OCR GCSE Biology A B2.1 Supplying the Cell Exam Questions

About OCR GCSE Biology A B2.1 Supplying the Cell

B2.1 looks at how substances move into and out of cells and how new cells are produced and specialised. On the OCR Gateway Biology A course it opens Topic B2 Scaling up, assessed in Paper 1 (Foundation) or Paper 3 (Higher). It builds on cell structure from B1.1 and leads into exchange surfaces and transport systems in B2.2, and stem cell medicine in B6.3. Examiners commonly test explanations of osmosis using water potential or concentration, the PAG osmosis practical with percentage change in mass calculations, the stages of the cell cycle, and the benefits and issues of using stem cells.

What you need to know

• Diffusion Diffusion is the net movement of particles from an area of higher concentration to an area of lower concentration, down a concentration gradient. It is passive and does not need energy from respiration, for example oxygen moving into cells.
• Osmosis Osmosis is the diffusion of water molecules from a dilute solution to a more concentrated solution through a partially permeable membrane. Animal cells may burst or shrivel; plant cells become turgid or plasmolysed.
• Active transport Active transport moves substances against a concentration gradient using carrier proteins and energy from respiration (ATP). Examples include root hair cells taking up mineral ions and glucose absorption in the gut.
• The cell cycle and mitosis Before dividing, the cell grows and copies its DNA and organelles. In mitosis, chromosomes line up and are separated to opposite ends, then the cytoplasm divides, producing two genetically identical diploid cells for growth and repair.
• Differentiation Differentiation is the process by which cells become specialised for a particular function. Most animal cells differentiate early in development, while many plant cells keep the ability to differentiate throughout life.
• Stem cells Embryonic stem cells can become almost any cell type; adult stem cells, such as those in bone marrow, can form a limited range of cells. Plant meristems at root and shoot tips produce unspecialised cells that can differentiate into any plant cell type.

Common mistakes in B2.1 Supplying the Cell

• Saying water moves from a high concentration to a low concentration of solute. Water moves from a dilute solution (high water concentration) to a more concentrated solution.
• Writing that diffusion requires energy. Diffusion and osmosis are passive; only active transport uses energy from respiration.
• Saying mitosis produces genetically different cells or gametes. Mitosis produces two genetically identical cells; gametes are made by meiosis.
• Calculating percentage change using the final mass as the denominator. Divide the change in mass by the starting mass, then multiply by 100.
• Stating plant cells burst in pure water. The cell wall stops them bursting, so they become turgid.

Try three B2.1 Supplying the Cell exam-style questions