NOTES: 7.3-7.4 CELL TRANSPORT & HOMEOSTASIS

Selectively permeable: ● property of biological membranes which allows some substances to pass more easily than others

Transport proteins: ● membrane proteins that transport SPECIFIC molecules or ions across biological membranes

GLUCOSE Binding Recovery Transport Dissociation

Movement across the cell membrane can be: 1) PASSIVE cell does not have to spend energy substance moves from where it is MORE concentrated to where it is LESS concentrated. 2) ACTIVE  cell “spends” energy to move a substance from where it is LESS concentrated to where it is MORE concentrated (“UPHILL”)

Passive Transport: DIFFUSION ● movement of a substance from where it is conc. to where it is less conc. (“down a concentration gradient”)

Passive Transport: FACILITATED DIFFUSION ● diffusion of solutes across a membrane, with the help of transport proteins (passive transport because it is movement down a concentration gradient; cell does not need to spend any energy)

Passive Transport / Fac. Diffusion: OSMOSIS ● diffusion of WATER through a selectively permeable membrane; water moves DOWN its concentration gradient (which is to say opposite the solute concentration!)

● OSMOSIS:(this is a type of facilitated diffusion…water moves through special channels in cell membrane called aquaporins)

OUTSIDE THE CELL INSIDE THE CELL

WATER MOVES FROM HYPO TO HYPERTONIC!!! the direction of water movement can be described / predicted based on if the cell’s ENVIRONMENT is: ● ISOTONIC: equal solute concentration compared to inside a cell ● HYPERTONIC: greater solute concentration than inside a cell ● HYPOTONIC: lower solute concentration compared to inside a cell WATER MOVES FROM HYPO TO HYPERTONIC!!!

In animal cells: ● in a HYPERTONIC environment, water exits the cell; cells shrivel and usually die ● in a HYPOTONIC environment, water moves into cell, causing it to swell and possibly burst

In cells with cell walls (i.e. plant cells): ● in a HYPERTONIC environment, water exits the cell; cells shrivel and usually die ● in a HYPOTONIC environment, water moves into cell, causing it to swell; cells become more TURGID.

ACTIVE TRANSPORT: energy-requiring process; molecules are moved across the cell membrane AGAINST their concentration gradient (“uphill”)

Active Transport: ● Molecular Transport ● Bulk Transport

Active Transport: ● Molecular Transport -small molecules & ions are moved across membranes by proteins that act like pumps

BULK TRANSPORT: ENDOCYTOSIS & EXOCYTOSIS ● transport of large molecules (e.g. proteins and polysaccharides) into or out of the cell

ENDOCYTOSIS EXOCYTOSIS *importing large molecules by forming vesicles out of the cell membrane **vesicle forms in a small region of cell membrane ***used by cells to bring in larger, extracellular substances (e.g. proteins)

ENDOCYTOSIS EXOCYTOSIS *exporting large molecules by vesicles fusing w / the cell membrane **vesicle buds from ER or Golgi and migrates to cell membrane ***used by cells to export products (e.g. cells in pancreas secreting insulin)

2 types of Endocytosis: 1) Phagocytosis: solid particles (“cell eating”) 2) Pinocytosis: fluid droplets (“cell drinking”)

Phagocytosis

Pinocytosis

7.4: Homeostasis & Cells ● sometimes an organism can be a single cell ● unicellular organisms dominate life on Earth…they include: -prokaryotes: bacteria -eukaryotes: protists (amoeba, paramecium, Euglena) -eukaryotes: unicellular fungi (yeast)

Unicellular Organisms: ● unicellular organisms must maintain homeostasis ● HOMEOSTASIS: relatively constant internal physical & chemical conditions ● to maintain homeostasis, unicellular organisms grow, respond to the environment, transform energy, and reproduce

Multicellular Life ● the cells in a multicellular organism must work together to maintain homeostasis ● in a multicellular organism, cells become specialized so that different cell types play different roles

CELL SPECIALIZATION: ● some cells are specialized to MOVE (i.e. muscle cells) ● some cells are specialized to RESPOND (i.e. nerve cells)

CELL SPECIALIZATION: ● some cells are specialized to transport substances (i.e. red blood cells) ● some cells are specialized to fight off pathogens (i.e. white blood cells)

LEVELS OF ORGANIZATION: ● CELLS…are organized into… ● TISSUES: group of similar cells performing the same function

LEVELS OF ORGANIZATION: ● ORGAN: group of tissues working together -ex: stomach ● ORGAN SYSTEM: group of organs working together -ex: digestive system (stomach, intestines, pancreas, etc.)

LEVELS OF ORGANIZATION: ● ORGANISM: collection of all of the above!...specialization and interdependence at all levels allows an organism to maintain homeostasis!

CELLULAR COMMUNICATION: ● Cells communicate with one another by using chemical signals (i.e. hormones) ● in order to respond to a particular chemical signal, a cell must have the appropriate RECEPTOR to which the signaling molecule can bind

CELLULAR COMMUNICATION: ● cells respond to chemical signals in a variety of ways: -muscle cell contracts -liver cell takes up & stores glucose from blood -skin cells divide to replace injured cells