AP Bio unit 2

ribosomes

Contains rRNA and proteins. synthesize proteins by translating mRNA into polypeptide chains. found in all living cells.

endoplasmic reticulum (ER)

helping cells maintain shape and plays a role in intracellular transport. ​

rough ER

has membrane bound ribosomes, allows for the compartmentalization of cells, and helps carry out protein synthesis

smooth ER

functions include the detoxification of cells and lipid synthesis​

Golgi complex

membrane-bound structure that consists of a series of flattened membrane sacs folding. 

 chemically modifies newly synthesized cellular products ​and packages proteins for trafficking​

mitochondria

have a double membrane that provides compartments for different metabolic reactions involved in aerobic cellular respiration. The outer membrane is smooth, while the inner membrane is highly convoluted, forming folds that enable ATP to be synthesized more efficiently​.

lysosomes

membrane-enclosed sacs that contain hydrolytic enzymes that digest material. also play a role in programmed cell death (apoptosis).​

chloroplasts

specialized organelles that are found in plants and photosynthetic algae. Chloroplasts contain a double membrane and serve as the location for photosynthesis.

vacuoles

membrane-bound sacs that play many different roles.​

In plant cells, a specialized large vacuole maintains turgor pressure through nutrient and water storage. ​

In animal cells, vacuoles are smaller in size, are more plentiful than in plant cells, and store cellular materials.​

Surface area-to-volume ratios

affect the ability of a biological system to obtain necessary resources, eliminate waste products, acquire or dissipate thermal energy

Smaller cells typically have

a higher surface area-to-volume ratio as well as a more efficient exchange of materials with the environment than do larger cells.

As cells increase in volume,

the surface area-to-volume ratio decreases and the demand for internal resources increase

he surface area-to-volume ratio can restrict

cell size and shape

More complex cellular structures (e.g., membrane folds) are necessary to

adequately exchange materials with the environment.

As organisms increase in size

their surface area-to-volume ratio decreases, affecting properties like rate of heat exchange with the environment. ​

As mass increases, both the surface area to-volume ratio and the rate of heat exchange

decrease

Smaller amounts of mass exchange proportionally

more heat with the ambient environment than do larger masses.

the smaller the organism, the higher the

metabolic rate per unit body mass.​

Phospholipids have both

hydrophilic and hydrophobic regions

The hydrophilic phosphate regions of the phospholipids are

oriented toward the aqueous external or internal environments

hydrophobic fatty acid regions face each other within the

interior of the membrane. ​

Embedded proteins can be

hydrophilic (with charged and polar side groups), or hydrophobic (with nonpolar side groups) or both.​

Hydrophilic regions of the proteins are either inside the

nterior of the protein or exposed to the cytosol (cytoplasm

Hydrophobic regions of proteins make up the protein surface that interacts with

the fatty acids in the interior membrane​

Plasma membranes consist of a structural framework of phospholipid molecules embedded with

proteins, steroids (such as cholesterol in vertebrate animals), glycoproteins, and glycolipids, which can move around the surface of the cell within the membrane, as illustrated by the fluid mosaic model.​

Plasma membranes separate

the internal environment of the cell from the external environment.

Selective permeability

result of the plasma membrane having a hydrophobic interior​

Small nonpolar molecules, including N2, O2 , and CO2 ,

freely pass across the membrane.

Hydrophilic substances, such as large polar molecules and ions,

move across the membrane through embedded channels and transport proteins

he nonpolar hydrocarbon tails of phospholipids

prevent the movement of ions and polar molecules across the membrane

Small polar, uncharged molecules, like H2O or NH3 (ammonia)

pass through the membrane in small amounts.​

Cell walls of Bacteria, Archaea, Fungi, and plants

provide a structural boundary as well as a permeability barrier for some substances to the internal or external cellular environments and protection from osmotic lysis.​

The selective permeability of membranes allows for

the formation of concentration gradients of solutes across the membrane. ​

Passive transport

the net movement of molecules from regions of high concentration to regions of low concentration without the direct input of metabolic energy. ​

Active transport

requires the direct input of energy to move molecules. In some cases, active transport is utilized to move molecules from regions of low concentration to regions of high concentration.​

The processes of endocytosis and exocytosis

require energy to move large substances or large amounts of substances into and out of cells. ​

In endocytosis,

the cell takes in large molecules and particulate matter by folding the plasma membrane in on itself and forming new (small) vesicles that engulf material from the external environment.

In exocytosis

internal vesicles release material from cells by fusing with the plasma membrane and secreting large molecules from the cell.​

Facilitated diffusion

requires transport or channel proteins to enable the movement of charged ions across the membrane. ​

After facilitated diffusion 

Membranes may become polarized by the movement of ions across the membrane. ​

Charged ions, including Na+ (sodium) and K+ (potassium),

require channel proteins to move through the membrane.​

Facilitated diffusion enables the movement

of large polar molecules through membranes with no energy input. In this type of diffusion, substances move down the concentration gradient

Aquaporins transport

large quantities of water across membranes

External environments can be

hypotonic, hypertonic, or isotonic to internal environments of cells.

Movement of water can also be described as moving from

hypotonic to hypertonic regions

Water moves by

osmosis from regions of high water potential to regions of low water potential.​

Osmoregulation

maintains water balance and allows organisms to control their internal solute composition and water potential

Water moves from regions of

low osmolarity or solute concentration to regions of high osmolarity or solute concentration.​

Metabolic energy (such as that from ATP) is required

or active transport of molecules and ions across the membrane and to establish and maintain electrochemical gradients.

Membrane proteins

are necessary for active transport. ​

The Na+/K+ pump and ATPase

contribute to the maintenance of the membrane potential.

Membranes and membrane-bound organelles in eukaryotic cells

compartmentalize intracellular metabolic processes and specific enzymatic reactions.

Internal membranes facilitate cellular processes by

minimizing competing interactions and by increasing surface areas where reactions can occur.​

Membrane-bound organelles such as mitochondria and chloroplasts

evolved from once free-living prokaryotic cells via endosymbiosis.​

​

Prokaryotes typically lack

Internal membrane bound organelles but have internal regions with specialized structures and functions. ​

Eukaryotic cells maintain internal membranes that

partition the cell into specialized regions​