Biology ISA/EMPA June 2011

DCPIP is decolourised more slowly when ammonium hydroxide is added. Use your knowledge of the light-dependent reaction to suggest three reasons why.

Ammonium hydroxide has slowed electron transfer along electron transport chain to DCPIP. Ammonium hydroxide accepts electrons and does not pass electrons along electron transport chain to DCPIP. Ammonium hydroxide affects pH. pH affects proteins in electron transport chain.

What was the purpose of using a blender?

Break open cells to allow release of chloroplasts.

There are large pieces of tissue and other organelles in your chloroplast suspension. Describe how you could isolate the chloroplasts from the other components in the suspension.

Centrifuge at low speed then again at a higher speed. Collect pellet.

In your investigation, the colour change in DCPIP was caused by the transfer of electrons from chlorophyll. Name the part of a chloroplast where this transfer of electrons takes place.

Chloroplast membrane. The thylakoid

The farmers decided that K would be the best herbicide to use. Explain why herbicide K would give a higher crop yield.

Fewer weeds left. Fewer weeds to produce seeds. Less contamination of crop by weeds. Fewer weeds to separate from crop. Less competition between crop and weeds.

Plant breeders are trying to produce barley plants with shorter stems. Explain how this would increase the Harvest Index.

Increases proportion of crop that is used (Greater proprtion of grain).

These questions relate to your investigation of the effect of ammonium hydroxide on the time taken for chloroplasts to decolourise DCPIP. You were told not to put the leaf midrib or leaf stalk in the blender (Step 2).Suggest why

No chloroplasts present in midrib. Midrib is tough material so it will not be cut up by blender.

One of the farmers told a local newspaper reporter of their findings. The newspaper published an article with the following headline: "Local farmers show scientists the way to bigger crop yields." Was this headline justified? Explain your answer.

No control field. The amount of herbicide may be different in different fields. The fields itself may have difference e.g. the type of soil may be different. There may be a different number of weeds in each field at the start of the investigation. No repeats, only one set of data. Field size may vary. Scientific research has led to greater yield.

The values for the biomass of the barley plants are different in each quadrat. Suggest an explanation for this difference.

Quadrats from different parts of field. Abiotic and biotic factors are different in different parts of the field.

The isolation medium was cold and was also isotonic with the spinach tissue. Explain why it was important that the isolation medium was isotonic with the spinach tissue.

Same water potential as plant tissue so no net movement of water by osmosis. This means the chloroplasts won't burst or shrivel.

Tube B was a control experiment (step 8). Explain how the results in this tube acted as a control experiment.

Shows that: The colour in X does not change in B. Colour change not due to isolation medium. Colour change is due to chloroplasts and not mitochondria.

The isolation medium was cold and was also isotonic with the spinach tissue.Explain why it was important that the isolation medium was cold.

Slows enzyme activity. Enzymes released during blending.Chloroplasts not damaged so photosynthesis continues. Blending produces friction and releases heat. Heat changes the tertiary structure of enzymes so it denatures enzymes. If solution is cold then chloroplasts won't be damaged.

Some weed killers are substances that accept electrons during photosynthesis.Suggest how these substances kill weeds.

Slows light-dependent so less ATP and reduced NADP are produced so it also slows the light-independent reaction.

Suggest one disadvantage of using these weed killers on weeds growing in a crop. Explain your answer

Substance in weed killer absorbed by crop. Reduces growth and yield of crop because weed killer is non-selective. Weed killer may have toxic effects on other wild life. Weed killer slows respiration.

The farmers carried out their investigation during the summer. Suggest one advantage and one disadvantage of carrying out this investigation during the summer.

The advantage is that weed grows faster during the summer because the rate of photosynthesis is faster. This means the effect of the weeds will be seen more clearly. Disadvantage is that there is no information about winter or any other season. Weeds growing fast could kill beneficial insects not growing fast.

The researchers measured the dry biomass of the barley plants and the barley grain. What is the advantage of using dry biomass for these measurements?

Water in plants and grain varies.