Lesson Notes By Weeks and Term v5 - Grade 10

Lesson Video

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Performance objectives

• Define a cell and explain the cell theory.
• Identify the structure and function of cell organelles.
• Differentiate between prokaryotic and eukaryotic cells.
• Explain cell specialization with examples.
• Describe the levels of organization in living things.

Lesson summary

This week, we delve deeper into the fundamental building blocks of all living organisms: cells. Understanding cells is crucial because they are the basis of all life processes, from growth and reproduction to responding to our environment. Without understanding how cells function, it's impossible to understand how our bodies work, how diseases affect us, or how we can develop treatments for those diseases. Consider the impact of HIV/AIDS in South Africa. Understanding how HIV affects cells is fundamental to understanding the disease and developing effective treatments. Similarly, understanding cell biology is essential for advancements in agriculture, ensuring food security for our nation.

Lesson notes

2. 1. What is a Cell? A cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of an organism that can be considered alive. Cells are responsible for carrying out all the processes necessary for life, such as metabolism, growth, reproduction, and responding to stimuli. 2.

2. The Cell Theory The cell theory is a fundamental principle of biology that states: All living organisms are composed of one or more cells. The cell is the basic structural and functional unit of life. All cells arise from pre-existing cells.

Historical Development: Robert Hooke (1665): Observed tiny compartments in cork and called them "cells." Anton van Leeuwenhoek (late 1600s): Observed living cells using improved microscopes.

Matthias Schleiden (1838): Concluded that all plants are made of cells.

Theodor Schwann (1839): Concluded that all animals are made of cells.

Rudolf Virchow (1855): Proposed that all cells arise from pre-existing cells ("Omnis cellula e cellula"). 2.

3. Prokaryotic vs. Eukaryotic Cells The two main types of cells are prokaryotic and eukaryotic. | Feature | Prokaryotic Cells | Eukaryotic Cells | |-------------------|-----------------------------------------------|----------------------------------------------------------| | Nucleus | Absent. DNA is located in the nucleoid region. | Present. DNA is enclosed within a membrane-bound nucleus. | | Organelles | Few or no membrane-bound organelles. | Many membrane-bound organelles. | | Size | Generally smaller (0.1-5 µm). | Generally larger (10-100 µm). | | Complexity | Simpler. | More complex. | | Examples | Bacteria and Archaea. | Protists, Fungi, Plants, and Animals. | | DNA Arrangement | Circular DNA. | Linear DNA organized into chromosomes. |

Example: Escherichia coli (E. coli) is a common bacterium found in the human gut. It is a prokaryotic cell. A human liver cell is a eukaryotic cell. 2.

4. Cell Organelles: Structure and Function Organelles are specialized subunits within a cell that perform specific functions.

Nucleus: The control center of the cell, containing the DNA (genetic material) in the form of chromosomes. It directs all cellular activities.

Cytoplasm: The gel-like substance within the cell membrane, excluding the nucleus. It contains all the organelles and is the site of many chemical reactions.

Cell Membrane: The outer boundary of the cell, separating the cell from its environment. It controls the movement of substances in and out of the cell. Made of a phospholipid bilayer with embedded proteins.

Cell Wall (Plant Cells): A rigid outer layer that provides support and protection to plant cells. Made primarily of cellulose.

Ribosomes: Sites of protein synthesis. They can be found free in the cytoplasm or attached to the endoplasmic reticulum.

Mitochondria: The "powerhouses" of the cell, responsible for cellular respiration, which produces energy (ATP).

Example: Muscle cells have a high number of mitochondria to provide the energy needed for contraction.

Chloroplasts (Plant Cells): Sites of photosynthesis, where light energy is converted into chemical energy (glucose). They contain chlorophyll, the green pigment that captures light.

Example: Leaf cells are rich in chloroplasts.

Endoplasmic Reticulum (ER): A network of membranes involved in protein and lipid synthesis and transport.

Rough ER: Contains ribosomes and is involved in protein synthesis.

Smooth ER: Lacks ribosomes and is involved in lipid synthesis and detoxification.

Golgi Apparatus: Modifies, sorts, and packages proteins and lipids for secretion or delivery to other organelles.

Lysosomes: Contain enzymes that break down waste materials and cellular debris.

Vacuoles: Storage sacs that can hold water, nutrients, and waste products. Plant cells have a large central vacuole that helps maintain cell turgor pressure. 2.

5. Cell Specialization Cell specialization (also known as cell differentiation) is the process by which cells become specialized to perform specific functions. Different types of cells have different structures and organelles to best suit their function.

Examples in Animals: Red Blood Cells: Specialized for oxygen transport. They are small, biconcave (disc-shaped) to increase surface area for oxygen diffusion, and lack a nucleus to maximize space for hemoglobin (the oxygen-carrying protein).

Nerve Cells (Neurons): Specialized for transmitting electrical signals. They have long extensions (axons) to transmit signals over long distances.

Muscle Cells: Specialized for contraction. They contain many mitochondria to provide energy and are packed with proteins that enable them to contract.

Examples in Plants: Xylem Cells: Specialized for transporting water and minerals from the roots to the rest of the plant. They are dead cells with thick, lignified walls to provide support.

Phloem Cells: Specialized for transporting sugars produced during photosynthesis from the leaves to other parts of the plant.