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where is the plasma membrane found?
on the surface of animal cells, and just inside the cell wall of plant cells.
give 2 functions of the plasma membrane.
1) regulates the movement of substances into and out of the cell. 2) responds to chemicals using its receptor molecules.
describe the structure of the nucleus.
large organelle surrounded by a nuclear envelope with many pores. contains chromatin and often a nucleolus.
what is the purpose of the nucleolus?
making ribosomes.
describe the structure of a lysosome.
a round organelle surrounded by a membrane, with no clear internal structure. contains digestive enzymes that are kept separate from the cytoplasm by the surrounding membrane.
what are 4 functions of a lysosome?
1) break down material ingested by phagocytic cells. 2) exocytosis. 3) digest worn-out organelles. 4) autolysis.
name 2 places in the cell where ribosomes can be found.
1) floating free in the cytoplasm 2) attached to the rough endoplasmic reticulum.
describe the structure of a ribosome.
a very small organelle with a small subunit and a large subunit.
what is the function of the smooth endoplasmic reticulum?
it synthesises and processes lipids.
describe the structure of the rough endoplasmic reticulum.
a system of membranes enclosing a fluid-filled space, covered in ribosomes.
what is the function of the rough endoplasmic reticulum?
it folds and processes proteins that have been made at the ribosomes.
describe the structure of the golgi apparatus.
a group of fluid-filled flattened sacs.
what are 5 functions of the golgi apparatus?
1) add carbohydrates to proteins to form glycoproteins. 2) produce secretory enzymes. 3) secrete carbohydrates. 4) transport, modify & store lipids. 5) form lysosomes.
describe the structure of a mitochondrion.
usually oval shaped. has a double membrane - the inner one is folded to form cristae. inside is the matrix, which contains enzymes involved in respiration.
where are mitochondria found in large numbers?
in cells that are very active and require a lot of energy.
what is the function of a mitochondrion?
it is the site of aerobic respiration.
formula for magnification
length of image / length of specimen
definition of resolution/resolving power
ability to distinguish between 2 very close points.
definition of autolysis
the complete breaking-down of cells after they have died.
when are lysosomes formed?
when the vesicles produced by the golgi body contain enzymes such as proteases & lipases.
which type of ribosome is found in eukaryotic cells?
80s type.
which type of ribosome is found in prokaryotic cells?
70s type.
what are 4 characteristics of lipids?
1) contain carbon, hydrogen & oxygen. 2) proportion of carbon and hydrogen is smaller than in carbohydrates. 3) insoluble in water. 4) soluble in organic solvents.
what are the 3 main groups of lipids?
triglycerides (fats & oils) phospholipids waxes
name 5 roles of lipids.
1) use in plasma membranes 2) an energy source 3) waterproofing 4) insulation 5) protection
what is the reaction for making a triglyceride?
glycerol + 3 fatty acids --> triglyceride + 3H2O
how is a phospholipid different to a triglyceride?
one of the fatty acid molecules is replaced by a phosphate molecule.
what is a fatty acid?
a carboxyl (-COOH) group attached to a hydrocarbon chain.
describe the test for lipids.
1) add ethanol to the sample and shake well. 2) pour solution into water. 3) any lipid will show up as a milky emulsion.
what are plasma membranes?
all membranes around and within cells.
what are 2 functions of extrinsic proteins of the cell-surface membrane?
1) give mechanical support to the membrane 2) act as cell receptors for molecules
what are 2 functions of intrinsic proteins of the cell-surface membrane?
1) act as carriers to transport water-soluble material across the membrane 2) enzymes
describe extrinsic proteins of the cell-surface membrane.
occur either on the surface of the bilayer or partly embedded in it, but never extend completely across it.
describe intrinsic proteins of the cell-surface membrane.
completely span the phospholipid bilayer from one side to the other.
what are the 2 types of glycocalix?
glycoprotein glycolipid
why is the plasma membrane a good barrier against most water-soluble molecules?
the hydrophobic tails of the phospholipids make it hard for water-soluble substances to get through.
how does the plasma membrane allow cell communication?
it contains receptor proteins that allow the cell to detect chemicals released from other cells.
how does the plasma membrane allow cell recognition?
glycocalixes in the membrane tell white blood cells that the cell is your own.
what effect does cholesterol have on the plasma membrane?
cholesterol molecules fit in between the phospholipids of the bilayer, making it more rigid.
what effect do unsaturated fatty acids have on the plasma membrane?
they make it more fluid.
what are 3 factors affecting rate of diffusion across a membrane?
1) concentration gradient 2) thickness of exchange surface 3) surface area
definition of water potential
the likelihood of water molecules to diffuse out of or into a solution.
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