Understanding Cells and Organisation in GCSE Biology

Cell Structure and Function

Cells are the fundamental units of life, and there are two main types: prokaryotic and eukaryotic. Prokaryotic cells (e.g., bacteria) lack a true nucleus and membrane-bound organelles, while eukaryotic cells (e.g., plant and animal cells) have a nucleus and specialized organelles.

Eukaryotic Cell Organelles

• Nucleus: Contains genetic material (DNA) and controls cell activities
• Cytoplasm: Jellylike substance where metabolic reactions occur
• Cell Membrane: Selectively permeable barrier regulating movement of substances in/out
• Mitochondria: Site of cellular respiration and ATP production
• Ribosomes: Synthesize proteins from mRNA
• Cell Wall (plants): Rigid outer layer providing structural support
• Chloroplasts (plants): Site of photosynthesis
• Vacuole: Storage compartment for water, nutrients, and waste

Cell Specialization and Microscopy

Cells can become specialized for specific functions within organisms. To study cells, scientists use microscopes like the light microscope and electron microscope (with higher magnification and resolution).

Microscope Calculations

Example: If an object's actual length is 2 μm and its image length is 20 cm, calculate the magnification.

Solution:

• Magnification = Image length / Actual length
• = 20 cm / 2 μm = 20 cm / (0.0002 cm)
• = 100,000 times

Cell Division and Organization

Mitosis is the process of cell division that produces two genetically identical daughter cells. It involves the cell cycle stages: interphase, prophase, metaphase, anaphase, and telophase. Stem cells are undifferentiated cells capable of dividing and developing into specialized cell types.

Movement Across Cell Membranes

• Diffusion: Net movement of particles from high to low concentration
• Osmosis: Diffusion of water molecules across a semi-permeable membrane
• Active Transport: Movement of particles against a concentration gradient, requiring energy

Organization in Organisms

Living organisms are organized in a hierarchy from cells to tissues, organs, and organ systems. In humans, major organ systems include:

• Digestive System: Breaks down food with enzymes for nutrient absorption
• Respiratory System: Facilitates gas exchange (oxygen and carbon dioxide)
• Circulatory System: Transports substances via the heart and blood vessels; includes red blood cells, white blood cells, and platelets

Plants are also organized into tissues like xylem (transports water and minerals) and phloem (transports dissolved food). Processes like transpiration and translocation facilitate the movement of water and nutrients.