Test Notes - Biology PDF

**3.1 Unicellular vs. Multicellular Organisms:** - **Unicellular organisms**: Made up of one cell (e.g., bacteria, yeast, phytoplankton). - **Multicellular organisms**: Made up of many cells (e.g., animals, plants, fungi). **DNA, Chromosomes, and Genes:** - **DNA**: A molecule carr...

**3.1 Unicellular vs. Multicellular Organisms:** - **Unicellular organisms**: Made up of one cell (e.g., bacteria, yeast, phytoplankton). - **Multicellular organisms**: Made up of many cells (e.g., animals, plants, fungi). **DNA, Chromosomes, and Genes:** - **DNA**: A molecule carrying genetic information. - **Genes**: Sections of DNA, each encoding instructions to make specific proteins. - **Chromatin**: Loose DNA strands in the nucleus; coils into **chromosomes** before cell division. - Chromosomes are pairs of tightly packed DNA, each with hundreds of genes. **Genetically Identical Cells:** - All cells in a multicellular organism carry the same number and type of chromosomes with the same sequence of genes. - Example: Human cells all have 46 chromosomes (23 pairs). **Gene Expression:** - **Definition**: When a gene is \"switched on,\" its instructions are used to make a specific protein. - **Regulation**: Controlled by regulatory proteins: - **Activators**: Bind to DNA near a gene to switch it **on**. - **Repressors**: Bind to DNA near a gene to switch it **off**. - Gene expression varies by: - Cell type - Time (e.g., after eating) - Developmental stage (e.g., puberty). - On average, a human cell expresses \~20% of its genes at any time. **Cell Specialisation:** - **Definition**: The development of different cell types with unique structures and functions in multicellular organisms. - Specialisation occurs through **cell differentiation**, where specific genes are expressed or repressed , producing a specific set of proteins for each cell type. **Examples of Specialised Cells:** - **Red blood cells**: - **Structure**: Biconcave shape, no nucleus. - **Function**: Increased surface area for oxygen absorption; space for haemoglobin enhances oxygen transport. - **Leaf cells**: - **Structure**: Large surface area, thin walls, chloroplasts. - **Function**: Maximises light absorption for photosynthesis; facilitates gas exchange. **Key Concepts:** 1. All cells in a multicellular organism are **genetically identical**. 2. **Gene expression** is responsible for **cell specialisation**. 3. Regulatory proteins control whether a gene is **switched on or off**. **Hierarchical Organisation** - Multicellular organisms are structured in a hierarchy: - **Cells → Tissues → Organs → Systems → Organism.** **Ex.** **-Cells**: **Muscle cells-Tissues**: **-Muscle tissue** (formed from muscle cells) **-Organs**: **Heart** (composed of muscle tissue, connective tissue, and others) **-Systems**: **Circulatory system** (includes the heart, blood vessels, and blood) **-Organism**: **Human body** (where the circulatory system works with other systems like the respiratory, digestive, etc.) - Each level builds upon the previous to allow for complexity and specialised functions. **Definitions and Examples** 1. **Tissues** - Groups of similar cells performing a shared function. - Examples: - **Animal:** - Muscle fibres contract for movement. - Red blood cells transport oxygen. - **Plant:** - Xylem transports water and nutrients. - Mesophyll performs photosynthesis. 2. **Organs** - Composed of different tissues working together for specific functions. - Examples: - **Animal:** - **Heart:** Pumps blood using cardiac muscle, epithelium, and blood tissue. - **Stomach:** Starts protein digestion and kills bacteria. - **Plant:** - **Leaf:** Produces sugar and oxygen via photosynthesis; facilitates water evaporation. - **Root:** Absorbs water and anchors the plant. 3. **Systems** - Groups of organs working together to perform overall functions. - Examples: - **Animal:** - **Circulatory System:** Transports substances and heat via blood vessels. - **Plant:** - **Shoot System:** Transports substances, supports the plant, and enables reproduction. 2. **Relationship Between Structure and Function** - **Cells:** - **Sperm cells**: Tail-like flagella enable movement towards an ovum. - **Root hair cells**: Thin walls and needle-like extensions improve water and mineral absorption. - **Tissues:** - **Leaf epidermis cells:** Tightly packed for protection against physical and chemical damage. - **Organs:** - **Heart wall:** Contains protective tissue, connective tissue for support, and cardiac muscle for pumping blood. **Interdependence of Systems** - Organ systems depend on each other for proper functioning: - Example: - **Respiratory System** provides oxygen for the **Circulatory System**, which transports it to tissues. - The **Circulatory System** returns carbon dioxide to the lungs for exhalation. **Lifestyle Choices and Organ Function** 1. **Positive Choices:** - Balanced diet supports digestive and heart health. - Regular exercise improves circulatory function and muscle strength. 2. **Harmful Choices:** - Smoking introduces carcinogens, leading to lung tissue mutations and diseases like cancer. - Excessive alcohol consumption increases the risk of liver disease and heart issues. **Structure of Leaves** - Leaves are part of the **shoot system** in plants. - Organised into multiple tissues: - **Upper and Lower Epidermis**: Protection; lower epidermis contains stomata for gas exchange. - **Mesophyll**: - **Palisade mesophyll**: Dense with chloroplasts for photosynthesis. - **Spongy mesophyll**: Loosely arranged for gas diffusion. - **Vascular Tissue**: - **Xylem**: Transports water. - **Phloem**: Transports sugars. - ### **Notes on the Exchange of Materials in Organisms** #### **1. Introduction to Material Exchange** - **Organisms take in and release materials** from and to their environment simultaneously. - **Materials taken in** by animals include: - Oxygen - Water - Organic molecules (such as carbohydrates) - **Materials given out** by animals include: - Wastes, such as carbon dioxide (CO₂) #### **. Exchange Surfaces** - **Unicellular organisms** (e.g. amoebas) can exchange materials directly with their environment through their **cell membrane**. - **Multicellular organisms** need specialized structures called **exchange surfaces** because not all cells are in direct contact with the environment. - **Exchange surfaces** must meet these criterifa: - **Thin**: Allows easier diffusion (e.g. one-cell thick epithelium) - **Moist**: Keeps surfaces wet for diffusion to occur - **Large Surface Area**: Maximizes the area for exchange - **Blood Supply**: In many animals, exchange surfaces are close to blood capillaries, enhancing exchange efficiency. #### **3. Examples of Exchange Surfaces in Animals** - **Alveolus** (in the lungs) for the respiratory system - **Villus** (in the small intestine) for the digestive system - **Nephron** (in the kidneys) for the excretory system #### **4. Gas Exchange and Diffusion** - The exchange of gases (e.g., oxygen and carbon dioxide) occurs by **diffusion**. - **Diffusion** is the passive movement of molecules from an area of high concentration to an area of low concentration. - This process **does not require energy** input from the organism. #### **5. The Respiratory System and Gas Exchange** - In mammals, the **respiratory system** enables gas exchange between the bloodstream (internal environment) and the atmosphere (external environment). - Gas exchange occurs at the **alveoli** in the lungs. - **Alveoli** are tiny, grape-like clusters surrounded by blood capillaries, facilitating diffusion. #### **6. Diffusion of Gases in Alveoli** - Oxygen moves from the **alveoli** (higher concentration) into the **blood** (lower concentration) by diffusion. - Simultaneously, carbon dioxide moves from the **blood** (higher concentration) into the **alveoli** (lower concentration) to be exhaled. - The process is passive and driven by **concentration gradients**. -  #### **7. Breathing Mechanism in Humans** - **Air Pathway**: - Air enters through the **nose or mouth**. - Passes through the **pharynx** and **trachea**. - Enters the **bronchi** and bronchioles. - Reaches the **alveoli** for gas exchange. #### **8. Structure of the Respiratory System** - The respiratory system is structured to ensure air reaches the alveoli for gas exchange. - **Alveoli** are surrounded by capillaries, ensuring efficient exchange of oxygen and carbon dioxide. #### **9. Oxygenation of Blood** - As blood flows through capillaries around the alveoli: - **Oxygen** diffuses into the blood (since oxygen concentration is higher in alveoli than in the blood). - **Carbon dioxide** diffuses out of the blood into the alveoli (since its concentration is higher in the blood). #### **10. Adaptations of the Alveoli for Gas Exchange** - **Thin walls**: Facilitate rapid diffusion of gases. - **Large surface area**: Increases the area available for gas exchange. - **Moist lining**: Necessary for gas to dissolve before diffusion. #### **11. Effect of Diseases on Gas Exchange** - **Pneumonia**: Inflammation and fluid accumulation in alveoli reduce the surface area and increase the diffusion distance, leading to inefficient gas exchange and difficulty breathing. ### **Key Concepts and Terms** - **Diffusion**: Movement of molecules from high to low concentration, a passive process. - **Exchange surfaces**: Specialised areas for material exchange in multicellular organisms. - **Alveoli**: Tiny air sacs in the lungs for gas exchange in mammals. - **Concentration Gradient**: Difference in concentration of a substance between two areas (important for diffusion). **3.4 Functions of Leaves** 1. **Photosynthesis** - Primary site where light energy is converted to chemical energy. - Requires carbon dioxide, absorbed via stomata. 2. **Gas Exchange** - Exchange of **carbon dioxide (CO₂)** and **oxygen (O₂)** via stomata. - **CO₂** diffuses into the leaf for photosynthesis. - **O₂**, a by-product of photosynthesis, diffuses out of the leaf. 3. **Transpiration** - Water vapour loss through stomata helps regulate temperature. **Gas Exchange in Leaves** - Occurs during **daylight hours** when photosynthesis is active. - **Stomata** allow gas diffusion: - **CO₂** diffuses in (higher concentration in atmosphere). - **O₂** diffuses out (higher concentration inside the leaf). - Gases move by **diffusion** (concentration gradient). **Stomata and Gas Exchange Control** - **Guard Cells** control stomata opening and closing: - **Open in the morning**: Light intensity increases. - **Closed at night**: Photosynthesis ceases, preventing water loss. - **Closed during high heat**: Reduces water loss during transpiration. **Water Loss and Transpiration** - **Transpiration** is the diffusion of water vapour from leaves: - Water evaporates from mesophyll cells. - Vapour diffuses out via stomata (higher internal water vapour concentration). - **Cooling Effect**: Prevents overheating of leaves. **Adaptations to Minimise Water Loss** 1. **Waxy Cuticle**: - Transparent layer on the upper epidermis reduces evaporation. 2. **Lower Stomatal Density**: - Fewer stomata reduce water loss. 3. **Stomata in the Lower Epidermis**: - Avoids direct sunlight, reducing evaporation rate. **1. Leaf Structure** - **Leaf Anatomy**: - **Upper and Lower Epidermis**: Protective layers; lower epidermis contains stomata for gas exchange. - **Mesophyll Tissue**: - **Palisade Mesophyll**: Contains chloroplasts; primary site of photosynthesis. - **Spongy Mesophyll**: Loosely packed cells for gas diffusion. - **Vascular Tissues**: - **Xylem**: Transports water. - **Phloem**: Transports sugars. **2. Gas Exchange in Leaves** - **Function**: Facilitates photosynthesis by allowing gases to move between the environment and mesophyll cells. - **Key Features**: - **Stomata**: Openings in the lower epidermis, controlled by **guard cells**. - **Diffusion**: - **Carbon Dioxide (CO₂)** enters the leaf through stomata (higher concentration in the atmosphere). - **Oxygen (O₂)** exits the leaf, produced by photosynthesis (higher concentration inside). **3. Stomata Control and Gas Exchange** - **Stomata Open**: - Morning/daylight: Increased light intensity promotes photosynthesis. - Wider stomata allow more **CO₂** entry. - **Stomata Close**: - Night: Photosynthesis ceases. - Hot conditions: Minimises water loss (transpiration). **4. Transpiration and Water Loss** - **Process**: - Water in mesophyll cells evaporates and forms **water vapour**. - Vapour diffuses out through stomata (higher internal water vapour concentration). - **Cooling Effect**: Prevents leaf damage from overheating. **5. Adaptations to Minimise Water Loss** 1. **Waxy Cuticle**: - Transparent layer prevents water evaporation. 2. **Stomata Placement**: - Located in the lower epidermis, avoiding direct sunlight. 3. **Low Stomatal Density**: - Fewer stomata reduce water loss. **6. Green Walls: Application and Benefits** - **Description**: Walls covered with plants exchange gases with the environment. - **Benefits**: - Remove **CO₂** from indoor air. - Increase **O₂** production, enhancing air quality. **3.5 Obtaining Nutrients from the Environment: Key Notes** **1. Animal Digestive System** - **Function**: Breaks down food and absorbs nutrients. **Key Processes** 1. **Mechanical Digestion**: - Physical breakdown of food (e.g., by teeth or stomach churning). 2. **Chemical Digestion**: - Enzymes break down food into soluble nutrients. **Digestive Enzymes** **Enzyme** **Location** **Digests** **Nutrient Produced** ------------ ------------------- --------------- ------------------------ Amylase Mouth, duodenum Carbohydrates Glucose Protease Stomach, duodenum Proteins Amino acids Lipase Duodenum Lipids Fatty acids & glycerol **Digestive System Structures and Functions** **Organ** **Structure** **Function** -------------------- ------------------------------- --------------------------------------------------------------------------- **Oral Cavity** Teeth, tongue Mechanical digestion, food movement. **Salivary Gland** Gland with ducts Secretes saliva (moistens food and contains amylase). **Oesophagus** Tubular, muscular walls Pushes food to the stomach via peristalsis. **Stomach** Elastic walls, muscle, glands Stores food, churns contents, secretes acid and protease enzymes. **Pancreas** Gland with ducts Produces pancreatic juice (neutralises acid, contains digestive enzymes). **Liver** Bile-producing tissue Produces bile to assist lipid digestion. **Gall Bladder** Gland with ducts Stores bile, releases it into the duodenum. **Duodenum** Tubular, glandular walls Completes chemical digestion, pushes contents to the ileum. **Ileum** Tubular, villi-lined walls Absorbs nutrients into the circulatory and lymphatic systems. **Colon** Tubular, muscular walls Absorbs water, moves waste to rectum for egestion. **Gut Microbiome** - Located mainly in the colon. - Functions: Maintains gut health, supports immunity, and promotes brain health. **2. Nutrient Absorption in Animals** - **Location**: Ileum of the small intestine. - **Structures**: - **Villi**: Finger-like projections with a large surface area. - Thin walls for easy diffusion. - Rich blood supply for nutrient transport. - Contains lacteals for lipid absorption. - **Processes**: - **Diffusion**: Passive movement of glucose and amino acids into capillaries. - **Active Transport**: Absorbs nutrients against a concentration gradient using energy (ATP). - **Endocytosis**: Lipids enter lacteals by membrane folding. **3. Nutrient and Water Uptake in Plants** - **Function**: Root hair cells in the root system absorb nutrients and water. - **Structure**: - Long, thin extensions increase surface area. - Thin cell walls reduce diffusion distance. - **Processes**: - **Water**: Absorbed by osmosis (high to low water concentration). - **Nutrients**: Enter via active transport. **3.6 Excretory System and Waste Removal Notes** **General Overview** - **Wastes:** Unwanted by-products of cellular reactions (e.g., urea, CO₂). - **Importance of Removal:** Prevents accumulation that could disrupt homeostasis. **Animal Excretory System** - **Components:** Kidneys, ureters, bladder, urethra. - **Blood Flow in Kidneys:** - Urea-rich blood enters kidneys via renal arteries. - Filtration and reabsorption occur at nephrons. - Urea-poor blood exits via renal veins. **Nephrons: Structure and Function** As urea-rich blood flows into capillaries that extend into a nephron (the **glomerulus**) and surround it, urea, water and small useful molecules are forced through the walls of the glomerular capillaries into a part of a nephron called the **Bowman's capsule**. At the same time, water and other small useful molecules move out of the nephron through the wall of part of it called the **proximal tubule** and re-enter blood in capillaries surrounding the proximal tubule. This exchange of materials, some leaving blood, others re-entering it, occurs continuously. Kidney Function and Physiology \| Biology for Majors II - **Glomerulus:** - Cluster of capillaries with high pressure. - Filters small molecules (e.g., urea, water). - **Bowman's Capsule:** - Cup-shaped, collects filtrate. - **Proximal Tubule:** - Thin walls allow selective reabsorption (e.g., nutrients, water). - **Loop of Henle:** - Creates a concentration gradient for water reabsorption. - **Collecting Duct:** - Pathway for urine; reabsorbs water if ADH is present. **Processes in the Kidney** 1. **Filtration:** - Removes urea and waste from blood at the glomerulus. 2. **Reabsorption:** - Selectively returns useful substances to blood (e.g., water, nutrients). **Urine Formation** - Composed of water, urea, dissolved wastes. - Moves from nephron → collecting duct → bladder. **Waste Removal in Plants** - **CO₂ Excretion:** Diffuses through: - Stomata (leaves). - Lenticels (stems). - Root hair cells (roots). - **Other Wastes:** - Stored in vacuoles or bark (shed later). - Salt excreted via leaf glands (e.g., mangroves). - **Guttation:** - Water and dissolved waste released through leaf hydathodes at night. **Comparing CO₂ Excretion** - **Mammals:** Excrete via lungs during breathing. - **Plants:** Release during cellular respiration or use for photosynthesis. **Effect of Alcohol on Urine Output** - **Inhibits ADH Release:** Reduces water reabsorption in collecting ducts. - **Result:** Increased urine output, potential dehydration.