Edexcel International GCSE Science Double Award: Biology Summary Notes

Eight Life Processes: All living things require nutrition, respire, excrete waste, respond to stimuli, move, control internal conditions (homeostasis), reproduce, and grow.
Levels of Organisation: Organisms are structured as organelles $ightarrow$ cells $ightarrow$ tissues $ightarrow$ organs $ightarrow$ organ systems.

Shared Features: Most cells contain a nucleus (controls activity, contains $46$ chromosomes), cytoplasm (site of metabolic reactions), cell membrane (selectively permeable), mitochondria (aerobic respiration), and ribosomes (protein synthesis).
Plant-Specific Structures: Include a cellulose cell wall (support), a permanent vacuole (cell sap), and chloroplasts (photosynthesis containing chlorophyll).
Key Organelle: Mitochondria are more numerous in high-energy cells like muscle or nerve cells.

Biological Catalysts: Enzymes are proteins that speed up metabolic reactions without being consumed.
Mechanism: The "lock and key" model describes a specific substrate fitting into the enzyme's active site.
Temperature Factors: Activity increases with kinetic energy until the optimum temperature (approx. $37\,^{\circ}C$ in humans). Above this, enzymes denature (active site changes shape).
pH Factors: Most enzymes have an optimum pH of $7$ , though stomach enzymes like pepsin function at pH $2$ .

Diffusion: Net movement of particles from high to low concentration down a gradient.
Osmosis: Net movement of water from high water potential (dilute) to low water potential (concentrated) across a partially permeable membrane.
Active Transport: Movement against a concentration gradient using energy from respiration (ATP).
Surface Area to Volume Ratio ( $SA:V$ ): Smaller cells or specialized surfaces (villi, alveoli) have larger $SA:V$ for efficient exchange.

ATP: The energy "currency" of the cell produced during respiration.
Aerobic Respiration: Requires oxygen; occurs in mitochondria. Equation: $C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + \text{energy}$ .
Anaerobic Respiration: Occurs without oxygen; releases less energy. - In Animals: $Glucose \rightarrow Lactate + \text{some energy}$ . - In Yeast: $Glucose \rightarrow Ethanol + CO_2 + \text{some energy}$ .

Eukaryotes: Includes Plants (multicellular, autotrophic), Animals (multicellular, heterotrophic, lack cell walls), Fungi (chitin walls, saprotrophic nutrition via mycelium of hyphae), and Protoctists (mixed microscopic group like Amoeba or Chlorella).
Prokaryotes: Bacteria (unicellular, no nucleus, circular DNA/plasmids, peptidoglycan walls). Examples: Lactobacillus bulgaricus, Pneumococcus.
Viruses: Non-living parasites consisting of a protein coat and a DNA/RNA core. Examples: Influenza, HIV, Tobacco Mosaic Virus (TMV).
Pathogens: Microorganisms that cause disease (viruses, bacteria, fungi, or protoctists).

Balanced Diet: Requires carbohydrates, lipids, proteins, vitamins (A, C, D), minerals (calcium, iron), water, and dietary fibre.
Alimentary Canal: Food moves via peristalsis (muscle contractions).
Enzymes: - Carbohydrases: Amylase (Starch $\rightarrow$ Maltose), Maltase (Maltose $\rightarrow$ Glucose). - Proteases: Pepsin/Trypsin (Protein $\rightarrow$ Peptides), Peptidases (Peptides $\rightarrow$ Amino Acids). - Lipases: Lipids $\rightarrow$ Fatty Acids + Glycerol.
Bile: Produced in the liver, stored in the gall bladder; neutralizes stomach acid and emulsifies lipids.
Absorption: Occurs in the ileum; adapted via villi/microvilli to increase surface area.

Thorax Structure: Includes ribs, intercostal muscles, diaphragm, trachea, bronchi, and alveoli.
Ventilation: Inhalation involves the diaphragm flattening and external intercostals contracting to increase volume/lower pressure.
Gas Exchange: Occurs in alveoli by diffusion; adapted by thin walls and high capillary density.
Heart: Double circulatory system. Right side pumps to lungs (pulmonary); left side pumps to body (systemic).
Blood Components: Plasma (transports nutrients/waste), Red Blood Cells (haemoglobin for oxygen), White Blood Cells (phagocytes ingest pathogens; lymphocytes produce antibodies), Platelets (clotting).

Nervous System: Fast, short-lived electrical impulses via neurones. Includes the CNS (brain/spinal cord). Reflex arcs involve receptor $\rightarrow$ sensory neurone $\rightarrow$ relay neurone $\rightarrow$ motor neurone $\rightarrow$ effector.
Endocrine System: Slower, long-lasting chemical messengers (hormones). Includes Insulin (lowers blood glucose), Adrenaline (fight or flight), Testosterone/Oestrogen (secondary sex characteristics).
Homeostasis: Maintenance of a constant internal environment (e.g., water, temperature at $37\,^{\circ}C$ ).
Skin and Temperature: Controlled via sweating (evaporative cooling), vasodilation (increased surface blood flow), and vasoconstriction (reduced flow to conserve heat).

Gametes: Haploid sex cells (sperm and egg) produced by meiosis.
Fertilization: Fusion of gametes to form a diploid zygote, which divides by mitosis into an embryo.
Development: Embryo implants in the uterus; placenta provides nutrition/waste exchange; amniotic fluid protects the fetus.
Menstrual Cycle: Controlled by oestrogen (line repair) and progesterone (maintains lining).

Photosynthesis: Conversion of light to chemical energy. Equation: $6CO_2 + 6H_2O \xrightarrow{\text{light/chlorophyll}} C_6H_{12}O_6 + 6O_2$ .
Leaf Structure: Adapted with a waxy cuticle, palisade mesophyll (high chloroplast count), spongy mesophyll (gas exchange), and stomata (pores).
Transport: Xylem (water and mineral ions via transpiration); Phloem (sucrose and amino acids via translocation).
Mineral Requirements: Nitrates (for amino acids/proteins); Magnesium (for chlorophyll).

Activity 1 (Starch Test): Why do you boil the leaf in ethanol? To remove chlorophyll so the blue-black color change with iodine is visible.
Activity 2 (Pondweed): How does light intensity affect photosynthesis? As distance from a lamp increases, the rate of oxygen bubble production decreases, indicating light is a limiting factor.
Activity 3 (Temperature and Respiration): Why did germinating seeds increase the temperature in the vacuum flask? Because respiration releases part of its energy as heat.
Question on Artery vs. Capillary: Why is an artery an organ but a capillary is not? An artery is composed of multiple tissues (muscle, elastic, epithelial) working together for a function, whereas a capillary is a single tissue layer.