Seminar 19: Multicellularity - origins & consequences Flashcards
(28 cards)
How to estimate when multicellularity evolved?
- Molecular clock data: technique used to estimate the time when 2 or more life forms diverge, based on mutation rate of DNA.
- Infer that last common ancestor of plants & animals are likely unicellular - Evolutionary tree via fossil record
Limitations to the way of estimating when multicellularity evolved?
Fossil record is incomplete, unaware if the common ancestor of plants & animals was single or multicellular
Benefits of multicellularity (3):
- Can undergo many functions at a given time (Division of biological labour so cells can be better at their job, more efficient)
- Increased complexity
- Shift higher in ecological system (avoid being prey)
Define diffusion
the passive movement of substances down their concentration gradient (req no energy).
What alters diffusion rate?
The molecule’s relative hydrophobicity
- more non-polar & negative = increased diffusion
- Charged ions & non-lipid soluble proteins can’t diffuse through the bilayer
What ensures that a dynamic equilibrium is maintained?
Random motion
- it causes particles to move across bilayer at a constant rate, no net movement to achieve dynamic equilibrium.
Define osmosis
the movement of only H2O across a semipermeable membrane down its conc gradient. High H2O conc > low until the gradient equalises
Define H2O potential
tendency of a solution plus the solutes in it to take up H2O from pure H2O across a membrane
- A lower/more negative the H2O potential, the greater the driving force for H2O movement across the membrane
What units of measurement for H2O potential?
Megapascals (MP a) = unit of pressure
What are the 2 components of H2O potential?
- Solute potential : the GREATER the conc of solutes the LOWER the potential
- Usually negative - Pressure potential : the GREATER the internal pressure, the HIGHER the potential
- Swelling occurs when a CLOSED compartment takes up H2O
- Usually positive
Water potential eqn =
Solute potential + Pressure potential
What is the plant equivalent to pressure potential?
Turgor potential
What happens under LOW TURGOR PRESSURE?
H2O will enter a plant cell by osmosis due to low solute potential
- Because overall, there is more NEGATIVE H2O potential in the cell compared to the external water
- H2O movement will continue until the turgor pressure increases to a point where it EXACTLY BALANCES the solute potential (no net flow of H2O in/out of the cell)
Why does SA:V affect the rate of exchange w/ external environment?
Because there is fewer contact w/ the external environment
- thus less opportunity for exchange as less of the interior of the organism is exposed to the external environment
What are the ways organisms evolved to deal w/ SA:V problem? (2)
- Evolution of internal aqueous environ
- Evolution of circulatory system
Desc the evolution of internal aqueous environ, how it alters SA:V:
allows exchange needs to be met as extracellular fluid that surrounds cells enables diffusion of respiratory gases, nutrients & wastes.
- Internal aqueous environ generated by a barrier (specialised cells on surface - epidermal cells)
- Internal environ kept stable by homeostasis
Desc the evolution of a circulatory system, how it alters SA:V
facilitates efficient exchange b/w cells of body & extracellular fluid & exchange organs to cells.
- Ensures high conc gradients for diffusion to occurs @ max rate, as pressure req to move fluids through transport system via “bulk flow”
- Highly branched which allows every cell of large plant/animal to be reached
- This increases the amount of force req to push extracellular fluid through
- The vessels of the transport system. In animals: use pumps (active process), plants: transpiration (passive
Features of exchange surfaces: (2)
- Large SA: flat, long, folded, branched
- Thin surface w/ small diffusion distance
Example of an organ w/ highly extensive exchange surface: (explain why its features allow this)
Lungs (high SA, maximised partial pressure gradient)
- lungs are well vascularised, lots of capillaries around air sacs
- able to maintain partial pressure gradient via continual breathing
- thin barrier of moisture to minimise diffusion distance as diffusion coefficient for respiratory gases is HIGHER in air than liquid
Equation for Fick’s law:
SA x Partial pressure gradient x Diffusion coefficient / Diffusion distance
Explain partial pressure gradient:
- Partial pressure is proportional to a gases’ conc in a medium (e.g air or H2O), - gradient = differences in the partial pressures at the 2 locations where diffusion is occurring
Explain diffusion coefficient:
solubility of a gas in a liquid & in air, diff for each gas
Explain diffusion distance:
length gas has to travel
When will high rates of diffusion occur? (refer to Fick’s law)
when there is high SA & high partial pressure gradient & a small diffusion distance (fully maximize rate of diffusion)
