Cell Transport, Photosynthesis, & Cellular Respiration Unit 6 Notes Cell Transport, Photosynthesis, & Cellular Respiration

4/3 Monday’s Notes: Cell Membrane and Passive Transport

Chapter 7: Cell Structure & Function Section 2: Cell Structure

Membrane Cells need to maintain homeostasis and to do so the cells must control what crosses the cell membrane; the lipid bilayer does this The Lipid Bilayer (Cell Membrane) is made of phospholipids; Phosophorus - hydrophilic head – polar 2 Lipids/Fatty Acids - hydrophobic tails - nonpolar The bilayer only allows few ions & nonpolar; most ions and polar substances are repelled

Membrane Proteins Various proteins are in the membrane; some face in, some face out, some face both inside & outside Proteins are amino acids, which are sometimes polar; they are therefore held in the membrane because they repel against the polar water on either side of the membrane & they are attracted to the nonpolar center of the cell membrane

Cell-Surface Marker: Receptor Proteins: Enzymes: Transport Proteins: A long chain of sugars that identifies each type of cell The sugars on the chain are attracted to the cell surface proteins; glycoproteins(which help cells work together) Receptor Proteins: Enable a cell to sense its surroundings by binding to certain substances outside the cell; this causes changes inside the cell Enzymes: Proteins in the cell membrane that help with important biochemical reactions inside the cell Transport Proteins: Aid in the movement of substances that cannot pass through the lipid bilayer across the cell membrane into & out of the cell

Chapter 7: Cell Structure & Function Section 3: Cell Transport

Cells move substances of varying size, electrical charge & composition in & out of themselves Sometimes cells require energy to move substances across its membrane, and sometimes they don’t Passive Transport is when cells do not require energy to move substances Active Transport is when cells require energy to move substances

Cell Transport Passive transport: The movement of substances across a cell membrane WITHOUT the use of cell energy Substances move from an area of high concentration to an area of low concentration

Types of passive transport Simple diffusion Facilitated diffusion osmosis

Concentration Gradient: In a solution the randomly moving molecules want to fill spaces evenly; when the spaces are filled evenly it is called equilibrium Concentration: The amount of a particular substance in a given volume The number of particles (solute) dissolved in a given amount of solution Concentration Gradient: When one area has a higher concentration than another area does

The direction of movement across the cell membrane depends on the concentration gradient Some substances diffuse through the lipid bilayer Other substances diffuse through transport proteins

Types of Passive Transport Diffusion: The gradual mixing of two or more substances by random motion Movement down the concentration gradient The movement to make the two areas equal in concentration; movement from high concentration to low concentration After diffusion the concentration will become equal on both sides of the cell membrane Examples: sugar dissolves (spreads out evenly) in water to make Kool-Aid Sugar cube dispersing in a beaker of water Ink dispersing in a beaker of water Eventually all of the molecules spread out evenly and reach equilibrium; equilibrium=when molecules are evenly spaced within a substance High Concentration Low Concentration

When small, nonpolar molecules pass directly through the lipid bilayer Simple Diffusion: When small, nonpolar molecules pass directly through the lipid bilayer Facilitated Diffusion: Occurs when many types of ions & polar molecules do not diffuse easily through the nonpolar lipid bilayer Transport proteins help these ions & polar molecules diffuse through the cell membrane Two types of transport proteins that assist are Channel Proteins & Carrier Proteins

Channel Proteins: Carrier Proteins: Ions, sugars, & amino acids diffuse through the aid of channel proteins Often called Pores Serve as tunnels through the lipid bilayer Each channel aids specific substances of a specific size and/or charge Carrier Proteins: Substances that fit with their binding sites are transported by carrier proteins Once the substance & protein bind the protein’s shape changes & transports the substance across the membrane where it is released

Simple Diffusion

Facilitated Diffusion

The size of the molecule The type of molecule What determines whether a molecule can diffuse across the cell membrane? The size of the molecule The type of molecule

The diffusion of water across a membrane Osmosis: The diffusion of water across a membrane Allows cells to maintain water balance as their environment changes If there is a concentration gradient for solutes, there must also be a concentration gradient for free water molecules; osmosis occurs as water molecules work for EQUILLIBRIUM and move from high concentration to low concentration

Osmosis is a form of facilitated diffusion Water is a polar molecule & therefore does not diffuse directly across the bilayer Water must use channel proteins that only water molecules can move through

Isotonic environment/solution: When the concentration of solute molecules inside the cell is equal to the concentration outside the cell Water goes in and out of the cell at the same rate There is no net change in water movement The cell remains the same size

Water moves out of the cell The cell loses water & therefore shrinks Hypertonic environment/solution: When the concentration of solute molecules outside the cell is greater than the concentration inside the cell Water moves out of the cell The cell loses water & therefore shrinks

Water moves into the cell The cell gains water & therefore expands Hypotonic environment/solution: When the concentration of solute molecules inside the cell is greater than the concentration outside the cell Water moves into the cell The cell gains water & therefore expands

The swelling caused by a hypotonic solution can cause a cell to burst The rigid cell walls of plants & fungi prevent cells from expanding too much Many unicellular organisms have contractile vacuoles that collect excess water inside the cell & force it out of the cell to prevent swelling Animal cells have the ability to avoid swelling by removing the dissolved solutes from the cell, which will leave the water & remove the particles causing the water concentration inside the cell to increase

Turgor Pressure: The pressure that water molecules exert against the cell membrane causes cells to swell up Plasmolysis When water leaves the cell and turgor pressure is lost The reason plants wilt (shrivel up) when they don’t get enough water When a cell takes in too much water it will eventually burst open This process is called cytolysis or lysis

Organism Images

Facilitated Diffusion: When substances move across the membrane with the help of protein carriers Even if there is a concentration gradient and molecules want to move across the cell membrane, some still can’t cross it They may be too large They may not dissolve in lipids (which make up the cell membrane)

Carrier Proteins carry molecules across the cell membrane during facilitated diffusion This requires no energy, so it’s a passive form of transport Carrier proteins are specific for the type of molecule A glucose carrier protein will only work for glucose

sodium (Na+) calcium (Ca2+) potassium (K+) chloride (Cl-) Diffusion through Ion Channels: When ions pass through the cell membrane through ion channels Ions can’t pass through the cell membrane on their own so they move through ion channels Examples of Ions that must pass through Ion Channels: sodium (Na+) calcium (Ca2+) potassium (K+) chloride (Cl-)