materials move across the cell’s membrane some materials move by diffusion –diffusion= the...
Post on 02-Jan-2016
219 Views
Preview:
TRANSCRIPT
MATERIALS MOVE ACROSS THE CELL’S MEMBRANE
• SOME MATERIALS MOVE BY DIFFUSION– Diffusion= the process by which molecules
spread out, or move from areas of high concentration to areas of less concentration
– Occurs because molecules are always in constant motion; cells use diffusion to carry out life functions
• SOME TRANSPORT REQUIRES ENERGY
• CELL SIZE AFFECTS TRANSPORT
DIFFUSION• Occurs naturally as particles move from area of high concentration to area of lower concentration
• The greater the difference in concentrations, the quicker diffusion occurs.
• Diffusion is how materials move in photosynthesis & cellular respiration.
• Diffusion is a type of passive transport (materials move without using cell’s energy.)
• Polar substances (sugar/salts/amino acids) diffuse via protein channel (still passive- no energy)
OSMOSIS• Diffusion of water
through a membrane is OSMOSIS.
• If you forget to water a plant, the soil dries, the roots dry, and water leaves the plant cells by osmosis, so the cell shrinks and the plant “wilts”.
Some Transport Needs Energy• ACTIVE TRANSPORT
– Uses energy to move material through membrane
– Marine iguanas that swim & feed in salty ocean which causes lots of salt in blood.
– They have special glands using active transport to remove salt from blood & blow it out of their nostrils.
– Similar to our kidneys filtering blood for us.
TRANSPORT REQUIRING ENERGY, CONTINUED
• ENDOCYTOSIS: large bits of material get captured in pocket of membrane
• Pocket breaks off and forms package that moves into cell.
• Cells use this to fight bacteria & viruses by absorbing them.
• EXOCYTOSIS: a membrane within the cell encloses material needed to be removed
• Package moves to cell membrane, joins with it, and expels material
• Cells use this to flush out waste or expel proteins & hormones made by the cell.
CELL SIZE AFFECTS TRANSPORT
• Most cells are very small; most human cells are about 50 micrometers (.05mm), while bacteria are only 3-5 micrometers.
• The amount of cell membrane limits the ability of a cell to transport materials into and out of a cell.
• As a cell gets larger, there is a time when its volume grows more than its surface area, so not enough resources can get into the cell to feed it.
• Thin, flat cells or long skinny cells (muscle & nerve) give lots of surface area for plenty of food and resources to get into the cell.
top related