Year 11 ATAR Human Biology Semester 1 Notes

1. CELLS AND TISSUES

Cell Structure:

• All living organisms are made up of cells (cell theory).

• Cell membrane: controls entry and exit of substances, selectively permeable, made of phospholipid bilayer.

  • Structure: Primarily composed of a phospholipid bilayer with embedded proteins. Phospholipids have a hydrophilic (water-loving) head and hydrophobic (water-fearing) tails. The bilayer arrangement ensures that only the hydrophilic heads interact with the aqueous environments inside and outside the cell.

  • Selective Permeability: The membrane allows certain molecules to pass through more easily than others. Small, nonpolar molecules like oxygen and carbon dioxide can diffuse directly across the membrane. Larger polar molecules and ions require the assistance of transport proteins to cross the membrane.

  • Transport Mechanisms:

  1. Passive Transport: Includes diffusion, osmosis, and facilitated diffusion. Requires no energy input from the cell.

     • Diffusion: Movement of molecules from an area of higher concentration to an area of lower concentration.

     • Osmosis: Movement of water across a semi-permeable membrane from an area of higher water concentration (lower solute concentration) to an area of lower water concentration (higher solute concentration).

     • Facilitated Diffusion: Movement of molecules across the membrane with the help of transport proteins (channels or carriers). Still does not require energy.

  2. Active Transport: Requires energy (ATP) to move molecules against their concentration gradient.

     • Primary Active Transport: Uses ATP directly to move molecules (e.g., sodium-potassium pump).

     • Secondary Active Transport: Uses the electrochemical gradient created by primary active transport to move other molecules (e.g., co-transport of glucose and sodium).

• Cytoplasm: jelly-like fluid inside the cell where organelles are suspended.

  • Composition: Primarily water, but also contains ions, salts, organic molecules, and enzymes.

  • Function: Provides a medium for biochemical reactions and suspends organelles.

• Nucleus: contains DNA, controls cell functions.

  • Structure: Enclosed by a double membrane called the nuclear envelope. Contains chromatin (DNA and associated proteins) and the nucleolus (site of ribosome synthesis).

  • Processes:

  1. DNA Replication: Occurs during cell division (S phase of interphase). DNA is duplicated to ensure each daughter cell receives a complete set of genetic information. Involves enzymes like DNA polymerase and helicase.

  2. Transcription: DNA is transcribed into RNA (mRNA, tRNA, rRNA). Carried out by RNA polymerase. The resulting RNA molecules are essential for protein synthesis.

  3. RNA Processing: mRNA molecules undergo processing, including splicing (removal of introns), capping (addition of a 5' cap), and polyadenylation (addition of a poly-A tail) to become mature mRNA.

• Mitochondria: site of cellular respiration; produces ATP.

  • Structure: Double-membraned organelle with an inner membrane folded into cristae, increasing surface area for ATP production.

  • Process: Cellular Respiration

  1. Glycolysis: Occurs in the cytoplasm. Glucose is broken down into pyruvate, producing a small amount of ATP and NADH.

  2. Pyruvate Decarboxylation: Pyruvate is converted to acetyl-CoA, which enters the Krebs cycle.

  3. Krebs Cycle (Citric Acid Cycle): Occurs in the mitochondrial matrix. Acetyl-CoA is oxidized, producing ATP, NADH, and FADH2.

  4. Electron Transport Chain (ETC) and Oxidative Phosphorylation: Occurs in the inner mitochondrial membrane. Electrons from NADH and FADH2 are passed along a chain of protein complexes, creating a proton gradient. ATP synthase uses this gradient to produce ATP.

• Ribosomes: site of protein synthesis; can be free or on the rough ER.

  • Structure: Made of ribosomal RNA (rRNA) and proteins. Consists of two subunits (large and small).

  • Process: Protein Synthesis (Translation)

  1. Initiation: mRNA binds to the small ribosomal subunit, and the initiator tRNA (carrying methionine) binds to the start codon (AUG).

  2. Elongation: tRNA molecules bring amino acids to the ribosome, matching the codon sequence of the mRNA. Peptide bonds are formed between amino acids, elongating the polypeptide chain.

  3. Termination: A stop codon (UAA, UAG, or UGA) is reached, and the polypeptide chain is released from the ribosome.

• Endoplasmic Reticulum (ER): rough ER (with ribosomes) transports proteins, smooth ER makes lipids.

  • Rough ER: Studded with ribosomes, involved in protein synthesis and modification.

  • Smooth ER: Lacks ribosomes, involved in lipid synthesis, detoxification, and calcium storage.

  • Processes:

  1. Protein Folding and Modification (Rough ER): Proteins are folded into their correct three-dimensional shapes with the help of chaperone proteins. Glycosylation (addition of carbohydrate groups) can also occur.

  2. Lipid Synthesis (Smooth ER): Synthesis of phospholipids, cholesterol, and steroid hormones.

• Golgi apparatus: modifies and packages proteins for secretion.

  • Structure: Series of flattened membrane-bound sacs called cisternae.

  • Process:

  1. Modification: Proteins are further modified, including glycosylation and phosphorylation.

  2. Packaging: Modified proteins are packaged into vesicles for transport to their final destinations (e.g., lysosomes, plasma membrane, or secretion out of the cell).

• Lysosomes: contain digestive enzymes to break down waste.

  • Structure: Membrane-bound organelles containing hydrolytic enzymes.

  • Process: Autophagy and Phagocytosis

  1. Autophagy: Lysosomes engulf and digest damaged organelles or cellular debris.

  2. Phagocytosis: Lysosomes fuse with vesicles containing foreign particles or bacteria, breaking them down.

Tissue Types:

• Epithelial tissue: covers surfaces (e.g., skin, gut lining).

  • Functions: Protection, secretion, absorption, excretion.

  • Types: Squamous, cuboidal, columnar, transitional, pseudostratified columnar.

• Connective tissue: supports (e.g., bone, cartilage, blood).

  • Components: Cells (e.g., fibroblasts, chondrocytes, osteocytes) and extracellular matrix (fibers and ground substance).

  • Types: Loose connective tissue, dense connective tissue, cartilage, bone, blood.

• Muscle tissue: contracts to cause movement (skeletal, cardiac, smooth).

  • Types: Skeletal (voluntary, striated), cardiac (involuntary, striated), smooth (involuntary, non-striated).

  • Mechanism of Contraction:

  1. Skeletal Muscle: Action potential triggers the release of calcium ions from the sarcoplasmic reticulum. Calcium binds to troponin, causing tropomyosin to move away from the myosin-binding sites on actin. Myosin heads bind to actin, forming cross-bridges. ATP hydrolysis powers the movement of myosin heads, causing the actin filaments to slide past the myosin filaments, shortening the sarcomere and contracting the muscle.

• Nervous tissue: transmits electrical impulses.

  • Cells: Neurons and glial cells.

  • Components

  1. Neurons: Conduct electrical signals (action potentials).

  2. Glial cells: Support and protect neurons.

  • Action Potentials: Rapid changes in membrane potential that propagate along the neuron. Involve the opening and closing of ion channels (sodium and potassium channels).

2. METABOLISM

• Metabolism: sum of all chemical reactions in the body.

• Anabolic reactions: build up complex molecules (e.g., protein synthesis).

  • Process:

  1. Monomer Activation: Requires energy (ATP) to form bonds.

  2. Polymer Assembly: Monomers join, releasing water (dehydration synthesis).

• Catabolic reactions: break down molecules (e.g., cellular respiration).

  • Process: Hydrolysis (addition of water) breaks bonds.

• Enzymes: biological catalysts, speed up reactions, specific to substrates.

  • Have an active site that binds to a substrate.

  • Affected by temperature and pH (denature if too extreme).

  • Mechanism:

  1. Substrate Binding: Enzyme binds to substrate at the active site.

  2. Transition State: Enzyme stabilizes the transition state, reducing activation energy.

  3. Product Formation: Product is released, and enzyme is ready for another reaction.

Cellular Respiration:

• Occurs in mitochondria.

• Aerobic respiration:

  • Glycolysis: Glucose is broken down into pyruvate, producing ATP and NADH.

  • Krebs Cycle: Pyruvate is converted to acetyl-CoA, which enters the cycle, producing ATP, NADH, and FADH2.

  • Electron Transport Chain: NADH and FADH2 donate electrons, creating a proton gradient that drives ATP synthesis.

• ATP is the energy currency of the cell.

3. CIRCULATORY SYSTEM

Structure of the Heart:

• Four chambers: right/left atria and ventricles.

  • Process:

  1. Atrial Contraction: Atria contract, pushing blood into ventricles.

  2. Ventricular Contraction: Ventricles contract, pumping blood into pulmonary artery and aorta.

• Valves prevent backflow (e.g., tricuspid, bicuspid, semilunar).

  • Function: Ensure unidirectional blood flow.

  1. Tricuspid: Right atrium to right ventricle

  2. Bicuspid: Left atrium to left ventricle

  3. Semilunar: Ventricles to pulmonary artery and aorta

• Pulmonary circulation: heart → lungs → heart.

  • Process: Deoxygenated blood is pumped to the lungs, where it picks up oxygen and releases carbon dioxide.

• Systemic circulation: heart → body → heart.

  • Process: Oxygenated blood is pumped to the body, where it delivers oxygen and picks up carbon dioxide.

Blood Vessels:

• Arteries: carry blood away from the heart; thick muscular walls.

  • Structure: Thick walls with smooth muscle and elastic fibers.

  • Function: Withstand high pressure.

• Veins: return blood to the heart; have valves to prevent backflow.

  • Structure: Thinner walls than arteries, with valves.

  • Function: Return blood to the heart against gravity.

• Capillaries: one cell thick; site of gas and nutrient exchange.

  • Structure: Single layer of endothelial cells.

  • Function: Facilitate diffusion of gases, nutrients, and wastes.

Blood Components:

• Plasma: transports substances.

  • Composition: Water, proteins, ions, nutrients, hormones.

• Red blood cells (RBCs): carry oxygen using haemoglobin.

  • Structure: Biconcave disc shape, no nucleus.

  • Function: Transport oxygen and carbon dioxide.

• White blood cells (WBCs): fight infection.

  • Types: Neutrophils, lymphocytes, monocytes, eosinophils, basophils.

  • Function: Immune response.

• Platelets: involved in blood clotting.

  • Process: Aggregate at injury sites, forming a plug. Release factors that initiate the coagulation cascade.

4. RESPIRATORY SYSTEM

Pathway of Air:

Nasal cavity → pharynx → larynx → trachea → bronchi → bronchioles → alveoli.

Alveoli:

• Site of gas exchange.

• Surrounded by capillaries.

• Oxygen diffuses into blood, carbon dioxide diffuses out.

  • Process: Oxygen moves from alveoli into blood; carbon dioxide moves from blood into alveoli.

Breathing Mechanics:

• Inhalation: diaphragm contracts (moves down), thoracic cavity expands, air drawn in.

  • Process: Diaphragm and intercostal muscles contract, increasing thoracic volume and decreasing pressure, causing air to flow into the lungs.

• Exhalation: diaphragm relaxes (moves up), air pushed out.

  • Process: Diaphragm and intercostal muscles relax, decreasing thoracic volume and increasing pressure, causing air to flow out of the lungs.

5. DIGESTIVE SYSTEM

Mechanical and Chemical Digestion:

• Mechanical: chewing (mouth), churning (stomach), peristalsis.

  • Process: Physical breakdown of food into smaller pieces.

• Chemical: enzymes break down food (amylase, protease, lipase).

  • Process: Enzymes catalyze the breakdown of complex molecules into simpler molecules.

Organs:

• Mouth: begins digestion (amylase in saliva).

  • Process: Chewing and saliva begin carbohydrate digestion.

• Oesophagus: transports food using peristalsis.

  • Process: Muscular contractions move food to the stomach.

• Stomach: acid and pepsin digest proteins.

  • Process: Gastric juices break down proteins into smaller peptides.

• Small intestine: absorption of nutrients (villi increase surface area).

  • Process: Nutrients are absorbed into the bloodstream.

• Large intestine: absorbs water, forms faeces.

  • Process: Water is absorbed, and waste is compacted into faeces.

• Liver: produces bile.

  • Process: Bile emulsifies fats, aiding digestion.

• Pancreas: secretes digestive enzymes.

  • Process: Enzymes break down carbohydrates, proteins, and fats.

6. EXCRETORY SYSTEM

Purpose:

• Removal of metabolic wastes: CO₂ (lungs), urea (kidneys), sweat (skin).

Kidney Function:

• Nephron: functional unit of kidney.

  • Filtration in glomerulus.

  • Process: Blood pressure forces water and small solutes into Bowman's capsule.

  • Reabsorption of useful substances.

  • Process: Nutrients, water, and ions are reabsorbed from the filtrate into the blood.

  • Secretion of waste into tubules.

  • Process: Wastes are secreted from the blood into the tubules.

  • Urine formed in collecting duct.

  • Process: Water is reabsorbed, and urine is concentrated.

7. MUSCULOSKELETAL SYSTEM

Bones:

• Provide support, protect organs, produce blood cells, store minerals.

• Made of compact and spongy bone.

Muscles:

• Skeletal: voluntary movement.

  • Process: Muscle contraction is initiated by nerve impulses.

• Smooth: involuntary, in organs.

  • Process: Controlled by autonomic nervous system and hormones.

• Cardiac: only in heart.

  • Process: Autorhythmic contractions coordinated by specialized cells.

Joints:

• Fibrous: no movement.

• Cartilaginous: limited movement.

• Synovial: free movement (e.g., hinge, ball and socket).

  • Process: Synovial fluid lubricates the joint, allowing smooth movement.

8. MICROSCOPY

• Light microscope: views cells/tissues.

• Electron microscope: views organelles/ultrastructure.

• Magnification = eyepiece × objective.

• Staining enhances visibility.

  • Process: Dyes bind to cellular structures, increasing contrast.

9. SURFACE AREA TO VOLUME RATIO

• Smaller cells = larger SA:V = more efficient exchange.

  • Process: Increased surface area allows for faster diffusion and transport.

• Structures like alveoli and villi increase surface area.

• Diffusion is faster when SA:V is high.

10. OSTEOPOROSIS

• Decrease in bone density.

• Bones become brittle and fracture easily.

• Risk factors: age, lack of calcium, menopause, inactivity.

• Prevention: weight-bearing exercise, calcium, vitamin D.

11. OSTEOARTHRITIS

• Degeneration of cartilage in joints.

• Causes pain, stiffness, swelling.

• Common in older adults.

• Treatment: pain relief, physiotherapy, sometimes surgery.

12. MICROSCOPIC BONE ANATOMY

• Compact bone: dense outer layer.

• Spongy bone: contains trabeculae and marrow.

• Osteon (Haversian system):

  • Central canal, lamellae, osteocytes in lacunae.

  • Canaliculi: connect osteocytes.

13. MACROSCOPIC BONE ANATOMY

• Diaphysis: shaft.

• Epiphysis: ends.

• Periosteum: outer covering.

• Medullary cavity: contains yellow marrow.

• Bones classified as long, short, flat, irregular.

14. OTHER ESSENTIAL CONCEPTS

Homeostasis:

• Maintaining stable internal conditions.

• Uses negative feedback loops.

  • Process: A change in a variable triggers a response that reverses the change.

Scientific Method:

• Hypothesis, variables (independent, dependent, controlled), method, data, conclusion.

  • Process: Systematic approach to investigating phenomena.

System Integration:

• Systems work together (e.g., respiratory and circulatory deliver