BIOL 1102 Midterm 2

Temperature affects rates of biochemical reactions which are catalyzed by enzymes, protein function, and membrane structure. Name four facts regarding this

1. temperature increases molecular motion + rate of reaction

2. enzymes have optimal performance temperature ranges

3. proteins denature at high temperatures

4. membranes can become rigid at low temperatures or leaky at high temperatures

Metabolism produces heat. What issues do large organisms face? Smaller organisms?

Larger organisms must get rid of heat while smaller organisms struggle with retaining heat

Elephant Example from class

elephants put mud on themselves and have big ears

• Big ears: high surface area to volume ratio → allows heat to dissipate through the ears 

Babies have “brown fat” that generates heat. Why is this important?

Babies cannot shiver as they have no muscles

endotherms

 rely on metabolic energy and physiological mechanisms to regulate body temperature

• Internal temperature can be very different from environmental temperature

• EX: mammals and birds

ectotherms

rely mainly on external energy sources to regulate body temperature 

• Internal temperature will match environmental temperature

• EX: Reptiles, many fish, invertebrate

heterotherms

Includes members of the above two categories who behave as endotherms sometimes, ectotherms other times

• EX: mammal that hibernates, groundhog 

Interpret Body Temperature of both the mouse and lizard with graph

Mouse: Across most of the natural temperatures, mouse temperature stays constant. After a certain point, the mouse becomes unable to regulate its temperature, and it rises

Lizard: The lizard’s body temperature directly correlates to the temperature of the surrounding boxes

What is metabolic rate?

how fast your body burns energy (calories)

Interpret Metabolic Rate of both the mouse and lizard with graph

Mouse: Metabolic heat rate decreases for mouse so that mouse can keep its body temperature constant 

• At cold temperatures, mouse needs a lot of energy to maintain body temperature

• As outside temperature gets closer to mouse’s internal temperature, mouse doesn’t need as much energy to keep body temperature constant 

• Thermoneutral zone: no additional metabolism is needed to maintain internal temperature of 37 degrees

• Rise in metabolic rate after 30 degrees = The mouse must cool itself (panting, sweating) so metabolic rate increases again 

Lizard: Don’t use any personal energy to generate heat 

• Get metabolic energy from the sun/environment (air, rocks, warm water, etc)

• Lowest temp = lowest environmental temperature 

• As environmental temperature increases, so does metabolic rate

Generally ectotherms are ____ and endotherms are ____

cold-blooded, warm-blooded

understand this picture

c:

Why don’t birds freeze when walking on ice?

Countercurrent heat exchange

Why is countercurrent heat exchange good?

1. While the blood in the foot gets really cold; it never actually gets to 0 so the blood is always flowing(or freezing) 

2. Blood that returns to body doesn’t cool down internal organs 

Explain what countercurrent heat exchange is + its advantage

• Warm blood travels down artery to feet and cold blood returns to body via vein

• The vessels are VERY close together → enables heat transfer from warm blood to cold blood (feet stay cold, body stays warm)

Advantage: system recycles heat before its lost to the environment; conserves energy and body heat 

At extreme temperatures, maintaining body temperature as an endo is ____

energetically costly

How is metabolic rate measured in endotherms?

consumption of O2 per unit

What is basal metabolic rate?

amount of energy your body is using when you aren’t doing anything extra

How do SA/V ratio differ in animals adapted to cold vs warm climates? Why?

SA/V determines how quickly an animal loses heat 

• Cold climates: LOW Surface Area to Volume (SA/V) ratio

  • Features: larger/more compact bodies, shorter limbs/ears, thick fur and insulation 

  • Reduced SA = less heat lost

• Warm climates: HIGH SA/V ratio

  • Features: long limbs or large ears, lean bodies, short fur

  • Increased SA = maximize heat dissipation + prevent overheating

selectively permeable membrane

membrane chooses what goes in and out of cell

hypertonic

outside of cell is more concentrated; water leaves cell

animal vs plant cell in hypertonic colution

animal cell: shrinks

plant cell: wilts (plasmolysis)

isotonic

same concentration in and outside; no net movement of water

animal vs plant cell in isotonic solution

animal cell: normal cell; ideal

plant cell: flaccid (not firm)

hypotonic

inside of cell is more concentrated; water moves in

animal vs plant cell in hypotonic solution

animal cell: cell swells/bursts (lysis)

plant cell: turgid (ideal)

If the solution is ___, the cells are ____

hypotonic, hypertonic —> inversely related

Cytosol: what is it? what is its significance?

intracellular fluid

• Since animal cells do not have a cell wall, they control their volume by maintaining a cytosol which is isotonic to the extracellular environment

Composition of cytosol and extracellular fluid are not identical. How are they different?

• Outside (extracellular fluid): High Na, Low K

• Inside (cytosol): High K, Low Na

goal: constant concentration between the extracellular and intracellular fluids

How can animal cells maintain their volume despite the constant movement of solutes in and out of the cell?

Sodium Potassium Pump

• If too many solutes enter an animal cell, cytosolic solute concentration would increase causing an influx of water and cell lysis

Explain how the sodium potassium pump works

1. 3 Na ions bind to cytoplasmic side of membrane (inside)

2. ATP hydrolyzed (ADP + P) and phosphate attached to pump → acts as energy

3. Phosphorylation causes pump to change shape and3 Na ions are released outside cell

4. 2 K+ ions bind to pump from extracellular (outside)  side

5. Phosphate group detaches from pump and pump returns to original 

6. 2 K+ ions are released into the cytoplasm (inside)

Main Points

1. 3 NA out, 2 K in

2. ATP as energy (active transport)

3. Goal: maintain concentration gradient / prevent swelling

How do plant cells control cell volume?

Plant cells (plant, bacteria, fungi) have a rigid cell wall that limits change in cell volume

• Influx of water when placed in a hypotonic solution leads to an intracellular increase in pressure, but not volume

• extracelullar space is hypotonic so water tends to move into plant cells

water potential

potential energy of water; quantifies tendency of water to move from one area to another (high to low)

water potential of pure water (open container) is ___?

zero

In what direction does water move?

• water moves towards more negative water potential

• moves from HIGH to LOW concentration

More free water molecules means what?

higher water potential

More solute = more ___ Ψ

negative (solutes bind water, lowering its ability to move) 

Water Potential Equation

Water potential = pressure potential + solute potential

• Ψ = Ψ_p + Ψ_s

As water enters a plant cell, pressure potential increases

solute potential

Adding solutes lowers the water potential; the higher the solute concentration, the lower (more negative) the solute potential.

• More solute = more negative ψs

• Less solute = less negative ψs

the solute potential of pure water is zero 

pressure potential

as plant cells take up water, they swell, but cell walls provide resistance which produces a pressure potential (greater pressure inside cell than out).

Pressure potential within a plant cell is typically ____. Explain how pressure potential could be both positive and negative.

positive

• Can be positive or negative 

  • Positive = pushing (EX: turgor pressure in plant cells)

  • Negative = pulling force (EX: water being pulled up xylem)

True or false? When water potential = 0 → no more water can enter the cell

True

Difference in water potential in turgid vs flaccid cell

Turgid Cell: ψ is 0  |  Flaccid Cell: ψ is - 

• Flaccid cell would have a lower pressure potential than a turgid cell

If isolated plant cells with water potential of -0.5MPa are placed into a solution with water potential of -0.3MPa, what is the outcome?

Water potential will flow into the cell and pressure potential will increase 

Value for water potential in root tissue was found to be -0.15MPa. If you place tissue in sucrose solution with water potential -0.23MPa, water flow would be ___

Root Tissue → sucrose solution 

Which of the following will happen if a plant cell decreases its cytoplasmic solute concentration?

Less Ψs = less negative Ψs = higher Ψ = water moves OUT of the cell

look at canvas for extra optional water potential practice question!!

c:

osmotic pressure

pressure that must be applied to solution to prevent inward flow of water across semipermeable membrane

turgor pressure

osmotic pressure within plant cells that pushes plasma membrane against cell wall; keeps plants upright 

osmoregulation

regulation of osmotic pressure or water content; keeps internal fluids from becoming too concentrated (high osmotic pressure) or too dilute (low osmotic pressure)

What happens when osmotic pressure is too high? Too low?

• Too high: can damage cell, sometimes even causing it to burst and thus disrupting some of the animal’s functions

• Too low: excessive dehydration impairs a cell’s metabolic function

To regulate water and solute levels, the cell controls the solute concentration of the inside of the cell relative to the solute concentration outside of the cell

osmoconformer

do not regulate internal osmolarity; changes with the environment 

• EX: mussels

osmoregulator

 regulate internal osmolarity 

• EX: brine shrimp 

True of False? Like endotherms, osmoregulators must adapt to their environments

true

Define hypoosmotic, its issue, and the solution

 lower solute concentration, higher free H2O concentration; freshwater

• Issue: water enters the body

• Solution: excrete excess water (urine)

Define hyperosmotic, its issue, and the solution

 higher solute concentration, lower free H2O concentration; salt water

• Issue: water leaves the body

• Solution: drink and/or retain water

Why is the ocean dehydrating to most animals?

Because ocean is so much saltier than internal fluids, water is lost from their bodies by osmosis 

Marine bony fish are hypoosmotic to seawater. What does this mean and how do they osmoregulate?

Issue: Hypoosmotic to seawater → constantly lose water and gain salt by diffusion + food they eat 

Solution: drink seawater, transport Cl ions out through skin and gills, very little urine 

Freshwater fish are hyperosmotic to seawater. What does this mean and how do they osmoregulate?

Issue: hyperosmotic to water → constantly gaining water by osmosis and losing salt by diffusion

Solution: large amounts of dilute urine, regain salts in food and active uptake of salts from surroundings

Why do plants need water? (3)

Transpiration and water balance in plants 

1. Photosynthesis: water is split (photolysis) to release electron to replace one in reaction center chlorophyll molecule that enters light reactions

2. Cell Structure: Interior of plant cells + compartments are filled with water (turgor pressure)

3. Nutrient Transport: Plants absorb minerals dissolved in water from soil

Importance of plant root hairs

root hairs increase SA, enabling plant to absorb more water + minerals from soil 

What is the trade off between CO2 Diffusion and Water Loss?

To get CO2, plant stomata must open. When plant stomata opens, water vapor escapes (transpiration) 

CO2 diffuses 10000x ___ in water than it does air

slower

Since CO2 diffuses much slower in water, how do plants work around this?

To assimilate a lot of CO2 in photosynthesis (efficiency!), chloroplasts must be close to air spaces inside leaf 

• Leaves contain internal air spaces in spongy mesophyll 

  • Enable CO2 to diffuse quickly to photosynthetic cells 

  • Inside cells, everything is surrounded by water/cytoplasm, so CO₂ would move very slowly if it had to travel far through water → air spaces in spongy mesophyll

How much water taken up is actually used by the plant?

~5%

What 2 forces enable water molecules to form continuous column in xylem?

1. Cohesion: water molecules stick to each other

2. Adhesion: water sticks to xylem walls

Path of water from xylem to stomata?

xylem → mesophyll cells → stomata

• evaporation causes tension (negative pressure) that pulls water up xylem

What is the xylem? 2 types of xylem cells?

1. tracheids

2. vessels

Both are tubular, elongated cells that have cell walls made of hardened lignin and are dead 

• Xylem cells are dead at maturity (no cytoplasm or organelles) 

tracheids

• long, thin cells with tapered ends (end gets narrower/pointy)

• Water moves from cell to cell through pits along their length

vessels

• Wider, shorter, thinner-walled, and less tapered than tracheids

• Align from end to end, forming pipes called vessels 

How is water transported through xylem?

uses negative pressure; sucked up, not pushed

• Cohesion-tension theory

What is the cohesion-tension theory?

• Relies on fact water is polar 

• Water is constantly lost by transpiration in lead. When one water molecule is lost, another is pulled along 

What is cavitation?

when a plant cannot supply xylem with adequate water so xylem gets an air bubble or embolism 

What causes cavitation?

Because of the tension from tension (negative pressure) inside xylem, air bubbles can form (cavitation). If this occurs, the continuous water column breaks and water transport stops.

conditions that lead to cavitation

• Hottest part of the day 

• Freezing conditions: solubility of gas in ice is very low, gas comes out of solution when water in xylem freezes

adaptations to minimize cavitation

• Pits in xylem allow water to move laterally from cell to cell

• Plates in between xylem cells trap air bubbles 

• Trachieds have narrower diameter than vessels → avoid cavitation because narrower column of water is better ablet o resist bubble formation/rupture 

• Narrower diameter = more stable water column = surface tension holds water together better = less prone to cavitation

trade off in type of xylem

• Tracheids: slower water transport but safer from cavitation 

• Vessels: faster water transport but higher cavitation risk 

stomata

pores on plant’s surface 

stomata is the site of ___

CO2 diffusion AND water → must balance need for CO2 and water conservation 

guard cells

change shape to open/close pore; each stoma is surrounded by two guard cells 

Stomata behavior for turgid guard cell vs flaccid guard cell

• Turgid guard cell = stomata open 

• Flaccid guard cell = stomata closed 

In general, when is the stomata opened? Closed?

In general, stomata are open during the day when light is available for photosynthesis. At night, when CO2 uptake is not necessary, stomata close to prevent water loss.

Conditions that cause stomatal opening/closure (4)

1. Light: blue light receptors in plasma membrane of guard cells sense light → guard cells take in K+ ions → water enters → cells become turgid → stomata open 

2. Low CO2 inside leaf: Low CO₂ signal → plant needs more CO₂ → stomata open

3. Internal Circadian Clock: plants naturally open stomata during day 

4. Drought Stress: water stress → ABA → stomata close

Conditions that cause evaporative water loss

1. Open stomata

2. Low relative humidity 

• If outside air is dry, since water moves HIGH → LOW, water evaporates out quickly 

3. Wind: wind blows away boundary layer 

• Boundary Layer: thin layer of moist air around leaf 

• Wind → removes moist boundary layer → faster transpiration

Adaptations to minimize water loss (4)

1. Reduce leaf surface area 

2. Boundary layer protection → traps humid air 

3. Sunken stomata → protects stomata 

4. Thick waxy cuticle

Fick’s Law of Diffusion

Define all the variables in Fick’s Law of Diffusion Equation

Q: rate of diffusion

D: diffusion coefficient (how easily molecule moves)

A: surface area of membrane

P1, P2: difference in partial pressure OR concentration

L: path length between locations / thickness of membrane

What changes would increase gas exchange across surfaces? Explain (3)

1. Surface Area Increases

• more area = more space for diffusion

2. Partial Pressure Difference Increases 

• Bigger gradient = faster diffusion 

3. Diffusion Path Length Decreases

• Decreased distance = more diffusion (thin barrier)

How does the body keep refreshing gases on each side of the membrane? (increasing partial pressure gradients) (2)

1. increasing partial pressure difference (P1-P2)

2. reducing diffusion path length (L)

increasing partial pressure difference (P1-P2)

• Ventilation (breathing): active movement of respiratory medium (air or water) over gas exchange surfaces; increases P1

  • Keeps fresh O2 rich air outside = stronger gradient

• Perfusion (circulation): active circulation of blood over the gas exchange surfaces; decreases P2 

  • Blood removes O2 quickly from exchange surface 

ventilation keeps O2 high outside and perfusion keeps O2 low in blood to keep steep gradient = fast diffusion

Reducing Diffusion Path Length (L)

gases are carried close to target tissues by respiratory and circulatory systems → decreases path length to target tissues

Fish and Gas Exchange: How do they do it?

Bony fish use countercurrent flow through their gills to maximize gas exchange → water flows in one direction and blood flows in the other 

1. Water enters mouth 

2. Water flows over gills

3. Water exits under opercular flap

blood inside gills flows opposite direction of water

Gill Structure

• Made up of gill filaments that are covered by folds (lamellae) which are very thin

• Constant water flow maximizes O2 partial pressure on external gill 

lamellae

folds that are the site of gas exchange; minimize diffusion path length (L) between blood and water 

• Very thin; filled with capillaries (blood vessels)

• Large SA and short diffusion distance = faster diffusion 

Explain how the gills work

Gill arch (main support) → gill filaments (long branches) → lamellae (tiny folds where gas exchange occurs)

• Deoxygenated (afferent) blood enters, oxygenated (efferent) blood leaves 

Key: Countercurrent flow improves diffusion efficiency

Respiratory System in Humans

Breathe → trachea → bronchi → bronchioles → alveoli (air-filled sacs)

Identify P1, P2, A, L in humans

• P1: inside alveoli (O2 exchange)

• P2: outside of alveoli (pink stripes on branches that lead to alveoli)

• A: surface area of alveoli → cluster has great SA

• L: distance between interior of alveoli and blood in capillaries (where diffusion/exchange is actually happening)

Identify P1, P2, A, L in fish

• P1: partial pressure in water flowing over gill lamellae

• P2: in blood entering gill capillaries

• A: gill filaments + lamellae (large SA)

• L: distance between water and blood across thin gill epithelium

emphysema

condition caused by smoking, air pollution, and other factors

• Develops over time and invlves gradual damage of lung tissue (destruction of alveoli)

What parameters of Fick’s Law would be affected by emphysema? How would gas exchange be affected?

emphysema reduces SA available for gas exchange due to destruction of alveolar walls

• Q and A decreases, L increases, gradient may decrease