses the genetic material. - Examples: Animal, plant, fungi, and protista cells. - Features: - Genetic material (DNA) forms structures called chromosomes. - Size range: $10\text{--}100\,\mu ext{m}$ in diameter. - Contain membrane-bound organelles (e.g., mitochondria).
Prokaryotic Cells - Definition: Simpler cells that evolved earlier; "pro" means earlier than, "karyo" means nucleus. They do not have a nucleus. - Examples: Bacterial cells. - Features: - Genetic material is free-floating in the cytoplasm (nucleoid). - May contain extra small rings of DNA called plasmids. - Size range: $0.1\text{--}5\,\mu ext{m}$ in diameter. - Cell wall does not contain cellulose. - May have a flagellum (for movement), a capsule, and a cell wall.

Cell Specialisation and Differentiation

Definition of Cell Differentiation - The process by which a cell develops and matures to become a specialised cell with a specific shape and function. There are approximately 200 different types of specialised cells in the human body.
Specialised Cell Examples and Adaptations - Red Blood Cells: Biconcave shape to increase surface area for oxygen absorption; no nucleus to make more room for haemoglobin. - Sperm Cells: Long tail (flagellum) for swimming; many mitochondria for energy; acrosome containing enzymes to penetrate the egg. - Muscle Cells: Contain many mitochondria to provide energy for contraction. - Root Hair Cells (Plant): Large surface area to maximize the absorption of water and minerals from the soil. - Nerve Cells: Long axons to carry electrical signals over distances.

Diffusion and Surface Area to Volume Ratio (SA:V)

Diffusion - Definition: The passive movement of particles from an area of high concentration to an area of low concentration until they are evenly distributed. - Factors Affecting Rate: 1. Temperature: Higher temperatures increase kinetic energy, making particles move faster. 2. Concentration Gradient: A larger difference in concentration leads to faster diffusion. 3. Surface Area: A larger surface area allows more room for particles to diffuse. 4. Diffusion Distance: Thinner surfaces/membranes result in a shorter distance for diffusion.
Biological Reliance on Diffusion - Oxygen diffusing into the body via alveoli. - Digested food particles diffusing into villi in the small intestine. - Carbon dioxide diffusing into leaves via stomata for photosynthesis.
Surface Area to Volume Ratio Calculations - $\text{Surface Area} = (\text{length} \times \text{height}) \times \text{number of sides}$ - $\text{Volume} = \text{length} \times \text{width} \times \text{height}$ - $\text{SA:V Ratio} = \frac{\text{Surface Area}}{\text{Volume}}$ - Implication: As cells increase in size, their SA:V ratio decreases. Very large cells cannot get enough raw materials (like oxygen) through their surface fast enough to reach the centre, which limits cell size.

Osmosis

Definition - The movement of water molecules across a partially permeable membrane from an area of higher water potential (dilute solution) to an area of lower water potential (concentrated solution).
Types of Solutions - Isotonic: The water potential outside the cell is the same as inside the cytoplasm; there is no net movement of water. - Hypotonic: The water potential outside the cell is higher than inside. Water enters the cell. - Animal cells: May swell and undergo lysis (burst) because they lack a cell wall. - Plant cells: Become turgid (swollen), as the cytoplasm pushes against the cell wall. - Hypertonic: The water potential outside the cell is lower than inside. Water leaves the cell. - Animal cells: Become crenated (shrivelled). - Plant cells: Become plasmolysed; the cytoplasm pulls away from the cell wall.
Required Practical: Measuring Water Potential in Potato Tissue - Procedure: 1. Extract potato cores using a cork borer and trim to equal length ( $2\,\text{cm}$ ). 2. Measure initial mass and length of each core. 3. Place cores in solutions of varying sucrose/salt molarities ( $0\,\text{M}$ , $0.2\,\text{M}$ , $0.4\,\text{M}$ , $0.6\,\text{M}$ , $0.8\,\text{M}$ ). 4. Leave for a set time (e.g., 20 minutes). 5. Remove, blot dry (to remove excess surface water), and re-weigh. 6. Calculate percentage change in mass: $\frac{\text{Final Mass} - \text{Initial Mass}}{\text{Initial Mass}} \times 100$ - Safety: Scalpels and cork borers are sharp; cut away from the body onto a white tile or chopping board.

Active Transport

Definition - The movement of substances against a concentration gradient (from an area of low concentration to an area of high concentration). This process is active, meaning it requires energy (ATP) released during respiration. - It utilizes carrier proteins within the cell membrane.
Biological Examples - Plant Roots: Root hair cells use active transport to absorb mineral salts from the soil when the concentration of minerals in the soil is lower than inside the cell. - Intestines: Cells lining the intestine use active transport to absorb glucose into the blood even when the concentration gradient is reversed.

Questions & Discussion

Plant and Animal Cell Comparison Quiz - Q: What is the function of the vacuole and what does it contain? - A: It contains cell sap and helps maintain the cell's shape and rigidity. - Q: Name a reaction that takes place in the cytoplasm. - A: Anaerobic respiration (or various chemical processes).
Microscopy Practice - Q: Why don't airlines advertise distances in centimeters? - A: The numbers would be too large and difficult to manage; kilometers provide a more practical scale for human understanding, just as micrometers and nanometers are necessary for microscopy.
Cell Structure Evaluation - Scenario: Student A labels the nucleus of an animal cell correctly. Student B points to a different area. - Discussion: The nucleus is the large, central organelle. Any label pointing to the outer boundary is the cell membrane, not the nucleus.
Diffusion vs. Osmosis vs. Active Transport Discussion - Q: How is osmosis different from diffusion? - A: Osmosis involves water molecules only and must pass through a partially permeable membrane. - Q: Does active transport require energy? - A: Yes, it requires energy (ATP) from respiration because it moves particles against the concentration gradient. - Q: What is the impact if a red blood cell was not biconcave? - A: It would have a smaller surface area to volume ratio, making oxygen exchange less efficient.