Physiology of Marine Organisms Notes

Ch. 6 Physiology of Marine Organisms

History of Cell Structure

• Robert Hooke
  • Used a light microscope to view thin slices of cork.
  • Observed tiny, repeated units.
• Marcello Malpighi & Nehemiah Grew
  • Described and drew plant tissue.
• Antony van Leeuwenhoek
  • Drew and detailed animal cells.
• Matthias Schleiden & Theodor Schwann
  • Proposed the cell theory:
    • "All living things are composed of cells, the smallest structural unit of an organism."
• Ernst Ruska
  • Developed the first electron microscope in 1931.

Microscopes

• Light Microscopes

• Maximum Magnification: ~1500x
• Uses a light source (bulb or mirror).
• Focuses using glass lenses.

• Maximum Magnification: >200,000x
• Sends a beam of electrons.

• Magnification
  • Enlarging an image.
  • Total Magnification: calculated by multiplying all lens magnifications.
  • Staining: Binds to structures to enhance visibility.
    • Methylene blue: for animal cell nuclei.
    • Iodine: makes starch structures black.
• Resolution (Resolving Power)
  • Level of detail.
  • The minimum distance between objects to be seen clearly.
  • Depends on the wavelength of light used.
    • $Resolution = (wavelength \over 2)$
    • Light microscope maximum resolution: ~200nm

Cell Organelles (Structure and Function)

• Cell membrane
• Nucleus
• Rough & Smooth ER
• Ribosomes
• Golgi body
• Mitochondria
• Chloroplasts
• Cell Wall
• Vacuole

Cell Membrane

• Many membranes exist within cells:
  • Cell membrane itself
  • Nuclear membrane
  • Organelle membranes (Golgi, ER, etc.)
• Selectively permeable, controlling substance movement.
• Receives signals/instructions from other cells (hormone binding).
• Other specializations/structures (e.g., microvilli for absorption).
• Structure: Fluid-Mosaic Model
  • Phospholipids
  • Proteins
  • Cholesterol
  • Proteins are mobile within the bilayer.

Phospholipids

• Phospholipid Bilayer
• Composed of:
  • Glycerol backbone
  • 2 fatty acids (non-polar/hydrophobic)
  • Phosphate group (polar/hydrophilic)
• In water, phospholipids form micelles: tails cluster together, excluding water.

Proteins

• Embedded in the bilayer.
• Intrinsic Proteins: Extend through the bilayer.
  • Involved in substance transport.
  • Channel/Carrier Proteins:
    • Allow hydrophilic substances to pass through the hydrophobic membrane.
    • Typically selective for specific molecules.
• Extrinsic Proteins: Bound to the membrane surface.
  • Receptors for hormone binding.
  • Molecules for cell recognition.
  • Glycoproteins: proteins with attached carbohydrates.

Cholesterol

• Small lipid molecule between phospholipid tails.
• Maintains membrane fluidity:
  • Low Temperatures: prevents solidification.
  • High Temperatures: prevents excessive fluidity.

Nucleus

• Large organelle, visible with both light and electron microscopes.
• Present in animal and plant cells.
• Contains Chromatin: DNA/RNA and bound proteins.
  • Heterochromatin: Dark, inactive genes.
  • Euchromatin: Light, active genes.
• Nucleolus: site of ribosome synthesis.
• Nuclear envelope: double membrane.

Endoplasmic Reticulum (ER)

• Network of interconnecting membranes throughout the cytoplasm.
• Rough ER (rER)
  • Predominant type.
  • Flat membranes called cisternae.
  • "Rough" due to ribosomes on the surface (protein synthesis).
  • Proteins are packaged into vesicles and transported to the Golgi apparatus.
  • All secreted proteins are made this way.
• Smooth ER (sER)
  • Less abundant, lacks ribosomes.
  • Does not synthesize proteins.
  • Main function: Synthesizing steroid hormones (e.g., estrogen and testosterone).
  • Testis & ovary cells have abundant sER.

Ribosomes

• Small organelles in all cells, made of protein and RNA.
• Bacterial ribosomes are slightly smaller.
• Main function: Protein synthesis.
• Found free in the cytoplasm and attached to rER.
• Cells needing to produce lots of protein have abundant ribosomes and rER.

Golgi Body/Golgi Apparatus

• Stacks of cisternae.
• Involved in chemical modification of proteins (e.g., addition of carbohydrates).
• All secreted and membrane proteins pass through.
• Receives vesicles from rER on the Cis Face.
• Vesicles of modified proteins leave the Trans Face.
• Move to the membrane, fuse, and release proteins.
• Produces cell wall substances.
• Produces lysosomes (containing digestive enzymes).

Mitochondria - "The Powerhouse of the Cell"

• Main function: ATP production via aerobic respiration (in both animals and plants).
• Cells with high energy needs (e.g., muscle cells) have many mitochondria.
• Double membrane:
  • Inner membrane folded into cristae, surrounded by a fluid enzyme matrix.
  • Matrix contains ribosomes and chromosomes (suggesting symbiotic origin).

Chloroplasts

• Only found in plant cells; carry out photosynthesis.
• Large organelles, easily visible with light microscopes.
• Double membrane, enclosing an inner liquid stroma (containing enzymes and sugars).
• Thylakoid membranes in the stroma are stacked into grana (large surface area).
• Grana contain pigments (e.g., chlorophyll) that trap light energy.
• Starch grains are found in the stroma.
• Chloroplasts contain DNA and ribosomes.

Cell Wall

• Absent in animal cells (present in plants, fungi, bacteria).
• AICE Marine focus: cellulose cell wall of plants.
• Provides strength and structure, preventing cells from bursting.
• Main component: Cellulose (a polysaccharide polymer of β-glucose).
  • Long, straight, linear molecule that forms hydrogen bonds with other strands.
  • Cellulose molecules bond to form microfibrils, then fibrils, providing strength.

Cell Wall - Layers

• Middle Lamella: Outer layer.
  • Composed of calcium pectate (binds neighboring cells together).
  • Used in jam-making.
• Primary Cell Wall: First layer produced.
  • Fibers align in one direction.
  • Mixed with calcium pectate and hemicelluloses for firmness.
• Secondary Cell Wall: Produced after plant cells stop growing.
  • Fibers organized in different directions for extra support.
  • May contain Lignin (wood) or Suberin (cork).

(Large Permanent) Vacuole

• Fluid-filled sacs of membranes.
• Only plants have a large permanent vacuole.
• Surrounded by a Tonoplast membrane.
• Storage of:
  • Sap (salts and sugars).
  • Low water potential (encourages water entry for support).
• Storage of pigments, waste, or toxins.
  • Pigments give flowers color.
  • Some plants separate chemicals in the cytoplasm from chemicals in the vacuoles.
    • Example: Onions
      • Allinase (enzyme) in vacuole and Allinin in cytoplasm.
      • React to form Allicin (eye irritant) when cells are broken.

Drawing Rules - For Cells

• Only draw what you see.
• Use a sharp pencil.
• Draw guidelines with a ruler.
• Use unbroken, firm lines.
• Do not shade or sketch.
• Include scale bars and magnification if appropriate.
• Print all labels.
• Give the diagram a title.
• Do not draw the diagram too small.

Calculating Magnification

• Calculate magnification of photomicrographs and electromicrographs.
• Determine the size of a cell or structure.
• Calculating from a Diagram:
  • Measure the length of the image with a ruler.
  • Ensure same units for actual and image length.
  • Use formula: $Magnification = \frac{Image \ Length}{Actual \ Length}$
    • Example:
      • An elodea cell is 81.8 µm long in real life.
      • Image length is 90mm.
      • $Magnification = \frac{90,000 \mu m}{81.8 \mu m} = x1100$

Calculating Actual Length

• Calculating from a Diagram with Magnification:
  • Measure the image length with a ruler (mm).
  • Rearrange the magnification formula: $Actual \ Length = \frac{Image \ Length}{Magnification}$
  • Change units to micrometers (µm).
    • Example:
      • Mitochondria image length: 60mm
      • Magnification: x40,000
      • $Actual \ Length = \frac{60,000 \mu m}{40,000} = 1.5 \mu m$
• Calculating from a Diagram with a Scale Bar:
  1. Calculate the magnification
     • Measure the length of the scale bar with a ruler.
     • Divide the image length by the scale length (over the scale bar) to get the magnification
  2. Measure the length of the image.
  3. Use the rearranged Magnification formula to calculate actual length.
     • Example:
       • Diatom scale bar image length: 20mm
       • Actual scale bar length: 25µm
       • Diatom image length: 85mm
       • $Magnification = \frac{20,000 \mu m}{25 \mu m} = x800$
       • $Actual \ Length = \frac{85,000 \mu m}{800} = 106.25 \mu m$

Interpreting Diagrams

• Use structure to infer function.
• Lots of mitochondria: high energy needs (e.g., muscle cell).
• Lots of Golgi: produces/secretes proteins.
• Microvilli and mitochondria in small intestines (surface area and energy).

Movement of Substances (Across Membranes)

• Diffusion
• Facilitated Diffusion
• Active Transport
• Osmosis

Diffusion

• Molecules are constantly moving randomly due to kinetic energy.
• Passive process (no energy required).
• Moves based on the concentration gradient (high to low).
  • Higher chance of molecules moving from high to low.
  • The process never truly stops, but it reaches equilibrium.
• Factors impacting:
  • Temperature
  • Concentration Gradient
  • Distance
  • Surface area of exchange.

Facilitated Diffusion

• Charged/hydrophilic particles cannot pass through the nonpolar phospholipid tails.
• Requires special transport proteins:
  • Channel Proteins: intrinsic, inner pore for water-soluble molecules, selective (e.g., Sodium ion channel).
  • Carrier Proteins: intrinsic, molecules bind, protein shape changes, molecule is transported.
• Still a passive process (molecules move down the concentration gradient).
• The amount of proteins in the membrane is a factor that impacts the rate

Active Transport

• Pumping substances across the membrane using energy (ATP).
• Moves against the concentration gradient.
• Carried out by carrier proteins ("pumps").
  • Molecule binds, ATP binds and breaks down into ADP (releasing energy), protein shape changes, substance moves across, protein returns to original shape.
• Only happens in living, respiring cells.
• Cells performing lots of active transport need lots of mitochondria.

Osmosis

• Specific type of diffusion for water molecules across a membrane.
• Cell membranes have aquaporins (special proteins for water).
• Based on water potential (potential energy of water in a solution compared to pure water).
  • Water moves from high to low water potential.
  • Pure water has the highest water potential (0 kPa).
  • Dissolving a solute decreases water potential.
• Osmometer: models osmosis using Visking tubing (selectively permeable membrane).

Solutions Vs. Cells

• Terms describe solution water potential compared to cells/tissues.
• Hypertonic: solution has lower water potential than cells (water exits cells).
• Isotonic: solution has the same water potential as cells (no net movement).
• Hypotonic: solution has a higher water potential than cells (water enters cells).

Organisms and Osmosis

• Salinity changes can cause water gain/loss, leading to damage.
• Animal Cells:
  • No Cell Wall
  • Excess water can cause bursting.
  • Water loss can stop chemical reactions, causing cell death.
• Plant Cells:
  • Cell Wall
  • Cannot burst
  • Turgor pressure gives support.
  • Water loss pulls membrane away from wall, causing wilting.

Gas Exchange

• Organisms need oxygen for respiration and release carbon dioxide as waste.
• Diffusive process.
• Factors affecting gas exchange:
  • Temperature
  • Concentration gradient
  • Diffusion Distance
  • Surface Area
• Refers to gas exchange across membranes of gills (and similar).

Gas Exchange in Marine Organisms

• More challenging than in air.
• Oxygen concentration in water is ~40x lower than in air.
• Oxygen concentration is more variable in water:
  • Higher Temperature/Salinity = Less Oxygen
  • Lower Temperature/Salinity = More Oxygen
• Water is more dense and viscous than air.
• Gills have two openings, an inlet & outlet apature while lungs use the same aperture for both.

Size & Shape of Organisms Vs. Gas Exchange

• Large surface area (SA) needed for efficient exchange.
• As organism size increases, SA and volume (V) also increase, but not proportionally.
  • Higher SA = higher rate of diffusion
  • Higher V = lower rate of diffusion
• Larger organisms have more cells:
  • Higher demand for Oxygen
  • Higher distance between air and center cells
• Small organisms: No special adaptations.
• Larger organisms: Gills, lungs, protrusions, etc.
• Round = Lower SA/V Ratio
• Flat/Folded = Higher SA/V Ratio

Circulatory System

• Method for delivering/transporting gases around the body.
• Red blood cells (hemoglobin): bind reversibly with oxygen to form oxyhemoglobin.
• Route through Fish:
  • Blood passes through tissues in capillaries, releases oxygen, and gains carbon dioxide.
  • Blood returns to the heart in Veins.
  • Blood is pumped out of the heart in arteries towards the gills.
  • Blood passes through capillaries on the gills, releasing carbon dioxide and gaining Oxygen.
  • Blood leaves the gills in the arteries and travels to muscles to deliver oxygen (In Tissues)

Fick’s Law and Gas Exchange Organs

• $Diffusion \ Rate = \frac{Surface \ Area \times Concentration \ Gradient}{Diffusion \ Distance}$
• Organs follow this rule.
  • ∝ means proportional to
• Fick's law predicts common features of gas exchange surfaces:
  • Large surface area
  • Steep concentration gradient of Oxygen/Carbon Dioxide
  • Short diffusion distances

Gas Exchange Example - Coral

• No special structures, exchanges across body wall.
• Simple diffusion only.
• SA/V ratio can be effective due to tentacles and increased surface area structures.
• Some move tentacles to move/bring in more oxygenated water.
• Some polyps pass oxygenated fluid between themselves, evening distribution

Gas Exchange Example - Grouper/Tuna (Fish Gills)

• Fish take in water through their mouths and pass it over their gills, forcing it out through their gill opening
• Operculum- a bony gill cover, that can open and close
• Gills are made up of filaments, containing folds (↑SA) called lamellae full of capillaries
• Lamellae are organized at 90° angles to the filaments
• Fish have different oxygen needs
  • Fast, active swimmers have high demands, high SA, and high respiration rate
    • Tuna, Mackerel, Swordfish (Pelagic, constantly moving)
  • Less active fish have lower needs, lower SA, and often use anaerobic respiration
    • Sole, Plaice, Flounder (Stationary, quick burst predators)

Concurrent VS. Countercurrent Exchange

• Concurrent Exchange:
  • Equilibrium is reached and diffusion stops.
  • Less efficient
• Countercurrent Exchange:
  • Water and blood flow in the opposite direction.
  • Equilibrium isn't reached, diffusion is constantly taking place.
  • More efficient because more oxygen absorbed.

Ventilation Movements

• Water needs to be passed over the gills for respiration.
• Methods Used in Fish:
  • Ram Ventilation:
    • Fish swim with an open mouth, forcing water over gills.
    • No Muscle contractions.
    • No extra energy used/needed.
    • Drawback => Fish must keep moving/swimming constantly.
    • Sharks, Fast Swimming fish.
    • Some fish can switch between, EX: Tuna, Ram Vent. at high speeds but can switch to Pumped Vent. at lower speeds
  • Pumped Ventilation:
    • Use muscles in the buccal cavity (mouth space) to move water over the gills.
    • Requires energy, can be very costly.
    • Can still respire while not moving, allowing to remain in place.
    • Adjustable ventilation rates: Faster swimming requires more respiration.
    • Grouper, Goldfish, Majority of fish

Process of Pumped Ventilation - Inflow of Water

• Mouth opens
• Volume of buccal cavity increased by muscle contractions and relaxation
• Lowers the pressure inside the cavity, below external pressure
• Operculum closes as water tries to flow back across gills
• Outflow of Water
  • Mouth closes
  • Volume of the buccal cavity is reduced by muscle contractions and relaxation
  • Pressure inside the cavity rises above external pressure
  • Water flows over the gills and the operculum is forces open, allowing outflow of water
  • Remember:
    • Water always flows from HIGH => LOW pressure
    • As V increases, Pressure decreases (And vice versa)

Osmoregulation

• For organisms that live in the ocean, what is their environment's water potential?
• Many marine organisms are isotonic to the surrounding water, BUT if salinities change they can still be stressed by water loss/gain
• Stenohaline: organisms that only survive in a narrow range of salinities
• Euryhaline: organisms able to tolerate a wide range of salinities

Osmoconformers

• Organisms isotonic with their environment's salinity.
• Do not regulate internal salinity, just match the water around them.
• Most are stenohaline invertebrates:
  • Not tolerant of salinity changes, and stress/die if things change around them
• Mussels are euryhaline osmoconformers (often live in estuaries)
  • When salinity changes, mussels can close their shells tight, separating body tissues from the water
  • Increase/Decrease the solute concentrations of cells as the external salinity changes
  • Most still have a specific salinity they are restricted to, but have some control over osmoregulation happening

Osmoregulators

• Maintain (using energy) a consistent internal salinity
• Most Bony fish are Stenohaline osmoregulators
• In Freshwater Fish
  • Drinks little water
  • Passively absorbs water and loses salt through the skin.
  • Actively uptakes ions through gills (along with the water)
  • Excretes dilute urine
• In Marine Fish
  • Passively loses water and absorbs salt through the skin.
  • Drinks ample water
  • Actively excretes ions through gills (along with water)
  • Excretes concentrated urine

Marine Fish

• Water constantly enters through the gills and skin through osmosis.
• In order to prevent excess water:
  • Drink small amounts of water
  • Gills pump sodium and chloride ions into the blood fluids, Uses ATP to run pumps
  • Produce lots of dilute urine
• Low salinity water
• Hypotonic

Freshwater Fish

• Water is drawn out of the body and salt diffuses into the body
• Constant loss of water can lead to dehydration
• In order to prevent excess water loss:
  • Constantly drink seawater, to replace water loss
  • Sodium & Chloride ions are actively secreted by gills, pumps use ATP
  • Magnesium and Sulfate ions are actively secreted into the urine by kidneys
  • Reabsorption of water by kidneys, produce very concentrated urine
• High salinity water
• Hypertonic

Euryhaline Fish

• Salmon and Eels are osmoregulators that can tolerate large ranges of salinities
• They change the direction of their ion pumps depending on the salinity of the water around them
• When in salt water:
  • Water is hypertonic
  • Salts pumped out of gills
• When in freshwater:
  • Water is hypotonic
  • Salts pumped into gills