A cell is the basic structural and functional unit of living organisms. It is the smallest independently functioning unit of life that can carry out essential processes necessary for an organism’s survival. Cells can vary in structure and function, but they share common features such as a cell membrane, cytoplasm, and genetic material (DNA or RNA).
GCSE Biology – Cell Types and Cell Structure #2
1. Unicellular and Multicellular Organisms:
Unicellular Organisms:
- Definition:
- Comprising a single cell, unicellular organisms are complete and independent living entities.
- Examples:
- Bacteria (e.g., Escherichia coli), Protists (e.g., Amoeba, Paramecium), and certain types of fungi (e.g., Yeast).
- Structure and Function:
- Carry out all life processes within a single cell, including metabolism, reproduction, and response to stimuli.
- Basic structure often includes a cell membrane, cytoplasm, and genetic material (DNA or RNA).
- Adaptability allows them to thrive in diverse environments.
Multicellular Organisms:
- Definition:
- Consisting of multiple cells organised into tissues, organs, and systems, multicellular organisms are more complex entities.
- Examples:
- Plants (e.g., Oak tree), Animals (e.g., Humans), and most fungi (e.g. Mushrooms).
- Structure and Function:
- Cells specialise and differentiate to perform specific functions within the organism.
- Cells organised into tissues (e.g., muscle, nervous), organs (e.g., heart, liver), and organ systems (e.g., circulatory, respiratory).
- Specialised cells collaborate for efficient functioning, allowing for a higher level of complexity in structure and function.
- Greater diversity in form and function compared to unicellular organisms.
2. Difference Between Unicellular And Multicellular
| COMPARISON | UNICELLULAR | MULTICELLULAR |
|---|---|---|
|
No. of Cells |
Consists of a single cell |
Composed of multiple cells |
|
Size |
Generally smaller in size |
Can range from microscopic to large organisms |
|
Adaptability |
Rapid adaptability due to individual autonomy |
Adaptation often involves coordination among specialised cells and systems |
|
Reproduction |
Reproduce through processes like binary fission or mitosis |
Reproduction involves complex processes such as sexual reproduction and embryonic development |
|
Nutrient Exchange |
Direct exchange with the environment |
Specialised structures (e.g., roots, digestive systems) facilitate nutrient absorption and distribution |
|
Lifespan |
Generally shorter lifespans |
Variable lifespans, often influenced by species and environmental factors |
|
Example |
Amoeba |
Humans |
Understanding the distinctions between unicellular and multicellular organisms sheds light on the diverse strategies these life forms employ to survive, reproduce, and interact with their environments.
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3. Conceptual Differences
Animal Cells vs. Plant Cells:
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4. Types of Cells
There are two main types of cells:
- Prokaryotic Cells:
- Lack a true nucleus; instead, the genetic material is present in the nucleoid region.
- Generally smaller and simpler in structure.
- Lack membrane-bound organelles.
- Examples include bacteria and archaea.
- Eukaryotic Cells:
- Have a true nucleus, where genetic material is enclosed within a nuclear membrane.
- Larger and more complex in structure compared to prokaryotic cells.
- Contain membrane-bound organelles like mitochondria, endoplasmic reticulum, and Golgi apparatus.
- Found in plants, animals, fungi, and protists.
These cell types represent the fundamental building blocks of life, each adapted to perform specific functions within different organisms.
Prokaryotic Vs. Eukaryotic Cells
5. Difference Between Animal and Plant Cell
Here are some key features of plant and animal cells:
Plant Cell:
- Cell Wall: Provides structural support and protection, composed of cellulose.
- Cell Membrane: Semi-permeable barrier surrounding the cell.
- Nucleus: Central control centre containing genetic material (DNA).
- Cytoplasm: Gel-like substance where organelles are suspended.
- Mitochondria: Organelles responsible for energy production through cellular respiration.
- Chloroplasts: Contain chlorophyll for photosynthesis, converting light energy into chemical energy.
- Vacuole: Large, central structure for storage of water, nutrients, and waste.
Animal Cell:
- Cell Membrane: Surrounds the cell, regulating the passage of substances.
- Nucleus: Central control centre housing genetic material (DNA).
- Cytoplasm: Gel-like substance supporting organelles and cellular activities.
- Mitochondria: Produces energy through cellular respiration.
- Endoplasmic Reticulum (ER): Involved in protein and lipid synthesis.
- Golgi Apparatus: Modifies, sorts, and packages proteins for secretion.
- Lysosomes: Contain enzymes for cellular digestion and waste removal.
Both plant and animal cells share common structures like the nucleus, cell membrane, and cytoplasm. However, plant cells have unique features such as a cell wall, chloroplasts, and a large central vacuole, while animal cells have organelles like lysosomes, endoplasmic reticulum, and a more flexible cell membrane.
PLANT VS ANIMAL CELLS – YouTube
When examining animal cells with methylene blue staining, the dye selectively colours certain cell structures, making them more visible under a microscope. Methylene blue tends to stain the nucleus and other structures in animal cells.
For plant cells with iodine solution staining, iodine interacts with starch present in plant cells, resulting in a characteristic colour change. Iodine staining highlights structures like the nucleus and starch-filled chloroplasts in plant cells, aiding in their observation and identification.
These staining techniques enhance the contrast and visibility of cell structures, enabling a clearer examination under the microscope.
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6. How To Draw Diagrams of Animal And Plant Cells
- Animal Cell Diagram:
- Draw a circular or oval shape to represent the animal cell.
- Label and depict the nucleus as a dark, central structure.
- Draw scattered small dots to represent ribosomes throughout the cytoplasm.
- Illustrate elongated structures to represent mitochondria.
- Add a thin line around the cell to represent the cell membrane.
- Plant Cell Diagram:
- Draw a rectangular or square shape to represent the plant cell.
- Label and depict the nucleus centrally.
- Include larger oval structures to represent chloroplasts (green for photosynthesis).
- Draw a large, central vacuole, representing the sap vacuole.
- Scatter small dots for ribosomes throughout the cytoplasm.
- Add a thin line around the cell to represent the cell membrane and a thicker one for the cellulose cell wall.
Remember to scale your structures appropriately and provide labels for each component.
7. Specialised Cells
- Definition: Cells that have unique structures and functions adapted to perform specific tasks within an organism.
- Examples:
- Red Blood Cells: Specialised for oxygen transport with a biconcave shape to increase surface area.
- Neurons: Specialised for transmitting electrical impulses in the nervous system.
- White Blood cells: They fight back with the pathogens. They build our immune system
8. Understanding Cellular Hierarchy:
- Cell: The basic unit of life.
- Tissue: A group of cells with similar structure and function.
- Organ: Composed of different tissues working together to perform a specific function.
- Organ System: A group of organs that work together to carry out complex functions.
- Organism: An individual living entity.
- Examples:
- Leaf (Organ): Contains tissues like epidermis, mesophyll, and veins working together for photosynthesis.
- Digestive System (Organ System): Comprising organs like stomach, liver, and intestines, working together for digestion.
9. Magnification Formula:
- Formula: Magnification = Image Size ÷ Actual Size
- Explanation: Magnification represents how much larger or smaller an image is compared to the actual size. It’s crucial in microscopy.
- Application: When measuring the size of a cell or structure under a microscope, use this formula to determine its actual size.
2.1.1 Cell Structure | CIE IGCSE Biology Revision Notes 2023 | Save My Exams
Understanding these concepts is essential for comprehending the organisation and functionality of living organisms, providing a foundation for further biological studies.
