OxfordAQA International GCSE Biology 3.1 Organisation Exam Questions

About OxfordAQA International GCSE Biology 3.1 Organisation

Organisation is the first section of OxfordAQA International GCSE Biology and sets up the vocabulary used everywhere else. It starts with the structure of animal, plant and bacterial cells, then builds up through tissues, organs and organ systems, using the stomach, the digestive system and the leaf as key examples. The second half covers how substances move into and out of cells by diffusion, osmosis and active transport, and why large organisms need specialised exchange surfaces. Examiners often ask you to link a cell or surface feature to its function, to interpret osmosis results as percentage change in mass, and to explain surface area to volume ratio.

What you need to know

• Cell structure Animal cells have a nucleus, cytoplasm, cell membrane, mitochondria and ribosomes. Plant cells also often have chloroplasts, a permanent vacuole filled with cell sap and a cellulose cell wall. Bacterial (prokaryotic) cells have cytoplasm, a membrane and a cell wall, but their genes are not in a distinct nucleus and some are found in circular plasmids.
• Levels of organisation Cells differentiate to carry out different functions. A tissue is a group of similar cells with a similar function, an organ is made of several tissues, and an organ system is a group of organs working together. The stomach contains muscular tissue (churns contents), glandular tissue (makes enzymes) and epithelial tissue (covers inside and outside).
• Digestive system organs Salivary glands and the pancreas produce digestive juices; the stomach and small intestine digest food; the liver produces bile; the small intestine absorbs soluble food; the large intestine absorbs water, leaving faeces.
• Plant tissues and organs Epidermal tissue covers the plant, palisade mesophyll carries out photosynthesis, spongy mesophyll has air spaces for gas diffusion, and xylem and phloem transport substances. Stems, roots and leaves are plant organs; you need the internal structure of a leaf and the position of xylem and phloem in a dicotyledonous root and stem.
• Diffusion and osmosis Diffusion is the net movement of particles from a higher to a lower concentration; a bigger concentration difference gives faster diffusion. Osmosis is the diffusion of water from a dilute to a more concentrated solution through a partially permeable membrane. Learn isotonic, hypotonic, hypertonic, turgor and plasmolysis.
• Active transport Active transport moves substances against a concentration gradient using energy from respiration. Examples are root hair cells taking in mineral ions from dilute soil water, and sugar being absorbed from the gut and kidney tubules.
• Exchange surfaces Small organisms have a large surface area to volume ratio and exchange across their surface. Effective exchange surfaces have a large surface area, a thin surface (short diffusion path), an efficient blood supply in animals and ventilation for gas exchange. Apply this to the small intestine, lungs, roots and leaves.
• Required practical In the separate Biology course you investigate the effect of different solution concentrations separated by a partially permeable membrane, for example potato cylinders in sucrose solutions, recording percentage change in mass.

Common mistakes in 3.1 Organisation

• Saying water moves from a high concentration of solution to a low one in osmosis. Water moves from a dilute solution (high water concentration) to a more concentrated solution.
• Saying plant cells burst when placed in water. The cell wall stops this; the cell becomes turgid. Animal cells, which have no wall, can burst.
• Describing active transport as faster diffusion. It moves substances against a concentration gradient and needs energy from respiration.
• Giving mitochondria the job of making energy. Energy is released in mitochondria by respiration; energy is never made.
• Comparing raw mass changes in osmosis experiments when starting masses differ. Calculate percentage change in mass so results can be compared fairly.

Try three 3.1 Organisation exam-style questions