ib biology midterm

What properties of RNA suggest it was the first genetic material?

RNA can store information, self-replicate, and catalyze reactions (ribozymes). It is versatile and central in modern cells (mRNA, tRNA, rRNA), supporting the “RNA world” hypothesis.

How does the genetic stability of RNA compare to DNA?

RNA is less stable (ribose sugar, single-stranded, higher mutation rate). DNA is more stable (deoxyribose, double-stranded, repair mechanisms).

What is a ribosomal ribozyme?

rRNA in the ribosome catalyzes peptide bond formation during translation, showing RNA’s catalytic role is still essential.

What evidence suggests LUCA lived near hydrothermal vents?

Fossilized microbial structures in ancient vent deposits and conserved genes adapted to high temperature and chemical-rich environments.

How is deductive reasoning used to predict LUCA’s habitat?

By analyzing LUCA’s genes for adaptations (thermophilic, anaerobic, metal ion-dependent), scientists infer a vent environment.

What conditions are present at hydrothermal vents?

High temperature, high pressure, anaerobic, mineral-rich water, and strong chemical gradients.

How do LUCA genes provide evidence for vent habitats?

Genes for anaerobic metabolism, thermophily, and metal ion-dependent enzymes suggest adaptation to vent conditions.

How do obligate anaerobes, facultative anaerobes, and obligate aerobes differ?

Obligate anaerobes: cannot tolerate O₂.
Facultative anaerobes: grow with or without O₂.
Obligate aerobes: require O₂ for survival.

How are vesicles formed from membranes?

Membrane bends and pinches off, often aided by clathrin, forming a vesicle carrying cargo

What are the main functions of vesicles?

Transport, secretion, storage, digestion (lysosomes), and endocytosis.

What happens when a vesicle fuses with a membrane?

Its contents are delivered, and membrane material is added to the target membrane.

Why are skeletal muscle fibers atypical?

Multinucleated, very long, cannot divide by mitosis.

Why are aseptate fungal hyphae atypical?

Continuous cytoplasm with many nuclei, no septa.

Why are red blood cells atypical?

Lack nucleus and organelles; cannot divide.

Why are phloem sieve tube elements atypical?

Lack nucleus and organelles; rely on companion cells.

Compare number of nuclei: skeletal muscle, fungal hyphae, RBCs, sieve tube elements.

Muscle & hyphae: many; RBCs & sieve tubes: none.

How do chemical gradients affect gene expression in embryos?

Morphogen concentrations vary by location, activating/repressing genes to guide cell differentiation.

Name 3 processes requiring cell proliferation.

Growth, tissue repair, development.

How does cell proliferation occur in meristems and embryos?

Plant meristems: stem cells divide and differentiate.
Embryos: rapid cleavage divisions increase cell number.

How does skin cell proliferation aid repair?

Cells divide to replace dead/damaged cells and restore tissue integrity.

Why must daughter cells receive at least one mitochondrion?

To generate ATP for survival and metabolic activity

Outline unequal cytokinesis in yeast and oogenesis.

Yeast: small bud grows, mother retains cytoplasm.
Oogenesis: secondary oocyte retains cytoplasm, polar body degenerates.

What happens to the nucleus during mitosis?

Nuclear envelope breaks down in prophase and reforms in telophase; nucleolus disappears and reappears.

Compare normal and cancerous cells in division and metastasis.

Normal: controlled division, no invasion.
Cancerous: uncontrolled division, can invade tissues and metastasize.

Define: primary tumor, secondary tumor, benign, malignant, metastasis, cancer.

Primary: original tumor

secondary: spread

benign: slow, localized

malignant: invasive

metastasis: spread

cancer: uncontrolled growth.

How is mitotic index calculated?

MI = (cells in mitosis / total cells) × 100

How is mitotic index used in cancer?

Indicates tumor aggressiveness, helps diagnose, and monitor treatment.

Compare saturated and unsaturated fatty acids in bilayers.

Saturated: straight, pack tightly, high melting point, less fluid.
Unsaturated: kinks, less tightly packed, lower melting point, more fluid.

Example of membrane adaptation to habitat.

Cold-adapted fish have more unsaturated fatty acids to maintain fluidity.

Structure and placement of cholesterol in membranes.

Steroid rings + OH group

OH aligns with polar heads, rings/tail with tails.

How does temperature affect membrane fluidity?

High temp: more fluid;

low temp: more rigid.

How does cholesterol modulate fluidity?

Stabilizes membrane at high temp; prevents rigidity at low temp.

Role of CAMs in tissue formation?

Mediate cell-cell and cell-ECM adhesion, forming structured tissues.

What happens if CAM function is lost?

Cells can detach, invade, and metastasize in cancer.

Where is epinephrine secreted and why?

Adrenal glands; prepares body for vigorous activity (“fight or flight”).

Mechanism of action of epinephrine.

Binds adrenergic receptors → G-protein → cAMP → activates enzymes/ion channels.

Effects of epinephrine on the body.

Skeletal muscles: more blood/energy

liver: glycogenolysis

bronchi: dilation

heart/ventilation: increase rate

vessels: dilate to muscles.

Role of SCN cells in circadian rhythm.

Primary biological clock, coordinates daily cycles.

How do SCN cells respond to light?

Retinal input via retinohypothalamic tract resets SCN activity.

Mechanism of action of melatonin.

Binds MT1/MT2 receptors → G-protein → changes in cAMP → alters neuronal activity.

Effects of melatonin.

Induces sleep, regulates circadian rhythms, lowers core temperature, antioxidant/immune modulation.

Function of cotransporters in indirect active transport.

Use the energy of one molecule moving down its gradient to transport another molecule against its gradient.

Role of glucose cotransport in intestine and kidney.

Small intestine (SGLT1): glucose + Na⁺ absorbed from lumen.
Kidney (SGLT2): glucose reabsorbed in nephron, preventing loss in urine.

why was the discovery of water in asteroid Itokawa important?

it showed that the “rubble pile” asteroids aren’t completly dry and that their water has the same isotopic signature (D/H ratio) as the Earth’s oceans

this suggests that they could have delivered much of Earth’s water

Which hypothesis for the origin of Earth’s water does this discovery support?

It supports the hypothesis that Earth’s water came from the inner solar system asteroids (like Itokawa), not from distant comets

What provides the “chemical clue” for identifying the source of water?

The ration of hydrogen isotopes (deuterium - d, and protium - h) which acts like chemical fingerprint to trace waters origins

why was early earth’s water lost after its formation?

high surface temperatures caused water to evaporate

the lack of an atmosphere let vapor escape into space

why was later-delivered water able to stay on earth

once earth developed an atmostphere through volcanic outgassing, it trapped water vapor, allowing it to condense into oceans.

also, the cohesion of water molecules helps water to stay in liquid or ice form through hydrogen bonding.

list two factors that allowed Earth to retain this water over geological timescales.

• gravity (prevents light molecules like water vapor from being permanently lost to space via thermal escapes)

• distance from sun (allows for optimal temperature, not too hot nor too cold)

Identify the primary celestial bodies hypothesized to be the first source of Earth’s water, and state the key evidence supporting this claim.

water rich asteroids (carbonaceous chondrites) originating from outer asteroid belt

the deuterium to hydrogen ration is earths oceans is a very close match

How might organisms adapt to move on high-gravity planets?

1. develop stronger muscles or skeletons to support movement

2. evolve compact, sturdy body shapes to conserve energy and move efficently

Explain why the presence of water is considered fundamental to the search for extraterrestrial life

• All known life depends on liquid water for survival and biochemical reactions.

• Water is an excellent solvent, allowing transport of nutrients and facilitating metabolic reactions.

Define “Goldilocks zone”

• The region around a star where conditions are “just right” — not too hot or too cold — for liquid water to exist on a planet’s surface.

• Too close to the star = water boils

• too far = water freezes.

Polar

Unequal sharing of electrons → O partially negative, H partially positive

Allows water to dissolve many substances

Hydrogen bonding

Attraction between partial charges of adjacent water molecules

Causes cohesion, adhesion, and high surface tension

Cohesion

Water molecules attract each other

Explains surface tension and water droplet formation

Adhesion

water molecules attract other polar surfaces

capillary action in plants

surface tension

cohesion at the surface forms a skin

allows insects to walk on water

hydrophopic

water-fearing, nonpolar

oil does not dissolve in water

hydrophillic

water loving, polar

salt dissolves easily in water

alpha glucose

OH group on carbon 1 points below the ring

beta glucose

OH group on carbon 1 points above the ring

paper clip example

surface tension (cohesion)

soap and pepper example

surface tension

water traveling example

capillary action

anti gravity experierment

cohesion and adhesion

what are the monomer, polymer, and macromolecule: carbohydrates

monosaccharide

polysaccharide

amylose and amylopectin in starch; cellulose

what are the monomer, polymer, and macromolecule:

proteins

amino acid

polypeptide

proteins

what are the monomer, polymer, and macromolecule:

nucleic acids

nucleotide

polynucleotide

DNA and RNA

what are the monomer, polymer, and macromolecule:

lipids

fatty acids and glycerol

triglyceride

fats and oils

hydrolysis

add water to break apart polymer to monomers

condensation

removal of water to synthesize monomers to polymer

how many sugar molecules are in glucose, ribose, and fructose

1

how many sugar molecules are in sucrose, maltose, and lactose

2

alpha =

down

beta =

up

starch is composed of what two polysaccharide molecules

• amylose

• amylopectin

amylose

long chains of alpha glucose molecules (not soluble in water)

amylopectin

long chains of alpha glucose with branching chains of alpha glucose (not soluble in water)

amylose and amylopectin allows for what..?

compact storage of starch grains in plant cells, without impacting osmotic pressure in the cells BECAUSE it is not soluble in water

glycogen

short term energy storage in animals

composed of chains of alpha glucose with bonds between carbon 1 and carbon 4

many branches of alpha glucose chains are present with alpha glucose bonding to carbon 6

glycogen is…

insoluble compact molecule, due to its many branching and coiling during polymerization

cellulose

composed of beta glucose molecules and is an unbranched polysaccharide

form groups → microfibrils held together with hydrogen bonds

cellulose microfibrils

cellulose molecules held together by hydrogen bonds

have high tensile strength, allowing them to maintain the structural integrity of the cell walls of the plants

fatty acids are composed of

1. carboxyl group

2. hydrocarbon chain

3. methyl group

unsaturated vs saturated fatty acids

saturated = straight

unsaturated = kink w double bond

monounsaturated vs polyunsaturated fatty acid

monounsaturated = one double bond

polyunsaturated = two double bonds

triglycerides are composed of

one glycerol molecule

3 fatty acid molecules

triglycerides function

• energy storage

  • lipids store twice as much energy as carbs

  • energy is stored in the carbon-carbon bond

  • stored lipids can be broken down to produce ATP through aerobic respiration

• Adipose tissue - insulation

  • low thermal conductivity = maintains constant body temp

  • cold temps = thicker adipose tissue under skin

  • warm temps = do not store fat under skin, will not prevent heat loss

amino acid structure

• amine group (NH2)

• hydrogen attached to central carbon

• side chain (r-group)

• carboxyl group (COOH)

the r-group of the amino acid determines…

the chemical properties

• hydrophobic

• hydrophillic

properties of triglycerides that make them suitable for long-term energy storage

• high energy density

• hydrophobic

function of adipose tissue

stores triglycerides as long term energy reserve

of the 20 amino acids…

11 can be synthesized by humans = nonessential

9 must be consumed by diet = essential

meat and animal products are …

complete proteins (contain all nine amino acids)

essential amino acids

must be obtained by diet

non-essential amino acids

can be synthesized by humans

proteasomes

= large protein complexes which break down unneeded proteins to amino acids through hydrolysis

amino acids are recycled to synthesize new proteins

formation of dipeptides form between what groups?

carbon of the carboxyl group in one amino acid

and the amine group of the second amino acid

(wherever there is a bond between C and N)

what is quaternary structure of a protein?

composed of more than one polypeptide chain into a functional protein complex