3.4 Passive & Active Transport

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Three Forms of Transport Across the Membrane

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Passive Transport

Simple Diffusion

Doesn’t require energy

Moves high to low concentration Example: Oxygen diffusing into a cell and carbon dioxide diffusing out.

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Passive Transport

Facilitated diffusion

Doesn’t require energy

Uses transport proteins to move molecules from a high to low concentration Examples: Glucose or amino acids moving from blood into a cell.

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Types of Transport Proteins • Channel proteins are embedded in the

cell membrane & have a pore for materials to cross

• Carrier proteins can change shape to move material from one side of the membrane to the other

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Active Transport

Requires energy or hydrolysis of ATP

Moves materials from LOW to HIGH concentration

AGAINST concentration gradient

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Active transport

Examples: Pumping Na+ (sodium ions) out and K+ (potassium ions) in against strong concentration gradients.

This is called Na+-K+ Pump

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Sodium-Potassium Pump

3 Na+ pumped in for every 2 K+ pumped out; creates a membrane potential

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More Active Transport – requires energy! EXOCYTOSIS – getting things out of the cell

Molecules are moved out of the cell by vesicles that fuse with the plasma membrane. Example: This is how many hormones are secreted and how nerve cells communicate with one another.

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Exocytosis vesicle immediately after fusion with plasma membrane.

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Exocytosis Large molecules that are manufactured in the cell are

released through the cell membrane.

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ENDOCYTOSIS – getting things INTO the cell

2 types: Pinocytosis and Phagocytosis

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Pinocytosis

Most common form of endocytosis.

Taking in dissolved (LIQUID) molecules-cell drinking - think pino colada!

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Phagocytosis

The cell engulfs large particles such as food, bacteria, etc. into vesicles – cell eating (food-phago)

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Phagocytosis About to Occur

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Phagocytosis - Capture of a Yeast Cell (yellow) by Membrane Extensions of an Immune System Cell (blue)

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Cystic Fibrosis – an abnormal protein channel

Review Summary Questions

1. What is a concentration gradient? How does it affect diffusion?

2. Explain the differences between active & passive transport. Why is it important to a cell?

3. In what way is a cell membrane selective?

4. Would you expect osmosis and diffusion to stop when substances are evenly distributed?

5. What type of evidence demonstrates active transport?

6. How do membranes regulate the movement of molecules into and out of the cell?

Answers to Review Questions

1. Refers to a change in solute concentration, from a high to low concentration, or from low to high.

2. Active transport uses energy to move molecules against their concentration gradient. Passive transport describes transport of molecules down their concentration gradient & is accomplished without the input of energy.

Answers cont.

3. The cell membrane allows small molecules to pass through but restricts the movement of large molecules. It uses a variety of transport proteins to help move certain large molecules wither with or against their concentration gradients. It also contains transport proteins that help transport ions across the membrane.

4. When substances attain equal distribution over an area, there is no longer any net movement of the substance, and diffusion (or osmosis) stops.

Answers cont.

5. Since substances cannot move against their concentration gradients, the observation that some substances do move into areas of higher concentration suggests that some energy-requiring process must be involved in this movement.

6. Membranes regulate movement of molecules by providing barriers to certain larger molecules. Other molecules are regulated by specific transport proteins or by coupling the movement of one type of molecule to the movement of another type of molecule.

3.5-3.8 Notes Gas Exchange (O2 and CO2 ) in Aquatic Organisms

How do Fish Breathe?

Countercurrent flow –gas exchange in fish

• The gills of fish utilize countercurrent flow, a very effective mechanism for removing the maximum amount of oxygen from the water flowing over them

• During countercurrent flow, two types of fluids (in this case blood and water) flow in opposite directions past one another. These fluids are separated by thin membranes.

• Countercurrent flow promotes diffusion of oxygen down its concentration gradient from water into the blood.

Gas Exchange in the Land Dwellers • In order for oxygen and carbon dioxide to

enter or leave the cell, they must be dissolved in water – SO that happens across a membrane.

• Exchange surfaces are in an interior space. It protects the surface from excess evaporation caused by contact with outside air.

Gas Exchange- Grasshopper

• Small branched air ducts. The ducts branch into smaller and smaller tubes providing a large surface area relative to volume.

Human Respiratory System

Alveoli with surfactant Surfactant – chemical that prevents alveoli from closing

Surfactant secreting cells…

Gas Exchange - Human • Alveoli-air sacs that make up the lungs. One cell thin

• Capillaries surround alveoli. Capillaries are also one cell thin

• Gas exchange occurs between alveoli & capillary walls

Transpiration in Plants • Gases leave through

openings in leaves-

called Stomates

• Leaves covered with

waxy cuticle to prevent

water loss

Human Urinary System/Excretory System

• MAINTAINS HOMEOSTASIS….

• Important for eliminating metabolic waste (waste produced from metabolism)

• Maintains the appropriate water-salt balance in the blood

• Maintains blood pressure

• Maintains Acid-base balance

of blood

• Secretes hormones

Organs of the Urinary System

• Kidneys – 2 • Ureters – 2 • Urinary bladder -1 • Urethra – 1

• Lump of glandular tissue on each kidney these are the adrenal glands.

Kidneys • Main organs of the Urinary System

• Bean shaped/reddish brown and fist sized

• Covered by a tough capsule of connective tissue – called the renal capsule

• Renal arteries bring blood to the kidneys

• Renal veins carry blood

away from the kidneys

• Anytime you see the

word renal – think kidneys

Ureters

• Extend from kidneys to bladder

• Peristalsis of ureters cause urine to enter the bladder

UrinaryBladder

• Recieves urine from the ureters

• Stores urine until it is expelled from the body

• Urine enters the bladder in spurts – 1-5 spurts per minute.

Urethra

• Small tube that extends from the bladder to an external opening

• When the urinary bladder fills to about 250 ml of urine, stretch receptors and nerve impulses cause the urinary bladder to contract, sphincters to relax -and you pee.

Anatomy of the Kidney

• Cortex- outer layer

• Medulla – middle that consists of tissue masses

• Pelvis – central space that is continuous with the ureter

• Each kidney is composed of over one million nephrons…

Nephrons (kidney tubules)

• Each kidney is composed of over one million microscopic nephrons

• Long, coiled tube with one cuplike end that fits over a mass of capillaries, the other end opens into a duct that collects urine.

• Cup of nephron – Glomerulus capsule or Bowman’s capsule

• Ball of capillaries within the cup - Glomerulus

• Filtration: fluid portion of the blood is forced into the glomerular capsule (filtrate)- blood cells and blood proteins NOT filtered.

• Reabsorption: Cells of tubules reabsorb substances needed by the body from the filtrate.

• Secretion: Cells of the tubules selectively remove substances that were left in the plasma after filtration or returned by reabsorption.

3 functions of the Nephron

1. Filtration – happens in the glomerulus and filtrate goes into the glomerlular (Bowman’s) capsule

2. Reabsorption – happens in the proximal kidney tubules of nephron

3. Secretion – happens at the distal kidney tubules of nephron.

Filtration: Water, salts, nutrients, nitrogenous waste

Reabsorption: Nutrients (glucose, amino acids) and salt molecules

Secretion: H+ ions, K+ ions, creatinine and drugs

So Urine Contains:

1. Substances that have undergone filtration but have not been reabsorbed 2. Substances that have undergone secretion

Urea comes from the breakdown of amino acids.

• Urea

• is the primary Nitrogenous end product of metabolism.

• Amino acids broken down in the liver causing the liver to release ammonia- toxic to cells. The liver combines the ammonia with carbon dioxide to make urea – not toxic to cells and can be released in urine.

• Creatinine •High energy phosphate reserve molecule in muscles

• Uric Acid •From the breakdown of nucleotides

More Kidney Functions

• Adrenal glands secrete the hormone Aldosterone

• Aldosterone regulates excretion of sodium and potassium

• When K+ levels are too high in the blood, aldosterone is released into the blood, stimulating the secretion of K+ ions from the blood into the tubule near the collecting duct lowering the aldosterone levels – feedback mechanism

More Kidney functions

• Regulating blood pressure:

• Dehydrated – brain secretes ADH (anti-diuretic hormone) so the cell membranes of the collecting ducts become more permeable to water. Water passes from the duct to the bloodstream and water volume in the blood is restored (higher blood pressure)

More Kidney functions

• Removes excess salt from body – in small concentrations

• When humans drink high salt solutions, the body loses water b/c while trying to eliminate the excess salt, the body excretes more water than taken in.