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Regarding Q12 of the ethology exam practice QNS, the answer for ‘The freezing behaviour in (4) is explained by mice forming an association between flashing lights and electrocution’ is false. However, in the explanation provided, it was mentioned that “ These mice form a false association between the non-threatening stimulus and electrocution. Therefore, the mice become scared of the non- threatening stimulus.”, which suggests that an association is formed with the flash and the electrocution, making the experimental mice freeze. How do we know the freezing behaviour is not caused by the association but by something else?

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Does germination of spore start before fern reproductive structures are formed?

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Q8: for statements B and C, I wanted to ask why these two options are false and not feasible as i thought they could have been true...?

8. [IBO 2021, Portugal]

Leeches are organisms belonging to the Phylum Annelida, Class Hirudinea. They are found predominantly in freshwater habitats, few are marine, and some are adapted to terrestrial life. As fluid feeders and bloodsuckers, leeches are more highly specialized than other Annelida. Figure 1 presents a transversal section of a leech at the intestine level and the arrows point to glandular cells identified just under the epidermis. What is their function?

Figure 1. Transversal section of a leech at the intestine level.

Indicate whether each of the following statements is true (T) or false (F).

A.   Allow the organism to glide better in the habitat

B.   Secrete substances that attract prey

C.   Secrete substances that repel predators

D.   Facilitate cutaneous respiration

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How does one know if primary succession is truly primary succession?

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Would temperatures increase or decrease upwelling?

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Is histamine a cytokine?

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Hello Mr Duncan,

I am Xin Ying from Class 2405. I would like to ask a question regarding Qn 12 in the exam practice questions you gave us.

For the 3rd statement, the answer states that "the potential of (4) becomes more negative when (2) alone fires" is false. However I chose the 'true' option, because I had thought that the neuron (2) would result in IPSP and is inhibitory. I would then like to ask, how am I able to tell that this neuron is not inhibitory and affects neuron 1 in another way, such that it is unable to reach threshold potential?

Thank you!

21 Oct 2024

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As per instructions given, I have attempted the Microbiolgy questions however I am unable to understand 2 processes in Qn12.

Firstly, how does process A shows option 2, the production of hydrolytic enzymes that inactive surrounding antimicrobial drug. My answer was originally option 3 as the antibiotic molecules can be seen being degraded into simpler substances.

Secondly, how does Process C show option 1 of modifying the antimicrobial drug target when right above it, enzymes inside the bacterium can be seen engulfing and digesting the antibiotic molecules? Wouldn't option 5 be more likely then in that case?

Thank you for your time.

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Qns regarding ecology:

1. Regarding the difference in length of food chains observed of ecosystems in arctic and sub-arctic, I noted that sunlight(and potentially temperature) plays a key factor in the length of the food chains as at sub-arctic regions, more sunlight is present as the region has a longer period of sun exposure compared to arctic region. This results in more microscopic algae being able to grow in water, which are consumed by microplankton. The microplankton population increases, resulting in more food for consumers such that the food chains can be longer due to increase in prey population which means more energy available to consumers.

I would like to better understand if this can be applied to other situations which have the independent variable of temperature, such as length of food chains from countries of equatorial region and tropical region, and if there are possible exceptions to this?

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For "Microbiology_P1 QNS" practice set #7, why can't <Option D peroxidase> be considered, since it can also digest bonds?