Chapter 3: Exchanging Materials with the Environment

Cellular Transport

Transport across the Membrane

Transport? • Cells need things…water, oxygen, balance of ions,

nutrients (amino acids, sugars..building blocks), nucleotides, hormones

• Cells need to get rid of things…waste (carbon dioxide, ammonia, any material that has been broken down)

• Transport…allows these materials into a cell and allows these materials to leave the cell across the cell membrane.

The Cell Membrane

• ALL cells have a cell membrane (also called the plasma membrane, phospholipid bilayer, fluid mosaic model).

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FLUID- because individual phospholipids and proteins can move side-to-side within the layer, like it’s a liquid.

MOSAIC- because of the pattern produced by the scattered protein molecules when the membrane is viewed from above.

Why is it called the FLUID MOSAIC MODEL?

Functions of the Cell Membrane

• Selectively Permeable – allows certain things to enter and leave the cell (transport).

• Acts as a protective barrier.

• Recognizes other cells/things nearby.

Parts to the Cell Membrane

proteins

proteins

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Phospholipids

Make up the cell membrane

Contains 2 fatty acid chains that are nonpolar (repel charged particles but let fat-soluble molecules to pass)

Head is polar & contains a Phosphate group & glycerol

• Membrane transport properties: The structure of the lipid bilayer dictates that most polar compounds are unable to pass through it unless assisted by some transport mechanism. Large molecules (macromolecules) cannot freely cross the membrane. Small non-charged molecules, particularly if they are lipid soluble, have no difficulty crossing the membrane. Gases can also diffuse through the lipid bilayer (ex. Lungs). Water passes into and out of cells with relative ease.

• Polar heads (phosphate heads) are hydrophilic (water loving)

• Nonpolar tails (fatty acid tails) are hydrophobic (water fearing)

• This makes the cell membrane “selective” in what crosses.

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Cell Membrane

Hydrophobic molecules pass easily; hydrophilic DO NOT

The cell membrane is made of 2 layers of phospholipids called the lipid bilayer

Another Look at the CM

proteins

proteins

Parts of Cell membrane Proteins

• Embedded throughout the cell membrane

• Receptor proteins

• Communication proteins

• Act as channels that allow materials through

• Hold glycoproteins that allow for cell recognition

Glycoproteins

• Carbohydrate chains attached to the proteins embedded in the cell membrane

• Act as antennae that detect cells and materials nearby

Importance of Protein Channels

Cholesterol?

• Major membrane lipid

• Similar to phospholipids-one end is hydrophilic and one end is hydrophobic

• Makes the membrane less permeable to most biological molecules

• Lowers the temperature that a membrane solidifies and it decreases fluidity at higher temperatures

Importance of Glycoproteins & Glycolipids

• Embedded in cell membrane

• Sometimes have sugar chains attached to the proteins or sugar chains attached to the phospholipids

• Function: act as antennae that receive chemical messages from other cells and function in cell recognition

Getting through the Cell Membrane

Can pass easily • Small hydrophobic nonpolar

molecules move through easily.

e.g. O2, CO2, N2, • Small uncharged polar

molecules that are soluble in lipids (fat-soluble) can pass easily

e.g. ethanol, glycerol, H2O

Cannot pass easily • Ions (charged particles),

hydrophilic molecules larger than water, and larger uncharged polar molecules do not move through the membrane on their own.

e.g. H+ ions, Ca+ ions, Na+ ions, Cl- ions, amino acids, glucose, nucleotides

So what determines if material can cross – write this down!

• Polarity – – In general, nonpolar molecules do not interact with

polar molecules (oil-nonpolar, water-polar)

– Polar molecules interact with polar molecules (salt –ion, water-polar)

• Hydrophobicity- – lipid bilayer is hydrophobic so would repel hydrophilic

molecules. Hydrophobic molecules can pass

• Charge- – the hydrophobic tails will not allow charged particles

to cross...they need special transport proteins

Review Questions

1. What materials need to be exchanged across a cell membrane?

2. In what way is an organism a protected compartment?

3. What is the significance of a membrane being selectively permeable?

Answers to Review Questions 1. CM must control the exchange of nutrients,

waste, water, and communication signals

2. An organism is a protected compartment in the sense that whether it is made of a single cell or many, each cell is completely surrounded by a protective membrane

3. A cell membrane must be selectively permeable so that the cell can exert some level of control over which types of molecules can pass through the membrane

3.3 Diffusion and Osmosis

• Movement of molecules from high concentration to low concentration (down the concentration gradient –like balls rolling down a hill).

Concentration Gradient

• Refers to a change in solute concentration, either from a low concentration to a high one or the opposite.

• Diffusion moves molecules down a concentration gradient, but it cannot transport molecules against a concentration gradient.

Diffusion

• Diffusion is a PASSIVE process – requires no energy from the cell

• Molecules will diffuse until the concentration is the same throughout

• Does diffusion increase

or decrease entropy of

a system?

Osmosis

• Diffusion of water across the cell membrane

• Water moves from high to low concentration

• Water will always move

to where there is more

solute!

• Does not require energy

from the cell (passive)

Water will always move to where there is more solute!

low solute high solute

Osmotic States of a Cell • Isotonic state – solute concentration inside

the cell and outside the cell is equal. No movement of water

• Hypotonic state – the solute concentration inside the cell is lower than outside the cell. Water will move out of the cell. The cell will shrink

• Hypertonic state – the solute concentration inside the cell is higher than outside the cell. Water will move into the cell. The cell will swell/expand

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Cell in Isotonic Solution

CELL

10% NaCL 90% H2O

10% NaCL 90% H2O

What is the direction of water movement?

The cell is at _______________.

ENVIRONMENT

NO NET MOVEMENT

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Cell in Hypotonic Solution

CELL

10% NaCL 90% H2O

20% NaCL 80% H2O

What is the direction of water movement?

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Cell in Hypertonic Solution

CELL

15% NaCL 85% H2O

5% NaCL 95% H2O

What is the direction of water movement?

ENVIRONMENT

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Cells in Solutions

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Isotonic Solution

NO NET MOVEMENT OF H2O (equal amounts entering &

leaving)

Hypotonic Solution

Cell bursts (CYTOLYSIS)

Hypertonic Solution

Cell shrinks & shrivels

(PLASMOLYSIS)

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Cytolysis & Plasmolysis

Cytolysis Plasmolysis copyright cmassengale

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Osmosis in Red Blood Cells

Isotonic Hypotonic Hypertonic

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Aquaporins

• Aquaporins are membrane water channels that play critical roles in controlling the water contents of cells. These channels are widely distributed in all kingdoms of life, including bacteria, plants, and mammals.

What happens in plant cells? • Plant cells have a cell wall (which means extra

protection from bursting)…animal cells do not.

• Turgor – is the outward pressure of a cell against its cell wall.

• Flaccid- opposite. Lacking firmness or turgor

Plasmolysis- when the cell membrane of a plant cell pulls away from the cell wall due to the loss of water through osmosis

Plasmolysis

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hypotonic hypertonic isotonic

hypertonic isotonic hypotonic

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3.4 Passive & Active Transport

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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.

Inside Cell Cell environment copyright cmassengale

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ENDOCYTOSIS – getting things INTO the cell

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2 types: Pinocytosis and Phagocytosis

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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Three Forms of Transport Across the Membrane

Cystic Fibrosis – why protein channels are important!

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.

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

Human Respiratory System

Alveoli with surfactant Surfactant – chemical that prevents alveoli from closing

Surfactant secreting cells…

Hemoglobin

O2 = transported by the hemoglobin molecule in the red blood cells.

• Each hemoglobin molecule carries 4 molecules of O2.

• Each polypeptide chain contains:

Bohr Shift-in muscle cells

• At rest, PO2 is lower, pH

Is normal, O2 is released

from hemoglobin

• During exercise, muscle

Releases more CO2,

decreasing

pH, and PO2 is higher so

hemoglobin releases MORE O2 (Bohr shift)

Bohr Shift • When the blood is fully

saturated all the erythrocytes are in the form of oxyhemoglobin.

• As the erythrocytes travel to tissues deprived of oxygen the partial pressure of oxygen will decrease.

• Consequently, the hemoglobin releases the oxygen to form hemoglobin

Breathing rate varies with exercise. Changes in carbon dioxide concentration leads to a lowering of blood pH. This is detected by chemosensors in the aorta and carotid arteries that send impulses to the breathing center of the brain. Nerve impulses are then sent to the diaphragm and the intercostal muscles to increase contraction or relaxation rates.

Asthma

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

3 Functions of the nephron

• Filtration

• Reabsorbtion

• Secretion

Filtration

• Filtration: fluid portion of the blood is forced into the glomerular capsule (filtrate)

• Happens in the glomerulus capsule

• Water, salts, nutrients (glucose, amino acids, small proteins), nitrogenous waste (urea)

• Blood cells and large blood proteins are NOT filtered

Reabsorption

Reabsorption –absorbing again (into blood)

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

• happens in the proximal (close to the capsule) kidney tubules of nephron

• Nutrients (glucose, amino acids) and salt molecules

Secretion Secretion: Process of secreting a substance from the

blood into the kidney tubules

• Happens between the nephron capillaries and the distal (far away from capsule) kidney tubules of the nephron (countercurrent exchange)

• Anything that wasn’t filtered at the glomerulus capsule or anything that was reabsorbed that shouldn’t have been

• 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: CH4N2O

• 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: C4H9N3O2 •High energy phosphate reserve molecule in muscles

• Uric Acid: C5H4N4O3 •From the breakdown of nucleic acids

Blood pressure regulation • ADH and aldosterone are two of the most important

hormones needed in the regulation of blood pressure.

• When blood pressure (BP) goes down, the body will automatically counter it by starting a systemic change to increase the BP.

• When the person is severely dehydrated, the body has no other option but to limit urine output and conserve more water for the body cells to use.

• These processes can be carried out by two hormones – aldosterone and ADH (Anti-diuretic hormone)

• Although both hormones have the same ultimate goal of water preservation or retention, they do it differently.

Aldosterone & ADH

Aldosterone – Adrenal cortex

ADH- Hypothalamus

ADH • ADH regulates the rate or amount of water

reabsorption at the distant tubules of the kidney’s nephrons

• ADH also has the ability to reabsorb urea which, in turn, reabsorbs water through osmosis

Aldosterone • Aldosterone, like ADH also acts on the distant

tubules, but also at the kidney’s collecting ducts.

• Water retention with the aid of aldosterone is more complex because it has to undergo the Sodium-Potassium exchange channels. In this set-up, potassium is excreted while sodium is retained

ADH vs. Aldosterone

• ADH is synthesized in the hypothalamus while aldosterone is made in the adrenal cortex of the adrenal glands on top of the kidneys.

• ADH conserves water directly through its reabsorption while aldosterone conserves water indirectly through the reabsorption of sodium.

Transpiration in Plants • Gases leave through

openings in leaves-

called Stomates

• Leaves covered with

waxy cuticle to prevent

water loss