Year 10 Triple Biology AQA GCSE (8461) Complete Study Notes B1–B5

B1 CELL BIOLOGY: Cell Structure, Types, and Specialized Functions

Cell Types: Eukaryotic and Prokaryotic

• Eukaryotic cell: A cell with genetic material enclosed inside a nucleus. Animal, plant, and algal cells are eukaryotic.

• Prokaryotic cell: A cell without a membrane-bound nucleus. Bacterial cells are prokaryotic. Their DNA is a single loop free in the cytoplasm. They may also contain plasmids, which are small rings of extra DNA.

Comparison of Cell Structures and Functions

Cell Specialisation and Differentiation

• Differentiation: The process by which a cell becomes specialised for its function by developing specific sub-cellular structures.

  • In animals, most differentiation occurs early in development.

  • In plants, differentiation can occur throughout life in the meristems.

• Specialised Cell Examples and Adaptations:

  • Sperm cell: Features a tail for movement; possesses many mitochondria for energy; contains an acrosome with enzymes to penetrate the egg.

  • Nerve cell: Has a long axon to carry electrical impulses over large distances; surrounded by a myelin sheath that speeds transmission.

  • Muscle cell: Contains contractile proteins (actin/myosin) and many mitochondria for sustained energy supply.

  • Root hair cell: Features a long extension for large surface area; has a large vacuole to maintain an osmotic gradient; contains no chloroplasts.

  • Xylem cell: Hollow with no cytoplasm to ensure unobstructed water flow; walls are lignified for structural support.

  • Phloem cell: Features sieve plates for sugar flow; companion cells provide the energy required for active loading.

B1 CELL BIOLOGY: Microscopy and Microbiology

Comparison of Microscopes

• Light Microscope:

  • Uses visible light and glass lenses.

  • Maximum magnification: ~$\times 1,500$.

  • Resolution: ~$200\,nm$.

  • Can view living specimens.

  • Cheap and widely available.

  • Shows: nucleus, vacuole, chloroplasts.

• Electron Microscope:

  • Uses a beam of electrons.

  • Maximum magnification: ~$\times 2,000,000$.

  • Resolution: ~$0.1\,nm$.

  • Specimens must be dead.

  • Very expensive.

  • Shows: ribosomes, fine membrane detail.

Maths Skills in B1

• Magnification Equations:

  • $\text{magnification} = \text{image size} \div \text{actual size}$

  • $\text{actual size} = \text{image size} \div \text{magnification}$

  • $\text{image size} = \text{magnification} \times \text{actual size}$

  • Note: Always use the same units for $\text{I}$ and $\text{A}$.

• Unit Conversions:

  • $1\,mm = 1,000\,\mu m$

  • $1\,\mu m = 1,000\,nm$

  • Standard form example: $7\,\mu m = 7 \times 10^{-6}\,m$

• Surface Area to Volume Ratio: $\text{SA:V} = \text{SA} \div V$. A smaller cell has a larger SA:V, leading to faster diffusion.

• Bacterial Growth: $N = N_0 \times 2^n$, where $n$ is the number of divisions.

• Area of Zone of Inhibition: $\text{Area} = \pi \times r^2$.

• Percentage Change in Mass: $\text{Percentage Change} = \frac{\text{final} - \text{initial}}{\text{initial}} \times 100$.

Triple/Biology Only: Culturing Microorganisms

• Binary fission: The method of bacterial reproduction where a cell divides into two identical daughter cells. In ideal conditions, some bacteria divide every 20 minutes.

• Aseptic technique: Methods used to prevent contamination of cultures by unwanted microorganisms.

  • Sterilise Petri dishes and media (autoclave) before use.

  • Sterilise inoculating loops in a Bunsen flame until they are glowing.

  • Briefly lift the lid; never fully remove it.

  • Tape the lid but do NOT seal it completely to allow gas exchange.

  • Incubate upside down at a maximum of $25^\circ\text{C}$ in schools.

  • Why $25^\circ\text{C}$? Harmful pathogens are less likely to grow at lower temperatures.

  • Why upside down? To prevent condensation from dripping onto the agar and spreading colonies.

B1 CELL BIOLOGY: Chromosomes, Mitosis, and Stem Cells

The Cell Cycle

1. Stage 1 — Growth: The cell grows and the number of sub-cellular structures (e.g., mitochondria, ribosomes) increases.

2. Stage 2 — DNA Replication: DNA is copied so each daughter cell receives a full set of chromosomes.

3. Stage 3 — Cell Division (Mitosis): Chromosomes separate to opposite ends; the nucleus divides; the cytoplasm and membrane divide, resulting in two genetically identical daughter cells.

• Mitosis is used for growth, repair, and replacement.

Stem Cells

• Stem cell: An undifferentiated cell that can divide and differentiate into specialised cell types.

B1 CELL BIOLOGY: Transport in Cells

Mechanisms of Transport

• Diffusion: The net movement of particles from a higher to a lower concentration (down the gradient). This is a passive process requiring no energy.

  • Examples: $O_2$ into cells; $CO_2$ out of cells; urea from cells into blood plasma.

  • Factors increasing rate: steeper gradient, higher temperature, larger surface area, shorter diffusion distance.

• Osmosis: The diffusion of water from a dilute solution (high water concentration) to a concentrated solution through a partially permeable membrane. This is a passive process.

  • Plant cells: Gaining water makes them turgid; losing water makes them flaccid or plasmolysed.

  • Animal cells: Gaining water may cause them to burst (lyse); losing water makes them crenated.

• Active Transport: The movement of substances from a lower to a higher concentration (against the gradient). It requires energy from respiration.

  • Examples: Root hair cells absorbing mineral ions from dilute soil water; absorption of glucose from the gut into the blood when blood glucose levels are already higher.

B1 REQUIRED PRACTICALS

Required Practical 1: Microscopy

1. Prepare a thin specimen on a slide and add a stain ($\text{iodine}$ for plant cells, $\text{methylene blue}$ for animal cells).

2. Lower the coverslip at a $45^\circ$ angle to avoid air bubbles.

3. Start on the lowest objective lens ($\times 4$); use the coarse focus, then the fine focus.

4. Draw cells with clean lines (no shading), label structures, and record magnification and a scale bar.

5. $\text{Total Magnification} = \text{eyepiece} \times \text{objective lens}$.

Required Practical 3: Osmosis

1. Cut equal potato cylinders and record their initial mass.

2. Place in a range of sucrose concentrations (e.g., $0–1\,mol/dm^3$) for 30 minutes.

3. Remove, blot dry with a paper towel, and reweigh.

4. Calculate the percentage change in mass and plot $\text{concentration (x-axis)}$ vs $\text{\% change (y-axis)}$.

5. Variables: Independent Variable (IV) = sucrose concentration; Dependent Variable (DV) = % change in mass; Control Variables (CV) = temperature, time, size of cylinder.

Triple Only — Required Practical 2: Bacterial Growth

1. Spread bacteria on agar using aseptic technique.

2. Place antibiotic or antiseptic-soaked discs on the agar.

3. Incubate upside down at $25^\circ\text{C}$ for 24–48 hours.

4. Measure the zones of inhibition around each disc. A larger zone indicates a more effective agent.

5. Calculate the area using $\pi \times r^2$.

B2 ORGANISATION: Principles and Digestion

Level of Organisation

• $\text{Cell} \rightarrow \text{Tissue} \rightarrow \text{Organ} \rightarrow \text{Organ System} \rightarrow \text{Organism}$

Digestive Enzymes

• Enzyme: A biological catalyst — a protein that speeds up a specific chemical reaction without being used up. It has an active site with a specific complementary shape for its substrate.

• Denaturation: A permanent change in an enzyme's active site shape due to extremes of temperature or pH; the substrate no longer fits and the reaction stops.

Role of Bile

• Made in: Liver | Stored in: Gall bladder | Released into: Small intestine.

• Neutralisation: Bile is alkaline, neutralising the $HCl$ from the stomach to create an optimum pH (~7–8) for intestinal enzymes.

• Emulsification: Breaks large fat globules into tiny droplets, increasing the surface area for lipase to speed up fat digestion.

• Note: Bile is NOT an enzyme; it does not chemically break down fat.

B2 ORGANISATION: The Heart, Blood Vessels, and Blood

Heart Structure and Vessels

• Four chambers: Right atrium, right ventricle, left atrium, left ventricle.

• The left ventricle has thicker walls to pump blood around the whole body at higher pressure.

• Valves prevent the backflow of blood.

• Key Vessels:

  • Aorta: Carries oxygenated blood from the left ventricle to the body.

  • Vena cava: Returns deoxygenated blood to the right atrium.

  • Pulmonary artery: Carries deoxygenated blood to the lungs.

  • Pulmonary vein: Carries oxygenated blood from the lungs to the left atrium.

  • Coronary arteries: Supply the heart muscle itself with blood.

Double Circulatory System

• Pulmonary: Right side of heart → lungs → left side. Blood becomes oxygenated.

• Systemic: Left side of heart → body → right side. Delivery of $O_2$ and collection of $CO_2$.

• Alveoli Adaptations: Large surface area, thin walls (one cell thick), rich capillary network, and ventilation to maintain steep concentration gradients.

Blood Vessels and Blood Components

• Plasma: Liquid part (~55%); transports glucose, amino acids, $CO_2$, urea, hormones, and heat.

• Red blood cells: Biconcave disc with no nucleus (more room for haemoglobin). Haemoglobin binds $O_2$ to form oxyhaemoglobin.

• White blood cells: Immune defence; phagocytes engulf pathogens, lymphocytes produce specific antibodies and antitoxins.

• Platelets: Cell fragments that trigger blood clotting at wounds to prevent blood loss and pathogen entry.

B2 ORGANISATION: CHD, Health, and Cancer

CHD Treatments

Health, Lifestyle, and Cancer

• Communicable disease: Caused by pathogens; can spread between organisms.

• Non-communicable disease: Cannot pass between organisms (e.g., CHD, cancer, Type 2 diabetes).

• Risk Factors: Linked to an increased probability of disease (Correlation $\neq$ Causation).

  • Diet/Smoking/Inactivity → Cardiovascular disease.

  • Obesity → Type 2 diabetes.

  • Alcohol → Liver disease/brain damage.

  • Smoking/Carcinogens/Ionising radiation → Cancer.

• Cancer:

  • Benign tumour: Growth contained in one area within a membrane; does not spread.

  • Malignant tumour: Invades nearby tissues and spreads in the blood to form secondary tumours (metastases).

B2 ORGANISATION: Plant Tissues and Transport

• Epidermal tissue: Outer surface protection; contains stomata in the lower epidermis for gas exchange.

• Palisade mesophyll: Upper leaf; main site of photosynthesis with many chloroplasts.

• Spongy mesophyll: Lower leaf; contains air spaces for gas diffusion.

• Xylem: Transports water and minerals upward; lignified for support.

• Phloem: Translocation of dissolved sugars from leaves to all parts of the plant.

• Meristem: At root and shoot tips; contains dividing cells for growth.

• Transpiration: Loss of water vapour from leaves through stomata, creating the transpiration stream. Rate increases with higher temperature, lower humidity, more air movement, and higher light intensity.

B2 REQUIRED PRACTICALS

Required Practical 4: Food Tests

• Starch: Add iodine → positive is blue-black.

• Reducing sugars: Add Benedict's + heat → positive is green/yellow/orange/brick-red.

• Protein: Add Biuret reagent → positive is lilac/purple.

• Lipids: Shake with ethanol, then add water → positive is cloudy white emulsion.

Required Practical 5: Effect of pH on Amylase

1. Mix amylase, buffer (set pH), and starch solution.

2. Every 30 seconds, drop the mixture onto iodine on a spotting tile.

3. Endpoint: When iodine remains orange-brown, starch is digested.

4. Calculate $\text{rate} = 1 \div \text{time}$. Repeat for a pH range (e.g., 3 to 11).

B3 INFECTION AND RESPONSE: Pathogens and Diseases

Communicable Diseases Table

• Vector: An organism, like a mosquito, that spreads a pathogen without getting ill itself.

Human Defence Systems

• Non-specific (Barriers): Skin (physical barrier/antimicrobial secretions); Nose (hairs/mucus); Trachea/Bronchi (mucus/cilia); Stomach ($HCl$).

• Specific Immune Response:

  • Phagocytosis: Engulfing and digesting pathogens.

  • Antibodies: Produced by lymphocytes; specific to antigens.

  • Antitoxins: Neutralise toxins from bacteria.

  • Memory cells: Ensure a faster response on re-exposure.

B3 INFECTION AND RESPONSE: Vaccines and Drugs

• Vaccination: Stimulates white blood cells to produce antibodies using dead/inactive pathogens. Leads to herd immunity when high proportions of the population are vaccinated.

• Antibiotics: Kill bacteria; do NOT work on viruses. Antibiotic resistance is a global threat.

• Drug Development: Drugs sourced from plants (e.g., digitalis from foxgloves, aspirin from willow) or microorganisms (penicillin). New drugs are tested for toxicity, efficacy, and dose.

  • Preclinical: Cells, tissues, animals.

  • Clinical trials: Healthy volunteers → patients → double-blind trials → peer review.

Triple Only Content

• Monoclonal Antibodies: Identical antibodies specific to one antigen. Produced by fusing mouse lymphocytes with tumour cells to create hybridoma cells. Uses include pregnancy tests (hCG), pathology, research, and cancer treatment (targeted toxins).

• Plant Disease signs: Stunted growth, spots, decay, growths, malformations, discolouration, pests.

• Mineral deficiencies:

  • Nitrate deficiency → stunted growth (needed for amino acids/proteins).

  • Magnesium deficiency → chlorosis (needed for chlorophyll).

• Plant Defences: Physical (cuticle, cell wall); Chemical (antibacterial, poisons); Mechanical (thorns, mimicry).

B4 BIOENERGETICS: Photosynthesis and Respiration

Photosynthesis

• Equation: $6CO_2 + 6H_2O \rightarrow C_6H_{12}O_6 + 6O_2$ ($\text{Endothermic}$).

• Limiting Factors: Light intensity, $CO_2$ concentration, temperature, and amount of chlorophyll.

• Higher Tier Only:

  • Inverse Square Law: $\text{Light Intensity} \propto 1 \div d^2$.

  • Greenhouse economics: Balancing cost of artificial $CO_2$/heat vs profit.

• Glucose Uses: Respiration, starch (storage), fats/oils (seeds), cellulose (walls), and proteins (with nitrate ions).

Respiration and Exercise

• Aerobic: $C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O$ ($\text{Exothermic}$).

• Anaerobic (Muscles): $glucose \rightarrow lactic\,acid$.

• Anaerobic (Yeast/Plants): $glucose \rightarrow ethanol + CO_2$ (Fermentation).

• Response to Exercise: Increased heart rate, breathing rate, and breath volume.

• Oxygen Debt (HT): Extra oxygen needed to react with lactic acid. Lactic acid is transported to the liver and converted back to glucose.

• Metabolism: The sum of all chemical reactions in a cell controlled by enzymes (e.g., lipid formation, urea production).

Required Practical 6: Light Intensity on Photosynthesis

1. Place pondweed in sodium hydrogencarbonate solution ($CO_2$ source).

2. Position lamp at measured distances and count $O_2$ bubbles per minute.

3. HT: Calculate light intensity $\propto 1 \div d^2$.

B5 HOMEOSTASIS AND RESPONSE

Principles of Homeostasis

• Homeostasis: Regulation of internal conditions (blood glucose, temperature, water levels) for optimum cell and enzyme function.

• Pathway: $\text{Stimulus} \rightarrow \text{Receptor} \rightarrow \text{Coordination centre (CNS)} \rightarrow \text{Effector}$.

• Reflex Arc: Receptor → sensory neurone → relay neurone (spinal cord) → motor neurone → effector. Synapses use chemical neurotransmitters to pass impulses across gaps.

Endocrine System and Hormones

• Glands: Pituitary (master gland), Pancreas (insulin/glucagon), Thyroid (thyroxine), Adrenals (adrenaline), Ovaries (oestrogen), Testes (testosterone).

Triple Only Content

• The Brain: Cerebral cortex (consciousness/memory); Cerebellum (balance); Medulla (unconscious activities). Study methods (HT): MRI, electrical stimulation.

• The Eye:

  • Near object: Ciliary muscles contract, ligaments loosen, lens thickens.

  • Distant object: Ciliary muscles relax, ligaments tighten, lens thins.

  • Myopia (short-sight): Concave lens. Hyperopia (long-sight): Convex lens.

• Thermoregulation:

  • Too hot: Vasodilation and sweating.

  • Too cold: Vasoconstriction and shivering.

• Kidneys: Filtration and selective reabsorption of glucose, ions, and water.

  • HT: ADH controls reabsorption via negative feedback (More ADH = concentrated urine).

  • Deamination (HT): Liver converts amino acids to ammonia, then urea.

Blood Glucose and Reproduction

• Blood Glucose: Insulin clears glucose from blood. HT: Glucagon converts glycogen back to glucose.

  • Type 1: Lack of insulin. Type 2: Insulin resistance (linked to obesity).

• Hormones in Menstrual Cycle (HT):

  • FSH: Egg maturation; stimulates oestrogen.

  • Oestrogen: Uterus lining; inhibits FSH; triggers LH surge.

  • LH: Ovulation.

  • Progesterone: Maintains lining; inhibits FSH/LH.

• Plant Hormones (Triple): Auxins control phototropism (growth to light) and gravitropism.

  • HT: Gibberellins (germination) and Ethene (ripening).

Required Practical 7: Reaction Time

1. Partner drops a catches a ruler.

2. Measure distance and convert to reaction time using a table.

3. Investigate factors like caffeine or distraction.

Triple Only — Required Practical 8: Plant Responses

1. Investigate phototropism and gravitropism using seedlings and directional light or gravity.

2. Record using accurate labelled biological drawings.