Edexcel IGCSE Biology 2B Unofficial Mark SchemeWatch
Advantages of having no leaves:
Fewer stomata through which transpiration can occur, resulting in less water loss.
Why plants in the desert are likely to be less affected by smaller leaves:
Higher light intensity increases the rate of photosynthesis to compensate for the decrease in surface area.
Why some plants have deep roots:
To reach into groundwater reserves and extract water from there.
Use of precipitation in germination:
Water activates enzymes needed for respiration to release energy from glucose (obtained from starch in food store), for growth. Water moistens seed coat and helps it to split.
Method of reproduction in bulbs:
Advantage of this type of reproduction:
Faster than sexual, can reproduce before the plant is killed by a lack of water.
Organ used in this type of reproduction:
Stem tubers/rhizomes/ stem (in the case of a runner)
Waste water containing waste organic material such as faeces/urine as well as chemical contaminants.
Effect of sewage:
Bacteria reproduce and decompose the organic material, using up oxygen in aerobic respiration. Water becomes anoxic.
Mineral ions (especially nitrates) used for growth of algae and then eutrophication.
Possibly higher turbidity reducing photosynthesis of marine plants as well as the effect of the algal bloom.
Why the plant produces a pesticide:
Kill other plants/weeds which grow near it which could compete for nutrients/light/water.
Genetically modifying yeast:
Cut out specific gene using restriction (or similar) enzyme.
Insert into a vector such as a virus (or I believe that there are yeast plasmids also)
Have the virus infect the yeast cell and insert this gene
Forming recombinant DNA
Nutrients for (glucose) respiration and growth
Oxygen for respiration via inlet
Stirrers to agitate the medium
Optimum temperature (cooling jacket/temperature probe)
Optimum pH (pH probe)
Energy content of food:
Measure initial mass of food
Add 20ml of water to boiling tube clamped to retort stand
Measure initial temperature of water
Ignite food on mount pin, hold under tube
Keep igniting until all has burned
Measure final temperature
E per gram = mc(dt) / initial mass of food
Repeat + average
Carbohydrates in plants:
Presence of light
Reason for thermometer:
To ensure a fair test since temperature is a limiting factor in photosynthesis.
Purpose of tube C:
Control experiment, show that the change in CO2 concentration is because of the leaf.
Why Tube A went red:
Photosynthesis > Respiration
Net absorption of CO2
Why Tube B went yellow:
Respiration > Photosynthesis (no light)
Net release of CO2
Leaves de-starched by placing in a dark room for 24 hours.
One leaf in a well-lit room, another in a dark room for another 24 hours.
Remove both leaves, boil in water and hold in boiling ethanol to remove chlorophyll. Add iodine to leaf on a white tile. If leaf turns blue/black, photosynthesis has occurred (should happen to the leaf that was in the light)
Structures (can't remember the order)
Function of arteriole and hair in cold environments:
Hair erector muscles contract and pull hair upright
Traps a layer of air which acts as an insulator and reduces heat loss by conduction.
Vasoconstriction in arterioles reduces blood flow to skin surface, so less heat is radiated away from the body.
Please do feel free to chip in for those that I've forgotten or quarrel with any of the above!