1.1.7 culturing microorganisms

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gcse

Biology

Cells

GCSE Biology

AQA

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<p>binary fission</p>

binary fission

each division of one cell produces two cells - no. of cells increases by power of 2 each time binary fission occurs

  • bacteria multiply by type of simple cell division: binary fission

  • in right conditions, bacterial cell prapares to divide by replicating genetic material before increasing in size

  • copies of each piece of circular DNA moves to each end of cell before cytoplasm divides, new cell walls form around each daughter cell

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growing bacterial cultures in lab

  • effects of disinfectants & antibiotics on microorganisms investigated using cultures of bacteria growth in lab

  • in correct conditions, some species of bacteria (such as coli) can multiply once every 20 minutes. this is good, as large cultures of bacteria for study can be grown in short periods of time

  • to multiply quick, bacteria require adequate supply of nutrients(carbohydrates,proteins,minerals & vitamins) and appropriate temperature(varies depending on species being grown)

    • warmer temps promote faster growth

      • school labs maximum temp allowed = 25°C

      • above 25°C more harmful pathogens are likely to grow

  • bacteria able to grow in nutrient broth solution or as colonies on agar gel plate

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uncontaminated cultures & aseptic techniques

  • vital that uncontaminated cultures of microorganisms are grown in lab

  • presence of competing spacies may affect growth of cultures & validity of study performed on them

<ul><li><p>vital that <mark data-color="blue">uncontaminated</mark> cultures of microorganisms are grown in lab</p></li><li><p>presence of <mark data-color="blue">competing</mark> spacies may affect <mark data-color="blue">growth</mark> of <mark data-color="blue">cultures</mark> &amp; <mark data-color="blue">validity</mark> of study performed on them</p></li></ul>
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calculating inhibition zone area

calculating area of clear zone = more accurate way of comparing effect of different substances on bacterial growth that judging by sight

inhibition - area where no bacterial growth has occurred, larger zone = more effective substance

  • effectiveness of different antibiotics, antiseptics or disinfectants can be determined by calculating area of inhibition zone around disc of tested substance

calculation in image

<p><strong><em>calculating area of clear zone = more accurate way of comparing effect of different substances on bacterial growth that judging by sight</em></strong></p><p><strong><em><mark data-color="blue">inhibition</mark> - area where no bacterial growth has occurred, larger zone = more effective substance</em></strong></p><ul><li><p><mark data-color="blue">effectiveness</mark> of different <mark data-color="blue">antibiotics</mark>, <mark data-color="blue">antiseptics</mark> or <mark data-color="blue">disinfectants</mark> can be determined by calculating <mark data-color="blue">area</mark> of <mark data-color="blue">inhibition zone</mark> around disc of <mark data-color="blue">tested substance</mark></p></li></ul><p><strong>calculation in image</strong></p>
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calculating bacteria in a population

  • average amount of time taken for bacterial cell in population to divide = mean division time

  • number of times cell divides & how many cells it produces determined if you know mean division time & how long division has been occurring

<ul><li><p><mark data-color="blue">average</mark> amount of <mark data-color="blue">time taken</mark> for bacterial cell in population to divide = mean division time</p></li><li><p>number of <mark data-color="blue">times</mark> cell <mark data-color="blue">divides</mark> &amp; how <mark data-color="blue">many</mark> cells it produces determined if you know mean division <mark data-color="blue">time</mark> &amp; how <mark data-color="blue">long</mark> division has been occurring</p></li></ul>