Plant fibres, xylem and phloemEdexcel A-Level Biology A: Flashcards
What these 14 flashcards ask
- What is a cellulose microfibril?
- What is secondary thickening?
- Why do the layers of microfibrils in a secondary wall lie at different angles?
- What does lignin do in a plant cell wall?
- What is the function of sclerenchyma fibres?
- Describe the shape of a sclerenchyma fibre.
- How are xylem vessels adapted to carry water?
- What is a pit in a xylem vessel wall?
- What do sieve tube elements transport?
- Why do sieve tube elements need companion cells?
- What is the order of tissues in a dicot vascular bundle from the outside inwards?
- Which variables should be controlled in the tensile strength practical?
- How do you calculate the breaking force of a fibre?
- Name two uses of plant fibres.
Exam questions on Plant fibres, xylem and phloem
- A student cuts a thin transverse section through a young sunflower stem, stains it with toluidine blue (which stains lignin blue-green and unlignified cellulose pink-purple) and examines one vascular bundle with a light microscope to identify the tissues.Suggest why the xylem vessels stain strongly blue-green with toluidine blue but the sieve tubes stain pink-purple.2 marks
- A rope manufacturer compares the strength of fibres extracted from hemp stems. A technician clamps a single fibre at its top end, hangs a mass holder from the lower end and adds 100 g masses one at a time until the fibre snaps. The distance between the clamp and the holder is the same for every fibre tested.Explain why the technician should use fibres of the same diameter when comparing fibres from different hemp plants.2 marks
- Some trees lift water to the top of a trunk more than 30 m tall. Water is pulled upwards through the xylem by transpiration, which puts the water columns under tension (negative pressure). The wood of the trunk also has to support the weight of a large crown of branches.Explain how the structure of xylem vessels adapts them to carrying water under tension.3 marks
Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).