IB Bio B2.1, 2.2, 2.3

questions taken from oxford biology textbook 2023 edition

composition of phospholipid bilayer

1. the head: made of phosphate, hydrophilic

2. two tails: made of hydrocarbon, hydrophobic

permeability of phospholipid bilayer

low permeability to hydrophilic particles, including:

1. ions with positive or negative charges

2. polar molecules like glucose and salts

the larger the molecule….

… the lower the permeability (ex: water molecules, slightly larger than oxygen atoms) can pass through more easily than larger molecules like glycoproteins

molecules move (up/down) concentration gradient

down, more particles move from an area of higher concentration to an area of lower concentration than the opposite direction

simple diffusion is:

a passive process in which molecules move down the concentration gradient without the need for energy or a transport protein

how and why does simple diffusion occur?

It occurs across a permeable membrane and is driven by the random motion of molecules. It allows for the movement of small, nonpolar molecules such as oxygen and carbon dioxide across cell membranes.

what molecules can’t easily difuse simply through cells?

• ions with positive or negative charges (because inside of membrane is hydrophobic)

• polar molecules (for the same reason)

what molecules can easily diffuse simply through membrane?

smaller, polar molecules like urea and ethanol

what is facillitated diffusion?

passive transport where specific proteins assist molecules in crossing the cell membrane, creating channels/carriers for the molecules to pass through.

what molecules use facilitated diffusion?

used for larger or charged molecules that cannot easily cross the membrane's lipid bilayer.

what is osmosis?

process where solvent molecules move from an area of low solute concentration to an area of high solute concentration through a semipermeable membrane.

what are integral proteins?

hydrophobic membrane proteins embedded in the hydrocarbon chains, spanning the entire membrane, with parts exposed inside and outside the cell

channel proteins

a ___________ is a type of protein that forms a connection in the cell membrane, allowing the passage of specific substances, usually only one type (ex: sodium or potassium ions but not both).

what are peripheral proteins?

hydrophilic proteins attached to the cell membrane but not embedded within the lipid bilayer, found on the inner or outer surface of the membrane

what is a pump protein?

aid in moving molecules or ions across cell membranes, require energy (like ATP) to transport substances against their concentration gradient, balancing ions and molecules inside and outside the cell.

what are examples of pump proteins?

Sodium-potassium pumps and proton pumps

what are the differences between channel and pump proteins?

1. energy: pump proteins require energy (active transport) whereas channel proteins do not (passive transport)

2. direction: pump proteins move particles only in one direction, but in channel proteins, particles can move both ways

3. concentration gradient: pump proteins move against, channel move with.

facilitated diffusion and active transport allow selective permeability because ____, while simple diffusion does not because ___.

1. channel and protein pumps only allow selective particles across

2. permeability across the membrane relies on size and polarity of the particle

which of the following is not selectively permeable: facilitated transport, active transport, simple diffusion?

simple diffusion

which of the following are selectively permeable: facilitated transport, active transport, simple diffusion?

facilitated transport, active transport

what are glycolipids?

biomolecules composed of a lipid tail and a carbohydrate head

what are glycoproteins?

proteins that have attached carbohydrate molecules, with the protein embedded in the cell membrane and the carb part in the extracellular region

what is the purpose of glycolipids?

helps cell recognize pathogens so they can be destroyed

what is the fluid mosaic model of membrane structure?

describes the structure of cell membranes. It states that the membrane is composed of a fluid lipid bilayer with embedded proteins. The lipids can move laterally, giving the membrane its fluidity. Proteins are scattered throughout, forming a mosaic pattern.

why do unsaturated fatty acids allow for more flexibility and permeability in the membrane than saturated fatty acids?

Unsaturated fatty acids have double bonds, allowing for kinks in the hydrocarbon chain. This prevents tight packing, increasing membrane fluidity and permeability.

cholesterol’s role in phospolipid bilayer

• hydrophilic and phobic ends

• keeps shape

• stabilizes at high temps

• prevents sat fatty acids from freezing at low temps

what is endocytosis?

Process by which cells engulf and internalize molecules or particles from their external environment through the formation of a vesicle.

what are examples of endocytosis?

used with larger, impermeable molecules that cant pass through membrane

• antibodies and nutrients going into the fetus

• pathogens or viruses can be absorbed and killed

what is exocytosis?

cellular process where vesicles fuse with the cell membrane, releasing their contents outside the cell.

how do voltage gated sodium work?

open in response to depolarization, allowing sodium ions to rush into the cell, generating an action potential.

how do potassium channels work?

Potassium channels open slowly, allowing potassium ions to exit the cell, repolarizing it and restoring the resting membrane potential.

which organelles have no membrane

• ribosome

• centrioles

• microtubules

• proteaosomes

• nucleoli

which organelles have a single membrane?

• smooth and rough endoplasmic reticulum

• Golgi apparatus

• Lysosome

• Vacuole

• Vesicle

which organelles have a double membrane

• Nucleus

• Mitochondria

• Chloroplasts

• amyloplasts

• chromoplasts

which type of cells have fewer organelles?

prokaryotic cells

what are advantages of compartmentalization?

• enzymes and substrates can be concentrated if they’re compartmentalism’s

• damaging substances can be kept inside cell

• pH levels can be maintained

in early embryos, cells are ______.

unspecialized

when a gene is used in a cell, we say the gene is being ______.

expressed

cell differentiation happens because _____

a different sequence of genes is expressed in different cells

what is a stem cell?

A type of unspecialized cell that has the ability to develop into different types of cells in the body and divide without limit. Stem cells have the potential to repair and regenerate damaged tissues and organs.

What makes cells know what it should differentiate into?

position in the cell

cells produced by division of a stem cell can remain as __ ____ ____ or _____ ___ ___ _____ ____

a stem cell, or differentiate into a different type of cell

what function do stem cells have in the adult body?

• found in bone, marrow, skin, and liver and allows them to regenerate and repair themselves

• inactive in striated muscle cells until injury, where they proliferate and replace damage

• hair follicles have stem cells which allows continuous generation

• can be simulated outside body to generate tissue in labs

what is a toripotent cell?

type of stem cell that has the ability to differentiate into any cell type in an organism, including both embryonic and extraembryonic tissues. they are found in zygotes and early embryos

what is a pluripotent cell?

type of stem cell that can differentiate into any cell in the body, except for those forming the placenta and umbilical cord.

what is a multi potent cell?

a type of stem cell that has the ability to differentiate into multiple, but not all, cell types in the body, for example, adult stem cells and cord blood cells

what would happen if the SA/V ratio is too low?

• substances won't be able to enter cell as quick as they need to

• waste products would accumulate

• cells would overheat because heat's

  produced faster than it's lost

what are type I pneumocytes?

adapted for oxygen and CO2 diffusion (passive)

• wide + thin

• area of diffusion is small, increasing gas exchange

what are type II pneumocytes?

secrete surfactant, wider and larger

what’s the difference between striated and cardiac muscle cells?

cardiac muscle cells are

• shorter

• mostly have one nucleus per cell

• inter calculated discs: connections between each cell, between cytoplasm and membrane, which allows electrical signal to be conducted

why is gas exchange more difficult with a larger cell?

because as the size increases, diffusion distances also increase and the ratio of surface area to volume drops.