CCEA GCSE Biology 1.1 Cells Exam Questions

About CCEA GCSE Biology 1.1 Cells

Cells is the opening topic of Unit 1 (Cells, Living Processes and Biodiversity) in CCEA GCSE Biology. You need to recognise the structures in animal, plant and bacterial cells and say what each one does, use a light microscope properly and calculate magnification. The topic also covers stem cells, how cells become specialised and are organised into tissues, organs and systems, and how substances move by diffusion. It links directly to osmosis in Unit 2, to gas exchange in leaves and lungs, and to absorption in the ileum. Examiners like magnification calculations with unit conversions, labelled cell diagrams and questions on the prescribed practical slide preparation.

What you need to know

• Animal and plant cells Both have a nucleus (contains genetic material and controls the cell), cytoplasm (where reactions happen), cell membrane (controls entry and exit) and mitochondria (aerobic respiration). Plant cells also have a cellulose cell wall for support, a large permanent vacuole containing cell sap and chloroplasts for photosynthesis.
• Bacterial cells Bacteria have no true nucleus: their DNA is a single loop free in the cytoplasm, and they may also have small rings of DNA called plasmids. They have a cell wall (not made of cellulose), a cell membrane and cytoplasm, and some have a flagellum for movement.
• Microscopy and magnification Magnification = image size / actual size. Convert to the same unit first: 1 mm = 1000 micrometres. Total magnification of a light microscope = eyepiece lens magnification x objective lens magnification.
• Prescribed practical: making a slide Place a thin layer of cells (for example onion epidermis) on a slide, add a drop of stain such as iodine solution, then lower a coverslip at an angle with a mounted needle to avoid air bubbles. Focus on low power first, then switch to a higher power objective and use the fine focus.
• Stem cells and specialisation Stem cells are unspecialised cells that can divide and differentiate into different cell types. Embryonic stem cells can become almost any cell; adult stem cells (for example in bone marrow) are more limited. Specialised cells are grouped into tissues, tissues into organs and organs into organ systems.
• Diffusion Diffusion is the net movement of particles from a region of higher concentration to a region of lower concentration, down a concentration gradient. It is a passive process, so it needs no energy from respiration. Examples include oxygen entering cells and carbon dioxide entering leaves.
• Surface area to volume ratio As an organism or cell gets bigger, its surface area to volume ratio gets smaller. Small organisms can rely on diffusion across their surface, but large organisms need specialised exchange surfaces and transport systems.

Common mistakes in 1.1 Cells

• Forgetting to convert units in magnification calculations. Always put image size and actual size into the same unit (usually micrometres) before dividing.
• Saying that all plant cells contain chloroplasts. Root hair cells and other cells that receive no light have no chloroplasts.
• Stating that bacteria have a nucleus. Bacterial DNA is free in the cytoplasm as a single loop, with extra DNA in plasmids.
• Describing diffusion as particles moving from high to low concentration without the word net or without mentioning the concentration gradient. Use the full definition.
• Writing that the cell wall controls what enters and leaves the cell. That is the job of the cell membrane; the cell wall gives support and is freely permeable.

Try three 1.1 Cells exam-style questions