B4 21st Century Science Notes Biology

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Keeping conditions inside the body the same is called homeostasis. It’s not easy. Lots of things have to happen, e.g. energy transferred between body and environment, carbon dioxide is a waste product of respiration and has to be transported by the bloodstream to the lungs where it is breathed out, waste and waste products are filtered out of the blood and excreted in the urine. An incubator has a temperature sensor, a thermostat with a switch and a heater. Negative feedback happens when one factor drops and another factor increases until they are in balance, for example is when the temperature drops, the heater turns on until the temperature goes up again. Feedback is when any change in the system results in an action that reverses the change. If two effectors have opposite effects they are called antagonistic effectors and are used to adjust the system as soon as there is a change, which means the response is more sensitive. Your body uses this system. Cell Structure and Function

Functions of the organisms
Cytoplasm- site of chemical reactions in the cell
Cell Membrane- controls what enters or leaves the cell (selectively permeable) Nucleus- contains nucleic acids, which code for the synthesis of specific proteins and control all activity in the cell. Mitochondrion- site of respiration

Chloroplast- site of photosynthesis
Cell Wall- made of cellulose which strengthens the cell and allows it to be turgid. Sap Vacuole- contains the cell sap and acts as a store of water or sugar or sometimes waste products the cell needs to excrete.

Enzymes are biological catalysts which are substances that increase the rate of reaction without ever being used up. It’s made up of proteins- large molecules made up of long chains of amino acids. Each enzyme has a unique shape and only catalyses one particular reaction. They work either by breaking down larger molecules or by joining small molecules together. The molecule must exactly into a part of the enzyme called the...
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