Microbial Culture
Class 12 · Biotechnology
4 ideas in Class 12 Biotechnology, explained in plain words, with games and quizzes to practise.
What Microbes Need to Grow
Part of: Feeding and Housing Microbes
Microbes multiply only when their needs are met: energy plus carbon, nitrogen, oxygen, iron, minerals, micronutrients and water. Self-feeding strains build everything from simple salts, while needy strains demand ready-made organic extras.
Why it matters. Feeding errors starve cultures or invite the wrong germs. Knowing each need helps you mix media that grow exactly your microbe.
Key words
- nutrient
- : Any substance a microbe needs to grow and divide.
- prototroph
- : A strain that builds all extras from simple salts.
- auxotroph
- : A strain that demands ready-made organic extras.
- micronutrient
- : A mineral needed in tiny amounts for growth.
- culture
- : A deliberate growth of microbes in prepared medium.
Try it in two minutes
- List the needs aloud: energy, carbon, nitrogen, air, iron, minerals, extras, water.
- Ask which need builds bodies and which gives energy.
- Sort two strains: one happy on plain salts, one demanding extras.
Try at home. Sort five microbes you read about into self-feeders and extra-seekers.
Culture Media
Part of: Feeding and Housing Microbes
Media are microbe meals built three ways. By recipe they are exact-chemical or rich natural brews; by firmness they are broths, jellies or in-between; by job they pick out, tell apart or boost wanted germs. Seaweed jelly firms plates without feeding most germs.
Why it matters. Picking the wrong meal grows the wrong crowd. These three splits let you read any recipe and predict who will bloom on it.
Key words
- synthetic medium
- : A meal mixed from exact known chemicals.
- complex medium
- : A meal brewed from rich natural extracts.
- selective medium
- : A meal that lets only wanted germs grow.
- differential medium
- : A meal that shows germs apart by looks.
- enrichment medium
- : A meal that boosts scarce wanted germs.
Try it in two minutes
- Sort recipes into exact-chemical versus rich brews.
- Sort firmness into broth, jelly and in-between.
- Sort jobs into pick-out, tell-apart and boost meals.
Try at home. Classify three kitchen recipes by recipe, firmness and job.
Sterilisation and Pure Cultures
Part of: Clean Work and Growth
Clean work starts with sterilising: wiping out all living forms including tough spores, unlike lighter cleaning that only trims germs. Heat, rays, filters and chemicals each suit different tools, and heat-sensitive add-ons must be filtered, never cooked. Pure colonies then come from streaking or spreading samples thin so single cells grow apart.
Why it matters. One dirty tool or mixed colony ruins results and can mislead whole studies. Knowing which method fits which tool keeps work sterile and strains pure.
Key words
- sterilisation
- : Wiping out all living forms including tough spores.
- disinfection
- : Trimming most harmful germs on surfaces.
- autoclave
- : A steam-pressure chamber for heat-proof tools.
- membrane filter
- : A fine sieve that strains germs from liquids.
- streak plate
- : Thinning a sample across jelly to part colonies.
Try it in two minutes
- Rank cleaning strengths: full wipeout versus lighter trims.
- Match tools to heat, rays, filters or chemicals.
- Ask why add-ons like selection chemicals must be filtered, not cooked.
Try at home. List which home items need full wipeout versus lighter cleaning.
Growth Curve
Part of: Clean Work and Growth
A plotted growth curve shows four acts: a settling lag, a doubling rush, a crowded standstill, and a dying decline. Warmth, acidity and air set the pace, and doubling maths predicts counts: each generation doubles the crowd, so tiny starts explode fast.
Why it matters. Phase reading tells when to harvest, when to feed, and when cultures turn toxic. Doubling maths turns vague growth into exact counts and times.
Formulas
- N = N0 x 2^n
- td = 0.693 / u
Key words
- lag phase
- : The settling span before rapid doubling starts.
- log phase
- : The rush span where cells double steadily.
- stationary phase
- : The crowded span where growth equals dying.
- generation time
- : The minutes one doubling round takes.
- death phase
- : The decline span where dying outruns dividing.
Try it in two minutes
- Walk the four acts: settle, rush, stall, fall.
- Ask what limits each act: adjusting, feasting, crowding, poisoning.
- Practise doubling: start 100, double thrice, count 800.
Try at home. Count doublings in one hour for a 20-minute doubling strain.
What your child will practise
- Culture Media: Ocean Quick Fire (Quick Fire)
- Growth Curve: Jungle Puzzle (Clue Puzzle)
- Growth Curve: Jungle Quick Fire (Quick Fire)
- Sterilisation and Pure Cultures: Candy Quick Fire (Quick Fire)
- What Microbes Need to Grow: Desert Puzzle (Clue Puzzle)
- Quiz: Culture Media (8 questions)
- Quiz: Growth Curve (8 questions)
- Quiz: Sterilisation and Pure Cultures (8 questions)
- Quiz: What Microbes Need to Grow (8 questions)