Biology Notes PDF

**Biology:** **1. Nutrition** - **Definition:** The process by which organisms obtain and use food for energy, growth, and repair. - **Key points:** - **Autotrophs (e.g., plants):** Make their own food via photosynthesis. - **Heterotrophs (e.g., animals):** Consume o...

**Biology:** **1. Nutrition** - **Definition:** The process by which organisms obtain and use food for energy, growth, and repair. - **Key points:** - **Autotrophs (e.g., plants):** Make their own food via photosynthesis. - **Heterotrophs (e.g., animals):** Consume other organisms for nutrients.   **2. Respiration** - **Definition:** The chemical reactions that release energy from food molecules (like glucose). - **Key points:** - Energy is used for cell processes such as growth, movement, and repair. - Can be **aerobic (with oxygen)** or **anaerobic (without oxygen)**.   **3. Excretion** - **Definition:** The removal of metabolic waste products made by cells. - **Examples of waste:** - **Carbon dioxide:** Released by respiration. - **Urea:** Removed by kidneys in humans. - **Oxygen (in plants):** Released during photosynthesis.   **4. Response to Surroundings** - **Definition:** Organisms detect and respond to changes in their external environment (stimuli). - **Key points:** - Plants grow towards light (phototropism). - Animals respond to danger, such as moving away from predators.   **5. Movement** - **Definition:** The ability to move either the whole organism or parts of it. - **Key points:** - Animals move using muscles and bones. - Plants can move parts (e.g., opening flowers or bending towards light).   **6. Control of Internal Conditions (Homeostasis)** - **Definition:** The maintenance of a constant internal environment despite external changes. - **Key points:** - Examples: Maintaining body temperature, blood glucose levels, and water balance. - In humans: Achieved through systems like the nervous and endocrine systems.   **7. Reproduction** - **Definition:** The production of offspring to ensure the survival of the species. - **Key points:** - **Asexual reproduction:** One parent produces genetically identical offspring. - **Sexual reproduction:** Two parents produce genetically varied offspring.   **8. Growth and Development** - **Definition:** Organisms increase in size and undergo changes as they mature. - **Key points:** - Growth: An increase in cell size or number. - Development: The process by which organisms become more complex and specialized.   **Summary Mnemonic:** Use **MRSGREN** to remember the 8 characteristics: - **M**ovement - **R**espiration - **S**ensitivity (Response to surroundings) - **G**rowth - **R**eproduction - **E**xcretion - **N**utrition **1. Common Features of Eukaryotic Organisms** **Plants** - **Structure:** Multicellular organisms with **cellulose cell walls**. - **Key Features:** - Contain **chloroplasts** for **photosynthesis**. - Store carbohydrates as **starch or sucrose**. - **Examples:** - **Cereal:** Maize. - **Herbaceous legume:** Peas or beans.   **Animals** - **Structure:** Multicellular organisms **without cell walls**. - **Key Features:** - **No chloroplasts**, so cannot photosynthesize. - Have **nervous coordination** and are capable of movement. - Store carbohydrates as **glycogen**. - **Examples:** - **Mammals:** Humans. - **Insects:** Housefly, mosquito.   **Fungi** - **Structure:** - Body typically consists of **mycelium** made from thread-like **hyphae** containing many nuclei. - Some fungi are **single-celled**. - **Key Features:** - **No photosynthesis.** - Cells have **chitin cell walls**. - Feed through **saprotrophic nutrition** (extracellular digestion followed by absorption). - Store carbohydrates as **glycogen**. - **Examples:** - **Mucor:** Typical hyphal structure. - **Yeast:** Single-celled.   **Protoctists** - **Structure:** Microscopic **single-celled** organisms. - **Key Features:** - Some resemble **animal cells** (e.g., **Amoeba**). - Others have **chloroplasts** and resemble **plants** (e.g., **Chlorella**). - Some are pathogenic (e.g., **Plasmodium** causes malaria).   **2. Common Features of Prokaryotic Organisms** **Bacteria** - **Structure:** Microscopic **single-celled** organisms. - **Key Features:** - Contain a **cell wall**, **cell membrane**, **cytoplasm**, and **plasmids**. - **No nucleus**, but have a circular chromosome of DNA. - Some can photosynthesize; most feed on living or dead organisms. - **Examples:** - **Lactobacillus bulgaricus:** Rod-shaped, used in yogurt production. - **Pneumococcus:** Spherical, causes pneumonia.   **3. Pathogens** **Definition of Pathogen:** - A microorganism that causes disease. - Pathogens can include: - **Fungi** (e.g., Candida causing thrush). - **Bacteria** (e.g., Pneumococcus causing pneumonia). - **Protoctists** (e.g., Plasmodium causing malaria). - **Viruses** (e.g., HIV causing AIDS).   **4. Viruses** **Key Features:** - **Not living organisms.** - Structure: - Smaller than bacteria. - Consist of a **protein coat** and contain **DNA or RNA** (but not both). - No cellular structure. - Reproduction: - **Parasitic:** Reproduce only inside living cells. - Infect all types of organisms. - **Examples:** - **Tobacco mosaic virus:** Prevents chloroplast formation in tobacco plants. - **Influenza virus:** Causes flu. - **HIV virus:** Causes AIDS.   These features help classify organisms and understand their functions within ecosystems and as pathogens. **1. Levels of Organisation** **Organelles** - **Definition:** Tiny structures within cells that perform specific functions. - **Examples of Organelles:** - **Nucleus:** Contains genetic material and controls cell activities. - **Mitochondria:** Site of aerobic respiration, producing energy. - **Chloroplasts:** Contain chlorophyll for photosynthesis (in plants). - **Ribosomes:** Site of protein synthesis. - **Cell membrane:** Controls entry and exit of substances.   **Cells** - **Definition:** Basic structural and functional unit of life. - **Examples of Cell Types:** - **Animal cells:** Have nucleus, cytoplasm, and cell membrane but no cell wall or chloroplasts. - **Plant cells:** Have cell walls, chloroplasts, and vacuoles in addition to the structures in animal cells. - **Key Function:** Cells carry out essential processes like respiration, protein synthesis, and reproduction.   **Tissues** - **Definition:** A group of similar cells working together to perform a specific function. - **Examples of Tissues:** - **Muscle tissue:** Contracts to allow movement. - **Epidermal tissue:** Covers and protects the surface of plants and animals. - **Xylem tissue:** Transports water in plants.   **Organs** - **Definition:** A structure made up of different tissues working together to perform a specific function. - **Examples of Organs:** - **Heart:** Pumps blood around the body. - **Lungs:** Carry out gas exchange. - **Leaf:** Performs photosynthesis.   **Organ Systems** - **Definition:** A group of organs working together to perform complex functions for the body. - **Examples of Systems:** - **Circulatory System:** Heart, blood, and blood vessels transport oxygen, nutrients, and waste. - **Digestive System:** Stomach, intestines, and other organs break down food and absorb nutrients. - **Nervous System:** Brain, spinal cord, and nerves coordinate responses to stimuli.    **Key Points to Remember:** - Each level builds on the previous one. - Organelles make up cells → Cells make up tissues → Tissues make up organs → Organs work together in systems. - Organisation allows multicellular organisms to perform complex processes efficiently.     **1. Cell Structures and Functions** **Nucleus** - **Structure**: Enclosed by a double membrane (nuclear envelope) with pores. - **Function**: - Contains **DNA** in the form of chromosomes. - Controls the cell\'s activities (e.g., growth, metabolism, reproduction). - Responsible for protein synthesis via mRNA. **Cytoplasm** - **Structure**: Jelly-like fluid containing organelles and enzymes. - **Function**: - Site of **chemical reactions** in the cell. - Provides a medium for organelles to remain suspended. **Cell Membrane** - **Structure**: Semi-permeable membrane made of a phospholipid bilayer. - **Function**: - **Controls entry/exit** of substances (e.g., nutrients, waste). - Maintains **cell structure**. **Cell Wall (Plant Cells Only)** - **Structure**: Made of **cellulose** (plants) or chitin (fungi). Rigid and fully permeable. - **Function**: - Provides **support** and shape to the cell. - Protects against mechanical damage. **Mitochondria** - **Structure**: Double-membraned, with an inner folded membrane (cristae). - **Function**: - Site of **aerobic respiration**, producing energy (ATP). **Chloroplasts (Plant Cells Only)** - **Structure**: Contain chlorophyll and enclosed by a double membrane. - **Function**: - Site of **photosynthesis** (convert light energy into glucose). **Ribosomes** - **Structure**: Small organelles found free in the cytoplasm or attached to the rough ER. - **Function**: - Site of **protein synthesis**. **Vacuole** - **Structure**: Large central sac in plants; smaller and temporary in animals. - **Function**: - Stores water, nutrients, and waste. - Maintains **turgor pressure** in plant cells.   **2. Similarities Between Plant and Animal Cells** - Both contain: - **Nucleus** - **Cytoplasm** - **Cell membrane** - **Mitochondria** - **Ribosomes**   **Key Summary** 1. **Plant cells** have additional structures: **cell wall**, **chloroplasts**, and a large **vacuole**, giving them distinct functions such as photosynthesis and structural support. 2. Both plant and animal cells share essential organelles (e.g., nucleus, cytoplasm, mitochondria, ribosomes). 3. **Animal cells** lack a cell wall and chloroplasts but can have small vacuoles and centrioles.   **1. Chemical Elements in Biological Molecules** - **Carbohydrates:** Contain **carbon (C)**, **hydrogen (H)**, and **oxygen (O)**. - **Proteins:** Contain **carbon (C)**, **hydrogen (H)**, **oxygen (O)**, **nitrogen (N)**, and sometimes **sulfur (S)**. - **Lipids (fats and oils):** Contain **carbon (C)**, **hydrogen (H)**, and **oxygen (O)**.   **2. Structure of Biological Molecules** - **Carbohydrates:** - Made of smaller units called **simple sugars** (e.g., glucose). - Complex carbohydrates like **starch** and **glycogen** are formed by joining multiple simple sugars in chains. - **Proteins:** - Made up of long chains of **amino acids** linked by peptide bonds. - Amino acids have a central carbon atom attached to an amine group (-NH₂), a carboxyl group (-COOH), and a side chain (R-group). - **Lipids:** - Made of **glycerol** and three **fatty acid** chains. - Known as triglycerides, formed by ester bonds.  **4. Enzymes and Their Role** - **Enzymes** are biological catalysts that speed up metabolic reactions without being consumed. - They lower the activation energy required for reactions to occur. - **Active Site:** - The part of the enzyme where the substrate binds. - Complementary in shape to the substrate (lock and key mechanism).   **5. Effects of Temperature on Enzymes** - **Optimum Temperature:** The temperature at which the enzyme works best (usually around 37°C in humans). - **Low Temperature:** Enzyme activity is slow due to reduced kinetic energy of molecules. - **High Temperature:** - Enzymes can denature (lose their specific shape). - The active site changes shape, and the substrate no longer fits. **Practical: Investigate Effect of Temperature on Enzyme Activity** - Use amylase to break down starch. - Mix starch and amylase in a test tube at different temperatures. - At regular intervals, test for starch using iodine. - Record the time taken for starch to disappear. - Enzyme activity is fastest at the optimum temperature and slows/stops at very low or high temperatures.   **6. Effects of pH on Enzymes** - Each enzyme has an **optimum pH** at which it works best (e.g., pH 2 for pepsin in the stomach). - **Extreme pH values** (too high or too low) denature enzymes by altering the shape of the active site.   **Key Summary** - Biological molecules are made of specific chemical elements and are tested using distinct methods. - Enzymes are vital for metabolism but are sensitive to changes in **temperature** and **pH**, which can affect their activity. **1. Processes of Movement** **Diffusion** - Definition: The **net movement of particles** (gas or liquid) from an area of **high concentration** to an area of **low concentration**, down a concentration gradient. - **Passive process**: Does not require energy. - Example: Oxygen diffusing into cells for respiration; carbon dioxide diffusing out. **Osmosis** - Definition: The **net movement of water molecules** from a region of **higher water potential** (dilute solution) to a region of **lower water potential** (concentrated solution), across a **partially permeable membrane**. - **Passive process**: Does not require energy. - Example: Water uptake by root hair cells or movement of water in/out of animal cells. **Active Transport** - Definition: The movement of substances **against a concentration gradient** (from low to high concentration), using **energy from respiration** (ATP). - **Active process**: Requires energy and protein carriers in the cell membrane. - Example: Absorption of mineral ions like nitrates into plant root hair cells.   **2. Factors Affecting the Rate of Movement** **1. Surface Area to Volume Ratio:** - Larger surface area to volume ratio = faster movement of substances. - Example: Small cells have a high surface area to volume ratio, enhancing efficiency in substance exchange. **2. Distance:** - Shorter diffusion distance = faster movement. - Example: Thin alveolar walls in the lungs facilitate rapid gas exchange. **3. Temperature:** - Higher temperature = more kinetic energy = faster particle movement. - Example: Higher body temperature increases diffusion rates. **4. Concentration Gradient:** - Steeper gradient = faster diffusion/osmosis. - Example: Oxygen moves more quickly into cells with low oxygen concentration during respiration.   **3. Practical Investigations: Diffusion and Osmosis** **Diffusion Practical** - **Living system**: Place agar cubes containing a pH indicator in hydrochloric acid. Measure how far the acid diffuses into the cubes over time. - Larger cubes show slower diffusion due to smaller surface area to volume ratio. - **Non-living system**: Place potassium permanganate crystals in water and observe the spread of color as the particles diffuse. **Osmosis Practical** - **Living system**: Use potato cylinders in different concentrations of sugar solution. Measure changes in mass: - **In dilute solution**: Water moves into the potato (osmosis); mass increases. - **In concentrated solution**: Water moves out; mass decreases. - **Non-living system**: Tie a partially permeable membrane (e.g., dialysis tubing) filled with a sugar solution. Place in water, observe water movement into the tubing.   **Key Summary** 1. **Diffusion** and **osmosis** are passive processes, while **active transport** requires energy. 2. Rates of movement depend on factors like surface area, temperature, concentration gradient, and diffusion distance. 2. Practical experiments demonstrate these processes using both living (e.g., potato cylinders) and non-living systems (e.g., agar cubes).   **Flowering Plants** **1. Photosynthesis** - **Definition**: Photosynthesis is the process by which plants convert light energy into chemical energy in the form of glucose. - **Importance**: Produces glucose for energy and growth; releases oxygen as a by-product. **Word Equation**: Carbon dioxide + Water → Glucose + Oxygen **Symbol Equation**: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂ **2. Factors Affecting the Rate of Photosynthesis** - **Carbon Dioxide Concentration**: Increasing CO₂ increases the rate until another factor becomes limiting. - **Light Intensity**: Higher light intensity boosts the rate but plateaus when saturation is reached. - **Temperature**: Optimal temperature increases enzyme activity; too high causes denaturation. **3. Leaf Structure and Adaptations** - **Upper Epidermis**: Transparent to allow light through. - **Palisade Mesophyll**: Contains many chloroplasts for photosynthesis. - **Spongy Mesophyll**: Air spaces for gas exchange. - **Stomata**: Openings for CO₂ entry and O₂ exit, controlled by guard cells. - **Vascular Bundle**: Xylem transports water; phloem transports nutrients. **4. Mineral Ions for Growth** - **Magnesium Ions**: Needed for chlorophyll synthesis. - **Nitrate Ions**: Required for amino acids and protein synthesis. **5. Photosynthesis Practical** - **Oxygen Evolution**: Use pondweed to measure bubbles of oxygen released. - **Starch Test**: Boil leaf, add iodine to show starch presence (blue-black color). - **Chlorophyll**: Use variegated leaves to prove its necessity. - **Light and CO₂**: Compare rates in light vs. darkness or with and without sodium bicarbonate (CO₂ source).   **Humans** **1. Balanced Diet** - **Components**: - **Carbohydrates**: Energy source. - **Proteins**: Growth and repair. - **Lipids**: Energy storage and insulation. - **Vitamins**: - Vitamin A: Vision and skin health. - Vitamin C: Healthy skin and gums. - Vitamin D: Calcium absorption for strong bones. - **Minerals**: - Calcium: Bone and teeth strength. - Iron: Hemoglobin formation. - **Water**: Maintains hydration and metabolic reactions. - **Dietary Fibre**: Prevents constipation.   **2. Energy Requirements** - **Vary Based On**: - **Activity Levels**: Active individuals require more energy. - **Age**: Younger individuals need energy for growth. - **Pregnancy**: Additional energy is required for the baby's development.   **3. Structure and Function of the Human Alimentary Canal** 1. **Mouth**: Mechanical digestion; salivary amylase begins carbohydrate digestion. 1. **Oesophagus**: Moves food to stomach via peristalsis. 2. **Stomach**: Acidic environment; protease enzymes digest proteins. 3. **Small Intestine (Duodenum & Ileum)**: - **Duodenum: Enzymatic digestion continues.** - **Ileum: Absorbs nutrients via villi.** 4. **Large Intestine**: Water absorption. 5. **Rectum**: Stores feces. 6. **Pancreas**: Secretes digestive enzymes and bicarbonate.   **4. Peristalsis** - **Definition**: Wave-like muscle contractions that move food along the gut.   **5. Digestive Enzymes** - **Amylase/Maltase**: Starch → Glucose. - **Proteases**: Proteins → Amino acids. - **Lipases**: Lipids → Fatty acids + Glycerol.   **6. Bile** - **Production**: By the liver. - **Storage**: In the gall bladder. - **Functions**: - Neutralises stomach acid (alkaline pH). - Emulsifies lipids, increasing surface area for lipase action.   **7. Small Intestine Adaptations** - **Villus Structure**: - **Large Surface Area**: Due to villi and microvilli. - **Thin Wall**: For faster diffusion of nutrients. - **Capillaries**: Transport absorbed glucose and amino acids. - **Lacteals**: Absorb fatty acids and glycerol.   **Key Takeaways** - Photosynthesis is vital for energy production in plants, influenced by external factors. - Balanced diets and proper digestion/absorption processes are essential for human health. - Enzymes and bile play crucial roles in chemical digestion, while villi maximize nutrient absorption. **1. Respiration and ATP Production** - **Definition of Respiration**: A chemical process that releases energy from glucose to produce ATP. - **ATP (Adenosine Triphosphate)**: - Energy currency of cells. - Provides energy for processes like active transport, muscle contraction, and cell division. **3. Aerobic Respiration** **Word Equation**: Glucose + Oxygen → Carbon dioxide + Water + Energy **Balanced Chemical Equation**: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + Energy (ATP)   **4. Anaerobic Respiration** **In Animals** - **Word Equation**:\ Glucose → Lactic acid + Energy - Occurs during vigorous exercise when oxygen is scarce. - Causes muscle fatigue due to lactic acid build-up. **In Plants and Yeast** - **Word Equation**:\ Glucose → Ethanol + Carbon dioxide + Energy - Used in fermentation (e.g., production of bread and alcohol).   **5. Practical: Investigating Respiration in Seeds or Other Organisms** **Measuring Carbon Dioxide Evolution** - **Apparatus**: Sealed container with respiring seeds or organisms, limewater, or hydrogen carbonate indicator. - **Observation**: - Limewater turns cloudy in presence of CO₂. - Hydrogen carbonate indicator changes from red to yellow. **Measuring Heat Production** - **Apparatus**: Two thermos flasks, one with germinating seeds and the other with boiled (dead) seeds. - **Observation**: The flask with germinating seeds shows an increase in temperature, indicating heat release.   **Key Takeaways** - Respiration releases energy stored in glucose to produce ATP. - Aerobic respiration is more efficient than anaerobic, producing more ATP. - Anaerobic respiration occurs in the absence of oxygen, producing different by-products in animals and plants. - Practical investigations demonstrate CO₂ and heat as evidence of respiration. **1. Structure of the Thorax** - **Key Components**: - **Ribs**: Protect the lungs and heart. - **Intercostal Muscles**: Found between the ribs; aid in ventilation by moving the ribcage. - **Diaphragm**: A dome-shaped muscle beneath the lungs; contracts and relaxes during breathing. - **Trachea**: Windpipe; reinforced with cartilage to keep it open. - **Bronchi**: Two branches of the trachea that lead to each lung. - **Bronchioles**: Smaller branches of the bronchi inside the lungs. - **Alveoli**: Tiny air sacs where gas exchange occurs. - **Pleural Membranes**: Surround the lungs, reducing friction during breathing.  **3. Adaptations of Alveoli for Gas Exchange** - **Large Surface Area**: Maximizes gas exchange. - **Thin Walls**: One-cell thick for short diffusion distance. - **Rich Blood Supply**: Dense capillary network maintains concentration gradients. - **Moist Lining**: Gases dissolve before diffusion.   **4. Biological Consequences of Smoking** **Lungs:** - **Tar**: Damages cilia in the trachea and bronchi, leading to mucus build-up and infections (e.g., bronchitis). - **Emphysema**: Alveoli walls break down, reducing surface area for gas exchange, causing breathlessness. **Circulatory System:** - **Nicotine**: Increases heart rate and blood pressure. - **Carbon Monoxide**: Reduces oxygen transport by binding to haemoglobin. - **Coronary Heart Disease**: Fatty deposits form in arteries, reducing blood flow to the heart, leading to heart attacks.   **5. Practical: Investigating Breathing in Humans** **Release of Carbon Dioxide** - **Apparatus**: Test tubes with limewater or hydrogen carbonate indicator. - **Observation**: - Exhaled air turns limewater cloudy or changes indicator from red to yellow, indicating CO₂ presence. **Effect of Exercise on Breathing** - **Method**: Measure breathing rate before and after exercise. - **Observation**: - Breathing rate increases after exercise to meet the higher oxygen demand and remove excess CO₂.   **Key Takeaways** - The thorax is structured for efficient ventilation and gas exchange. - Alveoli are adapted for diffusion of oxygen and carbon dioxide. - Smoking damages the respiratory and circulatory systems. - Breathing experiments show CO₂ production and the impact of exercise on breathing rates. **1. Diffusion in Unicellular Organisms** - **Why Simple, Unicellular Organisms Rely on Diffusion**: - **Small Size**: Unicellular organisms have a large surface area to volume ratio, which allows diffusion to efficiently meet their needs for gas exchange, nutrients, and waste removal. - **Diffusion**: Substances can move directly through the cell membrane (e.g., oxygen, carbon dioxide, and nutrients) by diffusion. There's no need for complex transport systems due to the small size and short distances involved.   **2. Need for a Transport System in Multicellular Organisms** - **Reason for Transport Systems**: - **Large Size**: Multicellular organisms have a smaller surface area to volume ratio. Diffusion is too slow over long distances to supply nutrients and remove waste from every cell. - **Specialized Cells**: Transport systems allow cells to be specialized and function efficiently without needing to be directly exposed to the environment. - **Transport of Materials**: A transport system is essential to move materials such as oxygen, nutrients, and waste products throughout the organism.   **3. Transport in Flowering Plants** **Phloem** - **Role**: - Transports **sucrose** (a type of sugar) and **amino acids** from the **leaves** (where they are made) to other parts of the plant (e.g., roots, stems, flowers). This process is known as **translocation**. - Phloem consists of **sieve tubes** (which carry the substances), **companion cells** (that help load/unload materials), and **phloem fibers** (providing structural support). **Xylem** - **Role**: - Transports **water** and **mineral ions** (e.g., magnesium, nitrate) from the **roots** to the rest of the plant, including the leaves where they are used for photosynthesis. - Xylem is made of **dead cells** that form long tubes, and it operates through **transpiration**, driven by water evaporation from the leaves. - **Xylem vessels** have thick, lignified cell walls to withstand the pressure of water moving upwards.   **4. Transport in Humans** **Blood Composition** - **Red Blood Cells (RBCs)**: - **Structure**: **Biconcave shape**, which increases surface area for gas exchange, **no nucleus** to maximize space for **haemoglobin**, which binds oxygen. - **Role**: Transport oxygen from the lungs to tissues and carbon dioxide from tissues to the lungs. - **White Blood Cells (WBCs)**: - **Structure**: Have a **nucleus**, and are larger than RBCs. They have the ability to change shape. - **Role**: Part of the immune system; involved in **phagocytosis** (engulfing pathogens) and producing **antibodies** to fight infections. - **Platelets**: - **Structure**: Small cell fragments with no nucleus. - **Role**: Involved in blood clotting, which prevents excessive blood loss from wounds. - **Plasma**: - **Structure**: A yellowish liquid that makes up about 55% of blood. - **Role**: Transports **carbon dioxide**, **digested food**, **urea**, **hormones**, and **heat energy** around the body.   **The Immune System Response** - **Phagocytes**: - Engulf pathogens (bacteria, viruses) through **phagocytosis**. The pathogen is enclosed in a vacuole and then digested. - **Lymphocytes**: - Release **antibodies** specific to pathogens, which helps to neutralize or destroy the pathogen. Lymphocytes can also release **antitoxins** to neutralize toxins released by pathogens.   **5. The Heart and Circulatory System** **Structure and Function of the Heart** - **Structure**: - The heart has **four chambers**: - **Right atrium** and **left atrium**: Receive blood. - **Right ventricle** and **left ventricle**: Pump blood to the lungs and the body, respectively. - **Valves**: Ensure one-way flow of blood (e.g., **bicuspid** valve, **tricuspid** valve, **semilunar** valves). - The **left ventricle** has the thickest wall, as it pumps blood at high pressure to the body. **Heart Rate Changes** - **During Exercise**: - The **heart rate** increases to supply more oxygen to muscles. - **Effect of Adrenaline**: - When released (e.g., during stress or exercise), **adrenaline** increases the heart rate and strength of contractions to ensure sufficient blood flow.   **6. Risk Factors for Coronary Heart Disease (CHD)** - **Factors**: - **Smoking**: Increases the risk of plaque build-up in arteries, causing blockages. - **High Cholesterol**: Leads to the accumulation of fatty deposits in arteries. - **High Blood Pressure**: Damages the blood vessel walls, increasing the risk of heart disease. - **Lack of Exercise**: Contributes to poor cardiovascular health. - **Poor Diet**: High-fat, high-sugar diets can increase the risk of obesity, high blood pressure, and cholesterol.   **7. Structure and Function of Blood Vessels** **Arteries** - **Structure**: Thick muscular walls to withstand high pressure. **Narrow lumen**. - **Function**: Carry oxygenated blood away from the heart (except pulmonary artery). **Veins** - **Structure**: Thinner walls, **larger lumen**, and have **valves** to prevent backflow. - **Function**: Carry deoxygenated blood towards the heart (except pulmonary veins). **Capillaries** - **Structure**: Very thin walls (one cell thick) to allow diffusion of gases and nutrients. - **Function**: Link arteries and veins; allow gas exchange and nutrient and waste product exchange with cells.   **8. The Circulatory System** - **System**: - Blood circulates through a **double circulatory system**: - **Pulmonary circulation**: Blood from the heart to the lungs and back. - **Systemic circulation**: Blood from the heart to the body and back. - **Blood Vessels**: - **Aorta**: Carries oxygenated blood from the heart to the body. - **Vena Cava**: Carries deoxygenated blood from the body back to the heart. - **Pulmonary Artery**: Carries deoxygenated blood from the heart to the lungs. - **Pulmonary Vein**: Carries oxygenated blood from the lungs to the heart.   **Key Takeaways** - Simple unicellular organisms rely on diffusion, but multicellular organisms need transport systems for efficient movement of substances. - The **phloem** and **xylem** in plants are crucial for transporting nutrients, water, and sugars. - In humans, blood plays a key role in transporting gases, nutrients, and waste, with specialized cells like **red blood cells** and **white blood cells**. - The heart pumps blood throughout the body, and factors like **exercise**, **adrenaline**, and **risk factors** influence heart function. - Blood vessels like **arteries**, **veins**, and **capillaries** have specialized structures suited to their functions. *\>* **1. Excretion in Flowering Plants** **Gas Exchange and the Origin of Carbon Dioxide and Oxygen** - **Origin of Carbon Dioxide**: - Carbon dioxide is produced as a **waste product** of **respiration** in plants. During **aerobic respiration**, plants break down glucose (from photosynthesis) to release energy, which results in the production of carbon dioxide. - This **carbon dioxide** is transported to the leaf and diffuses out of the leaf via the **stomata**. - **Origin of Oxygen**: - Oxygen is a **by-product** of **photosynthesis**. During photosynthesis, plants take in **carbon dioxide** and **water**, using **light energy** to produce **glucose** and **oxygen**. The oxygen is released as a waste product. - The oxygen diffuses out of the leaf through the **stomata** and into the surrounding air. - **Role of Stomata**: - **Stomata** are small pores on the surface of leaves and stems that control the **exchange of gases** (oxygen and carbon dioxide) and the **loss of water vapor** in a process called **transpiration**. - **Guard cells** control the opening and closing of the stomata, regulating the balance between gas exchange and water conservation.   **2. Excretion in Humans** **Organs of Excretion** The human body has several organs that are responsible for the removal of waste products from metabolism. These include: - **Lungs**: - **Excretory Product**: **Carbon dioxide** (CO₂) and **water vapor**. - **Excretion Process**: - Carbon dioxide is produced as a waste product of **cellular respiration**. - The carbon dioxide is transported in the blood to the lungs, where it diffuses from the bloodstream into the alveoli and is exhaled out of the body. - Water vapor is also excreted as part of the respiratory process (from the moist surfaces in the lungs). - **Kidneys**: - **Excretory Products**: **Urea**, **excess water**, and **ions** (e.g., sodium, potassium, chloride). - **Excretion Process**: - The kidneys filter the blood, removing waste products such as urea, which is produced when proteins are broken down in the liver. - The kidneys regulate the balance of water and salts (ions) in the body through **ultrafiltration** and **reabsorption**. - The filtered waste, along with excess water, forms **urine**, which is excreted via the **ureters**, stored in the **bladder**, and eventually excreted from the body through the **urethra**. - **Skin**: - **Excretory Products**: **Excess salts**, **urea**, and **water**. - **Excretion Process**: - The skin excretes waste products through **sweat**. - Sweat is produced by sweat glands and contains **water**, **salts**, and **urea**. - Sweat helps in regulating **body temperature** through **evaporation**, but it also plays a minor role in excretion of metabolic wastes.   **Key Takeaways:** - **Flowering Plants**: - **Carbon dioxide** is a waste product of **respiration**, and **oxygen** is a by-product of **photosynthesis**. Both gases are exchanged through the **stomata** on the leaves. - **Humans**: - **Lungs** excrete **carbon dioxide** and **water vapor**. - **Kidneys** excrete **urea**, **water**, and **ions** (through urine). - **Skin** excretes **water**, **salts**, and **urea** through sweat, helping with both excretion and temperature regulation. **1. Response to Environmental Changes** **2.80 How Organisms Respond to Changes in their Environment** - Organisms can detect and react to environmental changes to **survive** and maintain **homeostasis** (a stable internal environment). - Responses are made to **stimuli** (changes in the surroundings), and they involve the **nervous** or **hormonal** communication systems.   **2.81 Homeostasis** - **Homeostasis**: The maintenance of a **constant internal environment** despite external environmental changes. - **Examples of Homeostasis**: - **Body Temperature Regulation**: Keeping the body at a constant temperature (around 37°C) despite external temperature fluctuations. - **Body Water Content**: Regulation of water balance to ensure cells are not dehydrated or over-hydrated.   **2.82 Coordinated Response** - A **coordinated response** involves three key components: 1. **Stimulus**: A change in the environment that the organism detects. 2. **Receptor**: Specialized cells that detect the stimulus (e.g., sensory cells in the skin or eyes). 3. **Effector**: Muscles or glands that carry out the response to the stimulus (e.g., sweating, shivering).   **2.83-2.85 Plant Responses to Stimuli** **2.83 Plant Response to Stimuli** - Plants respond to environmental stimuli such as light, gravity, and touch to grow towards or away from these stimuli. These responses are **important for survival and growth**. **2.84 Geotropic and Phototropic Responses** - **Geotropism (Gravitropism)**: The growth response to gravity. - **Roots** show **positive geotropism** (grow towards gravity) to anchor the plant and absorb water and nutrients. - **Stems** show **negative geotropism** (grow away from gravity) to maximize exposure to light. - **Phototropism**: The growth response to light. - **Stems** exhibit **positive phototropism** (grow towards light) to capture light for photosynthesis. - **Roots** typically show **negative phototropism** (grow away from light) to remain underground for stability and water absorption. **2.85 Role of Auxin in Phototropism** - **Auxins** are plant hormones that control growth. - In **phototropism**, auxins accumulate on the **shaded side** of the stem, causing the cells on that side to elongate more than those on the lit side, making the stem **bend towards the light**. - This allows the plant to maximize light absorption for photosynthesis.   **2.86 Nervous and Hormonal Communication in Humans** **Nervous Communication:** - **Nervous system** controls **rapid responses** to stimuli. - Involves **electrical impulses** transmitted along neurons. - Fast, short-lived responses. **Hormonal Communication:** - **Endocrine system** controls **slower, long-lasting responses**. - Hormones (chemical messengers) are produced by **glands** and transported via the bloodstream to target organs. - Slow, long-lasting effects.   **2.87-2.90 The Nervous System and Reflexes** **2.87 Central Nervous System (CNS)** - The **CNS** consists of the **brain** and **spinal cord**, which process information and coordinate responses. - The CNS is linked to **sense organs** (eyes, ears, skin) by **nerves**, which carry electrical impulses to and from the brain. **2.88 Receptor Stimulation and Impulse Transmission** - Receptors in **sense organs** detect stimuli and send electrical impulses through nerves to the CNS, which processes the information and coordinates a response. **2.89 Neurotransmitters at Synapses** - **Synapses** are junctions between two neurons. - **Neurotransmitters** are chemicals that transmit signals across synapses from one neuron to another. **2.90 Reflex Arc** - A **reflex arc** is a rapid, involuntary response to a stimulus. - **Example**: Withdrawing a finger from a hot object. - **Stimulus**: Heat from the hot object. - **Receptor**: Sensory receptor in the skin detects the heat. - **Neuron**: Impulse sent to the spinal cord. - **Effector**: Motor neuron activates muscles to pull the finger away.   **2.91 Structure and Function of the Eye** - The eye is a **receptor** for **light stimuli**. It detects light and forms visual images for interpretation by the brain. **Focusing on Near and Distant Objects:** - **Accommodation** is the process by which the eye adjusts the shape of the **lens** to focus on objects at different distances. - For **near objects**, the lens becomes **more curved**. - For **distant objects**, the lens becomes **flatter**. **Response to Light Intensity:** - **Pupillary reflex**: The **pupil** constricts in bright light (to protect the retina from damage) and dilates in dim light (to allow more light in).   **2.92-2.94 Temperature Regulation and Hormonal Control** **2.92 Skin in Temperature Regulation** - **Skin** helps to **regulate body temperature** through processes such as: - **Sweating**: Sweat evaporates, cooling the body. - **Vasoconstriction**: Blood vessels constrict to conserve heat. - **Vasodilation**: Blood vessels dilate to release heat. **2.93 Hormones Involved in Homeostasis** - **Adrenaline**: Released from the adrenal glands in response to stress or excitement. It increases heart rate and prepares the body for a \"fight or flight\" response. - **Insulin**: Produced by the pancreas, it lowers blood glucose levels by allowing cells to absorb glucose. - **Testosterone**: Male sex hormone responsible for the development of male characteristics. - **Progesterone and Oestrogen**: Female sex hormones involved in the menstrual cycle and pregnancy.   **Key Takeaways:** - **Homeostasis** involves regulating internal conditions, such as temperature and water balance, to maintain stability in response to environmental changes. - The **nervous system** provides **rapid responses**, while the **endocrine system** regulates **longer-term processes** through hormones. - **Reflex arcs** provide **rapid, automatic responses** to protect the body from harm (e.g., withdrawing a finger from a hot surface). - **Auxin** regulates **phototropism** in plants, allowing them to grow towards light for photosynthesis. - **The eye** focuses light and adjusts to changes in light intensity for clear vision. - **Temperature regulation** involves mechanisms like sweating, vasoconstriction, and vasodilation to maintain the body at an optimal temperature. **3.1 Sexual vs Asexual Reproduction** **Sexual Reproduction:** - Involves the fusion of **two gametes** (male and female). - Produces **genetically diverse offspring**. - **Gametes** are specialized reproductive cells: sperm (male) and egg (female). - Involves **fertilisation** to form a **zygote** that develops into an embryo. - Examples: Humans, animals, most plants. **Asexual Reproduction:** - Involves **one parent** and no fusion of gametes. - Offspring are **genetically identical** to the parent (clones). - **No gametes** involved. - Examples: Bacteria, some plants (e.g., strawberries via runners).   **3.2 Fertilisation and Embryo Development** - **Fertilisation**: The fusion of a **male gamete** (sperm) and a **female gamete** (egg). - This forms a **zygote**, which contains the combined genetic material from both parents. - The zygote undergoes **cell division** (mitosis) to form an **embryo**. - The embryo develops and eventually grows into a fully formed individual.   **Flowering Plants: Pollination and Fertilisation** **3.3 Insect-pollinated vs Wind-pollinated Flowers** - **Insect-pollinated flowers**: - **Brightly coloured petals** to attract insects. - **Scented flowers** and **nectar** to reward insects for pollination. - **Sticky pollen** to attach to insects. - **Stigma** positioned to receive pollen from insects as they move from flower to flower. - Example: Peas, sunflowers. - **Wind-pollinated flowers**: - **Small, green, often inconspicuous flowers** (no need to attract insects). - **Light, non-sticky pollen** that is easily carried by the wind. - **Long styles** and **exposed anthers** to release pollen into the air. - **Feathery stigmas** to catch the windborne pollen. - Example: Grass, trees like oak and birch. **3.4 Pollen Tube Growth and Fertilisation** - After **pollination**, the **pollen grain** lands on the **stigma** and germinates. - The **pollen tube** grows down the style, reaching the ovule in the **ovary**. - The male gamete (sperm cell) travels through the pollen tube and fuses with the female gamete (egg cell) in the **ovule** to form a **zygote**. - This leads to the formation of **seeds** and eventually **fruit** (as the ovary develops into fruit around the seed).   **3.5 Practical: Conditions for Seed Germination** - **Conditions needed for seed germination**: 1. **Water**: Activates enzymes that start metabolic reactions. 2. **Oxygen**: Required for respiration to provide energy for growth. 3. **Temperature**: A suitable temperature range is needed for enzymes to work efficiently. 4. **Light**: Some seeds need light to germinate, while others prefer darkness.   **3.6 Seed Germination and Food Reserves** - During **germination**, the seed absorbs water, activating enzymes that convert stored food reserves into energy. - **Cotyledons** (seed leaves) initially provide nutrients to the young plant. - Once the seedling develops **leaves**, it can start **photosynthesis** to produce its own food.   **3.7 Asexual Reproduction in Plants** **Natural Asexual Reproduction:** - **Runners**: Horizontal stems (e.g., strawberries) that grow along the ground and produce new plants at nodes. - **Buds**: Some plants can produce new individuals from **buds** (e.g., potato tubers). **Artificial Asexual Reproduction:** - **Cuttings**: A piece of a plant is cut and planted to grow into a new plant (e.g., rose cuttings). - **Grafting**: Joining two parts of plants together so that they grow as one.   **Humans: Reproductive Systems and Development** **3.8 Male and Female Reproductive Systems** - **Male reproductive system**: - **Testes**: Produce sperm and the hormone **testosterone**. - **Penis**: Used to introduce sperm into the female reproductive system. - **Scrotum**: Holds the testes at a cooler temperature than the body to produce sperm. - **Female reproductive system**: - **Ovaries**: Produce eggs (ova) and hormones **oestrogen** and **progesterone**. - **Fallopian tubes**: Carry eggs from the ovaries to the uterus; fertilisation usually occurs here. - **Uterus**: Where the embryo develops. - **Vagina**: Passage for childbirth and sperm entry.   **3.9 Roles of Oestrogen and Progesterone in the Menstrual Cycle** - **Oestrogen**: - Stimulates the **thickening of the uterine lining**. - Stimulates **LH (luteinizing hormone)** secretion, leading to ovulation. - **Progesterone**: - Maintains the **uterine lining** after ovulation. - Inhibits the production of **FSH** (follicle-stimulating hormone) to prevent further ovulation during pregnancy.   **3.11 Role of the Placenta in Nutrition** - The **placenta** is an organ that forms in the uterus during pregnancy. - It provides **nutrients** (e.g., glucose, amino acids) and **oxygen** to the developing embryo. - It also removes **waste products** (e.g., carbon dioxide, urea) from the embryo. - **Maternal and fetal blood** flow close together in the placenta, but they **do not mix**.   **3.12 Protection of the Developing Embryo by Amniotic Fluid** - **Amniotic fluid** surrounds the developing embryo in the **amniotic sac**. - It **cushions** the embryo and protects it from mechanical shock. - It **prevents desiccation** (drying out) and provides a stable **temperature**. - It allows **freedom of movement** for the developing fetus.   **3.13 Hormones and Secondary Sexual Characteristics** - **Oestrogen** (in females): - Responsible for the development of **female secondary sexual characteristics**, such as breast development and widening of hips. - **Testosterone** (in males): - Responsible for the development of **male secondary sexual characteristics**, such as facial hair, deepening of the voice, and muscle development.   **Key Takeaways:** - **Sexual reproduction** involves the fusion of male and female gametes to produce genetically diverse offspring, while **asexual reproduction** results in offspring that are genetically identical to the parent. - In plants, **pollination** and **fertilisation** lead to the formation of seeds and fruits, with **auxins** controlling plant responses like phototropism. - In humans, the **reproductive systems** are designed for the production of gametes and the growth of embryos, with hormones like **oestrogen** and **testosterone** regulating the development of secondary sexual characteristics. - The **placenta** provides nutrients and removes waste from the developing embryo, and **amniotic fluid** offers protection and supports growth. **3.14 Genome and Genes** - **Genome**: The entire set of **DNA** in an organism, which contains all the genetic information required for the growth, development, and functioning of that organism. - **Gene**: A specific segment of DNA located on **chromosomes** that codes for a particular protein. Genes determine inherited traits and can be expressed as physical characteristics.   **3.15 Nucleus, Chromosomes, and Genes** - **Nucleus**: A membrane-bound structure in eukaryotic cells that contains the **genetic material** (DNA). - **Chromosomes**: Long, coiled structures made of **DNA and proteins**. Humans have 46 chromosomes (23 pairs) in each cell. - **Genes**: Located on chromosomes, each gene carries instructions for making proteins that control various traits and functions of the organism.   **3.19 Alleles and Inherited Characteristics** - **Alleles**: Alternative forms of a gene that can exist in different versions. Alleles determine the variations of inherited characteristics (e.g., eye colour, hair texture). - Example: A gene for **flower colour** might have alleles for **red** or **white** flowers.   **3.20 Genetic Terms: Dominant, Recessive, Homozygous, Heterozygous, Phenotype, Genotype** - **Dominant allele**: An allele that **expresses** its trait even if only one copy is present (e.g., \"A\" for brown eyes). - **Recessive allele**: An allele that only **expresses** its trait if two copies are present (e.g., \"a\" for blue eyes). - **Homozygous**: When an individual has **two identical alleles** for a gene (e.g., \"AA\" or \"aa\"). - **Heterozygous**: When an individual has **two different alleles** for a gene (e.g., \"Aa\"). - **Phenotype**: The **physical expression** or appearance of a trait in an organism (e.g., brown eyes). - **Genotype**: The **genetic makeup** of an organism, describing the alleles an individual has (e.g., \"AA\", \"Aa\", or \"aa\").   **3.22 Polygenic Inheritance** - **Polygenic inheritance**: Many traits are controlled by **multiple genes**, not just one. This results in continuous variation rather than discrete categories. - Example: **Height**, **skin colour**, and **intelligence** are influenced by several genes. - These traits typically show a **bell-shaped curve** in populations.   **3.24 Interpreting Family Pedigrees** - A **pedigree** is a family tree that shows the inheritance pattern of a particular trait over generations. - **Shaded circle/square**: Individuals with the trait. - **Unshaded circle/square**: Individuals without the trait. - **Lines** represent family relationships (parents, siblings). - Pedigrees help to track dominant or recessive inheritance patterns.   **3.25 Probability of Outcomes from Monohybrid Crosses** - The **probability** of offspring inheriting a specific combination of alleles can be predicted using **genetic diagrams** or **Punnett squares**. - For example, in a cross between **heterozygous (Pp)** parents for pea plant colour: - **50% chance** of offspring being heterozygous (Pp). - **25% chance** of offspring being homozygous dominant (PP). - **25% chance** of offspring being homozygous recessive (pp).   **3.26 Sex Chromosomes and Sex Determination** - **Sex chromosomes**: These determine the sex of an individual. - **Females** have **two X chromosomes (XX)**. - **Males** have one X and one Y chromosome (XY). - **Sex determination**: During fertilisation, the egg (X) can be fertilised by either an X sperm (female) or a Y sperm (male). - Female: **XX** → female offspring. - Male: **XY** → male offspring.    **3.28 Mitosis and Cell Division** - **Mitosis**: The process by which a **diploid cell** divides to produce **two genetically identical daughter cells**. - Occurs during **growth**, **repair**, and **asexual reproduction**. - **Diploid cells** have two complete sets of chromosomes (46 in humans). - **Stages of mitosis**: - **Prophase**: Chromosomes condense and become visible. - **Metaphase**: Chromosomes align at the centre. - **Anaphase**: Chromatids are pulled apart. - **Telophase**: Nuclear membranes reform. - **Cytokinesis**: The cytoplasm divides, resulting in two daughter cells.   **3.29 Purpose of Mitosis** - Mitosis ensures that organisms grow and repair damaged cells. - **Cloning**: Identical offspring produced through asexual reproduction, such as in plants (e.g., strawberries through runners).   **3.30 Meiosis and Genetic Variation** - **Meiosis**: A type of cell division that produces **haploid gametes** (sperm or eggs), each containing half the number of chromosomes (23 in humans). - It involves two rounds of division, resulting in four genetically **unique** haploid cells. - **Meiosis** leads to **genetic variation** due to **crossing over** and **independent assortment** of chromosomes.   **3.31 Genetic Variation through Fertilisation** - **Random fertilisation**: The combination of random sperm and egg cells leads to genetic variation in offspring. This variation is important for natural selection.   **3.32 Diploid and Haploid Numbers in Humans** - **Diploid number**: The total number of chromosomes in a body cell, which is **46** in humans. - **Haploid number**: The number of chromosomes in a gamete (egg or sperm), which is **23** in humans.   **3.33 Genetic, Environmental, and Combined Variation** - **Genetic variation**: Differences in traits due to differences in genes (inherited from parents). - Example: **Eye colour**, **blood type**. - **Environmental variation**: Differences in traits caused by environmental factors. - Example: **Height**, **weight**, **skin tone** can be influenced by diet and lifestyle. - **Combined variation**: Many traits are influenced by both genetic and environmental factors.   **3.34 Mutation** - **Mutation**: A random change in the genetic material (DNA) that can be inherited. - Mutations can result in new alleles and contribute to **genetic variation**. - Mutations are rare and can be beneficial, neutral, or harmful.   **3.38 Darwin's Theory of Evolution by Natural Selection** - **Natural selection**: Organisms with advantageous traits are more likely to survive and reproduce, passing those traits on to the next generation. - Over time, these traits become more common in the population. - **Survival of the fittest**: Individuals best suited to their environment are more likely to survive and reproduce.   **3.39 Antibiotic Resistance in Bacteria** - **Antibiotic resistance**: When bacteria evolve to become resistant to antibiotics, making infections harder to treat. - Resistance can occur due to **mutations** in bacterial DNA. - Overuse or misuse of antibiotics leads to the survival of resistant bacteria, which then reproduce, passing on the resistance.   **Key Takeaways:** - **Sexual reproduction** involves the fusion of gametes and results in genetic variation, while **asexual reproduction** produces genetically identical offspring. - The **genome** contains all the genetic material in an organism, and **genes** control inherited traits. - **Meiosis** and **random fertilisation** contribute to genetic variation. - **Darwin's theory of evolution** explains how natural selection drives changes in populations over time. - **Mutation** is a key mechanism of evolution, providing new genetic variations that can be beneficial or harmful. **4.1 Key Ecological Terms** - **Population**: A group of individuals of the **same species** living in the **same area** at the same time. For example, all the oak trees in a forest form a population. - **Community**: A group of different species living in the **same area** at the same time. For example, the community in a pond may include plants, fish, amphibians, and microorganisms. - **Habitat**: The physical environment in which an organism lives. This includes both **abiotic** (non-living) factors, like temperature and soil, and **biotic** (living) factors, such as other organisms. For example, the habitat of a fish could be a river or lake. - **Ecosystem**: A biological community of interacting organisms and their physical environment. An ecosystem includes both the **biotic** and **abiotic** components. For example, a forest ecosystem includes trees, animals, microorganisms, water, soil, and air.   **4.2 Practical: Investigating Population Size with Quadrats** - A **quadrant** is a square frame used to estimate the **population size** of an organism in a particular area. **Steps to use quadrats to measure population size**: 1. **Select areas for sampling**: Choose a location, and randomly place quadrats to ensure unbiased results. 1. **Count organisms**: In each quadrat, count the number of individuals of the species you are investigating (e.g., number of dandelions). 2. **Calculate population density**: To estimate the total population, calculate the average number of individuals per quadrat and multiply by the total area of the habitat (in quadrats). **Example**: If you sample five quadrats in a 10m² area and find 4 dandelions in each quadrat on average, you would estimate: - Population size = average number per quadrat × total area / area of one quadrat.   **4.5 Abiotic and Biotic Factors Affecting Population Size and Distribution** - **Abiotic factors**: **Non-living** components that affect where and how organisms live. These include: - **Temperature**: Can determine where organisms can survive. For example, certain plants only grow in specific temperature ranges. - **Light**: Light intensity can affect the rate of photosynthesis in plants, influencing plant growth and distribution. - **Water availability**: Organisms in desert areas are adapted to survive with little water, while those in wetlands are adapted to a water-rich environment. - **Soil pH and minerals**: Plants grow best in certain soil types. For example, acid-loving plants thrive in acidic soil. - **Oxygen and carbon dioxide**: Availability of gases, especially for aquatic organisms, can influence distribution. - **Biotic factors**: **Living** components that affect the population and distribution of organisms. These include: - **Predation**: The presence of predators can reduce the population size of prey species. - **Competition**: Organisms compete for limited resources such as food, space, and mates. For example, plants in a dense forest compete for light. - **Disease**: Disease outbreaks can reduce the population size of organisms. - **Mutualism**: Symbiotic relationships where both species benefit (e.g., bees pollinating flowers), which can enhance the survival and distribution of both species. - **Herbivory**: Grazing animals can affect the distribution of plants by feeding on them. **Example**: - If the temperature drops significantly in an area, it may limit the growth of certain species, leading to a decline in their population. Similarly, a disease might reduce the population of a species, impacting the entire community and ecosystem.   **Key Takeaways:** - **Population** refers to individuals of the same species in an area, while a **community** includes different species. - **Habitat** is the environment where an organism lives, and an **ecosystem** includes both living and non-living components. - **Quadrats** are used to estimate population size by sampling a specific area. - **Abiotic factors** (temperature, water, light) and **biotic factors** (competition, predation) both influence the distribution and population size of organisms.   **4.6 Trophic Levels in an Ecosystem** In an ecosystem, organisms are classified into **trophic levels** based on their position in the food chain. These include: 1. **Producers**: These are organisms that can produce their own food through **photosynthesis**. They form the base of the food chain. Examples include **plants** and **algae**. 1. **Primary Consumers**: These organisms are **herbivores** that eat producers. For example, **cows** (which eat grass) or **rabbits** (which eat plants). 2. **Secondary Consumers**: These are **carnivores** that feed on primary consumers. An example would be a **fox** eating a rabbit. 3. **Tertiary Consumers**: These are predators that feed on secondary consumers. For instance, a **hawk** that preys on a fox. 4. **Decomposers**: These organisms break down dead matter and waste products, recycling nutrients back into the ecosystem. Examples include **fungi** and **bacteria**.   **4.7 Food Chains, Food Webs, and Ecological Pyramids** - **Food Chain**: A food chain shows a simple, linear sequence of who eats whom in an ecosystem. It begins with a producer and follows the flow of energy and nutrients through consumers.\ **Example**:\ Grass → Rabbit → Fox → Hawk - **Food Web**: A food web is a more complex and realistic representation of feeding relationships in an ecosystem, showing how many food chains are interconnected. It includes multiple producers, consumers, and decomposers.\ **Example**: In a forest ecosystem, a rabbit may be eaten by both a fox and an owl, and various plants might serve as food for many herbivores. - **Pyramids of Number**: A pyramid of numbers shows the number of organisms at each trophic level. Usually, the number of producers is greater than primary consumers, which in turn is greater than secondary consumers, and so on. - **Limitation**: It does not consider the size of organisms; a large producer may be counted as one, which might not reflect the true energy available. - **Pyramids of Biomass**: A pyramid of biomass represents the **total mass of living material** at each trophic level. This is more accurate than the pyramid of numbers as it takes into account the size and weight of the organisms at each level. - **Limitation**: Biomass can be affected by the moisture content of organisms. - **Pyramids of Energy Transfer**: This pyramid shows the amount of **energy** available at each trophic level. The energy decreases as you move up the pyramid because energy is lost at each trophic level.   **4.8 Transfer of Substances and Energy Along a Food Chain** - **Energy Transfer**: Energy flows through the food chain from producers to consumers. **Sunlight** is captured by plants during photosynthesis, and energy is transferred to herbivores, then to carnivores, and so on. - **Producers** use sunlight to make **food** (glucose) through **photosynthesis**. - **Consumers** get their energy by eating other organisms. The energy is stored in their bodies, but not all of it is passed to the next trophic level. - **Decomposers** break down dead organisms and waste, recycling nutrients back into the ecosystem. - **Substances**: The cycle of materials, such as water, carbon, nitrogen, and oxygen, moves through ecosystems. For example, carbon dioxide is taken up by plants, and animals then consume plants to get carbon-based molecules.   **4.9 Energy Transfer Efficiency** - **Energy Loss**: Only about **10% of the energy** from one trophic level is transferred to the next. The rest is lost through: - **Respiration**: Organisms use energy for movement, growth, and maintenance, which is lost as heat. - **Excretion**: Energy is lost in waste products (e.g., feces and urine). - **Not all parts of an organism are consumed** (e.g., bones, hair, or feathers), so some energy remains unavailable to the next consumer. - **Energy Efficiency**: The energy efficiency of transfer between trophic levels is generally low, and this limits the number of trophic levels in a food chain. Higher trophic levels contain fewer organisms as energy diminishes at each level.   **Key Points to Remember:** - **Trophic levels** include producers, primary consumers, secondary consumers, tertiary consumers, and decomposers. - **Food chains** are simple sequences of who eats whom, while **food webs** are more complex and interconnected. - **Pyramids of number**, **biomass**, and **energy transfer** show how the amount of organisms, their total biomass, and energy decrease as you move up trophic levels. - Only about **10% of energy** is transferred between trophic levels due to losses through respiration, excretion, and undigested parts. The **carbon cycle** is a process by which carbon atoms are recycled through various components of the Earth's ecosystem. This cycle involves several key stages where carbon is transferred between living organisms, the atmosphere, the oceans, and the Earth's surface. Below are the main stages of the carbon cycle:         **Key Points in the Carbon Cycle:** - **Photosynthesis**: Converts atmospheric CO₂ into organic carbon (glucose) in plants. - **Respiration**: Releases CO₂ back into the atmosphere from all living organisms. - **Decomposition**: Breaks down dead organisms, releasing CO₂ and methane into the atmosphere. - **Combustion**: Burns organic materials, releasing CO₂ into the atmosphere.   **Interactions in the Carbon Cycle:** - **Carbon sinks**: The oceans, forests, and soil act as **carbon sinks**, absorbing and storing carbon. Forests act as major carbon reservoirs because trees capture carbon in the form of glucose during photosynthesis. - **Fossil Fuels**: Over millions of years, dead plants and animals, if not decomposed, can become fossil fuels (coal, oil, and gas), which store carbon in the Earth\'s crust. When burned, these release large amounts of CO₂ back into the atmosphere, contributing to climate change.   **Human Impact on the Carbon Cycle:** - **Deforestation**: Removing trees reduces the amount of carbon absorbed from the atmosphere by photosynthesis, contributing to higher atmospheric CO₂ levels. - **Burning of Fossil Fuels**: The combustion of fossil fuels releases large amounts of stored carbon into the atmosphere, leading to an increase in the greenhouse effect and global warming.   **Summary of Carbon Cycle Stages:** 1. **Photosynthesis**: Plants absorb CO₂ and convert it into glucose. 1. **Respiration**: Living organisms release CO₂ back into the atmosphere. 2. **Decomposition**: Dead organisms are broken down, releasing CO₂ and methane. 3. **Combustion**: Burning organic material releases CO₂ into the atmosphere. The carbon cycle ensures that carbon is recycled and reused in ecosystems, but human activities are disrupting the balance, leading to increased levels of carbon dioxide and other greenhouse gases in the atmosphere.   These stages collectively maintain the balance of carbon in the environment, supporting life processes and contributing to climate regulation **4.12 Biological Consequences of Air Pollution by Sulfur Dioxide and Carbon Monoxide** **Sulfur Dioxide (SO₂):** - **Source**: Mainly produced by the burning of fossil fuels (coal, oil) in power stations, vehicles, and industrial processes. - **Effects on the environment**: - **Acid rain**: When sulfur dioxide mixes with water vapour in the atmosphere, it forms sulfuric acid, leading to acid rain. Acid rain damages aquatic ecosystems, soil quality, and plant life. - **Health effects**: Sulfur dioxide can cause respiratory problems, particularly for individuals with asthma or other lung diseases. It irritates the airways and exacerbates existing conditions. **Carbon Monoxide (CO):** - **Source**: Produced by incomplete combustion of fossil fuels in vehicles, industry, and biomass burning. - **Effects on the environment**: - **Air quality**: Carbon monoxide is a harmful air pollutant that reduces the oxygen-carrying capacity of the blood when inhaled. - **Health effects**: Inhalation of carbon monoxide can lead to dizziness, fatigue, headaches, and even death in high concentrations, as it binds to haemoglobin, reducing oxygen transport.   **4.13 Greenhouse Gases: Water Vapour, Carbon Dioxide, Nitrous Oxide, Methane, and CFCs** **Greenhouse Gases:** Greenhouse gases trap heat in the Earth\'s atmosphere, contributing to the **greenhouse effect**. These gases include: - **Water Vapour (H₂O)**: Natural greenhouse gas, which contributes significantly to the greenhouse effect. However, its concentration is largely controlled by temperature. - **Carbon Dioxide (CO₂)**: Produced by respiration, combustion of fossil fuels, deforestation, and other human activities. - **Nitrous Oxide (N₂O)**: Emitted from agricultural practices, the burning of fossil fuels, and some industrial processes. - **Methane (CH₄)**: Released by livestock (digestive processes), rice paddies, landfills, and the burning of fossil fuels. - **Chlorofluorocarbons (CFCs)**: Synthetic compounds used in refrigeration and air conditioning. They are potent greenhouse gases but are being phased out due to their role in ozone depletion. **Role of Greenhouse Gases:** - These gases trap heat in the Earth\'s atmosphere, warming the planet, a phenomenon known as the **greenhouse effect**.   **4.14 Human Activities Contributing to Greenhouse Gases** Human activities have significantly increased the concentration of greenhouse gases in the atmosphere, leading to an enhanced greenhouse effect. Key activities include: - **Burning Fossil Fuels**: Combustion of coal, oil, and natural gas for energy in power stations, industry, and transport releases large amounts of CO₂. - **Deforestation**: Reducing the number of trees that can absorb CO₂ from the atmosphere exacerbates the increase in CO₂ levels. - **Agriculture**: Livestock farming produces methane, and the use of nitrogen-based fertilisers increases nitrous oxide emissions. - **Industrial Processes**: Certain industrial processes, such as cement production and the use of CFCs, release greenhouse gases into the atmosphere.   **4.15 Enhanced Greenhouse Effect and Global Warming** **Enhanced Greenhouse Effect:** - The enhanced greenhouse effect occurs when human activities release large amounts of greenhouse gases, particularly CO₂, methane, and nitrous oxide, into the atmosphere. This causes more heat to be trapped, intensifying the natural greenhouse effect. **Consequences of Global Warming:** - **Rising Global Temperatures**: Average global temperatures increase, causing weather patterns to become more extreme. - **Melting Polar Ice Caps**: Higher temperatures cause polar ice caps and glaciers to melt, contributing to rising sea levels. - **Rising Sea Levels**: Melting ice and thermal expansion of water due to higher temperatures cause coastal flooding and habitat loss for humans and wildlife. - **Extreme Weather Events**: More frequent and severe storms, droughts, and heatwaves, impacting agriculture, water resources, and human settlements. - **Impact on Biodiversity**: Changing temperatures and ecosystems affect species distribution, threatening biodiversity and leading to species extinction.   **4.16 Biological Consequences of Water Pollution by Sewage** - **Source**: Sewage waste from homes, industries, and agriculture is released into rivers and oceans. - **Impact on aquatic ecosystems**: - **Eutrophication**: Sewage contains high levels of nutrients, particularly nitrogen and phosphorus. These nutrients promote excessive growth of algae, which depletes oxygen levels in the water, killing fish and other aquatic organisms. - **Pathogens**: Sewage contains harmful microorganisms such as bacteria, viruses, and parasites, which can spread diseases like cholera and typhoid, affecting human and animal health.   **4.17 Biological Consequences of Eutrophication Caused by Leached Minerals from Fertilisers** **Eutrophication Process:** - **Source**: The leaching of nitrogen and phosphorus compounds from agricultural fertilisers into water bodies. **Biological Effects:** - **Algal Bloom**: The excess nutrients in water promote rapid algae growth, forming an algal bloom. - **Depletion of Oxygen**: When the algae die and decompose, they consume large amounts of oxygen, leading to **hypoxic conditions** (low oxygen levels). This can result in fish kills and the collapse of aquatic ecosystems. - **Loss of Biodiversity**: The decreased oxygen levels and changes in nutrient availability can make it impossible for other species to survive, leading to a reduction in biodiversity.   **Summary of Key Points:** 1. **Air Pollution**: Sulfur dioxide and carbon monoxide can lead to respiratory issues and environmental damage (acid rain, poor air quality). 1. **Greenhouse Gases**: Water vapour, CO₂, nitrous oxide, methane, and CFCs are all greenhouse gases contributing to the greenhouse effect. 2. **Human Activities**: Human activities like burning fossil fuels, deforestation, and agriculture have increased greenhouse gas emissions, intensifying global warming. 3. **Global Warming**: Enhanced greenhouse effect leads to higher global temperatures, rising sea levels, and more extreme weather events. 4. **Water Pollution**: Sewage pollution leads to eutrophication and the spread of diseases, harming aquatic ecosystems and human health. 5. **Eutrophication**: Leaching of minerals from fertilisers into water bodies causes algal blooms, oxygen depletion, and loss of biodiversity. These pollution processes contribute to significant environmental and biological consequences that affect ecosystems and human societies. **Crop Plants** **5.1 Glasshouses and Polythene Tunnels** - **Glasshouses**: Enclosed structures with transparent walls that allow light to enter and provide controlled conditions. - **Polythene Tunnels**: Long, tunnel-shaped plastic covers used to protect crops from weather and pests. - **How they increase yield**: - Protect crops from extreme weather, pests, and diseases. - Maintain **optimum conditions** for growth, e.g., temperature, humidity, and light. - Enhance the growing season by enabling year-round cultivation.   **5.2 Effects of Increased Carbon Dioxide and Temperature on Yield** - **Increased Carbon Dioxide**: - Boosts the rate of **photosynthesis**, leading to faster growth and higher yields. - CO₂ levels can be increased artificially in glasshouses using burners. - **Increased Temperature**: - Maintains the optimum temperature for **enzyme activity**, speeding up photosynthesis and respiration. - Overheating is avoided by ventilation or shading. - Combining both factors maximizes crop production.   **5.3 Use of Fertilizers** - Fertilizers supply essential **nutrients** (e.g., nitrogen, phosphorus, potassium) to plants. - **Nitrogen**: Encourages leafy growth. - **Phosphorus**: Aids root development. - **Potassium**: Improves flower and fruit production. - Fertilizers replenish nutrients in the soil, prevent nutrient deficiencies, and boost crop yield.   **5.4 Pest Control** - **Reasons for Pest Control**: - Pests (e.g., insects, fungi, weeds) damage crops, reducing yield. - Control ensures healthy growth and prevents economic losses. **Advantages and Disadvantages**: 1. **Pesticides**: - **Advantages: Rapid, effective, kills specific pests.** - **Disadvantages: Can harm non-target species, develop resistance, and leave residues.** 1. **Biological Control**: - **Advantages: Eco-friendly, long-term, targets specific pests.** - **Disadvantages: Slower, may disrupt ecosystems, may fail to control pests completely.**   **Micro-organisms** **5.5 Yeast in Food Production** - Yeast is a **fungus** used in bread-making and brewing. - **Bread-making**: - Yeast undergoes **anaerobic respiration (fermentation)**, producing **CO₂** that makes the dough rise. - The ethanol produced evaporates during baking.   **5.6 Practical: Investigating Anaerobic Respiration in Yeast** - **Aim**: Test how different conditions (e.g., sugar concentration, temperature) affect yeast fermentation. - **Setup**: - Mix yeast with a sugar solution in a sealed container with a gas collection tube. - Measure the rate of **CO₂ production** as an indicator of anaerobic respiration. - **Variables**: - Independent: Temperature, sugar concentration. - Dependent: Amount of CO₂ produced. - Control: Same yeast type, same sugar volume.   **5.7 Bacteria (Lactobacillus) in Yoghurt Production** - **Lactobacillus** bacteria are used in yoghurt production. - Process: 1. Milk is pasteurized (heated) to kill harmful bacteria. 2. Milk is cooled, and **Lactobacillus** is added. 3. Bacteria ferment **lactose** (milk sugar) into **lactic acid**. 4. Lactic acid causes milk proteins to coagulate, thickening into yoghurt.   **5.8 Industrial Fermenter** - **Purpose**: Large-scale production of microorganisms (e.g., yeast, bacteria) for food, medicines (e.g., antibiotics), and enzymes. - **Key Features**: - **Aseptic Conditions**: Prevent contamination by unwanted microbes. - **Nutrients**: Provide glucose and minerals for growth. - **Optimum Temperature and pH**: Maintain ideal conditions for enzyme activity and growth. - **Oxygenation**: For aerobic microorganisms, oxygen is supplied via spargers. - **Agitation**: Stirring or mixing ensures even distribution of nutrients and temperature. **5.10 Selective Breeding in Plants** - **Definition**: Selective breeding is the process of choosing parent plants with desirable characteristics to produce offspring with enhanced traits. **Steps in Selective Breeding for Plants:** 1. Identify plants with the desired traits (e.g., high yield, disease resistance, better taste). 1. Cross-pollinate these plants. 2. Grow the seeds from the cross-pollination. 3. Select offspring that show the desired traits. 4. Repeat the process over several generations to stabilize the desired characteristics. **Examples of Desired Characteristics:** - **Higher yield**: Developing crop varieties that produce more fruit, grain, or vegetables. - **Disease resistance**: Creating plants that are less likely to be affected by pathogens. - **Improved taste and appearance**: Breeding fruits and vegetables with better flavors and colors. - **Adaptability**: Producing crops that thrive in specific climates or soils.   **5.11 Selective Breeding in Animals** - **Definition**: Selective breeding in animals involves mating individuals with desirable characteristics to produce offspring that inherit these traits. **Steps in Selective Breeding for Animals:** 1. Identify animals with beneficial traits (e.g., high milk production, fast growth). 1. Mate selected individuals. 2. Assess the offspring for the desired characteristics. 3. Select the best offspring for further breeding. 4. Repeat over multiple generations to enhance the desired traits. **Examples of Desired Characteristics:** - **Higher productivity**: E.g., cows bred for increased milk production, hens for more eggs. - **Faster growth rates**: E.g., livestock that grow more quickly to market size. - **Resistance to diseases**: E.g., animals less susceptible to infections. - **Physical traits**: E.g., dogs bred for size, strength, or specific behaviors like herding.   **Advantages of Selective Breeding:** 1. **Improved yield**: Both plants and animals become more productive. 1. **Better quality**: Enhanced traits like flavor in plants or milk composition in cows. 2. **Economic benefits**: Higher efficiency in farming leads to greater profits.   **Disadvantages of Selective Breeding:** 1. **Reduced genetic variation**: - **Leads to inbreeding, increasing the risk of genetic disorders.** 1. **Vulnerability to disease**: - **Low diversity makes populations more susceptible to widespread infections.** 2. **Ethical concerns**: - **Some selective breeding practices in animals may lead to health issues (e.g., breathing problems in flat-faced dog breeds).**   By using selective breeding, humans can enhance specific traits in plants and animals, making them more suitable for agricultural or commercial purposes. However, care must be taken to manage the risks associated with this process. **5.12 Restriction Enzymes and Ligase Enzymes** - **Restriction Enzymes**: - Enzymes that cut DNA at specific sequences, called **recognition sites**. - Produce **sticky ends** (unpaired bases) or **blunt ends**. - Used to isolate specific genes from DNA. - **Ligase Enzymes**: - Join pieces of DNA together by forming bonds between sugar and phosphate backbones. - Essential for inserting a desired gene into a vector (e.g., a plasmid).   **5.13 Plasmids and Viruses as Vectors** - **Vectors**: DNA molecules used to transfer genetic material into a host cell. - **Plasmids**: - Small, circular DNA molecules found in bacteria. - Can replicate independently of the bacterial chromosome. - Used to carry the desired gene into bacterial cells. - **Viruses**: - Infect host cells by inserting their genetic material. - Used as vectors to deliver recombinant DNA into eukaryotic cells. - **Recombinant DNA**: - DNA formed by combining genetic material from two different sources (e.g., a human gene inserted into a bacterial plasmid). - The vector with recombinant DNA is introduced into host cells, which then express the inserted gene.   **5.14 Production of Human Insulin Using Genetically Modified Bacteria** 1. **Identifying the Insulin Gene**: - **The human gene for insulin production is located and isolated using restriction enzymes.** 1. **Inserting the Gene into a Plasmid**: - **The insulin gene is inserted into a bacterial plasmid using ligase enzymes.** - **The plasmid acts as a vector and is reintroduced into bacteria.** 2. **Growing Bacteria in a Fermenter**: - **Genetically modified (GM) bacteria are cultured in an industrial fermenter.** - **Conditions (e.g., nutrients, oxygen, pH, and temperature) are optimized to promote growth and insulin production.** 3. **Harvesting Insulin**: - **The bacteria produce human insulin, which is purified for medical use.** **Benefits**: - Large-scale, efficient production. - Human insulin reduces allergic reactions compared to animal insulin.   **5.15 Genetically Modified (GM) Plants for Food Production** - **What are GM Plants?** - Plants with genes from other species inserted into their DNA to improve characteristics. - **Examples**: - **Pest resistance**: Bt corn contains a bacterial gene that produces a toxin to kill pests. - **Herbicide resistance**: Allows farmers to use herbicides without harming the crop. - **Increased nutritional value**: Golden rice is genetically modified to produce vitamin A. - **Advantages**: - Higher yields and reduced crop loss. - Reduced use of chemical pesticides. - Improved nutritional content for combating malnutrition. - **Disadvantages**: - Potential risks to ecosystems (e.g., transfer of genes to wild plants). - Ethical concerns and resistance from consumers.   **5.16 Transgenic Organisms** - **Definition**: - A transgenic organism contains **genetic material from another species**. - Example: Bacteria producing human insulin contain a human gene. - **How it Works**: - Genetic material is transferred across species using vectors (e.g., plasmids or viruses). - The foreign gene is incorporated into the organism\'s genome, and the new protein is expressed. - **Applications**: - Medicine: Producing insulin, vaccines, and other proteins. - Agriculture: Creating pest-resistant or drought-tolerant crops.   **Key Definitions** - **Restriction Enzyme**: Cuts DNA at specific sequences. - **Ligase Enzyme**: Joins DNA fragments together. - **Vector**: A vehicle (e.g., plasmid or virus) used to transfer genetic material. - **Recombinant DNA**: DNA made by combining genetic material from different sources. - **Transgenic**: An organism containing genes from a different species. These notes summarize the key concepts and processes involved in genetic engineering and biotechnology for the exam!