Physiology of Marine Organisms Study Notes

General Cell Structure and Historical Context

The Origin of Cell Biology: * The term cell was first utilized by the English scientist Robert Hooke (1635–1702). * In 1665, Hooke observed thin slices of cork using an early light microscope and noted they were formed of tiny, repeated units resembling the small rooms (cells) occupied by monks. * Marcello Malpighi (1628–1694), an Italian scientist, and Nehemiah Grew (1641–1712), an English plant scientist, described plant tissue structures via detailed drawings. * The first animal cells were described in 1676 by the Dutch microscopist Antony van Leeuwenhoek (1632–1723), who designed his own microscopes. * Van Leeuwenhoek referred to single-celled organisms as 'animacules' and identified structures in sperm cells and red blood cells.
The Formulation of Cell Theory: * In 1839, German scientists Matthias Schleiden (1804–1881) and Theodor Schwann (1810–1882) proposed that all living things are composed of cells and that cells are the smallest structural unit of an organism.
Evolution of Microscopy: * Development in the 19th and early 20th centuries identified internal organelles: cell wall, cytoplasm, cell surface membrane, nucleus, chloroplast, mitochondrion, and Golgi body. * In 1931, Ernst Ruska (1906–1988) developed the first electron microscope, allowing for much higher magnification and the discovery of the rough and smooth endoplasmic reticulum.
Verbatim Definitions: * Organelle: A specialized structure within a cell that has a specific function. * Cell: The smallest structural unit of an organism that is capable of independent functioning.

Microscopes, Magnification, and Resolution

Light Microscopes: * The primary tool in laboratory settings for observing living cells. * Uses a visible light source and glass lenses for magnification. * Typical maximum magnification is approximately $\times 1500$ . * Resolution: Limited by the wavelength of light; at best, it is approximately $200\,nm$ ( $0.0002\,mm$ ). * Staining: Used to visualize structures. Methylene blue stains animal cell nuclei; iodine stains starch-containing plant structures black.
Electron Microscopes: * Used in research institutes; utilizes a beam of electrons and electromagnets instead of light/glass. * Magnification can exceed $\times 200000$ . * Resolution: Higher resolving power, often less than $1\,nm$ (specifically $0.2\,nm$ ). * Limitations: Specimens must be in a vacuum (thus cannot be living), treated with heavy metals (lead or osmium), and equipment is expensive and requires high skill levels.
Technical Definitions: * Magnification: The process of enlarging the size of an image. * Resolution (Resolving Power): The smallest distance between two points that can be detected; a measure of visual detail. * Wavelength: The distance between two corresponding points of a wave.
Formula for Magnification: * $\text{total magnification} = \text{magnification of objective lens} \times \text{magnification of eyepiece lens}$ . * Example: A $\times 4$ objective and $\times 10$ eyepiece yields $\times 40$ .

Cell Organelle Structures and Functions

Cell Surface Membrane: * Selectively permeable boundary controlling substance movement. * Involved in cell signaling (e.g., binding hormones). * Specializations include microvilli in gut epithelial cells to increase surface area.
Nucleus: * Contains nucleic acids and proteins joined as chromatin. * Heterochromatin (darker areas) and Euchromatin (lighter areas, active genes). * Nucleoli: Circular areas inside the nucleus that synthesize RNA for ribosomes. * Nuclear Envelope: A double membrane containing nuclear pores.
Ribosomes: * Composed of protein and RNA; function is protein synthesis. * Found free in cytoplasm or attached to rough ER.
Endoplasmic Reticulum (ER): * Rough ER (rER): Covered in ribosomes; synthesizes, folds, and packages secreted proteins into vesicles. * Smooth ER (sER): Tubular structure without ribosomes; synthesizes steroid hormones (e.g., oestrogen, testosterone).
Golgi Body (Golgi Apparatus): * Consists of stacks of parallel membrane pouches called cisternae. * Modification: Adds carbohydrates to proteins. * Transport: Receives vesicles at the cis face and releases modified proteins from the trans face. * Lysosomes: Produces these membrane spheres containing digestive enzymes.
Mitochondria: * Cylindrical site of aerobic respiration; produce ATP. * Structure: Outer membrane, folded inner membrane (cristae), fluid matrix. * Contains circular DNA and ribosomes, suggesting symbiotic bacterial origins.
Chloroplasts (Plants Only): * Site of photosynthesis; contains stroma (enzymes/sugars) and thylakoid membranes stacked into grana containing chlorophyll.
Large Permanent Vacuole (Plants Only): * Surrounded by a tonoplast; stores cell sap (salts/sugars). * Maintains cell pressure (turgor) and stores pigments or waste products (e.g., allinase in onions).
Cell Wall (Plants Only): * Made of cellulose (polymer of $\beta$ -glucose). * Structure: Cellulose molecules $\rightarrow$ microfibrils $\rightarrow$ fibrils. * Layers: Middle lamella (calcium pectate glue), Primary cell wall (first layer), Secondary cell wall (inner layer for strength, sometimes containing lignin or suberin).

Calculation and Unit Conversions

Metric Magnitudes (Factors of $1000$ ): * $1\,m = 1000\,mm$ * $1\,mm = 1000\,\mu m$ * $1\,\mu m = 1000\,nm$
The Magnification Triangle: * $M = \frac{I}{A}$ * $A = \frac{I}{M}$ * $I = A \times M$ * Where $I = \text{image length}$ , $A = \text{actual length}$ , and $M = \text{magnification}$ .
Example Calculation from Scale Bar: * If scale bar image is $20\,mm$ and actual length is $25\,\mu m$ : * $\text{Magnification} = \frac{20000\,\mu m}{25\,\mu m} = \times 800$ . * If a diatom image measures $85\,mm$ : $\text{Actual length} = \frac{85\,mm}{800} = 0.10625\,mm = 106.25\,\mu m$ .

Movement of Substances

Diffusion: * Passive random net movement of particles from higher to lower concentration. * Factors: Temperature (kinetic energy), concentration gradient, distance, and surface area.
Facilitated Diffusion: * Passive movement of polar/hydrophilic molecules through channel proteins (pores) or carrier proteins (shape-shifting) across the hydrophobic bilayer.
Active Transport: * Movement against a concentration gradient requiring energy from ATP. * Uses specific carrier proteins (pumps).
Osmosis: * Net movement of water from higher water potential to lower water potential through a selectively permeable membrane via aquaporins. * Water Potential: Pure water has the highest potential ( $0\,kPa$ ); adding solutes makes it more negative. * Hypertonic: Higher solute concentration (lower water potential); water leaves cells. * Isotonic: Equal solute concentration; no net water movement. * Hypotonic: Lower solute concentration (higher water potential); water enters cells.
Biological Impact of Osmosis: * Animal Cells: Lack cell walls; shrivel in hypertonic solutions or burst in hypotonic solutions. * Plant Cells: Cell wall prevents bursting; hypotonic conditions create turgor pressure; hypertonic conditions cause plasmolysis (membrane peels from wall).

Gaseous Exchange Principles

Diffusion Parameters: * Proportional to Surface Area and Concentration Gradient; inversely proportional to Diffusion Distance (Fick's Law). * $\text{diffusion rate} \propto \frac{\text{surface area} \times \text{concentration gradient}}{\text{diffusion distance}}$ .
The SA:Vol Ratio: * $\text{SA:Vol Ratio} = \frac{\text{surface area}}{\text{volume}}$ . * Small organisms (protozoa) have high ratios and do not need gas exchange organs. * Large organisms have lower ratios and require gills or lungs.
Water as a Medium: * Oxygen in water is $40$ times lower than in air. * Solubility decreases as temperature and salinity increase. * Water is denser and more viscous, requiring more energy to move.

Specialized Gaseous Exchange Methods

Coral Polyps: * No specialized organs; diffusion occurs across the thin body epidermis. * High surface area provided by many tentacles.
Fish Gills (Groupers and Tuna): * Operculum: Protective bony flap covering gills. * Gill Arches: Support filaments (primary lamellae). * Secondary Lamellae: Folds on filaments that increase surface area and contain capillaries. * Pillar Cells: Slow blood flow in lamellae to facilitate exchange.
Counter-current Mechanism: * Blood and water flow in opposite directions, maintaining a diffusion gradient across the entire length of the gill.
Ventilation Types: * Ram Ventilation: Swimming with an open mouth (e.g., tuna, sharks). Saves energy but requires constant motion. * Pumped Ventilation: Active muscular pumping of the buccal cavity (e.g., grouper). Allows breathing while stationary but is energetically costly.

Osmoregulation in Marine and Freshwater Environments

Definitions: * Stenohaline: Cannot tolerate wide salinity changes. * Euryhaline: Can tolerate wide salinity changes (e.g., salmon). * Osmoconformer: Body fluid salinity matches external environment (e.g., mussels). * Osmoregulator: Actively regulates internal salinity.
Marine Bony Fish (Hypertonic Environment): * Lose water via osmosis; gain salts via diffusion. * Adaptations: Drink seawater, active secretion of $Na^+$ and $Cl^-$ via gills (ATP required), secrete $Mg^{2+}$ and $SO_4^{2-}$ in concentrated urine.
Freshwater Bony Fish (Hypotonic Environment): * Gain water via osmosis; lose salts. * Adaptations: Drink little water, active uptake of $Na^+$ and $Cl^-$ via gills, produce large volumes of dilute urine.
Salmon in Transition: * Able to reverse the direction of ion pumping depending on whether they are in the ocean ( $3.5\%$ salinity) or fresh water (<0.1\% salinity).

Case Studies and Ecological Implications

Case Study: The Lungfish: * Found in Australia, South America, and Africa. * Utilize lungs with small air sacs and rich blood supply. * Estivation: African lungfish can bury in mud for up to two years during dry seasons, dropping respiration rates significantly.
Case Study: The Aral Sea Disaster: * Originally the 4th largest lake; salinity was $10\,g\,dm^{-3}$ in 1960. * Diversion of Amu Darya and Syr Darya for cotton irrigation led to an $80\%$ volume decrease by 1998. * Salinity rose to $45\,g\,dm^{-3}$ (1998) and later even higher, killing native fish. * Ecological/Economic Impact: Loss of $40000$ fishing jobs; increase in respiratory diseases due to toxic salt dust storms. * Restoration: The North Aral Sea has seen partial salinity reduction and fish return due to a dam completed in 2005.

Questions & Discussion

Marine Survival and Environmental Change: * Q: How do changes to physical and chemical ocean nature impact survival? * A: Global warming increases temperature (lowering dissolved oxygen), pollution alters solute ratios, and increased $CO_2$ causes acidification.
Microscopy Comparison: * Q: Why were mitochondria and ribosomes not visible with Hooke's microscope? * A: Light microscopes lack the required resolution ( $200\,nm$ limit) and magnification to visualize small organelles like ribosomes which are visible only via electron microscopy.
Practical Inquiries: * Q: Why dry potato pieces before weighing? * A: To ensure that only the internal mass change is measured, rather than surface water clinging to the outside. * Q: What happens to red blood cells in pure water? * A: They would absorb water via osmosis and burst due to the lack of a cell wall.
Respiration and Activity: * Q: Why do deep-sea fish have low activity levels? * A: Potential adaptations to lower oxygen availability and pressures, requiring energy conservation.
Salmon Growth: * Q: Why do salmon in hypertonic water grow slower? * A: Significant energy (ATP) is diverted to active transport for osmoregulation (pumping salts out) rather than being used for somatic growth.