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Biology Gateway (OCR)
Topic B1: Cell Level Systems
B1.1 Cell Structures
The Cell Theory: Understand that cells are fundamental to life.
All living things are made of cells.
Cells are the basic structural and functional units of life.
All cells come from pre-existing cells.
Animal Cell Components:
Nucleus - The Command Center:
Function: Contains chromosomes made of DNA, which carry the genetic instructions for cell function and development. It controls all cellular activities, including growth, reproduction, and metabolism.
Analogy: Like the CEO's office in a company, directing all operations.
Cytoplasm - The Cellular Jelly:
Function: A gel-like substance filling the cell, holding organelles in place. It's the site of many metabolic reactions, like the first stages of respiration. It also facilitates the transport of substances within the cell.
Analogy: The factory floor where all the machinery (organelles) operates.
Cell Membrane - The Gatekeeper:
Function: A thin, flexible outer boundary. It's selectively permeable, meaning it controls which substances can enter and leave the cell. This is crucial for maintaining the cell's internal environment.
Analogy: The security gate of a factory, controlling access.
Mitochondria - The Power Generators:
Function: The primary sites of aerobic respiration. They break down glucose in the presence of oxygen to release energy in a usable form (ATP - Adenosine Triphosphate). The more active a cell, the more mitochondria it will have.
Analogy: The power plant of the cell, generating energy.
Ribosomes - Protein Factories:
Function: Tiny organelles responsible for protein synthesis. They read genetic code from the nucleus and assemble amino acids into proteins. Ribosomes can be free in the cytoplasm or attached to the rough endoplasmic reticulum.
Analogy: The assembly line of the cell, producing proteins.
Plant Cell Components - Beyond Animal Cells:
Cell Wall - The Structural Support:
Function: A rigid layer outside the cell membrane, made mainly of cellulose. It provides structural support, gives the plant cell a definite shape, and prevents the cell from bursting when it takes in water. It is fully permeable (unlike the cell membrane).
Analogy: The brick walls of a building, providing structure and protection.
Vacuole - Storage and Support:
Function: A large, fluid-filled sac. In plant cells, it's usually central and large. It stores water, sugars, salts, and waste products (cell sap). It also helps maintain turgor pressure, which keeps the cell firm and the plant upright.
Analogy: The storage warehouse and water tower of the cell.
Chloroplasts - Photosynthesis Sites:
Function: Organelles containing chlorophyll, the green pigment that absorbs light energy. Chloroplasts are the sites of photosynthesis, where plants convert light energy, carbon dioxide, and water into glucose and oxygen.
Analogy: The solar panels of the cell, capturing energy from sunlight.
Specialised Cells - Form Follows Function:
Red Blood Cells: Adapted for oxygen transport. Biconcave shape increases surface area for oxygen diffusion. No nucleus to maximise space for haemoglobin (oxygen-carrying pigment).
Nerve Cells (Neurons): Adapted for rapid signal transmission. Long and thin to transmit signals over distances. Myelin sheath insulates and speeds up signal transmission. Synapses allow communication with other nerve cells.
Muscle Cells: Adapted for contraction and movement. Contain protein filaments that slide past each other to cause contraction. Many mitochondria to provide energy for contraction.
Root Hair Cells: Adapted for efficient water and mineral absorption. Long 'hair-like' projection increases surface area for absorption. No chloroplasts as they are underground and don't photosynthesise.
B1.2 What Happens in Cells (and What do Cells Need)?
Life Processes - The MRS GREN Acronym: Remember these fundamental processes:
Movement: Internal movement (cytoplasm streaming, organelle movement) and external movement (whole organism or cell movement, like amoeba).
Respiration: The chemical reactions that break down nutrient molecules in living cells to release energy for metabolism. Crucial for all other life processes.
Sensitivity: The ability to detect and respond to changes in the environment (stimuli) - light, temperature, chemicals, touch, etc.
Growth: A permanent increase in size and dry mass by an increase in cell number or cell size or both.
Reproduction: The process of producing offspring. Can be sexual (involving gametes) or asexual (one parent).
Excretion: The removal of metabolic waste products (toxic and excess substances) from the body or cell. Not to be confused with egestion (removal of undigested food).
Nutrition: Taking in and using nutrients. Involves obtaining food and assimilating it for growth, repair, and energy.
Cellular Requirements:
Oxygen (for Aerobic Respiration): Essential for efficient energy release in most animal and plant cells. Used as the final electron acceptor in the electron transport chain in mitochondria.
Glucose (Energy Source): A simple sugar that is the primary fuel for respiration. Obtained from food (animals) or photosynthesis (plants).
Water (Solvent and Reactant): The universal solvent in cells. Essential for many biochemical reactions, transport, and maintaining cell turgidity.
Nutrients (Minerals and Ions): Required for building complex molecules (proteins, DNA, etc.), enzyme function, and maintaining osmotic balance. Examples include nitrates, phosphates, potassium ions, etc.
Waste Removal (Maintaining Cellular Health): Cells must efficiently remove waste products like carbon dioxide, urea (in animals), and excess salts to prevent toxic build-up and maintain optimal internal conditions.
B1.3 Respiration
Respiration - More Than Just Breathing: Distinguish between breathing (ventilation) and cellular respiration. Breathing is the physical process of gas exchange, while respiration is the chemical process of energy release within cells.
Aerobic Respiration - Oxygen Dependent:
Process: A series of enzyme-controlled reactions that occur in the mitochondria. Glucose is fully broken down using oxygen.
Word Equation: Glucose + Oxygen → Carbon Dioxide + Water + Energy (ATP). The energy is released and captured in ATP molecules, which act as the cell's immediate energy currency.
Efficiency: Aerobic respiration is much more efficient at energy release than anaerobic respiration, yielding a significantly larger amount of ATP per glucose molecule.
Anaerobic Respiration - Oxygen Independent (But Less Efficient):
Animal Cells (Lactic Acid Fermentation): Occurs when oxygen supply is insufficient, like during intense exercise. Glucose is partially broken down to lactic acid.
Word Equation: Glucose → Lactic Acid + Energy (ATP). Less ATP is produced.
Consequences of Lactic Acid Build-up: Muscle fatigue, pain, and oxygen debt (the need to repay the oxygen deficit after exercise to break down lactic acid).
Plant and Yeast Cells (Alcoholic Fermentation): Used by yeast in bread making and brewing. Glucose is broken down into ethanol (alcohol) and carbon dioxide.
Word Equation: Glucose → Ethanol + Carbon Dioxide + Energy (ATP). Again, less ATP is produced than in aerobic respiration.
Uses of Fermentation: Bread making (CO2 makes dough rise), brewing (ethanol production).
Uses of Energy from Respiration - Cellular Work:
Muscle Contraction: Energy is needed for the protein filaments in muscle cells to slide past each other, causing movement.
Active Transport: Energy is required to move substances against their concentration gradient across cell membranes (e.g., nutrient uptake, waste removal).
Building Larger Molecules (Synthesis): Energy is used to join smaller molecules (like amino acids) into larger, complex molecules (like proteins).
Cell Division: Energy is needed for DNA replication, chromosome separation, and cell growth during cell division.
Maintaining Body Temperature: In mammals and birds (endotherms), respiration generates heat, which helps maintain a constant body temperature.
B1.4 Photosynthesis - Light to Chemical Energy Conversion
Photosynthesis - The Basis of Food Chains: Understand that photosynthesis is the primary source of energy input into most ecosystems.
Location - Chloroplasts and Chlorophyll:
Chloroplasts: Organelles within plant cells, especially in leaves, containing chlorophyll.
Chlorophyll: The green pigment within chloroplasts that absorbs light energy, primarily in the red and blue wavelengths of the visible spectrum. This absorbed light energy drives the photosynthetic process.
Word Equation: Carbon Dioxide + Water → Glucose + Oxygen (in the presence of light energy and chlorophyll).
Process:
Light-dependent Reactions: Light energy is absorbed by chlorophyll and converted into chemical energy (ATP and NADPH). Water is split, releasing oxygen as a byproduct.
Light-independent Reactions (Calvin Cycle): Carbon dioxide from the air is combined with the chemical energy (ATP and NADPH) from the light-dependent reactions to produce glucose.
Inputs and Outputs - Raw Materials and Products:
Inputs (Raw Materials):
Carbon Dioxide (CO2): Taken in from the atmosphere through stomata (pores) in leaves.
Water (H2O): Absorbed from the soil by roots and transported to leaves via the xylem.
Sunlight (Light Energy): Captured by chlorophyll.
Outputs (Products):
Glucose (C6H12O6): A simple sugar, the primary product of photosynthesis. Used as food for the plant and as a building block for other molecules.
Oxygen (O2): Released as a byproduct into the atmosphere through stomata. Essential for aerobic respiration in most organisms.
Uses of Glucose in Plants - Plant Growth and Storage:
Respiration (Immediate Energy): Some glucose is immediately used for respiration to provide energy for plant cell activities.
Starch (Storage): Glucose is converted into starch, an insoluble carbohydrate, for storage in roots, stems, and leaves. Starch is a long-term energy reserve.
Cellulose (Structural Material): Glucose is used to make cellulose, the main component of plant cell walls, providing structural support.
Proteins and Fats/Oils (Building Blocks): Glucose, along with mineral ions absorbed from the soil (like nitrates), is used to synthesise proteins and fats/oils for growth and other cellular processes.
Factors Affecting Photosynthesis - Limiting Factors:
Light Intensity: As light intensity increases, the rate of photosynthesis generally increases, up to a point (light saturation point). Light is often the limiting factor at night or in shaded environments.
Carbon Dioxide Concentration: Increasing CO2 concentration generally increases the rate of photosynthesis, up to a point (CO2 saturation point). CO2 can be a limiting factor in enclosed environments like greenhouses.
Temperature: Photosynthesis is enzyme-controlled. Enzymes have an optimum temperature. Too low or too high temperatures will decrease the rate of photosynthesis. Temperature can be a limiting factor in cold or very hot climates.
Water Availability: Water is a reactant in photosynthesis. Water stress (lack of water) will close stomata to reduce water loss, but this also reduces CO2 uptake, limiting photosynthesis. Water is often a limiting factor in dry environments.
Chlorophyll Concentration: The amount of chlorophyll in leaves can be a limiting factor, especially in nutrient-deficient conditions (e.g., lack of magnesium, needed to make chlorophyll).
Topic B2: Scaling Up
B2.1 Supplying the Cell - Transport Mechanisms
Movement of Substances - Essential for Cell Survival: Cells need to exchange substances with their environment to obtain nutrients, oxygen, and remove waste.
Diffusion - Passive Movement Downhill:
Definition: The net movement of particles (atoms, molecules, ions) from an area of high concentration to an area of low concentration, down a concentration gradient. "Net" movement means that while particles move randomly in all directions, more particles move from high to low concentration.
Passive Process: Diffusion does not require energy input from the cell. It's driven by the random motion of particles and the concentration difference.
Factors Affecting Diffusion Rate:
Concentration Gradient: Steeper gradient (larger difference in concentration) = faster diffusion.
Temperature: Higher temperature = faster diffusion (particles have more kinetic energy).
Surface Area: Larger surface area = faster diffusion (more area for exchange).
Diffusion Distance: Shorter diffusion distance = faster diffusion (less distance to travel).
Examples in Organisms:
Gas Exchange in Lungs (Alveoli): Oxygen diffuses from alveoli (high concentration) into blood capillaries (low concentration); Carbon dioxide diffuses from blood (high concentration) into alveoli (low concentration).
Gas Exchange in Gills (Fish): Oxygen diffuses from water (high concentration) into blood in gill filaments (low concentration); Carbon dioxide diffuses from blood into water.
Waste Product Removal from Cells: Waste products (like urea, CO2) diffuse from cells (high concentration) into blood (low concentration).
Osmosis - Water Diffusion Across Membranes:
Definition: The diffusion of water across a selectively permeable membrane from an area of high water concentration (dilute solution, low solute concentration) to an area of low water concentration (concentrated solution, high solute concentration). Water moves down a water potential gradient.
Selectively Permeable Membrane: A membrane that allows water molecules to pass through but restricts the passage of larger solute molecules (like sugars, salts).
Passive Process: Osmosis does not require energy input.
Water Potential: A measure of the relative tendency of water to move from one area to another. Pure water has the highest water potential. Adding solutes lowers water potential. Water moves from areas of higher water potential to lower water potential.
Examples in Organisms:
Water Uptake by Plant Roots: Water moves from soil (high water concentration) into root hair cells (low water concentration) by osmosis.
Water Balance in Cells: Osmosis is crucial for maintaining the correct water content of cells. Cells can swell or shrink if placed in solutions of different concentrations.
Active Transport - Movement Uphill Against the Gradient:
Definition: The movement of substances against a concentration gradient (from an area of low concentration to an area of high concentration). This is like moving uphill.
Energy Requirement: Active transport requires energy from respiration. This energy is used to operate "protein pumps" in cell membranes.
Protein Pumps: Carrier proteins in cell membranes that bind to specific molecules and use energy (ATP) to move them across the membrane against the concentration gradient.
Examples in Organisms:
Uptake of Glucose in the Small Intestine: Even when glucose concentration in the blood is higher than in the small intestine, active transport ensures all glucose is absorbed from the gut into the bloodstream.
Uptake of Mineral Ions by Plant Root Hair Cells: Mineral ions in the soil are often at a lower concentration than in root hair cells. Active transport is used to absorb these essential mineral ions from the soil into the root cells.
B2.2 The Challenges of Size - Overcoming Diffusion Limits
Surface Area to Volume Ratio (SA:V Ratio) - Key to Efficiency:
Concept: As an object (like a cell or organism) increases in size, its volume increases faster than its surface area. This means the SA:V ratio decreases.
Implications for Diffusion: Diffusion rate is proportional to surface area and inversely proportional to diffusion distance. A low SA:V ratio in larger cells/organisms means:
Reduced surface area relative to volume for exchange with the environment.
Increased diffusion distance to reach the center of the cell/organism.
Diffusion becomes too slow to efficiently supply the needs of larger cells or organisms.
Small Cells - Efficient Exchange: Small cells have a high SA:V ratio. Diffusion is efficient enough to meet their needs.
Large Organisms - Need for Specialised Systems: Larger organisms cannot rely on diffusion alone. They require specialised exchange surfaces and transport systems to overcome the limitations of a low SA:V ratio.
Diffusion Distance - The Time Factor:
Diffusion is Slow Over Long Distances: Diffusion is effective over short distances but becomes very slow over longer distances.
Larger Organisms - Increased Diffusion Distances: In larger organisms, cells are further away from the external environment or exchange surfaces. Diffusion alone would be too slow to deliver oxygen and nutrients to all cells and remove waste products quickly enough.
Need for Transport Systems - Overcoming Diffusion Limits:
Circulatory System (Animals):
Function: A system of organs (heart, blood vessels, blood) that actively transports substances throughout the body. Overcomes the limitations of diffusion distance.
Components:
Heart: Pumps blood, creating pressure to drive circulation.
Blood Vessels (Arteries, Veins, Capillaries): Form a network for blood flow.
Blood: The transport medium, carrying oxygen, carbon dioxide, nutrients, hormones, waste products, etc.
Vascular System (Plants):
Function: A system of specialised tissues (xylem and phloem) that transports water and minerals (xylem) and sugars (phloem) throughout the plant.
Components:
Xylem: Transports water and mineral ions from roots to leaves (transpiration stream).
Phloem: Transports sugars (produced in photosynthesis) from leaves to other parts of the plant (translocation).
Specialised Exchange Surfaces - Maximising Surface Area:
Lungs (Alveoli in Mammals): Tiny air sacs in lungs provide a huge surface area for gas exchange. Thin walls and a rich blood supply further enhance diffusion.
Gills (Fish): Thin filaments with lamellae provide a large surface area for gas exchange in water. Countercurrent flow maximises oxygen uptake from water.
Roots (Root Hairs in Plants): Microscopic extensions of root epidermal cells greatly increase the surface area for water and mineral ion absorption from the soil.
Leaves (Stomata and Spongy Mesophyll in Plants): Stomata (pores) allow gas exchange. Spongy mesophyll cells have irregular shapes and air spaces, creating a large internal surface area for gas exchange within the leaf.
Small Intestine (Villi in Mammals): Finger-like projections in the small intestine lining increase the surface area for absorption of digested food molecules into the bloodstream.
Adaptations of Exchange Surfaces - Features for Efficiency:
Large Surface Area: Folded or branched structures (alveoli, villi, root hairs, lamellae) to maximise the area available for diffusion/osmosis.
Thin Walls (Short Diffusion Pathway): Exchange surfaces are typically one cell thick (alveoli, capillary walls, gill lamellae) to minimise the distance substances need to diffuse.
Good Blood Supply (Animals) / Good Ventilation (Plants) - Maintaining Gradients:
Animals (Blood Supply): Dense network of capillaries around exchange surfaces (alveoli, gills, villi) ensures a constant flow of blood, maintaining a steep concentration gradient for efficient exchange.
Plants (Ventilation): Air spaces in leaves (spongy mesophyll) and stomata allow for efficient ventilation, maintaining a concentration gradient for CO2 uptake and O2 release.
Moist Surface (Gas Exchange) - Facilitating Diffusion: Gases (oxygen, carbon dioxide) must dissolve in water to diffuse across cell membranes efficiently. Exchange surfaces for gas exchange (alveoli, gills, leaf mesophyll) are kept moist.
Topic B3: Organism Level Systems
B3.1 Coordination and Control - The Nervous System - Rapid Responses
Need for Coordination - Complex Organism, Complex Responses: Multicellular organisms need sophisticated coordination systems to:
Respond to Stimuli: Detect and react to changes in the environment (e.g., predators, temperature changes, food sources).
Control Internal Processes: Regulate body functions like heart rate, breathing rate, digestion, and body temperature (homeostasis).
Integrate Body Functions: Ensure different parts of the body work together in a coordinated way (e.g., movement, digestion, reproduction).
The Nervous System - Fast and Specific Communication:
Function: A rapid, electrochemical communication system that allows for quick and precise responses to stimuli.
Central Nervous System (CNS) - Processing and Control:
Brain: The main control center, responsible for processing information, thinking, learning, memory, and coordinating complex responses.
Spinal Cord: A long column of nerve tissue extending from the brain down the back. It relays signals between the brain and the rest of the body and also controls reflex actions.
Peripheral Nervous System (PNS) - Sensory and Motor Pathways:
Nerves: Bundles of nerve fibres (axons of neurons) that transmit impulses between the CNS and the body.
Sensory Neurons: Part of the PNS, carry sensory information from receptors (sense organs) to the CNS.
Motor Neurons: Part of the PNS, carry motor commands from the CNS to effectors (muscles and glands).
Neurons (Nerve Cells) - The Communication Units:
Structure:
Cell Body: Contains the nucleus and most organelles.
Dendrites: Branch-like extensions that receive signals from other neurons or receptors.
Axon: A long, slender projection that transmits nerve impulses away from the cell body to other neurons or effectors.
Myelin Sheath: An insulating layer around the axon (in some neurons), made of Schwann cells. Speeds up nerve impulse transmission (saltatory conduction).
Axon Terminals (Synaptic End Bulbs): Branched endings of the axon that form synapses with other neurons or effector cells.
Types of Neurons:
Sensory Neurons: Transmit impulses from sensory receptors (e.g., in skin, eyes, ears, taste buds) to the CNS. Have receptors at one end to detect stimuli.
Relay Neurons (Interneurons): Located within the CNS (brain and spinal cord). Connect sensory neurons to motor neurons. Process and relay signals within the CNS.
Motor Neurons: Transmit impulses from the CNS to effectors (muscles or glands), causing a response. Have axon terminals that form neuromuscular junctions with muscle cells or synapses with gland cells.
Synapses - Chemical Communication Between Neurons:
Synaptic Cleft: A tiny gap between two neurons at a synapse.
Neurotransmitters: Chemical messengers stored in vesicles in the axon terminal of the presynaptic neuron.
Synaptic Transmission Process:
Nerve impulse arrives at the axon terminal of the presynaptic neuron.
This triggers the release of neurotransmitters into the synaptic cleft.
Neurotransmitters diffuse across the synaptic cleft and bind to receptors on the membrane of the postsynaptic neuron.
Binding of neurotransmitters to receptors triggers a new nerve impulse in the postsynaptic neuron (if excitatory neurotransmitter) or inhibits an impulse (if inhibitory neurotransmitter).
Neurotransmitters are then broken down or reabsorbed to prevent continuous stimulation or inhibition.
Reflex Actions - Automatic Protection:
Definition: Rapid, automatic, and involuntary responses to stimuli that bypass conscious control. Designed to protect the body from harm.
Importance: Fast responses are crucial for survival in dangerous situations (e.g., withdrawing hand from hot object, blinking to protect eyes).
Reflex Arc: The pathway of a reflex action:
Stimulus: The change in the environment that triggers the reflex (e.g., heat, pain, bright light).
Receptor: Sensory receptor that detects the stimulus (e.g., pain receptors in skin).
Sensory Neuron: Transmits impulse from receptor to the spinal cord (CNS).
Relay Neuron (Spinal Cord): Relays impulse within the spinal cord, often connecting sensory to motor neuron directly (in simple reflexes).
Motor Neuron: Transmits impulse from the spinal cord to the effector.
Effector: Muscle or gland that carries out the response (e.g., muscle in arm).
Response: The action taken (e.g., muscle contraction to withdraw hand).
Example: Withdrawal Reflex: Touching a hot object:
Heat stimulus detected by pain receptors in skin.
Sensory neuron carries impulse to spinal cord.
Relay neuron in spinal cord transmits impulse to motor neuron.
Motor neuron carries impulse to muscle in arm (effector).
Muscle contracts, withdrawing hand from hot object. This happens before you consciously feel the pain.
B3.2 Coordination and Control - The Endocrine System - Slower, Widespread Effects
The Endocrine System - Chemical Messengers in the Blood:
Function: A slower, but longer-lasting, communication system that uses hormones to regulate body functions.
Hormones - Chemical Signals:
Definition: Chemical substances produced by endocrine glands and transported in the bloodstream to target organs or cells, where they bind to receptors and trigger a specific response.
Specificity: Hormones only affect target cells that have specific receptors for that hormone.
Slower Action, Longer Duration: Hormonal responses are generally slower to initiate than nervous responses, but their effects are longer-lasting and more widespread throughout the body.
Endocrine Glands - Hormone Production Sites:
Pituitary Gland: Located at the base of the brain. Often called the "master gland" because it produces hormones that control other endocrine glands, as well as hormones that directly affect target organs. Examples: Growth hormone, ADH, FSH, LH.
Thyroid Gland: Located in the neck. Produces thyroxine, which controls the metabolic rate (how quickly chemical reactions occur in the body). Thyroxine also affects growth and development.
Adrenal Glands: Located above the kidneys. Produce adrenaline in response to stress or excitement. Adrenaline prepares the body for "fight or flight" by increasing heart rate, breathing rate, blood glucose levels, and diverting blood flow to muscles.
Pancreas: Located near the stomach. Produces insulin and glucagon, which regulate blood glucose levels. Insulin lowers blood glucose, glucagon raises it.
Ovaries (Females): Located in the pelvic cavity. Produce oestrogen and progesterone, which are involved in the menstrual cycle and female secondary sexual characteristics.
Testes (Males): Located in the scrotum. Produce testosterone, which is involved in sperm production and male secondary sexual characteristics.
Hormonal Control Examples - Regulation of Body Functions:
Blood Glucose Regulation (Insulin and Glucagon):
High Blood Glucose: Pancreas releases insulin. Insulin causes liver and muscle cells to take up glucose from the blood and store it as glycogen. Blood glucose level decreases.
Low Blood Glucose: Pancreas releases glucagon. Glucagon causes liver cells to break down glycogen into glucose and release it into the blood. Blood glucose level increases.
This is a negative feedback loop, maintaining blood glucose within a narrow range (homeostasis).
Menstrual Cycle (Oestrogen and Progesterone): A complex cycle controlled by hormones from the pituitary gland and ovaries. Oestrogen and progesterone regulate the development and release of eggs, prepare the uterus lining for pregnancy, and control the cycle.
"Fight or Flight" Response (Adrenaline): Adrenaline prepares the body for immediate action in stressful or dangerous situations. Effects include:
Increased heart rate and breathing rate (more oxygen to muscles).
Increased blood flow to muscles and away from digestive system.
Increased blood glucose levels (more energy available).
Dilated pupils (increased light intake).
Increased alertness.
Growth (Growth Hormone): Growth hormone, produced by the pituitary gland, stimulates growth in children and adolescents. It affects bone growth, muscle development, and overall body size.
B3.3 Maintaining Internal Environments (Homeostasis) - Balance is Key
Homeostasis - Stability Within:
Definition: The maintenance of a relatively constant internal environment in the body, despite changes in the external environment or internal activities. "Dynamic equilibrium" - conditions fluctuate within a narrow range around a set point.
Importance: Essential for optimal enzyme activity and cell function. Enzymes are sensitive to changes in temperature, pH, and concentration. Homeostasis ensures these conditions are kept within the optimal range.
Examples of Homeostatic Control - Key Variables:
Body Temperature (Thermoregulation): Normal human body temperature is around 37°C. Controlled by the thermoregulatory centre in the hypothalamus region of the brain.
Mechanisms for Cooling Down (Overheating):
Sweating: Evaporation of sweat from skin surface removes heat.
Vasodilation: Blood vessels near the skin surface widen (dilate), increasing blood flow to the skin, allowing more heat to radiate away.
Panting (in some animals): Evaporation of water from the tongue and respiratory passages.
Mechanisms for Warming Up (Cooling Down):
Shivering: Rapid muscle contractions generate heat.
Vasoconstriction: Blood vessels near the skin surface narrow (constrict), reducing blood flow to the skin, conserving heat.
Hair Erection (Piloerection): Hairs stand on end, trapping a layer of insulating air near the skin (less effective in humans).
Blood Glucose Concentration: Normal blood glucose level is tightly regulated. Controlled by insulin and glucagon from the pancreas (as explained in B3.2).
Water Balance (Osmoregulation): Controlled by the kidneys and ADH (Antidiuretic Hormone) from the pituitary gland.
Dehydration (Water Loss): Pituitary gland releases ADH. ADH causes kidneys to reabsorb more water back into the blood, producing less urine. Thirst is also stimulated.
Overhydration (Excess Water): Pituitary gland releases less ADH. Kidneys reabsorb less water, producing more dilute urine. Thirst is suppressed.
Ion Balance (Electrolyte Balance): Controlled by the kidneys. Kidneys regulate the levels of ions (like sodium, potassium, chloride) in the blood by adjusting their reabsorption and excretion in urine.
Negative Feedback - The Control Mechanism:
Definition: A control mechanism in homeostasis where a change in a variable triggers a response that opposes the initial change, bringing the variable back towards the set point. Like a thermostat in a house.
Components of a Negative Feedback Loop:
Receptor: Detects a change in the variable.
Control Center: Processes information from the receptor and determines the appropriate response (often the brain or endocrine gland).
Effector: Organ or tissue that carries out the response to restore the variable to the set point (e.g., muscles, glands).
Example: Blood Glucose Control:
Stimulus: Blood glucose level rises after a meal.
Receptor: Pancreas detects high blood glucose.
Control Center: Pancreas releases insulin.
Effector: Liver and muscle cells take up glucose and store it as glycogen.
Response: Blood glucose level decreases back towards the set point.
Stimulus: Blood glucose level falls too low (e.g., after exercise or fasting).
Receptor: Pancreas detects low blood glucose.
Control Center: Pancreas releases glucagon.
Effector: Liver cells break down glycogen into glucose and release it into the blood.
Response: Blood glucose level increases back towards the set point.
Topic B4: Community Level Systems
B4.1 Ecosystems - Interacting Living and Non-Living Components
What is an Ecosystem? - A Holistic View:
Definition: A community of interacting organisms (biotic components) and their physical environment (abiotic components) in a specific area. Ecosystems are dynamic and complex systems.
Scale of Ecosystems: Ecosystems can range in size from very small (e.g., a puddle, a rotting log) to very large (e.g., a forest, an ocean).
Examples: Ponds, forests, grasslands, deserts, coral reefs, tundra, rainforests.
Biotic Factors - The Living World Within:
Producers (Autotrophs) - The Foundation of the Food Web:
Definition: Organisms that make their own food from inorganic substances, usually through photosynthesis (using light energy) or chemosynthesis (using chemical energy).
Examples: Plants (trees, grasses, flowers), algae (seaweed, phytoplankton), cyanobacteria (blue-green algae).
Role in Ecosystems: Producers form the base of food chains and food webs. They convert light energy into chemical energy in glucose, which is then available to other organisms.
Consumers (Heterotrophs) - Feeding on Others:
Definition: Organisms that cannot make their own food and must obtain energy by eating other organisms.
Types of Consumers:
Primary Consumers (Herbivores): Eat producers (plants or algae). Examples: Rabbits, cows, caterpillars, zooplankton.
Secondary Consumers (Carnivores or Omnivores): Eat primary consumers. Examples: Foxes, frogs, birds of prey, some fish.
Tertiary Consumers (Top Carnivores): Eat secondary consumers. Often at the top of the food chain, with few or no predators. Examples: Lions, sharks, eagles.
Omnivores: Eat both plants and animals. Examples: Humans, bears, crows.
Detritivores: Consume dead organic matter (detritus). Examples: Earthworms, woodlice. Help break down dead material.
Decomposers (Saprotrophs) - Recyclers of Nutrients:
Definition: Organisms that break down dead plants and animals and waste products into simpler inorganic substances.
Examples: Bacteria and fungi (moulds, mushrooms).
Role in Ecosystems: Decomposers are essential for nutrient cycling. They release nutrients (like carbon, nitrogen, phosphorus) back into the soil and atmosphere, making them available to producers again. Without decomposers, nutrients would be locked up in dead organisms, and ecosystems would collapse.
Abiotic Factors - The Non-Living Environment:
Light Intensity: Affects the rate of photosynthesis in producers. Influences plant growth and distribution, and consequently, the entire food web.
Temperature: Affects enzyme activity and metabolic rates of all organisms. Determines which species can survive in a particular ecosystem.
Water Availability: Essential for all life processes. Determines the types of plants and animals that can live in an ecosystem. Water scarcity is a major limiting factor in many ecosystems.
Nutrient Availability (in Soil): Essential nutrients like nitrates, phosphates, potassium ions are needed for plant growth and therefore affect the entire food web. Nutrient-poor soils limit plant growth and ecosystem productivity.
Oxygen and Carbon Dioxide Levels:
Oxygen: Essential for aerobic respiration in most organisms. Oxygen levels can be limiting in aquatic environments or in polluted areas.
Carbon Dioxide: Essential for photosynthesis. CO2 levels in the atmosphere affect the rate of photosynthesis and also influence climate (greenhouse gas).
Wind: Affects water loss from plants (transpiration), seed dispersal, and temperature. Strong winds can damage ecosystems.
Soil pH: Affects nutrient availability and the types of plants that can grow.
Salinity: Salt concentration, particularly important in aquatic and coastal ecosystems.
Food Chains and Food Webs - Energy Flow and Trophic Levels:
Food Chain: A linear sequence showing the transfer of energy and nutrients from one organism to another when one organism eats another. Arrows indicate the direction of energy flow (from the organism being eaten to the organism that eats it).
Trophic Levels: Each step in a food chain is a trophic level:
Trophic Level 1: Producers (plants, algae).
Trophic Level 2: Primary consumers (herbivores).
Trophic Level 3: Secondary consumers (carnivores/omnivores).
Trophic Level 4 (and higher): Tertiary and higher-level consumers (top carnivores).
Food Web: A more complex representation of feeding relationships in an ecosystem. Interconnected food chains showing that many organisms eat and are eaten by multiple species. Food webs are more realistic than food chains as they show the complexity of ecological interactions.
Nutrient Cycles - Recycling is Vital:
Concept: Nutrients (matter) are recycled within ecosystems. Unlike energy (which flows through and is eventually lost as heat), nutrients are constantly reused. Decomposers play a crucial role in nutrient cycling.
Carbon Cycle: The movement of carbon through the ecosystem. Key processes:
Photosynthesis: Plants take in CO2 from the atmosphere and convert it into glucose (carbon compounds).
Respiration: Organisms release CO2 back into the atmosphere through respiration.
Consumption: Carbon compounds are transferred through food chains as organisms eat each other.
Decomposition: Decomposers break down dead organisms, releasing CO2 back into the atmosphere and carbon compounds into the soil.
Combustion: Burning of fossil fuels (formed from dead organisms over millions of years) releases large amounts of CO2 into the atmosphere.
Water Cycle: The continuous movement of water on, above, and below the surface of the Earth. Key processes:
Evaporation: Water turns into water vapour and rises into the atmosphere (from oceans, lakes, rivers, soil, plants).
Transpiration: Water is released from plant leaves as water vapour.
Condensation: Water vapour cools and turns back into liquid water, forming clouds.
Precipitation: Water falls back to Earth as rain, snow, hail, or sleet.
Collection: Water collects in rivers, lakes, oceans, and groundwater.
Interdependence - All Connected:
Concept: Organisms in an ecosystem are interdependent. They rely on each other and their environment for survival. Changes in one part of the ecosystem can have ripple effects throughout the system.
Examples of Interdependence:
Predator-Prey Relationships: Predators depend on prey for food; prey populations are influenced by predator populations.
Pollination: Many plants rely on insects or animals for pollination.
Seed Dispersal: Animals may disperse seeds of plants they eat.
Nutrient Cycling: Decomposers are essential for recycling nutrients needed by producers.
Consequences of Ecosystem Change: If one species is removed or an abiotic factor changes significantly, it can disrupt the balance of the ecosystem, potentially leading to population declines, species extinctions, or ecosystem collapse.
Sampling Techniques - Studying Ecosystems in the Field:
Quadrats: Square frames of known area used to sample plants and slow-moving animals in a representative area. Used to estimate population density and species frequency.
Transects: Lines or belts across a habitat along which quadrats are placed at regular intervals. Used to study how species distribution changes across an environmental gradient (e.g., from woodland edge to open field).
Pitfall Traps: Containers buried in the ground to catch ground-dwelling invertebrates (beetles, spiders, etc.). Used to estimate relative abundance of these organisms.
Sweep Nets: Nets swept through vegetation to catch flying insects and other invertebrates. Used to sample aerial insect populations.
Limitations of Sampling: Sampling provides estimates, not exact counts. Sample size and location are important to ensure representative data. Environmental conditions and observer skill can affect results.
Topic B5: Genes, Inheritance and Selection
B5.1 Inheritance - Passing on the Genetic Blueprint
Genes and Chromosomes - The Language of Heredity:
Genes: Short sections of DNA that code for a specific protein. Proteins determine many of our characteristics (phenotype). Genes are the units of heredity.
DNA (Deoxyribonucleic Acid): A complex molecule that carries genetic information. DNA is a double helix structure made of nucleotides. Each nucleotide contains a deoxyribose sugar, a phosphate group, and a nitrogenous base (Adenine, Thymine, Cytosine, Guanine - A, T, C, G). The sequence of bases in DNA is the genetic code.
Chromosomes: Thread-like structures made of DNA and protein. Found in the nucleus of eukaryotic cells. DNA is tightly coiled and packaged into chromosomes. Humans have 46 chromosomes in body cells, arranged in 23 pairs. One chromosome of each pair comes from each parent. Sex cells (gametes) have 23 single chromosomes.
Alleles - Variations of a Gene:
Definition: Different versions of a gene. Arise due to mutations in the DNA sequence. Individuals inherit two alleles for each gene, one from each parent.
Example: Gene for eye colour. Alleles could be for blue eyes, brown eyes, green eyes, etc.
Genotype and Phenotype - Genes and Appearance:
Genotype: The genetic makeup of an individual for a particular trait. Refers to the alleles an individual possesses for a gene. Often represented by letters (e.g., BB, Bb, bb).
Phenotype: The observable characteristics of an individual. Determined by the genotype and environmental factors. Examples: Eye colour, hair colour, height, blood group.
Homozygous and Heterozygous - Allele Combinations:
Homozygous: Having two identical alleles for a particular gene. Also called purebred.
Homozygous Dominant: Two dominant alleles (e.g., BB). Phenotype will express the dominant trait.
Homozygous Recessive: Two recessive alleles (e.g., bb). Phenotype will express the recessive trait.
Heterozygous: Having two different alleles for a particular gene. Also called hybrid. (e.g., Bb). Phenotype will usually express the dominant trait (if dominance exists).
Dominant and Recessive Alleles - Masking and Expression:
Dominant Allele: An allele that is always expressed in the phenotype, even if only one copy is present in the genotype. Represented by a capital letter (e.g., B for brown eyes). Masks the effect of the recessive allele when heterozygous.
Recessive Allele: An allele that is only expressed in the phenotype if two copies are present in the genotype (homozygous recessive). Represented by a lowercase letter (e.g., b for blue eyes). Masked by the dominant allele when heterozygous.
Inheritance - Passing Genes to the Next Generation:
Gametes (Sex Cells): Sperm cells (male) and egg cells (female). Produced by meiosis (cell division that reduces chromosome number by half). Gametes are haploid - they contain half the number of chromosomes as body cells (23 single chromosomes in human gametes).
Fertilisation: The fusion of a sperm nucleus with an egg nucleus. Restores the full number of chromosomes (diploid) in the zygote (fertilised egg). The zygote contains a mixture of genetic material from both parents.
Punnett Squares - Predicting Inheritance Patterns:
Purpose: Diagrams used to predict the possible genotypes and phenotypes of offspring from a genetic cross. Based on the genotypes of the parents and the principles of Mendelian inheritance.
How to Use:
Determine the genotypes of the parents for the trait being studied.
Determine the possible gametes (alleles in sex cells) each parent can produce.
Draw a square grid (Punnett square). Place gametes of one parent along the top and gametes of the other parent along the side.
Fill in each box of the grid by combining the alleles from the corresponding row and column. These boxes represent the possible genotypes of the offspring.
Determine the phenotypes of the offspring based on their genotypes and the dominance relationships of the alleles.
Calculate the ratios of genotypes and phenotypes in the offspring.
Family Pedigrees - Tracing Traits Through Generations:
Purpose: Diagrams that show the inheritance of a particular trait (phenotype) through generations of a family. Used to track genetic disorders or specific characteristics and determine inheritance patterns (dominant, recessive, sex-linked).
Symbols:
Squares: Represent males.
Circles: Represent females.
Shaded shapes: Individuals affected by the trait.
Unshaded shapes: Individuals not affected by the trait.
Horizontal lines: Represent mating/marriage.
Vertical lines: Connect parents to offspring.
Analyzing Pedigrees: By examining the patterns of affected and unaffected individuals across generations, you can deduce the mode of inheritance (e.g., autosomal dominant, autosomal recessive, X-linked recessive).
B5.2 Natural Selection and Evolution - Change Over Time
Variation - The Raw Material for Evolution:
Definition: Differences in characteristics among individuals within a population of the same species. No two individuals are exactly alike (except identical twins).
Sources of Variation:
Genetic Variation: Differences in alleles between individuals. Arises from:
Mutations: Random changes in DNA sequence. Can create new alleles.
Sexual Reproduction: Meiosis (produces gametes with different combinations of chromosomes) and fertilisation (combining genetic material from two parents) create new combinations of alleles in offspring.
Environmental Variation: Differences in the environment that individuals experience. Environmental factors can influence phenotype. Examples: Sunlight exposure affecting skin colour, diet affecting body size.
Natural Selection - Survival of the Fittest:
Definition: The process by which individuals with advantageous inherited characteristics (adaptations) are more likely to survive, reproduce, and pass on their genes to the next generation, while individuals with less advantageous characteristics are less likely to do so. Leads to a gradual change in the frequency of alleles in a population over time.
Steps of Natural Selection:
Variation: Within a population, there is genetic variation. Individuals have different alleles for different traits, resulting in a range of phenotypes. This variation is the foundation for natural selection.
Overproduction and Competition: Organisms tend to produce more offspring than the environment can support. This leads to competition for limited resources (food, water, mates, space, shelter). "Struggle for survival".
Survival of the Fittest (Differential Survival and Reproduction): Individuals with advantageous phenotypes (traits that make them better suited to their environment) are more likely to survive the competition and reproduce successfully. "Fitness" in evolutionary terms means reproductive success. "Fittest" are not necessarily the strongest or fastest, but those best adapted to their specific environment.
Inheritance: The advantageous phenotypes are often due to heritable alleles (genes). Survivors pass on these advantageous alleles to their offspring. Offspring inherit the beneficial traits.
Evolution: Over many generations, the frequency of advantageous alleles increases in the population. The population becomes better adapted to its environment. This is evolution at the genetic level. Over long periods, this can lead to significant changes in the characteristics of a species and even the formation of new species.
Evolution - Change in Species Over Time:
Definition: The gradual change in the inherited characteristics of a population over many generations. Evolution is driven by natural selection and other mechanisms (like genetic drift). Evolution occurs at the population level, not within individuals.
Adaptation: A heritable characteristic that increases an organism's ability to survive and reproduce in its environment. Adaptations are the result of natural selection. Examples: Camouflage, sharp teeth, drought resistance in plants.
Evidence for Evolution - Supporting the Theory:
Fossil Record: Fossils provide a historical record of life on Earth. Fossil sequences show how organisms have changed over millions of years. Fossil evidence shows transitional forms between different groups of organisms, supporting the idea of common ancestry and gradual change.
Similarities in Anatomy (Homologous Structures): Homologous structures are structures in different species that have a similar underlying structure but may have different functions. They are evidence of common ancestry. Example: The pentadactyl limb (five-fingered limb) found in vertebrates (humans, bats, whales, lizards) - bones are arranged in a similar pattern despite different functions (grasping, flying, swimming, walking).
DNA Evidence (Comparative Genomics): Comparing DNA sequences between different species reveals evolutionary relationships. Species that are more closely related evolutionarily have more similar DNA sequences. DNA evidence provides strong support for common ancestry and evolutionary relationships.
Speciation - The Birth of New Species:
Definition: The process by which new species arise from existing species. Usually occurs when populations of a species become reproductively isolated from each other and evolve along different paths.
Mechanism - Often Geographical Isolation (Allopatric Speciation):
Geographical Isolation: A population is split into two or more isolated populations by a geographical barrier (mountain range, river, ocean, etc.).
Different Environmental Conditions: The isolated populations experience different environmental conditions.
Natural Selection in Different Directions: Natural selection acts differently on each isolated population, favouring different adaptations in each environment.
Genetic Divergence: Over many generations, the isolated populations evolve independently. Their allele frequencies change in different directions due to natural selection and genetic drift.
Reproductive Isolation: Eventually, the populations become so genetically different that they can no longer interbreed and produce fertile offspring, even if the geographical barrier is removed. They have become separate species.
Selective Breeding (Artificial Selection) - Human-Driven Evolution:
Definition: A process where humans select individuals with desired characteristics and breed them together. Humans act as the "selective agent," choosing which individuals reproduce. Leads to changes in the characteristics of domesticated animals and cultivated plants over generations.
Contrast with Natural Selection: In natural selection, the environment is the selective agent. In selective breeding, humans are the selective agent, choosing traits they find desirable.
Examples of Selective Breeding:
Dog Breeds: Breeding dogs for specific traits like herding ability, hunting ability, appearance.
Crop Plants: Breeding crop plants for higher yield, disease resistance, improved flavour, larger fruit size.
Livestock: Breeding farm animals for increased milk production, meat production, wool quality.
Process of Selective Breeding:
Identify Desired Traits: Determine the characteristics that are wanted in the offspring (e.g., high milk yield in cows, disease resistance in wheat).
Select Breeding Stock: Choose parent individuals that exhibit the desired traits.
Breed Selected Individuals: Allow the selected individuals to reproduce.
Select Offspring with Desired Traits: From the offspring, select those that show the desired traits most strongly.
Repeat Over Generations: Continue breeding the selected offspring over many generations, consistently selecting for the desired traits. This process gradually enhances the desired characteristics in the population.
Topic B6: Global Challenges
B6.1 Monitoring and Maintaining the Environment - Our Planet Under Pressure
Pollution - Contaminating Our World:
Definition: The introduction of harmful substances (pollutants) into the environment, causing adverse effects on living organisms and ecosystems.
Types of Pollution:
Air Pollution: Contamination of the atmosphere.
Causes: Burning fossil fuels (coal, oil, gas) in power plants, vehicles, and industries. Industrial processes. Agricultural activities (e.g., ammonia from livestock).
Pollutants:
Carbon Monoxide (CO): A poisonous gas produced by incomplete combustion of fuels. Reduces oxygen-carrying capacity of blood.
Sulfur Dioxide (SO2): Released from burning fossil fuels containing sulfur. Causes acid rain and respiratory problems.
Nitrogen Oxides (NOx): Formed in combustion engines at high temperatures. Contribute to acid rain, smog, and respiratory problems.
Particulate Matter (PM): Tiny solid particles and liquid droplets suspended in the air (e.g., soot, dust, pollen). Can penetrate deep into lungs and cause respiratory and cardiovascular problems.
Greenhouse Gases (CO2, Methane, etc.): Contribute to global warming and climate change.
Impacts:
Respiratory Problems: Asthma, bronchitis, lung cancer.
Acid Rain: Damages forests, lakes, and buildings.
Global Warming and Climate Change: Trapping heat, leading to rising temperatures, sea level rise, extreme weather events.
Smog: Reduces visibility and irritates eyes and respiratory system.
Water Pollution: Contamination of water bodies (rivers, lakes, oceans, groundwater).
Causes: Sewage (untreated wastewater), fertilisers (nitrates and phosphates runoff from agriculture), pesticides (from agriculture), industrial waste (chemicals, heavy metals), plastic pollution.
Impacts:
Eutrophication: Excess nutrients (nitrates and phosphates) from fertilisers cause algal blooms in water bodies. When algae die and decompose, oxygen levels in water decrease, leading to death of aquatic organisms (fish, invertebrates).
Spread of Waterborne Diseases: Contaminated water can spread diseases like cholera, typhoid, dysentery.
Harm to Aquatic Life: Toxic pollutants can directly kill aquatic organisms or disrupt their physiology and reproduction. Plastic pollution can entangle and harm marine animals.
Land Pollution: Contamination of soil and land.
Causes: Landfill waste (household and industrial waste), pesticides and herbicides (from agriculture), industrial waste (heavy metals, chemicals), litter.
Impacts:
Soil Contamination: Pollutants can accumulate in soil, making it infertile and toxic to plants and soil organisms.
Water Contamination: Pollutants can leach from soil into groundwater and surface water.
Harm to Wildlife: Pollutants can accumulate in food chains, harming animals. Litter can entangle and harm wildlife.
Deforestation - Losing Our Forests:
Definition: The clearing of forests for other land uses, such as agriculture, urban development, logging, and mining.
Causes of Deforestation:
Agriculture: Clearing forests for farmland (crops, pasture for livestock).
Logging: Harvesting timber for wood products.
Urban Expansion: Clearing forests for housing, roads, and infrastructure.
Mining: Clearing forests to access mineral deposits.
Paper Production: Demand for paper products.
Impacts of Deforestation:
Habitat Loss: Destruction of habitats for countless species, leading to biodiversity loss and extinctions.
Soil Erosion: Trees protect soil from erosion. Deforestation leads to increased soil erosion by wind and rain, degrading soil quality and leading to sedimentation of rivers and lakes.
Flooding: Forests help regulate water cycles and reduce flooding. Deforestation increases flood risk.
Climate Change (Reduced Carbon Dioxide Absorption): Forests are important carbon sinks, absorbing CO2 from the atmosphere through photosynthesis. Deforestation reduces carbon sequestration and releases stored carbon back into the atmosphere, contributing to global warming.
Loss of Biodiversity: Forests are biodiversity hotspots, home to a vast number of plant and animal species. Deforestation is a major driver of species extinction.
Global Warming and Climate Change - A Changing Planet:
Global Warming: The increase in the average temperature of the Earth's atmosphere and oceans. A key aspect of climate change.
Climate Change: Long-term shifts in weather patterns and climate around the world, including changes in temperature, precipitation, sea level, and extreme weather events. Driven by global warming.
Greenhouse Effect: A natural process where certain gases in the Earth's atmosphere (greenhouse gases) trap heat from the sun, warming the planet. This is essential for making Earth habitable, but enhanced greenhouse effect due to human activities is causing global warming.
Greenhouse Gases: Gases that trap heat in the atmosphere. Major greenhouse gases:
Carbon Dioxide (CO2): Most significant greenhouse gas from human activities. Released primarily from burning fossil fuels, deforestation, and industrial processes.
Methane (CH4): Released from agriculture (livestock, rice farming), natural gas leaks, and decomposition of organic waste in landfills. More potent greenhouse gas than CO2 over a shorter timeframe.
Water Vapour (H2O): A natural greenhouse gas. Its concentration in the atmosphere is influenced by temperature (warmer air holds more water vapour).
Nitrous Oxide (N2O): Released from agriculture (fertilisers), industrial processes, and burning fossil fuels.
Other Greenhouse Gases: Fluorinated gases (HFCs, PFCs, SF6) used in refrigerants and industrial processes. Very potent greenhouse gases, but released in smaller quantities than CO2 and methane.
Causes of Increased Greenhouse Gases:
Burning Fossil Fuels: Combustion of coal, oil, and gas releases large amounts of CO2 into the atmosphere. Major source of increased greenhouse gas concentrations.
Deforestation: Reduces carbon sequestration by forests and releases stored carbon when trees are burned or decompose.
Agriculture: Livestock farming (methane from animal digestion), rice farming (methane from flooded paddies), and fertiliser use (nitrous oxide release) contribute to greenhouse gas emissions.
Industrial Processes: Some industrial processes release greenhouse gases (e.g., cement production, chemical manufacturing).
Impacts of Climate Change:
Rising Sea Levels: Melting glaciers and ice sheets and thermal expansion of seawater cause sea levels to rise, threatening coastal communities and ecosystems.
Extreme Weather Events: Increased frequency and intensity of heatwaves, droughts, floods, storms, and wildfires.
Changes in Species Distribution: Species are shifting their ranges to track changing climates. Some species may not be able to adapt or migrate quickly enough, leading to extinctions.
Threats to Food Security: Climate change impacts crop yields and livestock production due to changes in temperature, rainfall patterns, and extreme weather.
Ocean Acidification: Increased CO2 absorption by oceans makes them more acidic, harming marine organisms (especially shellfish and corals).
Maintaining Biodiversity - Protecting Life's Variety:
Biodiversity - The Variety of Life: The variety of life on Earth at all levels, from genes to ecosystems. Includes the number of different species, their genetic diversity, and the variety of ecosystems.
Importance of Biodiversity:
Ecosystem Stability: Biodiverse ecosystems are more resilient and stable. They are better able to withstand disturbances (e.g., climate change, disease outbreaks).
Food Security: Biodiversity provides a wide range of food sources (crops, livestock, wild foods). Genetic diversity in crops and livestock is important for resilience to pests and diseases.
Medicines: Many medicines are derived from natural sources (plants, fungi, microorganisms). Biodiversity is a source of potential new medicines.
Resources: Biodiversity provides many other resources, including timber, fibres, fuels, and raw materials.
Ecosystem Services: Biodiversity provides essential ecosystem services, such as pollination, water purification, climate regulation, and nutrient cycling.
Intrinsic Value: Many people believe that biodiversity has intrinsic value and that we have a moral obligation to protect it.
Threats to Biodiversity:
Habitat Destruction: Deforestation, habitat fragmentation, urban development, agriculture. The biggest driver of biodiversity loss.
Pollution: Air, water, and land pollution can directly kill species or degrade habitats.
Climate Change: Rapid climate change is altering habitats and threatening species that cannot adapt quickly enough.
Overexploitation: Overfishing, overhunting, unsustainable harvesting of resources.
Invasive Species: Introduction of non-native species that can outcompete native species, disrupt ecosystems, and cause extinctions.
Conservation Measures - Protecting Biodiversity:
Protected Areas (National Parks, Reserves): Establishing protected areas to conserve habitats and species.
Captive Breeding Programmes: Breeding endangered species in captivity to increase their populations and potentially reintroduce them to the wild.
Seed Banks: Storing seeds of diverse plant species to conserve genetic diversity and provide a backup in case of extinction in the wild.
Controlling Invasive Species: Managing and controlling populations of invasive species to reduce their negative impacts on native ecosystems.
Reducing Pollution: Implementing measures to reduce air, water, and land pollution.
Sustainable Practices: Promoting sustainable agriculture, forestry, fishing, and development to minimise environmental impacts and conserve biodiversity.
B6.2 Feeding the Human Race - Food for Billions
Food Security - Access to Nourishment:
Definition: A state where all people at all times have physical, social, and economic access to sufficient, safe, and nutritious food that meets their dietary needs and food preferences for an active and healthy life. More than just having enough food; it's about access, affordability, and nutrition.
Four Pillars of Food Security:
Availability: Sufficient quantities of food are available on a consistent basis.
Access: People have adequate resources to obtain appropriate foods for a nutritious diet.
Utilisation: Food is safely and effectively used to meet nutritional needs. Includes proper food processing, storage, preparation, and individual health status.
Stability: Food security is stable over time. Populations have access to food at all times and are not at risk of losing access due to shocks like economic crises, climate change, or conflict.
Challenges to Food Security - Threats to Our Food Supply:
Increasing Population: The global population is growing rapidly, increasing the demand for food. Need to produce more food to feed billions of people.
Changing Diets: As incomes rise in developing countries, there is increasing demand for meat and dairy products. Meat production is more resource-intensive than plant-based food production (requires more land, water, and energy).
Climate Change: Climate change is impacting agricultural production through:
Changes in Temperature and Rainfall Patterns: Can reduce crop yields in many regions.
Extreme Weather Events (Droughts, Floods, Heatwaves): Can damage crops and disrupt food production.
Sea Level Rise: Threatens coastal agricultural land.
Pests and Diseases: Pests and diseases can devastate crops and livestock, causing significant food losses. Climate change can exacerbate pest and disease problems.
Cost of Food Production: Rising costs of energy, fertilisers, pesticides, and labour increase the cost of food production, making food less affordable, especially for low-income populations.
Conflict and Famine: Conflicts and political instability can disrupt food production, distribution, and access, leading to food shortages and famine.
Sustainable Agriculture - Farming for the Future:
Definition: Agricultural practices that meet current food and fibre needs without compromising the ability of future generations to meet their own needs. Focuses on environmental, economic, and social sustainability.
Principles of Sustainable Agriculture:
Efficient Food Production (Maximising Yield): Using technologies and practices to increase crop yields and livestock productivity per unit of land and resources, while minimising environmental impact.
Reducing Waste (Minimising Food Loss and Waste): Reducing food waste at all stages of the food supply chain, from farm to consumer. Improving storage, transportation, processing, and consumption practices.
Maintaining Soil Quality (Soil Health): Practices that improve and maintain soil health, such as:
Crop Rotation: Planting different crops in sequence to improve soil fertility, reduce pest and disease build-up, and improve soil structure.
Reduced Tillage (No-Till Farming): Minimising soil disturbance by reducing or eliminating ploughing. Helps conserve soil organic matter, reduce erosion, and improve water infiltration.
Organic Fertilisers: Using compost, manure, and green manures instead of synthetic fertilisers. Improves soil structure and fertility and reduces reliance on chemical inputs.
Conserving Water (Water Use Efficiency): Efficient irrigation methods (drip irrigation, sprinkler irrigation) to reduce water use in agriculture. Water harvesting and rainwater collection.
Reducing Reliance on Fossil Fuels (Energy Efficiency): Using renewable energy sources in agriculture, reducing fertiliser use (synthetic fertilisers are energy-intensive to produce), and promoting energy-efficient farming practices.
Controlling Pests and Diseases Sustainably (Integrated Pest Management - IPM): Strategies to manage pests and diseases in an environmentally friendly way, such as:
Biological Control: Using natural enemies of pests (predators, parasites, pathogens) to control pest populations.
Crop Rotation: Disrupting pest life cycles.
Resistant Varieties: Planting crop varieties that are resistant to pests and diseases.
Careful Use of Pesticides: Using pesticides only when necessary, and choosing pesticides that are less harmful to the environment and human health.
Genetic Modification (GM) in Crops - Engineering for Food Security:
Definition: Altering the genes of crop plants using genetic engineering techniques to introduce new traits or enhance existing ones. Creating genetically modified organisms (GMOs) or genetically engineered (GE) crops.
Examples of GM Traits in Crops:
Increased Yield: GM crops can be engineered to produce higher yields, potentially increasing food production.
Pest Resistance (Bt Crops): GM crops can be engineered to produce their own insecticide (e.g., Bt cotton, Bt maize), reducing the need for synthetic pesticides.
Herbicide Tolerance (Herbicide-Resistant Crops): GM crops can be made tolerant to certain herbicides, allowing farmers to use herbicides to control weeds without harming the crop.
Improved Nutritional Content (Biofortification): GM crops can be engineered to have increased levels of vitamins, minerals, or other nutrients (e.g., Golden Rice engineered to produce beta-carotene, a precursor to vitamin A).
Drought Tolerance: GM crops can be engineered to be more tolerant to drought conditions, improving crop production in water-scarce regions.
Potential Benefits of GM Crops:
Increased Food Production: Higher yields and reduced losses to pests and diseases can contribute to increased food production and food security.
Reduced Pesticide Use: Pest-resistant GM crops can reduce the need for synthetic pesticides, potentially benefiting the environment and human health.
Improved Nutritional Value: Biofortified GM crops can help address micronutrient deficiencies in populations that rely on staple crops.
Concerns and Controversies about GM Crops:
Environmental Impacts:
Development of Herbicide-Resistant Weeds: Overuse of herbicides with herbicide-tolerant GM crops can lead to the evolution of herbicide-resistant weeds, requiring even stronger herbicides.
Impacts on Non-Target Organisms: Bt toxins produced by pest-resistant GM crops can potentially harm beneficial insects (e.g., bees, butterflies).
Gene Flow (Outcrossing): Genes from GM crops could potentially spread to wild relatives through pollen, with unknown ecological consequences.
Health Concerns:
Allergenicity: Concerns that GM crops could introduce new allergens into food. Rigorous testing is required to assess allergenicity.
Long-Term Health Effects: Some concerns about potential long-term health effects of consuming GM foods, although extensive research has generally not found evidence of harm.
Ethical Issues:
Corporate Control of Food Supply: Concerns about large corporations controlling the seed supply and food production through GM technology.
Access and Equity: Concerns that GM technology may not benefit small-scale farmers in developing countries.
Labelling and Consumer Choice: Debates about mandatory labelling of GM foods to allow consumers to make informed choices.
B6.3 Monitoring and Maintaining Health - Global Health Challenges
Disease - Disrupting Normal Body Function:
Definition: A condition that impairs the normal functioning of the body or mind. Can be caused by various factors, including pathogens, genetic defects, environmental factors, and lifestyle choices.
Types of Diseases:
Communicable Diseases (Infectious Diseases): Diseases caused by pathogens (microorganisms) that can be transmitted from person to person, animal to person, or through the environment.
Pathogens: Microorganisms that cause disease.
Bacteria: Single-celled prokaryotic organisms. Examples: Tuberculosis (TB), cholera, bacterial pneumonia. Treated with antibiotics.
Viruses: Non-cellular infectious agents that can only replicate inside living cells. Examples: Flu, measles, HIV/AIDS, COVID-19. Antibiotics are ineffective against viruses. Antiviral drugs can be used for some viral infections.
Fungi: Eukaryotic organisms, some of which can cause infections, especially in immunocompromised individuals. Examples: Athlete's foot, ringworm, thrush. Treated with antifungal drugs.
Protists (Protozoa): Single-celled eukaryotic organisms. Examples: Malaria, amoebic dysentery. Treated with antiprotozoal drugs.
Transmission of Communicable Diseases:
Direct Contact: Physical contact between infected and uninfected individuals (e.g., touching, kissing, sexual contact). Examples: Common cold, skin infections.
Airborne Transmission (Droplet Infection): Pathogens spread through droplets expelled when coughing, sneezing, or talking. Examples: Flu, measles, tuberculosis.
Waterborne Transmission: Contaminated water can spread pathogens. Examples: Cholera, typhoid.
Foodborne Transmission: Contaminated food can spread pathogens. Examples: Salmonellosis, E. coli infection.
Vector Transmission: Pathogens spread by vectors (animals that transmit pathogens without getting sick themselves, often insects). Examples: Malaria (mosquitoes), Lyme disease (ticks).
Prevention and Control of Communicable Diseases:
Hygiene: Handwashing, proper sanitation, food hygiene, safe water supply. Reduces pathogen transmission.
Vaccination: Stimulates the immune system to provide immunity against specific pathogens. Highly effective in preventing many infectious diseases.
Antibiotics (for Bacteria, not Viruses): Medicines that kill bacteria or inhibit their growth. Effective against bacterial infections, but not viral infections. Overuse leads to antibiotic resistance.
Antiviral Drugs (for Viruses): Medicines that can inhibit viral replication. Used to treat some viral infections (e.g., HIV, flu).
Vector Control: Measures to control populations of vectors (e.g., mosquito control for malaria prevention).
Non-communicable Diseases: Diseases that are not caused by pathogens and cannot be spread from person to person. Often chronic (long-lasting) and develop over time.
Examples: Cardiovascular diseases (heart disease, stroke), cancers, diabetes, chronic respiratory diseases (asthma, COPD), mental health disorders.
Risk Factors for Non-communicable Diseases:
Genetic Factors (Inherited Predisposition): Some people are genetically predisposed to certain non-communicable diseases.
Lifestyle Factors:
Unhealthy Diet: High in saturated and trans fats, salt, sugar, and low in fruits and vegetables.
Physical Inactivity (Lack of Exercise):
Smoking: Major risk factor for cardiovascular disease, cancer, respiratory diseases.
Excessive Alcohol Consumption:
Environmental Factors:
Air Pollution:
Exposure to Carcinogens (Cancer-Causing Substances):
Prevention and Management of Non-communicable Diseases:
Lifestyle Changes: Adopting a healthy diet, regular physical activity, quitting smoking, reducing alcohol consumption. Key for prevention and management.
Medication: Medicines to manage symptoms and slow disease progression (e.g., blood pressure medication, insulin for diabetes).
Screening Programs: Early detection of some non-communicable diseases (e.g., cancer screening) can improve treatment outcomes.
Surgery: Surgical interventions for some conditions (e.g., heart surgery, cancer surgery).
Vaccination - Building Immunity:
Definition: The process of introducing weakened or inactive pathogens (or parts of pathogens, like antigens) into the body to stimulate the immune system to produce antibodies and memory cells against that specific pathogen. Provides acquired immunity (long-term protection) against future infection.
Types of Vaccines:
Live Attenuated Vaccines: Contain weakened versions of the pathogen. Provide strong, long-lasting immunity, but may not be suitable for everyone (e.g., immunocompromised individuals). Examples: Measles, mumps, rubella (MMR) vaccine, chickenpox vaccine.
Inactivated Vaccines (Killed Vaccines): Contain inactivated (killed) pathogens. Safer than live vaccines, but may require multiple doses for full immunity. Examples: Flu vaccine (injection), polio vaccine (injection).
Subunit, Recombinant, Polysaccharide, and Conjugate Vaccines: Contain specific components of the pathogen (e.g., proteins, sugars, capsid). Safe and effective, but may require multiple doses. Examples: Hepatitis B vaccine, HPV vaccine, whooping cough vaccine.
Toxoid Vaccines: Contain inactivated bacterial toxins. Protect against diseases caused by bacterial toxins. Examples: Tetanus vaccine, diphtheria vaccine.
mRNA Vaccines: Newer type of vaccine that uses messenger RNA (mRNA) to instruct cells to make viral proteins, triggering an immune response. Examples: COVID-19 mRNA vaccines (Pfizer-BioNTech, Moderna).
Herd Immunity: When a high percentage of a population is vaccinated against a communicable disease, it becomes difficult for the disease to spread, even to unvaccinated individuals. Vaccination of the majority protects those who cannot be vaccinated (e.g., infants, immunocompromised individuals). The threshold for herd immunity varies depending on the disease (e.g., higher for measles than for flu).
Antibiotics - Fighting Bacteria, Not Viruses:
Definition: Medicines that kill bacteria (bactericidal antibiotics) or inhibit their growth (bacteriostatic antibiotics). Work by targeting essential bacterial processes (e.g., cell wall synthesis, protein synthesis, DNA replication). Ineffective against viruses.
Antibiotic Resistance: A serious global health threat. Bacteria can evolve resistance to antibiotics through natural selection.
Mechanism of Resistance: Bacteria can develop mutations that make them resistant to antibiotics. Antibiotic use selects for resistant bacteria. Resistant bacteria survive and multiply, while non-resistant bacteria are killed. Over time, resistant strains become more common.
Causes of Antibiotic Resistance:
Overuse of Antibiotics: Using antibiotics when they are not needed (e.g., for viral infections like colds and flu).
Misuse of Antibiotics: Not completing the full course of antibiotics, sharing antibiotics.
Antibiotic Use in Agriculture: Antibiotics used in animal agriculture can contribute to antibiotic resistance in bacteria that can then spread to humans.
Consequences of Antibiotic Resistance: Bacterial infections become harder to treat. Increased risk of serious illness, hospitalisation, and death. Spread of multidrug resistant bacteria ("superbugs").
Preventing Antibiotic Resistance:
Use Antibiotics Only When Necessary: Only for bacterial infections, as prescribed by a doctor. Not for viral infections.
Complete the Full Course of Antibiotics: Even if you feel better, finish the entire course to kill all bacteria and reduce the risk of resistance developing.
Do Not Share Antibiotics:
Develop New Antibiotics: Research and development of new antibiotics is crucial to combat antibiotic resistance.
Improve Hygiene: Good hygiene practices (handwashing, sanitation) reduce the spread of infections and the need for antibiotics.
Monitoring Health - Public Health Surveillance:
Public Health Monitoring (Surveillance): Systematic collection, analysis, interpretation, and dissemination of health data to inform public health action. Used to track diseases, identify outbreaks, monitor health trends, and evaluate public health interventions.
Surveillance Systems:
Disease Registries: Databases that collect information on cases of specific diseases (e.g., cancer registries, birth defect registries).
Surveys: Population-based surveys to collect data on health behaviours, risk factors, and health status.
Sentinel Surveillance: Monitoring health trends in selected populations or locations to detect early warning signs of outbreaks or changes in disease patterns.
Laboratory Surveillance: Monitoring laboratory data to track pathogens and antimicrobial resistance.
Syndromic Surveillance: Monitoring symptoms and health complaints reported by healthcare providers or through public health hotlines to detect potential outbreaks early.
Data Analysis: Statistical analysis of surveillance data to:
Identify Outbreaks: Detect clusters of cases of a disease that may indicate an outbreak.
Track Disease Trends: Monitor changes in disease incidence, prevalence, and mortality over time.
Identify Risk Factors: Determine factors that increase the risk of disease.
Evaluate Public Health Interventions: Assess the effectiveness of public health programs and policies.
Public Health Interventions: Actions taken based on surveillance data to protect and improve public health.
Vaccination Programs:
Health Education Campaigns: Public awareness campaigns to promote healthy behaviours and prevent disease.
Screening Programs:
Quarantine Measures: Isolating individuals with infectious diseases to prevent further spread.
Environmental Health Measures: Improving sanitation, water quality, and air quality to reduce disease risks.
