Edexcel iGCSE Biology 4BI1 - Paper 1B -Cloning- Exam Style Questions- New Syllabus
▶️ Answer/Explanation
(a)(i) D (T and U)
A is not the answer as P and Q are not both the male parts
B is not the answer as P and R are not both the male parts
C is not the answer as S and T are not both the male parts
(a)(ii) A (P)
B is not the answer as pollen grains do not germinate on R
C is not the answer as pollen grains do not germinate on S
D is not the answer as pollen grains do not germinate on T
(a)(iii) C (R)
A is not the answer as P does not become the seed
B is not the answer as Q does not become the seed
D is not the answer as T does not become the seed
(b)(i) A description that makes reference to two of the following:
• uses runners / stolons / eq (1)
• stem / shoot (grows along ground) / eq (1)
• breaks off / grows roots / produces new plant / clone / eq (1)
(b)(ii) An answer that makes reference to four of the following:
1. (use sexual reproduction) cross with different variety / different plant / selective breeding / eq (1)
2. transfer pollen / cross pollinate / eq (1)
3. to produce different flavour / new flavour / desired flavour / variation / eq (1)
4. (use asexual) / runners / cuttings / micropropagation / eq (1)
5. produces genetically identical plants / clones / eq (1)
6. many offspring produced / large numbers / eq (1)
▶️ Answer/Explanation
(a)(i) C (Y)
A is incorrect because V is the ovary.
B is incorrect because X is the stigma.
D is incorrect because Z is the filament.
(a)(ii) A (V)
B is incorrect because W does not become a fruit.
C is incorrect because X does not become a fruit.
D is incorrect because Y does not become a fruit.
(b)(i) 96 (\( \times \))
Stages of calculation:
• Convert mm to \( \mu m \): 30 mm = \( 30 \times 1000 = 30000 \) \( \mu m \).
• Magnification = \( \frac{\text{image size}}{\text{actual size}} = \frac{30000}{313} \).
• Calculation: \( \frac{30000}{313} \approx 95.85 \).
• To nearest whole number = 96.
(b)(ii) • spikes / hooks / sticky / eq (1)
(c) An answer that makes reference to two of the following:
• asexual reproduction (1)
• cuttings are genetically identical / have same alleles / same genes / are clones / eq (1)
• faster / can be produced at any time of year / can be done from only one plant / no need to have insects / eq (1)
▶️ Answer/Explanation
(a)(i) A
Explanation: Fertilisation, the fusion of a sperm cell nucleus with an egg cell nucleus to form a zygote, normally occurs in the oviduct, also known as the Fallopian tube. This is the structure labelled A in the diagram. The ovary (B) is where eggs are produced and released, the uterus (C) is where the embryo implants and develops, and the vagina (D) is the birth canal.
(a)(ii) Oestrogen: Repairs / thickens the lining. Progesterone: Maintains / retains the lining.
Explanation: Oestrogen, produced by the developing follicles in the ovary, causes the repair and proliferation of the endometrium (the lining of the uterus, structure C) after menstruation. Progesterone, secreted by the corpus luteum after ovulation, maintains this thickened, blood vessel-rich lining, making it suitable for the implantation of a fertilised egg. A drop in progesterone levels at the end of the cycle is what triggers the shedding of this lining, leading to menstruation.
(b)(i) A sperm cell fuses with an egg cell to form a zygote. The zygote then undergoes a series of mitotic cell divisions to form a ball of cells called an embryo.
Explanation: During IVF, eggs are collected and mixed with sperm in a Petri dish. If successful, a single sperm will penetrate the egg’s outer layers, and their nuclei will fuse. This single-celled fertilised egg is called a zygote. The zygote does not increase in size but divides repeatedly by mitosis – first into 2 cells, then 4, then 8, and so on. This process of cell division forms a multicellular structure which, by the time it is transferred to the uterus, has developed into an embryo.
(b)(ii) Limiting embryos has significantly reduced multiple births (as shown by the graph’s steep decline post-2007), making IVF safer by reducing health risks for both parent and babies. However, the table shows success rates decrease with age. For older individuals with lower success rates, transferring two embryos balances the higher risk of twins against the low chance of success with one embryo. For younger people with high success rates, one embryo minimizes risk without drastically reducing their chance of pregnancy.
Explanation: This answer requires an evaluation of the policy based on the provided data. The graph provides clear evidence that the policy was effective in its primary goal: reducing multiple births. The table provides the rationale for the age-specific nature of the policy. The discussion balances the benefit (reduced health risks) with a drawback (potentially lower success rates for older recipients) and uses the data to justify why the age limit is set where it is.
Most-appropriate topic codes (Edexcel IGCSE Biology):
• 6(a): Food production — part (b)
• 6(d): Cloning — context of plant biotechnology (implied)
▶️ Answer/Explanation
(a)
Answer: The plasmid is modified by using the same restriction enzyme to cut both the plasmid and the target gene, creating complementary sticky ends. The gene for making the insect poison is then inserted into the plasmid. Finally, the ligase enzyme is used to join the gene into the plasmid, forming recombinant DNA.
Detailed Explanation:
The process of creating recombinant DNA involves several key steps. First, scientists use a specific restriction enzyme to cut open the plasmid from the Agrobacterium bacterium. This same enzyme is also used to cut out the target gene from another organism – in this case, the gene that codes for the insect poison. The restriction enzyme creates what are called “sticky ends” on both the plasmid and the target gene, which are complementary in shape.
Next, the target gene containing the insect poison code is inserted into the opened plasmid. The complementary sticky ends allow the gene to fit precisely into the plasmid. Finally, an enzyme called ligase is used to permanently join the gene into the plasmid, essentially “gluing” the pieces together. This creates what we call recombinant DNA – DNA that contains genetic material from different sources.
(b)
Answer: The farmer’s decision can be supported because GM plants are specific in killing only target insects, reduce the need for pesticide application, and avoid issues like pesticide resistance and environmental contamination. However, concerns include potential cross-pollination with other species, possible harm to beneficial insects, development of insect resistance to the GM poison, consumer reluctance to buy GM crops, and dependence on seed companies due to patents.
Detailed Explanation:
The farmer’s decision to grow GM plants instead of using pesticides has both advantages and disadvantages that need careful consideration.
Arguments supporting the decision: GM plants that produce their own insect poison are highly specific – they typically target only the particular insect pests that damage that crop, unlike broad-spectrum pesticides that can kill beneficial insects too. This specificity helps preserve the ecosystem balance in the farm environment. GM plants also significantly reduce the need for repeated pesticide applications, saving the farmer time, labor, and money. Since the plants continuously produce the insect poison, there’s no need for frequent respraying. Additionally, insects can develop resistance to conventional pesticides over time, requiring stronger or different chemicals, whereas GM plants offer a different mode of action. Pesticides can also contaminate soil and water systems and enter food chains through bioaccumulation, potentially causing health problems for humans and wildlife.
Arguments against the decision: There are valid concerns about GM crops. The pollen from GM plants could potentially cross-pollinate with related wild species or non-GM crops, spreading the modified genes unintentionally. The insect poison produced by GM plants might harm beneficial insect pollinators like bees if they come into contact with the pollen. Just as with pesticides, insects could eventually develop resistance to the poison produced by GM plants. Many consumers are hesitant to buy GM products due to health or environmental concerns, which could affect marketability. Furthermore, GM seeds are often patented, making farmers dependent on seed companies for their supply each planting season.
In conclusion, while GM crops offer significant advantages in pest control efficiency and reduced chemical use, the farmer must carefully weigh these benefits against the potential environmental and market concerns.