1. Cell structure
A section of Biology, 9700
Listing 10 of 513 questions
Animal cells, plant cells and prokaryotic cells have similarities and differences in their structure. Table 1.1 lists five organelles found in cells. Complete Table 1.1 by placing a tick (3) to show whether the organelle is present in animal cells, plant cells and prokaryotic cells or a cross (✗) if the organelle is absent. Put a tick (3) or a cross (✗) in every box. The first row has been completed for you. Table 1.1 organelle cell type animal cells plant cells prokaryotic cells nucleus ✗ large permanent vacuole rough endoplasmic reticulum Golgi body centrioles shows a section through part of an epithelial cell found in the digestive system of an animal. The cell is specialised for absorption of digested food. P Q The structures labelled P and Q in are involved in the absorption of digested food. Name the structures labelled P. Explain how the organelle labelled Q in is involved in this process.
9700_w24_qp_21
THEORY
2024
Paper 2, Variant 1
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People who become infected with human immunodeficiency virus (Hare at risk of developing HIV/AIDs, particularly if antiretroviral therapy (ART) is not available. In people infected with HIV, the use of ART also helps to reduce transmission of the virus to uninfected people. Outline two control methods, other than ART, that can be used to reduce the transmission of HIV. In people with HIV/AIDs, a serious lung disease known as pneumocystis pneumonia can result from infection by an opportunistic pathogen known as Pneumocystis jirovecii. shows P. jirovecii cells in one stage of their life cycle, as seen using a light microscope at a magnification of ×600. 0.4 μm Define magnification. shows that P. jirovecii is a unicellular organism. Although the cells of many species of bacteria are the same size as those of P. jirovecii, research concluded that the organism is a eukaryote and is not a bacterium. In 1988, analysis of ribosomal RNA (rRNA) resulted in P. jirovecii being classified as a fungus. Studies of the structure of P. jirovecii have identified that the cell wall is made of polysaccharides such as chitin and 1,3‑β‑D‑glucan. Explain why this feature helped scientists to confirm that P. jirovecii is not a bacterium. Scientists have identified other features of the cell structure of P. jirovecii. Some of these are listed in Table 2.1. Complete each row of Table 2.1 so that the table shows: • four structural features identified in P. jirovecii • one function for each structural feature • whether the structural feature is present (✓) or absent (✗) in bacterial cells. Table 2.1 structural feature of P. jirovecii function present (✓) or absent (✗) in bacterial cells ribosomes protein synthesis smooth endoplasmic reticulum Golgi body modification of proteins and lipids aerobic respiration P. jirovecii can adhere to squamous epithelial cells of the alveoli and to the network of fibrous proteins that support the alveolar wall, known as the extracellular matrix (ECM). Examples of proteins in the ECM are elastin and collagen. Adhesion of P. jirovecii to alveolar epithelial cells and the ECM stimulates the growth of its population. Cell surface glycoproteins known as gpA glycoproteins are essential in allowing P. jirovecii cells to adhere to alveolar epithelial cells and ECM proteins. Suggest how a gpA glycoprotein is able to adhere to alveolar epithelial cells and ECM proteins. One consequence of the pneumonia that results from P. jirovecii infection is a decrease in the quantity of oxygen that is delivered to body tissues. Explain why a severe P. jirovecii infection results in a decrease in the quantity of oxygen that is delivered to body tissues. P. jirovecii produces an enzyme known as 1,3‑β‑D‑glucan synthase. The enzyme catalyses the synthesis of 1,3‑β‑D‑glucan. The therapeutic drug caspofungin is a non‑competitive inhibitor of 1,3‑β‑D‑glucan synthase. With reference to the mechanism of action of caspofungin, explain how the drug may be useful to treat cases of pneumonia caused by P. jirovecii.
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THEORY
2024
Paper 2, Variant 2
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A student constructed a table to compare the structural features of a plant cell, a prokaryotic cell and a virus. Complete Table 6.1. Table 6.1 feature plant cell prokaryotic cell virus external structure cell wall composed of cellulose cell wall composed of ….……………………… capsid composed of ….………………………… size of ribosomes 80S and 70S ….……………………… no ribosomes nucleic acids DNA and RNA DNA and RNA ….……………………… The cholera bacterium releases a protein toxin called choleragen. The toxin causes the loss of chloride ions and water from epithelial cells into the lumen of the intestine. shows the events that occur in cells lining the intestine when choleragen binds to the membrane of one of these cells. lumen of intestine cytoplasm of epithelial cell binding causes endocytosis of choleragen choleragen stimulates exit of chloride ions and water choleragen H2O Cl – State one likely source of an outbreak of cholera. With reference to , state why choleragen molecules are described as having quaternary structure. State the type of cell membrane component that forms the receptor for choleragen. The process by which chloride ions leave the epithelial cell requires energy. Name the phosphorylated nucleotide that is needed for this process. Explain why water also moves from epithelial cells into the lumen of the intestine when choleragen is present.
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THEORY
2024
Paper 2, Variant 3
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is an electron micrograph of part of an animal cell. A centriole is labelled. A B centriole X 10, 000 C Name the structures labelled A to C. A B C Describe the roles of centrioles in animal cells. Explain why it is possible to see the internal membranes of a cell in electron micrographs, such as , but it is not possible to see them when using the light microscope. A student investigated the effect of temperature on beetroot tissue. Beetroot cells contain a dark red pigment known as betalain, which is stored inside their vacuoles. The student • cut the beetroot tissue into cubes of the same size • washed the cubes thoroughly in distilled water • placed the same number of cubes into distilled water at seven different temperatures. After 30 minutes, samples of the water were removed and placed in a colorimeter to measure the transmission of light. The lower the percentage transmission the more betalain is present in the water. The results are shown in . temperature / °C percentage transmission Using the information in , describe the student's results; explain the effect of increasing temperature on the beetroot tissue.
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THEORY
2008
Paper 2, Variant 0
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Questions Discovered
513