General Biology Chapter 4 Cellular Transport Cells and

General Biology Chapter 4 Cellular Transport Cells and Their Environment

Cellular Transports Two Major Types Passive Transport – Diffusion – Osmosis – Facilitated Diffusion Active Transport – Sodium Potassium Pumps – Endocytosis – Exocytosis

CELL MEMBRANE Membranes are selectively permeable and allow only certain substances to move across them. The interior portion of a cell membrane forms a nonpolar zone that prevents ions and most large molecules from passing through the membrane. Membranes have ion channel gates that close the pores of some ion channels in response to – – – Stretching of the cell membrane Change in electrical charge The binding of specific molecules to the channel

PASSIVE TRANSPORT Passive Transport - requires NO ENERGY does NOT use ATP to move molecules – Diffusion = random dispersion of molecules from an area of HIGH concentration to an area of LOW concentration. (Molecules down the concentration gradient) – Osmosis = is the diffusion of WATER molecules from an area of HIGH concentration to an area of LOW concentration (water down the concentration gradient) – Facilitated Diffusion = Uses CARRIER PROTEINS to transport specific subs. (sugar/amino acids) down a concentration gradient.

Diffusion-PASSIVE As a result of diffusion, the concentration of many types of substances eventually become balanced on both sides of a membrane. Dispersal of ink or sugar in a beaker of water is an example of diffusion. Cell does not expend energy (no energy used) Substances always flow from an are of high concentration to an area of LOW concentration.

Facilitated Diffusion-PASSIVE Use of transport proteins called carrier proteins that bind to a specific subs. Carry the subs. across the membrane and then release the subs. Amino acids and Sugars cross the membrane in this manner NO energy is required to transport the subs.

OSMOSIS-PASSIVE Diffusion of WATER into or out of a cell Is a type of PASSIVE transport. Diffusion of water down the concentration gradient. (from HIGH to LOW) Three water concentrations. – Hypertonic – Hypotonic – Isotonic

PASSIVE- Hypertonic A solution that causes a cell to shrink More solute than water If a cell is placed into a hypertonic solution water will flow out of the cell When a plant cell shrinks it loses Turgor pressure. A strong salt solution = hypertonic solution/more salt than water. Therefore the cell would shrink.

PASSIVE -Hypotonic When water diffuses into the cell and the cell swells. If a cell is placed into a hypotonic solution the cell will swell and may burst. When the concentration of water molecules is higher outside a cell than inside the cell, water will diffuse into the cell

PASSIVE -ISOTONIC No net water movement. Water diffuses into and out of the cell at the same rate. Fluid inside and outside is the same. The cell stays the same – equilibrium

ACTIVE TRANSPORT USES ENERGY USES ATP Moves against the concentration gradient. Moves molecules from an area of LOW to HIGH concentration Energy is required to move a substance across a cell membrane Unlike passive active REQUIRES ENERGY

ACTIVE TRANSPORT Three types Sodium Potassium Pumps Endocytosis Exocytosis Cell will use energy supplied by ATP

ENDOCYTOSIS-ACTIVE Transports molecules that are to large to be moved through the membrane can be transported into the cell by Endocytosis Requires Energy to carry out Endocytosis. Usually supplied by ATP Endocytosis is a process that uses vesicles to capture substances and bring them into the cell Endocytosis the cell membrane extends to engulf substances that are too big to pass through the cell membrane

EXOCYTOSIS - ACTIVE Ridding the cell of materials by discharging the materials in vesicles Helps rid the cell of waste Molecules that are to large to be moved across the cell membrane can be removed by Exocytosis requires ENERGY to expel proteins and other materials from the cell

Paramecium Unicellular aquatic organisms Paramecia are aquatic (live in water) unicellular protists. They have a number of characteristics also found in animals – – Need to ingest food in order to obtain energy (Heterotrophs) NO cell wall. Surrounded by a cell membrane Have some of the same organelles as animals ( nucleus/mitochondria/ribosomes/cilia) – In addition – paramecium have CONTRACTILE VACUOLES Contractile vacuoles expel excess water. Contractile vacuoles are found in unicellular aquatic organisms.

Question A How can you explain the observed relationship between the salt concentration and the rate of contractile vacuole concentration?

Answer A When there is less salt there is more water causing the contractile vacuoles pump faster.

Question B If something happened to a paramecium that caused its contractile vacuole to stop contracting, what would you expect to happen?

Answer B The water would build up inside the paramecium causing it to swell and then burst resulting in death.

Question C Would this result occur more quickly if the paramecium was in water with a high salt concentration or in water with a low salt concentration? Why?