Monoclonal Antibodies & Plant Disease Detection

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Monoclonal Antibody Production

1. Inject a mouse with a specific antigen to stimulate mouse B-lymphocytes to produce complementary antibodies. 2. Fuse extracted lymphocytes with fast-dividing tumour (myeloma) cells using detergent to form a hybridoma cell. 3. Clone the single hybridoma cell to produce millions of identical cells, then collect and purify the monoclonal antibodies.

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Uses of Monoclonal Antibodies

1. Diagnosis: pregnancy tests (binding to hCG hormone). 2. Laboratories: measuring hormone/chemical levels in blood or detecting pathogens. 3. Research: attaching fluorescent dye to locate specific molecules in cells/tissues. 4. Treatment: delivering radioactive isotopes, toxic drugs, or cell-division blockers directly to cancer cells without harming healthy body cells.

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Symptoms & Identification of Plant Disease

Common signs include stunted growth, spots on leaves, areas of decay (rot), growths/galls, malformed stems/leaves, discolouration, and the presence of pests (like aphids). Identified using gardening manuals/websites, taking infected plants to a lab to culture pathogens, or testing with monoclonal antibody test kits.

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Mineral Ion Deficiencies (Nitrates & Magnesium)

Non-communicable plant conditions: Nitrate deficiency causes stunted growth because nitrates are required to make amino acids for protein synthesis. Magnesium deficiency causes chlorosis (yellowing of leaves) because magnesium ions are a essential component of chlorophyll molecules.

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Physical & Chemical Plant Defences

Physical barriers that block pathogen entry: cellulose cell walls, tough waxy cuticles on leaves, and layers of dead cells (bark) on stems that fall off. Chemical defences: antibacterial chemicals (e.g., mint and witch hazel) and poisons to deter herbivores (e.g., tobacco plants, foxgloves, and deadly nightshade).

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Mechanical Plant Adaptations

Structural adaptations that deter animals from feeding on or laying eggs on the plant: thorns and hairs (stop herbivores eating stems), leaves that droop or curl when touched (e.g., Mimosa pudica knocks insects off), and mimicry (e.g., passion flower yellow spots mimic butterfly eggs to deter female butterflies).

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1. Q1

   Describe how monoclonal antibodies specific to a prostate cancer antigen are produced in a laboratory. [5 marks]

   Check Mark Scheme

   Click “Check Mark Scheme” to compare your answer, 1. Inject a mouse with the specific prostate cancer antigen to stimulate its immune response [1 mark]. 2. Extract the mouse spleen B-lymphocytes that produce antibodies complementary to the cancer antigen [1 mark]. 3. Fuse a B-lymphocyte with a fast-dividing myeloma (tumour) cell to create a hybridoma cell [1 mark]. 4. Select the hybridoma cell that produces the correct antibody and clone it so it divides rapidly into millions of identical cells [1 mark]. 5. Collect and purify the large quantities of identical monoclonal antibodies produced by the cloned hybridoma cells [1 mark].

2. Q2

   Explain how a pregnancy test stick uses monoclonal antibodies to show both a positive result and that the test is working properly. [4 marks]

   Check Mark Scheme

   Click “Check Mark Scheme” to compare your answer, 1. The reaction zone contains mobile monoclonal antibodies (attached to blue dye beads) that are complementary to the hormone hCG found in pregnant women's urine [1 mark]. 2. If hCG is present, it binds to these mobile antibodies and is carried up the stick by the urine [1 mark]. 3. In the first window (test window), immobilised antibodies specific to hCG bind the hCG-antibody complex, concentrating the blue beads to form a blue line [1 mark]. 4. In the second window (control window), immobilised antibodies specific to the mobile antibodies themselves bind any leftover mobile antibodies, forming a second blue line that proves urine flowed up the strip properly [1 mark].

3. Q3

   A farmer notices that wheat plants in one corner of a field are stunted and have yellow leaves. Explain how a deficiency in two different mineral ions could account for both symptoms. [4 marks]

   Check Mark Scheme

   Click “Check Mark Scheme” to compare your answer, 1. Stunted growth is caused by a deficiency of nitrate ions in the soil [1 mark]. 2. Plants require nitrate ions to convert glucose into amino acids, which are joined together to make proteins needed for cell growth [1 mark]. 3. Yellow leaves (chlorosis) are caused by a deficiency of magnesium ions [1 mark]. 4. Magnesium ions are needed to synthesise chlorophyll; without enough chlorophyll, leaves turn yellow and photosynthesis slows down [1 mark].

4. Q4

   Describe three different ways (one physical, one chemical, and one mechanical) that plants defend themselves against pathogens and herbivores. [3 marks]

   Check Mark Scheme

   Click “Check Mark Scheme” to compare your answer, 1. Physical defence: Leaves are covered in a tough waxy cuticle (or cells have cellulose cell walls / stems have bark) which acts as a physical barrier to stop pathogens entering [1 mark]. 2. Chemical defence: Plants like foxgloves or deadly nightshade produce toxic poisons to deter herbivores from eating them (or mint produces antibacterial chemicals to kill bacteria) [1 mark]. 3. Mechanical defence: Rose or bramble stems have sharp thorns to make it painful for herbivores to eat them (or Mimosa leaves curl up when touched to knock insects off) [1 mark].

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