Biology - Section A: Organisms and Life Processes

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Life Processes

There are 7 different life processes most organisms have in common:

  • Movement
  • Respiration
  • Sensitivity (response to stimuli)
  • Nutrition
  • Excretion
  • Reproduction
  • Growth (and development)

Cell Structures - Plant

Unspecialised plant cells all have:

  • cell membrane - controls the movement of substances into and out of the cell
  • cytoplasm - site of cell reactions
  • nucleus - controls cell reactions and activities
  • mitochondria - site of areobic respration which realeases energy
  • cellulose cell wall - keeps the shape of the cell
  • permanent vacuole - contains cell sap
  • chloroplasts- found in green plant cells, contains chlorophyll for photosynthesis 

Cell Structures - Animal

Unspecialised animal cells have:

  • cell membrane - controls the movement of substances into and out of the cell
  • cytoplasm - site of cell reactions
  • nucleus - controls cell reaction and activities, contains the DNA 
  • mitochondria - site of aerobic respiration

A cell is the smallest functional unit of an organism. Some organisms consist of only one cell e.g. amoeta, paramecium and yeast however other organisms are made up of many cells.

unicellular - an organisim with one cell

multicellular - organism made up of many cells

cells ----> tissues ----> organs ----> organ systems ----> organism

Enzymes

Enzymes are biological catalysts which speeds up the rate of biological reactions. They are made up of proteins and control all the reations in a cell. 

How do enzymes work?

Enzymes work by the mechanism of the lock and key theory. Enzymes have an active site, and when a substrate collides with the active site, it binds to the active site of the enzyme. A reaction occurs and products are made which leave the active site. The active site becomes denatured (changes shape).

The effect of pH and temperature

The shape of the active sites depends the shape of the protein molecule. Temperature and pH affect this shape. High temperatures denature the enzyme and change the active site so that the enzyme…

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