2004
YEAST CELLS PRODUCE ETHANOL IN A PROCESS CALLED FERMENTATION. IS THIS PROCESS AFFECTED BY TEMPERATURE ?
Yes. Because the rate of enzyme action is affected by temperature.
DRAW A LABELLED DIAGRAM TO SHOW THE STRUCTURE OF RHIZOPUS.
DESCRIBE THE STAGES INVOLVED IN THE SEXUAL REPRODUCTION OF A ZYGOSPORE (DIAGRAM)
- Occurs between + strain and - strain. When hyphae of opposite strains grow close together, swellings form on both strains and touch each other
- Nuclei from both hyphae move into these swellings which are now called progametangia
- cross walls form to produce gametangia
- The walls of the gametangia dissolve and a number of fertilisations take place producing a diploid zygote nuclei.
- A zygospore forms around these nuclei. A zygospore is a tough walled capsule.
- When conditions are suitable the zygospore germinates.
- A hyphae grow out of the zygospore and produces a sporangium at the tip
- The sporangium opens releasing many haploid spores which grow into new individuals.
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2005
EXPLAIN THE TERM SAPROPHYTIC AND PARASITIC FUNGI
Saprophytic : live off dead organic matter
Parasitic : live off a living host
STATE A ROLE FOR EACH OF THESE TYPES
Saprophytic fungi obtain nutrients from dead material. As they digest it, minerals are released and recycled. Responsible for decay. Eg Mushrooms
Parasitic fungi: They are used to control population numbers.
STATE A FUNCTION FOR THE FOLLOWING.
Rhizoids: provide extra surface area for absorption of the digested material and help anchor the rhizopus.
Sporangium: Make spores
Gametangium: involved in sexual reproduction.The walls of the gametangia dissolve and a number of fertilisations take place producing a diploid zygote.
Zygospore: is a tough walled capsule that forms around nuclei. When conditions are suitable the zygospore germinates. (Survival) Also helps involved in dispersal. A hyphae grows out of the zygospore and produces a sporangium tip, The sporangium opens releasing many haploid spores which grow into new individuals.
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2007
WHAT IS A NUTRIENT MEDIUM
Material allowing growth
STERILE: all microorganisms are destroyed.
NAME NUTRIENT MEDIUM USED IN GROWTH ON LEAF YEAST.
Malt agar
DESCRIBE HOW YOU CONDUCTED THIS INVESTIGATION.
- Collect leaves from ash tree.
- Wipe down all lab surfaces, instruments and hands with disinfectant. This prevents unwanted microorganisms from contamination.
- Use a sterilised cork borer to cut 5 discs from a leaf
- Turn malt agar plate upside down to avoid air-borne contamination. Remove lid.
- Use sterilised forceps to stick leaf discs (undersides facing down) onto the inside of the agar plate. Use vaseline to stick them.
- Seal with tape.
- Place leaf discs with uppermost into an incubator of 25 C for 24 hours. Then place the plate upside down for 3 days.
RESULTS
Yeast colonies are seen as circular pink growths on agar.
Control = no growth.
GIVE A ROLE OTHER THAN ANCHORAGE FOR HYPHAE/RHIZOIDS
Digestion of nutrients
The hyphae release enzymes onto the substrate. Enzyme breaks down starch.This is absorbed back in.
2 EXAMPLES OF HARMFUL FUNGI
Athletes foot and ringworms
SUGGEST A STIMULUS WHICH TRIGGERS SEXUAL REPRODUCTION
Dehydration