B2

Cell Cycle Overview - Topic 1

The cell cycle is a series of stages that cells go through to grow, replicate DNA, and divide, allowing organisms to grow, repair tissues, and replace old cells.

Stages of the Cell Cycle:

  1. Growth (G1 Phase): The cell grows, increases in size, and prepares to replicate DNA.

  2. DNA Replication (S Phase): DNA duplicates, ensuring that each daughter cell will have a complete set of chromosomes. In humans, this means 23 pairs (46 chromosomes total).

  3. Mitosis (M Phase): The nucleus divides, ensuring that each new cell receives an identical set of chromosomes.

  4. Cytokinesis: The cell splits, creating two identical daughter cells, each with a full set of DNA.

Key Concepts:

  • Cell Division: Allows growth, tissue repair, and reproduction in organisms.

  • Chromosomes: Structures that organize DNA for accurate division.

  • Mitosis Mechanics: Ensures proper chromosome separation.

  • Cytokinesis: Divides the cell’s cytoplasm to form two new cells.

Mitosis and Its Importance - Topic 2

Mitosis is the process of nuclear division that produces two identical daughter cells. It is essential for growth, tissue repair, and some forms of reproduction (asexual reproduction).

Stages of Mitosis:

  1. Prophase: Chromosomes condense and become visible. The nuclear envelope (membrane) dissolves, and spindle fibers begin to form.

  2. Metaphase: Chromosomes align at the cell’s equator, each attaching to spindle fibers from opposite poles of the cell.

  3. Anaphase: Spindle fibers pull the chromosomes apart, moving each set to opposite ends (poles) of the cell.

  4. Telophase: New nuclear membranes form around each set of chromosomes, completing nuclear division.

Key Functions of Mitosis:

  • Growth and Repair: Mitosis replaces old or damaged cells with identical ones.

  • Asexual Reproduction: Mitosis allows organisms to reproduce offspring that are genetically identical to the parent.

Cell Differentiation and Stem Cells - Topic 3

Cell Differentiation: The process by which unspecialized cells become specialized to perform specific functions, such as muscle or nerve cells.

Types of Stem Cells:

  • Embryonic Stem Cells: Can develop into any cell type, essential for early development.

  • Adult Stem Cells: Limited to specific types of cells (e.g., blood cells).

  • Plant Stem Cells: Found in meristems, allowing plants to grow throughout their lives.

Transport Mechanisms in Cells - Topic 4

  1. Active Transport: Moves molecules from low to high concentration, using energy (ATP).

    • Example: Root hair cells absorb minerals from the soil through active transport.

  2. Diffusion: Passive movement of particles from high to low concentration, requiring no energy.

    • Example: Gas exchange in the lungs, where oxygen enters and carbon dioxide exits.

Factors Affecting Diffusion:

  • Concentration Gradient: A larger difference in concentration increases the rate of diffusion.

  • Temperature: Higher temperatures speed up diffusion.

  • Surface Area: Larger surface areas allow more diffusion.

Osmosis Overview - Topic 5

Osmosis: The passive movement of water molecules from an area of high water concentration to low, across a partially permeable membrane.

Key Points:

  • Passive Process: Requires no energy.

  • Water Movement: Essential for processes like water uptake in plants and balancing cell water levels.

Exchange Surface - Topic 6

Gas Exchange:

  • Alveoli: Small sacs in the lungs with a large surface area, allowing efficient gas exchange.

  • Function: Oxygen diffuses into the blood, while carbon dioxide exits.

  • Structure: Thin walls facilitate quick diffusion.

Surface Area to Volume Ratio - Topic 7

Importance:

  • High Ratio in Small Organisms: Small organisms rely on diffusion due to their high surface area-to-volume ratio.

  • Low Ratio in Larger Organisms: Larger organisms need specialized systems (e.g., lungs) to transport substances efficiently.

Specialized Exchange Surfaces - Topic 8

Key Features:

  • Large Surface Area: Increases diffusion rates (e.g., alveoli in lungs).

  • Thin Membranes: Shorten diffusion distances.

  • Permeable Surfaces: Facilitate easy movement of substances.

  • Good Blood Supply: Maintains concentration gradients, aiding absorption.

The Heart and Circulatory System - Topic 9

Key Functions:

  • Transport: Carries oxygen, nutrients, and other essentials.

  • Heart Structure: Four chambers (two atria and two ventricles) enable efficient circulation.

  • Double Circulation: Blood passes through the lungs for oxygenation and the body for nutrient delivery.

  • Pacemaker Cells: Regulate heartbeat.

  • Coronary Arteries: Provide oxygen to the heart muscle.

Blood Vessels Overview - Topic 10

Types of Blood Vessels:

  • Arteries: Carry oxygenated blood away from the heart at high pressure.

  • Capillaries: Thin-walled vessels where nutrient and gas exchange occur.

  • Veins: Return deoxygenated blood to the heart, equipped with valves to prevent backflow.

Plant Cell Organization - Topic 11

Key Structures:

  • Plant Structure: Includes cells, tissues, and organs.

  • Leaves: Adapted for photosynthesis and gas exchange; stomata regulate water loss.

  • Waxy Cuticle: Prevents excessive water loss.

  • Water Conservation: Guard cells open and close stomata to balance water levels.

Transpiration and Translocation - Topic 12

Key Processes:

  • Phloem and Translocation: Transport sugars from leaves to other parts of the plant.

  • Xylem and Transpiration: Move water from roots to leaves, driven by evaporation.

  • Factors Affecting Transpiration: Light, temperature, airflow, and humidity influence water movement.