triple paper 1 biology content

Explain how bacteria replicates.

Bacteria multiply by simple cell division (binary fission) as often as every 20 minutes if they have enough nutrients and a suitable temperature.

How can bacteria be cultured?

• Nutrient broth solution

  • Contains lots of bacteria

  • Contains nutrients for the bacteria to grow and replicate

• Agar gel plate

  • Contains nutrient broth solution set into a jelly (using agar)

  • Bacteria grow into visible colonies on the plate

What is aseptic technique?

Used when preparing an uncontaminated bacterial culture.

• Sterilise Petri dishes, bacterial nutrient broth, and agar

• Sterilise inoculating loop (used to spread bacteria on plate) by passing it through a bunsen burner flame

• Attach the lid of the Petri dish using tape to stop unwanted microorganisms entering + lid falling off

• Place agar plate upside down to stop moisture dripping onto the dish

• In school labs, incubate at 25ºC - this reduces the chances that harmful bacteria will grow

Required Practical: Effect of antibiotics on bacterial growth

1. Clean the bench with disinfectant solution; this kills microorganisms that could contaminate our culture.

2. Sterilise an inoculating loop by passing it through a Bunsen burner flame.

3. Open a sterile agar gel plate near a Bunsen burner flame. The flame kills airborne bacteria.

4. Now use the loop to spread the chosen bacteria evenly over the plate.

5. Place sterile filter paper discs containing antibiotic onto the plate.

6. Incubate the plate at 25ºC.

What is a zone of inhibition?

On an agar plate, in the areas where bacteria has not grown. We can measure the effect of the antibiotic by calculating the area of the zone of inhibition.

What can plants be infected by?

Viral (e.g. tobacco mosaic virus), bacterial and fungal (e.g. black spot) pathogens as well as insects (e.g. aphids, which extract nutrients from the plant - stunting its growth).

How can plant diseases be detected?

• Stunted growth

• Spots on leaves

• Areas of decay (rot)

• Growths

• Malformed stems or leaves

• Discolouration

• The presence of pests

How can plant diseases be identified?

• Garden manual / website

• Taking infected plants to a lab to identify the pathogen

• Using testing kits containing monoclonal antibodies

Name how plants can be damaged from some ion deficiency conditions.

• Nitrate deficiency - stunted growth (as nitrate is needed for protein synthesis and therefore growth)

• Magnesium deficiency - chlorosis (as magnesium is needed to make chlorophyll, and in chlorosis, leaves become yellow)

Name examples of both physical and chemical responses in a plant.

• Physical - makes it difficult for microorganisms to penetrate the plant so protects from attack

  • Cellulose cell walls

  • Tough waxy cuticle on leaves -

  • Layers of dead cells around stems (e.g. bark on trees) - bark eventually falls off and is replaced

• Chemical

  • Antibacterial chemicals - kill bacteria + prevent them attacking the plant

  • Poisons to deter herbivores - stops the plant being eaten

Name examples of mechanical adaptations in a plant.

• Sharp thorns and hairs - deter animals (thorns stop herbivores eating, hairs irritate the herbivores mouth)

• Leaves which droop or curl when touched - scares herbivores

• Mimicry to trick animals - where plants look like dangerous plants to deter animals