CIE Biology AS Level Questions and Answers 100% Pass

CIE Biology AS Level Questions and Answers 100% Pass eukaryote organisms who possess nuclei; includes plants, animals, fungi and unicellular organisms known as protoctists; DNA is linear and bound to proteins to form chromatin. prokaryote organisms that lack nuclei; usually 1000 x - 10000 x smaller in volume than eukaryotes; DNA is circular and free in the cytoplasm; known as simplest cells; contain 70s ribosomes. virus consists of self-replicating molecule of DNA or RNA; has protective coat of protein molecules; range from 20 nm to 300 nm in size; all viruses are parasitic because they can only reproduce by taking over living cells. cell theory the basic unit of structure and function of all living organisms is the cell. partially permeable membrane an effective barrier between the cell and its surrounding materials. It allows a controlled traffic of materials across it in both directions. freely permeable membrane an ineffective barrier that would not keep anything out. instead the chemicals of the cell would simply mix with the surrounding chemicals by diffusion and nothing would exist. cell surface membrane a very thin membrane (about 7 nm diameter) surrounding all cells; it is partially permeable and controls the exchange of materials between the cell and its environment; seen as having three layers (trilaminar appearance). microvilli extensions of the cell surface membrane; used to increase surface area. microtubules make up cytoskeleton; made of tubulin. nucleus a relatively large organelle found in eukaryotic cells, but absent from prokaryotic cells; the nucleus contains the cell's DNA and therefore controls the activities of the cells. nuclear envelope the two membranes surrounding the nucleus; the outer membrane of the nuclear envelope is continuous with the endoplasmic reticulum. nuclear pores allow and control exchange between the nucleus and the cytoplasm. DNA Deoxyribonucleic acid; a molecule which contains the instructions that control the activities of the cell. nucleolus a small structure, one or more of which is found inside the nucleus; the nucleolus is usually visible as a densely stained body; its function is to manufacture ribosomes using the information in its own DNA. rough endoplasmic reticulum covered with ribosomes; proteins are often modified as they move through the rough ER. ribosomes sites of protein synthesis; found in cytoplasm or on the rough ER. endosymbiont theory cytoplasmic ribosomes are 80s while those of bacteria, mitochondria and chloroplasts are 70s. cytoplasm the contents of a cell, excluding the nucleus. smooth endoplasmic reticulum lacks ribosomes; makes lipids and hormones. lysosomes breakdown of unwanted structures; in white blood cells, lysosomes are used to break down bacteria. oranelles functionally and structurally distinct parts of a cell. compartmentalism organelles themselves being surrounded by membranes so that their activities can be separated from the surrounding cytoplasm. division of labour each type of organelle having its own function and therefore sharing the entirety of the work between different specialized organelles. mitochondria the organelle in eukaryotes in which aerobic respiration takes place; synthesizes lipids. golgi body an organelle found in eukaryotic cells; the golgi apparatus consists of a stack of flattened sacs, constantly forming at one end and breaking up into golgi vesicles at the other end; golgi vesicles carry their contents to other parts of the cell, often to surface membrane for secretion; the golgi apparatus chemically modifies the molecules it transports; collects, processes, and sorts molecules (particularly proteins from Rough ER). centriole one of two small, cylindrical structures, made from microtubules, found just outside the nucleus in animal cells, in a region known as the centrosome they are also found in the bases of cilia and flagella. centrosome assemble microtubules during nuclear division.