IB Biology HL Paper 2 Question Bank

SECTION: B

1.)

a) Explain the process of translation.

There are three stages in translation: initiation, elongation and termination. mRNA translated in a 5′ → 3′ direction. mRNA binds to ribosomes. The tRNA binds to start the codon. tRNA anticodon binds to mRNA codon by complementary base pairing. AUG is the start codon. Second (charged) tRNA binds to ribosome / to mRNA. Large subunit binds to small subunit. The amino acid on the first tRNA is joined to the amino acid on the second tRNA by condensation. As a result, a peptide bond formed. The ribosome moves (in a 5′ → 3′ direction) by one triplet/codon. Now, the tRNA in the exit site leaves and a new/third (charged) tRNA Binds. This repeats until reaches a stop codon and polypeptide is released. tRNA-activating enzymes join the correct amino acid to its specific tRNA.

b) Explain how control of metabolic pathways can be brought about by end-product inhibition.

The product of the metabolic pathway can act as an inhibitor of the enzyme earlier in the pathway. This is Non-competitive inhibition. The enzyme is an allosteric enzyme. The allosteric enzyme has an allosteric. (shape of an) allosteric enzyme alternates between active and inactive (form). Inhibitor binds to the allosteric enzyme and alters the shape of the active site. The more product there is, the more the pathway is inhibited. As the product gets used up inhibition decreases. This is negative feedback

c) Outline how meiotic division results in almost infinite genetic variation in the gametes produced.
Meiotic division, also known as meiosis, is a type of cell division that occurs in sexually reproducing organisms. It is a specialised form of cell division that reduces the chromosome number by half, resulting in the production of gametes such as eggs and sperm.
One of the key features of meiotic division is that it results in almost infinite genetic variation in the gametes produced. This is due to a number of factors:

1. Chromosome crossing-over: During meiosis, the chromosomes that carry genetic information (called homologous chromosomes) pair up and exchange genetic material. This process, known as crossing-over, results in the shuffling of genetic information and the creation of new combinations of genes.
2. Independent assortment: During meiosis, the chromosomes are randomly distributed into the gametes. This process, known as independent assortment, results in the creation of new combinations of genes.
3. Fertilization: When an egg and sperm combine during fertilization, the resulting zygote has a unique combination of genes inherited from both parents.
   Together, these processes result in almost infinite genetic variation in the gametes produced, as the combination of genes inherited by each gamete is unique. This genetic variation is important for the survival of a species, as it allows for the creation of offspring with different traits and characteristics that can adapt to changing environments.

2.)

a) Explain antibody production.
Antigen causes the production of antibodies specific to that Antigen. Antigen taken up by macrophage. Antigen presented on the surface of the macrophage to helper T-cell / TH cell. Helper T-cell divides into a clone of active cells. Active helper T-cell activates B-cell with antibodies specific to the antigen. B-cell activates and divides into clones of active. Memory cells are creatives. Active B-cells / plasma cells secrete large quantities of antibody

b) Outline how the fluid in the proximal convoluted tubule is produced by the process of ultrafiltration.
The proximal convoluted tubule is a part of the kidney’s nephron responsible for the reabsorption of filtrate from the glomerular capsule. The formation of fluid in the proximal convoluted tubule occurs through the process of ultrafiltration, which is the movement of fluid and solutes across a semi-permeable membrane under the influence of hydrostatic pressure. The fluid in the proximal convoluted tubule is produced by ultrafiltration in the glomerulus, a network of capillaries located in the Bowman’s capsule. Blood is brought to the glomerulus by the afferent arteriole and exits via the efferent arteriole. The afferent arteriole has a larger diameter than the efferent arteriole, creating a higher blood pressure in the glomerulus.
This high pressure forces blood plasma through the glomerular capillary walls and into the Bowman’s capsule, creating a filtrate that contains water, ions, glucose, amino acids, and waste products like urea. The filtration barrier is composed of three layers: the fenestrated endothelium of the capillaries, the basement membrane, and the podocytes of the Bowman’s capsule.

The fenestrated endothelium of the capillaries allows for the passage of solutes and small proteins, while the basement membrane acts as a size-selective filter that prevents the passage of larger molecules like proteins. The podocytes form foot processes that wrap around the capillaries and create small gaps called filtration slits, which further restrict the passage of larger molecules.

c) Explain how the cells of the proximal convoluted tubule are adapted to carry out selective reabsorption.
The proximal convoluted tubule is a section of the nephron, which is the functional unit of the kidney responsible for filtering blood and eliminating waste products. The cells of the proximal convoluted tubule are highly specialized and are adapted to carry out selective reabsorption, which is the process of returning useful substances from the filtrate back into the bloodstream.

One key adaptation of the cells of the proximal convoluted tubule is the presence of numerous microvilli on their surface. Microvilli are tiny, finger-like projections that increase the surface area of the cell and allow for more efficient reabsorption.

Another adaptation is the presence of specific transport proteins on the cell membrane. These proteins are responsible for recognizing and binding to specific substances in the filtrate, such as glucose, amino acids, and electrolytes. Once bound, the transport proteins can either actively transport the substance across the cell membrane and into the bloodstream, or they can facilitate the passive diffusion of the substance across the membrane.

The cells of the proximal convoluted tubule are also able to adjust their reabsorptive capacity in response to changes in the body’s needs. For example, if the body is in need of more glucose, the cells of the proximal convoluted tubule will increase the expression of glucose transport proteins and reabsorb more glucose from the filtrate.

Overall, the adaptations of the cells of the proximal convoluted tubule allow for the efficient and selective reabsorption of useful substances from the filtrate, which helps to maintain the balance of nutrients and electrolytes in the body.

8.)

a.) Explain the process of genetic engineering in relation to the production of recombinant DNA.
Genetic engineering involves manipulating an organism’s genetic material to introduce desired traits or characteristics. In the production of recombinant DNA, a specific gene or DNA sequence of interest is isolated from one organism and inserted into the DNA of another organism. This is achieved by using enzymes, such as restriction enzymes, to cut the DNA at specific points, allowing the gene of interest to be inserted into a vector, such as a plasmid. The recombinant DNA is then transferred into host cells, which replicate and express the inserted gene, resulting in the production of the desired protein or trait.

b.) Discuss the potential benefits and risks associated with the use of genetically modified organisms (GMOs) in agriculture and food production.
Benefits of GMOs in agriculture and food production include increased crop yields, enhanced nutritional content, improved resistance to pests, diseases, and harsh environmental conditions, and reduced need for chemical pesticides and herbicides. GMOs can also help address food shortages and improve food security. However, there are also risks associated with GMOs. Concerns include potential environmental impacts, such as the unintended spread of genetically modified traits to non-target organisms, the development of pesticide resistance in pests, and the loss of biodiversity. Additionally, there are concerns about the potential long-term effects of consuming GMOs on human health, although scientific consensus supports the safety of approved GMOs.

c.) Compare and contrast the techniques of gene cloning and polymerase chain reaction (PCR) in genetic engineering, highlighting their applications and limitations.
Gene cloning and polymerase chain reaction (PCR) are both techniques used in genetic engineering, but they serve different purposes.
Gene cloning involves isolating a specific gene or DNA fragment and inserting it into a vector, such as a plasmid, to create multiple copies of the gene. This technique allows for the amplification and production of large quantities of a particular gene of interest. Gene cloning is often used in research, medical diagnostics, and the production of recombinant proteins.
PCR, on the other hand, is a technique used to amplify a specific DNA sequence without the need for cloning. It involves a cyclic process of heating and cooling DNA samples in the presence of specific primers, DNA polymerase, and nucleotides. PCR is highly sensitive and can amplify a target DNA sequence exponentially, making it valuable in DNA sequencing, forensics, and diagnosing genetic diseases.

Comparing the two techniques, gene cloning can produce large quantities of DNA fragments, whereas PCR amplifies a specific DNA sequence. Gene cloning requires the use of vectors and host cells, while PCR can be performed in a test tube. Both techniques have their limitations, such as gene cloning being time-consuming and labour-intensive, and PCR being prone to contamination and requiring prior knowledge of the DNA sequence being amplified.
In summary, gene cloning is used for the production of multiple copies of a specific gene, while PCR is used for amplifying a specific DNA sequence. Both techniques have applications in genetic engineering, but they differ in their processes, requirements, and limitations.