BIOG 1440 Prelim 2

What is symbiosis?

The living together between organisms; interaction and possibly co-evolution with associated microbes

What is mutualism?

A symbiotic relationship where BOTH organisms benefit (e.g. flower gets pollinated, bee gets nectar)

What is commensalism?

A symbiotic relationship where one organism benefits and the other is UNAFFECTED (e.g. barnacles on a whale)

What is parasitism?

A symbiotic relationship where one organism benefits and the other is HARMED (e.g. tick feeding on a cat)

What is the endosymbiotic theory?

The theory that the eukaryotic cell arose from a symbiotic union of primitive prokaryotic cells

How did mitochondria evolve according to endosymbiotic theory?

A primitive prokaryote engulfed an O2-respiring bacterium but didn't break it down; the ingested prokaryote gave rise to mitochondria

How did chloroplasts evolve according to endosymbiotic theory?

Same as mitochondria, but the ingested prokaryote was an oxygenic phototrophic bacterium that gave rise to chloroplasts

What are endosymbionts?

Microbes that reside WITHIN the cells of an organism (endo- = in); e.g. Rhizobium bacteria inside legume root nodule cells

What is microbiota?

The diverse community of microorganisms associated with a host, living ON or IN the host

What is the rhizosphere?

The region surrounding plant roots (rhizo- = associated with roots/plants)

What is the plant microbiota?

Communities of microorganisms on leaf surfaces and in the rhizosphere

What is the human microbiota?

Microbes living in or on the human body

Does a healthy human microbiome have intracellular bacteria (endosymbionts)?

No — endosymbionts are found only in certain diseases in humans

What are PGPRs?

Plant Growth-Promoting Rhizobacteria; produce antibiotics that protect plants from disease and help increase nutrient availability

What are AMF?

Arbuscular Mycorrhizal Fungi; mutualistic symbiosis between plants and fungi that increases nutrient availability

What forms of nitrogen can plants absorb?

NO3– (nitrate) and NH4+ (ammonium) — NOT N2 gas

What do nitrogen-fixing bacteria do?

Generate NH4+ from N2 gas

What do nitrifying bacteria do?

Generate NO3– from NH4+

What do ammonifying bacteria do?

Also generate NH4+

What is the Legume-Rhizobium symbiosis?

The most efficient mutualism between plants and N2-fixing bacteria; Rhizobium gets sugar from the plant, plant gets fixed nitrogen from Rhizobium

What is the agricultural benefit of the Legume-Rhizobium symbiosis?

Legume crops rotated with other crops restore nitrogen to the soil; generates more usable nitrogen than all industrial fertilizers today

What chemical signals do root cells release to initiate the Legume-Rhizobium relationship?

Flavonoids

How do Rhizobia respond to flavonoids?

They produce Nod factors (signals sent back to the plant)

What do Nod factors do?

Alter root cell activity to allow formation of nodules where Rhizobium bacteria can live

How many microbes are on your body per square inch?

Millions

How does the number of microbial cells compare to human cells?

Your body hosts more microbial cells than human cells (~30 trillion human cells vs. ~100 trillion non-pathogenic microorganisms)

What domains are represented in the human microbiota?

All three — Bacteria, Archaea, and Eukarya (e.g. fungi)

What are the key functions of the gut microbiota?

Immunity, metabolic roles, and chemical modulation

How does the gut microbiota support immunity?

Prevents pathogen colonization (antimicrobial proteins, antibodies), educates the immune system, stabilizes gut barrier function

What is caloric salvage?

Energy extraction from indigestible food by gut microbiota (produces short-chain fatty acids via fermentation of indigestible carbs)

What vitamins does the gut microbiota produce?

Vitamin K and folate (Vitamin B9)

What is the chemical modulator role of the gut microbiota?

Participates in drug metabolism (activation or catabolism) and deconjugates bile acids

What is the gut-brain axis?

The bidirectional connection between intestinal physiology and behavior/brain function

What systems are involved in the gut-brain axis?

Nervous system, endocrine (hormonal) system, and chemical signals

How does microbiota affect behavior?

Microbes make chemical signals (e.g. neurotransmitters, SCFAs) affecting memory, emotions, and behavior

How can you keep your gut microbiota healthy?

Diverse fiber-rich diet (prebiotics), fermented foods, use antibiotics only when needed, store probiotics

What are prebiotics?

Food for microflora (dietary fiber that feeds beneficial microbes); more specifically: specialized, non-digestible plant fibers that act as "fertilizer" for the beneficial bacteria (probiotics) in your gut

What is dysbiosis?

Disruption of the gut microbiota, which can lead to disease

What conditions are linked to gut microbiota disruption?

Insulin resistance, glucose intolerance, atherosclerosis, fatty acid metabolism issues, Autism, Parkinson's, cardiovascular disease, some cancers

What is FMT?

Fecal Microbiota Transplant — healthy microbiota from a donor is transferred to an infected individual via filtered fecal sample in saline

What is autologous FMT?

Storing your own healthy fecal sample prior to major surgery to restore your microbiome if it gets disrupted

Why can't large organisms rely solely on diffusion?

Diffusion is effective only over short distances; rate of diffusion is inversely proportional to distance

What systems did large multicellular organisms evolve to solve the size problem?

Circulatory system (move nutrients/waste), respiratory system (gas exchange), excretory system (remove waste)

What is bulk flow?

Movement of a liquid solution carrying molecules through vessels along pressure gradients; much faster than diffusion over long distances

What does bulk flow require?

(1) A plumbing system and (2) a source of pressure

How do plants differ from animals in pressure use?

Plants use BOTH negative and positive pressure; animals use only positive pressure (like a pump)

What are the two vascular systems in plants?

Xylem and Phloem

What does xylem transport?

Water and minerals — UNIDIRECTIONAL (roots to leaves)

What does phloem transport?

Organic materials / sugars (e.g. sucrose) — BIDIRECTIONAL (source to sink)

Where does xylem/phloem occur in herbaceous plants?

In vascular bundles

In woody plants, what is the xylem?

The heartwood (inner wood)

What are the two cell types in xylem?

Tracheids (long, elongated, high SA:V ratio, good at holding water via adhesion) and vessel elements (shorter, wider, only in angiosperms, stack with perforation plates to form open columns)

What two forces move water through xylem?

Cohesion (water molecules stick to each other) and adhesion (water sticks to xylem walls)

What is transpiration and how does it drive xylem flow?

Water evaporating from leaves pulls the entire water column up like a chain via cohesion

What kind of pressure is xylem sap normally under?

Negative pressure (tension)

What are sieve elements?

Living cells (without a nucleus at maturity) that compose phloem tubes

What is a sugar source in phloem?

An organ that is a net PRODUCER of sugar (e.g. mature leaves)

What is a sugar sink in phloem?

An organ that is a net CONSUMER of sugar (e.g. roots, developing fruit/flower)

Can source/sink roles reverse?

Yes — a young leaf is a sink (can't photosynthesize yet); a mature leaf becomes a source

How does positive hydrostatic pressure drive phloem flow?

Sugar loaded into sieve tube → water enters by osmosis → high pressure at source (leaf) → fluid flows to low pressure at sink → sugar unloaded

What are the three components of a circulatory system?

A circulatory fluid, a set of interconnecting vessels, and a muscular pump (heart)

What is an open circulatory system?

Blood is NOT always in vessels; it gets pumped out and floods the body cavity, bathing organs directly, then drains back through pores in the heart

What are the advantages of an open circulatory system?

Simpler, less energy to maintain, fine for small/slow animals

What are the disadvantages of an open circulatory system?

Slow circulation (blood sloshes around), no control over where blood goes

What is a closed circulatory system?

Blood stays entirely within vessels (arteries, capillaries, veins) at all times; exchange happens through vessel walls into interstitial fluid

What are the advantages of a closed circulatory system?

Fast/high-pressure/directed flow, precise blood distribution control, supports large active animals

What are the disadvantages of a closed circulatory system?

More complex and energetically costly

What are the 3 types of vessels in a closed circulatory system?

Arteries (heart → periphery), veins (periphery → heart), capillaries (connect arteries and veins, allow tissue exchange)

What is an arteriole?

A small branch of an artery

What is a venule?

A small branch of a vein

What are the two (types of) chambers of the heart?

Atrium (collects blood; thin-walled; primes the pump) and ventricle (pushes blood into vessels; thick-walled; is the pump)

What happens to vessel number, diameter, and flow velocity as you move from aorta to capillaries?

Number increases dramatically, diameter decreases, velocity slows down

How many capillaries does the body have and what is their diameter?

~10 billion capillaries; 5–9 μm diameter

Why is blood flow slowest at capillaries?

Intentional — slow flow allows time for tissue perfusion (exchange of O2, nutrients, and waste)

What is the aorta's approximate diameter and how many are there?

1 vessel, ~1.1 cm diameter

What is the equation for flow?

Flow = velocity × cross-sectional area

What is blood flow (Q)?

Movement of blood through a vessel

What is resistance (R)?

The slowing or blocking of blood flow

What is the relationship between radius, resistance, and flow?

Less resistance and larger radius = more flow

What is vasoconstriction?

Vessel getting SMALLER in radius

What is vasodilation?

Vessel getting BIGGER in radius

What controls flow in capillaries?

Arterioles (capillaries don't change their own diameter)

What is the myogenic response?

Distension (stretching) of vessels due to blood pressure triggers smooth muscle contraction, preventing change in capillary diameter

What is vascular tone?

How contracted the smooth muscle in vessel walls is; changes perfusion of a tissue

What does increased vascular tone do?

Decreases arteriole radius → decreases flow → increases resistance → alters blood volume distribution

What are precapillary sphincters?

Smooth muscle cells that control blood flow into capillary beds; influenced by nerve and hormone signals

What happens when precapillary sphincters are RELAXED?

Blood diffuses along the capillary bed → nutritive exchange occurs

What happens when precapillary sphincters are CONTRACTED?

Blood bypasses capillary bed → sent directly to venule → minimal nutrient exchange

Give an example of precapillary sphincter control in flight-or-fight response

Sphincters RELAXED to skeletal muscles (more blood), CONSTRICTED to digestive system (less blood needed)

What is Poiseuille's Law?

Flow rate = ΔP/R = 0.4 × ΔP × r⁴ / (viscosity × length)

Why is radius so important in Poiseuille's Law?

Radius is raised to the 4th power — small changes in radius have a HUGE impact on flow rate

What determines total resistance of the circulatory system?

The number of arterioles that are open

What is distributive shock?

When all arterioles open (e.g. sepsis, anaphylaxis) → massive increase in radius → massive decrease in pressure → decreased blood flow to brain

What determines vascular tone of arterioles?

Various chemical signals including O2, CO2, and temperature (e.g. cold → vasoconstriction to keep warm blood from surface)

What is systole?

Ventricle contracts hard → blood rushes into aorta → aortic walls stretch outward to accommodate it

What is diastole?

Ventricle relaxes → aortic walls snap back inward → recoil pushes blood forward and maintains pressure

What is a typical blood pressure reading and what are the units?

120/80; measured in mmHg

In which direction does blood flow with respect to pressure?

From areas of HIGH pressure to LOW pressure

What is blood pressure?

The force that blood exerts in all directions, including against the walls of blood vessels

Why does pressure drop across capillaries and arterioles?

Their narrow diameters cause high resistance; a greater proportion of blood is close to the walls, increasing friction