BTEC National Applied Science Revision Guide Notes

Biology: Brain Chemicals, Parkinson’s Disease, and Depression

  • Parkinson’s disease and depression are linked to imbalances in brain chemicals.

  • This knowledge facilitates the development of drugs for treatment.

Dopamine and Parkinson’s Disease

  • Symptoms of Parkinson’s Disease:

    • Muscle tremors (shakes)

    • Stiffness of muscles and slowness of movement

    • Poor balance and walking problems

    • Difficulties with speech and breathing

    • Depression

  • Parkinson’s disease is associated with the death of dopamine-secreting neurons in the brain, leading to reduced dopamine levels.

  • Dopamine:

    • A neurotransmitter active in neurons in the frontal cortex, brain stem, and spinal cord.

    • Associated with the control of movement and emotional responses.

  • Treatment of Parkinson’s Disease:

    • Aims to increase dopamine concentration in the brain.

    • Dopamine cannot cross the blood-brain barrier.

    • L-dopa, a precursor molecule, can be converted into dopamine in the brain to manage symptoms.

Serotonin and Depression

  • Serotonin:

    • A neurotransmitter linked to feelings of reward and pleasure.

    • Lack of serotonin is linked to clinical depression (prolonged feelings of sadness, anxiety, hopelessness, loss of interest, restlessness, insomnia).

  • Ecstasy (MDMA):

    • Prevents the reuptake of serotonin, maintaining a high concentration of serotonin in the synapse.

    • Causes mood changes in users.

  • Serotonin Selective Reabsorption Inhibitor (SSRI):

    • Prozac is an example of an SSRI used to reduce depression.

    • SSRIs bind to reuptake proteins, preventing serotonin reabsorption.

    • Increased serotonin levels in synapses allow continuous binding to receptors in postsynaptic membranes, increasing feelings of reward and pleasure.

How Synapses Are Affected by Drugs

  • Drugs interfere with the normal functioning of a synapse via several mechanisms:

    • Affecting the synthesis or storage of neurotransmitters.

    • Affecting the release of neurotransmitters from the presynaptic membrane.

    • Affecting the interaction between neurotransmitters and receptors on the postsynaptic membrane.

    • Stimulatory action by binding to receptors and opening sodium ion channels.

    • Inhibitory action by blocking receptors on the postsynaptic membranes, preventing neurotransmitter binding.

    • Preventing the reuptake of neurotransmitters back into the presynaptic membrane.

    • Inhibiting enzymes involved in breaking down neurotransmitters in the synaptic cleft.

Skills: Using CO_2 as a Refrigerant – Ideal Gas Equation and Thermodynamics

  • CO_2 is increasingly used as a refrigerant due to the damaging climate change impact of other gases.

  • Density of CO_2: 1.977 kg
    m^{−3} at 0 °C and atmospheric pressure.

Ideal Gas Equation and Volume Calculation

  • Problem: Calculate the volume of air displaced by a spill of 100 g of CO_2 into a room at 18 °C.

  • Density formula: \rho =

    \frac{m}{V}

  • Volume at 0 °C (273 K): V_{273} =

    \frac{m}{\rho} =

    \frac{0.100 kg}{1.977 kg
    m^{−3}} = 0.0506
    m^3

  • Ideal gas equation: pV = nkT (Pressure, p, and number of molecules, n, are constant; V is proportional to T).

  • Volume at 18 °C (291 K): V{291} = V{273}
    \times

    \frac{291}{273} = 0.054
    m^3 or 54 liters.

Calculating Total Internal Energy Change, \Delta U

  • Context for the calculation: Using data about CO2 to calculate \Delta U for 1 kg of CO2 passing through the evaporator.

  • CO_2 liquid at -20 °C has a density of 1256 kg
    m^{−3}, while the saturated vapor has a density of 62.3 kg
    m^{−3} and exerts a pressure of 2.0 MPa.

Work Done Calculation

  • Formula: W = p\Delta V and V =

    \frac{m}{\rho}

  • For 1 kg of CO2, \Delta V = V{vapor} − V_{liquid} =

    \frac{1}{62.3} −

    \frac{1}{1256} = 0.0153
    m^3

  • Work done: W = 2.0
    \times 10^6
    \times 0.0153 = 3.06
    \times 10^4 J = 30.6 kJ

Key Points for Calculations

  • Show relevant working, including the unit.

  • Round the result based on the uncertainty in the data items.

  • The example rounds to two significant figures due to the least precise data.

  • Show formulas and all working steps clearly, especially for multi-step calculations.

  • Units must be included with the answer.

Biology: Cells and Microscopy

  • All living things are made of cells.

  • Cells are the basic units of life, originating from other cells.

  • Microscopes magnify images for clear observation of cells and their structures.

Light Microscope

  • Magnification:

    • Total magnification = magnification of eyepiece lens × magnification of objective lens.

    • Eyepiece lens usually has ×10 magnification.

    • Objective lens can magnify up to ×100.

    • Greatest total magnification is usually ×1000.

  • Specimen Preparation:

    • Material must be thin for light or electron beam to pass through.

    • Coverslip protects the specimen and the lens.

    • Stains help distinguish different features.

Electron Microscopes

  • Invented in the mid-twentieth century.

  • Provide far greater magnification than light microscopes.

  • Can only examine dead material.

Calculation Example

  • A structure viewed at ×400 magnification using a light microscope measures 7 divisions, where each division is 0.06 mm.

  • Real length of the structure calculation:

    • 7
      \times 0.06 mm = 0.42 mm

Electron Micrograph Example

  • Calculate the width of structure P at ×16000 magnification between points A and B.

  • Given: magnification = \frac{size
    of
    image}{size
    of
    real
    object}

  • So, 16000 =

    \frac{20mm}{size
    of
    real
    object}

  • Rearrange: width of P = \frac{20mm}{16000} = 0.00125mm

Biology: Cells – Common Features and Ultrastructure

Common Features of All Cells

  • All cells contain DNA, cytoplasm, ribosomes, and a plasma membrane.

  • These structures can differ between prokaryotic and eukaryotic cells.

Discovery of Cells

  • Robert Hooke discovered cells in 1665 using a microscope.

Limitations of Light Microscopes

  • Limited by the wavelength of light.

  • Electron beams have shorter wavelengths, revealing more detail with electron microscopes.

  • Electron microscopes can only be used on dead material.

Eukaryotic Cell Ultrastructure

  • Eukaryotic cells contain organelles with specialized functions, often membrane-bound.

  • Only the plasma membrane, nucleus, and nucleolus are visible under a light microscope.

Organelles and Their Functions

  • Nucleolus:

    • Region of dense DNA and protein.

    • Makes ribosomes.

  • Nucleus:

    • Surrounded by a double membrane (envelope).

    • Contains pores.

  • Centrioles:

    • Two hollow cylinders arranged at right-angles to each other.

    • Make the spindle in cell division.

  • Lysosome:

    • Enclosed by a single membrane.

    • Contains digestive enzymes.

    • Destroys old organelles and pathogens.

  • Golgi Apparatus:

    • A series of single, curved sacs enclosed by a membrane.

    • Many vesicles cluster around it.

    • Modifies and packages proteins in vesicles for transport.

  • rER (Rough Endoplasmic Reticulum):

    • A series of single, flattened sacs enclosed by a membrane.

    • Has ribosomes on the surface.

    • Proteins are made here.

  • sER (Smooth Endoplasmic Reticulum):

    • A series of single, tubular sacs made of membrane.

    • Lipids are made here.

  • Mitochondrion:

    • Surrounded by a double membrane (envelope).

    • Inner membrane is folded into finger-like projections called cristae.

    • Central area contains a jelly called the matrix.

    • Contains 70S ribosomes and DNA.

    • Site of respiration.

  • Ribosomes:

    • 80S ribosomes are the site of protein synthesis in eukaryotes.

    • 70S ribosomes are present in prokaryotes.

  • Cytoplasm:

    • Fluid filling the cell.

    • Contains dissolved molecules (enzymes, sugars, amino acids, fatty acids).

    • Site of many metabolic processes.

  • Vesicle:

    • Small, membrane-bound sac.

    • Transports and stores substances in the cell.

  • Plasma Membrane:

    • Protects the cell from its surroundings.

    • Regulates the movement of substances in and out of cells.

Biology: Prokaryotes – Bacteria

Prokaryotic Cells

  • Bacteria are prokaryotes, made of a single cell with no membrane-bound organelles.

Gram-Positive vs. Gram-Negative Bacteria

  • Gram-Positive Bacteria:

    • Retain the gram stain (crystal violet) due to a thick peptidoglycan wall that absorbs the stain.

    • Do not have an outer membrane.

  • Gram-Negative Bacteria:

    • Do not retain the gram stain because their cell wall has an outer layer.

    • The thin peptidoglycan cell wall is stained red with another stain like safranin.

    • More resistant to antibiotics because the outer membrane protects them.

Bacterial Cell Structures

  • Capsule:

    • Polysaccharide layer outside the cell wall.

    • Protects cells from drying out and being engulfed by white blood cells.

    • Helps cells stick to surfaces.

  • Nucleoid:

    • Region where a single, circular length of DNA is folded.

    • DNA carries all essential information.

  • Cell Wall:

    • Made of peptidoglycan (sugar and amino acids).

  • Ribosome:

    • Makes proteins.

    • 70S (S is a Svedberg unit).

  • Plasmids:

    • Double-stranded DNA in a circular structure.

    • Often contain additional genes for antibiotic resistance or toxin production.

  • Size: 0.5–5 μm

Biology: Plant Cells

Comparison of Animal, Plant, and Bacterial Cells

  • Key differences: cell wall, chloroplasts, nuclear membrane, cell membrane, ribosomes, and centrioles.

Plant Cells

  • Eukaryotic, but differ from animal cells.

  • Contain all structures found in animal cells (except centrioles), plus:

    • Chloroplasts (for photosynthesis).

    • Vacuole (stores water and other substances).

    • Tonoplast membrane (controls movement of molecules into and out of the vacuole).

    • Cell wall (for support and protection).

    • Amyloplasts (store starch).

    • Middle lamella (sticks cells together).

    • Plasmodesmata and pits (allow communication between cells).

Biology: Specialised Plant Cells – Root Hair and Palisade Cells

Specialised Plant Cells

  • Organs of plants contain cells specially adapted for their function (e.g., leaves and roots).

Root Hair Cells

  • Found in the epithelium near the root tip.

  • Adaptations:

    • Fine protrusion (hair) increases surface area to volume ratio for water and mineral absorption.

    • Thin cell wall facilitates water absorption.

    • Many mitochondria supply energy for active transport of minerals.

Palisade Cells

  • Cylindrical-shaped cells packed tightly in the upper part of a leaf.

  • Adaptations:

    • Many chloroplasts capture maximum light energy for photosynthesis.

    • Large vacuole maintains cell and leaf rigidity.

Biology: Specialised Animal Cells – Sperm, Egg, Red and White Blood Cells

Mammalian Gametes and Blood Cells

  • Specialised for their functions.

Sperm Cell

  • Undulipodium: for movement to swim to the egg

  • Haploid Nucleus: contains only one set of chromosomes, restoring the full complement at fertilization.

  • Acrosome: contains enzymes to digest the outer layers of the egg.

  • Mid Region: with mitochondria to provide energy for movement.

Egg Cell

  • Haploid Nucleus: contains half the chromosomes of a body cell

  • Cytoplasm: full of energy-rich material.

  • Follicle Cells (Corona Radiata): supply vital proteins.

  • Zona Pellucida (Jelly Layer): stops more than one sperm fertilizing the egg.

  • Cortical Granules: contain a substance that prevents multiple sperm fertilization.

Red Blood Cells

  • Biconcave Discs: with no nucleus

  • Cytoplasm: contains hemoglobin to carry oxygen

  • Adaptations:

    • Optimize surface area to volume ratio for better oxygen and carbon dioxide diffusion.

    • Small size and shape allow them to squeeze through narrow blood vessels.

White Blood Cells

  • Function: fight pathogens.

  • Types: Phagocytes and Lymphocytes

Biology: Epithelial Tissue – Squamous and Columnar Epithelium

Epithelial Tissue

  • Lines surfaces in contact with the external environment or internal organs (e.g., lungs).

Squamous Epithelium

  • Characteristics:

    • Very flat and thin with egg-shaped nuclei.

    • Often only one cell thick.

    • Good for surfaces where diffusion occurs, such as in the lungs.

Columnar Epithelium

  • Location: lines the upper airway (trachea and bronchi).

  • Characteristics:

    • Ciliated cells with many mitochondria.

    • Cilia move mucus away from the lungs.

    • Goblet cells produce mucus to trap inhaled particles.

Chronic Obstructive Pulmonary Disease (COPD)

  • More common in smokers due to lung damage.

  • Cigarette smoke damages cilia, causing mucus build-up.

  • This clogs airways, causes coughing, and ruptures alveolar epithelial cells, reducing surface area for gas exchange.

  • Provides a good environment for pathogens to grow.

Biology: Blood Vessels and Atherosclerosis

Blood Vessels

  • Lined with endothelial tissue.

Endothelial Tissue

  • Single layer of flat, long cells oriented lengthwise in the direction of blood flow.

  • Function: Provides a smooth surface for easy blood flow.

  • Capillaries only have an endothelium.

Arteries and Veins

  • Made of the same tissues in different proportions.

  • Outer layer: Connective and elastic tissue; thicker in veins to prevent collapse.

  • Middle layer: Smooth muscle, connective and elastic tissue; thicker in arteries to maintain blood pressure.

Atherosclerosis

  • Disease process leading to coronary disease and strokes.

  • Fatty deposits (atheroma) block arteries or increase the risk of blood clot formation (thrombosis).

  • Development involves:

    • damage to the endothelial tissue lining of the artery

    • accumulation of low-density lipoproteins (LDL cholesterol) in artery wall

    • buildup of LDL cholesterol, white blood cells, calcium salts, and fibers

    • narrowing of artery and loss of elasticity

    • increased risk of blood clotting

    • raised blood pressure

    • inflammation

Smoking and Atherosclerosis

  • Cigarette smoke contains toxic chemicals that lead to atherosclerosis.

  • Increases blood thickness, causing fatty deposits on artery walls and raising clotting risk.

  • Increases blood pressure and heart rate, damaging the endothelium.

Biology: Fast and Slow Twitch Muscle Fibers

Muscle Tissue

  • Soft tissue that contracts to maintain position or produce movement.

Muscle Structure

  • Made of bundles of muscle fibers (cells).

  • Muscle fibers are made of myofibrils.

Types of Muscle Fibers

Slow Twitch Muscle Fibers

  • Slow, sustained contraction for long periods of exercise.

  • Many mitochondria supply energy from aerobic respiration (requires oxygen).

  • Lots of capillaries.

  • Does not tire easily.

  • Large oxygen and glucose stores.

Fast Twitch Muscle Fibers

  • Rapid, intense contractions in short bursts.

  • Few mitochondria; energy for contraction from anaerobic respiration (no oxygen needed).

  • Few capillaries.

  • Tires easily.

  • Little stored oxygen and glucose.

Muscle Contraction

  • Made of thick (myosin) and thin (actin) protein filaments.

  • Actin filaments move between myosin filaments, shortening the sarcomere and overall muscle length.

Biology: Types of Neurones

Structure of the Nervous System

  • The nervous system is divided into the central nervous system (CNS) and the peripheral nervous system.

  • CNS: brain and spinal cord

Neurones

  • Nerves are made up of cells called neurones, which carry messages in the form of electric signals from one part of the body to another.

Types of Neurones

  • Sensory Neurone

  • Relay Neurone

  • Motor Neurone

Structure of a Neurone

  • nucleus

  • cell body

  • axon

  • myelin sheath

  • dendrite

  • Schwann cell

  • node of Ranvier

  • axon terminals

Myelin Sheaths

  • Most nerve cells are myelinated.

Comparing Non-Myelinated and Myelinated Nerve Cells

Non-Myelinated

  • do not have a myelin sheath

  • grey

  • transmit impulses slower

  • do not have nodes of Ranvier

Myelinated

  • have a myelin sheath

  • white

  • transmit impulses very fast

  • do have nodes of Ranvier

Biology: Nerve Impulse

Nerve Impulse

  • Neurons send electric impulses generated by changes in the concentrations of ions inside and outside the nerve cell, causing a potential difference (PD), called an action potential.

Changes in Polarity

  • The action potential is triggered by the depolarization of the nearby membrane, changing the PD to the threshold potential.

  • A new action potential cannot be generated in the same section of membrane for about 5 milliseconds, ensuring that the impulse travels in one direction along a nerve fiber.

  • Between the action potentials, the cell is at resting potential (between −60 and −70mV, depending on the nerve cell).

Saltatory Conduction

  • The only region of a myelinated nerve fiber that can depolarize is at the nodes of Ranvier where there is no myelin.

  • This means that nerve impulses can travel a much longer distance and faster—the impulse jumps from one node to the next.

Biology: Electroencephalogram (EEG)

Electroencephalogram (EEG)

  • An EEG records electrical activity in the cerebral cortex of the brain by placing electrodes on the head at specific positions.

  • Different electrodes record activity from different known areas of the brain.

EEG Use Cases

  • EEGs are mainly used to diagnose and investigate epilepsy.

  • Also used to investigate problems such as sleep disorders, dementia, head injuries, and encephalitis (inflammation of the brain).

Brain Waves

| Rhythm | Freq (Hz) | Amp (μV) | Presentation                             |
| :------ | :-------- | :------- | :--------------------------------------- |
| Alpha   | 8−13      | 20−200   | when awake with eyes closed              |
| Beta    | 13−30     | 5−10     | when awake                               |
| Delta   | 1−5       | 20−200   | during sleep                             |
| Theta   | 4−8       | 10       | young children and adults in deep sleep |

Biology: Synapses

Synapses

  • Synapses are gaps between nerve cells.

  • Action potentials cannot pass between nerve cells across the synapse; therefore, transmitter substances are used.

Structure of a Synapse

  • A synapse is the junction between two neurons.

  • The presynaptic membrane releases chemicals (neurotransmitters) to stimulate impulses in the postsynaptic cell.

Acetylcholine

  • First neurotransmitter to be discovered; stimulates muscles.

  • Largely made in the brain.

  • Broken down in the synaptic cleft by acetylcholinesterase.

Synapse Action

  • An action potential arrives, depolarizing the membrane.

  • Calcium ion channels open; calcium ions enter the neuron.

  • Calcium ions cause synaptic vesicles containing neurotransmitter to fuse with the presynaptic membrane.

  • Neurotransmitter is released into the synaptic cleft and binds with receptors on the postsynaptic membrane.

  • Sodium channels open; sodium ions flow through the channels.

  • The membrane depolarizes and initiates an action potential.

  • The neurotransmitter is either taken up across the presynaptic membrane or diffuses away and is broken down.

Chemistry: Writing Formulae and Equations

Formulae

  • Important ions to remember:

    • Nitrate: NO_3^−

    • Carbonate: CO_3^{2−}

    • Sulfate: SO_4^{2−}

    • Hydroxide: OH^−

    • Ammonium: NH_4^+

    • Zinc: Zn^{2+}

    • Silver: Ag^+

Predicting Charges on Ions

  • Metals in groups 1, 2, and 3 form 1+, 2+, and 3+ ions, respectively.

  • Non-metals in groups 5, 6, and 7 form 3−, 2−, and 1− ions, respectively.

Writing a Balanced Equation

  • Atoms cannot be created or destroyed, so the numbers of each atom on both sides of an equation have to balance.

Steps

  1. Write the correct formula for all reactants and products.

  2. Check that the numbers of each atom balance. If not, use numbers in front of reactants or products to balance atoms.

  3. Add state symbols if required: (s) = solid, (l) = liquid, (g) = gas, (aq) = aqueous solution.

Working out Formulae

  • Deduce the formula of an ionic compound using the formulae and charges of the ions involved.

Example

  • Combustion of methane:

    • CH4 + 2O2 → CO2 + 2H2O

Chemistry: Electronic Structure of Atoms

Bohr’s Model

  • Electrons are found in atoms in shapes in space

Energy Levels or Shells

  • Electrons orbit the nucleus in shells; the further the shell is from the nucleus, the higher its energy.

n

Shell

Number of Electrons

1

1st shell

2

2

2nd shell

8

3

3rd shell

18

4

4th shell

32

Rules for Arranging Electrons

  1. Start at the lowest shell and add electrons one at a time to build up the configuration.

  2. Fill each sub-level before starting on the next.

  3. Fill each orbital singly in a sub-level before pairing electrons.

Atomic Orbitals

  • Orbitals can be confused with sub-shells. Any orbital, regardless of the sub-shell it is in, can hold up to two electrons.

  • Each shell consists of atomic orbitals (regions in space where electrons may be found).

Chemistry: Ionic bonding

Ionic Bonds

Strong electrostatic attractions between positive and negative ions.

Ionic Compounds and Giant Ionic Structures

  • Ions arranged in a regular, three-dimensional pattern, called a lattice.

  • Electrostatic forces between the ions act in all directions, holding the structure together.

  • Large number of these strong electrostatic attractions gives ionic compounds high melting points.

Strength of Ionic Bonds

To compare the relative strength of ionic bonds, the ionic charge and ionic radius have to be considered, sometimes called the charge/size ratio.

Positive Ions

Generally formed by metal atoms losing electrons
Have a positive charge equal to the group number if formed from a group 1, 2 or 3 element

Negative Ions

Generally formed by non-metal atoms gaining electrons from metal ions
Have a negative charge equal to 8 minus the group number of the element
Sometimes exist as polyatomic ions, such as CO3^{2−}, SO4^{2−}, NO_3^− and OH^−, whose charges should be learnt

Chemistry: Covalent bonds

Covalent Bonds

  • Electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms.

How do atoms form covalent bonds?

  • A covalent bond forms when atoms share a pair of electrons.

  • Each atom in the bond contributes one electron to the pair, but a covalent bond consisting of an electron pair derived from one of the atoms is called a dative covalent (coordinate) bond.

Strength of covalent bonds

  • Bond length and bond strength in covalent bonds are inversely related. This means that the shorter the covalent bond length, the greater the covalent bond strength.

Chemistry: Metallic bonding

Metallic Bonding

  • Metallic bond is a strong electrostatic attraction between the positive metal ions and the delocalised electrons.

Properties of metals

  • Electrical and thermal conductivity due to the delocalised electrons, which are free to move

  • High melting and boiling points due to strong electrostatic attractions between positive ions and electrons

  • Malleability – can be shaped

  • Ductility – can be pulled into wires

Trends in melting points

  • The melting points decrease as the atoms get larger

  • Larger metals have more electrons and more electron shells. This means they have more shielding between the nucleus and delocalised electrons, so the electrostatic attraction force between them is weakened

  • Each group 2 metal has a higher melting point than the group 1 metal in the same period

Chemistry: Intermolecular forces

Intermolecular Forces

  • Interactions between molecules caused by either permanent or induced dipoles.

London forces

  • Electrons are moving randomly within the shells of a molecule or atom, which can cause an uneven distribution in the molecule, resulting in an instantaneous, temporary dipole

  • This can induce a temporary dipole in a nearby molecule, resulting in a weak attraction, called a London force.

Dipole–dipole interactions

  • Polar molecules such as HCl have permanent dipoles due to the much greater electronegativity of the chlorine atom and the fact that the molecule is not symmetrical.

Hydrogen bonds

  • This type of intermolecular force is the attraction between an electron-deficient hydrogen atom (\delta +) and a lone pair on oxygen, nitrogen or fluorine atoms

  • Water molecules can form hydrogen bonds between each other.

Chemistry: Relative masses

Relative Masses

  • As atoms are so small, scientists use the idea of relative masses to compare the mass of atoms, elements and compounds.

Relative atomic mass

  • The atoms in a sample of an element may have slightly different masses, so relative atomic mass is often useful as a way of comparing the masses of different elements.

  • It is defined as: Mean mass of atoms of the element (in a sample) compared with \frac{1}{12} of the mass of a carbon-12 atom.

Relative molecular mass

  • This term is used when comparing the mass of molecules with simple covalent structures.

  • It is the sum of the relative atomic masses of all the atoms present in the substance.

Relative formula mass

  • This term is used when referring to substances with giant structures.

  • It is the sum of the relative atomic masses of all the atoms in the formula of the substance.

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