Learn: Cells and Movement Across Membranes

Welcome!Welcome to your lesson on Cells and Movement Across Membranes. I've designed this lesson to help you strengthen your understanding of cell structure and how substances move in and out of cells, which are key topics in the WJEC GCSE Biology specification.

What are cells?Cells are the building blocks of all living organisms. They are the smallest unit of life. There are different types of cells, including animal cells and plant cells, each with their own specialised structures.

Structures in animal and plant cellsAnimal and plant cells have some common structures, like the cell membrane (controls what enters and leaves the cell), cytoplasm (jelly-like substance where chemical reactions occur), and nucleus (contains genetic material and controls the cell). Plant cells also have additional structures, such as a cell wall (provides strength), chloroplasts (site of photosynthesis), and a large vacuole (for storage).

Levels of biological organisationIn living organisms, cells are organised into tissues (groups of similar cells working together), which form organs (structures performing specific functions). Organs work together in organ systems, and these systems make up the entire organism.

Movement across membranesSubstances move in and out of cells via three main processes: diffusion (movement of particles from high to low concentration), osmosis (movement of water across a selectively permeable membrane), and active transport (movement against the concentration gradient using energy).

DiffusionDiffusion is the movement of particles from an area of high concentration to an area of low concentration down a concentration gradient. It happens naturally, without energy. For example, oxygen diffuses into cells for respiration, and carbon dioxide diffuses out.

OsmosisOsmosis is the movement of water across a selectively permeable membrane from an area of high water potential to an area of low water potential. For example, plant roots use osmosis to absorb water from the soil.

Active transportActive transport moves substances against their concentration gradient, from low to high concentration. This process requires energy, which is supplied by ATP produced during respiration. An example is the uptake of minerals by plant root hair cells.

Review Time!Great work! You've learned about cell structure, biological organisation, and movement across membranes. Let's test your understanding with a few questions!