AQA GCSE Biology Higher Tier Paper 1H May 2023 Study Notes

Plant Tissues and Stem Cells

• Roots as Organs: A plant root is defined as a plant organ composed of many different types of tissue working together to perform specific functions.
• Definition of Tissue: A tissue is defined as a group of cells with similar structure and function working together.
• Stem Cells in Roots: The tip of a plant root contains a specific tissue that houses stem cells, which have the ability to differentiate into any type of plant cell.
• Meristem Tissue: The specific type of tissue in plants that contains these stem cells is the meristem.

Origins and Extraction of Drugs From Plants

• Aspirin: Aspirin is a common painkiller that originally originated from the willow tree.
• Deadly Nightshade (Chemical A): Scientists have extracted a painkiller referred to as "Chemical A" from the deadly nightshade plant.
• Distribution of Chemical A: Table 1 provides the mass of Chemical A found in $100\,g$ of different plant tissues:
  • Roots: $1.3\,g$
  • Leaves: $1.2\,g$
  • Berries: $0.7\,g$
• Preference for Berries: Despite having a lower concentration than roots or leaves, scientists typically extract Chemical A from the berries. One reason for this is because berries are easier to harvest or can be picked without killing the plant, unlike harvesting roots.

Quantitative Analysis: Chemical A and Chlorosis

• Chlorosis Condition: A deadly nightshade plant exhibiting chlorosis (yellow leaves) has a reduced concentration of Chemical A. Specifically, the mass found is only $60\%$ of the healthy mass shown in Table 1.
• Calculating Mass in Chlorotic Leaves: To find the mass of Chemical A in $200\,g$ of leaves with chlorosis:
  • Step 1: Determine mass in $100\,g$ of healthy leaves = $1.2\,g$.
  • Step 2: Calculate mass in $200\,g$ of healthy leaves: $1.2\,g \times 2 = 2.4\,g$.
  • Step 3: Apply the chlorosis reduction: $2.4\,g \times 0.60 = 1.44\,g$.
  • Step 4: Convert to milligrams ($mg$): $1.44 \times 1000 = 1440\,mg$.
  • Final Answer: The mass of Chemical A is $1440\,mg$.
• Causes of Chlorosis: One major reason leaves may develop chlorosis is a deficiency in magnesium ions ($Mg^{2+}$), which are necessary for the production of chlorophyll.

Drug Testing and Clinical Trials

• Importance of Clinical Trials: It is critical for drugs to be tested in clinical trials before public approval for two main reasons:
  1. To check for safety and ensure the drug is not toxic to humans.
  2. To verify the efficacy of the drug (to see if it actually works) and to determine the optimum dosage.
• Identifying Bias: Reports regarding the effects of chemicals like Chemical A may be biased if they are funded or written by the company that produces the drug, as they have a financial interest in the results.
• Scientific Validity: Scientists ensure that claims about new drugs are valid by having the claims peer-reviewed by other scientists in the same field.

The Human Circulatory System

• Heart Anatomy (Oxygenated Blood): The part of the heart that receives oxygenated blood directly from the lungs is the left atrium.
• Heart Anatomy (Deoxygenated Blood): The part of the heart that pumps deoxygenated blood toward the lungs is the right ventricle.
• The Pacemaker: The resting heart rate is controlled by a group of cells called the pacemaker, which is located in the right atrium.
• Structural Differences: Artery vs. Vein:
  1. Arteries have thicker muscle and elastic tissue layers compared to veins to withstand high pressure.
  2. Veins have valves to prevent the backflow of blood, whereas arteries do not.
  3. Arteries have a narrower lumen, while veins have a wide lumen.

Coronary Heart Disease (CHD)

• Pathology: CHD involves the narrowing of coronary arteries due to a build-up of fatty material, which can lead to blockages.
• Blood Flow Data: Table 2 illustrates the relationship between blockage percentage and blood flow in $cm^3/minute$:
  • $0\%$ blocked: $100\,cm^3/min$
  • $10\%$ blocked: $64\,cm^3/min$
  • $20\%$ blocked: $42\,cm^3/min$
  • $50\%$ blocked: $8\,cm^3/min$
  • $80\%$ blocked: $2\,cm^3/min$
• Trend: As the percentage of the coronary artery that is blocked increases, the blood flow decreases significantly (a non-linear decrease).
• Health Effects of Blockage:
  • Reduced blood flow means less oxygen and glucose reach the heart muscle cells.
  • This results in a lower rate of aerobic respiration.
  • The heart muscle has less energy to contract, potentially leading to chest pain (angina), fatigue, or a heart attack if cells die.
• Treatments:
  1. Stents: A metal mesh tube is inserted into the artery to keep it open, ensuring blood can flow through.
  2. Statins: Drugs taken to reduce blood cholesterol levels, which slows down the rate of fatty material deposit.

Infection and Response: Salmonella

• Causes of Symptoms: Salmonella bacteria cause vomiting and diarrhoea by releasing toxins that affect the body.
• Vaccination Mechanism:
  • When animals are vaccinated, dead or inactive forms of the Salmonella pathogen are injected.
  • White blood cells (lymphocytes) produce specific antibodies to the antigens on the bacteria.
  • If the animal is later infected, memory cells ensure a rapid response, killing the bacteria before they can multiply and spread.
  • This prevents the bacteria from entering the human food chain (e.g., through meat or eggs).
• Aseptic Techniques for Bacterial Investigation:
  1. Sterilizing the Petri dish and culture media (e.g., using an autoclave) before use.
  2. Flaming the inoculating loop in a Bunsen burner flame until it is red hot.
  3. Securing the lid of the Petri dish with tape (but not sealing it completely) and only opening it at an angle.
• Incubation Temperatures:
  • Scientists use $37^\circ C$ because it is human body temperature, allowing for the fastest growth rate of bacteria that affect humans.
  • Students use $25^\circ C$ as a safety measure to prevent the growth of dangerous human pathogens.
• Experimental Controls: A paper disc with no antibiotic (a control disc) is used to prove that any clearing of bacteria (zone of inhibition) is due to the antibiotic itself and not just the paper.
• Antibiotic Resistance: If an antibiotic (e.g., Antibiotic B) no longer works after a year, it is likely because the bacteria have mutated, leading to antibiotic resistance through natural selection.
• Bacterial Lysis: Some antibiotics damage the cell wall. This causes the cell to burst because water enters the cell via osmosis (moving from a dilute solution outside to a more concentrated solution inside the cell), and the weakened wall cannot withstand the internal turgor pressure.

Exercise, Respiration, and Performance

• Anaerobic Respiration: Occurs during vigorous exercise when oxygen supply is insufficient.
  1. Effect 1 (Lactic Acid): Incomplete oxidation of glucose leads to a build-up of lactic acid in the muscles, causing muscle fatigue and pain.
  2. Effect 2 (Oxygen Debt): The body creates an oxygen debt, requiring heavy breathing after exercise to provide the oxygen needed to break down the lactic acid in the liver.
• Athletic Investigation Design: To test the effect of different exercises on heart rate:
  1. Select a group of athletes (ensure similar age/fitness for a fair test).
  2. Measure resting heart rate using a pulse sensor or stopwatch.
  3. Perform a specific type of exercise (e.g., running) for a set duration (e.g., 5 minutes).
  4. Measure heart rate immediately after exercise.
  5. Allow for a full recovery period.
  6. Repeat for different types of exercise (e.g., swimming, cycling) and repeat the entire process for reliability.
• Anabolic Steroids: These drugs increase muscle mass, which can improve performance by allowing the athlete to run faster or move with more power.

Monoclonal Antibodies

• Production Process:
  1. A mouse is injected with a specific antigen (e.g., the anabolic steroid).
  2. Lymphocytes that produce the desired antibody are extracted.
  3. These lymphocytes are fused with a tumour cell to create a Hybridoma cell.
  4. Hybridoma cells can both produce the antibody and divide rapidly.
  5. The cells are cloned to produce large quantities of identical monoclonal antibodies.
• Testing Property: The use of monoclonal antibodies for detection relies on the fact that they are highly specific and will only bind to one specific antigen/chemical.
• Urine Test Strips:
  • The control area in a test strip is designed to show that the test is working correctly (that the urine/monoclonal antibodies have traveled up the strip).
  • In the case of Athlete B (Figure 6), the test failed because there is no blue dye in the control area, suggesting a possible manufacturing defect or expired strip.
  • Athlete D tested positive for steroids because both the test area and control area turned blue.

Malaria and Cell Biology

• Vector: A mosquito acts as a vector, an organism that passes a pathogen (the malarial protist) from one person to another.
• Eukaryotic vs. Prokaryotic Structure: The malarial protist (eukaryotic) differs from prokaryotic cells in that it has:
  1. A nucleus (genetic material is enclosed).
  2. Mitochondria.
  3. No plasmids (circular loops of DNA).
• Tiredness in Malaria: The protist causes red blood cells to burst. Because red blood cells carry oxygen (via haemoglobin) for aerobic respiration, fewer cells mean less oxygen is transported to tissues, resulting in less energy released and increased tiredness.
• Reproduction Comparison:
  • Sexual: Involves two parents; involves the fusion of gametes; results in genetic variation in offspring.
  • Asexual: Involves one parent; no fusion of gametes (mitosis only); offspring are genetically identical (clones).
• Drug Interaction with Mitosis: A drug that stops the synthesis of new DNA bases prevents mitosis because DNA must be replicated before the cell can divide to ensure both daughter cells have a full set of genetic information.
• The Mitosis Process:
  1. The DNA/chromosomes replicate to form two copies of each chromosome.
  2. The nuclear membrane breaks down, and the chromosomes line up at the center of the cell.
  3. One set of chromosomes is pulled to each end of the cell.
  4. The nucleus divides, followed by the division of the cytoplasm and cell membranes to form two identical daughter cells.
• Disorder S and Malaria (Interaction): Data in Table 4 shows that children with "Disorder S" have a lower incidence of malaria across all ages compared to children without the disorder, with the greatest protection occurring between ages 8 and 10 ($45\%$ incidence).

Photosynthesis and Light Wavelengths

• Symbol Equation: $6CO_2 + 6H_2O \rightarrow C_6H_{12}O_6 + 6O_2$
• Limiting Factors: In a graph of light intensity vs. rate of photosynthesis, the linear portion ($y = mx + c$) occurs when light intensity is the limiting factor (e.g., from $0$ to $5000\,lux$).
• Experimental Variables:
  • Independent Variable: The colour of the light.
  • Dependent Variable: The time taken for leaf discs to reach the surface.
• Procedural Details:
  • Air must be removed from leaf discs so they are dense enough to sink initially.
  • Sodium Hydrogencarbonate ($NaHCO_3$): Used to provide a source of carbon dioxide for the leaf discs, ensuring $CO_2$ is not a limiting factor.
  • Movement to Surface: Leaf discs move to the surface because oxygen is produced during photosynthesis. This oxygen becomes trapped in the leaf tissue, making the discs more buoyant.
• Chlorophyll Absorption: Plants benefit from having two types of chlorophyll because it allows them to absorb a wider range of wavelengths (colours) of light, maximizing energy capture for photosynthesis.
• Color Analysis:
  • Blue light ($450-499\,nm$) is highly absorbed by both types of chlorophyll, leading to a high rate of photosynthesis and a fast rise time ($115\,s$).
  • Green light ($500-570\,nm$) is reflected rather than absorbed by green leaves, resulting in a very low rate of photosynthesis and the slowest rise time ($831\,s$).