A-LevelBiologyImmunity9700/22 · Feb/Mar 2021 · Q39 Marks
T-helper lymphocytes and Leydig cells are two types of mammalian cells. The main role of T-helper lymphocytes and Leydig cells is to synthesise and secrete cell-signalling molecules. T-helper lymphocytes synthesise proteins known as cytokines. Leydig cells synthesise the steroid (lipid) hormone testosterone from cholesterol. Leydig cells also synthesise cholesterol.
- (a)State one way in which cytokines are involved in an immune response.[1]
- (b)(i)Fig. 3.1 shows part of a mammalian cell. State, with reasons, whether Fig. 3.1 shows part of a Leydig cell or part of a T-helper lymphocyte. [Figure 3.1][2]
- (b)(ii)Underline the correct name for the type of image shown in Fig. 3.1 and explain your choice. photomicrograph scanning electron micrograph transmission electron micrograph explanation[2]
- (c)(i)Testosterone molecules and cytokine molecules are transported in the circulatory system to reach their target cells. Testosterone molecules are able to enter their target cells and bind to receptors within the cytoplasm. Outline one way in which testosterone molecules could enter their target cells.[2]
- (c)(ii)Cytokine molecules are not able to enter their target cells. Suggest and explain why cytokine molecules are not able to cross the cell surface membrane to enter their target cells.[2]
This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.
Mark scheme
Marking points from the official mark scheme (Feb/Mar 2021). The mark or mark type is shown in brackets.
- [1] 3(a) any one from: stimulate / enhance / AW, macrophage response ; stimulate / enhance / AW, B-lymphocyte / B-cell / humoral, response; A described part of humoral response e.g. increase antibody production stimulate / enhance / AW, T-killer / T-cytotoxic, response; AVP; e.g. suppresses immune response (during recovery) role in inflammation ref chemotaxis
- [2] 3(b)(i) any two from: Leydig cell/not T-helper lymphocyte, because: much / many / high proportion of, smooth endoplasmic reticulum ; (smooth endoplasmic reticulum present) that functions to synthesise, cholesterol / testosterone / steroid hormones / lipids; no / little, rough endoplasmic reticulum ; rough endoplasmic reticulum is for polypeptide / protein synthesis ;
- [2] 3(b)(ii) transmission electron micrograph; plus one from: cell ultrastructure can be seen / high resolution; A detail e.g. membranes of mitochondrion cristae nuclear, envelope / membranes endoplasmic reticulum I rough / smooth (very) thin section / not surface contours / AW ; I ref. to magnification
- [2] 3(c)(i) one correct mechanism stated plus one associated detail (passive / simple) diffusion; R facilitated diffusion / diffusion through (membrane) protein from high(er) to low(er) concentration / down a concentration gradient ; AVP; e.g. via phospholipid bilayer / hydrophobic core / fatty acid tails / AW or endocytosis; description / pinching in / vesicle formation; AVP; e.g. ATP / energy, required
- [2] 3(c)(ii) any two from hydrophilic / water soluble / polar ; cannot cross, hydrophobic core (of phospholipid bilayer) / AW ; too large (to pass through gaps in fatty acid tails); no (specific), transport / carrier, proteins;
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