IB BIO SL Y1 Semester exam

Water polarity

uneven charge distribution (O = δ−, H = δ+)

Hydrogen bonds

weak attractions between water molecules (2 other h and one O)

Cohesion

attraction between water molecules

Adhesion

attraction between water and other substances

Surface tension

elastic surface caused by cohesion

Hydrogen bonds (how they form)

Hydrogen bond forms between H (δ+) of one molecule and O (δ−) of anothe

Condensation (dehydration synthesis)

Joins monomers → polymer

Releases water

Forms covalent bonds

Hydrolysis

Breaks polymers → monomers

Uses water

Peptide bond

covalent bond between amino acids

Dipeptide

2 amino acids, 1 water removed

Tripeptide

3 amino acids, 2 waters removed

Peptide bond formation removes:

OH from carboxyl group

H from amino group

Amphipathic molecules

both hydrophilic & hydrophobic regions

Phospholipid heads

polar, hydrophilic

Phospholipid tails

nonpolar, hydrophobic

Steroids (e.g. testosterone)

Lipid

Hydrophobic

Insoluble in water

Starch

Storage polysaccharide

Found in plants

Made of glucose

Easily broken down for energy

Cellulose

Structural polysaccharide

Found in plant cell walls

Provides rigidity

Structural difference

Different glucose linkages → different function

Lock-and-key model

Active site = rigid

Substrate fits exactly

Induced-fit model

Active site changes shape

Improves binding efficiency

Activation Energy

Enzymes lower activation energy

They orient substrates to make bond breaking/forming easier

Increasing substrate concentration

increased rate

Plateau occurs when:

All active sites are saturated

Enzyme becomes limiting factor

Rising temperature for enzymes

increased enzyme activity (more collisions)

Optimum temperature

peak activity

High temperature → denaturation

Bonds break

Active site loses shape

Enzymes have an optimum pH

Deviating pH alters charges

Extreme pH → denaturation

Graph interpretation:

• Steepest slope = highest activity

• Lower slope = reduced activity

Anabolic reactions

Build complex molecules

Require energy

Examples: photosynthesis, protein synthesis

Catabolic reactions

Break molecules down

Release energy

Examples: respiration, digestion

Ribosomes

Protein synthesis

Translate mRNA

Rough ER

Protein folding and transport

Golgi apparatus

Modifies, packages proteins

Mitochondria

• ATP production

• Cellular respiration

Exocrine Cells

Abundant RER → enzyme production

Large Golgi → packaging

Vesicles → exocytosis

Prokaryotes

No nucleus

Circular DNA

No membrane-bound organelles

Smaller

Eukaryotes

-Nucleus present

• Linear DNA

• Membrane-bound organelles

Light microscope

Uses visible light

Lower resolution

2D images

SEM

Uses electrons

3D surface images

High resolution

Why electron microscopes show more detail

Shorter wavelength

Less diffraction

Atypical Cells

Multinucleated muscle cells

Anucleate red blood cells

Fungi with shared cytoplasm

Cell Specialization

• Bryophyte cells

Cell wall

Chloroplasts

Large vacuole

Red blood cells

Biconcave shape

No nucleus

Maximizes oxygen transport

Stem Cells

Undifferentiated cells

Can become specialized

Important for:

• Growth

• Repair

• Regeneration

Gene Expression

• Turning specific genes on/off

All cells have same DNA, different expression

Phospholipid bilayer:

Hydrophilic heads outward

Hydrophobic tails inward

Embedded proteins:

• Channels

• Carriers

• Receptors

Simple diffusion

Passive

Small nonpolar molecules

Facilitated diffusion

Passive

Channel or carrier proteins

Active transport

Requires ATP

Against concentration gradient

Osmosis

Movement of water

From high → low water concentration

Through semipermeable membrane

Hypotonic

Water enters cell

Cell swells

Hypertonic

Water leaves cell

Cell shrinks

Isotonic

No net movement

Plant vs Animal in Hypertonic Solutions

Animal cell → shrinks

Plant cell

• Membrane pulls from wall

• Plasmolysis

• Cell wall remains rigid

Why Active Transport Needs Energy

• Moves substances against gradient

• Requires ATP

Paramecium

Food vacuoles → digestion

Contractile vacuole → water balance

Specialized organelles maintain life

Contractile Vacuole

• Pumps excess water out

• Prevents bursting

• Critical in hypotonic environments

Compartmentalization

Increases efficiency

Allows:

• Optimal conditions

• Separation of reactions

• Greater control

Vesicle Transport

• Proteins made in RER

• Modified in Golgi

• Transported in vesicles

• Released via exocytosis

Membrane Fluidity

Higher temperature → more fluid

Unsaturated tails → more fluid

Saturated tails → less fluid

Cholesterol

• Prevents membrane from becoming too rigid or too fluid

High SA:V

faster diffusion

Surface Area : Volume Ratio

Small cells more efficient

Large organisms compensate with:

• Membrane folds (microvilli)

• Transport systems

• Specialized shapes