Chapter 5 Section 1 Passive Transport Passive Transport

Chapter 5 Section 1: Passive Transport

Passive Transport • substances can cross the membrane without any input of energy by the cell.

Diffusion • Movement of molecules from an area of higher concentration to an area of lower concentration. • Simplest type of passive transport. • Driven by kinetic energy.

Diffusion • Molecules are in constant motion. • Go in a straight line- hit something- then straight line in a new direction. • MOLECULES MOVE DOWN THE CONCENTRATION GRADIENT (HIGH TO LOW)

Concentration Gradient • Difference in the concentration of molecules across a distance.

Concentration Gradient • SUGAR CUBE IN CUP OF WATER

Equilibrium • Concentration of molecules is the same throughout the space the molecules occupy. • Movement of molecules balance one another and equilibrium is maintained. • Molecules are just as likely to move in one direction as another.

Diffusion Across Membranes • Membrane is semipermeable. • If the substance can pass- it will go from an area of high concentration on one side to an area of lower concentration on the other side. • Called simple diffusion

Diffusion Across Membranes • Molecules that can dissolve in lipids may pass directly through the membrane. • Molecules that are small but not soluble in lipids may diffuse across membrane through pores.

Solution • Solution: solute dissolved in a solvent • Sugar- solute • Water- solvent • In cells: • Solute- organic and inorganic compounds • Solvent- water

Osmosis • The process by which water molecules diffuse across a cell membrane from an area of higher concentration to an area of lower concentration. • Does not require cells to use energy • Example of passive transport.

Direction of Osmosis • Net direction of osmosis depends on the relative concentration of solutes on the two sides of the membrane. • HYPOTONIC • HYPERTONIC • ISOTONIC.

Table 5 -1 Direction of Osmosis

Hypotonic • Concentration of solute molecules outside the cell is lower than the concentration in the cytosol. • Water diffuses into the cell until equilibrium is established. .

Hypertonic • Concentration of solute molecules outside the cell is higher than the concentration in the cytosol. • Water diffuses out of the cell until it reaches equilibrium.

Isotonic • Concentrations of solutes outside and inside the cell are equal. • Water diffuses into and out of cell at equal rates. • No net movement of water. .

Contractile Vacuoles • Organelles that remove water. • Collect excess water and then contract, pumping water out of the cell. • This action requires energy.

Contractile Vacuoles • Figure 5 -2 • Paramecium

Osmosis • Cells response to hypotonic environment by pumping solutes out of the cytosol • Water molecules are less likely to diffuse into the cell.

Osmosis • Plants are surrounded by water- so water diffuses by osmosis into the plant. • Cell wall is strong enough to resist the pressure exerted by the water inside the cell. • TURGOR PRESSURE- pressure that water molecules exert against the cell wall.

Plasmolysis • The contraction or shrinking of the cell membrane of a plant cell in a hypertonic solution in response to the loss of water by osmosis.

Human Red Blood Cells • Lack contractile vacuoles, solute pumps, and cell walls. • Change shape when in hypertonic or hypotonic environment. • Hypertonic environment- water leaves cells making them shrivel. • Hypotonic- water diffuses into cells causing them to swell and eventually burst. • Cytolysis- bursting of cells.

Human Red Blood Cells Figure 5 -4

Facilitated Diffusion • Type of passive transport. • Molecules that cannot readily diffuse through the cell membrane even when there is a concentration gradient across the membrane. • Either not soluble in lipids or too large. • Movement assisted by carrier proteins.

Carrier Proteins • Figure 5 -5

Transport of Glucose • Facilitated diffusion • 1. can help substances move into or out of a cell. • 2. carrier proteins involved in facilitated diffusion are each specific for one type of molecule

Ion Channels • Transport ions from an area of higher concentration to an area of lower concentration. • Na+, Cl-, Ca 2+ • Ions cannot diffuse across the membrane without assistance. • Each ion channel is specific to one type of ion.

Ion Channels • Some ion channels are always open • Other ion channels have gates • Gates may open or close in response to three kinds of stimuli • Stretching of the cell membrane • Electrical signals • Chemicals in the cytosol or external environment

Quick Quiz • True/False- In diffusion substances always move down the concentration gradient. • True/False- Osmosis is a type of diffusion.

Chapter 4 Section 2: Active Transport

Objectives: 11/26 • Do Now • Day 3 of Lab • Lab Questions • Lab Error • Reading Comprehension

Day 3 of Lab • • Dump out the corn syrup and water from the cups. Do not pop the egg. Measure the circumference of the egg. After you take measurements, place the egg in the front of the room. • Clean up lab station • Work with lab group to complete the post lab questions. • Hand in lab paper, work on reading comprehension

Active Transport • In some cases- cells must move materials from an area of lower concentration to an area of high concentration. • up the concentration gradient • This type of transport requires the cell to expend energy • The energy needed is supplied directly or indirectly by ATP

Types of Active Transport • Sodium-Potassium Pump • Endocytosis • Exocytosis

Cell Membrane Pumps • Ion channels and carrier proteins help with active transport. • Cell membrane pumps- move substances from lower concentration to higher concentration.

Sodium-Potassium Pump • Carrier protein that transports Na+ ions and K+ ions up their concentration gradients. • Some animals cells must have higher concentrations of these- so the sodium-potassium pumps maintain the concentration differences.

Sodium Potassium Pump

Sodium – Potassium Pump pumps three Sodium ions out of cell pumps two Potassium ions into cell

Movement in Vesicles • Endocytosis and Exocytosis • Used to transport large quantities of small molecules into and out of cells. • Require cells to expend energy.

Endocytosis- 2 main types • Pinocytosis- transport of solutes or fluids • Phagocytosis- movement of large particles or whole cells. • Certain cells in animals use phagocytosis to ingest bacteria and viruses • phagocytes

Endocytosis- 2 main types • Pinocytosis- transport of solutes or fluids • Phagocytosis- movement of large particles or whole cells. • Certain cells in animals use phagocytosis to ingest bacteria and viruses • phagocytes

Endocytosis 42

Exocytosis • Process by which a substance is released from the cell through a vesicle that transports the substance to the cell surface and then fuses with the membrane to let the substance out of the cell. • Reverse of endocytosis • Release protein, waste products, or toxins

Exocytosis 44