IB biology 2025-2026 (junior year)

what do all living things require most?

water

where do most cells function and contain?

function in and contain in aqueous solutions

what are aqueous solutions

solutions where the solvent is water

what is water?

a polar molecule

what is a polar molecule?

molecules that have an uneven distribution of charge

opposite ends have opposite charges

what are hydrophilic molecules

“water loving molecules” that dissolve in water and are also known as polar molecules

what are hydrophobic molecules?

“water fearing molecules” that do not dissolve in water and are also known as non-polar molecules

what does water’s polarity allow it to do?

allows it to have an ability to form hydrogen bonds with other molecules

what are hydrogen bonds?

loose attractions between polar molecules

what is electronegativity?

a property that describes how molecules share/take electrons

what does electronegativity cause?

polarity in molecules

what is the order of relative electronegativity in bio molecules?

O>N>C-H

what does biotic means?

living

what does abiotic mean

nonliving

what is water required for?

effective interaction of naturally forming molecules (allows growth and copying of molecules)

formation of compartments (allows development of internal chemistry to be different from the surrounding environment)

what is metabolism?

all the chemical reaction within a living organism also an enzyme catalyzed reaction in an organism to convert food to energy

why are hydrogen bonds weak? why are they strong?

weak because the charges are partial but strong because there are so many of them

what is cohesion?

when like (water) molecules are mutually attracted to each other

stops water from evaporating

what does cohesion do?

it pulls water molecules together/to each other

what do hydrogen bonds cause with water/liquids?

causes/increases surface tension

what is desiccation?

the process of removing/extracting water content

what is adhesion?

water sticking to other things, force attraction between different types of molecules

the reason why xylem tubes are narrow

what is capillary movement?

ability of a liquid to move through narrow tubes as a result of adhesion, cohesion, and surface tension

when does capillary movement occur?

when adhesion is greater than cohesion

what uses capillary movement?

used by plants to move water into plants

why is cytoplasm important?

it allows cells to control their composition, respond to the environment, and maintain function of life

metabolism takes place here

what is the cell membrane?

the boundary of a biological cell which controls movement in and out the cell

relies on some hydrophobic areas/properties to keep things out the cell

proteins in the membrane help give different cells specific properties (aquaporins)

what are aquaporins?

specialist proteins that facilitate the transport of water across cell membranes and are anchored by a hydrophobic exterior but has a hydrophilic interior

what does water’s ability to dissolve substances allow it to do?

it allows it to be the medium for transportation from cell to clee

what are the physical properties of water?

buoyancy

viscosity

thermal conductivity

specific heat capacity

Density

what is buoyancy?

a force that counteracts gravity

what does buoyancy allow aquatic animals to do?

allows aquatic animals to stay afloat and move around move around easily

also allows cellular components to do the same

critical for aquatic life

what is viscosity?

resistance to flow

is related to how much energy is needed to change the shape of liquids

low viscosity compared to liquids, high compared to air

what does density cause/create?

creates buoyancy

what is unique about water’s solid form?

it is less dense then its liquid form because of the pattern of h bonds as water solidifies

can therefore act as an insulator for lakes

what is thermal conductivity?

the ability of a substance to transfer heat when there is a temperature difference

has high thermal conductivity compared to other liquids (besides metal)

what is specific heat capacity?

how much energy is needed to raise the temperature of a substance

why does water have a high specific heat capacity?

because of the hydrogen bonds between water molecules

the intermolecular forces need to be overcome

what does water’s (low) viscosity allow?

allows/permits objects (both on a cellular level and macro level) to mvoe through water easily

why is wate'r’s high specific heat capacity important?

keeps water temperature relatively constant and protects life from cell destroying temp fluctuations

does water have a relatively high or low thermal conductivity?

has relatively high thermal conductivity

what does water’s high thermal conductivity allow it to do?

allows water to act as a heat sink and pull heat away from organisms and helps living organisms maintain a fairly constant internal temperature

water example 1 - black throated loon

feathers - insulation to retain body heat

body and webbed feat - aerodynamic/hydrodynamic and reduces drag

hydrophobic feathers

dense bones

what is drag?

resistant force

water example 2 - ringed seal

blubber - helps with buoyancy/floating and for insulation to retain body heat

flippers/body - streamlined shape to reduce drag

webbed flippers - navigate/fight viscosity

what are emergent properties?

characteristics that appear in higher systems but not in the individual components

adhesion and cohesion are examples of this

what is a xylem?

specialized tubes that functions to facilitate the movement of water throughout vascular plants

uses cohesion and adhesion

what is capillary action?

the flow of liquid in narrow spaces such as small tubes called capillaries

smaller the tube the greater the adhesion property

what does capillary action use/happen?

the combined affects cohesion and adhesion

what does cohesion create?

surface tension which allows some animals to walk on water

what are vascular bundles

bundles of xylem tubes

how do water and non-polar molecules actually interact?

water seeks out more favorable molecules while the non polar molecules are in the way not interacting this is because the nonpolar molecules cannot make h bonds

is glucose hydrophobic or hydrophilic?

hydrophilic and the basic fuel for all life

hydrogen bonds form between these groups and water. This interaction is the reason glucose can dissolve in water

outline the mechanism for transport in the blood of hydrophilic molecules

blood is primarily water

what hydrophilic molecules are dissolved and transported by blood?

glucose

many amino acids (those with polar/ionic R groups)

Ions (minerals like Na+, K+, Cl-, etc)

what are some hydrophobic substances that are also essential to life?

some amino acids (depends on the side chain)

cholesterol (primarily a non-polar hydrocarbon despite a small O-H end)

fats (lipids, phospholipids, steroids)

oxygen gas (it’s symmetrical)

outline the mechanisms of transport in the blood for hydrophobic molecules

because hydrophobic molecules cannot dissolve in water, they have evolved unique methods of transport

what molecules must be transported by special lipo-protein packages?

cholesterol

fats

oxygen (must bind to hemoglobin in red molecules)

these specialized “fat sacs” have hydrophobic interiors and hydrophilic exteriors

what allows water to be liquid and retained on earth?

the earth’s moderate temperature keeps water liquid and gravity allows it to be retained. It’s cohesive properties also stop it from immediately dispersing allowing water to stay liquid.

what is the concept of the goldilocks zone?

the orbital area around a sun where a planet or natural satellite might have liquid water