Comprehensive Study Notes: Human and Comparative Biology (Respiration, Circulation, and Senses)

Principles of Cellular Respiration

  • Definition of Cellular Respiration: A chemical reaction between food and oxygen occurring within every cell of the body to provide energy for life.

  • Chemical Reaction and Waste Products: During this process, food combines with oxygen and is broken down into carbon dioxide gas (CO2CO_2) and water (H2OH_2O). These are waste products that must be released from the body.

  • Biological Utilization of Energy: The energy released is utilized in three primary ways:

    • Body-Building: Manufacture of proteins and other essential materials for growth and repair of cells.

    • Muscular Work: Contraction of muscles for whole-body movement, the heart muscle, and gut muscles.

    • Chemical Work: Processes in the liver, kidneys, brain, and nerves (transmission of nerve impulses) and the movement of chemicals in and out of cells.

Comparative Respiratory Systems and Gaseous Exchange

  • Gaseous Exchange: The process of exchanging carbon dioxide gas produced by respiration for oxygen gas required for respiration.

  • Aquatic Organs (Gills):

    • Fish: Utilize four pairs of gills located in a gill chamber. Water containing oxygen is sucked into the mouth, passed over gills containing numerous blood capillaries—which absorb oxygen and release carbon dioxide—and then exits through an opening behind the gill cover.

    • Prawns: Possess feathery gills inside gill chambers along the sides of the body. Movement of the legs creates the water flow necessary for gas exchange.

  • Terrestrial Organs:

    • Insect Tracheal System: A network of branched tubes called tracheae that start at surface openings called spiracles and reach every part of the body. Breathing in occurs by expanding the body (sucking air in), and breathing out occurs by contracting the body (squeezing air out).

    • Human Lungs: Organs designed to exchange gases with the air. A dolphin, as a mammal, must come to the surface to breathe through its nostril.

Human Respiratory Anatomy and Physiology

  • Structural Dimensions: Human lungs have an internal surface area roughly equivalent to a singles tennis court and contain enough blood vessels to span from London to New York.

  • Key Anatomy:

    • Voice Box (Larynx): A structure with walls made of gristle containing thin skin sheets called vocal cords. Vibration of these cords by air produces sound.

    • Wind-pipe (Trachea): Connects the mouth to the lungs. It is stiffened by rings of cartilage (gristle) to ensure it remains open for free breathing.

    • Bronchial Tubes: The trachea divides into two tubes (one per lung), which further branch into progressively smaller tubes.

    • Air Sacs (Alveoli): The narrowest bronchial tubes end in clusters of tiny bubbles, approximately 0.2 mm0.2\,mm in diameter. There are about 300×106300 \times 10^6 air sacs in a set of human lungs, giving them a sponge-like appearance.

  • Mechanism of Gas Exchange: Air sacs fill during inhalation. Oxygen dissolves in a moisture film lining the sac, passes through the sac walls into capillaries, where red cells absorb it. Carbon dioxide passes from the blood into the air sacs to be exhaled.

The Mechanics of Breathing

  • Relaxed Breathing: Driven by the diaphragm, a sheet of muscle forming the floor of the chest cavity.

    • Inhalation: Diaphragm contracts and flattens, sucking air down the trachea and inflating the lungs.

    • Exhalation: Diaphragm relaxes into its original upward-curved shape, pushing air out.

  • Deep Breathing During Exercise: Muscles require more oxygen and produce more carbon dioxide during exertion.

    • Inhalation Enhancement: Muscles between the ribs contract to lift the rib cage, sucking in significantly more air than the diaphragm alone.

    • Exhalation Enhancement: Another set of rib muscles contracts to pull the cage downward, forcibly expelling air.

Principles of Biological Transport Systems

  • Microscopic Organisms (Diffusion): Small organisms like Amoeba use diffusion—the movement of substances from plentiful areas to scarce areas—to transport oxygen into and carbon dioxide out of the cell.

  • Plant Transport Systems: Ferns and seed plants use a system of tubes (visible as veins in leaves) to transport water and minerals from roots to leaves and sugars from leaves to the rest of the plant.

  • Circulatory Systems:

    • Open Circulatory System: Found in insects and arthropods. Blood travels partly in vessels but completes the circuit by flowing through open body spaces, coming into direct contact with organs.

    • Closed Circulatory System: Found in vertebrates. Blood remains entirely enclosed within blood vessels throughout the circuit.

Composition and Function of Human Blood

  • Total Volume: Adult humans contain approximately 5.5 litres5.5\,litres of blood.

  • Components:

    • Red Blood Cells: Bi-concave discs containing haemoglobin to carry oxygen. There are approximately 30×101230 \times 10^{12} red cells in an adult. They are produced at a rate of 2×1062 \times 10^6 every second in the bone marrow and last about four months before destruction by the spleen.

    • White Blood Cells: Larger than red cells (2×2 \times the size) but fewer (5000×5000 \times more red cells than white). They destroy germs by engulfing them (phagocytosis) or producing antibodies to neutralize pathogens and toxins.

    • Platelets: Tiny cell fragments from bone marrow that form a pad of fibres over wounds to trap red cells and form a clot (puncture repair).

    • Plasma: A watery liquid carrying dissolved food, CO2CO_2, urea (waste from liver to kidneys), and hormones. It also transports the cells and platelets.

Human Cardiovascular Anatomy

  • The Heart: A muscular pump weighing approximately 300 g300\,g. It beats about 7575 times per minute at rest, rising to 140140 during exercise. In a lifetime, it pumps approximately 340×106 litres340 \times 10^6\,litres across 2500×1062500 \times 10^6 beats.

  • Chambers:

    • Atria: Two upper compartments with thin muscular walls.

    • Ventricles: Two lower compartments with thick muscular walls; the left ventricle is responsible for pumping blood to the whole body.

  • Valves:

    • Atrioventricular Valves: Flaps held by tendons that permit one-way flow from atria to ventricles.

    • Pocket (Semilunar) Valves: Located at heart exits; they fill with blood to prevent backflow into the ventricles during relaxation.

Blood Vessels and Circulatory Pathways

  • Types of Vessels:

    • Arteries: Thick muscular walls to withstand high pressure as they carry blood away from the heart.

    • Capillaries: Extremely narrow (sometimes narrower than red cells) with walls thin enough for liquid to leak out, delivering oxygen and food to cells.

    • Veins: Thinner walls than arteries; carry low-pressure blood back to the heart and contain pocket valves to prevent backflow.

  • Dual Circulation:

    • Pulmonary Circuit: Right ventricle → pulmonary artery → lungs → pulmonary vein → left atrium.

    • Systemic Circuit: Left atrium → left ventricle → main artery (aorta) → body organs → main vein (vena cava) → right atrium.

  • The Pulse: A ripple felt in artery walls (e.g., wrist or neck) each time the heart pumps blood into the aorta.

Cardiovascular Disease and Treatment

  • Clogged Arteries: Caused by cholesterol build-up inside coronary arteries, which supply the heart muscle with oxygen. This can lead to heart failure.

  • Risk Factors: High intake of animal/dairy fats, lack of exercise, smoking, and psychological stress (tension, anxiety).

  • Medical Interventions:

    • Electric Shock Treatment: Up to 200 volts200\,volts applied to the chest to restore a regular beat in a fluttering heart.

    • Artificial Pacemakers: Battery-operated devices (lasting 55 years) inserted under the skin to send regular shocks to stimulate contraction.

    • Transplants: Replacing a diseased heart with a donor heart. Uses a heart-lung machine to oxygenate and pump blood during the operation.

    • Immune Rejection: The body may treat a transplant as a germ. Drugs can dampen the immune system but increase the risk of infections like pneumonia.

Temperature Control and Excretion

  • Thermoregulation: Maintaining a constant temperature of 37 ∘C37\,^{\circ}C.

    • Heat Response: Skin blood vessels widen (vasodilation) to release heat via radiation; sweat glands release water for evaporative cooling. Sweating can lose up to 12 litres12\,litres of water and 30 g30\,g of salt daily.

    • Cold Response: Skin blood vessels narrow (vasoconstriction); muscles shiver to generate heat; liver respiration rate increases.

  • Excretory Organs:

    • Lungs: Excrete CO2CO_2 and water vapour.

    • Liver: Excretes bile and converts unwanted protein parts into urea.

    • Kidneys: Filter blood to remove urea, unwanted water, sugar, and salts to form urine. Urine travels through ureters to the bladder and exits via the urethra.

Biomechanical Support and Skeletons

  • Hydrostatic Support: Soft-bodied creatures (jellyfish in water, slugs/earthworms on land) are supported by water pressure inside their body spaces or cells.

  • External Skeleton (Exoskeleton): Arthropods like crabs or insects have a hard cuticle made of plates and tubes. It protects, prevents drying, and provides muscle attachment. They must undergo moulting to grow.

  • Internal Skeleton (Endoskeleton): Found in vertebrates. Made of bone and gristle (cartilage). Includes a skull, backbone (vertebrae), and often limbs and rib cages.

    • Bone Composition: Living cells embedded in hard calcium salts.

    • Bone Marrow: Tissue inside bones that produces blood cells.

Muscles and Joints

  • Connective Tissues:

    • Ligaments: Tough, flexible fibres holding bones together at joints.

    • Tendons: Fibres attaching muscles to bones.

  • Joint Types:

    • Pivot: Allows twisting (e.g., top of the backbone/neck).

    • Hinge: Moves in one direction (e.g., elbow).

    • Ball-and-Socket: Allows multi-directional movement (e.g., hip).

  • Muscle Action: Muscles only pull by contracting (shortening). They work in antagonistic pairs:

    • Flexor: Bends the joint.

    • Extensor: Straightens the joint.

Plant and Animal Senses

  • Plant Sensitivities:

    • Light (Phototropism): Shoots grow toward light for photosynthesis.

    • Gravity (Geotropism): Roots grow downward; shoots grow upward.

    • Water (Hydrotropism): Roots can grow toward water sources, overriding gravity.

    • Touch (Thigmotropism): Tendrils curl around supports (e.g., sweet peas).

  • Skin Receptors: Specialized nerve endings (receptors) detect touch, heavy pressure, pain (warning signal), and temperature (sensitive to changes as small as 0.5 ∘C0.5\,^{\circ}C).

  • Chemical Senses:

    • Smell (Olfactory Organs): Located in the nasal roof; chemicals must dissolve in moisture to be detected.

    • Taste (Taste Buds): Receptors on the tongue sensitive to salt, sweet, sour, and bitter.

Vision and Hearing

  • The Human Eye: Functions like a camera.

    • Structure: Cornea (window), Iris (amount of light/pupil size), Lens (focusing), Retina (light-sensitive layer), Optic nerve (sends impulses to brain).

    • Focusing (Accommodation): Radial muscles contract to flatten the lens for distant objects; circular muscles contract to allow the lens to bulge for near objects.

    • Retina Specifics: The fovea is sensitive to color (bright light only); the blind spot lacks receptors where the optic nerve exits.

  • Hearing and Balance:

    • Hearing Pathway: Pinna → ear drum → ear ossicles (hammer, anvil, stirrup) → oval window → liquid-filled cochlea → auditory nerve.

    • Balance: Three liquid-filled semi-circular canals detect movement to inform the brain of body position.

Nervous Systems and the Brain

  • Cell types: Sensory neurons carry impulses to the CNS; motor neurons carry impulses to muscles; connector neurons link them.

  • Comparative Nervous Systems:

    • Paramecium: Uses nerve fibrils for cilia co-ordination.

    • Hydra: A simple interconnected nerve net.

    • Insects: Clusters of nerve cells called ganglia connected by nerve cords.

    • Vertebrates: Central Nervous System (CNS) consisting of a brain and spinal cord.

  • Reflex Action: An automatic, protective response (e.g., pulling a finger away from a sharp object).

  • The Human Brain (1.5 kg1.5\,kg):

    • Cerebrum: Largest part; handles memory, problem-solving, and decision-making.

    • Cerebellum: Maintains balance and co-ordinates walking/cycling.

    • Medulla Oblongata: Controls involuntary rates (breathing, heartbeat, blood pressure).