Cambridge International GCSE Biology Exam Notes

Overview of Biology in CIE GCSE
Suitable for separate/triple biology, coordinated/combo biology.
Emphasis on essential information for studying.

• Cells

• All life consists of cells.

• Cells observed using light and electron microscopes (better resolution).

• Magnification equation: Magnification = Image Size / Object Size.

• Groups of cells:

  • Eukaryotic Cells:
    Contain nucleus (e.g., plants, animals) and membrane-bound organelles, allowing for compartmentalized functions within the cell.

  • Prokaryotic Cells:
    Lack a true nucleus and membrane-bound organelles; typically smaller than eukaryotic cells (e.g., bacteria). Prokaryotes often have plasmids, which are small, circular pieces of DNA.

• Cell Organelles

• Cell membrane: Semi-permeable structure that regulates the entry and exit of substances.

• Plant cells:

  • Cell wall (cellulose): Provides rigidity and structural support, allowing plants to remain upright.

  • Chloroplasts: Site for photosynthesis, converting light energy into chemical energy stored in glucose.

• Hydration Structures:

  • Cytoplasm: Gel-like fluid where chemical reactions occur and organelles are suspended.

  • Mitochondria: Known as the powerhouse of the cell; site for respiration; energy release through ATP (adenosine triphosphate).

  • Ribosomes: Sites of protein synthesis where amino acids are assembled into proteins.

• Transport Mechanisms

• Diffusion: Passive movement of molecules from a region of high concentration to low concentration until equilibrium is reached; important in nutrient absorption and gas exchange.

• Osmosis: Specific diffusion of water molecules across a semi-permeable membrane, influenced by solute concentrations (e.g., movement of water into plant root cells).

• Factors affecting the rate of transport include:

  • Concentration difference: Greater differences lead to faster rates.

  • Temperature: Higher temperatures increase molecular movement.

  • Surface area: Larger surface areas facilitate faster exchange.

• Active Transport: Movement of molecules against their concentration gradient, requiring energy (ATP); essential for nutrient uptake (e.g., uptake of minerals by root hair cells).

• Tissues to Organ Systems

• Tissues (e.g., epithelial, muscle, connective, nervous) combine to form organs (e.g., heart, lungs), which work together to form organ systems (e.g., circulatory system).

• Digestive System Functions:

• Breakdown of food through mechanical and chemical processes, utilizing stomach acid and enzymes (bile, produced in the liver) to help digest fats.

• Types of teeth function differently:

  • Incisors: Cutting food.

  • Canines: Tearing food.

  • Premolars: Crushing and grinding food.

  • Molars: Grinding food into smaller pieces for digestion.

Parts of a Tooth:

• Crown: Visible part of the tooth above the gum line.

• Root: The part of the tooth embedded in the jawbone, anchoring it in place.

• Enamel: Hard, outer surface that protects the tooth.

• Gum:

• Pulp: The innermost part of the tooth, containing nerves and blood vessels.

• Enzymes

• Biological catalysts that accelerate chemical reactions; specific to substrates (lock and key model).

• Example:

  • Amylase: Breaks down starch into glucose for energy use.

• Enzyme Activity Factors:

  • Temperature and pH levels affect enzyme shape, thus impacting activity; specific enzymes function optimally at certain pH and temperature ranges.

The lock and key model describes how enzymes interact with substrates to form products. According to this model:

• The enzyme is likened to a lock, while the substrate is compared to a key.

• The active site of the enzyme has a specific shape that exactly fits the shape of the substrate, allowing for precise binding.

• When the substrate binds to the active site, it forms an enzyme-substrate complex, facilitating the chemical reaction.

• The model emphasizes the specificity of enzymes for their substrates, meaning that each enzyme only works with a specific substrate due to the complementary shapes.

• Once the reaction occurs, the products are released, and the enzyme remains unchanged, ready to catalyze another reaction.
  This model helps illustrate the concept of enzyme specificity and the crucial role of active site structure in enzymatic activity.

• Nutritional Needs

• A balanced diet includes various components:

  • Carbohydrates (energy source), proteins (growth and repair), fats (energy storage), vitamins (essential for biochemical functions), minerals (supporting physiological processes).

• Respiratory System

• Distinction between breathing (physical process) and respiration (chemical process of energy release).

• Process: Air enters through the nose/mouth -> Trachea -> Bronchioles -> Alveoli (site of gas exchange) -> Oxygen diffuses into blood.

• Oxygen transport by hemoglobin in red blood cells; carbon dioxide is transported back to the lungs for exhalation.

• Circulatory System

• Double circulatory system: Blood enters the heart twice in one complete circulation.

• Blood flow path:

  • Deoxygenated blood enters right atrium via vena cava, sent to lungs for oxygenation, then returned to left atrium.

• Differences between blood vessels:

  • Arteries have thicker walls to handle high pressure and contain oxygenated blood (except pulmonary artery).

  • Veins have thinner walls and valves to prevent backflow; they contain deoxygenated blood (except pulmonary veins).

• Heart requires oxygen delivered through coronary arteries to function effectively.

• Plant Organization and Transport

• Leaves play critical roles in photosynthesis and transpiration; stomata regulate gas exchange.

• Roots are crucial for water and mineral uptake from the soil; xylem is unidirectional (upward transport of water), while phloem enables bidirectional transport (sugars).

• Homeostasis

• Regulation of internal conditions (e.g., temperature, blood sugar) is vital for optimal enzyme function and metabolism.

• Involves nervous and endocrine systems: Receptors detect changes, and effectors (muscles/glands) respond to restore balance.

• Reproductive Systems

• Female Hormonal Cycle: The roles of Follicle Stimulating Hormone (FSH) and Luteinizing Hormone (LH) in regulating the ovulation cycle, including the menstrual cycle phases (follicular, ovulation, luteal).

• Plant Hormones: Auxins influence growth directions, flower and fruit ripening, and responses to light and gravity (phototropism and gravitropism).

• Genetics

• Concepts of DNA structure (double helix), genes, and the differences between genotypes and phenotypes.

• Use of Punnett squares for visualizing and predicting genotype ratios in offspring.

• Advantages and disadvantages of sexual vs. asexual reproduction in various organisms.

• Evolution and Genetics

• Theory of natural selection, emphasizing survival of the fittest and adaptation of species.

• Evidence of evolution through genetic variations in populations, such as antibiotic resistance in bacteria.

• Ecosystem Dynamics

• Importance of both abiotic (non-living) and biotic (living) factors in influencing ecosystems and their health.

• Food chains illustrate energy transfer and the complexity of trophic levels within ecosystems, examining predator-prey relationships and population dynamics.

• Environmental Concerns

• Importance of biodiversity for ecosystem stability and resilience.

• Human impacts on ecosystems including pollution, resource depletion, and climate change, which threaten global biodiversity.

• Promotion of sustainable practices in agriculture and fishing to minimize negative environmental impacts and conserve resources.

• Biotechnology and Genetic Engineering

• Applications in medicine (e.g., production of insulin through recombinant DNA technology) and agriculture (e.g., genetically modified crops for resistance to pests and diseases).