DISSECTION AND MICROSCOPY OF PLANT VASCULAR TISSUE LEARNING OUTCOMES

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DISSECTION AND MICROSCOPY OF PLANT VASCULAR TISSUE LEARNING OUTCOMES
DISSECTION AND SCIENTIFIC DRAWING STUDENT SUPPORT SHEET INTRODUCTION THE

DISSECTION AND MICROSCOPY OF PLANT VASCULAR TISSUE LEARNING OUTCOMES DISSECTION AND MICROSCOPY OF PLANT VASCULAR TISSUE LEARNING OUTCOMES


Dissection and microscopy of plant vascular tissue

Learning outcomes


Introduction

These learning outcomes aim to cover subject knowledge requirements for this part of A-level Biology in three specifications (OCR, AQA and Edexcel). You may need to adapt this information for your specification.

This information can be used to produce learning resources, revision materials, quizzes etc.

DISSECTION AND MICROSCOPY OF PLANT VASCULAR TISSUE LEARNING OUTCOMES

Students should be able to:

  1. List the types of cells found in plant stems (*=cell types named in specifications)

*Xylem vessels

*Phloem – sieve tube elements and companion cells

*Sclerenchyma fibres

Parenchyma (make up cortex and pith – which can be mainly hollow)

Collenchyma

Epidermis

Cambium


  1. State the function of xylem vessels, phloem and sclerenchyma fibres in plant stems

Xylem vessels – transport water and mineral ions from the roots to the rest of the plant. They also provide some structural support for the plant.

Phloem – transport sugars from a source to a sink. Photosynthetic cells are sources, cells requiring sugars are sinks (root cells, growing regions). Areas of a plant that store carbohydrates are sinks when they are building up a store but sources when that store is being utilised by the plant.

Sclerenchyma fibres – provide structural support to the plant.


  1. List the two components of phloem and explain why both are needed

Sieve-tube elements – provide the vessels for transport of carbohydrates (relatively hollow tubes provide reduced resistance to flow).

Companion cells – provide the metabolic needs of the sieve-tube elements.


  1. Describe the structure of xylem vessels, phloem and sclerenchyma fibres

Xylem vessels are hollow tubes made up of dead cells. The cells are arranged end on end and the cell walls between each cell are broken down to produce the long hollow tube. The cells have lost all cell contents and have thickened cell walls that have been impregnated with lignin. Xylem vessels also have holes in their walls that connect adjacent vessels.

Phloem are hollow tubes made of up many connected cells (sieve tubes elements). The cell walls between each of the cells are perforated into structures called sieve plates. Each cell contains very little cytoplasm and no nucleus. These cells have cytoplasmic connections with companion cells.

Sclerenchyma fibres are separate cells, pointed at each end, attached together to form fibres. The cells are dead and hollow and have very thickened cell walls that are impregnated with lignin.



  1. Identify xylem vessels, phloem and sclerenchyma fibres in preparations, photos and diagrams of plant stems

DISSECTION AND MICROSCOPY OF PLANT VASCULAR TISSUE LEARNING OUTCOMES

A





DISSECTION AND MICROSCOPY OF PLANT VASCULAR TISSUE LEARNING OUTCOMES DISSECTION AND MICROSCOPY OF PLANT VASCULAR TISSUE LEARNING OUTCOMES DISSECTION AND MICROSCOPY OF PLANT VASCULAR TISSUE LEARNING OUTCOMES


DISSECTION AND MICROSCOPY OF PLANT VASCULAR TISSUE LEARNING OUTCOMES

Sclerenchyma fibres



DISSECTION AND MICROSCOPY OF PLANT VASCULAR TISSUE LEARNING OUTCOMES DISSECTION AND MICROSCOPY OF PLANT VASCULAR TISSUE LEARNING OUTCOMES DISSECTION AND MICROSCOPY OF PLANT VASCULAR TISSUE LEARNING OUTCOMES


DISSECTION AND MICROSCOPY OF PLANT VASCULAR TISSUE LEARNING OUTCOMES

Phloem



DISSECTION AND MICROSCOPY OF PLANT VASCULAR TISSUE LEARNING OUTCOMES

Xylem




B


DISSECTION AND MICROSCOPY OF PLANT VASCULAR TISSUE LEARNING OUTCOMES DISSECTION AND MICROSCOPY OF PLANT VASCULAR TISSUE LEARNING OUTCOMES DISSECTION AND MICROSCOPY OF PLANT VASCULAR TISSUE LEARNING OUTCOMES DISSECTION AND MICROSCOPY OF PLANT VASCULAR TISSUE LEARNING OUTCOMES

Sclerenchyma fibres

Phloem

Xylem











Photomicrographs



A: Transverse section of part of a young stem of a buttercup (Ranunculus sp.). Image by John Bebbington FRPS

B: Transverse section of a vascular bundle of a young stem of a buttercup (Ranunculus sp.). Image by John Adds

C: Longitudinal section of xylem vessels from stem of Sunflower (Helianthus annuus). Image by Leighton Dann







DISSECTION AND MICROSCOPY OF PLANT VASCULAR TISSUE LEARNING OUTCOMES

C







DISSECTION AND MICROSCOPY OF PLANT VASCULAR TISSUE LEARNING OUTCOMES

Xylem










A and B: Preparations of transverse sections through celery stalks [petioles] (Apium graveolens var dulce)

C and D: Preparations of longitudinal sections through celery stalks [petioles]

Preparations of celery petioles (leaf stalks) using this method (Apium graveolens var dulce)


DISSECTION AND MICROSCOPY OF PLANT VASCULAR TISSUE LEARNING OUTCOMES DISSECTION AND MICROSCOPY OF PLANT VASCULAR TISSUE LEARNING OUTCOMES DISSECTION AND MICROSCOPY OF PLANT VASCULAR TISSUE LEARNING OUTCOMES DISSECTION AND MICROSCOPY OF PLANT VASCULAR TISSUE LEARNING OUTCOMES

Xylem

A



















DISSECTION AND MICROSCOPY OF PLANT VASCULAR TISSUE LEARNING OUTCOMES







Phloem





DISSECTION AND MICROSCOPY OF PLANT VASCULAR TISSUE LEARNING OUTCOMES









B






DISSECTION AND MICROSCOPY OF PLANT VASCULAR TISSUE LEARNING OUTCOMES DISSECTION AND MICROSCOPY OF PLANT VASCULAR TISSUE LEARNING OUTCOMES DISSECTION AND MICROSCOPY OF PLANT VASCULAR TISSUE LEARNING OUTCOMES

Xylem

DISSECTION AND MICROSCOPY OF PLANT VASCULAR TISSUE LEARNING OUTCOMES

Phloem

 DISSECTION AND MICROSCOPY OF PLANT VASCULAR TISSUE LEARNING OUTCOMES DISSECTION AND MICROSCOPY OF PLANT VASCULAR TISSUE LEARNING OUTCOMES

C

D





Diagrams

A: Cross-section through a plant stem (from http://www.saps.org.uk/secondary/teaching-resources/1324)



DISSECTION AND MICROSCOPY OF PLANT VASCULAR TISSUE LEARNING OUTCOMES

B: Overview of a longitudinal section of a plant stem (image from www.saps.org.uk/animations)





DISSECTION AND MICROSCOPY OF PLANT VASCULAR TISSUE LEARNING OUTCOMES

C: Detailed longitudinal section of a plant stem (image from www.saps.org.uk/animations)





DISSECTION AND MICROSCOPY OF PLANT VASCULAR TISSUE LEARNING OUTCOMES

Diagrams

******* get better diagrams – from SAPS?





  1. Describe how the structure of xylem vessels, phloem and sclerenchyma fibres are adapted for their specific function


Xylem


Feature

Function

Dead cells

Allows the vessels to be hollow

Hollow cells

Provides a hollow vessel that provides minimum resistance to the flow of water (also reduces weight)

Cells connected end on end

Provides a continuous vessel for the transport of water

Cell walls between cells broken down

Reduces the resistance to the flow of water

Thickened cell walls

Gives the vessels extra strength

Lignified cell walls

Waterproofs areas of the vessels to reduce water loss and give the vessels extra strength

Holes connecting adjacent tubes

Allows for horizontal movement of water to maintain vertical movement of water even if there are blockages in the vessels


Phloem


Feature

Function

Living cells

Allows the cells to take part in active processes such as the loading of sucrose into the tubes

Cells contain little cytoplasm and no nucleus

Allow the cells to be relatively hollow

Relatively hollow cells

Provides a relatively hollow vessel that provides minimum resistance to the flow of dissolved sugars (also reduces weight)

Cells connected end on end

Provides a continuous vessel for the transport of dissolved sugars

Perforated cell walls between cells (sieve plates)

Reduces the resistance to the flow of dissolved sugars

Cytoplasmic connections with companion cells

Allow the companion cells to have metabolic control over the sieve tube elements such as providing the sieve tube element with ATP



Sclerenchyma


Feature

Function

Dead cells

Allows the vessels to be hollow

Hollow cells

Reduces weight (increases strength to weight ratio)

Pointed connected cells

Provides a large surface area for one cell to be connected to another to give the fibres greater tensile strength

Very thickened cell walls

Give the vessels extra strength to support the plant

Lignified cell walls

Give the vessels extra strength to support the plant





  1. Identify similarities and differences between xylem vessels, phloem and sclerenchyma fibres


Feature

Xylem vessels

Phloem

Sclerenchyma fibres

General structure

Vessels = hollow tubes made of many connected cells

Vessels = hollow tubes made of many connected cells

Separate cells joined together to form fibres

Dead / Alive

Dead cells

Living cells – sieve tube elements kept alive by connections to companion cells

Dead cells

Function

Transport of water and mineral ions

Structural support

Transport of dissolved carbohydrates

Structural support

Cell wall

Thickened and possess lignin

No special modifications (plasmodesmata between sieve tube element and companion cells, also sieve plates at the end of cells)

Thickened and possess lignin

Cell contents

Completely hollow – some perforated or slitted end plates of cells remain

Hollow centre with thin layer of cytoplasm around the edge. Sieve plates at the end of each cell.

Hollow dead cells



Science & Plants for Schools: www.saps.org.uk

Dissection and microscopy of plant vascular tissue – Learning outcomes: p. 6


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