Competencies explain transport mechanisms in cells (diffusion osmosis,facilitated transport, active transport) STEM_BIO11/12-Ig-h-13 2. differentiate exocytosis and endocytosis - STEM_BIO11/12-Ig-h-14

Activity (15 mins) Video on Cell Membrane and Transport Guide Questions 1. What is cell membrane and its composition based on the video? 2. Initially, what is Cell Transport? Describe each type. 3. Why is Transport necessary in Cell?

Membrane Transport Passive Transport Active Transport Motion of substances in and out of the cell Cell membranes are Selectively permeable Two Types of Transport Mechanisms: Passive Transport Active Transport

Membrane Transport Passive transport is movement of molecules through the membrane in which no energy is required from the cell Active transport requires energy expenditure by the cell

Types: A. Simple Diffusion – unassisted diffusion 1. Passive Movement – requires no energy Types: 1. Diffusion – process of scattering molecules from an area of greater to a lesser concentration. Types: A. Simple Diffusion – unassisted diffusion   1. Osmosis – movement of solvent materials 2. Dialysis – movement of solute materials. B. Facilitated Diffusion – provides protein carriers as transport vehicle. 2. Filtration – process by which water and solute are forced thru a membrane by fluid or hydrostatic pressure

2. Active Transport – when cells uses ATP supply to move substances across the membrane.   Types: 1. Solute Pumping – similar to facilitated diffusion that requires carriers that reversibly with substances to be transported across membrane. 2. Bulk Transport – some substances that cannot get through the plasma membrane in any other way are transported with the help of ATP into or out of cell.

Passive Transport A process that does not require energy to move molecules from a HIGH to LOW concentration Diffusion Facilitated Diffusion

Diffusion is the movement of small particles across a selectively permeable membrane like the cell membrane until equilibrium is reached. These particles move from an area of high concentration to an area of low concentration. outside of cell inside of cell

Diffusion is movement of solute molecules from high concentration to low concentration

1. Passive Transport There are two types of diffusion Simple Diffusion Facilitated Diffusion

1. Passive Transport Simple Diffusion Substances pass directly through the cell membrane The cell membrane has limited permeability to small polar molecules, water, and ions The motion of water across the membrane is known as osmosis

HIGH to LOW concentration Diffusion HIGH to LOW concentration

Semi-permeable membrane is permeable to water, but not to sugar Osmosis is the diffusion of water through a selectively permeable membrane like the cell membrane Water diffuses across a membrane from an area of high concentration to an area of low concentration. Semi-permeable membrane is permeable to water, but not to sugar

Passive Transport Osmosis Osmosis is the movement of water from an area of high to low concentration of water movement of water toward an area of high solute concentration in osmosis, only water is able to pass through the membrane Osmosis moves water through aquaporins

Osmosis Osmotic concentration is determined by the the concentration of all solutes in solution Relative Osmotic Concentrations Hypertonic solutions: have a higher relative solute concentration Hypotonic solutions: have a lower relative solute concentration Isotonic Solutions: have equal relative solute concentrations

1. Passive Transport Facilitated Diffusion Substances must pass through transported proteins to get through the cell membrane The cell membrane is selectively permeable

Proteins that form channels (pores) are called protein channels Facilitated Diffusion is the movement of larger molecules like glucose through the cell membrane – larger molecules must be “helped” Proteins in the cell membrane form channels for large molecules to pass through Proteins that form channels (pores) are called protein channels outside of cell inside of cell Glucose molecules

Facilitated Diffusion Selective permeability: integral membrane proteins allow the cell to be selective about what passes through the membrane. Channel proteins have a polar interior allowing polar molecules to pass through. Carrier proteins bind to a specific molecule to facilitate its passage.

Channel Proteins Channel proteins include: - ion channels allow the passage of ions (charged atoms or molecules) which are associated with water - gated channels are opened or closed in response to a stimulus the stimulus may be chemical or electrical

Fig. 5.10 ion channels

Channel Proteins Ion channels allow the passage of ions (charged atoms or molecules) across the membrane A concentration gradient of ions across the membrane creates a membrane potential a membrane potential is a charge difference between the two sides of the membrane

Fig. 5.10 ion channels + + + + + + + + + +

Carrier Proteins Carrier proteins bind to a specific molecule to facilitate its passage.

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Hypertonic Solutions: contain a high concentration of solute relative to another solution (e.g. the cell's cytoplasm). When a cell is placed in a hypertonic solution, the water diffuses out of the cell, causing the cell to shrivel. Hypotonic Solutions: contain a low concentration of solute relative to another solution (e.g. the cell's cytoplasm). When a cell is placed in a hypotonic solution, the water diffuses into the cell, causing the cell to swell and possibly explode. Isotonic Solutions: contain the same concentration of solute as another solution (e.g. the cell's cytoplasm). When a cell is placed in an isotonic solution, the water diffuses into and out of the cell at the same rate. The fluid that surrounds the body cells is isotonic.

Interactive Red Blood Cell Click

Organisms can maintain osmotic balance in different ways: 1. Some cells use extrusion in which water is ejected through contractile vacuoles. 2. Isosmotic regulation involves keeping cells isotonic with their environment. 3. Plant cells use turgor pressure to push the cell membrane against the cell wall and keep the cell rigid.

B. Active Transport Active transport is the movement of molecules from LOW to HIGH concentration. Energy is required as molecules must be pumped against the concentration gradient. Proteins that work as pumps are called protein pumps. Ex: Body cells must pump carbon dioxide out into the surrounding blood vessels to be carried to the lungs for exhale. Blood vessels are high in carbon dioxide compared to the cells, so energy is required to move the carbon dioxide across the cell membrane from LOW to HIGH concentration. outside of cell inside of cell Carbon Dioxide molecules

ANALOGY: ENERGY NEEDED: Active Transport NO ENERGY NEEDED: Diffusion Osmosis Facilitated Diffusion ENERGY NEEDED: Active Transport

2. Active Transport Active transport Requires energy – ATP is used directly or indirectly to fuel active transport Able to moves substances against the concentration gradient - from low to high concentration allows cells to store concentrated substances Requires the use of carrier proteins

Active Transport Carrier proteins used in active transport include: -uniporters – move one molecule at a time -symporters – move two molecules in the same direction -antiporters – move two molecules in opposite directions

1. Solute Pumping Sodium-potassium (Na+-K+) pump An active transport antiport mechanism Uses an antiporter to move 3 Na+ out of the cell and 2 K+ into the cell ATP energy is used to change the conformation of the carrier protein The affinity of the carrier protein for either Na+ or K+ changes so the ions can be carried across the membrane

Active Transport Sodium-potassium (Na+-K+) pump Used by animal cells to maintain a high internal concentration of K+ ions and a low internal concentration of Na+ ions Maintains a concentration gradient that is used to power many other important physiological process

Fig. 5.15-1

Fig. 5.15-2

Fig. 5.15-3

Active Transport Coupled transport Uses the energy released when a molecule moves by diffusion to supply energy to active transport of a different molecule A symporter is used Glucose-Na+ symporter captures the energy from Na+ diffusion to move glucose against a concentration gradient

2. Bulk Transport Bulk transport of substances is accomplished by 1. Endocytosis – movement of substances into the cell 2. Exocytosis – movement of materials out of the cell

Ex: White Blood Cells, which are part of the immune system, surround and engulf bacteria by endocytosis.

Bulk Transport Endocytosis occurs when the plasma membrane envelops food particles and liquids. 1. phagocytosis – the cell takes in particulate matter 2. pinocytosis – the cell takes in only fluid 3. receptor-mediated endocytosis – specific molecules are taken in after they bind to a receptor

Bulk Transport Exocytosis occurs when material is discharged from the cell. Vesicles in the cytoplasm fuse with the cell membrane and release their contents to the exterior of the cell Used in plants to export cell wall material Used in animals to secrete hormones, neurotransmitters, digestive enzymes

(10mins) Application:   1. What did you learn today? 2. How do you relate the Cell Transport to real life situation? Make an analogy