Models and Pracs Flashcards
Root cell microscope mitosis
Description:
- A cutting from a root cell was placed under a light microscope and examined for mitosis. As the root tip is the area of cell division, mitosis could be seen occurring in many cells.
Pros:
- Allowed the phases of mitosis to be studied: one cell was undergoing anaphase at the time the cutting was made, as chromosomes were separating towards opposite ends of the cell. In another cell, the cell was in telophase
- Enabled mitosis to be observed in real life, not just on a diagram
Cons:
- The root cells were dead, so the progression of mitosis within a single cell could not be observed
- Magnification limit of light microscope prevented the phases of mitosis to be observed in greater detail - separating chromosomes could only be seen as small black masses
Judgement: up to you
Jenisha judgement: helpful in allowing real life mitosis to be observed
Josie judgement: Very interesting as different slides depicted different stages of mitosis, allowing in-depth study of process of mitosis
DNA Origami model
Description:
- An origami DNA model was constructed from a single sheet of A4 paper folded into accordion folds and twisted to give the helical structure of a DNA molecule.
Pros:
- The model allowed for the visualisation of the helical structure of DNA
- The model showed complementary base pairs in between the sugar phosphate backbones using colour coding
Cons:
- The model showed DNA as structure as diametrically opposite instead of skewed, making it scientifically inaccurate
- The model was simplistic and did not provide further insights into DNA structure that students did not already know
- The model was difficult to construct, making it inaccessible
Judgement: up to you
Jenisha judgement: it was not useful
Josie’s judgement: limited usefulness, as it did not contribute to student’s understanding, and was an inaccurate visualisation.
DNA Replication 2D diagram drawing
Description:
- A 2D representation of DNA replication was drawn on an A3 sheet of paper. The diagram showed the unwinding of the double helix by Helicase, the direction of the replication fork, and the synthesis of new DNA strands from each of the two parent strands. The diagram depicted the enzyme polymerase synthesising nucleotides continuously on the leading strand and in Okazaki fragments on the lagging strand.
Pros:
- The diagram was detailed, clearly showing the role of each enzyme in DNA replication, the direction of replication, and the process of replication.
- Visual representation was informative and easy to understand.
Cons:
- The diagram was a 2D representation of a complex biological process, so failed to accurately represent the chemical reactions involved in the synthesis of a new strand of DNA
- The diagram used simple shapes to represent the enzymes, risking scientifically inaccurate representations of enzymes
Judgement: up to you
Jenisha judgement: it was highly useful because detailed
Josie’s judgement: very useful as it included a lot of detail that showed the whole process of DNA replication (unwinding to polymerising) - also consolidated student’s knowledge.
Polypeptide synthesis bead
Description:
- An interactive activity to model protein synthesis was carried out by stringing beads on a chain. 3 students: Messenger (receives DNA code and converts to mRNA), Transferer (identifies correct coloured bead), Connector (creates the chain)
Pro:
- Messenger modelled mRNA: how DNA transcription results in the formation of RNA, and mRNA leaves the nucleus for further processing.
- Transferer modelled tRNA: acquisition of beads (amino acids) to follow mRNA code that represents codons - 3 letters for one colour.
- Function of ribosome depicted by attachment of beads to chain.
- Polypeptide structure modelled by beads on a chain, mimicking how it begins as a strand and can be folded up.
Con: highly simplified that does not depict enzymes involved.
- tRNA modelled without anticodons
- Messenger does not show how mRNA is formed from DNA (e.g. unwinding, RNA polymerase)
- The structure of mRNA, tRNA and ribosomes are not represented. Although the genetic sequences are represented as letters, it does not show the helix structure or sugar/phosphate.
Jenisha judgement: useful in showing the role of mRNA, tRNA, and ribosomes in polypeptide synthesis
Josie’s judgement: useful in showing the role of stuff in polypeptide synthesis, but does not explain the process. Lacks detail, but does show different stages of synthesis
Yeast budding prac
Description:
- A practical investigation was carried out to determine the effect of temperature on the rate of yeast reproduction. Yeast, a fungi, reproduce asexually by budding. Budding involves numerous enzymes, including for the replication of genetic material. 3 water baths were set up at 15, 20, and 30C. Yeast samples were left in each for 2 hours and then a drop of each sample was examined under a microscope. From this it could be seen that yeast budding occured the least at 15C, and the most at 30C, evidencing that 30C was closest to the optimal temperature range in which the enzymes involved in yeast budding functioned.
Pros:
- Examining yeast samples under a microscope allowed budding to be seen, making this an effective qualitative way of determining the rate of yeast reproduction at different temeperatures
- The experiment was easy to carry out, making it accessible
Cons:
- Did not reveal new information that the optimal temperature range of biological enzymes is around 30C
- Due to the limited magnification and resolution of light microscopes, it was sometimes difficult to see budding in the sample
Judgement: up to you
Jenisha judgement: helpful to see how environmental conditions impact rate of asexual reproduction in organisms
Josie’s judgement: useful in understanding and viewing asexual organisms - linking reproduction and enzyme rates too
Gametogenesis/non-disjunction diagram
Description:
- Three diagrams showing the stages of gametogenesis were drawn. Both oogenesis and spermatogenesis were represented. Spermatogenesis was depicted beginning with meiosis I, followed by meiosis II, and finally specialisation into 4 sister sperm cells. Oogenesis was shown beginning with meiosis I, which resulted in a secondary oocyte and a polar body, followed by meiosis II, in which the secondary oocyte divided into a mature egg cell and another polar body. The polar body from meiosis I was shown dividing into 2 further polar bodies. The third diagram showed fertilisation. Each diagram showed a mutation, for example nondisjunction leading to trisomy 21 and monosomy 21 in meiosis II for oogenesis.
Pros:
- The diagram showed the progression of gametogenesis in a clear, comprehensible way
- The diagram showed how mistakes can occur during cell replication and the consequences of these errors
- Showed the importance of meiosis in creating gametees - and therefore consequences
Cons:
- The diagram did not show how oogenesis is arrested at different stages of life in females. Instead, it represented oogenesis as a continuous process from the first division of the primary oocyte to the formation of a mature egg cell, with no stops in between meiotic divisions.
- The diagram did not show the disintegration of the polar bodies resulting from oogenesis
Judgement: up to you
Jenisha judgement: it was helpful because it distilled the essence of the process of oogenesis and spermatogenesis, even if it did not accurately represent the chronological pauses between stages of oogenesis
Josie’s judgement: useful in visualising the process of meiosis, and the influence of crossing over, independent assortment in contributing to genetic variation. Also visualised the impact of non-disjunction. Comparison of gametogenesis between sexes
