Biology Paper 1 Comprehensive Study Notes

Biological Molecules and Cell Structures

• Carbohydrates: Used for respiration to provide energy.     * Starch: The storage form of glucose in plants.     * Glycogen: The storage form of glucose in animals and fungi.     * Glucose: The basic breakdown product of carbohydrates.     * Elemental Composition: Contains Carbon, Hydrogen, and Oxygen.

• Lipids: Used for insulation and energy storage.     * Breakdown Products: Broken down into fatty acids and glycerol.     * Elemental Composition: Contains Carbon, Hydrogen, Oxygen, Nitrogen, and sometimes Sulfur.

• Proteins: Used to repair worn-out tissues.     * Breakdown Products: Broken down into amino acids.     * Elemental Composition: Contains Carbon, Hydrogen, Oxygen, and Nitrogen.

• Vitamins and Minerals:     * Vitamin A: Used to prevent night blindness.     * Vitamin C: Used to prevent scurvy (bleeding gums).     * Vitamin B: Used to strengthen bones and prevent rickets (weak bones).     * Water: Vital to keep the body hydrated.     * Fibre: Prevents constipation.     * Calcium Ions: Strengthens bones.     * Iron: Essential for the formation of haemoglobin.

• Cell Walls:     * Plant Cell Wall: Made of the carbohydrate cellulose; it gives the cell its shape.     * Fungi Cell Wall: Made of chitin.

Prokaryotes and Pathogens

• Prokaryotic Organisms (Prokaryotes): Organisms that lack a nucleus and membrane-bound organelles. They contain a plasma membrane and an acid well cell membrane. Primarily consists of bacteria.

• Examples of Bacteria:     * Lactobacillus     * Bacterium     * Pseudomonas     * Yeast     * Penicillium     * Rhizopus     * Mucor     * Aspergillus

• Protostels (Protists) Examples:     * Amoeba     * Chlorella     * Plasmodium (causes Malaria).

• Pathogens and Diseases:     * Viruses: Cause AIDS (specifically HIV) and COVID-19.     * Bacteria: Cause Pneumonia.     * Tobacco Mosaic Virus: Prevents the infection of chloroplasts, which causes leaves to turn yellow.

Cell Functions and Organelles

• Vacuole: Stores end products of photosynthesis and handles osmoregulation.

• Nucleus: Stores the cell's DNA.

• Mitochondria: The site for respiration to release energy.

• Ribosomes: The site for protein synthesis.

• Cytoplasm: A jelly-like substance that makes up most of the cell.

• Chlorophyll: A green pigment that absorbs light for photosynthesis.

• Chloroplast: The specific site where photosynthesis occurs.

Enzymes and Biological Catalysts

• Catalyst: A chemical substance that speeds up a reaction.

• Enzymes: Biological catalysts.

• Temperature Effects:     * Enzymes work best at an optimum temperature, producing the highest rate of reaction.     * Below the optimum, enzyme activity decreases and works slowly, resulting in a slower reaction rate.     * Above the optimum, enzymes denature. The shape of their active site changes, and the substrate no longer fits.

• pH Effects: A pH other than the optimum changes the shape of the active site, preventing the substrate from fitting.

Movement of Substances

• Diffusion: Movement of molecules from a high concentration to a low concentration.

• DISSOLVES (Osmosis): The movement of water molecules from a high water potential to a low water potential through a semi-permeable membrane.

• Advanced Transport (Active Transport): Movement of molecules from a high to low concentration (Note: transcript says high to low, typically low to high is implied for energy use) by the use of ATP ($Adenosine \, triphosphate$) energy.

• Factors Increasing the Rate of Movement:     * High surface area to volume ratio.     * Short distance.     * High temperature.     * Steep concentration gradient.

• Cell Tonicity Scenarios:     1. Hypertonic solution (Transcript states 'cooler'): Water moves from the beaker into the cell through osmosis; the cell becomes turgid.     2. Sodium Chloride solution: Water moves from the cell to the beaker by osmosis; the cell becomes flaccid.     3. Isotonic solution: A solution of equal concentration with no net movement of water.

Photosynthesis and Plant Nutrition

• Process: Plants make glucose and oxygen using light and chlorophyll.

• Equation: $6CO_2 + 6H_2O \xrightarrow{\text{light}} C_6H_{12}O_6 + 6O_2$

• Rate Factors:     * Increase in rate: Increased $CO_2$ concentration, light intensity, and temperature.     * Decrease in rate: Decreased $CO_2$ concentration, light intensity, and temperature.

• Plant Structure and Transport:     * Phloem: Translocates (transports) food/sucrose from leaves to other parts.     * Xylem: Transports water and mineral salts from roots to leaves.     * Spongy Mesophyll Layer: Contains air spaces for gaseous exchange.     * Palisade Mesophyll Layer: Contains many palisade cells with chloroplasts.     * Stomata: Central opening and closing controlled by guard cells.

• Mineral Requirements:     * Magnesium Ions: Required for the manufacture of chlorophyll.     * Nitrate Ions: Required for amino acids.

Human Nutrition and Digestion

• Balanced Diet: A meal containing all food groups in their proper proportions.

• Energy Requirements Factors:     * Activity Levels: Active people need more energy.     * Age: Young people need more energy for growth, whereas older people need less.     * Pregnancy: Energy is needed for the mother and the developing embryo.

• The Digestive System:     * Mouth: Digestion of starch via amylase.     * Oesophagus: Moves food through peristalsis (waves of muscular contraction).     * Stomach: Contains pepsin (digests proteins to amino acids) and HCl (kills pathogens).     * Small Intestine (Ileum): Absorbs nutrients. It is approximately $6\,meters$ long and highly coiled. Contains villi and microvilli (plus hairs on the epithelial lining) to increase surface area for absorption.     * Large Intestine: Absorbs water.     * Liver: Produces bile, which is stored in the gall bladder.     * Pancreas: Produces pancreatic juice containing digestive enzymes.

• Digestive Enzymes:     * Protease: Proteins $\rightarrow$ Amino acids.     * Lipase: Lipids $\rightarrow$ Fatty acids and glycerol.     * Amylase: Starch $\rightarrow$ Glucose.

• Bile Functions: Neutralises stomach acidity and emulsifies fats.

Respiration and Gas Exchange

• Respiration Definition: Oxidation of glucose to produce ATP energy in the mitochondria.

• Aerobic Respiration: Breakdown of glucose in the presence of oxygen to release more energy.     * Equation: $C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + \text{energy}$

• Anaerobic Respiration: Breakdown of glucose in the absence of oxygen releasing little energy.     * In Yeast and Plants (Microbial): $C_6H_{12}O_6 \rightarrow 2C_2H_5OH + 2CO_2 + \text{little energy}$     * In Animals: $C_6H_{12}O_6 \rightarrow 2C_3H_6O_3 + \text{little energy}$

• Breathing Mechanism:     * Inhalation: External intercostal muscles contract, Internal intercostal muscles relax, Ribs move up and out, Diaphragm flattens. Thorax volume increases, pressure decreases, air volume increases.     * Exhalation: External intercostal muscles relax, Internal intercostal muscles contract, Ribs move in and out, Diaphragm becomes dome-shaped. Thorax volume decreases, pressure increases, air volume decreases.

• Alveoli: Moist surface for gas dissolution, dense capillary network for fast diffusion, and large surface area.

• Consequences of Smoking:     * Emphysema: Alveolar walls break down, reducing surface area.     * Bronchitis: Thick mucus and bacteria block airways.     * Lung Cancer: Carcinogens cause cells to divide uncontrollably into tumors.

Transport in Humans

• Blood Composition:     * Plasma: Distributes heat and contains dissolved nutrients and oxygen.     * Red Blood Cells (RBCs): Transport oxygen. No nucleus (to maximize hemoglobin packaging) and biconcave shape (increases surface area).     * White Blood Cells: Lymphocytes (produce antibodies) and Phagocytes (engulf and digest pathogens).     * Platelets: Involved in blood clotting.

• Blood Vessels:     * Arteries: Transport blood from the heart; narrow lumen; no valves.     * Veins: Transport blood to the heart; wide lumen; have valves.     * Capillaries: Link arteries and veins.

• Heart Structures: Left atrium, bicuspid/mitral/tricuspid valves, left ventricle, vena cava, right ventricle.

• Circulatory Flow: Head and arms $\rightarrow$ Vena cava $\rightarrow$ Aorta $\rightarrow$ Pulmonary artery/vein $\rightarrow$ Lungs $\rightarrow$ Hepatic vein/portal vein $\rightarrow$ Liver $\rightarrow$ Renal artery $\rightarrow$ Kidneys.

Homeostasis and Response

• Homeostasis: Maintenance of a constant internal environment (e.g., temperature, water).

• Plant Tropisms:     * Stems/Leaves: Positive phototropic and negative geotropic.     * Roots: Negative phototropic and positive geotropic.     * Phototropism: Growth toward light.     * Geotropism: Growth toward gravity.     * Auxin: Growth hormone found at the tips of leaves; migrates from the tip to shaded areas to produce curvature.

• Thermoregulation:     * Vasoconstriction: Narrowing of blood vessels to reduce heat loss.     * Vasodilation: Widening of blood vessels to increase heat loss.

The Nervous System and the Human Eye

• Nervous vs. Endocrine Response:     * Nervous: Impulses travel via nerves; faster response; transport impulses.     * Endocrine: Hormones released into bloodstream; slower response; transport hormones.

• Reflex Arc: Receptor $\rightarrow$ Sensory Neurone $\rightarrow$ Relay Neurone $\rightarrow$ Motor Neurone $\rightarrow$ Effector.

• The Eye:     * Iris: Controls pupil size.     * Lens: Focuses light on retina.     * Retina: Light-sensitive layer with rods (night vision) and cones (color vision/sharp vision at fovea).     * Optic Nerve: Passes impulses to the brain.     * Cornea: Repairs/refracts light for focusing.     * Blind Spot: Point without rods or cones where the optic nerve leaves.

• Iris Reflex:     * Bright Light: Circular muscles contract, radial muscles relax, pupil decreases in size.     * Dim Light: Circular muscles relax, radial muscles contract, pupil dilates.

• Accommodation:     * Distant Objects: Ciliary muscle relaxes, suspensory ligament pulled tight, lens flattened.     * Near Objects: Ciliary muscles contract, suspensory ligaments slacken, lens more rounded.

Hormones and the Endocrine System

• Pituitary Gland: Produces FSH (stimulates egg development and oestrogen), LH (stimulates ovulation and progesterone), and ADH (controls water content).

• Thyroid Gland: Produces Thyroxine (controls metabolic rate).

• Pancreas: Produces Insulin (lowers glucose) and Glucagon (raises glucose).

• Adrenal Glands: Produces Adrenaline (increases heart/breathing rate, dilates pupils, increases mental awareness for fight or flight).

• Testes: Produces Testosterone (male secondary sexual characteristics).

• Ovaries: Produces Oestrogen (female characteristics) and Progesterone (regulates menstrual cycle and maintains pregnancy).

Reproduction

• Sexual vs. Asexual:     * Sexual: Involves gametes, fertilization, meiosis, and genetic variation; produces 4 daughter cells (haploid - transcript error says diploid).     * Asexual: No gametes, no fertilization, mitosis, no variation; produces 2 daughter cells (diploid).

• Reproductive Physiology:     * Fertilization: Fusion of male and female gamete to produce a diploid zygote.     * Placenta: Exchanges nutrients/oxygen from mother to embryo and urea/$CO_2$ from embryo to mother.     * Amniotic Fluid: Acts as a shock absorber to protect from mechanical damage.

• Plants:     * Flowers: Insect-pollinated (bright, big, sticky stigma) vs. Wind-pollinated (green, small, feathery stigma).     * Post-fertilization: Ovule becomes seed, ovary becomes fruit.     * Germination conditions: Warm temperature (for enzymes), Water (for reactions), and Oxygen (for respiration).

Genetics and Evolution

• Definitions:     * Genome: Entire DNA of an organism.     * Gene: Section of DNA coding for a specific protein.     * Allele: Different forms of a gene.     * Dominant Allele: Expressed in heterozygote (Aa).     * Recessive Allele: Only expressed if homozygous (aa).     * Homozygous: Same alleles ($AA$ or $aa$).     * Heterozygous: Different alleles ($Aa$).     * Phenotype: Physical appearance.     * Genotype: Genetic makeup.

• Cell Division:     * Mitosis: Produced identical daughter cells (2 diploid cells). Used for growth, repair, cloning, and asexual reproduction.     * Meiosis: Produces genetically different daughter cells (haploid). Human Diploid = $46\,chromosomes$, Haploid = $23\,chromosomes$.

• Natural Selection:     * Variation arises via mutation (random change in DNA).     * Acquisition of advantageous alleles leads to survival and reproduction.     * Alleles passed to next generation, creating a new population.     * Antibiotic Resistance: Bacteria mutate to acquire resistant alleles, which are passed on to create resistant populations.

Ecology and Environment

• Terminology:     * Population: Organisms of the same species in a habitat.     * Community: All species in a particular area.     * Habitat: Where an organism lives.     * Ecosystem: Community of living organisms and their non-living environment.

• Investigating Population: Use a quadrat; place randomly, count organisms, calculate average, then multiply by field area.

• Factors Affecting Size: Biotic (competition, food) and Abiotic (temp, light, pH).

• Pollution:     * Sulfur Dioxide: Causes acid rain.     * Carbon Monoxide: Binds with haemoglobin, reducing oxygen supply.     * Greenhouse Gases: $CFC's$, Methane, Water vapour, $CO_2$, Nitrous oxide.     * Eutrophication: Pollution by sewage or fertiliser causes algae blooms, blocking light, reducing photosynthesis/respiration, and killing organisms.

Biotechnology

• Bread Production: Yeast undergoes respiration producing $CO_2$ (rises dough) and ethanol (evaporates during baking).

• Yogurt Production: Lactobacillus bacteria break down lactose into lactic acid.

• Genetic Engineering (Insulin):     1. Extract human insulin gene using restriction enzyme.     2. Cut bacterial plasmid with restriction enzyme.     3. Join gene and plasmid using DNA ligase to create recombinant DNA.     4. Insert recombinant plasmid into bacterium.     5. Grow bacterium in an industrial fermenter to produce insulin.     6. Collect human insulin from the fermenter.