Cambridge IGCSE Biology 2 Organisation of the Organism Exam Questions

About Cambridge IGCSE Biology 2 Organisation of the Organism

Organisation of the organism covers the building blocks of every other topic in Cambridge IGCSE Biology. You need to identify and state the functions of the structures in animal, plant and bacterial cells, describe specialised cells such as ciliated cells, root hair cells and red blood cells, and use the terms cell, tissue, organ, organ system and organism. The second part, size of specimens, is mostly mathematical: the magnification formula and, for Extended candidates, converting between millimetres and micrometres. Examiners regularly ask you to label a cell drawing, link a specialised cell's structure to its function, and calculate actual size from a scale drawing or photomicrograph.

What you need to know

• 2.1 Animal and plant cells Both have a cell membrane, cytoplasm, nucleus, ribosomes and mitochondria. Plant cells also have a cellulose cell wall, chloroplasts and a large permanent vacuole containing cell sap.
• 2.1 Bacterial cells Bacteria have a cell wall, cell membrane, cytoplasm and ribosomes, with a circular DNA molecule and small circles of DNA called plasmids. They have no nucleus.
• 2.1 Organelle functions Mitochondria are the site of aerobic respiration; ribosomes are the site of protein synthesis; the nucleus contains genetic material that controls the cell; chloroplasts absorb light for photosynthesis; the cell wall gives support and stops the cell bursting.
• 2.1 Specialised cells Ciliated cells move mucus in the trachea and bronchi; root hair cells absorb water and mineral ions; palisade mesophyll cells carry out photosynthesis; neurones conduct electrical impulses; red blood cells transport oxygen; sperm and egg cells are used in reproduction.
• 2.1 Levels of organisation A tissue is a group of cells with similar structures working together to perform a shared function. An organ is a structure made of a group of tissues working together. An organ system is a group of organs with related functions.
• 2.2 Magnification Magnification = image size / actual size. Measure the image in mm. Extended candidates convert units: 1 mm = 1000 micrometres. Magnification has no units and is written as, for example, x 400.

Common mistakes in 2 Organisation of the Organism

• Saying the cell membrane is fully permeable or that the cell wall controls what enters. The membrane is partially permeable and controls entry and exit; the cell wall is freely permeable.
• Stating that mitochondria make energy. Mitochondria release energy by aerobic respiration; energy cannot be made.
• Forgetting to convert units in magnification calculations. Measure the image in mm, then multiply by 1000 if the answer must be in micrometres.
• Writing that plant cells have no mitochondria because they have chloroplasts. Plant cells have both.
• Adding units to magnification, such as 400 mm. Magnification is a ratio and has no units.

Try three 2 Organisation of the Organism exam-style questions