Additional Notes Homeostasis and Transport in the Cell
Organelles and Cell Transport • Proteins are made by the ribosomes on the Rough ER • Proteins are placed in sacs called vesicles. • The vesicles are then transported to the Golgi where they are moved along, packaged, and modified. • The vesicles then move to the cell membrane and release the contents or transport the vesicle to another part of the cell where the protein is needed for the cell to function.
Plasma Membrane and Cell Transport • The plasma membrane is made of two layers of phospholipids and proteins. • Selectively permeable – limits entry of certain molecules • Glycoproteins and glycolipids in the membrane act as antennae to receive chemical messages from other cells • Cells need the right balance of nutrients and ions, such as calcium, magnesium, sodium, potassium and hydrogen to maintain homeostasis. • The membrane controls gas exchange, water balance, intake of nutrients and elimination of wastes to maintain homeostasis
Molecules Not all molecules can dissolve through the membrane easily. Factors that determine if they can move include: • Polarity of molecule – Polar or nonpolar • Size – large or small • Electric charge - positive or negative
Concentration Gradient – the difference in concentrations across a distance – usually the difference on either side of the cell membrane. • The membrane acts like a dam holding back water. • A great amount of potential energy is held back behind the membrane just like the water behind a dam has a great potential to rush out if the dam is opened. • The cell depends on this potential energy of the concentration gradient to get certain things across the membrane.
Maintaining Homeostasis • Thermoregulationis the ability of an organism to keep its body temperature within certain ranges, even when the surrounding temperature is very different. • Vertebrates can regulate their body temperatures in 2 different ways
Ectotherms– reptiles, fish and amphibians – warm body by absorbing heat from its surrounding. • Aquatic animals have body temperatures close to the water temp. • Terrestrial (land dwelling) animals change location to get more sun/shade as needed. Can’t live in very cold climates
Endotherms – mammals and birds – have fast metabolism which makes heat needed to warm body. Also have insulation such as hair, feathers, fat
Water regulation (osmoregulation) is the control of water concentrations in the bloodstream which controls the amount of water available for cells to absorb. • Kidneys: mammals – regulates the amount of water in body by adjusting the concentration of various salts in the blood. Also removes waste products of metabolism • Contractile vacuoles: unicellular; Paramecium– contracts to squeeze out excess water, salts and CO2 Contractile vacuole
Spiracles – Insects – openings on abdomen – can open & close • Stomata – Plants – openings on leaf surface – can open & close
Oxygen regulation O2 levels must be regulated according to activity level. Lungs • Muscle contraction of diaphragm to move air into highly branched tube-like passages • Passages end in millions of alveoli – increases the surface area for gas exchange. Spread out, alveoli would cover the size of 2 large parking spaces!!
Book lungs – spiders - similar to alveoli, but in tissue layers that are like pages in a book
Gills – fish, aquatic worms, crustaceans • Water contains dissolved oxygen – moves in by diffusion. Carbon dioxide moves out by diffusion. • Highly efficient • Large surface area – many fine, threadlike filaments. • Skin – earthworms – slime layer on outer surface – direct exchange – no special organs